Estimation of genetic improvement of maize in Ghana under three levels of nitrogen application

Recent release of quality protein maize (QPM) hybrids by the Crops Research Institute and promotion of hybrid maize production in Ghana necessitated a study of the genetic gain made with the introduction of the hybrid maize. This study was conducted to estimate the genetic improvement of maize in Ghana under three levels of nitrogen fertilizer application. The experiment was conducted in the 2002 major and minor seasons at Fumesua and Kwadaso representing four planting environments. Fumesua (latitude 60 43’ N, longitude 10 36’ W) and Kwadasb (latitude 6° 43’ N, longitude 10 36’ W) are located in the forest zone of Ghana with Ferric Acrisol soils classified as Asuansi and Kumasi series, respectively. Three land-races and seven improved open pollinated varieties and two QPM hybrids released from 1972 to 1997 were evaluated in a two factor, randomized complete block design in a split-plot arrangement, with four replications in each environment. Nitrogen levels (0, 45, 90 kg N/ha) were randomized in the main plots and the 12 varieties were randomized in the sub-plots. Agronomic and post- harvest data were recorded on the two-row plots of each variety. Analyses of variance showed that effects due to environments were highly significant (P<0.01) for grain yield and other agronomic traits measured. Nitrogen fertilizer levels were highly significant (P<0.0l) for grain yield, days to mid-sillc, days to mid-anthesis, anthesis-silking interval, plant height, ear height, open tip, cob aspect, dry stover weight, cob length, cob diameter, but significant (P<O.05) for grain depth. Differences among genotypes were highly significant (P<0.0l) for grain yield and other agronomic traits. Genotype x Environment interactions were highly significant (P<0.0 1) for grain yield, days to mid-silk, days to mid-anthesis, plant height, ear height, total lodging, rust, blight, cob aspect, shelling percentage, dry stover weight, 1000 seed weight, cob length, grain depth, grain diameter, but significant (P<O.05) for anthesis-silking interval and cob diameter. Genotype x nitrogen interactions were highly significant (P<0.01) for grain yield, shelling percentage and blight disease but significant (P<0.05) for cob diameter and rotten ears. At zero nitrogen fertilizer application the QPM hybrids significantly yielded higher (3.1 ton/ha) compared to the least yield of 2.6 ton/ha for the local varieties. At 45 kg N/ha, mean yields for the local varieties, open pollinated varieties (OPVs) and the hybrids were 3.2 ton/ha, 3.8 ton/ha and 5.3 ton/ha, respectively. At 90 kg N/ha, mean yields for the local varieties, OPVs and hybrids were 3.9 ton/ha, 4.3 ton/ha and 5.7 ton/ha, respectively. Linear regression analysis showed that yield gains attributed to genetic improvement were 12.5 kg/ha/year at zero fertilizer N, 35.1 kg/ha/yr at 45 kg N/ha and 33.1 k•• •yr at 90 kg N/ha and were all highly significant (P<0.01). Linear changes due to genetic Improvement were also highly significant (P<O.0l) for anthesis-silking interval (ASI) and ear height and significant (P<0.05) for days to mid-silk, total lodging, rotten ears, cob length, 1000 seed weight and rust disease score. Correlation coefficients between grain yield and 19 agronomic traits were highly significant (P<0.0 1) for ASI and significant (P<O.05) for days to mid-silk and ear height. ft was concluded from the study that (1) progress has been made in improving yield potential of maize under low to medium levels of soil fertility, (ii) breeding also resulted in the improvement of other agronomic traits, including days to mid-silk, ASI, ear height, total lodging, rotten ears, cob length, 1000 seed weight and rust disease score, (ill) there was a 41% and 33% yield advantage of planting the QPM hybrids over the OPVs at 45 kg N/ha and 90 kg N/ha, respectively and a 49 to 63 % yield increase by replacing the local varieties with the QPM hybrids, depending on nitrogen fertilizer rate (45 or 90 kg N/ba), (iv) economic analysis indicated a marginal rate of return (MRR) of 2176% and 194% by replacing the focal varieties with the hybrids at zero N and using hybrids at 45 kg N/ha respectively and (v) the genetic gain in grain yield of 35 kg/ha/year at 45 kg N implied a contribution of approxImately 34 billion cedis (4 million US dollars) annually to farm income. Widespread adoption of the hybrids is recommended to boost maize production in Ghana.

Source: KNUST