Evaluation of wheat(triticum aestivum l.)gentypes for nitrogen and water use efficiency

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Mushekwa, Sakumona
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Wheat is increasing becoming an important staple food crop in Zambia particularly in the urban and per-urban communities where shift in food tastes and preferences to wheat products has occurred. Production and yield are however severely limited by cost of irrigation water and nitrogen fertilisers. A study was carried out at the National Irrigation Research Station (Nanga) in 2011 dry season to evaluate wheat genotypes for nitrogen and water use efficiency and identify wheat morphological traits that influence nitrogen and water use efficiency. The experiment was arranged in a Split-split plot in a Randomised Complete Block Design with three replications. Three water regimes (100%, 75% and 50% crop water requirement) were used as main factor, three nitrogen rates (240,160 and 80 kg ha-1) as sub-factor and twelve spring wheat genotypes as sub-sub factor. Grain yield, water use efficiency (WUE), nitrogen use efficiency (NUE), ear length, above ground biomass, plant height, thousand kernel weight, grains per ear, harvest index, spikes per ear, days to 50 % flowering and leaf rolling were assessed and analysed. Correlation and stepwise multiple regression analyses were done to study the parameter relationship. The results revealed that there were highly significant differences among the twelve genotypes for grain yield, morphological traits, WUE and NUE. Varying water regimes significantly affected most parameters measured except thousand kernel weight, spikes per ear and ear length. The factor nitrogen also had significant effect on most of the parameters except spikes per ear, plant height, days to 50% flowering and ear length. All factor interactions were significant for the parameters measured apart from that of water by nitrogen interaction for spikes per ear which was not affected by the interaction of water regime by nitrogen rate and plant height which was non-significant. Genotypes Mampolyo and Sahai I gave the highest grain yield of 5,064 kg ha-1 and 4,979 kg ha-1 respectively, NUE of 36.88 kg/ha kg N-1 and 36.68 kg/ha kg N-1 respectively and WUE of 13.60 kg/ha mm-1 and 13.82 kg/ha mm-1 respectively. In low water supply, Sahai I and Loerie II showed the highest NUE and WUE while under limited nitrogen application rates Sahai I, Choza and Nduna recorded the highest NUE and WUE. There were highly significant positive correlations between WUE and thousand kernel weight (r = 0.352**), harvest index (r = 0.183**) and leaf rolling (r = 0. 201**) and highly significant negative between WUE and plant height (r = - 0.175**) and days to 50% flowering (r = - 0.214**). Apart from thousand kernel weight (r = - 0.138*) and leaf rolling (r = - 0.297**) which were negative and significantly, all traits were positive and significantly correlated to NUE. The relationship between WUE and NUE (r = - 0.054) was negative and non-significant. In low water and nitrogen application rates, plant height and harvest index were identified as the most important traits that explained variation in WUE and NUE of genotypes. These traits accounted for 52.4% of the variation in NUE and 42.5% of variation in WUE. The results of this study indicate that wheat breeders could deliberately select for NUE and WUE under low input supply. Since the correlation between WUE and NUE was non-significant, this indicates that it is possible to improve these two traits simultaneously without improvement in one reducing the other. In the process targeting plant height and harvest index as traits and use genotypes such as Sahai I, Choza, Nduna and Loerie II which showed superior WUE and NUE in low water and nitrogen application rates as parental material in wheat improvement programme under low input supply.
Wheat --Genetics--Zambia , Wheat