The water resource is essential for food production, with priority optimize it today. In this sense, it is recommended to adopt and implement strategies that involve socio-economic and environmental aspects, such as ground cover. This feature provides benefits in soil and water conservation, reducing water consumption by culture. In irrigated agriculture, it is important to know the culture of evapotranspiration values (ETc) and crop coefficient (Kc) in local conditions. Thus, the aim of the present work to obtain the ETc and Kc for cowpea and corn crops in their different stages of development, at conditions of Boa Vista, Roraima, in soil with and without mulch. The ETc's were obtained by drainage lysimeter, while the reference evapotranspiration (ETo) was estimated by the Penman-Monteith methods and Jensen-Haise. It was found that the ground cover provided different and lower values of ETc's and Kc's for cowpea and maize, for the same variables in the bare soil. The values of ETc of cowpea in bare soil were 311.0mm over cycle; while the ETc for soil coverage was 260.4mm. For corn, the ETc observed in bare soil was 421.5 mm; whilst, ETc in soil coverage was 351.0mm. The Kc's cowpea grown in bare soil, according to phenological stages and the Penman-Monteith method, showed the values 0.42; 0.82; 1.60 and 0.79, while for cowpea grown in soil with cover was 0.30; 0.73; 1.46 and 0,56. The corn crop Kc's in bare soil, according to phenological stages and the Penman-Monteith method, were 0.40; 0.84; 1.59 and 0.81; while the corn crop Kc's for cover soil were observed values of 0.28; 0.64; 1.49 and 0.48.The ETo values by Jensen-Haise were higher than those estimated by Penman-Monteith, resulting in different values ETc and Kc for cowpea and maize.
Key words: Cover the soil, use of optimization of water, cowpea, maize.
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