我国典型农田长期施肥的氮肥真实利用率及其演变特征

【目的】传统氮肥利用率是指当季作物吸收肥料氮占施用的肥料氮的比例,没有反映肥料氮在土壤中的残留及其利用情况。利用长期定位试验能反映土壤氮库变化的优势,分析不同施肥条件下作物的传统氮肥利用率(氮肥表观利用率)和真实利用率,揭示我国典型区域氮肥的真实利用和损失状况。【方法】本研究选用了两种旱地土壤(北京褐潮土和郑州轻壤质潮土)和两种水旱轮作土壤(重庆紫色土和武汉黄棕壤)上的长期定位试验(15~31年)在4种施肥处理,即不施肥(CK)、单施化肥氮(N)、化肥氮磷钾配施(NPK)和化肥氮磷钾与有机肥配施(NPKM)处理取样分析比较作物吸氮量、土壤全氮演变、年均氮肥表观利用率与真实利用率,并计算了不同施肥条件下的氮肥表观损失率与真实损失率。【结果】3个施肥处理,褐潮土、轻壤质潮土、紫色土和黄棕壤上的平均氮肥真实利用率为47.6%、56.6%、57.0%和56.3%,显著高于氮肥表观利用率(33.6%、42.1%、37.8%和25.8%)。这是因为NPK和NPKM处理的肥料氮在土壤氮库中的每年速率积累为N 6.26~37.3 mg/kg的。氮肥真实利用率在褐潮土和轻壤质潮土上比表观利用率高10.9%~17.5%在紫色土和黄棕壤上高18.6%~32.9%,说明传统氮肥利用率更为低估水田轮作下作物的真实利用率。NPK和NPKM处理,褐潮土和轻壤质潮土的氮肥表观利用率以每年1.76~2.49个百分点的速率显著上升,氮肥真实利用率以每年1.50~2.29个百分点的速率显著上升,说明华北旱地上化肥均衡施用和化肥与有机肥配施可增加氮肥的利用率,减少氮肥的损失。黄棕壤上的氮肥真实利用率在显著增加而表观利用率没有显著增加,是由于NPK和NPKM处理的黄棕壤全氮含量以每年N17.5~37.3 mg/kg的速率在显著增加说明化肥均衡施用和化肥与有机肥配施可增加黄壤的氮库库容。【结论】目前我国农田氮肥利用率普遍被低估约20%尤其是在土壤全氮含量变化较大的水旱轮作农田。

Real nitrogen use efficiency of crop as affected by long-term fertilization in typical soils of China

【Objectives】 Nitrogen use efficiency (NUE) or apparent NUE (ANUE) is the percentage of applied N uptaken by one season crop, which does not consider the N residue in soil. Long-term ferlilization experiment is able to reflect the variation of soil N storage. In this article, we analyzed the ANUE and real NUE (RNUE) in different fertilization trentments using long-term experiments to calculate real contribution and real loss of N fertilizer in agricultural production. 【Methods】 Four long-term experiments (31 years) were chosen in this study, aqni-cinnamon soil in Beijing and fluvo-aquic soil in Kaifeng with cropping system of wheat-corn rotation, and purplish soil in Sichuan and yellow-brown soil in Hubei with cropping system of rice-wheat rotation. Crop and soil samples were collected from the treatments of no fertilizer(CK), chemical N(N), chemical N, P and K fertilizers(NPK), and NPK comlined with manure(NPKM). The aurnual N uptake by crop, soil total N content were analyzed, and the ANUE and RNUE were calculated. 【Results】 The average RNUEs are 47.6%, 56.6%, 57.0% and 56.3% in aqui-cinnamon soil, fluvo-aquic soil, purplish soil and yellow-brown soil under the three fertilization, respectively, which are significantly higher than ANUE (33.6%, 42.1%, 37.8% and 25.8%). RNUEs in purplish soil and yellow-brown soil are 18.6%-32.9% higher, and in aqui-cinnamon soil and fluvo-aquic soil 10.9%-17.5% higher than ANUEs, indicating that the traditional NUE is underestimated at a higher extent in upland-paddy soil than in upland soil. The ANUE and RNUE are increased annually at rates of 1.76%-2.49% and 1.50%-2.29%, respectively, in upland soils, under the NPK applied treatments (NPK and NPKM), attributed to the N 17.5-37.3 mg/(kga) increase of soil total N content, significant increases are observed at RNUE but not at ANUE during the fertilization period in yellow-brown soil, indicating that of the NPK and NPKM treatments could improve the N accumulation in soil with a higher extent in upland-paddy soils than in upland soils.【Conclusions】 NUE is generally underestimated about 20% in China, especially in the paddy-upland rotation with a high change of soil total N.