The sample was stored in a 2 mL chromatography vial at 4 °C. For the quality control, all the experimental steps were carried out with the blank sample, the final sample solution was also stored in the 2 mL vial for further analysis.For the microplastics ranging 10–500 μm, the solution containing microplastics was ultrasonicated for 10–20 min. 20 μL of the sample was dropped on a glass slide each time until all the liquid was transferred. After the ethanol was evaporated, the slide was analyzed by the automated LDIR Imaging system . The automated particle analysis protocol within the Agilent Clarity software was used for all analysis. In the selected test area, the software used a fixed wave number at 1800 cm−1 to quickly scan the selected area and identified the particles . The software automatically selected a non–particle area as the background, collected the background spectrum, and performed morphological identification and infrared full spectrum acquisition on the identified particles. Sensitivity was set to the maximum. After obtaining the particle spectrum, the software automatically made a qualitative analysis with the standard spectra in the self-established database of Agilent. The setup was tested with standard PE pellets , and the hit quality index was >90 %. Considering the aging of MPs in environmental samples, hit quality was set to 65 % for identifying polymer compositions. Additionally, the information including the picture, size, and area of each particle was displayed in the quantitative results. For the 500 μm–5 mm microplastics, the suspected microplastic particles were selected under a stereoscope . ATR–FTIR was used to further identify the polymer composition. The spectrum range was 400–4000 cm−1 with a spectral resolution of 4 cm−1 ; 24 scans were performed. The spectra were compared to the standard spectra in the siMPle database . The polymer type, size, and shape were recorded by the software.Due to the limitation of Agilent 8700 LDIR imaging, that is, the thickness of MPs could not be detected, and fragments were classified as films. As shown in Fig. 5,procona florida container the abundance of microplastics with different shapes was film ≫pellet > fiber , with film accounting for 88.2 %, pellet accounting for 9.0 %, and fiber accounting for 2.8 %.

However, all the detected particles were films in the previous visual results in similar cotton fields , which meant that the detection method could affect the findings of MPs shapes. As shown in Fig. 6, PVC, PP, PE, and PA accounted for a relatively high proportion of the three shapes in all the soil samples. For instance, the proportions of PVC were 37.7 %, 25.3 %, and 13.8 %, respectively in fibrous, film, and pellet microplastics in the soil with 5-year mulching. PTFE also accounted for a relatively high proportion in the fibrous form in the soil with mulching years of 10 and >30 years. For all three shape categories of microplastics, the compositions of polymer types were greatly distinct. For example, in all the soil samples, the proportion of PA in the pellet was higher than that in the fiber and film, while the proportion of PP in the fiber was slightly higher than that in the film and pellet. In the soil with 20 years of mulching, the proportion of PVC in the pellet was more than those in the other shapes, while the proportion of PVC in other samples was fiber > film > pellet. The proportion of PTFE in the film was slightly higher than that in the fiber and the pellet. No clear pattern was observed for the rest of the polymer types.As is shown in Fig. 2, the exponential increase of microplastic abundances with the decrease of their sizes was observed, which is consistent with other studies . This may be caused by the further fragmentation of microplastics over time. Since microplastics in small sizes account for the vast majority, the detection limits of different quantification methods can significantly influence the findings of microplastics. To further understand the ranges of microplastic contaminations in agricultural soils, we performed literature research with respect to microplastic detection in farmlands . The highest abundance in previous studies was 320–12,560 particles/kg soil , accounting for <1 % of this study. The abundance of microplastics in this study was 100–106 times higher than that in other regions. In addition to the different regions of sampling, the quantitative method also greatly impacts the results. For example, visual identification under stereoscope which is most commonly used in soil microplastics studies can cause high false-positive circumstances when it comes to small sizes .

It is generally believed that one can correctly identify microplastics only for particles above 100 μm , and the false detection rates grow with the size decrease. Although the FTIR, Raman spectroscopy, or heating method has been used to assist the microplastic identification, most studies did this process after visual detection, which may still ignore the particles with small sizes. We have previously conducted a microplastic quantitative study with the visually microscopical method in the same place . The result showed that the abundances of microplastics were 80.3 ± 49.3, 308 ± 138.1, 1075.6 ± 346.8 particles/kg soil, respectively, in the cotton fields with 5, 15, and 24 years of film mulching, and all particles were PE identified by FTIR. In the current study, different methods were used to quantify the microplastics in the soils located in the sameregion, planted with the same crop, and mulched with a similar period. A total of 26 polymer types of microplastics were detected, and the abundance was approximately 103 times higher than those reported in our previous study. Therefore, with a different detection method, our finding suggested that the previous quantitative studies of soil microplastics may seriously underestimate the abundances and types of soil microplastics. Previous studies showed that the PE film mulching was a source of microplastics in farmland . The current study also observed that almost all microplastics with the size of 500 to 5,000 μm were PE film residual microplastics , which confirmed that mulching film was an important source of microplastics in agricultural soils. In the sampling region, where the sunshine is intense and the temperature difference between day and night is large, the plastic film was more susceptible to the harsh environmental conditions, become brittle, and fragmented into microplastics. The abundance of PE MPs ranging from 10 to 500 μm was about 100 times as much as that of PE MPs ranging from 500 μm −5 mm . The abundance of PE microplastics in the soil with film mulching for >30 years was significantly higher than that in the fields with less film mulching time, suggesting that the residual microplastics from the film may continuously accumulate in the soil. However, there was no significant increase of PE films in the smaller size than in the larger size in all samples.

This may be due to the dynamic equilibrium of MPs fragmentation as well as the detection limit. New films are applied every year thus MPs with relatively large sizes continuously enter the fields, and meanwhile, MPs constantly break into smaller pieces. Due to the detection limit of LDIR, MPs smaller than 10 μm are undetectable. If MPs’ detection technology breaks through the limitation of detection limit one day, the increase of PE films in smaller sizes may be observed. Considering that plastic film plays an irreplaceable role in agricultural production, future development of biodegradable film material would be essential. However, the polymer types of microplastics in 10–500 μm showed a significant difference from larger sizes , which suggested that microplastics with smaller sizes had other dominant sources. For example, irrigation was believed to be an important source of microplastics in farmlands , and may explain the high proportions of PP and PVC in this study. PP is one of the plastic types with the highest yield and consumption in the world , which has been widely used in daily life, such as small appliances, toys, plastic bags, clothing, water supply, and heating systems. Therefore, previous studies have observed PP microplastics in the wastewater treatment plants. For instance, Wang et al. investigated the microplastics in the influents and effluents from approximately 25 wastewater treatment plants and reported that PP, PE, and PS made up almost 83 % of the total microplastics. In this study, the irrigation water was from the Moguhu reservoir, the confluence of the effluents of several sewage wastewater treatment plants. Even though we did not investigate the microplastics in this reservoir, considering the wide application and frequent detection, we may conclude that the PP microplastics detected in the cotton fields were from the irrigation water. Parallelly,procona London container all the buried pipelines in the drip irrigation system were PVC plastic. The small particles falling off from the drip system may contribute to the PVC microplastics in the soils. This study indicated that the microplastics in soil were mainly distributed on the size of 10–50 μm, which could not be detected by visual counting methods. However, many studies have shown that fine-grained microplastics have a more serious negative impact on soil ecosystems . To establish the ecological baseline of microplastics, it is essential to establish a more precise standard detection method, and simultaneously study the environmental impact of microplastics with different particle sizes.The agricultural sectors of the United States and other developed countries have been subjected to a myriad of policies and regulations that have contributed to unsatisfactory production patterns and resource allocations both within and between countries. Furthermore, such policies have imposed heavy financial burdens on governments that have transferred substantial resources to support the farm sector. The General Agreement on Tariffs and Trade strives to improve the efficiency of agricultural trade and production patterns globally. It is proposed that GATT will reduce the set of permissible agricultural policy instruments, thereby eliminating some policy options that have contributed to several of the undesired consequences in the past. Used correctly, the feasible set of policies is believed to allow for a gradual down scaling of agriculture’s excess supply and to make the sector more flexible and progressive. Ultimately, once the restricted set of policies is introduced, it is expected that a sustainable growth path will be achieved.

A framework for assessment and setting of agricultural policy instruments is introduced in this paper It is used to investigate the impacts of some of the instruments considered for the policy reform following GATT; to analyze operational principles that allow effective implementation of these policies; and to consider issues of eligibility criteria, monitoring, and enforcement. This framework is derived from a political economic perspective on the characteristics of agriculture in developed countries, the causes for past policy interventions in agriculture and their shortcomings, and the ingredient for effective design and implementation of policy reform. This perspective is based mostly on the findings of research on political economics and is presented in the next two sections. It is followed by an analysis of the objective of the agricultural policy form , J model of setting specific policy instruments, and criteria for their analysis. These will be used in the last two sections to analyze a subset of proposed policy instruments and to address dynamic adjustment and implementation aspects of the policy reform. New innovations and practices have been introduced almost continuously. They have altered market conditions and have led changes in the structure of agriculture. Both public and private research contribute to this technological evolution. Hayami and Ruttan have demonstrated that economic conditions induce innovations, and the direction and nature of new technologies are affected by resource scarcities, relative prices, and regulations. The importance of economic incentives and conditions in affecting the evolution of agricultural technology in the United States is emphasized in Cochrane’s book. He argues that labor scarcity was the main problem of U.S. agriculture during the 19th century and that the major innovations during this period were mostly laborsaving devices StIch as reapers, thrashers, combines, and steel plows. These innovations allowed for fast expansion of the land base with relatively small numbers of settlers. While the yields per year of did not change much during the 19th century, U.S. output grew substantially as acreage increased.