Nitrogen cycling and balance in agricultural ecosystem in piedmont plain of Taihang Mountains

The piedmont plain of MT Taihang,an important agricultural area in North China,usually growing wheat in winter and maize in summer,is characterized by intensive cereal production.For the purpose of maximizing crop yield,irrigation and N fertilizer are commonly oversupplied.As the result large N is lost via volatilization,denitrification and leaching and come into being a great harm to the environment.The main nitrogen cycling pathways,such as nitrificationdenitrification,ammonia(NH3) volatilization,nitrate(NO3--N) leaching and N uptake by crops,were monitored in a wheat-maize rotation field with acreage being one hectare.The dominant N loss way was evaluated.The characters of N inputs and outputs on farmland of Piedmont Plain of MT Taihang were quantificationally illuminated and the N balance was analyzed so as to provide some important information for establishing optimized N management to diminish N losses and increase N use efficiency.The results indicated that NH3 volatilization and NO3--N leaching losses were the dominant pathways of N loss resulting in low N use efficiency.The annual NH3 volatilization rate was N 60 kg/ha and NO3--N leaching loss rate was N 684 kg/ha,accounting for 15% and 1.4%20.3% of the applied N fertilizer,respectively.The nitrification-denitrification loss was not a very important pathway of N loss,but its effect on environment cannot be ignored.The annual nitrification-dinetrification loss was N 2.0210.49 kg/ha,accounting for 0.51%1.37% of applied N.NH3 volatilization,nitrification-denitrification and NO3--N leaching mainly took place after N applied and irrigation or heavy rainfall events occurred and the N loss in the time of maize growing was much larger than that of winter wheat growing.The N was oversupplied in wheat-maize rotation field under traditional agricultural management in the study area.The range of N surplus under wheat was N +115.5+124.5 kg/ha,higher than those under maize.The N balance under maize was lightly surplus or wane resulted from heavy N loss.The measurements should be taken,such as improving N applied methods to decrease NH3 volatilization,reducing irrigation amount especially avoiding heavy irrigation to(diminish) NO3--N leaching,to improve crop yields and N use efficiency.