Elevada densidade de semeadura aumenta a produtividade da soja? Respostas da radiação fotossinteticamente ativa

Abstract

Recent studies have addressed the use of the high sowing density of soybean. However, the field results of this practice are still unclear. Thus, research on this area is important in order to explain the direct effects of this management practice, for example, interference in the use of photosynthetically active radiation (PAR). Therefore, this study aimed to evaluate the dynamics of PAR in different seeding densities in soybean. A field experiment was conducted in randomized blocks with treatments distributed in a 3 × 5 factorial arrangement: three varieties of RR® soybeans (P98Y12, TMG 132 and M-Soy 9056) and five seeding densities (20, 30, 40, 50 and 60 plants·m–2) with four replications. The dry matter, photosynthetically active radiation in the lower canopy (PAR-L) and in the higher one (PAR-H), interception of PAR, crop growth rate (CGR), relative growth rate (RGR), net assimilation rate (NAR), radiation use efficiency (RUE), light extinction coefficient (k), grain harvest index (GHI), 1,000 grains weight and productivity were evaluated. Regardless of the variety, the densities of 20 and 30 plants·m–2 provided the highest values of NAR, RGR, k, GHI and productivity. The use of RUE, CGR and intercepted PAR does not provide accurate information to predict the efficiency of soybean density cultivation. Cultivation densities traditionally used overlap the others regarding the quality of PAR in the canopy and soybean productivity.