Soil Mn Availability to Soybeans as Affected by Mono and Diammonium Phosphate1

Abstract

AbstractWith increasing efforts toward greater soybean (Glycine max (L.) Merr.) production, Mn deficiency undoubtedly will appear more frequently. To determine if Mn deficiency can be alleviated by locally placed common fertilizer materials, monoammonium phosphate (MAP) and diammonium phosphate (DAP) were added to a Mndeficient Sebewa loam (Typic Argiaquoll) in both greenhouse and field studies. Soil and plant analyses and soybean yields were used to evaluate the treatments.In the greenhouse, soil pH was depressed slightly and exchangeable Mn increased by the ammonium phosphate treatments. The Mn deficiency was alleviated partially by localized applications of 10 or 20 ppm P as DAP or 20 ppm P as as MAP. These treatments produced plants that were significantly larger and showed less severe Mn deficiency symptoms than plants in control pots without P added.Deficiency of Mn in the field was alleviated by P applications of 17 and 34 kg/ha either as MAP or DAP. Plant weights, leaf Mn concentrations and soybean yields from the P‐treated plots were significantly higher than those from control plots. Plant weights and bean yields from P treatments were not different from the bandapplied Mn treatment (22 kg Mn/ha). However, leaf Mn concentrations resulting from the application of 34 kg P/ha as MAP or from 17 or 34 kg P as DAP were significantly higher than from the Mn treatment.