化肥氮对冬小麦氮素吸收的贡献和土壤氮库的补偿

  【目的】  小麦对氮素的吸收消耗了土壤氮库，土壤中残留的化肥氮则可补偿土壤氮库的消耗，综合考虑这两方面的影响，核算施氮量和秸秆还田对小麦当季土壤氮库盈亏的影响。  【方法】  收集1980年以来国内报道的小麦15N示踪试验的研究结果，分析化肥氮和土壤氮对小麦当季氮吸收的贡献，小麦当季氮吸收、化肥氮的去向、土壤氮库的盈亏分别与施氮量之间的关系，以及秸秆还田对小麦当季土壤氮库盈亏的影响。  【结果】  施氮量与化肥氮对小麦当季氮吸收的贡献之间呈显著正相关 (P = 0.029)，而与土壤氮的贡献之间呈显著负相关 (P = 0.031)。小麦当季氮素吸收源于土壤的比例约为2/3，源于化肥的比例约为1/3，追施氮对小麦氮吸收的贡献约是基施氮的1.5倍。施氮量与氮肥有效率 (氮肥利用率+氮肥残留率) 之间呈极显著负相关 (P = 0.004)，而与氮肥损失率之间呈极显著正相关 (P < 0.001)。在秸秆不还田和还田条件下，小麦季土壤氮库的盈亏均与施氮量之间呈极显著正相关 (P ≤ 0.001)。  【结论】  在施氮量为N 60～500 kg/hm2时，小麦吸收的氮素1/3来自化肥，2/3来自土壤。冬小麦季化肥氮的3个去向为:地上部吸收、土壤残留和损失，其所占比例分别约为36%、33%和31%。在秸秆不还田和还田条件下，土壤氮库达到平衡的施氮量分别为N 308和233 kg/hm2。

Contributions of fertilizer N to winter wheat N uptake and compensation of soil N pool in farmland

  【Objectives】  This study investigated the effects of chemical fertilizer N and straw returning on the soil N balance in the wheat season, by considering the replenishing effect of residual fertilizer N and straw returning to soil N pool consumption by wheat.  【Methods】  This study collected the publications on 15N tracer experiments of winter wheat in China since 1980, and analyzed the contribution of chemical fertilizer N and soil N to N uptake by wheat, the relationship between N application rate and N uptake by wheat, the fate of fertilizer N and soil N pool budget, and also investigated the effect of straw returning on soil N pool budget in the wheat season through literature review.  【Results】  The N fertilizer application rate was significantly and positively related to the proportion of N uptake from fertilizer N in wheat (P = 0.029), but significantly and negatively related to the proportion of N from soil N (P = 0.031). The ratio of wheat N uptake derived from fertilizer N and soil N was about 1∶2, and the contribution of topdressing N to wheat N was 1.5 times of that of basal N. The N application rate showed significantly negative linear correlations with fertilizer N efficiency (N recovery + N residual rate, P = 0.004), and significantly positive linear correlations with N loss rate (P < 0.001). Without returning straw or with returning straw to field, there were the significantly positive correlation between soil N pool budget and N fertilizer application rate over the wheat season (P ≤ 0.001).  【Conclusions】  Within the range of N 60–500 kg/hm2, the applied fertilizer N in wheat season has three main fates, wheat uptake, soil residue and loss, with ratios in average of 36%, 33% and 31%, respectively. The contribution from chemical fertilizer in the nitrogen uptake of wheat is about 1/3, and that from soil is 2/3. The soil N pool could reach balance when N application rate is 308 kg/hm2 without straw incorporation and 233 kg/hm2 with straw incorporation, respectively.