Category Archives: Agriculture

Enforcement of immigration laws or immigration reform could raise labor costs

The main reason for this was that breaking the application into smaller hydraulic loadings resulted in O2 concentrations to recover to background atmospheric conditions faster than the larger allat-once application in scenario S1. In fact, the O2 concentration differed slightly between S2 and S3. Because O2 inhibits denitrification, we conclude that these conditions resulted in the different denitrification capacity across application frequency and duration. In summary, we find that larger amounts of water applied all-at-once increased the denitrification capacity of the vadose zone while incremental application of water did not. However, NO3 – movement to deeper depths was slower under S2 and S3. Because initial saturation conditions impact nitrogen leaching, we also simulated the impact of wetter antecedent moisture with 15% higher saturation levels than the base case simulation for the ERT profile. Simulated profiles of liquid saturation, NO3 – , NO3 – :Cland acetate for the simplified ERT stratigraphy under wetter conditions are shown in Figure 10. Model results demonstrate that the water front moved faster and deeper into the soil profile under initially wetter conditions for all three scenarios. Within the shallow vadose zone , across AgMAR scenarios, O2 concentrations were similar initially, but began differing at early simulated times, with lower O2 under wetter antecedent moisture conditions than with the base-case simulation. In addition, both oxygen and nitrate concentrations showed significant spatial variation across the modeled column. Notably,fodder system nitrate concentrations were 166% higher in the preferential flow channel compared to the sandy loam matrix under wetter conditions, while only 161% difference was observed under the base case simulation .

Nitrate movement followed a pattern similar to water flow, with NO3 – reaching greater depths with the wetter antecedent moisture conditions. Under S1, however, at 150 cm-bgs, NO3 – decreased more quickly under the wetter antecedent moisture conditions due to biochemical reduction of NO3 – , as evidenced by the decrease in NO3 – :Clratio, as well as by dilution of the incoming floodwater. In the wetter antecedent moisture conditions, 39%, 31%, and 30% of NO3 – was denitrified under S1, S2, and S3, respectively. For S1, where water was applied all at once, more denitrification occurred in the wetter antecedent moisture conditions, however, the same was not true of S2 and S3 where water applications were broken up over time. This could be due to the hysteresis effect of subsequent applications of water occurring at higher initial moisture contents, allowing the NO3 – to move faster and deeper into the profile without the longer residence times needed for denitrification to occur. Thus, wetter antecedent moisture conditions prime the system for increased denitrification capacity when water is applied all at once and sufficient reducing conditions are reached, however, this is counteracted by faster movement of NO3 – into the vadose zone. Simluations from our study demonstrate that low-permeability zones such as silt loams allow for reducing conditions to develop, thereby leading to higher denitrification in these sediments as compared to high permeability zones such as sandy loams. In fact, the homogenous silt loam profile reported the maximum amount of denitrification occurring across all five stratigraphic configurations . Furthermore, the presence of a silt loam channel in a dominant sandy loam column increased the capacity of the column to denitrify by 2%. Conversely, adding a sandy loam channel into a silt loam matrix decreased the capacity of the column to denitrify by 2%. These relatively simple heterogeneities exemplify how hot spots in the vadose zone can have a small but accumulating effect on denitrification capacity . Note that differences in denitrification capacity maybe much greater than reported here because of increased complexity and heterogeneity of actual field sites when compared to our simplified modeling domains.

Another observation of interest for silty loams is the prominence of chemolithoautotrophic reactions and Fe cycling observed in these sediments. In comparison, sandy loam sediments showed persistence and transport of NO3 – to greater depths. A reason for this is that oxygen concentration was much more dynamic in sandy loams, rebounding to oxic conditions more readily than in silt loams, even deep into the vadose zone . Dutta et al. found similar re-aeration patterns in a 1 m column experiment in a sand dominated soil, with re-aeration occurring quickly once drying commenced. Even with the presence of a limiting layer, defined by lower pore gas velocities and higher carbon concentration, a sandy loam channel acted as a conduit of O2 into the deep vadose zone maintaining a relatively oxic state and thus decreasing the ability of the vadose zone to denitrify. In systems with higher DOC loadings to the subsurface, oxygen consumption may proceed at higher rates creating sub-oxic conditions in the recharge water and more readily create reducing conditions favorable to denitrification in the subsurface . We note here that microbial growth, which was not modeled in this study, could also affect the rates of O2 consumption and re-aeration, which could lead to underestimation of O2 consumption . Overall, denitrification capacity across different lithologies was shown to depend on the tight coupling between transport, biotic reactions as well as the cycling of Fe and S through chemolithoautotrophic pathways. Under large hydraulic loadings , overall denitrification was estimated to be the greatest as compared to the lower hydraulic loading scenarios . The main reason for the higher denitrification capacity was the significant decline in O2 concentration estimated for this scenario, whereas such conditions could not be maintained below one meter with lower hydraulic loadings under scenarios S2 and S3. However, nitrate was also transported deeper into the column under S1 as compared to S2 or S3. Tomasek et al. found the reverse in a floodplain setting, where intermittent indundation with flood water, comparable to our S2 and S3 contexts, resulted in higher rates of denitrification in the zone that was always inundated, due to priming of the microbial community and pulse releases of substrates and electron donors.

Future studies examining the impact of AgMAR on denitrification should include processes such as mineralization to see if the same behavior would be observed. It seems that there may exist a threshold hydraulic loading and frequency of application that could result in anoxic conditions and therefore promote denitrification within the vadose zone for different stratigraphic configurations, although this was not further explored in this study. In another study, Schmidt et al. found a threshold infiltration rate of 0.7 m d-1 for a three hectare recharge pond located in the Pajaro Valley of central coastal California, such that no denitrification occurred when this threshold was reached. For our simulations, we used a fixed, average infiltration rate of 0.17 cm hr-1 for our all-at-once and incremental AgMAR scenarios, however,fodder system for sale application rates can be expected to be more varied under natural field settings. Our results further indicate that the all-at-once higher hydraulic loading, in addition to causing increased levels of saturation and decrease in O2, resulted in leaching of DOC to greater depths in comparison to lower, incremental hydraulic loading scenarios . Akhavan et al. 2013 found similar results for an infiltration basin wherein 1.4% higher DOC levels were reported at depths down to 4 m when hydraulic loading was increased. Because organic carbon is typically limited to top 1 m in soils , leached DOC that has not been microbially processed could be an important source of electron donors for denitrification at depth. Systems that are already rich in DOC within the subsurface are likely to be more effective in denitrifying, and thus attenuating, NO3 – , such as floodplains, reactive barriers in MAR settings, or potentially, organically managed agroecosystems .. This finding can also be exploited in agricultural soils by using cover crop and other management practices that increase soluble carbon at depth and therefore remove residual N from the vadose zone . While lower denitrification capacity was estimated for scenarios S2 and S3, an advantage of incremental application was that NO3 – concentration was not transported to greater depths. Thus, higher NO3 – concentration was confined to the root zone. If NO3 – under these scenarios stays closer to the surface, where microbial biomass is higher, and where roots, especially in deep rooted perennial systems such as almonds, can access it, it could ultimately lead to less NO3 – lost to groundwater. While there is potential for redistribution of this NO3 – via wetting and drying cycles, future modeling studies should explore multi-year AgMAR management strategies combined with root dynamics to understand N cycling and loading to groundwater under long-term AgMAR. Simulation results indicate that wetter antecedent moisture conditions promote water and NO3 – to move deeper into the domain compared to the drier base case simulation. This finding has been noted previously in the literature, however, disagreement exists on the magnitude and extent to which antecedent moisture conditions affect water and solute movement and is highly dependent on vadose zone characteristics. For example, in systems dominated by macropore flow, higher antecedent soil moisture increased the depth to which water and solutes were transported . In a soil with textural contrast, where hydraulic conductivity between the topsoil and subsoil decreases sharply, drier antecedent moisture conditions caused water to move faster and deeper into the profile compared to wetter antecedent moisture conditions.

In our system, where a low-permeability layer lies above a high permeability layer , the reverse trend was observed. Thus, a tight coupling of stratigraphic heterogeneity and antecedent moisture conditions interact to affect both NO3 – transport and cycling in the vadose zone, which should be considered while designing AgMAR management strategies to reduce NO3 – contamination of groundwater. Furthermore, dry and wet cycles affect other aspects of the N cycle that were not included in this study . Specifically, the effect of flood water application frequency on mineralization of organic N to inorganic forms should be investigated to assess the full N loading amount to groundwater under AgMAR.The value of California’s fruit, nut, and vegetable crops was $20 billion in 2009, almost 60% of the state’s farm sales of $35 billion. California dominates U.S. production of these crops and currently accounts for about half of the U.S. fresh vegetable production and about half of total fruit production. Many of these fruits and vegetables are labor intensive; labor costs for fruit and vegetables average 42% of variable production costs. Over half of the state’s hired farm workers are unauthorized, and most move on to non-agricultural employment within a decade of beginning to work in the fields. The California produce industry depends on a constant influx of new, foreign-born labor attracted by wages above those in their countries of origin, primarily Mexico.Enforcement of immigration laws has increased recently in two major ways. First, the U.S. government has erected fences and vehicle barriers on a third of the 2,000 mile Mexico–U.S. border to deter unauthorized entries. Second, the Immigration and Enforcement Agency that enforces immigration laws inside the United States has begun to audit more of the I-9 forms completed by newly hired workers and their employers. After these audits, employers are asked to inform workers whose data do not match government records to clear up discrepancies. Most workers instead quit, which has prompted some farm employers to invest in housing in order to hire legal H-2A guest workers . H-2A workers must be paid at least the so-called Adverse Effect Wage Rate , which in 2011 is $10.31 an hour in California, higher than the state and federal minimum wages. AEWRs were established in the 1960s to prevent the presence of legal foreign workers from depressing the wages of U.S. farm workers. Immigration reform could also raise farm labor costs by legalizing currently unauthorized farm workers and encouraging farm employers to turn to H-2A guest workers if legalized workers find non-farm jobs, which could raise labor costs. Efforts to enact immigration reform between 2005 and 2007 failed, but in his 2011 State of the Union speech, President Obama urged Congress to try again. He said: “I know that debate will be difficult. I know it will take time. But tonight, let’s agree to make that effort.” This paper reviews the three most likely adjustments in the fruit and vegetable industry to higher labor costs: mechanization, imports, and labor aids.U.S. production of fresh-market fruit and vegetables has increased in the last two decades—up 12% for fresh fruit and 41% for fresh vegetables .

What Are The Easiest Plants To Grow With Hydroponics

Hydroponics can be a great way to grow a variety of plants, and some are easier to cultivate using this method than others. Here are some of the easiest plants to grow with hydroponics,dutch buckets making them suitable choices for beginners:

  1. Lettuce: Lettuce is a popular choice for hydroponic cultivation due to its rapid growth and relatively simple nutrient requirements. Various types of lettuce, such as leaf lettuce and romaine, thrive in hydroponic systems.
  2. Herbs: Herbs like basil, cilantro, parsley, and mint are well-suited to hydroponics. They have compact root systems and grow quickly, making them ideal for small-scale hydroponic setups.
  3. Spinach: Spinach is another leafy green that does well in hydroponic systems. It grows quickly and doesn’t require a lot of space.
  4. Swiss Chard: Swiss chard is a nutrient-dense leafy green that can be grown hydroponically. It’s relatively easy to maintain and produces colorful, edible stems.
  5. Kale: Kale is a hardy leafy green that is well-suited to hydroponics. It’s a nutrient-rich plant and can thrive in a controlled hydroponic environment.
  6. Cherry Tomatoes: Compact varieties of cherry tomatoes, such as “Tiny Tim” or “Patio Princess,” can be grown in hydroponic systems. They require some support for the vines but can yield a good harvest.
  7. Peppers: Bell peppers and chili peppers can be grown hydroponically. They thrive in warm conditions and can produce abundant fruits with proper care.
  8. Cucumbers: Compact cucumber varieties like “Bush Pickle” or “Spacemaster” can be grown in hydroponic systems. Trellising is essential to support their growth.
  9. Green Onions: Green onions, also known as scallions, are easy to grow hydroponically. They don’t require much space and have a relatively short growth cycle.
  10. Radishes: Radishes are fast-growing and can be cultivated hydroponically. They are a good choice for those looking for a quick harvest.

Remember that successful hydroponic gardening requires attention to factors like water quality, nutrient levels, pH, and lighting. While these plants are generally considered easy to grow hydroponically,grow bucket it’s important to research each plant’s specific requirements and tailor your hydroponic system accordingly. Additionally, starting with a simple system and gaining experience will help you become a more proficient hydroponic gardener over time.

Hedgerows may therefore represent a source of bee diversity in the landscape

Of the species only at controls, 80% were represented by a single individual. The species only at hedgerows tended to have more specialized nesting requirements , whereas those only at controls were primarily generalists . Also, although the majority of the species were found at both hedgerows and unrestored controls , species ranging from relatively rare to common were infrequent at controls and more abundant in hedgerows . Interestingly, the three species observed over 100 times, Lasioglossum incompletum, Halictus tripartitus and Halictus ligatus, all small-bodied floral and nesting resource generalists, were at similar abundances in hedgerows and unrestored controls, if not slightly more abundant in controls .Although hedgerows may help counter homogenization of pollinator communities in simplified agricultural landscapes, comparing the spatial heterogeneity they support to that which is observed in natural communities is important in assessing their overall conservation value. In remnant chaparral/oak woodland communities in the same ecoregion and adjacent to our study landscapes , an average of 30% of species were not shared across sites located within 3.5–50 km of each other. The Central Valley, which was once described as ‘one vast, level, even flower-bed’ , has been extensively converted to agriculture, likely limiting the species pool due to local extinctions. Even so, at hedgerows an average of 15 km apart, we found between 36% and 67% of species were not shared between sites, depending on the year. Both the spatial scale and biota of our study and that of are comparable, suggesting that hedgerows are, in fact,grow strawberry in containers restoring spatial heterogeneity to approximately the same range as might occur in adjacent natural systems. In addition, in the disparate landscape of the southwestern United States, a diversity hot spot for bees , 61% of species were not shared across sites within 1–5 km of each other .

Although the species pool is richer in the southwest, the amount of species turnover at hedgerows is not unlike what is observed in that highly heterogeneous region . Thus, across many aspects of biodiversity, hedgerows might provide a valuable measure for conserving biodiversity . Only mature hedgerows in this study supported higher trait and b-diversity when compared to non-restored farm edges. Thus, the processes that lead to a buildup of spatial turnover in pollinator communities are slow and may take considerable time before observably affecting pollinator communities. However, we have recently shown that hedgerow restoration leads to increased rates of colonization and persistence of pollinators in maturing hedgerows and that this effect becomes stronger over time . Further, we found that maturing hedgerows differentially support more specialized species over time . These two temporal studies on the early phases of hedgerow maturation show that hedgerows begin to impact pollinator communities much earlier than 10 years. Combined, these findings suggest a possible mechanism whereby restoration might lead to increases in species turnover; as a hedgerow matures, species with a wider variety of life-history traits are better able to colonize and persist there, thus leading to the accumulation of differences in community composition between sites over time. This then leads to greater spatial heterogeneity in pollinator communities at hedgerows. Conversely, in unrestored areas, the rate of colonization and persistence is lower, particularly for species with more specialized habitat requirements, thereby creating an ecological filter that limits the total diversity and, thus, turnover that is possible. This above-described process can be, in part, deterministic; restored and non-restored farm edges differ fundamentally in which pollinator species are able to colonize and/or persist in them . Thus, pollinators respond to the differences in the plant communities between hedgerows and controls, and the pollinator community at mature hedgerows tracks floral hosts. Interestingly, however, the pollinator communities at hedgerows that were closer to one another were not necessarily more similar than sites that were further apart.

In addition, hedgerows maintain b-diversity in the landscape by supporting unique combinations of species, and we did not find evidence that communities at hedgerows were nested subsets of one another . Because hedgerows are planted, the floral communities the pollinators are tracking will not necessarily be spatially structured like natural communities. In addition, bees are known to be highly spatially and temporally variable and thus, stochastic processes that do not result in spatial structuring are likely operating as communities assemble. In contrast to within hedgerows, the dissimilarity of pollinators at unrestored controls responded positively to geographic distance. Because the conditions at controls are relatively uniform across space, this suggests a role for dispersal limitation in determining pollinator community composition at unrestored controls . In addition, the number of shared species between hedgerows and controls was also positively related to distance , suggesting the communities at controls may be influenced by landscape context such as the presence of nearby hedgerows.Here we focus on the effects of hedgerows on b-diversity, but there are likely other contributions to spatial heterogeneity in our landscape. There are a number of crops that provide floral resources to pollinators in our area, including mass-flowering sunflower, melons, and almonds . Different crops attract different pollinators and thus may affect the spatial heterogeneity of communities. In addition, some crops might also pull resident species from the hedgerows , while others may attract species that may subsequently colonize hedgerows . Differences in adjacent crops between hedgerows and unrestored controls thus may add noise to the underlying signal of b-diversity. However, because hedgerows and controls are matched for crop type, while there may be a contribution of crop type on b-diversity, it should be a random one affecting hedgerows and controls simultaneously. To achieve sustainable food production while protecting biodiversity, we need to grow food in a manner that protects, utilizes, and regenerates ecosystem services, rather than replacing them .

Diversification practices such as installing hedgerows, when replicated across a landscape, may provide a promising mechanism for conserving and restoring ecosystem services and biodiversity in working landscapes while potentially improving pollination and crop yields .Increasing population and consumption have raised concerns about the capability of agriculture in the provision of future food security. Te overarching effects of climate change pose further threats to the sustainability of agricultural systems. Recent estimates suggested that global agricultural production should increase by 70% to meet the food demands of a world populated with ca. 9.1 billion people in 2050. Food security is particularly concerning in developing countries, as production should double to provide sufficient food for their rapidly growing populations. Whether there are enough land and water resources to realize the production growth needed in the future has been the subject of several global-scale assessments. Te increase in crop production can be achieved through extensifcation and/or intensifcation. At the global scale, almost 90% of the gain in production is expected to be derived from improvement in the yield,hydroponic nft channel but in developing countries, land expansion would remain a significant contributor to the production growth. Land suitability evaluations, yield gap analysis, and dynamic crop models have suggested that the sustainable intensification alone or in conjugation with land expansion could fulfil the society’s growing food needs in the future. Although the world as a whole is posited to produce enough food for the projected future population, this envisioned food security holds little promise for individual countries as there exist immense disparities between regions and countries in the availability of land and water resources, and the socio-economic development. Global Agro-Ecological Zone analysis suggests that there are vast acreages of suitable but unused land in the world that can potentially be exploited for crop production; however, these lands are distributed very unevenly across the globe with some regions, such as the Middle East and North Africa , deemed to have very little or no land for expansion. Likewise, globally available fresh water resources exceed current agricultural needs but due to their patchy distribution, an increasing number of countries, particularly in the MENA region, are experiencing severe water scarcity.

Owing to these regional differences, location-specific analyses are necessary to examine if the available land and water resources in each country will suffice the future food requirements of its nation, particularly if the country is still experiencing significant population growth.As a preeminent agricultural country in the MENA region, Iran has long been pursuing an ambitious plan to achieve food self- sufficiency. Iran’s self- sufficiency program for wheat started in 1990, but the low rate of pro-duction increase has never sustainably alleviated the need for grain imports. Currently, Iran’s agriculture supplies about 90% of the domestic food demands but at the cost of consuming 92% of the avail-able freshwater. In rough terms, the net value of agricultural import is equal to 14% of Iran’s cur-rent oil export gross revenue. Located in a dry climatic zone, Iran is currently experiencing unprecedented water shortage problems which adversely, and in some cases irreversibly, affect the country’s economy, ecosystem functions, and lives of many people. Te mean annual precipitation is below 250 mm in about 70% of the country and only 3% of Iran, i.e. 4.7 million ha, receives above 500 mm yr−1 precipitation . The geographical distribution of Iran’s croplands shows that the majority of Iran’s cropping activities take place in the west, northwest, and northern parts of the country where annual precipitation exceeds 250 mm . However, irrigated cropping is practiced in regions with precipitations as low as 200 mm year−1, or even below 100 mm year−1. To support agriculture, irrigated farming has been implemented unbridled, which has devastated the water scarcity problem.The increase in agricultural production has never been able to keep pace with raising demands propelled by a drastic population growth over the past few decades, leading to a negative net international trade of Iran in the agriculture sector with a declining trend in the near past . Although justified on geopolitical merits, Iran’s self-sufficiency agenda has remained an issue of controversy for both agro-ecological and economic reasons. Natural potentials and constraints for crop production need to be assessed to ensure both suitability and productivity of agricultural systems. However, the extents to which the land and water resources of Iran can meet the nation’s future food demand and simultaneously maintain environmental integrity is not well understood. With recent advancement in GIS technology and availability of geospatial soil and climate data, land suitability analysis now can be conducted to gain insight into the capability of land for agricultural activities at both regional and global scales. Land evaluation in Iran has been conducted only at local, small scales and based on the specific requirements of a few number of crops such wheat, rice and faba bean. However, there is no large scale, country-wide analysis quantifying the suitability of Iran’s land for agricultural use. Herein, we systematically evaluated the capacity of Iran’s land for agriculture based on the soil properties, topography, and climate conditions that are widely known for their relevance with agricultural suitability. Our main objectives were to: quantify and map the suitability of Iran’s land resources for cropping, and examine if further increase in production can be achieved through agriculture expansion and/or the redistribution of croplands without expansion. The analyses were carried out using a large number of geospatial datasets at very high spatial resolutions of 850m and 28m . Our results will be useful for estimating Iran’s future food production capacity and hence have profound implications for the country’s food self-sufficiency program and international agricultural trade. Although the focus of this study is Iran, our approach is transferrable to other countries, especially to those in the MENA region that are facing similar As a preeminent agricultural country in the MENA region, Iran has long been pursuing an ambitious plan to achieve food self- sufficiency. Iran’s self- sufficiency program for wheat started in 1990, but the low rate of production increase has never sustainably alleviated the need for grain imports. Currently, Iran’s agriculture supplies about 90% of the domestic food demands but at the cost of consuming 92% of the available freshwater. In rough terms, the net value of agricultural import is equal to 14% of Iran’s current oil export gross revenue. Located in a dry climatic zone, Iran is currently experiencing unprecedented water shortage problems which adversely, and in some cases irreversibly, affect the country’s economy, ecosystem functions, and lives of many people.

The coefficients indicate that all three inputs impacted knowledge production positively

Expenditures on salaries act as an incentive system to make the current advisor FTE more productive, which enhances productivity, as is indicated by our results. Expenditures on infrastructure have a positive impact on knowledge production before the threshold level is reached, beyond which the impact becomes negative. In this respect, our findings for the extension system in California suggest that the research and dissemination by agricultural extension is similar to that of a research only system. The quadratic behavior of the expenditures on infrastructure was found significant, with a negative sign for the quadratic term. This finding is similar to the results in Roper and Hewitt-Dundas , Jordan and O’Leary , and Charlot et al. . Such results suggest an inverse U-shaped relationship between knowledge production and fixed infrastructure investment. The support in findings on the inverse U-shaped impact of research infrastructure on knowledge production we get from literature on non-agricultural research, is very helpful for validating the results in our analysis with focus on agricultural research and extension in California.We found that expenditures on infrastructure per-unit FTE as a research input has diminishing marginal effects on knowledge production. Marginal product of advisor FTE calculated at the mean value of the input and knowledge index equals 106.33; this implied that one unit increase in county FTE led to nearly 106 additional counts of knowledge production. Marginal products of expenditures on salaries per FTE and infrastructure per FTE are 0.003and −0.0003,respectively. Marginal products values calculated at the mean emphasized the importance of advisor FTE as a research input.

hey also brought forward the issue of diminishing returns on investments in incentives and infrastructures. We conducted several robustness checks by running regression for models using each of the three broad categories of knowledge production and dissemination instead of the calculated knowledge index. The three broad categories are: direct contacts, indirect contact, and publications and research projects as dependent variables. The results of the robustness checks are reported in Appendix Tables A2, A3, and A4. The results suggest similar range of coefficients for each of the variables,hydroponic bucket similar signs and significance levels across the various estimated models. Thus, these results suggest that the empirical knowledge function we use is robust. Endogeneity, if exists, could be found in the sphere of budget allocation for extension work at the county level. It could be argued that level of budget allocation is a function of the agricultural performance of the county, and thus introducing endogeneity biases in our estimates. However, following interviews with county directors, decisions on budget allocations among the counties in California are made based on political negotiations between the county directors and the UCCE system. Furthermore, as suggested by Guttman , Rose-Ackerman and Evenson , Pardey and Pardey and Craig , political rather than just economics efficiency criteria influence the allocation of public agricultural research and extension resources.We have estimated the contemporaneous impact of UC Cooperative Extension on the production of knowledge through research and extension work that is conducted in all California counties. Available data on R&D expenditures and knowledge products was used to construct a unique data set for seven years, spanning from 2007 to 2013. The data contained information on extension advisor FTE, expenditures on advisor FTE salaries, and on advisor FTE infrastructure. We obtained data on a number of knowledge production and dissemination methods. They are categorized into 11 subcategories, and three broad categories.

We computed a weighted average knowledge index variable with the weights provided by UCCE county directors via an electronic survey. The contribution of this work is the quantification of extension research input and in the fact that the trends and relative importance of research variables found in an extension research and dissemination system in California are similar to previous results of the agricultural research system in the USA, and previous results from several industrial research and development activities around the world. Both these similarities suggest that a research and dissemination agricultural extension behaves similarly to industrial research systems. One limitation of the study is that we were able to capture only the contemporaneous impact of research inputs on the production and dissemination of knowledge, due to data constraints. With further availability of data, analysis of long-run impact will enable policymakers to make informed decisions on investments in research inputs. This will enable sustained knowledge production and dissemination. Another limitation of the study is the lack of information on components of the research inputs, such as attributing research outcomes and extension impact to advisors, rather than distinguishing among advisors, based on seniority and experience. Such a distinction related to university research was performed in a study by Gurmu et al. . Some potential issues with the variable specifications deserve a mention. The variable FTE includes UCCE county advisors. Incorporation of detailed data on knowledge produced and disseminated by UCCE specialists at the county level would provide a more complete picture of the knowledge production mechanism. Data on FTE experience and expertise could also refine our results and understanding of the input-output relationship. Research-based agricultural knowledge is one of the most important inputs in the enhancement of agricultural productivity , and evidence suggests significant impacts on current productivity from the past 35 years of research-based knowledge . Therefore, better understanding of relevant research inputs, environments in which substitution between inputs is viable, and long-term impact of shifts in investments in research inputs have a great deal of importance for policy purposes.

This paper poses and provides answers to some of these questions and indicates possible directions for future study on this issue. Another point to address is the international and national relevance of this work to the literature and to policy practitioners. California is a leader in agricultural production. California extension system is a leader in extension knowledge that feeds into the agricultural production in the state. Therefore, understanding the process of knowledge creation by agricultural extension in California is of interest to researchers and practitioners in other states and countries. The finding in this study suggests that data collection and analysis for public extension activities are essential for proper policy consideration of a public knowledge system, which faces budget pressure world-wide. While the coefficients estimated for the case of California represent California situation, the trends of the coefficients are general and relevant to other states and countries around the world. With the data challenges we faced in this study, our results indicate the importance of the policymaker to be able to quantify the process of knowledge production in the agricultural extension systems. California ranks first among the top five national agricultural producers,stackable planters according to the California Statistical Review 2014–15 , with crop cash receipts amounting $53.5 billion . Irrigated agriculture in California consumes on average about 85% of the available renewable water resources in the state . Agricultural extension plays a major role in keeping agriculture sustainable and profitable . Therefore, the need for a reliable system of data collection on agricultural extension activities and knowledge produced at the state and county levels would enhance the ability to identify the determinants of knowledge production by the extension system. Finally, we observed, as Pardey and Alston et al. also did, that the public budget allocated to agricultural and extension has declined over time. The lesser funding allocated to UCCE over time is not because knowledge has decreased; in fact, we claim that it is the opposite, knowledge production has declined because there was less funding due to recession or/and budgetary constraints in the University of California system as a result of financial difficulties faced by the state of California during the years we analyze.Human-altered landscapes are expanding globally and are often associated with declining natural habitat, non-native species, fragmentation, and transformations in structure, inputs, climate, and connectivity. These changes collectively have resulted in shifts in both spatial distributions and species diversity across many taxa including birds, mammals, reptiles, amphibians, invertebrates, and plants.

One common driver of global change is urbanization, which in the extreme is associated with a reduction in biodiversity compared to habitats in their more natural state. However, in moderately urbanized areas, the effects of urban impacts on species distribution and diversity can vary greatly and depends on region, type of change, and taxonomic group, among other factors. Documenting the effects of urbanization compared to natural communities has proven problematic, making predictions of community change associated with urbanization difficult. Human-altered landscapes are often associated with many non-native species which add to species diversity but also can obscure changes in community dynamics. Thus, to assess accurately the complex impacts of land use change on ecological communities, one must look beyond species richness to investigate ecological processes themselves. Ecological processes are the links between organisms in a functioning ecosystem, and are critical in understanding how altered biodiversity can lead to changes in ecosystem functioning. Global environmental change has been found to have a wide variety of impacts on ecological processes in different systems. Pollinator-plant relationships in particular are found to be particularly vulnerable to land use change, resulting in decreases in interaction strength and frequency. Pollination services are crucial ecosystem processes in natural systems, but also in agricultural and urban areas. Bees provide the majority of animal-mediated pollination services on which it is estimated 87.5% of flowering plants depend. The value of pollination in agriculture is estimated at $200 billion worldwide, largely due to many foods that are essential for food security and a healthy human diet, including numerous fruits, vegetables, and nuts that require bee pollination. As urban areas expand, there has been increasing interest in urban agriculture to ensure food security and access to healthy foods for growing populations, and these systems also depend on pollination. For example, Kollin estimated that the economic value of urban fruit trees to be worth $10 million annually in San Jose, California. Despite the important role of pollinators and concerns about bee declines, there remain many uncertainties regarding the impact of land use change on pollinators. Urbanization has resulted in more interfaces with both natural and agricultural landscapes, creating new transitional zones of peri-urbanization. While there has been extensive pollinator research in agricultural and natural systems, less attention has focused on pollination in neighboring urban areas and how the changing landscape has impacted pollination. In addition, very few studies of urban areas have looked beyond changes in bee diversity to understand explicitly the effect of urbanization on pollinator-plant interactions. Here, we investigate the effect of land use change on pollinator plant ecosystem processes. We make use of a ‘‘natural experimental design’’ in which urban, agricultural, and natural areas intersect. Bees visit flowers for both pollen and nectar resources, and floral visitation is a commonly used as an index of pollination services. However, depending on the flower, certain bee groups are much more effective pollinators than others. Thus, while visitation is important, it alone does not definitively indicate whether pollination services were received by the plant. When pollen is limited by other factors, consequences for plant fitness can include failure to set seed, production of smaller fruits, and even complete lack of reproduction. By looking at rates of bee visitation and comparing this with other measures of plant fitness, such as seed set, we can develop a more complete understanding of how shifts in bee distributions between areas that differ in land use are impacting pollination services. To study the impact of changing land use on pollinator-plant interactions, we focus on bee pollination of a widespread plant, yellow starthistle , a common weed found in natural, agricultural, and urban habitats. Using standardized observations of floral visitation and seed set measurements of yellow starthistle, we test the hypotheses that increasing urbanization decreases 1) rates of bee visitation, 2) viable seed set, and 3) the efficiency of pollination . In addition to contributing to a better understanding of how change in landscape use, particularly urbanization, affects pollination-plant interactions, the study illustrates the importance of use of neighboring lands for pollination services.We observed visits by all bee species to yellow starthistle at all sites 3 times for a 30 min period for a total of 90 min of total observation time per site within the same 2 wk period in August 2011.

Can You Grow Blueberries Hydroponically

Yes, it is possible to grow blueberries hydroponically, although it can be a bit more challenging compared to other crops. Blueberries are typically grown in soil, and they have specific requirements for soil pH and nutrient levels. When growing blueberries hydroponically,large plastic pots you’ll need to create an environment that mimics their natural soil preferences. Here are some key considerations:

  1. Acidic pH: Blueberries require acidic soil with a pH level between 4.5 and 5.5. In a hydroponic system, you will need to monitor and adjust the pH of the nutrient solution regularly to keep it within this range.
  2. Nutrient Solution: Blueberries have specific nutrient requirements, including elements like iron and manganese, which they may not readily uptake in hydroponic systems. Using a specialized blueberry nutrient solution or carefully adjusting the nutrient mixture to match their needs is essential.
  3. Growing Medium: In hydroponics, you can use various growing mediums like coconut coir, perlite, or a mix of these. Ensure the chosen medium allows for good aeration and drainage.
  4. Lighting: Blueberries require plenty of light, ideally full sun. If you’re growing them indoors or in a controlled environment, provide high-intensity lighting such as LED grow lights to mimic natural sunlight.
  5. Temperature and Humidity: Blueberries prefer cooler temperatures, generally around 60-70°F (15-24°C). Humidity levels should be moderate.
  6. Pruning: Like traditional blueberry bushes, hydroponically grown blueberries benefit from regular pruning to encourage healthy growth and fruit production.
  7. Variety Selection: Some blueberry varieties may be better suited for hydroponic growth than others. Consider researching and selecting varieties that are known for adaptability to controlled environments.
  8. Pollination: If you are growing blueberries indoors, you may need to hand-pollinate the flowers since there may not be natural pollinators like bees indoors.

It’s important to note that hydroponic blueberry cultivation can be more resource-intensive and may require more attention to detail than traditional soil cultivation. You may need to experiment and fine-tune your hydroponic system to meet the specific needs of blueberries. Additionally,plastic pots for plants some blueberry varieties may be better suited to hydroponic cultivation than others, so consult with experienced growers or agricultural experts for advice and guidance specific to your location and setup.

Adjustment in the diet to reduce the heat increment and minimize yield loss is a subject of intense research

In this report, they indicated that warmer temperatures during the crop-growing season were favorable to the cooler regions of California, but unfavorable to the arid regions. This result was consistent with national studies which showed that crop productivity increased with temperature in more northern latitudes of the United States, and decreased with increased temperatures in some of the southern regions of the Country. This may be explained by crop productivity in cooler regions benefiting from additional degree-days of warming, whereas crops in warm regions may already be at the heat threshold level . As discussed above, there are shortcomings with the simple quadratic equation approach, and crops may actually respond more strongly to increased temperature and CO2 than indicated in these studies For specialty crops such as stone fruits and grapes, water stress, temperature and the timing of precipitation can be extremely important for sustainable yields and maximizing fruit quality . However, for rain-fed crops and grazed lands, where the most productive seasons are late fall, winter and early spring, water use patterns may change markedly as a result of higher evapotranspiration . Adams et al. found that most regions and climate change scenarios for California indicated an increased demand for water over time. Also, increased precipitation did not affect water use or crop yields because many California crops are irrigated . For some crops, increased precipitation in the summer or fall would result in an increased incidence of fruit rot and decreased fruit quality. However, elevated levels of CO2 reduce crop ET,growing hydroponically primarily through a reduction in stomatal aperture, and controlled experiments that measured crop water use under elevated CO2 have shown that most crops produce similar or increased yields with less water .

Future crop water use is difficult to predict due to climate variability, increasing temperatures, and increasing CO2 concentrations. Increasing CO2 and temperatures may balance ET overall, however, water storage in the snow pack of California is predicted to decrease , which will alter the amount and timing of water available to agriculture for irrigation . As a result, California will need to cope more effectively with the constraints of its Mediterranean-type climate than it has done in the past. Even if precipitation increases, water storage will remain an important problem, and issues will arise that require that more research is devoted to understanding crop water responses, and effects of rainfall on crop quality.California agriculture can ultimately respond to the physiological impacts of climate change through cultivar selection and crop management practices designed to respond to changes in crop development. Observed cultivar variation in heat tolerance and access to germplasm from regions with higher temperatures may provide opportunities to breed better adapted cultivars for a variety of crops . Better understanding of plant physiological responses to elevated CO2 and the interacting effects of mineral nutrition, temperature, and O3 are is required to effectively guide breeding for crop performance in a changed atmosphere. Additionally, management practices such as the manipulation of planting dates and timing of thinning can be adjusted to take advantage of changes in crop development and available resources . However, adoption of new cultivars and timing of management practices will be more easily implemented for annual than perennial crops, which require more time and greater investment for cultivar development and crop establishment. Heat stress in cattle is alleviated by shade because it reduces the external radiant heat load . Cooling of the drinking water and acclimation of the animals are other useful strategies to help cattle maintain homeothermy.Selection for heat tolerance may be in conflict with maximizing high yield. In the last 50 years, metabolizable energy for milk production and heat energy have been steadily increasing. Thus, breeding for increased milk production has also changed the thermal regulatory physiology of cows .

Climate change, both within California and globally , is likely to have a significant impact upon the types, abundance and impacts of agricultural weeds, pests, and diseases. While climate change may be advantageous to some species that provide ecosystem services , such benefits will likely be offset by population increases in groups such as invasive exotics, invertebrate pests and disease causing microbes . Predicting these changes rests on better understanding of their ecophysiology and the complexity of the multi-trophic and multi-factor interactions in which they are involved. Here we review literature on agricultural weeds, pests, and disease causing microbes and how they may be impacted by climate change in the context of California agriculture. Noxious and invasive weeds infest over 20 million acres in California and are estimated to cost hundreds of millions of dollars in control expenses and lost productivity annually . Both the direct economic impacts and many of the indirect impacts of these plants such as reduced plant diversity, threatened rare and endangered species, reduced wildlife habitat and forage, altered fire frequency, increased erosion, and depleted soil moisture and nutrient levels may well be exacerbated by interactions with a changing climate . The nature of these interactions, and their variation between different commodities and growing regions, poses a serious problem for decision–maker’s response to changes in the climate of California, but are germane to achieving agricultural sustainability in California.Although increased atmospheric concentrations of CO2 may favor C3 species thereby altering competitive interactions between C3 and C4 species , higher temperatures are expected to favor plants utilizing the C4 photosynthetic pathway . Some efforts to understand these interactions have been made; for example, Tremmel and Patterson studied the growth and allocation of five weed species treated with a gradient of CO2 concentrations and two temperature regimes. Their results demonstrate that generalizations about interactions are difficult; different species and different populations within the same species showed different responses to the same treatment. Similarly, Taylor and Potvin demonstrated that even single factor experiments yield unpredictable outcomes when conducted in an ecosystem context.

In summary, though the effect of individual factors on specific functional groups is well-understood, interactions between these factors often yield unpredictable outcomes which are likely to become even less predictable in natural settings. One example of how such changes could manifest themselves in California involves experiments conducted on Hemizonia congesta, a late-season California native which is similar in phenology and in other respects to Centaurea solstitialis , a problematic Californian weed that us unpalatable except when young. Elevated atmospheric concentrations of CO2 can benefit H. congesta through increased late-season water availability ,growing strawberries hydroponically suggesting that the weed may also benefit. This may be reason for concern because many invasive plants share traits with this endemic species and because water is often limiting in hot, dry summers typical of a Mediterranean climate.Many invasive plants and agricultural weeds are expected to expand their range in response to climate change in a fashion which will likely increase their impact in California. One way to assess northern range limits of tropical and warm temperature annual species is by accumulated heat sum, measured in degree days , during the growing season . Since the number of degree days are expected to increase , new invaders and weeds may become prevalent as appropriate habitats develop and these species extend their range. It has been suggested, for example, that C4 grass weeds which are problematic in the southern U.S., may expand into higher latitudes as a result of global warming ; similar effects may be seen with elevation. Given the prolific nature of most weeds and invasive plants and their exceptional colonization capacities , these C4 grass weeds may be among the first to exhibit such range expansion. The effects of a warmer, more extreme climate, and the relatively disturbed nature of much of California, especially in the Central Valley, may predispose susceptible agricultural systems to quickly encounter new and more vigorous weeds .A complimentary contraction of southern range boundaries of weed species is not necessarily expected. It is now known that detectable adaptive divergence evolves on a time scale comparable to change in climate; within decades for herbaceous plants and within centuries or millennia for longer lived trees . Because many weeds become reproductive at an early age and are highly fecund, rapid rates of evolution will likely play a significant role in their response to climate change. While range expansions are to be expected for many species, range contractions are less likely in rapidly evolving species with significant populations already established.

Similarly should range contractions occur, it is likely that new or different weed species will fill the emerging gaps/niches. Many successful invaders and weeds such as field bindweed , giant reed , and jubata grass , reproduce primarily asexually and their populations might therefore more readily be reduced do to climate change due to their clonal nature. However, asexually reproducing clonal plants on average are not less genetically variable non-clonal plants , and thus the potential for an evolutionary response exists. There are however, large knowledge gaps regarding the evolutionary genetics of clonal plants, making any definitive conclusion difficult .California farmers contend with thousands of crop-damaging invertebrate and vertebrate pest species. As a result of adaptation to climate change, their abundance, types, and activities will likely be altered in the future . This is especially true of invertebrate pests which have rapid generation times, and as such an ability to change to a gradual shift in selection pressures, almost certainly more rapidly than their host plant species , and that of weeds . In 2002 the cost of pesticide use in California was $49.25 million . In recent years California agriculture has adopted Integrated Pest Management , an ecosystem-based strategy that focuses on long-term prevention of pests through a combination of biological control, changes in cultural practices and the use of resistant varieties, as well as chemical control when necessary , for pest management. The efficacy of these different control measures are to a certain extent determined by climate. Invertebrates cause problems such as damaging of crops, vectoring disease, contamination of food and fiber, and export and quarantine problems. Vertebrate pests transmit diseases and parasites, burrow and disturb crop plants and pastures, and damage trees resulting in sap loss and allowing infestation by harmful insects and/or pathogens. Any pest management strategy must be carefully designed, so that beneficial organisms are not negatively impacted and are able to persist. For example, many Californian farmers use IPM, including encouraging bats, burrowing owls, and kestrels on to their properties in order to help control damaging insects, rodents and other pests. Biological control agents, such as parasitoids and predators, and other beneficial species such as pollinators provide important services to agriculture ; Norris and Kogan, 2000. Impacts of a changing climate on pest species and their control are discussed here.Agriculture impact assessments do not account for all impact factors, such as potential yield losses due to changes in pest dynamics and density under climate change . While the Agricultural Assessment Group with the US Global Change Research Program considered the effect of pesticides in their model, they did not account for the effect that changing pest populations had on yield losses . This deserves further attention. For example, in a study of a pest aphid species in Britain Aphis gossypii Glover , the aphids migrated 3-6 days earlier as temperatures increased by 0.4o C over 25 yrs, which has significant implications for epidemiology of aphid vectored virus diseases in economically important crops such as barley and sugar beet . Accurate prediction of insect development and emergence are essential for effective pest management, but can be challenging as it is virtually impossible to measure the micro-environments in which pests actually live. Pest management decisions should take into consideration oquantitative information on dispersal of invertebrate pests, but such information is often lacking . Additionally, invertebrate pests are hard to detect and monitor. Farmed landscapes may need to provide opportunities for natural enemy species to disperse between habitats . However, great diversity of crops along with its own complement of pests creates logistical challenge for planning and implementing successful pest management programs, in a changing climate. This is especially true of California given its many different agricultural commodities and regions .

Weed block fabric is commonly used in organic and hydroponic production systems

Fabric was unrolled and pinned by hand to cover the post-row surface between raspberry beds prior to post installation. The fabric remained in place during the experiment and was unpinned and rolled up at the end of the project for potential reuse. Yard waste mulch from local suppliers was delivered to the project sites. Mulch was a woody < 2-inch screened material with < 20% fine components. Different mulch sources at the two sites were used because the distance between sites and volume requirements for each site were prohibitively large to source from a single supplier. Mulch was delivered by tractor to post rows, where it was spread with rakes to cover the entire post row with a 2- to 3-inch thick layer. At both locations mulch was applied once prior to post installation and persisted throughout the trial period. Polyacrylamide , a nontoxic soil-binding polymer, was applied prior to rain events at a rate of 2 pounds per acre. In 2016–2017, PAM was mixed with water and applied with a backpack sprayer, but due to plugging of nozzles we dispersed dry PAM to post rows instead in 2017–2018 and observed similar efficacy and increased ease of application.In the 2016–2017 season, we collected runoff samples by hand within 30 min from the beginning of the runoff generation, approximately 25 feet away from the ends of each of the treatment post rows . About 250 milliliters of runoff water in each sample were brought from field sites to the UC Cooperative Extension Ventura County lab and immediately tested for turbidity using a turbidimeter , acidified with sulfuric acid to reach pH 3 and either shipped immediately to the ANR analytical lab at UC Riverside or stored at 4°C until shipment. Levels of nitrogen forms and total nitrogren and phosphorus were determined using a Discrete Analyzer AQ2 . In 2017–2018,blueberry box we collected grab samples as described above. We also collected runoff in 5-gallon buckets installed at 25 feet from the end of post rows to intercept first flush of runoff at soil surface level.

Additionally, we installed suction lysimeters about 30 feet away from the ends of the post rows at 8-inch depth at Santa Maria and 8- and 24-inch depths at Somis and collected leachate after rains. In 2017–2018 we also collected sediment from the buckets after runoff occurred, and the sediment samples were dried and weighed at the UCCE Ventura County lab. In April 2018, we took soil samples that were analyzed for soil moisture, nitrate nitrogen and phosphorus content. We calculated the costs of each treatment for the 1,800– square foot experiment plot and then extrapolated the costs into a per acre basis for one tunnel use period. A tunnel use period covers a 3-year production cycle of raspberry from establishment until termination. Costs of treatments included materials, labor and equipment when applicable. Granular dry PAM formulation application to soil was used in the analyses. We also adjusted the treatment’s costs if it provided weed control benefit. In addition, some treatments can serve for more than one tunnel use period. Therefore, we distributed the costs accordingly.Not all treatments had runoff during light rains. Barley cover crop and yard waste mulch likely interfered with low flows and aided water retention in post rows. We observed slower flows and greater puddling in post rows with barley or mulch than in other treatments or untreated soil . Soil sampled 3 days after rain in March 2018 at Somis had 8% to 12% greater moisture content at both sampling depths under mulch compared with other treatments . Mulch also conserved more soil moisture than fabric at Santa Maria .Combined nitrite and nitrate levels in runoff samples ranged from 0.29 to 6.48 milligrams per liter over two seasons of sampling. This variability is due to the intensity and frequency of the rains during this period, which also affected the accumulated fertigated nitrogen that occurred between rain events. Fabric and PAM did not reduce nitrate or nitrite in runoff compared with untreated soil at any of the sampling dates at both locations and sampling seasons , while mulch was equally ineffective in 2016–2017 in reducing NOx in runoff at both locations. During one out of five runoff events in 2016–2017, barley reduced NOx levels in runoff by 48% compared with untreated soil, but not significantly during other rain events of that season.

During two out of five runoff events at Somis in 2017–2018, barley reduced NOx levels in runoff by 71% and 82% and mulch reduced them by 67% and 91% compared with untreated soil, but reductions were not significant at other sampling events. At Santa Maria, none of the treatments had significant impact on NOx in runoff when compared with untreated soil . All treatments at Somis were effective in reducing ammonium in runoff in 2016–2017 compared with untreated soil , but only barley was effective in 2017–2018. The overall greater average levels of ammonium in 2017–2018 were likely due to use of passive samplers that intercepted the first flush of runoff, which may have had a greater concentration of pollutants than runoff collected later . Ammonium is typically carried on sediments, so lower ammonium would indicate less sediment movement. This suggests that barley cover crop and yard waste mulch can reduce both the concentration of dissolved ammonium nitrogen in runoff and the volume of runoff, leading to potential reductions in nitrogen losses to the environment compared with untreated soil. Soil under barley and mulch had significantly less nitrate nitrogen compared with other treatments in March 2018 at Somis . At Santa Maria, all treatments except for mulch had 25% to 81% less nitrate nitrogen than that of untreated soil, although mulch was also similar to all other treatments. Mulch deterioration might have reduced its efficacy at Santa Maria. At Santa Maria, nitrate nitrogen levels in leachate collected at 8-inch depth on all sampling dates ranged from 12 to 27 parts per million in PAM and untreated plots, which was 52% to 80% greater than those in other treatments . At Somis a similar trend was observed: nitrate nitrogen levels in leachate under PAM and untreated soil were 7 to 22 ppm, which was 80% to 90% greater than those under barley or mulch. Leachate nitrate concentrations under fabric were not different from those in untreated soil . These results suggest that barley and mulch can reduce nitrate nitrogen in soil and leachate. Mulch and cover crop act as a barrier to runoff water with dissolved nitrogen and sediment and may retain nitrogen to be used for cover crop growth and for residue and mulch decomposition. Turbidity in first flush of runoff was reduced 5- to 10-fold by all treatments compared with untreated soil at both locations in 2018 . These results were similar to turbidity in grab samples taken in 2017 and 2018 , which suggests that all treatments were effective in reducing waterborne sediments on site. Additionally, 75% to 97% less sediment was collected from passive samplers in all treated post rows compared with those in untreated soil, as shown for March 10, 2018 .

Relatively high sediment load in fabric treatment resulted from deposits of soil on top of the fabric during removal of plastic from raspberry beds. Similar to the March 10 rain event, we observed significantly lower sediment levels after other rains in all treated post rows compared with untreated rows . We also observed fewer erosion channels in treated post rows compared with untreated plots at both sites during the trial. Besides the agronomic benefits,blueberry package retaining soil in the field is also a good pesticide management practice because soil-adsorbed pesticides will stay in the field and not end up in receiving bodies of water. In a previous study, Mangiafico et al. showed that concentrations of the harmful insecticide chlorpyrifos in runoff were linearly related to sample turbidity. This suggests that retaining waterborne sediments on-site is an effective method for mitigating runoff of this pesticide. Preventing soil movement with these post row treatments may also reduce the costs of sediment removal from receiving waterways and associated environmental impacts . Phosphorus levels in the first flush of runoff samples were reduced by 24% to 85% in all treatments compared with untreated soil at Somis in 2018, except for PAM on Feb. 27, 2018 . Lack of efficacy of PAM on that date may have resulted from deterioration of the PAM seal due to soil disturbance after PAM application and before runoff sample collection. At Somis in 2016–2017 and Santa Maria in 2018, we observed a similar reduction in phosphorus by all post row treatments compared with untreated soil . Since phosphorus is normally adsorbed to soil particles , reduction in turbidity and phosphorus in runoff samples from treated post rows followed a similar trend. Reducing losses of phosphorus from production fields may help prevent eutrophication in receiving waterways when this micro-element is limiting for algal growth . Since tunnel post rows receive water and retain soil moisture, conditions are favorable for weed growth. At both locations weed barrier fabric provided nearly complete weed control with only occasional weed germination in areas where soil was deposited on the top of the fabric.

Application of PAM did not provide control, and weed densities in PAM-treated rows were similar to those in untreated plots. Yard waste mulch provided 81% to 90% weed control at Somis but did not control weeds in two out of three evaluation dates at Santa Maria . Mulch at Santa Maria was much finer compared with the one at Somis, and likely decomposed more rapidly, allowing weed growth. Barley cover crop provided 86% and 42% weed control on two evaluation dates at Somis, but after barley was reseeded, high germination of little mallow occurred . Incorporation of barley during reseeding likely disturbed hard-coated weed seeds sufficiently to break dormancy; however, mallow was controlled before seed production when barley was mowed in spring. Barley cover cropat Santa Maria provided 87% and 43% weed control at two out of three evaluation dates. At Somis in 2018, we observed 3.5 more volunteer raspberry shoots in post rows with mulch compared with other treatments or untreated plots . Unlike weeds, raspberry shoots were able to penetrate mulch and establish, likely benefiting from the greater soil moisture content under it . These results show that weed barrier fabric, mulch and barley can effectively reduce weed control costs in raspberry tunnel post rows, but greater volunteer raspberry shoot management may be required if mulch is used.Although the diversity and economic size of California’s agricultural production may increase its resilience and resistance to perturbations such as urbanization, higher temperatures and increasing resource costs are forecast for the next 100 years , and there is great uncertainty as to how producers will respond to a changing climate both within California and globally. Producers may face significant challenges as regional temperatures, precipitation and weather pattern variability, and national and international markets are altered by global climate change. As commodity prices are dependent on global production and demand, any assessment of the impacts of climate change on California agriculture must be done in the context of both regional and global changes in yields. The magnitude and direction of these yields will be determined by climatic factors such as temperature, precipitation, and weather variability, and production factors such as biotic responses to elevated atmospheric CO2 concentrations, the availability and application of nutrients, and the ability of producers to adapt to these changes. Furthermore, as global markets develop for carbon trading, opportunities may arise for California agricultural producers to mitigate greenhouse gases . Therefore, adjustments in global food and mitigation markets together will no doubt significantly determine California agricultural producers’ response to climate change. Furthermore, since agriculture is not only of economic significance, but also secures the livelihood of most of the world’s population, impacts of climate change on food and farm security are of particular importance . Predicting yields in the coming century requires complex modeling that integrates both global and regional climate change models, crop growth models and economic models, with the expectation that climate change will likely impact different regions of the world in distinct ways .

Are geographic and economic mobility linked for workers who get non-farm jobs?

The United States and Mexico appeared close to agreement on a program to legalize farm and other workers before September 11, 2001. However, after the war on terror was declared, the momentum for a new meant that more tons of vegetables were produced from the same acreage, while acreage of fruits and nuts rose from 2 million acres in 1990 to 2.4 million acres in 2000, a 19% increase over the 1990s. Many FVH commodities are labor intensive, with labor accounting for 15% to 35% of production costs. Most of the workers employed on FVH farms are immigrants from Mexico, and a significant percentage are believed to be unauthorized . In recent years, several proposals have aimed to reduce unauthorized worker employment in agriculture . In September 2001, Mexican President Vincente Fox called for a U.S.-Mexico labor migration agreement so that “there are no Mexicans who have not entered this country [U.S.] leguest-worker program and the legalization of immigrants already in the country slowed. In summer 2003, there were several new proposals for a migration agreement with Mexico to legalize the status of currently unauthorized workers and allow some to earn immigrant status by working and paying taxes in the United States. There is little agreement, however, on what impacts such a program would have on California’s farm labor market. We used a unique database to examine farm employment trends in California agriculture. The data suggests that: about three individuals are employed for each year-round equivalent job, helping to explain low farm worker earnings; there was a shift in the 1990s from crop farmers hiring workers directly to farmers hiring via farm labor contractors ; and there is considerable potential to improve farm labor market efficiency,growing bags by using a smaller total workforce with each worker employed more hours and achieving higher earnings.

California employers who pay $100 or more in quarterly wages are required to obtain an unemployment insurance reporting number from the California Employment Development Department . The EDD then assigns each employer or reporting unit a four-digit Standard Industrial Classification or, since 2001, a six-digit North American Industry Classification System code that reflects the employer’s major activity . Major activities are grouped in increasing levels of detail; for example, agriculture, forestry and fisheries are classified as a major industrial sector and, within this sector, SIC 01 is assigned to crops, 017 to fruits and nuts and 0172 to grapes. We defined “farm workers” as unique Social Security numbers reported by farm employers to the EDD, and then summed their California jobs and earnings. This enabled us to answer questions such as how many farm and non-farm jobs were associated with a particular SSN or individual in 1 year, and in which commodity or county a person had maximum earnings. We adjusted the raw data before doing the analysis. Farm employers have reported their employees and earnings each quarter since 1978, when near universal UI coverage was extended to agriculture. Although it is sometimes alleged that farm employers, especially FLCs, do not report all their workers or earnings, there is no evidence that under reporting of employees or earnings is more common in agriculture than in other industries that hire large numbers of seasonal workers, such as construction. We excluded from the analysis SSNs reported by 50 or more employers in 1 year . We also excluded wage records or jobs that had less than $1 in earnings and jobs, or that reported earnings of more than $75,000 in one quarter. These adjustments eliminated from the analysis 2,750 SSNs, 62,571 wage records or jobs and $803 million in earnings. These exclusions were about 0.25%, 2.7% and 6.1% of the totals, respectively, and are documented more fully in Khan et al. .

There is no single explanation for the outlier data we excluded. In some cases, several workers may share one SSN, while in others our suspicion that a SSN had “too many” jobs may represent data-entry errors. During the 1990s, the Social Security Administration cleaned up SSNs, including threatening to fine and reject tax payments from employers with too many mismatches between SSNs and the names associated with those SSNs, which should have reduced the number of SSNs reported by employers. We think the rising number of SSNs reflectsmore individuals employed in agriculture, not more noise in the data.Agricultural employment can be measured in three major ways: at a point in time, as an average over time or by counting the total number of individuals employed over some period of time. In the non-farm labor market the three employment concepts yield similar results. If 100 workers are employed during each month and there is no worker turnover from month to month, then point in time, average and total employment is 100. However, agricultural employment during the six summer months may be 150, versus 50 during the six winter months, meaning that point, average and total employment counts differ. We began with all SSNs reported by agricultural employers , summed the jobs and earnings of these SSNs within each SIC code, and assigned each SSN to the four-digit SIC code in which the worker had the highest earnings. This means that a SSN reported by a grape employer as well as by an FLC would be considered a grape worker if his highest-earning job was in grapes. The number of individuals or unique SSNs reported by California agricultural employers has been stable over the past decade — 907,166 in 1991, 966,593 in 1996 and 1,086,563 in 2001 .Farm workers had a total of 1.5 million farm jobs in 1991, 1.7 million in 1996 and 1.8 million in 2001. One-quarter also had at least one non-farm job — about 407,000 workers were both farm and non-farm workers in 1991, 453,000 in 1996 and 697,000 in 2001 . The total California earnings of persons employed in agriculture were $11.1 billion in 1991, $12.0 billion in 1996 and $15.8 billion in 2001 . The share of total earnings for farm workers from agricultural employers was 77% in 1991, 77% in 1996 and 71% in 2001, indicating that in the late 1990s, farm workers tended to increase their supplemental earnings via non-agricultural jobs.

Average earnings per job were highest in livestock, $13,800 per job in 2001. There was little difference between average earnings per job in agricultural services and crops . Average earnings per job were higher for the non-farm jobs of agriculture workers than for agriculture jobs .In 2001, California’s farm workers held 2.5 million jobs, including 1.8 million jobs with agricultural employers. These agricultural jobs included 630,000 in crops, 69,000 in livestock and 1.1 million in agricultural services. The agricultural services sector includes both farm and non-farm activities, such as veterinary and lawn and garden services; FLCs accounted for 70% of the employees reported by farm agricultural services. Fruits and nuts accounted for 53% of the crop jobs, dairy for 39% of the livestock jobs and FLCs for 58% of the agricultural services jobs. The major change between 1991 and 2001 was the drop of 54,000 jobs in crop production and increase of 313,000 jobs in agricultural services. We placed SSNs in the detailed commodity or SIC code that reflected the maximum reported earnings for the worker,nursery grow bag and considered workers to be primarily employed in the SIC with maximum earnings. In 2001, there were 877,000 primary farm workers, and they included 322,000 reported by crop employers, 50,000 reported by livestock employers and 504,000 reported by agricultural service employers. Fruit and nut employers accounted for 47% of the crop-reported workers, dairy for 40% of the livestock-reported workers and FLCs for 44% of the agricultural services–reported workers. The major change between 1991 and 2001 was the increase in number of SSNs with their primary job in agriculture — from 758,000 to 877,000. There was a slight drop in the number of workers reported by crop employers, a slight increase in livestock workers and a sharp 135,000 increase in agricultural services workers, anchored by a 59,000 increase in workers reported by FLCs in 2001. Most farm workers had only one job. In 2001, 53% of the SSNs were reported by only one employer to the EDD, 26% were reported twice, 12% three times, 5% four times and 4% five or more times. During the 1990s, about 65% of farm workers were reported by one agricultural employer only, 17% to 21% by two agricultural employers, 5% by at least two agricultural employers and one non-farm employer, and 9% to 12% by one farm and one non-farm employer. In the three-digit SIC codes representing more detailed commodity sectors, 60% to 83% of the employees had only one job. For example, in 2001 79% of the employees reported by dairy farms had one dairy farm job, while 7% also had a second agricultural job — 3% had a dairy job, a second farm job and a non-farm job, and 11% had a non-farm job in addition to the dairy job. About two-thirds of the employees of FLCs and farm management companies had only jobs with one such employer; 22% had another farm job; 6% had an FLC job, another farm job and a non-farm job; and 6% had a non-farm job in addition to the FLC job. Even more detailed four-digit SIC codes showed the same pattern: the commodities or SICs most likely to offer year-round jobs such as dairies and mushrooms had 70% to 80% of employees working only in that commodity, while commodities or SICs offering more seasonal jobs, such as deciduous tree fruits and FLCs, had 53% to 63% of employees working only in that commodity.

At the four-digit, SIC-code level, the five largest SICs accounted for about 45% of the agricultural wages reported.Agricultural employers paid a total of $11 billion in wages in 2001, an average of $10,200 per worker . Earnings were highest for the 64,000 workers primarily employed in livestock; they averaged $14,800, followed by those primarily employed by crop employers and those employed by agricultural farm services, custom harvesters and FLCs . There was considerable variation in earnings among workers in agricultural farm services: workers in soil preparation services averaged $21,100 in 2001, versus $12,700 for crop preparation services for market and $4,400 for FLC employees. The average earnings of primarily farm workers varied significantly, even within detailed four-digit SIC codes — in most cases, the standard deviation exceeded the mean wage . Median earnings were generally less than mean earnings, reflecting that higher wage supervisors and farm managers pulled up the mean. If the workers in detailed commodities are ranked from lowest-to-highest paid, the lowest 25% of earners in an SIC category generally earned less than $4,000 a year. For example, among workers primarily employed in vegetables and melons in 2001 , the first quartile or 25th percentile of annual earnings was $3,000. This reflects relatively few hours of work — if these workers earned the state’s minimum wage of $6.25 an hour in 2001, they worked 480 hours. The 25th percentile earnings cutoff was lowest for those employed primarily by FLCs, only $634, suggesting that FLC employees receiving the minimum wage worked 101 hours. The highest 25th percentile mark was in mushrooms , $9,491, which reflects 1,519 hours at minimum wage. The 75th percentile marks the highest earnings that a non-supervisory worker could normally expect to achieve — 75% of workers reported earning less than this amount and 25% earned more. The 75th percentile varied widely by commodity: $6,172 for those primarily employed by FLCs, $10,572 for those in grapes and $29,465 for those in mushrooms.The number of individuals and jobs reported by agricultural employers increased in the 1990s, reflecting increased production of labor-intensive fruit and vegetable crops and, the data suggests, more farm workers each worked a fewer number of hours. With the state’s minimum wage at $6.25 per hour after Jan. 1, 2001 , the earnings reported by employers suggest that most farm workers are employed fewer than 1,000 hours per year . FLCs increased their market share in the 1990s, but dependence on them varied by commodity. For example, FLCs rather than citrus growers reported many citrus workers, while dairy employers reported most dairy workers. FLCs are associated with low earnings, which suggests few hours of work — the median earnings reported by FLCs for their employees in 2001 were $2,650, or 400 hours if workers earned the state’s $6.25 minimum wage. California’s farm labor market has large numbers of workers searching for seasonal jobs; FLCs are matching an increasing share of these workers with jobs, resulting in lower earnings for FLC employees. Workers who avoid FLCs experience higher earnings in agriculture or in the non-farm labor market. If FLCs are most likely to hire recently arrived and unauthorized workers, as the National Agricultural Worker Survey suggests, FLCs serve as a port of entry for immigrant farm workers. The impact of guest workers, legalization and earned legalization will depend on the details of any new program. If the status quo continues, the percentage of unauthorized workers is likely to rise. Alternatively, if there were a legalization program, farm workers might more quickly exit the farm workforce. However, an earned legalization program could slow this exit if workers were required to continue working in agriculture to earn full legal status. The next step in this analysis is to examine the mobility of individual farm workers over time and geography, examining where workers migrate during 1 year and patterns of entrance to and exit from the farm workforce . Do farm workers who increase their earnings by moving to non-farm jobs stay in non-farm jobs, or do they sometimes return to agriculture? Answers to these questions will help to determine the trajectory of the farm labor market.

We geocoded maternal residential addresses listed on the birth certificates using an automated approach

Since most pesticide applications are spatially explicit and the usage may vary over years, these studies face challenges of lacking high spatial and temporal resolution for exposure assessment, on top of the known ecological fallacy. On the other hand, individual level GIS-based studies that assessed exposure to agricultural pesticides in proximity to residences, have shown inconsistent findings. A recent Spanish study explored the possible association between childhood renal tumors and residential proximity to environmental pollution sources by calculating the percentage of total crop surface within a 1-km buffer around each individual’s last known residence and discovered that children living in the proximity of agricultural crops have higher risk of developing renal cancer . However, US studies of individual measures of agricultural pesticides in proximity to residences, mostly suggested no association with childhood cancers, or at best modest associations for certain types of cancers and chemicals or chemical groups. A Texas study measured crop field density within a 1-km buffer of residence at birth for both cases and controls born in 1990-1998 to study the risk for childhood cancers by sub-types and found no evidence of elevated risk associated with residential proximity to cropland for most childhood cancers, except for modestly positive associations with non-Hodgkin lymphoma , Burkitt lymphoma , and other gliomas. A California population-based case-control study of early childhood cancer used mothers’ residential addresses at the time of birth to evaluate risks associated with residential proximity to agricultural applications of pesticides during pregnancy and also found no associations with most specific chemicals and chemicals groups,plastic planters except for modestly elevated ORs for leukemia associated with probable and possible carcinogen use and with nearby agricultural applications of organochlorines and organophosphates.

They suggested that the few elevated risk associations for specific chemicals including metam sodium and dicofol in this study are likely due to chance from multiple comparisons . Another Northern California study assessed residential proximity within a half-mile of pesticide applications by linking address histories with reports of agricultural pesticide use and examined the association of the first year of life or early childhood pesticide exposures and childhood acute lymphoblastic leukemia and suggested elevated ALL risk was associated with lifetime moderate exposure to certain physicochemical groups of pesticides, including organophosphates ,cholorinated phenols , and triazines , and with pesticides classified as insecticides or fumigants.These results vary by chemicals or chemical groups examined, and methods of exposure assessment, and therefore produced inconsistent results. In addition, many of the above studies found no or week associations between all cancer types grouped together and proximity to crop fields, agricultural activities, specific agents, or groups of chemicals. It may problematic because the etiologies of most childhood cancer sub-types remain largely unknown and may not share the same causal pathway mediated by pesticides. As mentioned before, these studies of ambient pesticide exposures in pregnancy or early childhood, often assign exposures based upon the child’s or mother’s residence. While large scale record-linkage studies can avoid selection and recall biases that often impact smaller studies with active subject recruitment, previous record-based studies often relied solely on maternal residential address at birth, which is readily available on many birth certificates and/or residential address at diagnosis, as was done in some childhood cancer studies . Previous evidence suggested that exposure to pesticides before or during pregnancy may harm the developing fetus. Nevertheless, increased risks were seen for postnatal period as well. For instance, a study of childhood leukemia tried to distinguish between pre-pregnancy, pregnancy and postnatal exposures as critical windows for household pesticide exposure, and insecticide exposures early in life appear to be significant, though the effect is not as strong as prenatal exposures .

After birth, children may also be more susceptible to the harmful effects of pesticides than adults, as they have more actively dividing cells , providing the rationale to studies of childhood cancers not only focus on prenatal but also early life exposures. The reliance on one address for assessment of exposures in the first year of life or early childhood implicitly makes the assumption that a child’s residence remained the same throughout the entire period of interest, or if they moved, that the exposure levels remained the same. Even if some studies assessed exposures as the children’s residential proximity to agricultural fields or pesticide applications at the time of birth, these exposure indicators at birth are assumed to reflect exposures in prenatal and/or postnatal period, which are believed to be critical windows of exposures for childhood cancers. Consequently, the “one-address” approach may lead to exposure misclassification for those who moved in early childhood especially for exposures with high spatial heterogeneity. In a 2003-2007 California statewide representative survey, only 14% of all women moved in the 2-7 months post-partum , but with increasing age of the child, the frequency of residential moves also increased. For more than 50% of childhood cancer cases under age 5 diagnosed in California between 1988 and 2005, address at birth differed from the address at cancer diagnosis , which raises concerns about using residence at birth to assess exposures in early childhood. Exposure misclassification due to moving is a ubiquitous problem encountered by nearly all record-based studies that lack a complete residential history for each child. Previous studies suggested that residential mobility may be associated with certain risk factors for childhood cancers such as maternal age, marital status, parity, family income, and other socioeconomic status metrics , resulting in non-differential or even differential misclassification of exposures. Currently, in the US, the privilege of having an accurate complete residential history still only belongs to interview-based environmental epidemiological studies, which are often quite small with hundreds of subjects because of high time and monetary costs of such interviews and likely under powered.

Small case-control studies typically asked for individuals’ lifetime residential histories , including the beginning and end dates for each address. Large cohort studies follow participants over for a long time and often update their addresses periodically from follow-up questionnaires, so they may not know the exact moving dates. Sometimes these studies additionally collect information from the US Postal Service change-of-address forms or major credit reporting agencies, but the date associated with each address does not necessarily capture an accurate “move-in” date, but rather reflects the first known date . While it is not feasible to acquire complete residential histories from interviews for all subjects in large record-based studies as a gold standard to compare against the recorded birth or diagnosis address, databases containing public records of individuals collected by commercial companies have become available in recent years, allowing us to trace individuals without a self reported residential history. For example, LexisNexis Public Records, Inc. , a commercial credit reporting company,plastic nursery plant pot provides all known addresses for a set of individuals upon request. If the commercial residential history data has relatively high accuracy, their low cost and broad coverage would provide valuable information to all studies requiring residential history data . The basic service provided by LexisNexis returns the latest three known addresses while the enhanced service, with a higher cost, returns all known addresses from at least 1995. This database was maintained primarily for the purpose of contacting study participants but not for scientific research use, and therefore may not be as accurate as residential history obtained from interviews or self-administrated questionnaires. Several earlier studies have attempted to compare reconstructed residential history based on LexisNexis records with interview-based residential history for enrolled subjects and validate its use for research purposes. A Michigan case-control study of bladder cancer first compared lifetime residential histories collected through written surveys and 3 residential addresses available in LexisNexis and reported 71.5% match rate . Their bladder cancer cases were less than 80 years of age upon diagnosis, and controls were selected from similar age groups. Both cases and controls had lived in 1 of the 11 counties in Michigan for more than 5 years before recruitment in 2008-2009. Another US-wide study selected a random sample of 1000 subjects originally enrolled in the National Institutes of Health-American Association of Retired Persons Diet and Health Study, with AARP members aged 50–69 years and living in one of six US states or two metropolitan areas at the time of enrollment. Authors found 72% and 87% detailed address match rates with the basic and enhanced services provided by LexisNexis, respectively . The most recent LexisNexis validation study looked into participants in California Teachers Study, a prospective cohort study initiated in 1995-1996 and originally designed to study breast cancer. These women aged between 22 to 104 years at enrollment , and lived throughout California. The study pointed out that though the overall match rate between the two sources of addresses was good , it was diminished among black women and younger women . In summary, such residential information from LexisNexis, if of high quality, could potentially augment existing address information and help us reconstruct residential histories for subjects in large record-linkage studies and provide more accurate exposure estimates.

However, researchers should be aware that residential mobility of young children or their mothers may be different from that of mid-aged or older population, who were the majority in all three validation studies discussed above and believed to have a more stable residence. In addition, differences in distributions of race/ethnicity, socioeconomic status, and geographic regions may influence residential mobility in various study populations as well.During the 1st decade of the 21st century, the estimated rates of preterm birthand low birth weightpeaked at 11%-13% and 7%-8% in the US, respectively . Though survival of infants born preterm and/or low birthweight has improved in the last decades due to advancements in prenatal and neonatal care, they are more susceptible to adverse health outcomes such as neurodevelopmental impairment, respiratory and gastrointestinal complications , obesity, diabetes mellitus, hypertension, and kidney disease ; they also result in substantially higher infant and childhood mortality rates . California is the largest agricultural state in the United States, with more than 150 million pesticide active ingredients applied every year . Previous experimental studies show that various pesticides, including organophosphates and pyrethroids, can influence prenatal development related to adverse birth outcomes .Proposed mechanisms include disturbance of placental functions , endocrine disruption , immune regulation and inflammatory mechanisms . Pesticides have been found in indoor residential dust in residences near agricultural fields, and may persist for years . However, epidemiologic studies yielded inconsistent results, specifically while ecological and cross-sectional studies reported positive associations for PTB and LBW and pesticide use in agriculture , results from studies assessing self-reported or occupational use of pesticides were inconsistent . A systematic review of 25 studies examining agriculture-related exposures from residential proximity to pesticide applications suggested weak or no effects on preterm birth and low birth weight, possibly due to the methodological difficulties of exposure assessment . More recent residential proximity studies using simple or aggregate-level exposure assessments provided some evidence for pesticide influencing birth outcomes . Two recent Geographic Information System -based studies restricted to the San Joaquin Valley of California reported conflicting results – one found pesticide exposures to increase preterm birth and low birthweight by 5-9% in those highly exposed to chemicals with acute toxicity as based on the US EPA Signal Word , while the other assessed 543 individual chemicals and 69 physicochemical groupings found negative associations for spontaneous preterm birth . Nevertheless, various small pesticide biomarker-based studies with measured organochlorines, organophosphates, or pyrethroids and their metabolic breakdown products in maternal blood or urine or umbilical cord blood suggested positive associations with preterm birth or with lower birthweight but results varied by chemicals and outcomes assessed . Here, we assessed GIS-derived exposures during pregnancy to selected agricultural pesticides applied near maternal residences and risks of preterm birth and term low birthweight, considering trimester-specific exposure windows in a large sample of births in agricultural regions of California.Birth addresses with a low geocode quality due to missing or non-geocodeable fields on the birth certificates accounted for ~12% of all addresses geocoded. We then calculated measures of residential ambient pesticide exposures using a GIS-based Residential Ambient Pesticide Estimation System, as previously described . In brief, since 1974 agricultural pesticide applications for commercial use are recorded in Pesticide Use Reports mandated by the CA Department of Pesticide Regulation .

Data-driven statistical approaches can provide complementary insight into these questions

Additionally, studies have found statistically significant negative associations between living in proximity to agriculture and adverse outcomes , but not with pesticide metabolite levels directly. Similarly counter intuitive results have illustrated that specific chemicals such as methyl bromide or OP pesticides have negative associations with some birth outcomes, but also unexpected positive associations for others.Large samples provide a powerful opportunity to control for various different demographic and environmental characteristics that may be obscuring the relationship between agricultural pesticide exposure and adverse birth outcomes in surrounding communities. Here we revisit the relationship between pesticide exposure and birth outcomes using a large sample of births , which includes individual-level data on maternal and birth characteristics, and pesticide exposure at a small geographical scale. We concentrate on the agriculturally dominated San JoaquinValley, California. California is the most populous state in the United States with roughly 12% of annual births. It is also the greatest user of pesticides with over 85 million kg applied annually, an amount equivalent to roughly 30% of the cumulative active ingredients applied to US agriculture. The San Joaquin Valley is the state’s most productive agricultural region, growing an abundance of high value, high chemical input, and labor-intensive fruit, vegetable, and nut crops. We evaluate pesticide exposure by summing active ingredients of agricultural pesticides applied over gestation, by trimester,round flower buckets and by grouped the United States Environmental Protection Agency’s acute toxicity categories, along with several additional robustness checks. For outcomes, we focus on birth weight, gestational age, and birth abnormalities.

Our sample of over 500 000 individual birth observations and fine-scale data on the timing and amount of pesticide applied allow us to detect statistically significant negative effects of pesticide exposure for all birth outcomes, but generally only for pregnancies exposed to the very highest levels of pesticides .To explore if either inaccuracies in geocoding or spillover of pesticides from surrounding areas contaminated our results we excluded births for mothers living within 200 m of a PLS Section boundary. We found a similar overall pattern of statistical significance as in the larger sample. Although the magnitude of the coefficients increased, the effects on birth weight and gestational length remained <1%, and the effects on the probability of low birth weight, preterm birth, and abnormalities were at most 13% higher for the high exposure group relative to the low exposure group . We also estimated the trimester model including pesticide use in the “fourth trimester” . As anticipated, exposure during the three months following birth did not have a significant effect on any outcomes observed at birth . This “placebo” analysis indicates that our empirical results are unlikely to be caused by omitted trends or factors that are correlated with both pesticide applications and infant health. To further ensure the robustness of our results and inference, we checked different exposure cutoffs as well as a continuous measure of exposure . The magnitude of effects was small and generally non-significant with the 75th percentile cutoff. Being in the top one percent of pesticide exposure led to an 11% increased probability of preterm birth, 20% increased probability of low birth weight, and ~30 g decrease in birth weight relative to lower exposure . We also evaluated models with different location fixed effects, different assumptions about clustering the standard errors to address spatial and temporal error correlation, different sample exclusion restrictions on gestational age and different calculations of trimester, as well as models with other environmental contaminants that can affect in utero infant health .

Although the exact magnitude and patterns of significance did change with these different models, all models consistently reported similar effect sizes. Overall, we report over 100 coefficients in the main text, of which 19 are significant. It is noteworthy that in all these tests, only a single significant coefficient in one model has the opposite sign from that expected. The fact that only one of roughly 20 statistically significant coefficients has the wrong sign is consistent with the notion that our empirical estimates are not plagued by omitted variable bias. Further, since we do not adjust p-values for multiple comparisons, the number of significant effects we report is an upper bound on the “true” number of significant effects. Applying a Bonferroni correction for multiple comparisons that accounts for five outcomes and up to five covariates of interest , the α-level for statistical significance would change from 0.05 to as small as 0.002 . The only three coefficients that remained statistically significant with this Bonferroni correction were those associated with a single covariate of interest, total pesticide exposure over the gestation . Of these, two were associated with preterm birth and one with log gestation .Concerns about the effects of harmful environmental exposure on birth outcomes have existed for decades. Great advances have been made in understanding the effects of smoking and air pollution, among others, yet research on the effects of pesticides has remained inconclusive. While environmental contaminants generally share the ethical and legal problems of evaluating the health consequences of exposure in a controlled setting and the difficulties associated with rare outcomes, pesticides present an additional challenge. Unlike smoking, which is observable, or even air pollution, for which there exists a robust network of monitors, publicly available pesticide use data are lacking for most of the world. As a result, studies have typically been either highly correlative at coarse resolutions or have included a small number of subjects. Both constraints make it difficult to assess whether residential agricultural pesticide exposure has no effector whether logistical and analytical barriers have obfuscated the identification of important effects. Our study bridges the gap between detail and scale by leveraging vast pesticide and birth data for the San Joaquin Valley, CA. Our study has far stronger statistical power to identify effects than previous studies owing to over a hundred thousand birth observations, individual maternal and birth characteristics, and the inclusion of fine-scale regional and temporal fixed effects .

As a result of our statistical design, we have the analytical power to identify extremely small, but statistically significant negative effects of pesticide exposure on several birth outcomes, if they occur. Furthermore, our study design and extensive pesticide data enable us to evaluate many details of the nature of pesticide exposure. For example, we can evaluate whether pesticide exposure in different trimesters or pesticides of different toxicity levels affected birth outcomes in different ways. Fetal susceptibility to environmental exposure varies through development. Similarly, different chemical toxicity can have different expected health outcomes. Here we focused on aggregate chemicals grouped into high and low toxicity pesticides by their EPA Signal Word, which reflects acute toxicity. Acute toxicity does not necessarily indicate impacts from long-term exposure. As such, chemicals suspected to cause negative birth outcomes, such as organophosphates or atrazine would be classified as low toxicity. Nevertheless, we consistently find effects of less than a 10% increase in adverse outcomes for individuals in the top 5% of exposure regardless of timing or toxicity of exposure, even though which effects are statistically significant depends on the model. Pesticide exposure has a highly skewed distribution in the San Joaquin Valley, where over half of births received no pesticides,plastic flower buckets wholesale the top quarter received about 250 kg and the top 5% received over 16 times that amount. Further, exposure to the top 25% levels had virtually no detectable effect whereas exposure to the top 1% had effects that were up to double the magnitude of effects observed for the top 5% of exposure. In other words, for most births, there is no statistically identifiable impact of pesticide exposure on birth outcome. Yet, for individuals in the top 5 percent of exposure, pesticide exposure led to 5–9% increases in adverse outcomes. The magnitude of effects were further enlarged for the top 1%, where these extreme exposures led to an 11% increased probability of preterm birth, 20% increased probability of low birth weight, and ~30 g decrease in birth weight. For perspective, other environmental conditions such as air pollution and extreme heat generally report a 5–10% increase in adverse birth outcomes, but from less extreme exposure. Similar magnitudes of effects are also observed for other, non-exposure conditions of pregnancy. For example, stress during pregnancy may increase the probability of low birth weight by ~6%, while enrollment in supplemental nutrition programs is estimated to reduce the probability of low birth weight by a similar amount. The significance of the negative effects of extreme pesticide exposure on birth outcomes is heightened by the fact that birth outcomes are persistent and costly. Reducing the incidence of adverse birth outcomes has obvious benefits for individuals, but also for society.

Healthier babies require less intensive care as infants, have better long term health and are higher achieving in terms of earnings and employment. Thus, even small reductions in adverse outcomes can economically offset societal investment in programs such as supplemental nutrition programs offered to millions of low-income women. Due to the concentration of negative outcomes at the very highest pesticide exposures, policies, and interventions that target the extreme right tail of the pesticide exposure distribution could largely eliminate the adverse birth outcomes associated with agricultural pesticide exposure documented in this study. As such, valuable and pressing future directions for research should focus on identifying the extreme pesticide users near human development and on the underlying causes for their extreme quantities of use. These insights are critical to designing appropriate and adaptive interventions for the population living nearby. For instance, crops vary dramatically in their average pesticide use. Commodities such as grapes receive nearly 50 kg ha−1 per year of insecticides alone in the San Joaquin Valley region, while other high value crops such as pistachios receive barely on third of that amount. Within these broad differences, there are also relevant differences among crops with regard to the chemical composition and seasonal timing of pesticide application. Finally, not all agricultural fields are in proximity to human settlement. Rather, as we illustrate, areas with consistent births and pesticides are a small fraction of the San Joaquin Valley. Thus, if extreme pesticide areas and vulnerable populations could be identified, strategies or interventions could be developed to mitigate the likelihood of extreme exposures. One further difficulty is isolating the roles of individual chemicals and their mixtures in driving the negative outcomes. Doing so is extremely challenging, because many chemicals are used in conjunction or in close spatial or temporal windows. Using a large scale data-driven approach could provide a starting point from which individual or community based studies could be built. For example, statewide birth certificate data could enable the identification of potential hot spots of negative birth outcomes while the Pesticide Use Reports provide a large sample of different pesticide mixtures. This could yield valuable information for targeting more detailed studies of individual exposures and difficult to observe outcomes towards regions and months of the highest concern. There are some important limitations to our study. As with other environmental contaminants, controlled experiments evaluating the effects of pesticide exposure on birth outcomes are impossible due to clear ethical and legal constraints. This presents challenges both for interpretation and estimation. With regard to interpretation, we cannot observe all individual adaptive responses to pesticide use, such as staying indoors to avoid exposure to pesticide. Further, we can only observe the effects on live births. As a result, our estimates reflect both the direct effect of exposure on live births and the mitigating effects of avoidance behaviors. With regard to identification and estimation, establishing causality without random assignment into pesticide exposure relies on quasi-experimental approaches, such as the panel data models used here with observational data. While there is no way to formally test if our methods have eliminated all sources of bias that preclude causal interpretation of the regression coefficients, our results are robust to multiple modeling approaches, including controlling for other environmental contaminants such as ambient concentration of pollutants and extreme temperatures. Similarly, we find no significant placebo effects of exposure in the 3 months following birth.Birth records do not fully capture adverse outcomes such as abnormalities that are difficult to observe at birth nor are they comprehensive with regards to socio-demographics. Measurement error on the outcome variable would not bias our estimates of the effects of pesticide exposure unless it was somehow correlated with pesticide use, yet it could reduce our precision and thus the likelihood of finding statistical significance.