Sulphur Dioxide Fumigations of Range Grasses Native to Southeastern Arizona

Abstract

For many years it has been known that certain gases discharged into the atmosphere by industrial installations have caused injury to crop plants and vegetation growing nearby. One of the principal pollutants in industrial waste is sulphur dioxide. The relationship between foliar loss due to SO2 and yield reduction on various vegetative and fructifying crops has been well established. The Selby Smelter Commission (1915)) reported the effects of SO2 on barley; Hill et al. (1933) established the correlation between foliage loss and the reduction in yield on alfalfa, while Brisley and Jones (1950) and Brisley et al. (1959) reported on effects of SO2 on. yield of wheat and cotton. It has been shown that the action of SO2 on vegetation is purely local in nature, causing no systemic influence or disease and that there is no translocation of toxic substances, the injury being confined to the areas which are visibly affected (Thomas et al., 1949). All investigators have reported that the resultant yield of crop plants is not reduced unless visible manifestations of SO2 injury are present. No studies have been reported on the effects, if any, of SO2 fumigations on range grasses. A limited number of exploratory experiments were conducted in 1936 to 1941 by Phelps Dodge Corporation but the tests were too few in number and the work was not conducted in sufficient detail to warrant publication. Since farm crops were of greater economic importance in the area, intensive research with native vegetation was postponed until 1958. At this time, an experiment was designed whereby the quantity of forage produced, the quality (food value) of the forage, the quantity of seed available for reseeding the range, and seed viability could all be measured. The difference, if any, between yields taken from plants which had been fumigated with SO2 and plants growing normally, could then be determined. Three grass species were selected, either because of their predominance on the local ranges, or because of their desirability as forage for cattle. They were tobosa (Hilaria mutica), blue grama (Bouteloua gracilis), and sideoats grama (Bouteloua curtipendula). During the past 40 years, field observations by numerous air pollution and range specialists on perennial range grasses native to Southeastern Arizona have revealed that these grasses are extremely resistant to SO2 and do not show leaf markings in their native habitat. The authors would like to express their thanks to Prof. K. A. Valentine and Dr. J. J. Norris, New Mexico State University, for their helpful advice and suggestions on planning experiments and Dr. R. 0. Kuehl, University of Arizona, for his statistical advice.