Resident hill country pasture production in response to temperature and soil moisture over 20 years in Central Hawke’s Bay

The production of resident pastures on rolling hill country was measured in three paddocks over 20 years at Poukawa in Central Hawke’s Bay. The pastures had been routinely fertilised with 250 kg/ha/yr of superphosphate but no pasture renovation, nor nitrogen fertiliser application, occurred during the measurement period. Total annual dry matter (DM) yield ranged from 4.5 to 12.8 t/ha/yr, which shows the level of variability to be expected in this summer-dry environment. The greatest proportion (60-90%) of growth occurred in winter/spring with consistent mean growth rates of 50-62 kg DM/ha/d in September and October. These rates were calculated to be 5.49±0.55 kg DM/ha/°Cd when spring moisture was non-limiting. The pastures had a mean water use efficiency of 16.9±0.34 kg DM/ha/mm of water available (R2 = 0.93). The amount of water available was calculated from a soil water budget based on a plant available water holding capacity of 124 mm (0-1.0 m depth). The results provide coefficients that can be combined with readily available climate data to predict pasture growth rates for feed budgeting purposes. Rainfall data collected on-site was highly correlated (r=0.94) with that predicted from the NIWA virtual climate station network.