Aspects of accumulated heat patterns (growing-degree days) and pasture growth in Southland

and patterns of accumulated heat are important limits on pasture growth, especially over the period from late autumn to spring, and data on these factors are crucial for best land-use management in the southern farming community. The Topoclimate South Project is mapping soil and climate characteristics over 805 000 ha of Southland/South Otago using a network of 900 automated dataloggers. Temperature data for individual sites, and from local climate stations are being used to generate 30-year daily temperature and, thereafter, growing degree-day (GDD) records. Literature reviews show that several authors report considerable growth of temperate pasture species at about 5°C, so a base temperature of 4°C is used as a threshold for pasture growth and, thus, in GDD computations. Strong relationships are evident when pasture growth rates and GDDs are compared. For data recorded at Winton, Southland in the period 1950-1961, GDD patterns strongly reflect patterns of both clover and grass growth, accounting for 88% of the variability in mean patterns of clover growth and 75% of the variability in total pasture production. In practice, rainfall seasonality, nutrients, solar radiation, pasture management, plant pests and plant ecotype will also affect growth rates. To ensure that information gathered is also communicated, Topoclimate South is issuing soil and GDD maps to participating farmers. They have also established a service to provide detailed information and interpretation for end users, be they farmers, scientists, teachers, consultants or other service providers to the agricultural community. Keywords: growing degree-day, pasture growth, temperature threshold, topoclimate