The Effects of Simulated Acid Rain on the Growth and Yield of Soybean

Abstract

This report described changes in the growth processes and yield of soybean plants exposed to simulated acid rain at pH 5.6, 4.0, 3.0 and 2.0 containing sulfate, nitrate and chloride by using analysis of growth parameters and seed yield components.
The analysis of growth parameters showed that LAR (leaf area ratio) and SLA (specific leaf area) for soybean plants at pH 2.0 from 1 week after the initiation of exposure were significantly smaller than those at pH 5.6. The application of simulated acid rain at pH 2.0 decreased RGR (relative growth rate) as compared with that at pH 5.6. Since RGR is expressed in the form of NAR (net assimiration rate)×LAR, lower RGR at pH 2.0 is associated with reduction of LAR due to small leaf area.
The yield component analysis indicated that the significant reduction of seed dry weight per plant at pH 2.0 were attributed to significant decrease in number of seeds per pod. Such a reduction in seed number at pH 2.0 resulted from increasing number of empty seeds.
pH of cultivated soil especially at the upper soil layer (0-5cm from surface) exposed to simulated acid rain for 9 weeks was decreased with increasing acidity of simulated acid rain. At the lower layer (25-30cm), however, there was no significant difference in soil pH among any treatments.
These results suggested that the exposure of simulated acid rain at pH 2.0 caused the reduction of dry weight growth and seed yield of soybean plant due to acute damage of leaf area growth. However, at a pH above 3.0 there was no significant effect on the growth processes and yield components of soybean plant. Based on our results current pH level of ambient rain in japan should not have an adverse impact on the growth and seed yield of soybean.