SEED YIELDS (QUANTITY AND QUALITY) OF FIELD‐GROWN SOYBEANS EXPOSED TO SIMULATED ACIDIC RAIN

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Abstract
Summary: Experiments were performed to determine changes in mass, protein content and carbohydrate content of seeds of soybean plants exposed to simulated acidic rain grown under standard agronomic practices and receiving ambient rainfall at Brookhaven National Laboratory during the summer of 1979. Plots were exposed three times per week to simulated rainfalls of pH 4·0, 3·1, 2·7 or 2·3 to provide inputs of 50, 397, 998 or 2506 μequiv. of hydrogen ions respectively, above ambient levels throughout the growing season. Control plots received no simulated rainfall treatments. The results indicate significant differences by both analysis of variance and two‐tailed t‐tests. These additional hydrogen ions decreased seed yields by 2·6, 6·5, 11·4 and 8·5%, respectively. A treatment‐response function was determined between the hydrogen ion concentration of the treatments and seed yield. This function, y= 21·06 – 1·01 log x, has a correlation coefficient of minus 090 and its slope is significantly different from zero. Decreased yields were attributed to a decrease in number of pods per plant since seed number per pod and mass per seed did not vary among the treatments. On a per plant basis, total seed protein decreased by 10 and 19% in plants exposed to simulated rainfalls of pH 4·0 and 3·1, respectively, compared with plants not exposed to simulated rainfalls. At these same treatment levels total non‐structural carbohydrates did not decrease significantly. The results show that additional increments of simulated acidic rain can decrease seed biomass and protein content of field‐grown soybeans.

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