Abstract Accurate quantification of consumptive water requirements (ETc, evapotranspiration) of cropping systems is a critical prerequisite for sustainable irrigation water management applications. For applying the ETc for irrigation scheduling across soils and climates other than the location in which it was measured, it is also critical to develop crop coefficients (Kc) that link a reference crop evapotranspiration computed from local weather data to ETc. A systematic study for deriving Kc for cotton (Gossypium hirsutum L.) - representing its growth stages from planting to harvest - in humid climates is lacking in the literature. In this study, we used an eddy covariance (EC) method to quantify ETc from irrigated cotton (Gossypium hirsutum L.) in a 250 ha field with a Tunica clay soil, in 2017 and 2018. In the EC experiment, an open-path infrared gas analyzer and a sonic 3-D anemometer were deployed in the constant flux layer above the cotton canopy for collecting crop-canopy water flux data. Using the measured ETc, Kc were derived for alfalfa (Kcr) and grass (Kco) reference crop ET computed from weather data. Cotton cv. Delta Pine Land 1522 was planted in the first week of May and harvested in the second week of September in both the years. Lint yield was 1269 kg ha−1 in 2017 and 1569 kg ha−1 in 2018. Measured monthly averaged daily ETc ranged between 2.5 mm in May/September to 4 mm in July in 2017, and between 2.9 mm in May and 4.4 mm in August in 2018. Maximum daily ETc in 2017 and 2018 crop seasons were 5.6 and 6.7 mm, respectively. Seasonal total ETc was 367 mm and 439 mm (on average 402 mm), respectively. Alfalfa (ETr) and grass reference crop ET (ETo) computed were 664 and 546 mm, respectively. Averaged across the two years, average daily Kcr ranged between 0.45 in May to 0.80 in August, and Kco ranged from 0.54 in May and 0.99 in August. On average, seasonal ETr was 18 % more than ETo. Seasonal ETr and ETo were, respectively, 39 % and 22 % more than ETc. The Kc data developed will be useful for irrigation scheduling in cotton grown in similar climates and soils.

中文翻译：

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使用涡流协方差方法量化棉花（Gossypium hirsutum L.）的蒸散量和作物系数

摘要 准确量化种植系统的耗水需求（ETc，蒸发量）是可持续灌溉用水管理应用的关键先决条件。为了将 ETc 应用于除测量地点以外的其他土壤和气候的灌溉计划，开发作物系数 (Kc) 也很重要，该系数将根据当地天气数据计算的参考作物蒸散量与 ETc 联系起来。文献中缺乏用于推导棉花 (Gossypium hirsutum L.) Kc 的系统研究 - 代表其从种植到收获的生长阶段 - 在潮湿气候中。在这项研究中，我们在 2017 年和 2018 年使用涡度协方差 (EC) 方法量化了 250 公顷具有 Tunica 粘土土壤的灌溉棉花 (Gossypium hirsutum L.) 的 ETc。在 EC 实验中，在棉花冠层上方的恒定通量层中部署了一个开路红外气体分析仪和一个声波 3-D 风速计，用于收集作物冠层水通量数据。使用测量的 ETc，根据天气数据计算出苜蓿 (Kcr) 和草 (Kco) 参考作物 ET 的 Kc。棉花 cv。Delta Pine Land 1522 在这两年的 5 月第一周种植，在 9 月第二周收获。2017 年皮棉产量为 1269 kg ha-1，2018 年为 1569 kg ha-1。测得的月平均每日 ETc 介于 5 月/9 月的 2.5 毫米至 2017 年 7 月的 4 毫米之间，5 月的 2.9 毫米至 4.4 毫米之间2018 年 8 月。 2017 年和 2018 年作物季节的最大每日 ETc 分别为 5.6 和 6.7 毫米。季节性总 ETc 分别为 367 毫米和 439 毫米（平均 402 毫米）。计算的苜蓿 (ETr) 和草参考作物 ET (ETo) 分别为 664 和 546 毫米。两年平均，日均 Kcr 介于 5 月的 0.45 至 8 月的 0.80 之间，而 Kco 介于 5 月的 0.54 和 8 月的 0.99 之间。平均而言，季节性 ETr 比 ETo 高 18%。季节性 ETr 和 ETo 分别比 ETc 高 39% 和 22%。开发的 Kc 数据将有助于在类似气候和土壤中种植棉花的灌溉计划。