THE RELATIONSHIP BETWEEN FINAL YIELD AND PHOTOSYNTHESIS AT FLOWERING IN INDIVIDUAL MAIZE PLANTS

In an attempt to explain plant-to-plant variation in dry weight of maize (Zea mays L.), a computer program was developed to predict daily assimilation per plant and its distribution throughout the shoot at flowering. Inputs to the model were meteorological data, photosynthetic rate-irradiance curves, measurements of intraplant assimilate distribution at flowering, and the positions of individual leaves of plants grown in the field at three densities (50 000, 100 000 and 150 000 plants/ha). Dry weights were recorded on these same plants following black layer formation. Predicted effects of plant density on shoot growth compared favorably with available data. The correlation coefficient between predicted assimilation 1 day after anthesis and grain yield on the same plants, with treatment effects removed, was 0.67 (N = 360). The coefficient of variation of predicted assimilate flux per plant increased significantly with increasing density, and the fluxes were generally normally distributed. Results supported the concept of a threshold assimilation rate per plant below which grain would not normally form, and this appears to be the cause of the bimodal frequency distribution of grain yield per plant observed at high densities.