Phosphate fertiliser application effects on seasonally dry hill country pasture and soil

A grazed trial established in 1980 evaluated the effects of superphosphate fertiliser application on pasture growth on Easy (10 degrees-20 degrees slope) and Steep (30 degrees-40 degrees slope) land in the Waikato, North Island, New Zealand. Continuous and rotational grazing showed no effects on pasture responses to fertiliser. Mean annual pasture dry matter (DM) production ranged from 11,275 to 14,155kgDMha(-1) on Easy, and 6413 to 7480kgDMha(-1) on Steep slopes through the range of 10-100kgha(-1)yr(-1) of phosphate (P) fertiliser rates. Initial fertiliser effects on Olsen P tests were in the 0-3cm depth only, and in the 7-15cm soil depth only in the 100kgha(-1)yr(-1) treatment by year 4. Near maximum (97%) annual production, derived from relative yield analysis, was obtained at 0-7cm depth soil tests of 30 on Easy slopes and at 12 on Steep slopes. Results from this trial are directly relevant to the variable fertiliser rate aerial application technology currently being developed.