Dynamics of Soil Salt and Nitrogen and Maize Responses to Nitrogen Application in Hetao Irrigation District, China

Sustainable development of Hetao Irrigation District (HID), the largest irrigation district in Northwest China, is threaten by soil salinization due to the high evaporation potential, large irrigation amount, and excessive chemical nitrogen fertilizer application. In this study, six nitrogen (N) treatments with application amounts of 0, 50, 100, 150, 200, and 250 kg ha–1in the 2013 season and 0, 100, 150, 200, 250, and 300 kg ha–1in the 2014 season, corresponding to N0, N50, N100, N150, N200, and N250 in the 2013 season and N0, N100, N150, N200, N250, and N300 in the 2014 season, were established to investigate the dynamics of soil salt and NO3-N concentrations, maize yield, and nitrogen use efficiency. The results show that nitrogen application linearly enhanced the soil salt and NO3-N concentrations when N application is higher than 150 kg ha–1. The highest grain yields of maize (16.9–17.1 ton ha–1) in both seasons were found in the N250 treatment, and were 6–9% higher than those for the N300 and N200 treatments and 13–40% higher than those for the N150-N0 treatment. Decreases in the 100-grain weight and grain numbers per ear were the two main reasons for the grain yield reduction in N0-N200 and N300 compared with N250. The maximum water productivity and irrigation water productivity were 3.7 and 4.7 kg m–3, respectively, found in the N250 treatment in both seasons. The nitrogen productivity and partial factor productivity generally decreased with increasing N application. Fully considering the salt balance and maize yield, a nitrogen application amount of 200–250 kg ha–1was recommended for HID.