Nitrogen balance under different N application rates in young apple orchards

A field and a microplot experiment were conducted at the same time combined to study nitrogen balance under different N application rates by using two-year-old Fujiapple trees (M. domestica Borkh. cv. Red Fuji/M. hupenensis Rhed) in young apple orchards. The results show that the biomass and N uptake capacity of apple trees are increased significantly under the application of nitrogen fertilizer, and the nitrogen use efficiency (NUE) is decreased significantly with increase of N application rates. NUEs of the N75, N150 and N225 treatments are 31.28%, 22.95% and 19.38%, respectively. With increase of N application rates, the N residuals in soil are sharply increased, and the majority of residual N is concentrated in 060cm layer, which indicates fertilizer nitrogen losses in deep soil layers are small. The N recovery rates in soil-crop system are sharply decreased with increase of N application rates, and the N loss rates are increased respectively. The N recovery rate of the N75 treatment is 60.41%, which is significantly higher than those of the N150 (46.41%) and N225 (40.88%) treatments, and the loss rate of the N75 treatment is the lowest (39.59%), which is significantly lower than those of the other two treatments. The amounts of ammonia volatilization are increased significantly with increase of N application rates, however, the N2O loss are same. The proportion of ammonia volatilization and N2O loses in nitrogen loses are very low, and more nitrogen are lost through denitrification and runoff.