利用15N示踪研究不同肥力土壤棉花氮肥减施的产量与环境效应

【目的】华北平原棉区中等肥力棉田经济最佳施氮量为300 kg/hm2左右，这一结果仅从产量效应得出，未充分考虑棉花对氮肥的回收利用和土壤中氮肥的残留。探讨低肥力土壤施氮量及施氮比例对棉花产量及氮肥利用率的影响，以及低、中、高肥力土壤条件下等量施氮效应，旨在为棉花减氮增效提供理论依据。【方法】田间试验选择了高 (S1)、中 (S2)、低 (S3) 三个肥力水平的地块，其全氮含量分别为0.83、0.74、0.60 g/kg。低肥力地块设置低氮 (N1 113 kg/hm2)、中氮 (N2 225 kg/hm2)、高氮 (N3 338 kg/hm2) 3个氮肥用量；中肥力和高肥力地块设低氮量处理，氮肥两次追施在苗期与初花期进行，氮肥比例为1∶2；此外，设置低肥力土壤低氮量，氮肥追施在苗期与初花期进行，氮肥分配比例为1∶1。在吐絮70%时采集棉株和土壤样品，用15N技术分析了棉株氮素吸收来源、籽棉产量、棉株氮肥回收率和土壤氮肥残留率。【结果】低氮处理，土壤肥力对棉花籽棉产量无显著影响，随土壤肥力提升，棉株吸收氮素来源于肥料的比例下降，相对增加了对土壤氮素的吸收。棉花植株15N回收率随施氮量增加显著下降，随土壤肥力提高呈下降趋势，低肥力土壤与中肥力土壤间棉花植株15N回收率差异不显著，但显著高于高肥力土壤。高肥力土壤15N残留率高于低肥力土壤和中肥力土壤。15N损失率随施氮量和土壤肥力提高显著增加。低土壤肥力低氮量条件下氮肥分配比例1∶2处理籽棉产量高于1∶1处理。低肥力土壤条件下，中氮处理籽棉15N积累量相对高于高氮和低氮处理，籽棉产量较优。【结论】在较低土壤肥力条件下，施氮225 kg/hm2籽棉产量和氮回收率均优于施氮338 kg/hm2，氮肥损失率较低，减氮增效是可行的。高肥力土壤条件下减少氮肥投入可减少肥料的浪费。

Using 15N tracing technique to study the yield and environmental effect of decreasing N fertilization on cotton in different fertility fields

Objectives]In the medium fertility field of cotton area in the Yellow River catchments, the North China Plain, the economic optimum nitrogen (N) rate for cotton is 300 kg/hm2, and the result was derived from cotton yield response to N fertilizer rate in field trials for many years, but the N application rate did not fully consider residual N in the soil of cotton field. This paper was to explore effects of different N application rates and ratios on seed cotton yield and N use efficiency under low fertility soil, and effects of the same N application rate under low, medium and high fertility soils in field conditions aimed to provide a theoretical basis for N fertilization management of cotton.Methods]Field trials of nitrogen fertilizer management were carried out using 15N tracer technique and cotton was used as tested material. Fields with soil total N content of 0.83, 0.74 and 0.60 g/kg were taken as high (S1), media (S2) and low (S3) fertility fields for the experiment. Three N application rates were set up for the low fertility field: 113 kg/hm2(N1), 225 kg/hm2(N2) and 338 kg/hm2(N3). The N fertilizer was divided into equal two parts and topdressed at the seedling and flowering stages. A treatment of twice N topdressing in ratio of 1:2 was also setup in the low fertility field with low N rate. Cotton and soil (0-60 cm) were sampled at 70% boll opening stage, the contribution of N absorbed from fertilizer and soil were determined using 15N tracer technique. The seed cotton yield, and 15N recovery rate of cotton plants were investigated.Results]For the low N rate, the soil fertility had no significant effect on seed cotton yields, the plant N uptake proportion deprived from fertilizer was declined with the increase of soil fertility, while the N uptake proportion deprived from soil nitrogen was increased. The 15N recovery rate of cotton plants was decreased significantly with the increase of N application rate, and declined with increase of the soil fertility. There were no significant differences between the low soil fertility and medium soil fertility for 15N recovery rate of cotton plant, but the recovery rate under the low soil fertility was significantly higher than that of the high fertility soil. The 15N residual rate of high fertility soil was higher than those of the low fertility soil and the medium fertility soil. The 15N loss rate was increased significantly with the increase of N application rate and soil fertility. Seed cotton yield for the low N rate at the ratio of 1:2 was higher than that at the ratio of 1:1. Under the condition of low fertility soil, seed cotton yield for N 225 kg/hm2 was relatively higher than those for N 113 kg/hm2 and N 338 kg/hm2 because of more 15N uptake by cotton plants.Conclusions]Under the condition of lower soil fertility, the seed cotton yield and 15N recovery rate for the moderate N rate (225 kg/hm2) were higher than those for high N rate (338 kg/hm2), and the N fertilizer loss rate was less, which demonstrated that it was feasible for improvement of both N use efficiency and seed cotton yield by decreasing input of N fertilizer. Low N input under the condition of high fertility soil could decrease N fertilizer loss.