Crop coefficient and water requirement of prickly pear in the Agreste region of Alagoas state, Brazil

Prickly pear cultivation has played an important role in the Brazilian livestock farming, being used as forage for animals in the Northeast region, especially during the drying season, because it is an excellent source of water. Thus, the objective of this study was to estimate the crop coefficient and water requirement of prickly pear in the Agreste region of Alagoas state, Brazil. Prickly pear crop evapotranspiration (ETc) was determined using five drainage lysimeters, made of polyethylene with dimensions of 0.35 x 0.40 m (side and depth). Four soil layers were separated and put into the lysimeters in the opposite sequence, in order to maintain it as close as possible to the initial soil structure. The reference evapotranspiration (ETo) was estimated by the Penman-Monteith, Hargreaves-Samani and FAO-Radiation methods, using climatic data from the meteorological station of the Instituto Nacional de Meteorologia (INMET) in the city of Arapiraca, AL, Brazil. Crop coefficient (kc) was calculated by the ratio between ETc and ETo. The average kc obtained was 0.72, 0.84 and 0.48 for the Penman-Monteith, Hargreaves-Samani and FAO-Radiation methods, respectively. Keeping the soil under field capacity during the experimental period, the total crop evapotranspiration was 637.84 mm, with daily value equal to 4.22 mm d-1.