Abstract
Using 15 years of grazing records from two trials with 31 different sulphur (S) and phosphorus (P) fertiliser combinations on a Tekapo/ Pukaki high‐country soil, the most profitable fertiliser combinations for long‐term sustainable production were determined from consideration of fertiliser composition, ex‐works, transport, and spreading costs, increase in sheep carrying capacities, and discount rates. In a soil with a high natural surface‐soil P level, the optimum returns were determined solely by elemental‐S fertiliser rates. The estimated greatest net returns from annual applications rates were at 53 kg S ha‐1 yr‐1, or between 24 and 39 kg S ha‐1 yr‐1 if ratio of return versus input was considered. Using carrying capacity response functions and elemental‐S oxidation rates, it was estimated that the best long‐term sustainable fertiliser strategy was for 5‐yearly applications of 250 kg ha‐1 of 2.2‐mm coarse‐particle elemental S.
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