Architectural Characteristics and Heliotropism May Improve Spray Droplet Deposition in the Middle and Low Canopy Layers in Soybean

Abstract

Leaf angle and plant architecture may determine the penetration of phytosanitary products in the low layer of soybean [Glycine max (L.) Merr.] plants, make the diseases control difficult, and promote losses in crop productivity. Strategies should be studied to increase the efficiency of deposition of phytosanitary products inside the canopy. The hypothesis of this work was that reversible leaf movements and plant architecture may change the penetration of spray droplets into the low layer of soybean plants. We evaluated whether plant architectural characteristics affect spray droplet deposition and monitored if heliotropic movements can increase the efficiency of applications of plant protection products. Four soybean cultivars were investigated. Plant architectural characteristics were evaluated in the V6, V9, R2, and R4 phenological stages, interception of photosynthetically active radiation was evaluated in the V9, R2, and R4 stages, and heliotropic movements were evaluated in the V6 and R4 stages. Sprayings were performed at 0800, 1100, 1400, and 1700 h in the R4 stage. Occurrence of diaheliotropic movements was greater in the V6 than in the R4 stage. The number of branches per plant in the R4 stage was 8, 14, 6, and 14, the branch size was 10.6, 25.8, 12.5, and 21.4 cm, and the leaf area index was 4.2, 4.7, 3.7, and 4.7 for cultivars ‘BMX Ativa RR’, ‘NA 5909 RG’, ‘95R51’, and ‘BMX Potência RR’, respectively. Those architectural characteristics played the most important role in droplet penetration into the low canopy layer. Droplet deposition in the low canopy layer was greater at daylight hours close to noon, showing that the paraheliotropism occurring in those daily hours is more helpful to droplet penetration deeper into the canopy than in other hours.