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

ABSTRACT 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.

摘要：梨果仙人掌（Prickly pear）种植在巴西畜牧业中发挥着重要作用，该国东北部地区常将其作为牲畜饲料，尤其在旱季时节，因其优异的水源特性而被广泛应用。本研究旨在估算巴西阿拉戈斯州阿格雷斯特地区梨果仙人掌的作物系数与需水量。本研究采用5个尺寸为0.35×0.40 m（边长与深度）的聚乙烯材质排水式蒸渗仪，测定梨果仙人掌的作物蒸散量（ETc）。将4层土壤按与原土层相反的顺序装填至蒸渗仪中，以尽可能维持初始土壤结构。参考蒸散量（ETo）分别通过彭曼-蒙特斯（Penman-Monteith）、哈格里夫斯-萨马尼（Hargreaves-Samani）及FAO辐射法（FAO-Radiation）进行估算，所用气象数据来源于巴西阿拉戈斯州阿拉皮拉卡市国家气象研究所（Instituto Nacional de Meteorologia, INMET）的气象站。作物系数（kc）通过ETc与ETo的比值计算得到，彭曼-蒙特斯法、哈格里夫斯-萨马尼法与FAO辐射法对应的平均作物系数分别为0.72、0.84与0.48。实验期间将土壤维持在田间持水量状态，总作物蒸散量为637.84 mm，日均值为4.22 mm·d⁻¹。