THE COUPLING EFFECT OF WATER AND NITROGEN TO THE WATER AND NITROGEN USE EFFICIENCY AND YIELD OF SOYBEAN UNDER DRIP IRRIGATION MODE

The soybean in China northeastern black soil has low yield, low use efficiency of water and fertilizer, which has overly high amount of nitrogen residual. Three different drip irrigation mode amount (300 mm, 350 mm, and 400 mm) and five different amount of nitrogen was designed in this paper to study the influence of water and nitrogen controlling to the water and fertilizer use efficiency and the amount of nitrogen residual under drip irrigation mode. According to our experiment results, the water consumption of soybean increased with the growth of drip irrigation mode amount, and in all treatment, soybean consumed the most amount of water at seed filling period. There is no significant difference in water consumption amount between each treatment during seedling period, but there were significant differences in the water consumption of soybean at branching period, flowering and pod period, and seed filling period. Nitrogen fertilizer alone does not have significant influence on soybean water, but the interaction between nitrogen fertilizer and soybean had significant difference in water consumption amount. The yield reached the biggest amount of 3250 kg/hm(2) when nitrogen drip amount was 400 mm, and nitrogen application rate was 81 kg/hm(2). The yield increased with the growth of irrigation amount, but the yield increase rate became slow. When the nitrogen application amount was at a low level, there was a positive interaction between water and nitrogen, which showed a synergistic acceleration effect. When the nitrogen application rate was at a high level, there was a negative interaction between water and nitrogen. When the drip irrigation mode amount was 350 mm and the nitrogen application rate was 81 kg/hm(2), the WUE was the highest, which was 0.60 kg/m(3). In a certain range of nitrogen application, increasing irrigation amount can promote WUE, while the amount was over a certain range, WUE decreased. After harvest, the amount of nitrate nitrogen residual in the 0-100 cm soil varied greatly among different nitrogen fertilizer treatments, and the nitrogen fertilizer application amount was greater, the nitrogen residual was greater. In the W3N3 treatment which has the highest yield, the yield was at 42 kg/hm(2) less than the W3N4 treatment at the highest amount of nitrate nitrogen residual, which is a reduction of 35.78%. The results showed that proper combination of water and nitrogen application could reduce nitrogen residual in soil after harvest. The research results can provide theoretical basis and technical support for the efficient utilization of water and fertilizer resources in the black soil region located in northeastern China.