EFFECT OF MAIZE MATURITY ON RADIATION-USE EFFICIENCY

Maize (Zea mays L.) production has expanded into short-season regions but it is not known whether the radiation-use efficiency (RUE, g MJ-1)1 of new early hybrids differs from those grown in traditional maize-growing regions. In this study, spectral reflectance measurements were used to derive estimates of photosynthetically active radiation (PAR) absorbed to compare the RUE of 10 maize hybrids that varied in adaptation from Iowa 110-d relative maturity to the earliest 60-d relative maturity hybrids commercially available. Reflectance measurements were made radiometrically in the visible and near-infrared regions of the electromagnetic spectrum at approximately weekly intervals in 1985, 1986, and 1988. The 10 maize hybrids were grown at three densities at Lethbridge, Alberta, on an irrigated silty clay loam soil (Typic Haploboroll). The Scattering by Arbitrarily Inclined Leaves (SAIL) model of canopy reflectance was inverted to produce daily estimates of the fraction of absorbed PAR, p. Multiplying p by daily PAR irradiance gave daily estimates of absorbed PAR (APAR, MJ m-2), which were summed for the season. Radiation use efficiency was obtained by dividing whole-plant yield at harvest by seasonal (emergence to harvest) APAR. Averaged over years, hybrids, and densities, RUE was 2.3 g MJ-1. Radiation-use efficiency increased with population density across hybrids regardless of maturity. Seasonal RUE was lower than reported in the literature but there is evidence that chilling injury due to low night temperatures at the high elevation and semi-arid location of the study reduced photosynthesis. The results suggest that spectral reflectance can be used effectively by breeders to identify hybrids that are more efficient users of PAR and that maize hybrids resistant to chilling injury may be needed at high latitudes.