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.
DownLoad: