Evaluation of soil sulfur fractions as sources of plant available sulfur using radioactive sulfur

Tsuji T.; Goh K. M.

When an apparent steady state condition was reached during the incubation of 3 soils with 35S-labeled gypsum under growth chamber conditions, perennial ryegrass plants (Lolium perenne L.) were grown and their S uptake was then related to levels of the various S fractions determined by 6 different methods. About 30-47% of the added S was taken up by plants. This uptake was related to decreases in extractable and HI-reducible S during cropping. The best correlation (r > 0.93) was obtained with S extracted with Ca(H2PO4)2-H2O and NaH2PO4-HOAc. The L values changed significantly with harvests in 2 of the soils studied. Mineralization of indigenous soil S was greater in the presence of plants, but the amount of added S immobilized was unaffected by plants and extractants.