Direct measurement of crop evapo-transpiration is not possible without lysimeter study. It is estimated through crop-coefficient of the target crop and evapo-transpiration of reference crop. The crop coefficients of any crop that grown in North-Eastern region have not been determined so far. The present study was, therefore, planned to determine crop coefficients for two important crops in Meghalaya i.e. Capsicum (var. California Wonder) and Tomato (var. Tomato Megha-3) through lysimeter study with the following objectives: 1) to derive the crop coefficient of Capsicum and Tomato and 2) to find out the error factor of crop coefficients determined through Lysimeter and field water balance method.

Penman Monteith method (Monteith et al., 1990) was used for the estimation of reference evapo-transpiration (ET0). Real time weather data viz. Maximum & Minimum temperature, Relative Humidity, Wind Speed and Net Radiation was collected from the Automatic Weather Station installed in the experimental field. Eight other popular methods (Modified Pemman Method, Hargreaves equation, Samini Hargreaves equation, Thorthwaite equation, Solar Radiation Method, Net Radiation Method, Blaney Criddle Method, Radiation Method were also used for estimation ET0 and compared with Pemman Monteith Method. Paired t-test was used for comparison. Out of these, only Balney-Criddle method was found to be statistically similar to Penman Monteith method. A mini UMS-GmBH Lysimeter was installed in the CPGS experimental farm. Water was regularly applied based on the daily value of ET0 for this location. The change of the weight due to loss and gain of water in the lysimeter was recorded through Load cell. Water balance method was adopted to calculate the ETc on daily basis which were then used to calculate the kc values as the ratio of ETc and ET0.

The values of ETc as measured and calculated through Lysimeter was varying from 1.11 mm sto 3.12 mm per day. The highest kc values was obtained during the period of maximum vegetative growth (8th WAT). The evapotranspiration for capsicum took place from the 1st WAT which gradually increased till the crop entered into reproductive stage. For capsicum it was found that kc ini, kc mid and kc end values were 0.33, 0.64 and 0.30, respectively. These values are however considerably lower as compared to the other similar crops as given in FAO Irrigation and Drainage Paper 56 (Allen et al. 1998). During tomato season the highest value of ET0 was found in the last week of the crop period and ET0 values gradually increased from the first week of trasnplanting as the temperture increased. The kc values of tomato were ranging from 0.51 mm to 1.07mm. The highest value of kc was estimated in the 11th week of after transplanting. For tomato it was found that kc ini, kc mid and kc end values were 0.51, 1.07 and 0.78, respectively. Crop coefficients for both the crops were also determined through field water balance. These values were compared with the values obtained through lysimeter studies. The kc values as obtained through field water balance were found to deviate from the values obtained from lysimeter by 18.75-63.33% in both the season.