Maize production potential and climatic risk in the South Island of New Zealand

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Abstract
Maize production is expanding in the South Island of New Zealand even though the climate is cool and variable, and marginal for reliable production of the crop. Its productivity in the region was assessed in field experiments conducted at Lincoln, Canterbury, during three contrasting seasons—two warmer and one cooler than average for the region. Three cultivars with different maturity characteristics were sown on several dates in each season. Even though the deviations from the long‐term mean seasonal temperature (14.5°C) were quite small (‐0.6 to +0.7°C) they had large effects on crop development and yield. Silage and grain yields were high (means 18.9 and 9.1 t/ha respectively) for all sowing dates of all cultivars in the warmest season, indicating good production potential in favourable years. However, in the other two seasons, yields were reduced in treatments that were sown late or where late‐maturing cultivars were used. In the coolest season, some crops failed to start grain growth before the first autumn frost; their yields were low and they produced poor quality silage. The climatic risk of growing maize in the region was quantified by analysing historical temperature records from eight locations together with a simple thermal‐time phenology model. Probabilities of failure to reach maturity 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 production is marginal because of variability in temperature and frost occurrence among seasons and the sensitivity of crop development rate to temperature. Crop failures are likely in cool seasons or when early autumn frosts occur, especially with late sowing or when late‐maturing cultivars are used. Locations differed in their suitability for maize production. Areas in the north (represented by Riwaka and Blenheim) were the least risky, and were the only places where both grain and silage production appear to be viable. At lower altitude, coastal locations in central Canterbury (Rangiora and Lincoln), levels of risk were acceptable for silage crops, but the area was beyond the climatic limit for reliable grain production. Although some crops completed grain growth, they probably would not have reached an ear moisture content low enough for commercial machine harvesting of grain. Higher altitude, inland locations 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.