Contribution Of Atmospheric Nitrogen Deposition To The N-Balance In Smooth Crabgrass/Winter Radish Rotation Ecosystem On Red Soil Upland

The experiment was carried out on Experiment Station of Red Earth Ecology,Chinese Academy(Yingtan,Jiangxi)of Sciences from 2005 to 2007.The atmospheric N deposition flux and N dry deposition velocities(V_d)were gotten by observations of onflow and factors of farmland microclimate,analysis of nitrides in the atmosphere and rain and the formula of energy equity.Smooth crabgrass(Digitaria ischaemum)and winter radish (Raphanus sativus)were cropped continuously.And input and output of nitrides were observed and calculated on upland red soil.The input N was from atmospheric N deposition,N fertilized and N of irrigation while the output N was from N absorbed by crops,N of ammonia volatilization,runoff and leaching water after N fertilizer applied.As a result,characteristics of N deposition and it contributed to N balance in the ration cropping system.1 Characteristics of N dry deposition on upland red soil1.1 The atmospheric N dry deposition velocities had a significant temporal variation with higher value in day time,lower at night.The hourly mean V_d of NO_x,NH₃,NO_x/NH₃ in the particle and HNO₃ were ranged respectively from 0.05 to 0.23 cm/s,from 0.17 to 0.34 cm/s,from 0.05 to 0.41 cm/s and from 0.62 to 1.27 cm/s.1.2 The daily mean V_d of NO_x,NH₃,NO_x/NH₃ in the particle and HNO₃ were respectively 0.12,0.25,0.17 and 0.88 cm/s.There were significance between those V_d and the season,which the dry deposition V_d of NO_x,NH₃,NO_x/NH₃ in the particle were higher while the dry deposition V_d of HNO₃ was lower in Winter.1.3 The max values of N dry deposition were ranged from 10.06 to 11.50 kg/hm² on upland red soil and those values appeared during February to April.2 Characteristics of N wet deposition on upland red soil The gross rainfall was 1843.4mm.Rain appeared mainly during February to June.And rainfall of those five months was account for 67.33%of the gross rainfall.The monthly input of N wet deposition was from 0.50 to 8.45kg/hm² with higher value in July and November.3 Deposition flux of the atmospheric nitrogen on upland red soil The total N of the atmospheric deposition was 132.6 kg/hm²,which the N dry deposition was 82.63 kg/hm², accounting for 67.94%of the total N in upland red soil system.4 Characteristics of N balance on upland red soil There had N surplus,which was from 4.33 to 124.76 kg/hm² with N(0～230 kg/hm²)of urea applied in the smooth crabgrass (Digitaria ischaemum)systems.While there was N surplus,which was from 2.16 to 75.99 kg/hm² with N(0～250 kg/hm²)of urea applied,except that N deficit appeared when N(70 kg/hm²)of urea was applied in the winter radish(Raphanus sativus)systems. 5 Contribution of N deposition/dry deposition to N balance in upland red soil system5.1 The N deposition was 26.28 kg/hm² during the growth of smooth crabgrass(Digitaria ischaemum).In the smooth crabgrass system,it accounted for 10.25%～100.00%of the gross N input and for 8.90%～40.25%of the gross N output.And it contributed to N absorbed by smooth crabgrass with 9.37%～4.57%.Meanwhile,N dry deposition was 15.25kg/hm²,which accounted for 5.95%～58.03%of the gross N input,for 5.16%～23.52%of the gross N output and for 5.43%～26.55%the N absorbed by smooth crabgrass.5.2 The N deposition was 4.5.92 kg/hm² during the growth of winter radish(Raphanus sativus).In this system,it accounted:for 15.49%～99.03%of the gross N input and for 20.84%～100.00%of the gross N output.And it contributed to N absorbed by winter radish with 21.57%～100.00%.Meanwhile,N dry deposition was 24.72 kg/hm²,which accounted for 8.34%～53.31%of the gross N input,for 11.22%～55.91%of the gross N output and for 11.61%～57.35%the N absorbed by smooth crabgrass.