Soil salinity studies. I—effect of calcium sulphate on the correlation between plant growth and electrical conductivity of soil extracts

Abstract

AbstractThe relation between the growth of lettuce and soil salinity (estimated by seven methods) was studied in the presence of varying levels of calcium sulphate. Lettuce were grown in pots receiving five levels of a mixture of potassium nitrate and diammonium hydrogen phosphate and four levels of calcium sulphate in factorial combination.Soil salinity was measured by the electrical conductivity of displaced soil solutions, saturation extracts, and soil suspensions prepared at water/soil (air‐dry) ratios of I: I, 2.5: I and 5: I. Direct measurements of electrical conductivity were also made in the saturation pastes, and a tentative procedure involving saturation of all 2.5: I soil suspensions with calcium sulphate was examined.Correlation between fresh weights of lettuce and conductivity measurements at water/ soil ratios of 5: I and 2.5: I was unsatisfactory, but was better at a ratio of I: I. Highly significant correlations of plant weight with measurements in saturation extracts and displaced soil solutions were obtained. Direct measurements in the saturation pastes gave correlations almost identical with those for filtrates from the pastes, but the effect of differences in soil texture on this relationship remains to be examined. The highest correlations of all were obtained in soil suspensions saturated with calcium sulphate.