Crop water productivity of an irrigated maize crop in Mkoji sub-catchment of the Great Ruaha River Basin, Tanzania

Crop water productivity (CWP) is a quantitative term used to define the relationship between crop produced and the amount of water involved in crop production. It is a useful indicator for quantifying the impact of irrigation scheduling decisions with regard to water management. This paper presents CWP quantified from field experimental data. Three fields were cultivated to maize under irrigation during the 2004 dry season in a traditional irrigation scheme in Tanzania. The maize crop was irrigated at eight different seasonal water application depths: 400, 490, 500, 510, 590, 600, 610 and 700 mm, in two of the three fields, and at five water application depths: 400, 590, 600, 610 and 700 mm in the third field. The variation in seasonal water application depth was achieved by skipping the weekly irrigation once after every other irrigation at some pre-defined stages of the crop growth. CWP were computed in terms of crop water use, water applied, and economic returns. The CWP in terms of crop water use was found to range from 0.40 to 0.70 kg/m3 among the treatments in the three fields, while the CWP in terms of water applied varied from 0.40 to 0.55 kg/m3. The amount of irrigation water applied at the different growth stages of the crop and the growth stage response to moisture stress influenced the status of CWP. CWP was maximized by withholding irrigation every other week at vegetative and grain filling and observing weekly irrigation at flowering growth stage. However, the grain yield loss associated with irrigation schedule was about 20–28%. Convincing farmers to accept a trade-off between maximizing CWP at the expense of yield reduction may remain one of the greatest challenges that will face irrigation water management stakeholders.