EFFECTS OF SPLIT FERTIGATION RATES ON THE DYNAMICS OF NITRATE IN SOIL AND THE YIELD OF MULCHED DRIP-IRRIGATED MAIZE IN THE SUB-HUMID REGION

In sub-humid regions of Northeast China, drip irrigation is increasingly used in maize (Zea mays L.) production to cope with frequent droughts occurring after planting and decreasing water allocated to agriculture. For conventional maize cultivation in this region, the total dose of nitrogen fertilizer is usually broadcast early in the season to avoid the accessibility difficulties to the field late in the season. Drip fertigation allows the application of fertilizers throughout the season. Field experiments were conducted in a sub-humid region of Northeast China to investigate the influence of the number of fertigation events and the nitrogen applied on the nitrate content in the soil, plant growth, nitrogen uptake, and grain yield during the maize growing seasons in 2011, 2012, and 2013. The experiments used a single early-season fertigation and three in-season split fertigation events. For each fertigation treatment, four nitrogen levels of 50, 100, 150, and 200 kg N ha(-1) were tested using a randomized complete block design (RCBD) with three replicates. The results indicated that, for a given amount of nitrogen applied, the split fertigation treatments increased the nitrate content in the root zone during the late growing season, reducing the fluctuation of nitrate content in soil during the growing season. An increasing number of fertigation events and amount of nitrogen applied resulted in an increased aboveground plant biomass and nitrogen uptake of maize during the physiological maturity stage. Furthermore, the split in-season fertigation produced a significantly higher yield (approximately 5% at a significance level of p < 0.05) than a single early-season fertigation. Higher amounts of nitrogen applied produced higher maize yields for either the single fertigation treatments or the split fertigation treatments during the three experimental years. However, the difference between the nitrogen rates of 150 and 200 kg ha(-1) was not statistically significant We recommend a management practice of 150 to 200 kg ha(-1) of nitrogen applied in three in-season fertigation events to obtain high production while reducing the risk of nitrogen leaching.