The effects of simulated acid rain with and without ambient rain on the growth and yield of field-grown soybeans

Abstract

Soybean [ Glycine max (L.) Merr, ‘Forrest’] was grown in the field to determine (1) whether sulfate (SO 4 2−), nitrate (NO 3 −), and hydrogen ion (H +) concentrations in simulated rainfall cause foliar injury, affect growth and yield, influence foliar elemental content or modify soil chemistry, and (2) whether exclusion of ambient rainfall affects these responses. Plants were exposed twice weekly from 14 June to 8 October 1983 to 1 cm of simulated rain at pH levels of 5.2, 4.2, 3.7, 3.2 and 2.7. One-half of the plots was shielded from ambient rain (covered) but received additional simulated acidic rain to match the amounts of ambient rainfall on plots not shielded from ambient rain (uncovered). There were four 2.5 m 2 plots randomly assigned to each pH level in both the covered and uncovered conditions. Simulated rain treatments at pH 2.7 significantly increased foliar S concentrations and caused slight (< 10%) foliar injury. Both effects were significantly greater in covered plots than in uncovered plots. Simulated rain above pH 3.2 caused no visible symptoms or measurable changes in leaf elemental concentrations. Simulated rain chemistry had no influence on soybean growth or yield components, and there were no obvious trends in either the covered or uncovered plots. Therefore, ambient acid rain probably does not affect the growth or yield of soybean cultivar ‘Forrest.’ Simulated rain at pH 2.7 significantly increased soil H + and soil SO 4S concentrations by the end of the treatment period; these changes were similar in the covered and uncovered plots. A conclusive test of the influence of ambient rain on plant response to simulated rain chemistry will require the use of species or cultivars that exhibit significant growth or yield responses to changes in H +, SO 4 2− or NO 3 − levels.