Relationship between accumulated NO3-N in soil profiles and apparent nitrogen budget in winter wheat fields under nitrogen fertilization

More than 20 field experiments designed with the 3414 plan were carried out in Huxian County and Zhouzhi County, Guanzhong Plain, Shaanxi during 2008 and 2009 to evaluate the NO3-N accumulation in soil profiles after harvesting winter wheat; and its relationship with the apparent N budget in soil was also studied. The results show the amounts of NO3-N accumulation in the soil profiles and their extents to leach into the deeper soil layers are increased significantly as the nitrogen fertilizer usage increased. When the N fertilizer rate reaches to 180240 kg/ha, positive budget of nitrogen in soil is observed in some experiment sites, and when N fertilizer rate reaches to the 270360 kg/ha, positive budget of nitrogen in soil is observed in all experiment sites. There is a positive correlation between the apparent balances of soil N and the accumulation of NO3-N in soil profiles (02 m). This indicates the amount of NO3-N in the soil profile is mainly determined by the apparent N budget balances in soil. The NO3-N accumulation in the soil profile is increased about 62.5 kg/ha when N balance in soil is at 100 kg/ha.