Effects of Planting Density of Spring Soybean on Canopy Photosynthetically Active Radiation and Yield in Northeast China

Abstract

Soybean is an important legume crop. Planting density of soybean directly affects the distribution of photosynthetically active radiation (PAR) in the canopy, which affects the physiological changes, such as photosynthesis of soybean, and leads to the change of yield. In this experiment, soybean variety Heinong 84 was adopted, and five planting densities were set as 200,000 plants/ha (D20), 250,000 plants/ha (D25), 300,000 plants/ha (D30), 400,000 plants/ha (D40) and 500,000 plants/ha (D50). The canopy PAR intensity was measured based on photosynthetically active radiation recorder, and the effects of different densities on soybean canopy PAR and yield were studied systematically. According to the results, with the extension of growth period, the PAR above and within the canopy of soybean decreased first and then increased, and the rules were consistent under different densities. During each growth period, PAR was above that of canopy > growth point > middle stem > cotyledon scar and decreased with the increase of density. The growth point changed significantly, followed by middle stem, but no significant change happened in cotyledon scar. The absorption photosynthetically active radiation (FPAR) showed a unimodal trend with the increase of density at V4 and R2 and had an upward trend at R4 and R6. The number of effective pods per plant and 100 seed weight of D20 are the highest, and the yield of D25 is the highest.