Sources of boron for foliar fertilization of cotton and soybean

Recent introduction of new boron (B) fertilizer materials prompted an examination of the efficacy of B uptake by cotton (Gossypium hirsutum L.) and soybean (Glycine max L.) from foliar‐applied B originating from various sources. Conducted as a greenhouse study at four participating universities, cotton (Deltapineland 90) and soybean (Pioneer 9761) were sprayed at a rate equivalent to 0.22 kgha‐1 B when plants were 6 weeks old. Sources of B were: 1) boric acid (17.5% B), 2) sodium borate (Solubor® 20.5% B), 3) Solubor® at the pH of boric acid, 4) Traco Liquid B (10% B), and, 5) Smith and Ardussi Liquid B (10% B). Control plants that did not receive B were sprayed with water. Four plants were grown in each pot in sandy loam soils with a pH greater than 6.0. Plants were harvested during the eighth week. To determine if the solvents used to prepare the foliar liquids affected B absorption, two of the harvested plants per pot were washed with distilled water and two plants were left unwashed. All plants were oven dried and analyzed for B. All B sources produced significantly more tissue boron than the water‐sprayed check. Within a state, there were variations in tissue B responses to the sources of B in cotton and soybean. Combined data for all states showed no differences in tissue B due to source of B in cotton or soybean. In cotton, the average tissue concentration increase from the foliar B applications ranged from 8 to 11 mg‐kg‐1. In soybean, the average increase ranged from 16 to 22 mg‐kg‐1 B. Washing created a significant decrease in tissue B in cotton, but not soybean.