FATE OF FERTILIZER N IN WINTER WHEAT/SUMMER MAIZE ROTATION SYSTEM ON HIGH-ERTILITY SOIL

A field trial with 15 N\|microplots was conducted to study the fate of fertilizer N on high\|fertility soil for winter wheat/summer maize rotation system,one of main cropping systems at North China.The results showed that when 120～360kg/hm\+2 of nitrogen applied,the recovery of fertilizer nitrogen were 23\^0%～44\^5% for winter wheat,26\^0%～51\^1% for summer maize and 28\^0%～51\^6% for one winter wheat/summer maize rotation,while less than 10% of fertilizer nitrogen taken up by the next crop.The soil residual nitrogen from fertilizer was in 30%～50% for current crop season and about 30% at the end of one winter wheat/summer maize rotation.While the loss of fertilizer nitrogen,regardless in amount or in % of nitrogen applied,increased with the N applied rate.For the whole rotation system,the cumulative loss of fertilizer nitrogen was only 18\^98% at nitrogen applied rate of 240kg/hm\+2 while 40\^50% at nitrogen applied rate of 720kg/hm\+2.There was not significant difference in soil N uptake by crops between low N applied rate treatments,but with the increase of N applied rate N uptake by crops got lower,indicating that so\|called “negative added nitrogen interaction” occurred.