| Recently, with the increasing shortage of water resources, there are a large number of farmland uses of sewage for irrigation. And this makes all kinds of pollutants into the soil system, which results in serious soil pollution. The pollution caused by toxic heavy metals always holds to be a long time; therefore, heavy metal pollution has become a widely studied subject.In this paper, the main object of study is formed by soils and crops in Kongjia farmland, analysis and evaluation by means of a variety of heavy metals in the soil-crop pollution status and distribution. Mainly the following conclusions:1. Research on surface soil in Kongjia, with a total of70sampling points, monitors soil properties and heavy metals, and uses optimal interpolation to draw contours maps. The results show that:Sewage irrigation accounts for60%of study area while clean irrigation accounts for40%. Soil is alkaline and shows moderate degree of salt damage. OM, TP and TN of soil are relatively deficient. OM, TP and TN contents in sewage irrigation area were17.11g/kg,483.89mg/kg and339.72mg/kg, respectively,81%,32%and6%higher than that in clean irrigation area. Salinity of the latter is1.89g/kg,23%higher than sewage irrigation area. Sewage irrigation increases soil fertility and is conducive to the growth of crops, while groundwater irrigation increases soil salinity and risk of Stalinization. Cd in sewage irrigation area holds the highest risk of contamination, and Cd contamination has occurred. As, Cr and Zn distribute more evenly. Cu and Pb near irrigation channel present the high content.2. Researcher on profile soil in Kongjia, with a total of27sampling points, indicates that:Sewage irrigation also increases OM, TP and TN of soil in profile direction. Sewage irrigation, sewage-clean irrigation and clean irrigation are three kinds of modes lead to the irregular distributions of heavy metals in these there profile samplings. In profile direction, six kinds of heavy metals fluctuate significantly, and the differences of accumulation due to the of different irrigation patterns. As, Cr, Cu, Pb and Zn accumulate in the profile within each layer, while Cd is concentrated in certain layers, showing a greater difference. Considering the distance between irrigation channel and sampling points, six kinds of heavy metals contents are similar with each other. Their contents are usually higher when they appear at a distance of 200m and700m, and their contents are the lowest levels at the range of400-500m.3. Research on corn for3different Profiles samples, which collected10corn around each sampling point and mean maize as result, shows that:The heavy metals in sewage irrigated corn are different from others, As, Cd, Cu and Pb root> stem> leaf, Cr root> leaf> stem, and Zn stem> root> leaf. Patterns and transfer of enrichment of heavy metals in corn under different irrigation approach are also very different, both the absorption and transfer of As are the slowest. Heavy metals inhibit the growth of corn:the higher the concentrations of heavy metals in surface soil are, the smaller plant height, ear height, ear length and ear diameter are. At the same time, Chlorophyll, carotenoids, nitrate reductase and catalase in the corn are in the lower levels as well. The differences in changes of the resistant enzymes are huge; indicating the different indicators of heavy metals caused different changes. |
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