Nitrogen use efficiency in stereoscopic planting rice field in North China

To control serious agricultural non-point source pollution and improve use efficiency of nitrogen (N) fertilizer in North China, this study investigated nitrogen use efficiency in different planting patterns of paddy fields in a typical rice cultivation zone in Baodi of Tianjin City. With an entire paddy field ecosystem as the basic research unit, N migration and transformation model in paddy field was established based on N input and output. In order to explore N uptake and use efficiency in coTo control serious agricultural non-point source pollution and improve use efficiency of nitrogen (N) fertilizer in North China, this study investigated nitrogen use efficiency in different planting patterns of paddy fields in a typical rice cultivation zone in Baodi of Tianjin City. With an entire paddy field ecosystem as the basic research unit, N migration and transformation model in paddy field was established based on N input and output. In order to explore N uptake and use efficiency in conventional rice field pattern (CK: rice monoculture) and stereoscopic planting rice field pattern (RF: rice-fish-shrimp-crab co-culture + bund + ditch), a field experiment was conducted to analyze the characteristics of N input and N output. The differences in N use efficiency and yield of rice between two paddy planting patterns were investigated too. Results showed that N input of two rice field patterns was mainly from irrigation, fertilization and precipitation. N input from fertilizer in RF system was 128.25 kg(N)·hm^-2, 11.75 kg(N)·hm^-2 less than that of CK, and was 14%52% less than that of other rice planting regions in South China. In RF system, N input at source was limited, thus reducing the risk of nutrient loss. N output of CK system was composed of soil fixation, ammonia volatilization, N loss via lateral seepage, and crop N uptake. In addition to components of N output of CK, N output of RF system contained N absorptions by fishes, shrimps and crabs. Due to special bund-ditch ecological purification in RF system, N loss through lateral seepage dropped by 9.33 kg(N)·hm^-2 and NO3-N was the main form of lateral seepage. N loss via ammonia volatilization in RF and CK systems was 8.91 kg·hm^-2 and 21.54 kg·hm^-2, respectively. Ammonia volatilization rate in RF system accounted for 6.9% of total amount of applied fertilizer, which was 8.5% less than that in CK and 10.3% less than the national average. Compared with CK, RF system harvested 6.65% higher rice yield. N uptake by rice and aquatic materials was 271.72 kg(N)·hm^-2 in RF system, 255.05 kg(N)·hm^-2 in CK system. The results suggested that breeding fishes, shrimps and crabs did not reduced rice yield. N use efficiency in RF system reached 64.3%, which was 19.7% higher than that in CK. RF not only achieved high rice yield, but also reduced N loss in paddy fields. Therefore stereoscopic planting rice field was feasible in North China where irrigation demands were well met. This study provided a critical reference for controlling agricultural non-point source pollution in North China.