Water requirement and crop coefficients of sorghum in Apodi Plateau

ABSTRACT Sorghum is of significant economic importance for Northeastern Brazil, since it exhibits high growth rates in regions with irregular rainfall distribution and high temperatures, and is an alternative to corn, which has greater water requirements. Despite being a traditional crop in the region, there are few studies on irrigation management in the Apodi plateau. The aim of this study was to determine the evapotranspiration of the crop and the crop coefficient (Kc) for the different stages of sorghum growth in two cycles, and establish the relationship between the Kc and the normalized difference vegetation index (NDVI) obtained by radiometry. Two weighing lysimeters were used to estimate crop evapotranspiration (ETc). Reference evapotranspiration (ETo) was estimated by the Penman-Monteith method (FAO) and the crop coefficient determined using two methodologies: simple Kc and dual Kc. Total crop evapotranspiration in the two cycles was 452 and 557 mm. The ETc value was 23% higher in the second cycle compared to the first. The maximum Kc values for the first and second cycles were 1.21 and 1.35, respectively, using the dual Kc methodology. The linear relationship found between the Kc values and the NDVI allows monitoring and estimating the water requirements of the crop.

摘要：高粱对巴西东北部地区具有重要经济价值，因其在降雨分布不均、高温环境下生长表现优异，且可作为需水量更高的玉米的替代作物。尽管高粱已是当地传统栽培作物，但针对阿波迪高原（Apodi plateau）的灌溉管理相关研究仍较为稀缺。本研究旨在明确两个种植周期内，高粱不同生育阶段的作物蒸散量（crop evapotranspiration, ETc）与作物系数（crop coefficient, Kc），并建立作物系数与通过辐射测量法获取的归一化植被指数（Normalized Difference Vegetation Index, NDVI）之间的关联。本研究采用两台称重式蒸渗仪估算作物蒸散量；参考蒸散量（reference evapotranspiration, ETo）通过FAO推荐的彭曼-蒙特斯（Penman-Monteith）方法进行估算，作物系数则通过两种方法确定：单一作物系数法与双作物系数法。两个种植周期的总作物蒸散量分别为452 mm与557 mm，第二个周期的ETc较第一个周期高出23%。采用双作物系数法计算得到的第一、第二周期的最大Kc值分别为1.21与1.35。本研究发现Kc与NDVI之间存在线性相关关系，该关系可用于监测并估算高粱的需水量。