Estimation of Crop Water Requirements and Irrigation Demand for Maize and Rice in Morogoro, Tanzania Using the CROPWAT 8.0 Model

This study assessed the crop water requirements (CWR) and irrigation demands of maize and rice in Mvomero District, Morogoro Region in Tanzania, under varying seasonal rainfall and soil conditions. Using the CROPWAT 8.0 model, agrometeorological parameters such as temperature, rainfall, evapotranspiration, and effective rainfall were integrated with crop-specific characteristics and soil properties to simulate irrigation demands and quantify water needs across different crop phenological stages. The analysis employed decadal climatic data and crop coefficients (Kc) to simulate both the net and gross irrigation requirements. The findings revealed that maize, cultivated predominantly on red loamy soils, had a seasonal CWR of 406.4 mm, which was effectively met by 409.4 mm of effective rainfall, with a minimal irrigation demand of 46.6 mm during the mid-season. In contrast, rice grown on black clay soils showed a higher CWR of 647.5 mm and gross irrigation demand of 754.1 mm, driven by high percolation losses (488.0 mm) and extended growing stages at the transplanting and early vegetative stages. Despite receiving 530.4 mm of effective rainfall, rice exhibited a net irrigation demand of 527.9 mm, implying its water-intensive nature and the influence of inefficient irrigation practices. These results highlight the critical need for crop- and site-specific irrigation planning to optimize water use efficiency. This study provides valuable insights for policymakers, irrigation planners, and agricultural stakeholders in Tanzania to develop sustainable water resource management strategies and ensure food security under increasing climate variability and competing water demands.