Transfer Characteristics Of Nitrogen Fixed By Leguminous Green Manures When Intercropped With Wheat Or Maize In Northwestern China

In order to cope with the pressure of resources and environment,the technology of wheat,maize intercropped with leguminous green manure was explored.In this technology pattern,the leguminous green manure can be used for biological nitrogen fixation and plow into field,which can not only provide nutrients for wheat or maize,but also effectively improve the cultivated land fertility.As an innovative practice,the effect and mechanism of maize,wheat intercropped with leguminous green manures are still lack of research.In this study,the characteristics of biological nitrogen fixation（BNF）of common vetch,hairy vetch in monoculture and intercropping systems and the utilization capacity of wheat,maize for biological fixed nitrogen were investigated by pot experiments.The nitrogen uptake effect in these cropping systems were studied by field experiments.The main results and innovative findings were as follows:（1）In the wheat/leguminous green manures intercropping systems,11.4～31.6%nitrogen accumulation of wheat was from biological fixed nitrogen of leguminous green manures in pot experiment.Compared with monoculture,nitrogen accumulation of wheat and leguminous green manures significantly reduced in intercropping systems except wheat in Xining.Total nitrogen accumulation of wheat and green manures in intercropping systems significantly increased than that of monocultured wheat.The proportion of nitrogen derived from atmosphere（%Ndfa）had no significance between monocultured and intercropping systems at both experiment sites.But accumulation of nitrogen derived from atmosphere（Ndfa）significantly reduced in intercropping systems except hairy vetch in Wuwei,i.e.,Ndfa of intercropped common vetch（0.24 g/pot,0.48 g/pot）decreased by82.1%and 38.5%than monoculture（0.88 g/pot,0.78 g/pot）in Xining and Wuwei,respectively,Ndfa of intercropped hairy vetch（0.38 g/pot）decreased by 51.2%than monoculture（0.81g/pot）in Xining.Moreover,%Ndfa and Ndfa of hairy vetch in Xining were significantly higher than that in Wuwei.No significance was found for%Ndfa of common vetch at the two experiment sites,and Ndfa of intercropped common vetch was higher in Wuwei than that in Xining.In Xining and Wuwei,nitrogen transfer accumulation（Ntransfer）were 132.70 mg/pot and 194.16 mg/pot,accounting for 31.6%and 24.7%of the wheat intercropped with common vetch,respectively;and the Ntransfer were 89.90mg/pot and 59.98 mg/pot,accounting for 23.8%and 11.4%of the wheat intercropped with hairy vetch,respectively.Path analysis showed that shoot dry biomass was the most important factor affecting Ndfa and Ntransfer.（2）In the maize/leguminous green manures intercropping systems,5.9～37.0%of maize nitrogen accumulation was from biological fixed nitrogen of leguminous green manures in pot experiment.Compared with monoculture,nitrogen accumulation of intercropped wheat and common vetch significantly reduced in two experimental sites but intercropped hairy vetch significantly increased in Wuwei.Total nitrogen accumulation of maize and green manures in intercropping systems significantly increased than that of monocultured maize.Compared with that in monocultured green manures,the%Ndfa in intercropping systems had no significant difference at either experimental site,except for that in hairy vetch in Xining.However,the Ndfa significantly reduced in intercropping systems except common vetch in Wuwei,i.e.,Ndfa of intercropped common vetch（0.77g/pot,0.55 g/pot）decreased by 36.8%and 50.0%than monoculture（1.16 g/pot,1.10g/pot）in Xining and Wuwei,respectively,Ndfa of intercropped hairy vetch（0.48 g/pot）decreased by 52.9%than monoculture（1.12 g/pot）in Xining.Moreover,%Ndfa and Ndfa of intercropped common vetch and monocultured hairy vetch in Xining were significantly higher than that in Wuwei.In the intercropping systems in Xining and Wuwei,the Ntransfers of common vetch were 21.54 mg/pot and 26.81 mg/pot,accounting for 32.9%and 5.9%of the nitrogen accumulation in maize,and the Ntransfer of hairy vetch were23.34 mg/pot and 39.61 mg/pot,accounting for 37.0%and 23.3%of the nitrogen accumulation in maize,respectively.The path analysis suggested that soil nutrient and green manure biomass were mainly factors affecting Ndfa,and Ntransfer was affected byδ¹⁵N in the soil.（3）Intercropped with leguminous green manures had no significant impact on the yield of wheat and maize,but increased the soil mineral nitrogen content.With nitrogen fertilizer application,the grain yield and nitrogen accumulation of wheat and maize significantly increased.Compared with monoculture,the LER of shoot dry biomass increased in wheat or maize/leguminous green manure intercropping systems,and the total biomass had an overall advantage.Compared with no nitrogen fertilizer,apply nitrogen fertilizer significantly increased the yield of wheat（except monocultured wheat in Wuwei）and maize by 29.8～66.7%and 33.2～75.1%,respectively.Moreover,nitrogen accumulation of wheat and maize significantly increased by 38.9～81.6%and 51.1～123.7%.Overall,wheat and maize could effectively use the biologically fixed nitrogen by leguminous green manure in intercropping systems.The Ndfa and Ntransfer were affected by green manure varieties and experimental sites,etc.Moreover,the potential of BNF of leguminous green manure could be stimulated by optimizing green manure varieties and cultivation measures,so as to promote wheat,maize use biological fixed nitrogen by leguminous green manure.