Pasture yield responses to phosphorus (P), sulphur (S), and potassium (K) were measured over four to eight years on different yellow-grey earth (pallic) soils at three non-irrigated (Timaru, Kauru, and Claremont soils) and one irrigated (Otiake soil) sites in North Otago. Large pasture yield responses to P at application rates up to 80 kg ha(-1) yr(-1) occurred on three sites with initial soil Olsen P levels of 6-11 mu g ml(-1), but only a small response up to this rate was measured on the Timaru soil with a higher initial soil Olsen P level (16 mu g ml(-1)). The relationship between soil Olsen P and relative annual pasture yield was similar and moderate (r(2) = 0.57) for the average of the three most responsive sites. The highest pasture yield response to S was measured at application rates up to 80 kg ha(-1) yr(-1) on an Otiake soil with an initial soil sulphate S level of 3 mu g g(-1). Smaller pasture yield responses at rates up to 40 kg S ha(-1) yr(-1) occurred on Kauru and Timaru soils with initial soil sulphate S levels of 8 and 4 mu g g(-1), respectively. In four of the eight years there was a pasture yield response up to 10 kg S ha(-1) yr(-1) on the Claremont soil with an initial soil sulphate S level of 9 mu g g(-1) Soil sulphate S only accounted for a small proportion (27%) of the average variation in relative yield. Three of the four sites had medium to high initial soil quick test (QT)K levels (9-19) and the fourth (Otiake soil) had a low level (4). Over four to eight years, the soil QT K in the nil K treatments declined to 2-7, but there was a pasture yield response only in the last four years at the lowest level, on the Otiake soil. Soil potassium tetra-phenyl boron levels were increased by K application and showed a lower decline than for no K. There was a moderate to strong relationship measured between relative yield (% of maximum yield) and %P (r(2) = 0.58) and %S (r(2) = 0.83) in mixed herbage on the Otiake soil but not at the other sites. %P was related to Olsen P (P = 0.52-0.69) on the Claremont and Otiake soils and %S was related to soil sulphate S (r(2) = 0.51) for the mean of all four sites. Overall, the results show that North Otago yellow-grey earth soils can be responsive to P, S, and K, and the size of the pasture yield response can be predicted with a reasonable degree of accuracy by the level of available soil P, S, and K, the amount of soil reserve K, and the P, K, and S concentration in mixed herbage.
