Effects Of Nitrogen Application Rate On Energy Sorghum Yield And Soil Nitrogen Availability In Marginal Land At Inner Mongolia

Nitrogen(N)management plays a major role in energy crop production maximization and environmental protection on marginal land.Reasonable utilization of nitrogen fertilizer on sorghum production is importent to promote energy sustainable development of biomass energy industry in China.A field experiment was conducted to investigate the effects of N fertilizer application rates on temporal-spatial changes in inorganic N,microbial biomass nitrogen?carbon,N surplus levels in soil and ethanol conversion potential beneath biomass sorghum(Var.GN-11)and sweet sorghum(Var.GT-8)(Sorghum bicolor(L.)Moench)on marginal land in Inner Mongolia,China,in 2014 and 2015.The purpose of this study is to explore the regularity of soil nitrogen availability in the marginal planting of energy sorghum,and to provide a theoretical basis for the large-scale promotion of energy sorghum.N application had significant effect on yield of the two varieties sorghum on the ground.The sorghum biomass increased as N fertilizer rate increased from 0 kg N hm-2 to 120 kg N hm-2,while remained stable from 120 kg N hm-2 to 240 kg N.Meanwhile,this article suggested that the energy sorghum leaf should be returned to the field in order to reduce the loss of soil nutrients and improve the conversion efficiency of bioethanol,because of the larger proportion of leaf biomass.The theoretical ethanol yield of energy sorghum stalks under N120 treatment was 2471.2 L/hm2.With incremental increases in N fertilizer application rates during each growing season,nitrate nitrogen(NO3--N)content in the 0?90 cm soil depth zone for two varieties significantly increased on elongation,anthesis and harvest dates,while ammonium nitrogen(NH4+-N)remained stable.NO3-N accumulation in the 0?90 cm soil layer at harvest significantly increased from 120 kg N hm-2 to 240 kg N hm-2.The maximum nitrate accumulation of GN-11 and GT-8 could reach 183.3 kg/hm2 and 115.4 kg/hm2 under N240 treatment.The apparent N surplus increased as N fertilizer rate increased.The N fertilizer of 120 N kg ha-1 improved dry matter yield and relatively reduced NO3-N accumulation and further N loss among five N rates.The application of nitrogen increased the content of soil microbial carbon and nitrogen during the energy sorghum growing season.Meanwhile,the contents of microbial carbon and nitrogen revealed an oppose trend with that of soil inorganic nitrogen.And N application had no significant effect on the contents of soil microbial biomass carbon and microbial biomass nitrogen.Both GN-11 and GT-8 showed greater requirement for nitrogen in early flowering stage Thus,Topdressing nitrogen at jointing stage using a ratio of more than 50%,base fertilizer and top dressing in the flowering period using a ratio of less than 20%and 30%under 120 kg N hm-2 treatment could further improve energy sorghum yield and reducing nitrogen loss.