Use of exchangeable potassium in assessing potassium availability in tasmanian soils
Graley, A.M.; Nicollis, K.D.
Australian Journal of Experimental Agriculture and Animal Husbandry 19(96): 72-81
Three sequential surveys of exchangeable K (Exch. K) in the surface 10 cm of major Tasmanian soils are presented, together with data from surface samples of profiles collected earlier. Soils with Exch. K less than 0.4 m [milliequilalents] 100/g are considered to be low or marginal in K readily available for pasture growth. Lateritic podzolic soils were lowest in Exch. K, with 4/5 of the sample sites below 0.4 meq 100/g (median value 0.21 meq 100/g). Podzols and humus podzols were similarly low. Available K was low to marginal in yellow podzolic soils on sandstone and solodized solenetz and solodic soils. Moderate contents were found in yellow podzolic soils on mudstone, the only soils with appreciable illite, and in organic alluvial soils. On basalt, krasnozems had moderate available potassium, but black earths and paririe soils were marginal. On dolerite, non-calcic brown soils had ample K (median Exch. K 0.93 meq 100/g), but grey-brown podzolic soils had much less. Most soils showed high variability between farms and 1 krasnozem soil series had high variability between paddocks within farms. Coefficients of variation ranged from 42-58%, in agreement with corresponding values reported by other workers. The contents of Exch. K found are interpreted in terms of soil formation and of land use.