Fig. 3

Effect of nitrogen dosages and irrigation regimes on soil total N, soil organic carbon, soil NO₃^−_N, and NH₄^+_N content. The bar represents the standard error (n = 4). The nitrogen treatments control, N200, N250, N300 and N350 represent the application of nitrogen at the rate of 0, 200, 250, 300 and 350 kg N ha^− 1. HW and LW represent the irrigation water at the rate of 80 and 60% of field capacity. The V9, R1, R3, and R6 stages represent the maize with 9 leaves, silking, milking, and maturity stages, respectively