Effect of Reduced N Application on Crop Yield in Maize-Soybean Intercropping System

Maize-soybean strip relay intercropping pattern is widely adopted in Southeast China. Whereas the traditional fertilized measures used by farmers are not good for high yield of soybean. In order to get high yield for both maize and soybean in this system, a field experiment was conducted to investigate the effect of reduced N application on photosynthetic characteristics and dry matter accumulation of soybean, and the system crop yield. The experiment included three planting patterns(maize monocropping, soybean monocropping and maize-soybean relay strip intercropping) and three rates of N fertilizer application(0, 180, 240 kg ha–1). The results demonstrated that, the net photosynthetic rate(Pn), transpiration rate(Gs), stomatal conductance(Ci), photosynthetic capacity(Tr), dry matter accumulation of soybean increased initially and then decreased in the later stage. Compared with soybean monocropping, the Pn, Gs, and Tr of intercropped soybean decreased significantly in the intergrowth stage(V5), but had no significant differences at R2, R4, and R6 stages. Although the below-ground, above-ground and total dry matter accumulation of soybean significantly decreased during the whole growth period, the crop growth rate from R4 to R6 stages and economic coefficient significantly increased. In the maize-soybean relay strip intercropping system, N application significantly enhanced the Pn, Gs, Tr, dry matter accumulation, pod number per plant, and grain yield of soybean. Compared with the conventional N application(240 N kg ha–1), Pn of soybean under the reduced amount of N application(180 kg N ha–1) increased by 3.57% and 11.82% at R4 and R6 stages, respectively. Furthermore, the total dry matter accumulation increased by 5.06% and 10.21% at R6 and R8 stages, and pod number per plant and grain yield increased by 8.30% and 10.15%, respectively. Finally, the maize-soybean relay strip intercropping system possessed the highest yield under the N application rate of 180 kg N ha–1, with the economic coefficient and land equivalent ratio(LER) of 0.49 and 2.17, respectively. Taken together, the reduced N application in maize-soybean relay strip intercropping system can increase the yield of soybean and whole the system through improving soybean photosynthetic characteristics and enhancing dry matter accumulation.