Study On The Transformation And Regulation Mechanism Of Nitrogen And Phosphorus In Three - Dimensional Breeding Model Of Paddy Field In Northern China

To control serious agricultural non-point source pollution and improve use efficiency of fertilizer in North China, this thesis has investigated the characteristics of nitrogen(N) and phosphorus(P) migration and transformation in a typical rice cultivation zone in Baodi of Tianjin. It is the first research on stereoscopic-planting rice field pattern (RF:rice-fish-shrimp-crab co-culture+bund+ditch) conducted in North China, which is of great significance to improving the effective utilization of fertilizer and reducing the environmental pollution caused by N and P losses. The research took an entire paddy field ecosystem as the basic research unit. N and P migration and transformation models in paddy field had been established based on N and P inputs and outputs. A field experiment had been conducted to explore N use efficiency, P loss load, N and P control measures in RF, and conventional rice field pattern (CK: rice monoculture) had been taken as the control. The main results are summarized as follows.(1) N and P inputs of different rice field patterns are mainly from irrigation, fertilization and precipitation. Due to the construction of irrigation-drainage circulatory system and bund-ditch interception system in RF, N and P effective outputs of RF and CK are different. N and P outputs of CK only include the absorption of rice. One part of N and P of RF is absorbed directly by rice and aquatic animals, and the other part is used indirectly by plants at bund and aquatic animals in ditch. Thus, N use efficiency in RF reaches 64.9%, which is 20% higher than that in CK. P loss load in RF reaches 20.4%, which is 17.1% lower than that in CK.(2) Because of the presence of aquatic animals and the use of organic fertilizer, ammonia volatilization rate of RF has been reduced effectively. It accounts for 6.9% of total amount of applied fertilizer, which is 8.5% less than that in CK and 10.3% less than the national average.(3) 52.2% of the P is fixed by soil, indicating that soil adsorption was the main way of P loss in RF.(4) Due to special bund-ditch interception system in RF, N and P losses through lateral seepage drop by 9.33 kg(N)·hm-2 and 3.71 kg(P)·hm-2 respectively. The construction of irrigation-drainage circulation system in RF has improved the utilization efficiency of water and fertilizer resources effectively.(5) Compared with CK, the RF rice yield is 6.65% higher than that of CK. N and P uptake by rice and aquatic animals is higher than those of CK. The results suggests that breeding fishes, shrimps and crabs did not reduce rice yield, but increased the N and P output of agricultural and fishery products.(6) Considering the environmental benefit, economic benefit and social benefit, RF is superior to CK. RF not only achieves high rice yield, but also reduces N and P loss in paddy fields. Therefore, stereoscopic-planting rice field is feasible in North China where irrigation demands are well met. This thesis provided a critical reference for controlling agricultural non-point source pollution in North China.