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

Abstract

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 μg 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 μg ml−1). The relationship between soil Olsen P and relative annual pasture yield was similar and moderate (r2 = 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 μg 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 μg 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 μg 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 (r2 = 0.58) and %S (r2 = 0.83) in mixed herbage on the Otiake soil but not at the other sites. %P was related to Olsen P (r2 = 0.52–0.69) on the Claremont and Otiake soils and %S was related to soil sulphate S (r2 = 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.