Effects of different cropping systems on food crop nitrogen utilization and soil nitrogen pool in North China Plain

Water and fertilizer utilization efficiency are subject to the planting system. Winter wheat-summer maize double cropping is an important rotation system mainly practiced in the North China Plain, low fertilizer-nitrogen use efficiency and excessive accumulation of soil nitrogen in the rotation system. A three-year field experiment was conducted from October 2010 to October 2013 in North China Plain. To explore the suitable planting system for efficient utilization of nitrogen in north China plain, the 15N tracer technology was used as a quantitative method to study the crop yield, 15N utilization rate, nitrogen destination and soil nitrogen pool apparent equilibrium under the three planting system of double cropping a year of winter wheat-summer maize with traditional and optimized water and nitrogen management, three cropping systems in two years of winter wheat-summer maize-spring maize rotation or winter wheat-summer soybean-spring maize rotation, and one crop per year of spring maize. The results showed that the yield of three cropping systems in two years of winter wheat-summer maize-spring maize was 32 248.52 kg/hm2, which was 22.16% and 52.88% higher than that of two crops and one crop in one year. The utilization rate of 15N was 33.36%, which was 26.12% higher than that of one harvest a year. The contribution rate and transference of nitrogen in a two-year triple cropping system was greater than double cropping, the amount of nitrogen transfer of four crops was showed that soil nitrogen higher than that of fertilizer nitrogen. The highest rate of nitrogen fertilizer in the three cropping systems was soil residue, followed by crop absorption and loss, the ratio of crop absorption, soil residue and loss in double cropping a year of winter wheat-summer maize with traditional water and nitrogen treatment was about 2:6:2, the ratio in a crop per year of spring maize treatment was 3: 6:1, and the ratio in others treatments was about 3:5:2. The maximum amount of nitrogen absorption of winter wheat-summer maize-spring maize was 151.82 kg/hm2, which was significantly higher than the other two planting systems. Soil nitrogen residue in double cropping a year of winter wheat-summer maize with traditional water and nitrogen treatment was 348.44 kg/hm2. It was the highest level in all of the systems. The 15N abundance of double-crop rotation system appeared the maximum peak at 0-60 cm, the nitrate nitrogen content was 71.96 mg/kg, and the 15N abundance of other cropping systems was small from top to bottom; the apparent surplus of soil nitrogen pool of double cropping a year of winter wheat-summer maize with traditional water and nitrogen treatment was 252.61 kg/hm2, and the apparent surplus of soil nitrogen pool of wheat-summer maize-spring maize rotation system was the lowest, only 21.22 kg /hm2. The yield of spring maize as a succeeding crop was 4 855.74-6 962.42kg/hm2 higher than that in summer maize after a rotation period. Therefore, the comprehensive analysis showed the three cropping systems in two years of winter wheat-summer maize and spring maize had the potential of sustainability in the stable yield and high yield, and the improvement of nitrogen utilization rate, which would be an ideal planting system for the north China plain in the future.