Evaluation of Reference-Crop Evapotranspiration Models, Crop Evapotranspiration Methods and Water Supply Methods for the Determination of Crop Coefficient of Kenaf in a Tropical Wet-and-Dry Climate.

Determining crop water requirements is the first step in reducing water used while maintaining profitable production. Quantitative assessment of Kc Kenaf is rare in tropical wet-and-dry climate, Nigeria. Field and pot experiment were conducted in the University of Agriculture, Abeokuta, to develop crop coefficients (Kc) for kenaf. Efficiency of lysimeters and Time Domain Reflectometery (TDR) in the measurement of ETc and the Cropwat and Instat+ models in estimating ETo were evaluated. The experiment involves three varieties of Kenaf (Ifeken 100, Cuba 108 and Tainung 2) and two water supply methods (rain-fed and irrigation). Physiological parameters and Kc estimated during the different phenological stages of kenaf grown were analyzed with respect to treatments. The result showed that Cropwat and Instat+ were related (p < 0.05) in their estimation of ETo. Positive linear relation (R2= 0.72, p < 0.05) was recorded between lysimeters and TDR measured crop evapotranspiration irrespective of variety and water supply method. The Kc were highest in mid-season (0.9- 1.2), followed by crop development period (0.5 -0.8), then late period (0.3 – 0.7) and initial stage (0.2- 0.4) for all varieties of crop shown irrespective of water supply methods. The Kc for the total growth period ranged between 0.6 - 0.7. The high Kc at crop development to mid-season can be attributed to the high moisture condition that resulted in high evaporation from soil thus increasing total Etc. However, the Kc determined by Lysimeter were about 10% higher than the TDR during the late mid- period and the late period. The field determined Kc were slightly higher than those in the container grown crop due to container surface area lower than the ground area for planting of crop. The study confirmed that variety selection of kenaf, water supply method and their interaction does not significantly (p> 0.05) influenced crop coefficient.