Temporal And Spatial Variability Of Soil Nitrogen And Phosphorus And Water Environmental Effect In The Typical Farmland Of Taihu Lake Region

Soil nutrient is a very important indicator to crop yield and quality; it is an important goal for precision fertilization in precision agriculture through predicting spatial variation of soil nutrients. As the foundation of precision agriculture research and implementation, the spatial variability of soil fertility could be used to analysis the relationship between soil fertility index and crop yield, predict the affection of precision fertilization in farmland. Then by determining the most appropriate fertilizer, it can guide people in reducing chemical fertilizers and increasing production while reducing environmental pollution, and achieving sustainable development of agriculture finally. In recent years, with the rapid development of industrial and agricultural production in Taihu Lake region, more and more nutrients such as nitrogen, phosphorus and others was put into the lake. The agricultural non-point source pollution especially caused by excessively using of fertilizers and pesticides in agricultural production has become one of the uppermost sources of water pollution in this region. Therefore, the study on the spatial and temporal variability of soil nitrogen and phosphorus and impact on water environment has important theoretical and practical significance.In this study, two types of soils in Taihu Lake region (White soil and Wushan soil) was studied. With the classical statistical and geostatistical method, this study evaluated the change law with time (different farming conditions) and space (soil profiles) of total nitrogen, nitrate nitrogen, ammonium nitrogen, total phosphorus, available phosphorus, organic matter content in two soils. Through the spatial structure analysis of soil nitrogen, phosphorus, and organic matter, the pollution status and temporal-spatial variability of nitrogen, phosphorus and other pollution factors were investigated. The main influencing factors of deterioration of water quality in different agro-ecosystem in Taihu Lake region were discussed. All above these information provided a scientific basis for scientific fertilization and pollution control.Through this study, results were as follows:(1) Spatial and temporal variation of soil nitrogen The content of soil total nitrogen, nitrate and ammonium nitrogen of white soil from three different soil layers in the study area decreased with the increase of soil depth. The reason was that available nutrient was more easily to leach loss. In addition, artificial cultivation management such as fertilization and irrigation was another influencing factor. Through the Kriging and mapping about the soil nitrogen and the pH value in the study area, the results indicated that distribution patterns of soil pH and nitrate were very similar. There was a strong spatial correlation between them.By analyzing and comparing the sampling data in the study area with Wushan soil after wheat and rice harvest, the content of total nitrogen and nitrate nitrogen in rice season was lower than wheat season in rice - wheat rotation system, because of the effect of cropping system and fertilization. The content of total nitrogen and nitrate nitrogen in surface soil layer (0～15 cm) was higher than sub-surface (15～28 cm) and bottom (28～42 cm). Because of fertilizer, nutrients in surface soil were higher. Meanwhile the higher oxygen content of the surface strengthened nitrification also resulted in increased of the content of nitrate. But with the role of irrigation and raining, the content of nitrate nitrogen in soil profile increased with the increase of depth. (2) Spatial and temporal variation of soil phosphorusThe spatial and temporal variability of total phosphorus and available phosphorus were studied in field scale in White soil. The results showed that the content of total phosphorus decreased with the depth increasing, while the content of available phosphorus first increased and then decreased with the depth increasing. The content of total phosphorus and available phosphorus has a similar spatial structure and spatial correlation distance. The available phosphorus in the study area was higher in the east and gradually reduced to west.The spatial variability of soil total phosphorus and available phosphorus were studied in field scale in Wushan soil. The content of total phosphorus and available phosphorus decreased with the depth increasing. The average of soil available phosphorus in three layers was slightly higher than the medium layer. This phenomenon indicated that there was little influence of specific value. There was a significant positive correlation between the content of pH and available phosphorus. But there was a negative correlation between pH and total phosphorus. The spatial distribution maps of different layers showed that the content of soil available phosphorus was largest in the middle of the study area, and gradually reduced to east. The content of soil phosphorus in Wushan soil in rice season was greater than in that of wheat season. There was a larger range in wheat season with a larger range of spatial correlation.(3) Spatial and temporal variation of soil organic matterWith the geostatistical methods, spatial analysis technology and interpolation on the data of the organic matter, the spatial and temporal variability of organic matter were studied in white soil and wushan soil in the Taihu Lake. The results showed a less spatial autocorrelation in soil organic matter of different layers. The range of White soil with a smaller spatial correlation was less than the Wushan soil. While the range of soil organic matter of Wushan was large and the spatial heterogeneity was more strongly. The characteristics of spatial structure of soil organic matter was related to the soil-forming conditions and cropping systems in the study area. The content of soil organic matter of Wushan soil in the west of the study area was high, and gradually reduced to east. The distribution patterns of the soil organic matter in three layers was similar. The spatial correlation of soil organic matter in Wushan soil in rice season was stronger than that of wheat season.(4) Impact of soil nitrogen and phosphorus on water environmentThe growth period of rice was from May to September in Taihu Lake region, which was the rainy season too. Rainfall and irrigation have a great effect on the content of nitrogen in groundwater during this period. The content of total phosphorus, total nitrogen and ammonium nitrogen in the study area were over standard most seriously, The content of total nitrogen content in dry season were significantly greater than rainy season. There were no obvious difference between the average of nitrate and ammonium nitrogen in surface water in the rainy season and dry season. Nitrate nitrogen was the main groundwater pollution source in the study area. The content of nitrate nitrogen in groundwater in rainy season was significantly higher than that of in dry season. The ammonium nitrogen was the major pollution source in surface water.