W. E. Loomis
1944 Plant Physiology  
The owner of land adjoining the Fort Dodge plant of the United States Gypsum Co. recently ascribed the rundown condition of his farm to injury by gypsum dust from the plant. Since the areas near the plant were obviously receiving considerable deposits of dust over a period of time, we were asked to investigate the possibilities of direct or accumulative injuries. Injury from dust deposits on growing crops was considered improbable on a number of grounds: 1. Gypsum (CaSO4-2H20) is a stable,
more » ... al salt with a solubility at saturation of about 0.2 per cent. A saturated solution of gypsum is frequently used as a source of Ca and SO4 in nutrient solutions, and such slight contact as might be made with the mesophyll cells through the cuticle and epidermis of the leaves could not be expected to be injurious. 2. Gypsum dust might reduce diffusion through the upper stomata of leaves, but the relatively large size of the dust particles and the readiness with which they form larger crystals when exposed to dew, together with the predominance of hypostomatal leaves, makes any important clogging improbable. 3. Dust layers would partially shade the leaves, particularly during hot, dry periods, but many published experiments indicate that 30 per cent. of full sunlight is near optimum for photosynthesis. Unpublished data for maize show little or no increase in photosynthesis above 25 per cent. of full sunlight. Since the dust would ordinarily be removed by rainfall during periods of cloudy weather, the probabilities of beneficial action from shading appear to be as good as or better than those of injury. Experimentation POT TESTS OF GYPSUM APPLICATIONS Possible accumulative effects of gypsum dust on the soil were investigated from two angles; the possible beneficial effects of potassium applications in balancing excess calcium accumulations, and the effects of large additional quantities of gypsum to soil from the area receiving the maximum dust deposits. Soil was collected from the plowed layer of a field adjoining the gypsum plant, after discarding 3-5 cm. of surface clods, stubble, etc., and used to fill gallon jars. Thirty-two hundred grams of dry soil was used, and salts added on an area basis and mixed with the soil for the various treatments. The data of the first experiment with oats are shown in table I. Yields are total shoot and grain growth per pot. Potassium chloride appeared to hasten maturity of the plants and thus to reduce their green weight at harvest but showed no effect on total dry 706 www.plantphysiol.org on August 21, 2017 -Published by Downloaded from
doi:10.1104/pp.19.4.706 pmid:16653957 fatcat:n2k7iiqtonebfcqu5d2olxdqtm