小麦-玉米轮作体系农田氮素淋失特征及氮素表观平衡

连续6年采用渗漏计法研究了不同施氮处理下陕西关中小麦-玉米轮作区农田土壤90 cm深度处氮素(N)淋失特征和土壤-作物体系氮素表观平衡状况.结果表明:该地区农田氮素淋溶主要发生在降雨量较多的玉米季,且集中在8月和9月.监测期内,TN和NO-3-N年平均流失量分别为2.72~23.07 kg·hm-2和1.53~18.72 kg·hm-2,年流失率分别为0.65%~3.44%和0.82%~3.32%,且年总氮、硝态氮流失量均随年施氮量增加呈指数增加.氮素淋失形态中,NO-3-N比例较高,可占总氮淋失量的56.00%~81.00%,且随着氮肥用量的降低,其占总氮淋失量的比例也随之减小.可见,施氮量的大小在一定程度上会影响淋失液中各形态氮的比例.氮素表观平衡结果显示,随着施氮量提高,氮素在土壤中的残留和表观氮盈余均呈现指数增加趋势.长期施氮条件下,土壤-作物体系氮素表观损失率的幅度为32.60%~55.20%,土壤表观残留率为-0.17%~8.20%.多年监测结果表明,优化施氮模式下,作物不仅可以获得较高的产量和氮肥利用率,农田氮素淋失量也大幅降低,在节约肥料资源的同时减轻了潜在的环境风险.

Characteristics of N leaching and apparent N budget in cultivated lands under a Winter wheat-summer maize rotation system

A six-year field experiment, using the Lysimeter method, was conducted in Guanzhong Plain of Shaanxi Province to investigate the effects of nitrogen (N) fertilizer application amount on N loss characteristics and N budget in the soil profile at 90 cm depth under winter wheat-summer maize cropping system. Results showed that N leaching mainly occurred in August and September, the rainy period of maize growing season. In the monitoring period, the average annual loss of total N and nitrate (NO₃^--N) were 2.72~23.07 kg · hm^-2 and 1.53~18.72 kg · hm^-2, respectively, and the average annual leaching rate from fertilizer for total N and NO₃^--N were 0.65%~3.44% and 0.82%~3.32%, respectively. N leached from the soil were mostly in the form of NO₃^--N comprising with 56.00%~81.00% of total N, whereas ratio of NO₃^--N decreased with low N fertilizers. Thus, different N fertilizer amounts affected the forms of nitrogen loss from the soil. The nitrogen budget result illustrated that the nitrogen application significantly enhanced N surplus and nitrate accumulation in the 90 cm depth of soil profile. The annual residual NO₃^--N and N surplus had a positive relationship with the annual N fertilizer inputs. Continuous N application resulted in N loss rate of 32.60%~55.20% and annual residual NO₃^--N in the 90 cm depth of soil of-0.17%~8.20%. According to the multi-year monitoring results, OPT treatment showed less nitrogen leaching amounts at high yield and better N use efficiency, reduced potential environmental risks and saved N fertilizer resources.