SEASONAL-VARIATIONS IN SOIL S FLUSH AND POSSIBLE CONTRIBUTIONS FROM PLANT-ROOTS IN THE MEASUREMENT OF SOIL MICROBIAL SULFUR, PHOSPHORUS, POTASSIUM AND NITROGEN

The seasonal changes of the flush of soil sulphur (S) after CHCI3fumigation were studied in a two-year field trial on a high-producing pastoral soil. The pattern was different from thatobserved for microbial P, and this may be explained by seasonal changes in the contributionof roots to the soil S flush. Roots extracted from sieved (<4 mm) soil were used to estimate the contribution of plant roots in the determination of soil microbial P, K, N and S. Increases in P, K and N extractedfrom roots after CHCI3fumigation made only a small contribution to the increases for thesoil(4%, 2%and7%for P, K and N respectively). The contribution of roots to the increasein S extracted from soil after fumigation was about 22%. © 1990 CSIRO. All rights reserved.