Effects of boron sources and rates on grain yield, yield components, nutritional status, and changes in the soil chemical attributes of soybean

Boron (B) deficiency has been demonstrated as a frequent problem in soybean crops, as soybean exhibits a large sensitivity to this nutrient, regardless of its uptake efficiency in the soil. The objective of this study was to evaluate the effects of B sources and rates on the yield, yield components, nutritional status, and changes in the chemical attributes of soil cultivated with soybean. The experimental design was completely randomized in a 2 x 5 factorial design with four replicates. The treatments consisted of two sources (H3BO3 and ulexite) and five B rates (0, 2, 4, 8, and 16 mg kg(-1)). The grain yield (GY), yield components, nutritional status, and soil chemical attributes were evaluated. B sources-rates interactions (S x R) were significant for most variables evaluated. The B (H3BO3) application resulted in higher B levels in the leaves and the soil cultivated with soybean than those obtained with ulexite. GY was highest with a B application of 4 mg kg(-1), exhibiting a toxic effect in H3BO3 at 8 and 16 mg kg(-1). The application of B increased N, S, Fe, and B concentrations while decreasing P and K in the leaves. The shoot dry weight yield, number of pods, grains per pot, and 100-grains weight were also influenced by the B rates. The highest GY ranged from 0.3- to 0.8 mg kg(-1) in the soil and 50- to 100 mg kg(-1) in the soybean diagnostic leaf.