| The long term field experiment on N fertilizer reduction under the conditions of straw incorporation was conducted to identify a suitable N rate and provide the theoretical basis of reasonable fertilization for the farmland in wheat-straw cropping system on Guanzhong Plain. Three treatments, conventional applied N, 15% and 30% reduction applied N, were performed by a randomized complete block design with three replications. The results showed that, in comparison with conventional N application treatment, averaged across three years from 2008 to 2011, N reduction by 15% and 30% did not significantly reduce crop grain and straw yields. During the crop growing seasons from 2010 to 2011, N reduction by 15% reduced straw N, P, K annual uptake and increased grain N, P, K annual uptake, especially for grain P uptake. N reduction by 30% significantly reduced grain N, straw N, K annual total uptake by 12.9%, 41.9%, 18.5% respectively. 30% N reduction treatment had the lowest N surplus after harvesting wheat and maize, the N surplus was only 11.3 kg·hm-2 when wheat was harvested, partially associated with a shortage of N. Taking into account into consideration of the yield, nutrients uptake and utilization, apparent soil N balance, the 15% N reduction treatment has an optimum N application rate (wheat season 127.5 kg·hm-2, maize season 159.4 kg·hm-2) in this region. |