EXPERIMENTAL AND EMPIRICAL ESTIMATION OF REFERENCE CROP EVAPOTRANSPIRATION

Abstract

Efficient and good water management strategy requires knowledge of crop water use of which reference evapotranspiration (RET) and crop curves are important inputs. Field experiments on bahama grass (cynodon dactylon) were conducted to estimate consumptive use using one weighing and four drainage microlysimeters. The grass was planted on 12m by 16m plot in which the microlysimeters were installed. The weighing microlysimeter was construction based on hydraulic principles using mercury-in-glass manometer. process. Its calibration was carried out using a static load process. Ten years of climatic data were used to estimate reference evapotranspiration using the following empirical methods; Penman (PEN), Jensen-Haise (J-H) , Blaney-Criddle(B-C) and Hargreaves (HG) models. The values obtained were compared to experimental values and were also subjected to standard statistical analysis. Crop curves were obtained from the ratio of lysimeter to reference evapotranspiration values (using empirical formulae). The crop curves were presented as a function of independent variables which were Days After Planting (DAP) and Thermal Time (T.T). For the crop curves based on DAP, the coefficient of determination (R2) and standard errors (SE) in the crop coefficients (K) estimates were 0.90 and 0.17 respectively for the J-H; 0.90 and 0.09 for PEN; 0.89 and 0.07 for B-C; 0.81 and 018 for HG. Based on TT method, R2 and SE for J-H were 0.90 and 0.18 respectively. 0.90 and 0.09 for PEN; 0.89 and 0.07 for B-C; and 0.81 and 0.18 for HG.