Available sulphur in some Manitoba soils as estimated by plant growth and chemical analyses

Abstract

Measurement of the water soluble sulfate content of several Manitoba soils indicated that most of the soils contained adequate amounts of sulfur. The lowest water soluble sulfate contents encountered were in the soils of the Stockton association. A more detailed study involving 9 sampling sites within the Stockton association showed that these soils are generally much lower in water soluble sulfate and soil sulfur content than other Manitoba soils. In a greenhouse experiment the yield of rape was significantly increased by sulfur fertilization on 7 of 11 surface soils involved. All those soils that yielded significant responses to sulfur fertilizer contained less than 2.0 p.p.m. water soluble sulfate. Sulfur uptake by rape was significantly correlated with the amount of water soluble sulfate, heat soluble sulfate and sulfate present after mineralization. The soil sulfur, HC1 soluble sulfur, and organic matter contents of the soils were not correlated with sulfur uptake. A second greenhouse experiment determined the critical level of sulfur in rape as .10% total sulfur, and 200 p.p.m. water soluble sulfate sulfur. Studies of the sulfate adsorption characteristics of Manitoba soils indicated that absorbed sulfate is not an important sulfur fraction in these soils. Water soluble sulfate should be a good measure of the sulfate that is available to plants. In a field experiment, consistent but not statistically significant increases in yield of rape seed were obtained by broadcasting 20 to 40 pounds of sulfur fertilizer on a Stockton soil. This soil contained 25.2 pounds of water soluble sulfate in the upper 48 inches. Most of the Stockton soils studied contain less than that amount of water soluble sulfate.