MAIZE PRODUCTION POTENTIAL AND CLIMATIC RISK IN THE SOUTH-ISLAND OF NEW-ZEALAND

Maize production is expanding in the South Island of New Zealand even though the climate is cool and variable, and marginal for reliable pro duction of the crop. Its productivity in the region was assessed in fi eld experiments conducted at Lincoln, Canterbury, during three contras ting seasons-two warmer and one cooler than average for the region. Th ree cultivars with different maturity characteristics were sown on sev eral dates in each season. Even though the deviations from the longter m mean seasonal temperature (14.5 degrees C) were quite small (-0.6 to +0.7 degrees C) they had large effects on crop development and yield. Silage and grain yields were high (means 18.9 and 9.1 t/ha respective ly) for all sowing dates of all cultivars in the warmest season, indic ating good production potential in favourable years. However, in the o ther two seasons, yields were reduced in treatments that were sown lat e or where late-maturing cultivars were used. In the coolest season, s ome crops failed to start grain growth before the first autumn frost; their yields were low and they produced poor quality silage. The clima tic risk of growing maize in the region was quantified by analysing hi storical temperature records from eight locations together with a simp le thermal-time phenology model. Probabilities of failure to reach mat urity were calculated for combinations of five cultivar maturities and four sowing dates spanning the ranges likely to be used in the region . The analysis confirmed that reliable maize silage or grain productio n is marginal because of variability in temperature and frost occurren ce among seasons and the sensitivity of crop development rate to tempe rature. Crop failures are likely in cool seasons or when early autumn frosts occur, especially with late sowing or when late-maturing cultiv ars are used. Locations differed in their suitability for maize produc tion. Areas in the north (represented by Riwaka and Blenheim) were the least risky, and were the only places where both grain and silage pro duction appear to be viable. At lower altitude, coastal locations in c entral Canterbury (Rangiora and Lincoln), levels of risk were acceptab le for silage crops, but the area was beyond the climatic limit for re liable grain production. Although some crops completed grain growth, t hey probably would not have reached an ear moisture content low enough for commercial machine harvesting of grain. Higher altitude, inland l ocations and areas further south were not suitable for reliable silage production because crops often failed to complete grain growth, even when early-maturing cultivars were sown early.