Effects of reducing N application on crop N uptake, utilization, and soil N balance in ricewheat rotation system

The effects of reducing N application on plant N uptake, utilization, and soil N balance in ricewheat rotation system were studied using field experiments. The results show that compared with farmers practice for N fertilization, N 225 kg/ha for wheat with 1/2 basal and 1/2 topdressing at the tillering stage and N 210 kg/ha for rice with the ratio of 3∶2 for the basal and tillering applications, the grain yields are not decreased under the N application amounts with a reduction by 20%-30%, while the N recovery efficiency, N agronomic efficiency, and N partial factor productivity are increased. Moreover, topdressing N fertilization can increase the grain yields and reduce the cost of the fertilization. Although both soil mineral N content and accumulation are reduced, the N absorptions by crops are not reduced accordingly. There is less residual soil mineral N in 0-100 cm layer at the harvest stages of wheat and rice compared to that of the farmers practice. In addition, the loss of apparent N in the ricewheat system is mainly occurred in the rice season. Therefore, it is preliminarily concluded that the reducing N application by 20%-30% is a feasible N management practice under the first ricewheat rotation system in the middlelower Yangtze plain with over N fertilization.