THE COBALT STATUS OF TASMANIAN SOILS

Summary Total cobalt was determined in 104 samples of Tasmanian surface soils. It was moderate to high (4-82 p.p.m.) in krasnozems and lateritic krasnozems, and high (1 1-94 p.p.m.) in brown earths, black earths, and prairie soils, all of which were derived from basalt or dolerite. It was also high in soils of the lateritic podzolic Cressy series, but low in another lateritic podzolic, the Brickendon series. Approximately halt' the samples of various kinds of podzolic soils had less than 3 p.p.m. The cobalt content of subterranean clover grown in pots on 92 soil samples from Tasmania showed large differences between the soil groups. The krasnozems stood out with generally low values, ranging from 0.05 to 0.30 p.p.m., with over 60% of samples less than 0.10 p.p.m. On the various podzolic soils the cobalt content of the clover ranged from 0.08 to 2.1 p.p.m., with over 80% of the samples between 0.10 and 0.55 p.p.m. On the brown-black earth group it was generally high, ranging from 0.17 to 0 -63 p.p.m. Soil pH did not account for these differences. Cobalt deficiency in sheep and cattle has been recorded on krasnozems and on podzolic soils in Tasmania but not on the brown-black earth group. It is suggested that ingestion of soil may be more important in the cobalt nutrition of the ruminant on krasnozems than on most other soils.