Pasture growth on dairy farms in the Golden Bay and West Coast of the South Island

Pasture growth was monitored on 22 farms covering Golden Bay, Nelson, Murchison and West Coast districts during 1994 to 1997. Pasture growth was measured monthly from grazed pasture using the rising plate meter (RPM) and the difference method. Pasture growth from the South Island sites were compared with growth at the WestpacTrust Agricultural Research Station (WTARS) in South Taranaki, measured by the more traditional trim method, and the difference method as used in the South Island study. The pasture growth recorded was then used by the dairy farm production model UDDER to predict the planned start of calving (PSC), stocking rate and milksolids (MS) production at maximum net financial return for seven districts. At WTARS the average pasture production recorded by the difference method was 16.3 t DM/ ha and by the trim method, 12.9 t DM/ha, the greatest difference between the two methods occurring in late spring/early summer. Pasture production on the south Island sites varied from 9.6 (Taramakau) to 16.1 (Grey Valley) t DM/ha. The major factor identified as influencing pasture growth, in an environment where rainfall for 91% of the sites exceeded 2000 mm, was number of frosts. A multiple regression combining pasture production climatic and soil nutrient variables identified number of frosts and Olsen P as the major factors influencing pasture production (R 2 = 0.25). The use of the growth from seven districts by UDDER showed a marked variation in management practices and MS output. PSC varied from the first 10 days in August (Takaka, Nelson, Westport) to the last 10 days in August (Murchison). Stocking rates ranged from 2.0 cows/ha at Motueka to 3.3 cows/ha on an irrigated farm in the Nelson district. MS production/ cow differed little among districts and MS production/ha reflected stocking rate, ranging from 650 kg/ha for Motueka to 1150 kg/ha for Nelson. The main factor driving stocking rate and PSC was winter pasture production.