Effects of dairy effluents irrigation on N balance in soil under winter wheat-summer maize rotation system

Abstract: With the development of intensive cultivation of livestock in China, a large number of effluents are produced. However, the treatment and utilization rate of livestock effluents are low, which causes nitrogen and phosphorus losses and the problems of water resource shortage and serious overexploitation of the groundwater for agricultural irrigation in the North China Plain. In order to control the non-point pollution, the experiment was conducted in the North China Plain for 3 years to test the effects of continuous dairy effluent irrigation on crop yield, nitrogen (N) use efficiency, residual inorganic N and N balance in winter wheat - summer maize rotation system. The study included five treatments with three replications: No fertilizer and freshwater irrigation in wheat growing season (CK), 2 times dairy effluent irrigation in wheat growing season (T1), 3 times dairy effluent irrigation in wheat growing season (T2), 4 times dairy effluent irrigation in wheat growing season (T3), customized fertilization, inorganic compound fertilizer of 375 kg/hm2 after planting, and 600 kg/hm2 urea application at wheat jointing stage, freshwater irrigation in wheat growing season (CF). The irrigation quota was 830 m3/hm2, and the irrigation quantity was controlled by water Ultrasonic flowmeters. The results showed that dairy effluent irrigation significantly increased the winter wheat and summer maize yield by 36.78% and 40.82% respectively. With the increasing of N application amount, the yield of winter wheat increased at first and then decreased. When the N application amount was 240 kg/hm2, the yield of wheat was the maximum. However, the yield of maize increased with the increasing of N application amount, and when the N application amount was 320 kg/hm2, the yield of maize was the maximum. The yield of wheat increased by 1.56%-12.47% and maize increased by 1.84%-7.27% in the three-year successive harvests, though the N application rates were reduced by 3.61%-51.81% for wheat and by 68.94%-74.89% for maize. The nitrogen accumulation amounts in plant and grain under the treatments with dairy effluent irrigation were significantly higher than those under the treatment CK. There was no significant deference among the treatments T1, T2, T3 and CF in 2011 and 2012, the nitrogen accumulations in winter wheat for the treatments T2, T3 and CF were significantly higher than that for treatment T1. The crop yield increased gradually with the increasing of dairy effluent irrigation span. The crop N use efficiency increased year by year, and in the third year the crop N use efficiency reached 47.87%-67.63%, which was the carryover effect of dairy effluent irrigation. After harvesting winter wheat, with the increasing of nitrogen amount of dairy effluent, the soil nitrate accumulation in 0-100 cm soil layer was increased. The soil nitrate accumulation in 100 cm soil layer of 4 times irrigation was significantly higher than that of 2-3 times irrigation. The dairy effluent irrigation significantly enhanced the residual inorganic N in 0-100 cm soil layer, and the residual nitrate N was apparently more than the residual ammonium N. The results of N balance showed that the N uptake by crop increased with the increasing of N application amount. After the irrigation using dairy effluent in wintering and elongation period of wheat, N use efficiency of crop was significantly greater than that cultivated by normal fertilization and irrigation. Residual inorganic N in 0-100 cm soil layer and apparent N loss were significantly less than that in other dairy effluent irrigation treatments, and decreased by 39.73% and 55.67% respectively than that in the normal fertilization irrigation treatment. Considering crop yield, accumulative N use efficiency and soil inorganic N balance, it is concluded that 2-3 times dairy effluent application is appropriate in winter wheat - summer maize rotation system.