The area selected should be readily accessible to farm equipment for site preparation and maintenance. The site should not disrupt normal farming operations or be in an area that could be easily overlooked and accidentally disked or sprayed. In addition, the site should be well drained to prevent ponding of water or plant die back.To prepare the area selected for a vegetated ditch, disk and shape the land to carry water and prepare a normal seedbed. Grasses should be planted in the fall when establishment is favored by cool weather and subsequent winter rains. After the seedbed is prepared, allow the winter rains to bring up the first flush of winter weeds. These should be either sprayed with Roundup or disked. The grasses should then be direct-seeded with a grain drill at 15 pounds per acre by late fall. They can also be broadcast at 20 to 25 pounds per acre and incorporated with a chain harrow followed by rolling. Buctril , MCPA , or 2,4-D can be used to control broad leaf weeds once the grasses have established and have been allowed to grow at least 3 to 4 inches tall to avoid injury to newly emerged seedlings. Be sure to contact the local agricultural commissioner for restrictions on the use of herbicides. For example, the phenoxys MCPA and 2,4-D cannot be used after March 1 in many counties. Once the grasses are established, they will compete well with weeds, requiring only occasional use of herbicides, hand weeding, or mowing.Since most of the sedimentation or particle retention occurs at the beginning of the filter strip, this area should be closely monitored, round pot for plants and excess sediment should be removed to keep water from diverting to new and easier drainage routes or channels. This may involve reestablishing the grasses by over seeding the area to ensure that a sheetlike flow is maintained as the water comes off farm fields.

Gophers and ground squirrels should be controlled and repairs made where channelization of water occurs. Irrigation runoff should supply the water needs of the vegetation in the ditches. Grasses may need to be mowed occasionally to prevent thatch from building up and to deter weeds. If the vegetated drain is grazed, the animals should be watched to prevent overgrazing and stand loss, especially on wet soils. Plant tissue testing may also be needed to ensure that nutrients concentrated in the filter strips have not built up to unhealthy levels for the animals.One method promoted for improving surface water quality runoff from furrow-irrigated agricultural fields is to apply a polyacrylamide to the irrigation water. PAM stabilizes the soil to minimize erosion and promotes the settling of suspended particles. PAM comes in tablet, granular, and liquid formulations. By itself, PAM is not toxic to aquatic life; however, the carriers in oil-based PAM can be toxic to aquatic life at recommended field application rates. For this reason, water-based formulations are recommended . In research trials conducted by the authors at the University of California, Davis, liquid PAM in a loam soil significantly reduced suspended sediment concentrations compared with a control of untreated water in surface runoff at PAM concentrations of 2.1 ppm and 7 ppm in the source irrigation water . Similar behavior occurred in a clay loam soil at a second field site at California State University, Chico, with a PAM concentration of 1.1 ppm. Terminating the liquid PAM injection once the water reaches the end of the furrows can be as effective as continuous PAM dosing, but this effect may depend on soil texture.Studies on tablet and granular PAM at Davis and Chico showed a similar response to the liquid PAM, with significant reductions in suspended sediment concentrations compared to untreated water . However, proper placement of dry PAM in the furrows was critical for efficacy. In studies in Idaho conducted by the USDA, dry PAM placed at the head of the furrow was effective.

However, at Davis and Chico similar placement of dry PAM at the furrow head resulted in the material being quickly covered by eroded sediment during irrigation, and the PAM lost its efficacy. In contrast, dry PAM material placed 100 to 300 feet down the field was not covered by sediment and was effective in reducing the sediment concentrations. Proper placement of dry PAM is particularly important for gated pipe systems, where water discharged from gates may cause considerable erosion at the head of the furrow. One way to lesson this erosion is to place irrigation socks over the gates. PAM applications had no effect on irrigation water infiltration rates for the soil types evaluated in the Sacramento Valley, whereas infiltration increased with the addition of PAM in an Idaho study .The cost of applying PAM depends on how it is applied to the field. The cost of dry PAM formulations placed in the furrows depends on the material cost, the furrow spacing, and the number of tablets per furrow. PAM application rates are based on recommended rates for each type of PAM material . The smaller the row spacing , the larger the cost will be for a given acreage. Whether to apply dry PAM directly into the irrigation water or use liquid PAM depends on the target PAM concentration in the irrigation water, the material cost, the flow rate of water into the field, and the injection time. Table 4 shows cost comparisons using different rates and formulations of PAM on an 80-acre furrow-irrigated row crop planted on 5-foot beds using data provided by a grower. Costs per acre are based on the total field acreage . In this field example, the time for the water to reach the end of 1,200-foot furrows is 12 hours; there are four irrigation sets ; a flow rate of 1,320 gallons per minute; and a furrow flow rate of 11 gallons per minute.

The lowest cost occurred for granules placed in the furrow, while the highest cost was for using liquid PAM. The high cost of liquid PAM reflected the cost of the material and the long injection time. Terminating the injection before complete advance to the end of the furrow would reduce the cost per acre but may increase sediment levels. While the cost per acre of applying liquid PAM in irrigation water is higher than the cost of dry PAM formulations, especially at a concentration of 5 ppm , our studies at Chico and Davis showed PAM concentrations of 1 to 2 ppm in the irrigation water to be effective in reducing the sediment load on loam and clay loam soils. As a result, growers should experiment with liquid PAM application rates to determine what works best on their farms, since the efficacy depends on sediment loads as affected by factors such as soil type and irrigation flow rates. The differences in field responses to PAM may be why the NRCS recommends a higher concentration of 10 ppm in irrigation water to reduce sediment loads in surface irrigation runoff; this rate should cover most sediment loads, but it would not be economical.Groundwater is an important water supply for more than two billion people around the world . It also provides more than 40% of the irrigation supply for global agricultural production on approximately 500 million ha of cropland . Given such intense use, it is not surprising that depletion of the resource is occurring in many parts of the world including the United States and California . Excessive groundwater extraction can decrease water levels, reduce surface-water flows, cause seawater intrusion, spread contaminants, and cause land subsidence . Sustainable resource management requires a combination of reduced extraction and increased recharge . Some reduced extraction may occur by increasing water use efficiency ; however, large round pot pronounced rates of extraction in many areas will likely necessitate modifying cropping patterns and fallowing cropland to address problems from over-pumping . Such changes will cause economic distress and likely bring political resistance. While avoiding strong measures to correct groundwater budget imbalances may not be possible, disruption might be reduced by increasing recharge where possible. Elements for successful artificial recharge projects have been reviewed in detail and may be programmatic or site-specific. Programmatic elements include sourcing, conveyance and placement of recharge water. Sources of recharge water may include urban storm water runoff and recycled water as wellas, notwithstanding water rights and permitting considerations , stormflows from streams and releases from reoperated surface-water reservoirs. Considerations include access to either existing canals and ditches, or the land required to construct these structures, as well as routing and capacity specifications. Options for placing water in recharge facilities range from constructing dedicated basins to repurposing existing gravel pits.

The recharge water could also be released to lands primarily used for other purposes but available on a seasonal basis such as sandy-bottomed drainage features, unlined canals and ditches, or croplands. Site-specific details include: location relative to conveyance and favorable hydrogeology, topography of the ground surface and presence of existing berms, type of irrigation technology present, timing of site availability relative to water available for recharge and cost to use the land under purchase, rent or option arrangements. Site-specific details regarding favorable hydrogeology directly relate to characteristics of the groundwater basin under consideration. Spatial variability of infiltration capacity is heavily influenced by the hydraulic conductivities of the soil and shallow geology as well as interconnectedness of higher hydraulic conductivity deposits at depth . Groundwater storage space is determined by the unsaturated zone thickness and its variations across the basin. The fate of recharged water over time relative to the recharge location can also be important . Recharge at some locations may offset local pumping and increase groundwater storage. At other locations, water entering the subsurface can quickly discharge from the groundwater system to surface water or flow across basin boundaries that are based on governance rather than physical characteristics. Data on the performance of managed aquifer recharge on croplands is limited and largely focuses on California and western USA. Dokoozlian et al. conducted a four-year pilot study flooding vineyards in the San Joaquin Valley of California during seasonal grapevine dormancy, observed no impact on crop yield, and concluded that the approach was viable for MAR. Bachand et al. performed a single-season pilot study for on-farm flood flow capture and recharge, also in the San Joaquin Valley, with both perennial and annual crops. They observed no impacts to crop yield and estimated the unit cost for the on-farm recharge as ~3–30 times cheaper than surface-water storage or dedicated recharge basins. Dahlke et al. investigated effects of winter flooding on established alfalfa fields at two locations in the Sacramento Valley of California and found that significant amounts of water could be applied without decreasing crop yield. Additional unpublished studies indicate that almonds may tolerate at least 2 ft of cumulative applied recharge water in a season without detrimental effects and some grapes have shown little to no productivity decline after more than 20 ft of recharge in one season . Some analysis on scaling up on-farm recharge for larger scale groundwater management has also occurred. Harter and Dahlke discussed the potential for on-farm recharge projects to improve conditions in California where groundwater has been stressed by overuse and drought. O’Geen et al. considered requirements for successful projects and presented a spatially explicit soil-agricultural-ground water banking index for recharge project suitability on agricultural lands in California. Niswonger et al. examined potential benefits from on-farm MAR for a hypothetical groundwater sub-basin in the semi-arid western USA. They developed an integrated surface-water diversion and subsurface flow model to simulate recharge operations and benefits to the groundwater system over a 24-year period. Scenarios considered recharge water from snowmelt in excess of water rights during wet years applied to croplands during two winter months each year. Among other points, the work concluded that increases in groundwater storage from AgMAR operations were spatially related to variations in groundwater depth and withdrawals across a basin as well as proximity to natural discharge areas and supported greater pumping supplies for agriculture. This work addresses planning-level analysis of Ag-MAR using water from reservoir reoperation for periodic flooding of croplands during winter months.