Effects of simulated acid rain on yield response of two soybean cultivars

An important component of the effects of acid rain on our ecosystem is its impact on the yield of agricultural crops. Field experiments were conducted for 3 yr to determine the effects of simulated acid rain on seed yield of two soybean [Glycine max (L.) Merr.] cultivars, 'Amsoy 71' and 'Williams 82'. Soybeans were grown on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) and protected from ambient rainfall by movable rain exclusion shelters. Plants were treated biweekly with simulated rain of pH 5.6, 4.6, 4.2, 3.8, 3.4, and 3.0. For Amsoy 71 there was a linear decrease in yield with increasing rainfall acidity for 1 of 3 yr but no significant effects for the other two. Thus acid rain appears to reduce the yield of some soybean cultivars slightly but this effect is not consistent from year to year. Amsoy 71 and Williams 82 soybean treated with the most acidic rain, pH 3.0, resulted in average yields for the 3 yr of the study of approximately 3 and 4% lower than the average yields for the other treatments, respectively. However, calculations from the response functions developed have shown that at current levels of rainfall acidities the effects on yield are very small. With an increase in rainfall acidity of 50% in Illinois the predicted yield decrease for Amsoy 71 and Williams 82 soybean would be less than 1%. Similarly the expected increase in yield of these cultivars would be 1% or less if acidity in the rainfall were reduced by 50%. While there may be beneficial effects of reduced S and N oxide emissions, these results suggest the resultant lower rainfall acidities are not likely to produce noticeable changes in yield of soybean.