Optimization Method For Nitrogen Fertilizer Application And Ammonia Volatilization Losing In Paddy Field Ecosystem

This article focus on the problems of large amount of nitrogen fertilizes application, low nitrogen efficiency and lacking of systematic research on nitrogen optimization method in rice-wheat rotation system in Taihu. For the objective, the characters, which were ammonia volatilization losing, the fate of nitrogen fertilizer and agronomic effect and environmental effect of nitrogen fertilizer, were studied in rice-wheat rotation system using the combining method of field testing, ¹⁵N micro area experiment under the experiment with different application method and amount of nitrogen fertilizer. The main purpose was to find out the feasible amount and manage method of nitrogen fertilizer in paddy field in Taihu, and provide a scientific theory of nitrogen fertilizer application and management for the area.The results showed that ammonia volatilization losing could be obviously reduced in rice-wheat rotation system with optimization method, and nitrogen efficiency was also improved. During the whole rotation cycle, ammonia volatilization losing with optimization method was 2.76% lower than that with normal method, and nitrogen apparent efficiency used by rice and wheat with optimization method was 2% and 6% higher respectively than that with normal method. So we think that the most suitable nitrogen fertilizer method in rice-wheat rotation system in Taihu is the optimization method in which nitrogen fertilizer was carried by water.The result, through researching on each kind of nitrogen variation in field surface water after applying urea, showed that the total nitrogen in field surface water increased greatly one day after fertilizing, after that it decreased with the time go. The concentration of NH4+-N reach its max value in three days after fertilized, and then decreased with the time go; the concentration of NO3-N and NH4+-N took a mutual ebb and flow relationship in one week after fertilized, and the concentration NH4+ had a obviously positive relation with ammonia flux. The concentration of each kind of nitrogen in field surface water is relative higher in one week after fertilizerd, and it increase with the increasing of nitrogen fertilizer, the each kind of nitrogen in field surface water with optimization method is lower than that with normal method, so the key period of surface water manage in paddy field is a week just after fertilized.The result of ammonia volatilization losing study showed that the difference of ammoniavolatilization losing between rice field (water) and wheat field (dry) is notable. The relationship between ammonia volatilization losing (7.30²9.70kg/hm² for optimization method, and 8.83³2.72kg/hm² for normal method) and the apply amount of nitrogen fertilizer take on a power relationship in rice field. However, in wheat field (7.36¹5.55kg/hm² for optimization method, and 9.66²1.22kg/hm² for normal method), the relationship is linearity relation. And in rice field, the ammonia volatilization losing last shorter time, which took place almost in a week after fertilizing, While in wheat field, it last longer, almost ten days. The rate of the ammonia volatilization losing whether in rice field on in wheat field took almost the part, and had nothing to do with the nitrogen fertilizer amount. In the whole rice-wheat rotation the rate of ammonia volatilization losing between optimization and normal method is 7.05±1.37% and 9.81±0.38% respectively, almost 50% of total ammonia volatilization losing took place during the first fertilization, so the main method to reduce ammonia volatilization losing is control the nitrogen amount at the first fertilization and reduce drain from paddy field.The result that the use of nitrogen fertilizer obsorbed by rice and wheat showed that, nitrogen apparent efficiency was 30.51 ±9.71% with optimization method and 28.87±5.61% with normal method in 2003, while in 2004, was 30.18±4.41% with optimization method, which was similar with that in 2003. In wheat field, the result was 5%⁸% higher than that in rice field, and which became lower if more nitrogen fertilizer was used. And through studying the gain exponent of rice and wheat, we get that compare with N-free area, the number was 10% lower in N-applying area, and the figure is 13% in 2004, and became lower if more nitrogen fertilizer was used. But the number was almost 10% higher in N-applying urea than that in N-free area, which is higher with optimization method.From the result of 15N micro-area experiment, we can see that the rate of nitrogen fertilizer obsorbed in paddy field was 21.68%³1.92%, while in wheat field was 17.78%³4.78%. And it became lower if more nitrogen fertilizer was used. The remain N in soil through three product season showed that the difference of nitrogen fertilizer remain was significant: in 2003, the rate of remain in soil is 5.27%¹3.78% in paddy field. In wheat field, the result is 17.38%⁴7.38%. And the rate is higher in wheat field than that in paddy field, the exceeding number is 11.71% with optimization method and 21.96% with normal method, and which became lower with more nitrogen fertilizer use. With optimization method, the rate of remain in soil in 2003 was 7.5% lower than that in 2004, which was 17.60±7.96%, and the difference remain in soil was relative large in 2004, the reason perhaps had some relation with the difference of soil fertility after long time rotation. The remain N in soil distributed mainly in 0⁴0cm deep, and almost 70% N remain in 0²0cm deep soil.