PERCEPTIVE RESEARCH ON WHEAT EVAPOTRANSPIRATION IN PAKISTAN

The Mehran model is developed based on the FAO-56 modified Penman-Monteith equation for computing reference and crop evapotranspiration with dual crop coefficients. Evapotranspiration (ET) of wheat in three field experiments with management-all owed depletion (MAD) of 45, 55 and 65% was observed through gypsum block readings and a drainage lysimeter. The seasonal crop ETs were observed as 363, 359 and 332 mm, and were computed as 383, 369 and 355 mm. The corresponding water use efficiencies (WUEs) were ascertained as 14.1, 15.0 and 13.4 kg (ha mm)(-1). The highest crop WUE was achieved with MAD at 55%; therefore, this research is more focused upon in the paper. The model relatively overestimated seasonal ET by 2.8%. Weekly root length and daily soil-moisture measurements revealed that wheat extracts most of its moisture from the 0-50 cm soil profile. When practising either scientific or traditional irrigation scheduling in the country, a seasonal water amount of 370 mm is suggested for wheat to achieve optimum yield and WUE. Statistical analysis (R-2 = 0.90, T = 2.09, and F = 999) showed good correlation between computed and actual seasonal ETs of crop with an experimental MAD of 55%. The Mehran model is found to be quite versatile and can be successfully used as a decision Support system (DSS) for irrigation scheduling of wheat in Pakistan. Copyright (C) 2008 John Wiley & Sons, Ltd.