| A consecutive 2-year field experiment of the spring maize was conducted in northeast China to investigate the optimal models of high-efficient and sustainable nitrogen(N) fertilization. The following N fertilization treatments(four replicates of each) were performed: farmers practice N rate(N210, 210 kg·hm-2, 100% fast-release N), 80% of N210(N165, 165 kg·hm-2, 100% fast-release N), 80% of N210(NOS, 165 kg·hm-2, 60% fast-release N +20% organic fertilizer N+20% slow-release N), 80% of N210(NOSB, NOS+2t/hm-2 biochar) and without N supplement(N0). Based on the estimations of different impacts of fertilization models on the efficiency of N agronomy, soil fertility and environment, the optimal mode of N fertilization was selected. The results were shown as follows:1. Compared with N210, the yields of N165 and NOSB increased by 6.6% and 13.8% in 2013, by 2.7% and 9.0% in 2014, respectively; the N use efficiency(UEN) of N165, NOS and NOSB significantly enhanced by 47.7%, 61.6% and 67.9% in 2013, by 48.5%, 53.1% and 74.6% in 2014, respectively(P<0.05); the partial factor productivity from applied N(PFPN) significantly increased by 35.9%, 75.5% and 81.2% in 2013, by 30.6%, 58.2% and 73.4% in 2014, respectively(P<0.05); the agronomic efficiency of applied N(AEN) enhanced by 66.7%, 135.2% and 162.0% in 2013, by 35.4%, 56.9% and 94.4% in 2014, respectively, and the AEN of NOSB was significantly higher than N210 during the two years(P<0.05); the economic benefits of applied N(EBN) of N165 and NOSB also raised by 56.8% and 76.4% in 2013, by 14.4% and 19.8% in 2014, respectively, both of N165 and NOSB were significantly higher than N210 in 2013(P<0.05); The result investigated that NOSB had a obvious advantage in improving N agronomic efficiency.2. Compared with N210, there was no significant difference among N165, NOS and NOSB treatments on the total N, available N, organic matter and available P in both years. The available K of NOSB increased significantly by 11.5% of maize maturation stage in 2014(P<0.05). The result showed that, in 2013, compared with N210, the soil microbial biomass C(SMBC) of N165 decreased significantly by 29.6% in maturation stage(P<0.05), NOS increased significantly by 34.6% in filling stage(P<0.05) and NOSB increased significantly by 37.3% and 13.5% in filling and maturation stage, respectively(P<0.05); in 2014, NOSB increased significantly by 28.1% in maturation stage(P<0.05); the soil microbial biomass N(SMBN) of NOSB significantly enhanced by 30.9% and 47.6%, respectively, in tasseling and filling stage of the maize in 2013(P<0.05) and enhanced significantly by 21.9% in maturation stage of the maize in 2014(P<0.05); the urease activity of NOSB increased significantly by 130.3% and 38.4%, respectively, in bell and tasseling stage of the maize in 2013(P<0.05); the sucrase activity of NOSB raised significantly by 56.2% in maturation of the maize in 2013(P<0.05) and increased significantly by 71.2% in maturation of maize in 2014(P<0.05). The result showed that NOSB had an obvious advantage on improving soil fertility, and the advantage was mainly on soil microbial biomass and enzyme activities.3. Compared with N210, The cumulative CO2 emissions of NOSB decreased by 2.9%, while that of N165 increased significantly by 33.4%(P<0.05), and NOS also increased by 2.3%; the cumulative N2 O emissions of N165, NOS and NOSB decreased by 27.2%, 17.5% and 171.5%, respectively, NOSB was significantly lower than N210(P<0.05); the cumulative CH4 emissions of NOSB decreased by 195.5%, while that of N165 and NOS increased by 138.2% and 276.2% respectively. The cumulative CH4 emissions of NOSB was significantly lower than that of N165 and NOS(P<0.05).4. The CO2 emission was the main factor of greenhouse gas emission in spring maize cropping system of black soil in Northeast China, N2 O followed, and CH4 contributed least. The global warming potential(GWP) of NOSB decreased by 8.1%, 40.2% and 9.7% compared with N210, N165 and NOS. The result indicated that NOSB was the optional fertilizer model for reductions of greenhouse gas emission in black soil of Northeast China.5. The analysis of gray relational on different fertilizer models indicated that, correlation degree of N210, N165, NOS and NOSB were 0.5105, 0.6201, 0.6665 and 0.9343 in 2013, and were 0.5311, 0.4639, 0.5844 and 0.9413 in 2014, respectively. It was shown that NOSB was better than other models on the efficiency of N agronomy, soil fertility and environment. Sustainability index(SI) was also computed to assess the sustainability of soil-maize system in northest China, the result indicated that NOSB got the highest score of sustainability index and was the sustainable fertilizer model in this area.The results obtained in the present study revealed that fertilizer N application could be reduced from the farmers practice rate of 210 to 165 kg N hm2 without loss of crop yields and significantly enhanced N use efficiency, improved soil fertility and reduced greenhouse gas emission to the environment, but should be combined with organic fertilizer, slow-release fertilizer and biochar. This combined approach represents a practical means for reducing excess N input while maintaining the sustainability of spring maize system in Northeast China. |
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