Phenological development and frost risk of ‘Challenger’ sweet corn (Zea mays) in response to phosphorus

Abstract

Sweet corn (Zea mays) yield responses to phosphorus (P) are well documented but impacts on development are less defined. For economic, practical, and environmental reasons sweet corn crops are sometimes grown with soil P levels below optimal for maximum yields. Any consequent maturity delay may also affect the risk of the crop failing to mature in the frost-free season. This research examined the response of sweet corn development to P in two consecutive field experiments on a low P site (6 μg P ml -1 ) at Lincoln, New Zealand. Overall, crops receiving 200 or 240 kg P ha -1 reached canning maturity 6-7 days earlier than crops receiving no Pfertiliser. However, much of this delay in maturity was overcome by the addition of the smallest amount of fertiliser (50kg P ha -1 ). The differences in maturity resulted from a change in the duration from emergence to silking. Crops with no added Prequired 725 and 645 degreedays (°C days) above a base temperature of 8°C to reach silking in the crops. Crops that of 50 kg P ha -1 required 665 and 590°C days to reach silking. Further additions of P gave comparatively small increases in development rate towards silking. The difference was probably because of a limitation of crop growth rate that caused an apparent delay in development rather than any physiological change in development rate. In a simulation analysis using these values for development phases and historical weather data for six locations in New Zealand, the risk of the crops failing to reach maturity before the first autumn frost was quantified. Sowing date and location were the dominant factors determining risk, but a limited P supply increased the risk of crop failure at all locations. The greatest differences in risk were between the two lowest simulated soil P supplies (6 and 10 μg ml -1 ); further increases in soil P supply had less impact on reducing risk. The greatest differences in risk between the low (6 μg ml -1 ) and high (30 μg ml -1 ) P soils were for late sown crops at southern locations.