The expansion of sugarcane crop to regions with lower water supply in Brazil has increased the importance of correct estimation of crop water requirements. Currently, the irrigation management is generally done using the crop coefficient (Kc) based on the FAO 56 bulletin. Kc is used to determine the potential water demand of the crop for a given period of time and is considered constant for each crop stage. However, some recent studies have shown that Kc can be significantly variable under different evapotranspiration (ETo) rates. This paper aimed to analyse sugarcane water consumption at different scales: plant (sap flow measurements by energy balance method); canopy (Bowen ratio energy balance method); and plant–atmosphere coupling (infrared gas analyser) to reduce the uncertainties on the irrigation practices. Measurements were taken at two experimental sites, where a modern Brazilian cultivar CTC 12 was grown under drip irrigation and an old main Brazilian cultivar (RB867515) was grown under sprinkler irrigation by a central pivot. The mean crop evapotranspiration (ETc) values by the Bowen ratio energy balance method were 2.92 and 3.68 mm d−1 for RB867515 and CTC 12, respectively, resulting in a mean Kc of 0.99 at the full vegetative growth stage. Kc values were dependent on ETo and varied between 0.2 and 1.7 for both cultivars. This occurred in a crop coupled to the atmosphere (Ω = 0.37) and was the same found in other coupled crops such as coffee and citrus. In conclusion, the sugarcane Kc for southeast Brazil presented temporal variability due to coupling conditions according to reference evapotranspiration, and this should be considered in irrigation management.

中文翻译：

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热带条件下解耦因子对甘蔗作物水分利用的作用

巴西将甘蔗作物扩展到供水量较低的地区，这增加了正确估计作物需水量的重要性。目前，灌溉管理一般采用作物系数（氯化钾) 基于粮农组织 56 号公告。氯化钾用于确定给定时间段内作物的潜在需水量，并且对于每个作物阶段被认为是恒定的。然而，最近的一些研究表明，氯化钾在不同的蒸散量下可以显着变化（电子托) 费率。本文旨在分析不同尺度的甘蔗耗水量：植物（通过能量平衡法测量汁液流量）；冠层（鲍文比能量平衡法）；和植物-大气耦合（红外气体分析仪），以减少灌溉实践的不确定性。在两个实验地点进行了测量，其中一个现代巴西品种 CTC 12 在滴灌下种植，一个古老的巴西主要品种 (RB867515) 在中央枢轴喷灌下种植。平均作物蒸散量 (等等) 鲍文比能量平衡法的值为 2.92 和 3.68 mm d-1分别用于 RB867515 和 CTC 12，得出平均值氯化钾在完全营养生长阶段为 0.99。氯化钾值取决于电子托两个品种在 0.2 和 1.7 之间变化。这发生在与大气耦合的作物中（Ω = 0.37），在咖啡和柑橘等其他耦合作物中发现的情况相同。总之，甘蔗氯化钾根据参考蒸散量，巴西东南部由于耦合条件而呈现出时间变化，这应在灌溉管理中加以考虑。