Monitoring of nitrogen cycling and balance in maize monoculture agro-ecosystem in northeast China black soil

摘要

Research the nitrogen cycling in agricultural ecosystem and quantitative analysis of the sources and destinations of nitrogen are important for the reasonable application of nitrogen fertilizer and promotion of the agricultural sustainability. The trial was aimed to monitor and assess nitrogen cycling and balance in maize monoculture agro-ecosystem in northeast China black soil. Ammonia volatilization, denitrification, nitrate leaching and crop nitrogen (N) uptake were measured in field experiments under different N applications, and nitrogen budget was quantitatively evaluated. Results showed that the N input was 30.56 ~ 330.56 kg ha-1 and the N output was 124.9 ~ 225.5 kg ha-1 in this black soil agro-ecosystem. The N input was mainly through chemical fertilizer, rainfall, biological fixation and seeds in maize monoculture agro-ecosystem, among which chemical N fertilizer contributed to 83.1%~88.2% of total N input. Meanwhile, nitrogen was removed from this agro-ecosystem primarily through crop uptake, ammonia volatilization and denitrification. Crop N uptake accounted for 90.3% ~ 95.2% of total N removal. With the increase of N fertilization application, N loss through ammonia volatilization and denitrification increased markedly. Ammonia volatilization is an important way of nitrogen loss in this agro-ecosystem, and N loss from ammonia volatilization was observed to be 5.38 ~ 18.85 kg ha-1 yr-1, which occupied 3.17% ~ 4.49% of the applied N fertilizer. The loss rate of fertilizer nitrogen caused by denitrification was only 0.08% to 0.23%. Compared with the northern wheat-maize rotation system, nitrogen loss from ammonia volatilization and denitrification in the maize monoculture system is lower, only equivalent to nitrogen loss from winter wheat season in the wheat-maize rotation system. There was a N deficiency in 3.05 ~ 94.34 kg ha-1 yr-1 when N input was less than 150 kg ha-1 yr-1 in this agro-ecosystem. However, there was a 124.57 kg ha-1 yr-1N surplus in this agro-ecosystem when farmer conventional fertilization was 300 kg ha-1 yr-1. Under N application of 225 kg ha-1 (two times of application) and optimized N application of 225 kg ha-1 (three times of application), there was a 51.36 and 30.06 kg ha-1 yr-1N surplus, respectively. Therefore, intensifying N management associated with increasing ratios of top dressing N to basal N fertilizer and times of top dressing might be a useful measure to reduce the N surplus and N loss, and maintain a positive nitrogen cycling and balance in maize monoculture agro-ecosystem.