Boron Nutrition of Sugar Beet, Cotton, and Soybean¹

The levels of boron in nutrient solutions suitable for plant growth are highest for sugar beet, ( Beta vulgaris ) lowest for soybean ( Glycine max ), and intermediate for cotton ( Gossipium hirsutum ). In spite of pronounced differences in B tolerance (and also of B requirement), tissue levels at which toxicity symptoms appear are similar in the three species. The species differences are therefore due more to B uptake and growth characteristics than to tissue sensitivity. Chlorotic tissues contain around 1,000 ppm B, necrotic tissues above 1,000 ppm. Beet yields and beet sugar contents in greenhouse experiments were not affected by B concentrations up to 40 ppm. Thus the sugar beet might be a suitable plant for high B soils, provided the result is not modified in the field by different climatic conditions. Boron distribution, patterns of B toxicity, leaf venation, correlation between B injury and leaf age all support the hypothesis that within the leaf, B moves largely in the transpiration stream and is accumulated to toxic levels as water is lost to the atmosphere.