Effects of Solar Radiation on the Performance of Maize in 41 Successive Monthly Plantings in Hawaii

The yields of maize (Zea mays L.) in the lowland tropics are generally very low compared with those of temperate regions, even with comparably high inputs. A major objective of this study was to determine the significance of incident light in this phenomenon. Total accumulated light during tropical maize growth is reduced greatly by shorter days, by higher cloud cover during major growing seasons, and by the shortening of growing season due to high temperatures. Forty-one monthly plantings of maize hybrids were made at the Waimanalo Research Station in Hawaii over a 44-month period, using two replications each of six hybrids for 20 months and of 15 hybrids for a succeeding 21 months. Yield averages of the 41 plantings ranged from 3.5 to 11.5 metric tons/ha (mean 7.8 metric tons/ha). These were highly correlated with monthly incident light values which ranged from 216 to 507 cal cm−2 day−1 (mean 383 cal cm−2 day−l). The cyclical change of grain yield and its components closely followed cyclical changes in solar radiation with a coefficient of determination of 78.5 %. Solar radiation was found to be the single most influential climatic factor affecting yield components. Average daily irradiance in the third month of growth (grain-fill period) explained more than 50% of the variation in grain yield and in all yield components except kernel weight and row number. A linear regression equation (yield in metric tons/ha = 0.023✕ − 0.33) accurately predicted grain yield over the range of 300 to 500 cal cm −2 day −1 (averages for growing season). As solar radiation increased 100 cal, an increase in grain yield of 2.3 metric tons/ha was observed. The rate of maturation of corn was determined largely by temperature. Temperatures varied from 21.8 to 25.8 C, generally paralleling amounts of incident radiation through the year. A decrease of 1 C was accompanied by an increase of 4.3 days of mid-silking. A major effect of cool temperature on yield was to extend duration of grain fill and increase total light interception, significantly enhancing yields when light values were low. The correlation of high yield with high elevation (low temperature) in the tropics is proposed to result largely from extended grain-filling periods under the cooler highland temperatures.