Field-Based Crop Coefficients (Kc) for a Maize Crop under Deficit Irrigation Scheduling

This study presents crop coefficient (Kc) values of TMV1-ST maize variety cultivated under deficit irrigation scheduling in Mkoji sub-catchment, Tanzania. Field experiments consisting of eight (8) treatments were conducted in 2004 and 2005 irrigation seasons. The treatments variation was irrigation intervals. The control treatment was irrigated on weekly basis while the other treatments were irrigated every other week at one or more growth stages of the maize crop. Surface irrigation method was used and soil moisture contents were monitored weekly throughout the crop growing season from which weekly crop actual evapotranspiration was computed. Weather data of the study location were used to compute weekly reference evapotranspiration based on the FAO-Penman- Monetieth model. Crop coefficients were computed as the ratio of crop actual evapotranspiration of the different treatments to reference evapotranspiration on weekly basis. Water stress coefficients were also computed. The crop coefficients had similar trend in the two seasons which make them reliable. The average crop coefficient (Kc) of the fully irrigated treatment for the two seasons for the establishment, vegetative, flowering and grain filling stages were 0.53,0.82,1.10, and 1.06, respectively, while the average crop coefficients of the deficit irrigated treatments (Kc') for the two seasons for the establishment, vegetative, flowering and grain filling stages were 0.53, 0.75, 0.94, and 0.78, respectively. Withholding regular irrigation at any crop growth stage reduced crop coefficient by between 17 to 30 %, while withholding regular irrigation at two or more successive growth stages of the maize crop reduced crop coefficient by about 40 %. The water stress coefficient (Ks) resulting from deficit irrigation at any one growth stage only of the maize crop were found to range from 0.74 to 0.83, while deficit irrigation at two or more successive growth stages ranged from 0.68 to 0.77. The crop and water stress coefficients developed from this study could be used in irrigation systems planning and design for the study area in Tanzania.