The present study was carried out on surface samples (0 to 30 cm) repre-senting 12 series from the Llanos Occidentales in Venezuela. These soils were grouped in three orders: Alfisol Entisol and Inceptisol. The study included the fractionation of soil K (K in 1 NH4OAC, K in HNO3 and total K), and a glasshouse experiment in which the supplying power or the soils was measured by depletion using sorghum as an index plant. Simul-taneously, measurements were made of K released by 0·01 N HCl and the results were correlated with those from the glasshouse experiment. Other solutions were used with the object of selecting those which showed the best correlation with K extracted by plants. The findings allowed the establishment of the Entisol-lnceptisol-Alfisol relationship both with regard to the K releasing capacity with HCl and the K supplying power by depletion. NH4OAC (exchangeable K) removed more K than one per cent citric acid and North Carolina solutions. There was a highly significant correlation between exchangeable K and K removed by five sorghum croppings. Contrariwise, non-exchangeable K was poorly correlated. The other solutions (one per cent citric acid and North Carolina) were also correlated with the potassium removed by plants.