EFFECT OF HIGH-TEMPERATURE ON GRAIN-GROWTH IN FIELD-GROWN MAIZE

Little information is available on the effect of high temperature on grain-growth and on final yield in field-grown maize (Zea mays L.). To redress this situation, a study was run on maize sown at five dates and grown in field plots in a tropical environment under high water and nutrient supply. For each sowing, mean temperature during grain-filling was relatively stable, but across sowings ranged from 25 to 32°C. The effects of these temperature regimes on the linear rate of grain-growth, the duration of the effective grain-filling period, the rate of development of milk-line and black-layer as indicators of maturity, the rate of increase in harvest index during grain-filling, and grain-yield were examined. The rate of grain-growth increased and the duration of grain-filling was shorter as temperature increased. However, contrary to other reports for maize grown in controlled environments, grain-yield was not responsive to temperature over the range from 25 to 32°C during grain-filling. This stability in grain-yield was associated with relatively similar incident-radiation receipt in all sowings. Whilst the rate of both milk-line and black-layer development increased with temperature, the development of milk-line was less variable and proved to be the better indicator of the end of effective grain-filling. Harvest index increased linearly during grain-filling in a similar manner to the rate of grain growth. The rate of harvest-index increase was relatively stable across sowings, with a mean value of 0.015 day-1. An important implication of the linear increase in harvest index is that grain-yield accumulation can be estimated from the crop biomass at any stage of grain-growth without knowledge of grain number nor the rate of grain-growth. © 1990.