Cover crops are widely planted in orchards for a variety of reasons. These include suppressing soil erosion, nutrient cycling, phytosanitary purposes, general orchard aesthetics etc. However, there is need to balance these benefits against use of scarce resources such as water and nutrients. Currently no information exists on how different cover crop species use water in orchards and how they cope with drought stress. The aim of this study was therefore to compare the transpiration dynamics of various cover crop types in order to identify species with conservative water use rates. Studied species included: 1) two exotic legumes i.e. Lupine (Lupinus albus L.), and Common vetch (Vicia sativa), 2) three exotic grasses i.e. Tall fescue (Festuca arundinacea), Rye grass (Lolium perenne), and Kikuyu grass (Pennisetum clandestium) and; 3) grasses that are indigenous to sub-Saharan Africa i.e. African Lovegrass (Eragrostis capensis) and Rhodes grass (Chloris gayana). The crops were planted in pots under controlled greenhouse conditions. Transpiration rates were quantified using miniature stem heat balance sap flow gauges and by manual weighing. Drought stress was imposed by withholding irrigation at selected intervals and the responses were quantified through changes in the water relations of the plants. The study showed that exotic legumes had the highest daily water use which peaked at about 2.4 L per square metre of leaf area per day, followed by exotic grasses at 1.5–2.0 L/m²/d. The indigenous grasses used the least water ranging from 0.8 to 1.2 L/m²/d. The indigenous grasses largely displayed an isohydric response to drought stress by maintaining their leaf water status with increasing soil water deficit. The exotic species, on the other hand, showed risk taking behaviour (anisohydry) wherein both the transpiration and leaf water status decreased sharply as drought stress increased. Consequently, some exotic species failed to recover when stress was relieved. From a water use perspective, this study demonstrates that indigenous grass species are more appropriate as cover crops in South African orchards because of their low transpiration rates and the ability to cope with extended periods of water deficit.

由于各种原因，覆盖作物被广泛种植在果园中。这些包括抑制土壤侵蚀、养分循环、植物检疫目的、一般果园美学等。然而，需要平衡这些好处与使用稀缺资源（如水和养分）。目前没有关于不同覆盖作物物种如何在果园中用水以及它们如何应对干旱压力的信息。因此，本研究的目的是比较各种覆盖作物类型的蒸腾动态，以识别具有保守用水率的物种。研究的物种包括：1）二异国豆类即羽扇豆（白羽扇豆大号。），和普通的野豌豆（豌豆），2）3个外来草即高羊茅（Festuca arundinacea )、黑麦草 ( Lolium perenne ) 和 Kikuyu 草 ( Pennisetum clandestium ) 和；3) 撒哈拉以南非洲本土的草，即非洲相思草 ( Eragrostis capensis ) 和罗得草 ( Chloris gayana)）。在受控温室条件下将作物种植在盆中。蒸腾速率使用微型茎热平衡液流计和手动称重进行量化。干旱胁迫是通过在选定的时间间隔停止灌溉来施加的，并且通过植物水分关系的变化来量化响应。研究表明，外来豆科植物的每日用水量最高，达到每天每平方米叶面积约 2.4 L 的峰值，其次是外来草类，为 1.5-2.0 L/m ² /d。土著草用水最少，范围从 0.8 到 1.2 L/m ²/d。通过在土壤水分亏缺的情况下保持叶片水分状态，本地草在很大程度上表现出对干旱胁迫的等水反应。另一方面，外来物种表现出冒险行为（缺水），其中随着干旱胁迫的增加，蒸腾作用和叶水状态都急剧下降。因此，当压力得到缓解时，一些外来物种未能恢复。从用水的角度来看，这项研究表明，本土草种更适合作为南非果园的覆盖作物，因为它们的蒸腾率低，并且能够应对长期缺水。