Time-spatial variability of ammonium and nitrate in farmland soil of Taihu Lake region
太湖地区农田土壤中铵态氮和硝态氮的时空变异

Time-spatial variability of ammonium and nitrate in soil profiles of farmland soil(three main paddy soils: White soil,Huangni soil and Wushan soil) during wheat and rice growth was studied.The results were as follows: the ammonium content was high in February and September and low in April and November in 2004.The spatial variability of ammonium content in soil profiles was gradually decreased from surface soil layer to bottom soil layer.It was stable below 40 cm.The nitrate content was lower than the ammonium content.The nitrate content of the wheat growth season(dry cultivation) was higher than that of the rice growth season(water cultivation) in a year.The spatial variability of the nitrate content in soil profiles was quickly decreased from surface soil layer to bottom soil layer during dry cultivation.But during the rice growth season,the nitrate content of the surface soil layer in soil profiles was lower than that of bottom soil layer.It was leaching phenomenon of nitrate.The nitrate content was in a sharp positive relation with the ammonium and changed with exponential function during dry cultivation.But there was not this relationship during water cultivation.The ammonium and nitrate were significant relation with soil organic matter in straight line.But the ammonium and nitrate content decreased with the soil clay content and pH value increased and changed with logarithmic function.