Nitrogen accumulation, allocation and translocation in wheat/maize/soybean relay intercropping system

【Objectives】The Sichuan Basin is hot but short of sunlight resources, the intercropping systems are popular in this area. Wheat/maize/soybean system is a typical efficient relay intercropping for the recycling use of the natural resources and sustainable development of agriculture. In this paper, the characteristics of nitrogen accumulation, distribution and translocation after anthesis stage of crops in the relay intercropping system were studied, so providing a base for the reasonable fertilization and high yield and high profitable production.【Methods】A field experiment was carried out in 2011 and 2012, and different nitrogen application rates in wheat (0, 60, 120, 180 and 240 kg/ha, marked as WN1,WN2,WN3,WN4 and WN5), maize (0, 97.5, 195, 292.5 and 390 kg/ha, marked as MN1,MN2,MN3,MN4 and MN5) and soybean (non-fertilized, marked as SN1, SN2, SN3, SN4 and SN5 according to the previouse crop N rates) were designed. 【Results】1) The nitrogen accumulation in different parts of wheat are all increased with the increase of nitrogen fertilizer application. Of the averaged 218.6 kg/ha of total N accumulation, 71.5% in grains, 12.2% in stems and sheaths, 9.2% in leaves and 7.1% in spike axes and kernel husks. Since anthesis, more nitrogen transfers from vegetative organs to grains with an average transform of 61.5%, but there is no significant difference among the N rate treatments. With the increase of nitrogen use, the proportions of N in wheat grains are reduced gradually, increased in other parts. The N application improves the yield of wheat, but there is no significant difference among WN3-WN5. 2) The amounts of nitrogen accumulation in different parts of maize are all increased with the increase of nitrogen fertilizer application. Of the average total N accumulation of 108.1 kg/ha, 67.2% is in grains, 3.9% in leaves, 11.8% in stems and sheaths, and 7.0% in husks and cobs. The largest nitrogen translocation from vegetative organs to grains and the most rapidly transfering rate are in treatment MN3, the highest nitrogen accumulation proportion in leaves, stems and sheaths are in treatment MN1. Significantly high proportion of N accumulates in maize grain are showed in the nitrogen treatments than in control, but there are no significant differences among the nitrogen treatments. The N application improves the yield of maize, and there is no significant difference between MN4 and MN5. 3) With the increase of nitrogen application, more N accumulates in the grains, stems and hulls of soybean in the harvest stage, and those of SN4 and SN5 are significantly higher than those of the other three treatments, and there are no significant differences among SN1-SN3 and between SN4 and SN5. The nitrogen accumulation rates in seeds, stems and hulls of soybean are not significantly different among all the treatments, with the averages of 82.2%, 5.2% and 12.6% respectively. The nitrogen transfer rates from vegetative organs to grains after the flowering is significantly reduced first and then increased in SN1-SN5, and the contribution rates and the transfer rates are not significantly different in all treatments, with the averages of 80.8% and 26.6% respectively. The soybean yields of SN4 and SN5 are significantly higher than those of the other three treatments, and there are no significant differences among SN1-SN3 and between SN4 and SN5.【Conclusions】Low nitrogen supply influences yields and nitrogen accumulations of wheat, maize and soybean in relay intercropping system, high nitrogen input hinder the shift of accumulated N from vegetative organs to grains. The suitable N rates for the annual wheat/maize/soybean relay intercropping system is 255-382.5 kg/ha, 120-180 kg/ha for wheat, 195-292.5 kg/ha for maize and no fertilizer for soybean.