| In order to investigate the effects of optimum (OPT) and conventional (CON) fertilization on spring
wheat yield，N utilization and soil nitrate accumulation, and simultaneously evaluate the apparent N balance in the soil-wheat system, a field experiment with Ningchun 11 and Ningchun 16 of spring wheat growing was conducted in the Yellow River Irrigation Region of Ningxia from 2009~2010, respectively. The results showed that both OPT and CON treat-ments significantly increased the grain yield, shoot biomass, grain N uptake and shoot N uptake compared with CK，but there was no siqnificant difference found between OPT and CON. Fertilization had no siqnificant influence on harvest in-dex of spring wheat，however, OPT was beneficial to improve the yield composition and some agronomical characteristics,
and achieve high grain yield. In contrast to CON，OPT treatment could increase more or less the recovery efficiency (RE)，agronomy efficiency (AE) and partial factor productivity (PFP) of applied N. Soil nitrate accumulation had the declining trend with the soil depth increasing， therefore， OPT treatment effectively decreased the soil nitrate accumulation in 0~100 cm soil. Apparent N balance in the soil- wheat system indicated that soil residual Nmin, mineralization and irrigation N input should be taken into account，and then reduced soil residual Nmin and apparent N losses by optimum fertil-ization. |