Determination of Actual Evapotranspiration and Crop Coefficient for Hot Pepper ( Capsicum annum L.) Inside Plastic Houses

Naem Mazahrih, INCARTT

Abstract
The limited water resources in arid and semi-arid regions, such as Jordan, are considered the greatest challenge facing agricultural development in the country. In addition, high population growth rate in Jordan increases pressure on the available water resources.
About 68% of the available water resources in Jordan is allocated for irrigated agriculture. Decision-makers have to look for methods to reduce water consumption in this sector through developing appropriate management to improve water-use efficiency. For these purposes, information about actual and potential plant water requirement under specified condition is necessary. Irrigation scheduling aiming for maximum crop yield production is determined based on crop transpiration in the field with soil moisture maintained at an optimal condition. The subject of evapotranspiration and crop water needs has been widely investigated by many researchers such as Doorenbos and Pruitt (1975), Jensen et. al., (1990), and Allen et. al. (1994). The accuracy of ET estimates depends primarily on the ability of the equations being used to describe the physical laws governing the processes and the accuracy of the meteorological and cropping data. (Jensen et al., 1990).
Evapotranspiration is a necessary parameter for proper irrigation scheduling and for establishing the duties and the dimension of the irrigation system. It allows better water management, by adjusting the volume and frequency of irrigation to meet crop requirements depending on the soil characteristics. Furthermore, it is a crucial factor on which irrigation management decisions are based. Managing limited water supplies as well as designing and evaluating irrigation systems, are all dependent on ET data. Studies concerning ET for alfalfa and grass have special importance since alfalfa and grass are being used as reference crops for reference evapotranspiration estimation (Allen et. al.,1994). Reference crop ET is the rate at which water will be evaporated from given plant and soil surfaces, with the surface specified, if water is readily available within the plant root zone. (Wright, 1996).