The impact of weather on the scheduling of sweet corn for processing 2. Variation in crop duration with cultivar, season, time of planting and site

A consistent relationship has previously been established between temperature and the time from sowing to maturity for several sweet corn cultivars grown at three sites in New Zealand. The present paper uses this relationship, together with 13 years of historical temperature records, to simulate the effects of cultivar, season, date of planting, and site on the date of harvest. Making such assessments from existing factory records alone is not feasible. Thermal time was used to characterise the maturity of each cultivar. Commercial cultivars that have been used in recent years in New Zealand require from 1134 to 1279 degree-days (base 6°C) to proceed from planting to 72% kernel moisture. The variation in simulated crop duration was separated into within-season and between-seasons components. Variation due to planting date within seasons can be allowed for by the processor when planning a planting schedule, whereas differences between seasons cannot. The relative importance and absolute levels of these two sources of variation in simulated harvest date were dependent on site, cultivar, and length of the period over which planting occurred. At Gisborne, the warmer site, where planting commonly extends over 75 days, the two components of variability were of equal magnitude. At a cooler site, Feilding, where planting extends over 45 days, the between-seasons component of variability was three times the within-season component. More importantly, the level of between-seasons variability at Feilding was twice that at Gisborne. The probability of a crop being harvested within ±3 days of the average expected harvest date is at best only about 40% for plantings of early maturing cultivars at Gisborne, and drops to about 25% for plantings of early maturing cultivars at Feilding. The effects of cultivar maturity and season length at different sites are considered in relation to crop and factory management strategies.