Comparison Of Annual Loss Of N And P From Paddy Soil Near Eastern Taihu Lake Under Different Agricultural Treatments

Study on the nitrogen and phosphorus loss on the Huangnitu Paddy soil and Qingzini Paddy soil region, west to Taihu Lake in rape and rice season, was conducted, the experiment revealed the way and the main factors of N and P loss. Comparison on N and P loss and agricultural economic profits provided a better approach to balance agricultural goal, environment and economical profits. Main results of the thesis are summarized as follows:In the experiment pot of a Huangnitu, into which a scheme of longterm fertilization treatments has been put for 13 years, analysis of mobile forms of phosphorus was attached. Total P content vaired in arrange of 0.3-0.5g·kg~-1 under a range of total P fertilizer input of 0-53 kg/(hm~2·a). As estimated from the total P pool values by mass balance principle, the soil had been subject to water loss of 2-8 kg P ha~-1, with that under chemical fertilizers only being the biggest. The ratio of soluble P to the total was in a range of 0.2%-0.4%, without significant influence by the different fertilization schemes. While chemical fertilizer plus pig slurry manure applications had remarkably enhanced the resin-P pool by 20-40 mg·kg~-1 P mobilization was not observed due to combined application of chemical fertilizers and straw amendments despite of the increase of the SOM. Therefore, P water loss might have been active under continuous chemical fertilization alone in agriculture of this region. To reduce the present prominent non-point source pollution of N and P in this region, it is suggested that chemical fertilizers be applied in combination with an appropriate amount of manure or straw return.In the experiment pot of Huangnitu, N loss and P loss were about lkg/hm2 and 0.03kg/hm2 respectively under three treatments in winter and spring. Surface runoff water did not happen until early spring. Land was subjected to little loss of N and P in winter, mainly due to low content of soil water, depite of much of fertilizer and precipitation being added in fields. The first pronounced loss of N comes out in early spring, significantly corresponded for the added fertilizer in the middle March. The concentration of P was low and lightly variable in the runoff water. In the rice season, much of fertilizer and manure were added into fields in June, shortly after when the contents of total N and P in surface and runoff water attained to 33-18mg/kg and 1.2-0.4mg/kg respectively. Runoff was theprominent way of loss of N and P, and which were mainly composed with dissolved N and particle P. The dissolved N derived from fertilization and particle P should be the most crucial items to be controlled. The rice field was subjected to the loss of 38.8kg N /hm2and 0.95kg P/hm2 and about 33%-50% of the total loss comes out of during the rainy period after fertilization. More attention should be paid to the period in June when the rice fields received much of precipitation and fertilizer. The loss of N and P in rice season, which is dominantly up to the incidental precipitation in early summer, is approximately 20-30 times than that of N and P in rape season.In rice season, the two kinds of soil test phosphorus in initial stages are of evidently high level, when there is much of risk and potential of P loss from the soil, and then descend. There is a larger deviation of soil test phosphorus in soil fractions than that of in original soil. Soil test phosphorus in >250um particles shows a keener response for the former fertilization than in the other two fractions. After 40 days, contents of soil test phosphorus were stable. In initial stages, soil test phosphorus in fractions between the two treatments was significantly different, and then not of difference. Initial loss of P was mainly influenced by the fertilization, while later loss of P mainly affected by the soil.Content of 20-250um particle shows high stability in rice season while content of <20um particle is high in June under continuous submergence which aggravates the loss of P with the coeffect of the former fertilization. Content of >250um particle sharply...