Phosphorus requirements of grazed pasture on pakihi and recent soils of the South Island west coast

Abstract

Abstract Trials on an Addison gley podzol and a Hokitika recent soil determined the production responses to applied superphosphate of pasture under sheep grazing over a 5-year period. Rates of 20 and 22 kg effective (i.e., citric acid soluble) P/ha resulted in 86 and 98% of maximum pasture production for the Addison and Hokitika soils, respectively. These rates were similar to predicted maintenance rates of 19 and 25 kg effective P/ha from the Computerised Fertiliser Advisory Scheme of the New Zealand Ministry of Agriculture and Fisheries. Pasture production was maintained at Olsen P levels of 8 μg/ml for the Addison soil and 22 μg/ml for the Hokitika soil, differing from the predicted Olsen P level of 17 μg/ml. When compared with earlier mowing-only trials with clippings returned, the use of short grazing durations at high sheep stocking densities and 4–6 week regrowth intervals resulted in similar pasture yield responses to added phosphorus.