Nitrogen loss via runoff and leaching from soil as a function of types of urea applied in wheat season

An experiment using large-sized undisturbed monolith lysimeters was carried out to study nitrogen loss via drainage and leaching from Wushan soil in the Taihu Region under a rice-wheat rotation system with different types of urea fertilizers applied in wheat seasons in the years of 2001 to 2003.The results show that dissolved N（DN）in the drainage flow can be partitioned as NO₃^--N representing more than 76.7% of the DN,and as NH₄⁺-N accounting for less than 23.3%N loss via drainage flow in the wheat seasons varied significantly from year to year.Interval between rainfall and fertilization was the key factor dominating nitrogen drainage losses.The NO₃^--N concentrations in leaching from all the treatments(The highest NO₃^--N concentration was 8.12 mg·L^-1) were lower than the criteria of NO₃^--N concentration for drinking water,but were higher than 0.02 mg·L^-1（the threshold concentration of DN for inland water eutrophication）.The amount of percolation in CK was higher than the other treatments.When N 150 kg·hm^-2 was applied,the N loss via percolation was not significantly increased by N application no matter whether the fertilizer was common urea or coated urea.But continuous N application with rates higher than the N demand by wheat will certainly increase the risk of N loss via percolation.