Supplemental bee pollination effect on the productivity of soybean grown in a low yield potential condition

Abstract

Brazil is the leading soybean producing country in the world, and soybean is the major crop of Brazilian agriculture, spread over 36 million hectares during the 2020/21 season, producing almost 125 million tons. The honey bee, Apis mellifera Linnaeus, 1758 (Hymenoptera: Apidae), and other bees are known as soybean flowers visitors, being potential pollinators of the crop, normally resulting in higher soybean yields. Over the last ten years, it has been observed an increasing interest of both beekeepers and soybean growers, to place honey bee colonies close to soybean fields, using the crop as a forage source. In the majority of the reports of soybeans growers, an increase of the soybean yield was observed when following this practice, while a small number claimed no yield modification. The purpose of the present work was to study the effect of visits of individuals of A. mellifera to soybean flowers and the consequent pollination on soybean productivity, when there is a constraint to the expression of the potential crop yield. The experiments were set up in Londrina, Brazil, during the 2016/17 and 2019/20 crop seasons, in areas with known sub superficial compaction layers, preventing soybean roots from deepening in the soil, therefore restricting the absorption of water and nutrients by the plants. Treatments consisted of 1) open plots, resembling a typical grower field with free access of bees; 2) a caged plot with an A. mellifera beehive inside, and 3) a caged plot with no bees or any other potential pollinating insect inside. Results indicated no yield differences due to the pollination of soybean flowers by the bees, compared to the treatment with the absence of bee visit. Among the yield components, only pods with 1 or 2 seeds were lower on caged plots with bees on the 1st experiment. No differences were detected for all others observed parameters on 1st and for all components on 2nd experiments. Observations of the honey bee behavior demonstrated that only 27.9% of the bee visits to soybean flowers resulted in nectar hoarding, with a time lapse of 4.52 seconds for a visit to a single flower. When a flower was only tested (72.1%), without nectar collection, the average time of a honey bee visit was 1.38 seconds. New studies should be performed to verify if other biotic or abiotic stresses that depress soybean yield also prevent the expression of the benefit of bees’ pollination to soybean yield.