Nitrogen loss in surface runoff from Chinese cabbage fields

A growth period of Chinese cabbage included seedling, rosette, anterior folding, middle folding, and posterior folding stages. To investigate characteristic of surface runoff, evolution of various nitrogen (N) forms at different growth stages, and contribution of N loss during a whole growth period to environment, 10 simulated rainfalls were applied on Chinese cabbage planted in two 2 m2 troughs (A and B), with two replicates. Troughs A and B were designed with slopes of 14° and 21°. Five simulated rainfalls were applied in each trough. Seedling and rosette stages were with rainfall intensities of 0.65 mm min−1 and folding stages were with 1.93 mm min−1, respectively. Fertilizers were applied at seedling and anterior folding stages at rate of 103 and 103 kg N ha−1, respectively. One rainfall event lasted for approximately 20 min. Conclusions were as follows: N loss mainly occurred at rosette stage and anterior folding stage. Nitrogen loss had a close relationship with runoff volume. Percentage of NH4+–N in TN had an ascending trend with growth of Chinese cabbage while percentage of NO3-–N had a descending trend. Folding stages had more percentages of undissolved N than seedling and rosette stages. Lower slope was advantageous to the concentrations of TN, NO3-–N, and NH4+–N and proportion of NO3-–N. Based on the results, we need to pay more attention to the NO3-–N pollution in Chinese cabbage filed at lower slope.