Pasture yield responses to phosphorus, sulphur, and potassium applicationson North Otago soils, New Zealand

Pasture yield responses to phosphorus (P), sulphur (S), and potassium (K) w ere measured over four to eight years on different yellow-grey earth (palli c) soils at three non-irrigated (Timaru, Kauru, and Claremont soils) and on e irrigated (Otiake soil) sites in North Otago. Large pasture yield respons es to P at application rates up to 80 kg ha(-1) yr(-1) occurred on three si tes 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 init ial soil Olsen P level (16 mu g ml(-1)). The relationship between soil Olse n 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 y ield 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) occu rred 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 i nitial 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. T hree of the four sites had medium to high initial soil quick test (QT)K lev els (9-19) and the fourth (Otiake soil) had a low level (4). Over four to e ight years, the soil QT K in the nil K treatments declined to 2-7, but ther e was a pasture yield response only in the last four years at the lowest le vel, on the Otiake soil. Soil potassium tetra-phenyl boron levels were incr eased by K application and showed a lower decline than for no K. There was a moderate to strong relationship measured between relative yield (% of max imum yield) and %P (r(2) = 0.58) and %S (r(2) = 0.83) in mixed herbage on t he 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 sulp hate S (r(2) = 0.51) for the mean of all four sites. Overall, the results s how 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 reas onable degree of accuracy by the level of available soil P, S, and K, the a mount of soil reserve K, and the P, K, and S concentration in mixed herbage .