[Effects of Biodegradable Film Raw Material Particles on Soil Properties, Wheat Growth, and Nutrient Absorption and Transportation].

Biodegradable plastic film is one of the effective ways to solve the problem of white pollution in agriculture. However, its impacts on soil-plant systems are not well documented. In order to provide a basis for the safety evaluation of large-scale application of biodegradable plastic film, pot experiments were conducted to investigate the effects of the types(H, S, and X) and doses(2.5, 10, and 40 g·kg-1) of biodegradable film raw material particles on the soil physiochemical properties, biological properties, growth, and nutrient absorption by wheat (Triticum aestivum L.). The results showed that three types of biodegradable film raw material particles significantly increased soil pH but had no significant effect on soil organic matter content; medium-high doses of H and low-medium doses of S plastic particles had a positive effect on soil nitrification and soil nitrogen availability, whereas X film particles had an inhibitory effect. H film particles increased soil available phosphorus content, and S and X had no significant effect. X film particles increased the content of soil available potassium, but S and H had no significant effect. The effects of three types of biodegradable raw material particles on soil enzyme activities varied with the types and doses of plastic film and enzyme types. With the increase in the doses of plastic film particles, the activities of three kinds of soil enzymes showed a downward trend. Except for the low and medium doses of the S treatment, the other treatments inhibited the growth of wheat, in which X film particles had the greatest inhibitory effect on the biomass of wheat roots, stems, leaves, and grain; with the increase in the doses of film particles, the inhibition effect of wheat biomass was more obvious. For wheat nutrients, the absorption of nitrogen was promoted at low doses and inhibited at high doses, and the three types of film particles inhibited the absorption of phosphorus and potassium. There were significant differences in the distribution ratio of nitrogen and phosphorus between the stems, leaves, and grains of wheat by all the film particles; however, there was no significant difference in the distribution ratio of potassium between those treatments. Correlation analysis showed that wheat biomass was the main factor affecting wheat nutrient accumulation.

[Determination of Heavy Metal Baseline Values and Analysis of Its Accumulation Characteristics in Agricultural Land in Chongqing].

In order to understand the accumulation of heavy metals of agricultural land in Chongqing and make clear priority control elements, the soil heavy metal baseline values need to be determined. Based on geochemical baselines, a total of 214 surface soil samples of six soil types were collected according to stratified sampling. Under strict quality control, the As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn content in each sample was measured. The baseline values of eight heavy metals were determined using mathematical statistics, iterative culling, and cumulative frequency curve methods. The accumulation of heavy metals in agricultural soils in Chongqing was evaluated using the geochemical baseline pollution and geological accumulation index methods. The mean baseline values of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in agricultural land in Chongqing were 5.83, 0.25, 66.78, 25.45, 0.069, 29.90, 26.18, and 78.44 mg·kg-1, respectively, which agreed with the historical findings. Evaluation of the geochemical baseline pollution index method showed that the accumulation of As, Hg, and Zn in soil was the most prominent, with 14.65%, 11.82%, and 3.88% of the samples reaching severe accumulation, respectively. The proportions of moderate accumulation of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were 12.12%, 6.50%, 3.79%, 6.50%, 15.27%, 5.29%, 5.45%, and 17.96%, respectively, of which As, Hg, and Zn were relatively large. The geological accumulation index indicated that more than 93% of the samples of Cd, Cr, Cu, Ni, and Pb were in a state of no accumulation. The proportions of mild accumulation of Hg, Zn, and As were 26.60%, 21.84%, and 21.21%, respectively. Only 5.56% and 0.49% of the samples had moderate accumulation of As and Zn. Different soil types have different properties. All soil types in the sample had different degrees of accumulation of the eight kinds of heavy metals. The accumulation of heavy metals in paddy and purple soils was lower than that in other soil types. For the soils of different geological and geomorphic types, the Ki values of As in the limestone middle and low mountain area of Daba Mountain in Northeast Chongqing and the low mountain area of the limestone of Wuling Mountain in Southeast Chongqing were relatively large; the rest were not significantly different, and all belonged to the non-accumulation and mild accumulation ranges. Both evaluation methods showed that the main accumulated heavy metals in agricultural land soil in Chongqing was As, followed by Hg and Zn, and management and prevention of the accumulation of these elements should be strengthened.