EFFECTS OF FREQUENCY AND DURATION OF SIMULATED ACIDIC RAINFALLS ON SOYBEAN YIELDS

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Abstract
Summary: An experiment to determine the effects of simulated acidic rain, applied at two frequencies and durations, on seed yields of two commercial cultivars of soybeans was performed during the summer of 1983. Plants were shielded from all ambient rainfalls automatically by two moveable exclusion covers and exposed to simulated rainfalls in quantities equal to the average amount of rainfall that occurs at the site during the growing season. Seed yields of soybeans (cv. Amsoy) exposed twice weekly to simulated rain of pH 41, 3.3 and 2.7 were, respectively, 0, 10 and 17 % below yields of plants exposed to simulated rain of pH 5.6. The linear treatment‐response function of seed yield versus rainfall pH for Amsoy was + 9.18 + 0.74x and had a correlation coefficient of 0.86 y is seed mass per plant and x is the pH of the simulated rain). The linear component of pH treatment differences showed a highly significant decrease in yield (P= 0.0034). For Amsoy plants exposed to simulated rainfalls daily, plants exposed to pH 4.1, 3.3 and 2.7 exhibited yields 10, 19 and 12%, respectively, below those exposed to simulated rainfalls of pH 56. A treatment‐response function (P= O.0713) of seed yield vs rainfall pH was y+ 7.35 + 0.56x and had a correlation coefficient of 0.84. Seed yields of the Williams cultivar were not affected by rainfall acidity. In both cultivars the daily, short duration rainfall regimen resulted in significantly lower yields compared with the twice weekly, longer duration rainfalls. The major portion of the differences in seed yield can be accounted for by the observed differences in number of pods per plant.