Effect of the length of the kernel filling period and the kernel filling rate on the grain yield of maize under different water supply conditions

Modem maize hybrids are found to have better stress tolerance and stay green longer than those available in the 80s and 90s. Physiological maturity takes place at ever lower values of grain moisture content. The lower the grain moisture content the slower the kernel filling rate. The length of the kernel filling period may thus limit further increases in grain yield. Hybrids belonging to the FAO 200-500 maturity groups were studied at the same five sites over four years in order to determine whether an increase in the kernel filling rate and/or in the effective kernel filling period would allow further increases in the grain yield. The results showed an unexpectedly large variability in both the kernel filling rate and the effective kernel filling period, indicating the existence of substantial reserves. The data suggest that in a non-limited environment the effective kernel filling period could be extended to cover the whole of the time available for kernel filling. If these reserves are to be exploited, more water must be made available during kernel filling (irrigation) and/or new lines and hybrids must be selected which are not only stress-resistant, but also utilise whatever quantity of water is available more efficiently than their rivals to give higher yields.