Balance And Loading Of Cropland Nitrogen In A Typical Rice-Based Agricultural Watershed Of Yangtze River Delta Region

Along with our industrialization, urbanization as well as new rural construction step's quickening, the environment questions of environmental pollution, ecological damage are prominent increasingly, the agricultural non-point source pollution occupied the increasingly proportion in the pollution. The nitrogen is the most important biological element and the main limit factor of crops growing. The nitrogen application is the important way for improving soil fertility. Therefore, it has the positive role in enhancing agricultural production and improving environmental quality that researching on the nitrogen balance of the ecosystem, strengthening management and controlling the pollution. It has the long-term significance to the region agricultural economy's sustainable development and the optimization ecological environment.In this paper, the jurong reservoir watershed in Jiangsu Province was selected as study area for a typical rice-based agricultural watershed in the Yangtze River Delta region of China, then, it was analyzed and extracted agricultural thematic information through interpreting the topographic map and high-spatial remote sensing images and so on with the GIS technology, and finally, the characters of N inputs and outputs of the agricultural watershed were quantified according to field investigation, indoor experiment and referred literature.According to the nitrogen balance based on the regularity of nitrogen loading development and the characteristics of temporal and spatial distribution from May 2007 to April 2008, the pollution potential of nitrogen for the area was forecasted through nitrogen loading. The paper is to provide scientific basis for preventing the environment pollution of the rice-based agricultural watershed effectively.The results were as follows:(1) Under high fertilizer application, the total input of nitrogen of the was 1589.1 t and the output is 1168.4 t in the area during the period, the nitrogen surplus of the farmland system was 144.5 kg-hm-2, the paddy fields and upland fields were 60.8 kg-hm-2 and 98.5 kg·hm-2. The results demonstrate that the utilization ratio of nitrogen was low, being 33.6% in paddy field and 34.9% in upland field.(2) The fertilizer application was the dominant source (1068.3 t, accounting for 67.2%), the organic fertilizer (225.6 t, accounting for 14.2%) was next, the biological fixation of nitrogen (189.2 t,11.9%), the deposition (96.1 t,6.1%) and the seed (9.9 t,0.6%) lead the nitrogen quantity to be few; Although the harvest of crops(545.3 t,46.7%) was the major way of nitrogen output, but the denitrification and the ammonia volatility creating the nitrogen loses were also quite considerable. (3) Due to the special tillage methods and the structure of Oxidation-Reduction processes in paddy soils, the denitrification of the paddy fields releasing nitrogen quantity occupied 1/3 of the output, added the ammonia volatility and crop straw burning which releasing NH3 and NOx, about half of the nitrogen output in paddy fields was lost in gaseous from, which caused the air pollution. In addition, the frequent precipitation and the surplus water after ponding in summer were also main pollution source.(4) The upland fields accumulated N03--N easily, causing the soil nitrate leaching. The massive nitrogen (occupied 36.3% of the input), was not only the huge nitrogen source for the next season crops, but also great source for water pollution.(5) In order to controlling the agriculture non-point source pollution effectively, the fertilizer application structure should be adjusted moderately for reducing pollution occurrence from source to runoff. Therefore, the mixed application of organic and chemical fertilizer should be emphasized. It's necessary to pay attention to the straw returning, the reasonable irrigation and fertilization, raising the nitrogen use efficiency, reducing the loading and preventing the nitrogen polluting the atmosphere and water.In summary, it was dangerous for higher nitrogen loading caused by heavy fertilizing and lower utilization to the atmosphere and the water environment, which causing the pollution. Well, the nitrogen hided in the soil was also dangerous for ours food through the plant transmission function. Therefore, It is realistic and urgent to adjust the nitrogenous fertilization reasonably and raise the nitrogen use efficiency.