Studies on performance of some open-pollinated maize cultivars in the Guinea savanna. II. Genetic contribution to productivity of four cultivars under varying population and nitrogen regimes

Abstract

Three late-maturing varieties of maize (Zea mays L.) released from 1972 to 1988 and one local cultivar were evaluated in replicated field trials at Nyankpala and Damongo in 1992 and 1993. Plant densities (30 000, 50 000, 70 000 plants ha-1) were assigned to the main-plots and 12 combinations of N fertilizer levels (0, 80, 160 kg N ha-1) and varieties (Local, Composite 4, Dobidi, Okomasa) were assigned to the sub-plots in four replicates. The objective was to determine the rate of increase in grain yield due to genetic improvement under the different levels of soil fertility and plant densities. Across location analysis for grain yield showed significant (P<0.05) differences among plant densities and highly significant (P<0.01) differences among nitrogen levels and varieties. The density x nitrogen and nitrogen x variety interactions were also significant. The overall variety mean grain yields were 3.08, 4.44, 4.48 and 4.60 t ha-1 for the local variety, Composite 4, Dobidi and Okomasa, respectively. Linear regression estimates of grain yield increases (yield gains) per year were 32.3 kg ha-1 at zero-N, 45.1 kg ha-1 at 80 kg N ha-1, and 56.4 kg ha-1 at 160 kg N ha-1. Linear estimates over the three N levels were significant and positive for grain yield, days to 50 per cent silk emergence, percent grain moisture content at harvest, and 1000-seed weight, but was negative for ear acceptability rating and percent total lodging. One thousand seed weight, stover weight and ears per plant had significant positive correlations with grain yield whereas ear rating and total lodging were negatively correlated with yield. The data showed that (i) significant progress has been made in genetic improvement of maize in Ghana since breeding programmes were initiated in the mid-1950s, (ii) breeding was effective in improving yield potential of maize under low as well as at high levels of soil fertility, (iii) increase in yield potential of the varieties resulted in corresponding increases in size and uniformity of ears, 1000-seed weight and tolerance to lodging, and (iv) increase in yield potential did not result in proportionate yield increases in farmers' fields.



Ghana Jnl.agric. Sci Vol.31(2), 1998: 153-160