Radiation use efficiency (RUE) is considered critical for calculation of crop yield. The crop productivity can be improved by increasing the interception of solar radiation and maintaining higher RUE for plants. Irrigation water and nitrogen (N) supply are the main limiting factors for RUE in maize (Zea mays L.) across the semi-arid environments. Field experiments were conducted during two consecutive growing seasons (2009-2010) to optimize RUE in relation to N application timings and rates with varying irrigation water management practices. In experiment 1, three N application timings were made, while in experiment 2, three possible water management practices were used. In both experiments, five N rates (100, 150, 200, 250, and 300 kg N ha) were applied to evaluate the effects of irrigation water and N on cumulative photosynthetic active radiation (PARi), dry matter RUE (RUE), and grain yield RUE (RUE). The results demonstrated that cumulative PARi and RUEs were not constant during the plant growth under varying the nutrients. The water and N significantly influenced cumulative PARi and RUEs during the both growing seasons. In experiment 1, the maximum cumulative PARi was observed by application of 250 kg N ha in three splits (1/3 N at V2, 1/3 N at V16, and 1/3 N at R1 stage), and the highest RUE was achieved by the application of 300 kg N ha. However, the highest RUE was observed by application of 250 kg N ha. In experiment 2, the maximum cumulative PARi was attained at normal irrigation regime with 250 kg N ha, while the highest RUE and RUE were recorded at normal irrigation regime with the application of 300 kg N ha. The regression analysis showed significant and positive correlation of RUE with grain yield. Therefore, optimum water and N doses are important for attaining higher RUE, which may enhance maize grain yield semi-arid environment; this may be considered in formulating good agricultural practices for the environmental conditions resembling to those of this study.

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-allowed 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)À1 . 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 ¼ 0.90, T ¼ 2.09, and F ¼ 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. L'analyse statistique (R 2 ¼ 0.90, T ¼ 2.09, et F ¼ 999) a montré la bonne corrélation entre l'évapotranspiration saisonnière calculée et réellement mesurée pour une irrigation rationnée à 55%. Le modèle de Mehran apparaît tout à fait souple et peut être employé avec succès en tant que système interactif d'aide à la décision pour le pilotage de l'irrigation du blé au Pakistan.