Greenhouse Evaluation of Four Boron Fertilizer Materials

Management of boron (B) in soils can be difficult since a narrow range exists between plant deficiency and toxicity. A greenhouse study was conducted to evaluate the effectiveness of four soil-applied B fertilizers varying in solubility (Granubor, Hydroboracite, Ulexite, and Colemanite) in supplying B to alfalfa (Medicago sativa L.). Boron was incorporated at rates of 0, 1, or 2 mg B kg−1 into Norfolk (fine-loamy, kaolinitic, thermic, Typic Kandiudults) or a Cecil (fine, kaolinitic, thermic Typic Kanhapludults) soil and planted with alfalfa. After establishment, shoots were harvested four times at approximately five-week intervals and analyzed for dry matter and B. Following the last harvest, soil samples were taken and analyzed for Mehlich-1 extractable B. There was no effect of fertilizer material, application rate, or their interaction on the dry weight of alfalfa. Boron concentrations in alfalfa did not significantly decline with each successive cutting, indicating that a sufficient amount was applied for the duration of the study. In the first cutting, plants grown with Granubor and Ulexite had higher concentrations of B than those with Hydroboracite, which was in turn higher than Colemanite, reflecting differences in solubility. However, by the third and fourth cuttings, there were no significant differences in tissue B concentrations among the four fertilizer sources. This indicates that given adequate time, even less-soluble fertilizer sources may provide sufficient B to growing plants.