THE INFLUENCE OF SULFUR ON POPULATIONS OF STREPTOMYCES SCABIES AND OTHER STREPTOMYCETES IN PEAT SOIL

Abstract

SULFUR HAS long been used as a soil amendment for control of potato scab (Streptomyces scabies (Thaxt.) Waksman and Henrici). Although results have been somewhat variable, there is general agreement that scab is, at least in part, reduced by acid soil conditions resulting from treatment with elemental sulfur. Most investigations of the effect of sulfur on potato scab incidence have been made on mineral soils, although recently the influences of sulfur on scab incidence, potato yields, and vine characteristics, have been described for Iowa peat soils (Hooker and Kent, 1950). In this study, scab control was attributed in large part to an increase in soil acidity. The purpose of this investigation was to determine: (1) whether soil populations of Streptomyces spp., as indicated by dilution plate techniques, could be used as a means of estimating the incidence of potato scab; and (2) at what time the influence of sulfur on populations of Streptomyces spp. became measurable. The study of soil population trends was made from field plots described in greater detail elsewhere (Hooker and Kent, 1950). Investigations on the evolution of H2S in sulfurtreated peat soils and the toxicity of 112S to S. scabies were made later in the laboratory. LITERATURE REVIEW.-Satisfactory reviews of the literature on scab control with sulfur and the influence of soil pH on scab have been published elsewhere (Dippenaar, 1933; KenKnight, 1941; Walker, 1946; Hooker and Kent, 1950). Studies on microbial populations by dilution plate techniques in sulfur-treated soils have been made, although such reports are not common. The authors are not aware of such a study on field plots prepared for potato scab control. Pitz (1916) found that bacterial counts were reduced after 44 davs in Miami silt loam soil containing 0.5 per cent or 1 per cent sulfur. This decrease was attributed to an increase in soil acidity. O'Gara (1917) observed relatively large increases in bacterial numbers in alkali soil to which 400 lb. of sulfur per acre had been applied. Rudolfs (1922) found that sulfur rates of less than 1000 lb. per acre applied to a fine sandy loam soil slightly increased bacterial numbers, whereas higher rates depressed bacterial counts. Fife (1926), working with diverse types of soil, observed in soils high in organic matter that bacterial counts were increased as sulfur rates were increased, whereas in soils low in organic matter bacterial counts decreased as the sulfur rates increased.