The fate of 15N-labelled urea in an alkaline calcareous soil under different N application rates and N splits

We aimed to quantitatively investigate the effects of rate and timing of nitrogen (N) application on fate of 15N-labelled urea in an alkaline calcareous soil during a winter wheat (WW) and summer maize (SM) seasons. The treatments consisted of conventional N application (i.e., WN300-2T or MN240-2T, 300 or 240 kg N ha−1 with two N splits to WW or SM), reduced N application (i.e., WN210-2T or MN168-2T, 210 or 168 kg N ha−1 with two N splits to WW or SM), recommended N application (i.e., WN210-3T or MN168-3T, 210 or 168 kg N ha−1 with three N splits to WW or SM), and control (N0). The result showed that the fate of 15N fertilizer was significantly influenced by rate and timing of the applied N. Compared with the conventional N treatment, crop 15N recovery in the recommended N treatment increased significantly by 16.7 % for WW and 17.2 % for SM, but total 15N losses reduced significantly by 12.3 and 13.5 %, respectively. Residual 15N in 100–200 cm soil layer was the lowest in recommended N treatment, preventing leaching of much 15NO3−–N to deeper soil layers. Our results indicated that the recommended N treatment at rate of 210 or 168 kg N ha−1 with three N splits to WW or SM would maintain crop yields but significantly increase N recovery efficiency and reduce the risk of environmental pollution caused by N losses.