| Nitrogen and phosphorus are nutrients necessary for plant growth, and the important components of the soil. Nitrogen and phosphorus of soil are not only the main way for plant absorbing nitrogen and phosphorus, but also extremely important ecological factors in ecosystem. Complementary soil nitrogen and phosphorus is an effective means in agricultural production to improve crop yield, however long-term large quantities of nitrogen and phosphorus fertilizers application can reduce the utilization rate, cause serious loss, thereby inducing a series of water pollution problems, especially eutrophication aggravation. Thus, the soil nitrogen and phosphorus content and its loss characteristic in field have aroused widespread concern in society.This study chose the area with rich soil in Yixing City around Taihu Lake Basin as the research area, collecting soil samples of different use type in high-density distribution, analyzing and plotting with Geo-statistics method, so as to grasp the soil nitrogen and phosphorus content and space variation in field. Also this study paid attention to the contributions of nitrogen and phosphorus from the paddy field drainage to external water, and took field experiments with wheat as a supplementary and complementary in high fertility soil, thus explored the comprehensive benefits of the best nitrogen and phosphorus application way.Through statistical analysis of soil samples of different use type, the results showed that total N, available P content were1.42g·kg-1and31.31mg·kg-1, respectively, and both belonged to the level I, which were related to the long-term high application of N and P fertilizer. As far as the soils of same use type, the variation coefficient of available P was0.58, which indicated its uneven spatial distribution, which was the common characteristic feature of soil available P distribution. Among soils of different use type, paddy soil’s total N content (1.6g·kg-1) and vegetable garden soil’s available phosphorus content (41.90mg·kg-1) were significantly higher than the other three types of soils, which suggested that the crop type, economic benefit and farming management and other social human factors had significant effect on soil N and P content.The result of analyzing parameters from Kringing’s semi-variance model shows that the soil use type had a close relationship with the spatial distribution of total N and available P. The total N among four soils range changes from small to large were vegetable garden soil (1.08), paddy soil (2.01), tea garden soil (2.67) and orchard soil (2.84), which indicated that N in the orchard soil with gradual change in a wide range, while vegetable garden soil had the weakest spatial correlation due to the obvious human effects. It was the similar to available P in soils of different use type. Among orchard soil, tea garden soil, paddy soil and vegetable garden soil, the Nugget/Still of soil total N were26.45%,28.64%,30.69%,44.87%, respectively, while that of available P were21.88%,34.04%,48.78%,58.82%, respectively. The Nugget/Still of total N and available P in orchard soil were around25%, with strong spatial correlation, and strongly affected by the soil parent material, soil type and topography and other natural structural factors. The Nugget/Still of available P in paddy soil and vegetable garden soil were high due to the obviously effects of fertilization, irrigation, and other human management factors.Kringing’s graph reflects that N and P spatial distribution in topsoil of different use type were with their own characteristics, and the differences were larger. Overall, N and P were unevenly distributed. In some region, paddy and vegetable garden soil were of rapidly accumulation of P and N. Lake District is high in soil P, while the orchard soil, tea garden soil in southwest and northeast study regions could be properly added N.The analysis of field correlation of N and P content in different paddy soil layers and field water showed that the total N and available P content were significantly positive correlated with the adjacent soil layers, and N was better in vertical migration than P. Total N content in arable layer soil was significantly positively correlated with the total N, nitrate N and ammonia N content in field water. Available P content was significantly positively correlated with the soluble orthophosphate and total P content. In paddy field drainage water, the total N and nitrate N content had reached a level of critical pollution, and the total P content were near the security line. The integrated pollution index was3.46, so the drainage water was heavily polluted, which would take a lot of N to the external water, thus causing environmental problems which should attach attention to.The results of wheat field experiment in high fertility field show that in the case of enriched soil and high regular fertilizing, appropriate reducing the amount of N and P fertiler in field could maintain the stability of yield and profit. It could also take into account the environmental benefits. Under this experimental condition, the use of N and P fertilizer decreased to85%of normal (191.3and63.8kg·hm-2respectively) could guarantee the yield, increase utilization of fertilizer, and reduce environmental risk. |
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