[Effect of Film Mulching Age and Organic Fertilizer Application on the Distribution Characteristics of Microplastics in the Soil of a Peanut Field].

The large input of mulch film and organic fertilizer have led to increasingly serious microplastic pollution in farmland soil of China. In this study, the microplastic pollution of peanut farmland in Dezhou City, Shandong Province was investigated. The effects of different mulching years (0, 3, 5, and 8 years) and organic fertilizer application on the abundance, particle size, color, and shape of microplastics in farmland soil were analyzed. The results showed that the average abundances of microplastics in peanut soil were 65.33, 316.00, 1 098.67, and 1 346.34 n·kg-1, respectively, after 0, 3, 5, and 8 years of film mulching. The abundance of microplastics decreased with the increase in soil depth. The abundance of microplastics in 0-10, 10-20, and 20-30 cm topsoil was 1 076.00, 603.5, and 440.25 n·kg-1, respectively, and the abundance of microplastics increased significantly with increasing years of film mulching and organic fertilizer application (P<0.05). The particle size of microplastics in the sample plot <1 mm accounted for 77.30% of the total content, and with the increase in film mulching age, the proportion of microplastics with small particle size (<1 mm) increased significantly (P < 0.05). With the increase in soil depth, the proportion of microplastics with small particle size also gradually increased, whereas the application of organic fertilizer had no significant effect on the particle size of microplastics. The color of microplastics in the plot was mainly transparent (49.77%), followed by black (16.35%) and white (16.27%). The planting age and organic fertilizer application had no significant effect on the color of microplastics in the soil (P > 0.05), but the mulching age significantly increased the proportion of transparent microplastics. The abundance proportion of the five types of microplastics were 49.77%, 25.41%, 19.15%, 3.26%, and 2.41%, respectively. These field soil microplastics were mainly composed of polyethylene (PE), polypropylene (PP), and polystyrene (PS) polymers, accounting for 21.37%, 18.57%, and 19.77% of the total, respectively. Therefore, microplastics were widely present in the soil of the peanut field cultivated layer in Dezhou, Shandong, and the applications of mulch film and organic fertilizer were the main source. This study provides an important basis for the prevention and control of soil microplastic pollution in peanut fields.

[Effects of Straw in Combination with Reducing Fertilization Rate on Soil Nutrients and Enzyme Activity in the Paddy-Vegetable Rotation Soils].

The effects of straw returning combined the reducing application of chemical fertilizer for crop yield, soil nutrients and enzyme activity were studied in a typical southwestern hilly area of China in a rice-vegetable (Brassica juncea var. gemmifera Lin.) cropping system. The purple soil was selected as the target type of soil, and the Pioneer Town, Jiangjin District, Chongqing, China was selected as the typical southwestern hilly area during 2013 and 2014.Scientific basis based on the optimized fertilization strategy and the recyclable utilization of straw was provided through a field in-situ experiment in this study. There were five treatments in the field experiment: F (conventional fertilizer), 90% F+AS (100% straw with 90% conventional fertilizer), 80% F+AS (100% straw with 80% conventional fertilizer), 70% F+AS (100% straw with 70% conventional fertilizer), 50% F+DS (200% straw with 50% conventional fertilizer), and the 100% straw was 7500 kg·hm-2. The results showed that the yields of rice and vegetable were all increased in straw with reduced fertilizer treatments (3.0%-17.9% in rice yield and 12.2%-36.4% in vegetable yield) compared with conventional fertilizer (F) treatment. Moreover, the yield of rice in the second season was also increased by 820-1240 kg·hm-2. Soil pH values in straw with reduced fertilizer treatments raised by 0.06-0.55 compared with F treatment, especially in straw with 70% and 80% of conventional fertilizer dosage which increased by 6.74-6.88 and 6.52-6.84, respectively. The highest content of soil organic matter was 41.01 g·kg-1 in straw with 80% of conventional fertilizer treatment. For the aspect of soil available nutrients, straw with 80% of conventional fertilizer treatment increased 110-178 mg·kg-1 content of soil available nitrogen and 31.3-64.0 mg·kg-1 content of soil available phosphorus. However, the excessive application of straw had negative effect on the accumulation of soil available phosphorus. In the same cultivation period, the contents of soil urease increased significantly in straw with 70% and 80% of conventional fertilizer treatments, which increased by 13.6%-76.4% and 20.1%-75.0% compared with F treatment. The contents of soil catalase in straw with reduced fertilizer treatments were significantly higher than F treatment; in first two seasons, soil catalase contents increased by 0.37 and 0.31 mL·(h·g)-1 relative to F treatment in straw with reduced fertilizer treatment (80% of conventional fertilizer). With the increasing time of planting, the soil phosphatase content in the third season was higher than those in first two seasons. Straw with 70% and 80% of fertilizer treatments increased the activity of soil phosphatase by 45.2% and 48.2% compared with F treatment. It was concluded that straw application with 70% or 80% dosage of conventional fertilizer could benefit the rice-vegetable rotation in the southwest hilly area of China.

[Predicting the cadmium bioavailability in the soil of sugarcane field based on the diffusive gradients in thin films with binding phase of sodium polyacrylate].

The diffusive gradients in thin films (DGT) technique with solid-state binding phases has been widely used for in situ collection and measurement of available heavy metals in waters, soils or sediments, whereas DGT with liquid binding phase is primarily used in the in situ analysis of heavy metals in waters. In this paper, rhizosphere soils of sugarcane were collected in Guangxi and the concentrations of cadmium (Cd) were determined by DGT with a solid-state binding phase of chelex100 (chelex100-DGT) and modified DGT with a liquid binding phase of sodium polyacrylate (CDM-PAAS-DGT). The result showed that the Cd contents in soils measured by DGT with both binding phases and Cd in the roots, leaves and unpolished stems of sugarcane had significant positive correlation. The extraction ability of the CDM-PAAAS-DGT was much higher than that of the chelex100-DGT. In addition, multivariate analyses were used to assess the impact of pH, cation exchange capacity (CEC), soil organic matter (OM) and texture. Two principal components were extracted and the linear regression models were established. The Cd bioavailability in soils could be accurately predicted by the CDM-PAAAS-DGT technique, which expanded its applicable area.