DEVELOPMENT AND EVALUATION OF A WEIGHABLE LYSIMETER TO DETERMINE CROP EVAPOTRANSPIRATION

Abstract

The development and evaluation of a weighable lysimeter to determine crop evapotranspiration is presented. A weighable lysimeter with a diameter of 31 cm and a depth of 37 cm was constructed. The lysimeter was evaluated by using it to estimate the crop evapotranspiration of waterleaf in Umudike in Southeastern Nigeria. The evapotranspiration (ETc) estimates by Pan Evapotranspiration, Blaney – Morin Nigeria, Blaney – Criddle and Modified Hargreaves – Samani methods were compared with the estimation of the weighable lysimeter which provides the most reasonable estimation of ETc and is one of the most reliable methods. The crop was irrigated daily and the daily data generated from the lysimeter were used to calculate the crop evapotranspiration (ETc Lysimeter) between the months of July/ August, 2013. Climatic data obtained for the same period were used to determine the crop evapotranspiration (ETc) using the Pan Evapotranspiration, Blaney – Morin Nigeria, Blaney – Criddle and Modified Hargreaves – Samani methods. The total crop evapotranspiration from the Lysimeter between July and August was 141.32 mm, while that of Pan Evapotranspiration (PE), Blaney – Morin Nigeria (BMN), Blaney – Criddle (BC) and Modified Hargreaves – Samani (MHS) were 147.72 mm, 136.81 mm, 131.61 mm and 132.52 mm, respectively. Test of hypothesis using z-Test indicates that there was no significant difference between the means of the ET by lysimeter and each of the other methods (Blaney Criddle, Pan Evapotranspiration, Modified Hargreaves Samani and Blaney Morin Nigeria) for a 5% level of significance as z-cal < z-critical for the growth period of 15 July to 18 August, 2013.