Content of boron and other elements in main stem and branch leaves and seed of soybean

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Abstract
Tissue testing is commonly used to determine nutrient status of crops, however, there may be differences in macro‐ and micronutrient content of main stem and branch leaves of plants. Macro‐ and micronutrient analyses of main stem and branch soybean (Glycine max [L] Merr.) leaves were performed separately to ascertain where foliar‐applied boron (B) was accumulating and to determine if other nutrients were partitioned differently between main stem and branch leaves in control plants and plants treated with foliar B. Foliar applications of 2.24 kg B/ha increased main stem leaf B content from 47 to 248 μg/g and caused leaf manganese (Mn) and aluminum (Al) content to decline. In a separate experiment, foliar applications of 1.12 kg B/ha onto soybean growing on a soil high in available Al increased B leaf content by over 50 μg/g and decreased leaf Al content by 100 μg/g. In other field experiments, foliar B applications of 0.90 kg/ha or more increased leaf B content in both main stem and branch leaves. Boron content was consistently higher in branch leaves than in main stem leaves. Branch leaves and seeds of soybean were higher in the phloem‐mobile elements potassium (K), magnesium (Mg), phosphorus (P), zinc (Zn), iron (Fe), and copper (Cu) than main stem leaves. With the exception of B, the relatively phloem‐immobile elements, calcium (Ca) and Mn were lower in branch leaves than in main stem leaves. The higher B content in branch leaves and seeds may indicate that B is more mobile in soybean than previously thought. The difference in macro‐ and micronutrient content of branch and main stem leaves and seeds should be noted when soybean leaves are being harvested for determination of macro‐ and micronutrient sufficiency, or when seeds are harvested for nutrient quality determinations.