RESPONSE OF SOYBEAN TO FOLIAR-APPLIED MAGNESIUM AND SOIL-APPLIED BORON

Annual plants may partition carbon (C) preferentially to reproductive structures slowing root elongation and subsequent nun-lent uptake. Alt hough foliar applications of nitrogen (N), phosphorus (P), potassium ( K), and sulfur (S) supplement uptake by roots, soybean [Glycine max (L .) Merr.] yield increases have not been found in most studies. Experim ents were designed to determine if foliar applications of boron (B), m agnesium (Mg), or B+Mg would increase soybean yield and if soybean wou ld respond to B applied to the soil several weeks prior to planting. F oliar B or Mg applied separately four times during reproductive growth did not affect soybean yield. However, four foliar applications of BMg increased soybean yield 12% at hit. Vernon and 4% at Columbia over a three-year period. Two foliar applications of B+Mg during the late r eproductive stages increased soybean yield 8% over a two-year period. The yield increase from foliar B+Mg treatment resulted from an increas ed number of pods on the main stem (18%) and branches (44%). A 2.8 kg/ ha B application to soil eight weeks prior to planting increased soybe an yield 11% during the first year and 13% the second year but had no effect on soybean yield by the third year after application. When resu lts from the first two years were combined, 2.8 kg/ha B applied to soi l increased the number of pods per branch by 17% and the number of bra nch pods per plant by 39%. Foliar applications of B+Mg increased soybe an yield in four of six site-years in the three-year experiments at tw o locations.