Optimising nitrogen fertilisation: A key to improving nitrogen-use efficiency and minimising nitrate leaching losses in an intensive wheat/maize rotation (2008-2014)

Optimising nitrogen (N) fertilisation is critically important for obtaining high crop yields with low environmental costs. A seven-year field experiment was conducted to evaluate the effects of the rate of N application on crop yield, N-use efficiency (NUE), nitrate residue (NR), and nitrate leaching in an intensive wheat/maize rotation system on the Loess Plateau of China. Five treatments were tested: a control (no N fertilisation) and conventional, low, moderate, and high rates of N fertilisation. Nitrates were leached mainly after heavy rains and with flood irrigation and varied notably between years. Annual nitrate-leaching loss (ANLL) averaged 3.4-17.3 kg N ha−1 y−1 at N rates of 165-495 kg N ha−1. Crop yields increased quadratically and NUE decreased linearly with increasing rates of N application. NR and ANLL increased exponentially. Compared with conventional management, moderate N fertilisation increased NUE and decreased NR and ANLL by 46 and 34%, respectively, without any significant decrease in crop yield. High yields can thus be achieved at a moderate N rate and an economically optimal N rate with less ANLL and acceptable soil NR. We recommend N-application rates of 150-170 and 180-200 kg N ha−1 for wheat and maize, respectively, for obtaining high crop yields with low environmental risks.