Determination of water productivity of maize varieties grown in Zimbabwe
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The quantification of water use in plants is necessary to maximize water use efficiency in semi -arid areas where water is often limiting. The main objective of the study was to quantify maize water productivity and apply the determined water productivity and harvest index to predict yields for different seasons. A field trial was carried out at the University of Zimbabwe farm located in Harare. Three varieties of maize (SC719, SC635 and SC 403) were grown. Reference evapotranspiration was computed from daily weather data using the FAO Penman Monteith equation. The BUDGET model was validated by comparing simulated and measured root zone water content and used to simulate maize transpiration. Water productivity was then determined by plotting aboveground biomass against the cumulative transpiration. Normalized Water productivity (WP*) was determined by plotting above ground biomass against the sum of the ratio of transpiration to reference evapotranspiration. The normalized water productivity and harvest index were then applied to predict yield for 3 varieties at ART farm for 3 seasons (2000/01; 2002/03 and 2004/05).The BUDGET model was validated satisfactorily with the trend of simulated water content closely following the observed water content Aboveground biomass increased linearly with cumulative transpiration with R2 value ranging between 0.95 and 0.96 for the three varieties. There were no significant differences in water productivity (p>0.05) due to variety. The maize water productivity obtained ranged between 7.7 and 9.5 g m-2 mm-1. With the lowest mean water productivity value in SC 403 (7.7 g m-2 m-1) There were no significant variety differences even after normalization (p> 0.05) and normalized water productivity showed a strong linear relationship with the values ranging between 30.4 to 39.0 g m-2. Application of the normalized water productivity and harvest index to maize yields for 3 seasons at ART farm showed a strong agreement between observed and simulated yields (R2 value of 0.98). The normalized water productivity for maize can be used to predict yield performance with aid of a validated BUDGET model.