Effects of acidity at high soil zinc, copper, and manganese on peanut, rice, and soybean

Abstract

Plant availability of zinc (Zn), copper (Cu), and manganese (Mn) are affected not only by the extractable concentration, but also by soil pH. However, the effect of acidity on uptake at high soil test levels of these nutrient elements is not clear. Three greenhouse experiments were conducted to evaluate the influence of pH on soil and plant tissue concentrations of Zn, Cu, and Mn and on the growth of peanut (Arachis hypogaea L.), rice (Oryza sativa L.), and soybean [Glycine max (L.) Merr.]. Two Inceptisols and five Ultisols that had received large amounts of Zn and/or Cu were used. Treatments included three replications of five pH levels from 5.0 to 7.0. Mehlich‐3 extractable soil Zn and Cu were affected little between pH 5.0 and 7.0. Likewise, soil Mn was affected little between pH 6.0 and 7.0, but there was an acidity by soil interaction between pH 5.0 and 6.0. Plant Zn increased with increasing soil Zn and decreased with increasing soil pH. Zinc in peanut and soybean also appeared to decrease with higher levels of soil Cu. Plant Mn also decreased with increasing soil pH. Plant Cu was not affected consistently by soil pH. Toxicity was expressed by a decrease in dry weight with increasing soil Zn. Peanut dry weight decreased at soil Zn levels between 60 and 300 mg dm‐3, but it was not clear from these data if this limit would be altered by a change in soil pH. A similar effect was shown for soybean. Soybean dry weight decreased with decreasing pH, but the opposite effect was noted for rice, apparently because of a pH effect on iron (Fe) utilization.