Comparison of materials of different solubility as sources of boron for plants

Abstract

Two borate minerals, colemanite and datolite, of medium and low solubility respectively, and powdered borosilicate glass were compared with highly soluble borates as sources of boron (B) for plants on a soil known to be low in available B. Despite the differences in solubility, all the materials, except glass, were equally effective as sources of B, when applied at rates based on total B content, and they prevented B deficiency in lucerne (Medicago sativa L.), red clover (Trifolium pratense L.), and sunflower (Helianthus annuus L.) in pot trials over 8 months. Colemanite applied at a high rate (based on water solubility) was extremely toxic to red clover and sunflower in the early stages. Lucerne was also affected by this treatment initially but quickly recovered and yield was not affected. Red clover and sunflower also recovered as the trial progressed. On the other hand, datolite when applied at a high rate was not toxic initially but caused some toxic symptoms on sunflower and lucerne at the final harvest. Plants showed toxicity symptoms when their B concentration was above 150 ppm B but yields were not reduced until B concentration exceeded 250 ppm B. It is concluded that B availability in colemanite is similar to that in the highly soluble borates. With datolite, B availability is lower initially, but it is still adequate to prevent B deficiency and it remains effective longer so this material may be a more effective B source in the long term. Trials are required to confirm this under field conditions and to determine the optimum application rate.

Keywords:

• boron
• borate minerals
• boron toxicity
• lucerne
• Medicago sativa L.
• red clover
• Trifolium pratense L.
• sunflower
• Helianthus annuus L.