| Michigan soybean (Glycine max) producers have observed antagonism of glyphosate efficacy in tank-mixtures with foliar manganese (Mn) fertilizers. The effects of four Mn fertilizer formulations on glyphosate efficacy, absorption, and translocation were evaluated. The fertilizers, Mn-lignin sulfonate (Mn-LS) and manganese sulfate (MnSO4), antagonized glyphosate efficacy by reducing glyphosate absorption and translocation. Mn-ethylaminoacetate (Mn-EAA) antagonized glyphosate efficacy by reducing translocation. Mn-EDTA did not antagonize glyphosate efficacy nor affect absorption and translocation. Adding ammonium sulfate (AMS) increased the efficacy, absorption, and translocation of glyphosate for each Mn fertilizer tank-mixture, but did not consistently overcome the antagonism. Citric acid and EDTA also increased glyphosate efficacy, but were no more effective than AMS. Mn-EAA, applied less than 3 d before glyphosate, reduced glyphosate efficacy on velvetleaf (Abutilon theophrasti ) but not giant foxtail (Setaria faberi) or common lambsquarters (Chenopodium album). Glyphosate efficacy declined as the amount of Mn in the tank-mixture was increased from Mn-EAA, Mn-LS, and MnSO4. Electron Paramagnetic Resonance (EPR) spectra showed that glyphosate coordinates with Mn2+ in aqueous solution. Producers should be cautious when tank-mixing glyphosate and Mn fertilizers, especially when environmental conditions favor poor weed control. A fully chelated Mn-EDTA formulation (1:1 molar ratio) is the least likely to reduce glyphosate efficacy. AMS at 2% (w/w) is needed for maximum glyphosate efficacy. Soybean producers with center-pivot irrigation systems in the Great Lakes region have reported inconsistent yield response to irrigation. Five irrigation schedules, based on soybean growth stage and the soil moisture, were evaluated for their effect on soybean grain yield. Deficit and full season treatments were irrigated to maintain volumetric soil moisture (VSM) at 25% and 50% of capacity, respectively, for the entire growing season. The growth stage treatments of flowering (R1-R2), pod development (R3-R4), and seed fill (R5-R6), were irrigated to maintain VSM at 25% of capacity before reaching the designated growth stage, and at 50% of capacity thereafter. Soil moisture was measured weekly to a depth of 0.9 m using a TDR technology. Yields of soybean in the full season, flowering, and pod development treatments were statistically equal each year. (Abstract shortened by UMI.)... |
