Preparing agricultural producers to cope with volatile weather changes, specifically drought, requires a better understanding of forage water-use efficiency (WUE) potentials. Options to improve farm resiliency to drought may include the use of C₄ annual and perennial forages, which have greater production efficiency during drought than commonly used C₃ forages. Our objective was to measure WUE through real-time gas exchange measurements of photosynthesis and transpiration in (1) a greenhouse study and (2) under field-grazing conditions. Growth parameters, instantaneous water use efficiency (iWUE), and mass-based WUE (mWUE) data were collected under greenhouse conditions in Study 1 for the following species: crabgrass (Digitaria sanguinalis cv. ‘Red River’), switchgrass (Panicum virgatum cv. ‘Alamo’), big bluestem (Andropogon gerardii cv. ‘OZ-70’), indiangrass (Sorghastum nutans cv. ‘Rumsey’), eastern gamagrass (Tripsacum dactyloides cv. ‘Pete’), bermudagrass (Cynodon dactylon cv. ‘Vaughn’s #1’), sorghum-sudangrass (Sorghum bicolor (L.) × Sorghum sudanese (P.) cv. ‘Greengrazer’), and tall fescue (Schedonorus arundinaceus (Schreb.) Dumort). Study 2 occurred from 2014 to 2016, and evaluated iWUE of crabgrass, switchgrass, bermudagrass, eastern gamagrass, and a big bluestem/indiangrass mix under field conditions. Overall, in situ iWUE of crabgrass, switchgrass, eastern gamagrass, and bermudagrass did not differ, while iWUE of the big bluestem/indiangrass was less than switchgrass and crabgrass, an advantage for these species if the standardized precipitation index drops below zero. Bermudagrass, switchgrass, sorghum-sudangrass, pearl millet, and indiangrass had comparable mWUE values under greenhouse-simulated drought. These results will aid in the development of forage species recommendations for mitigating drought and improving resiliency.

中文翻译：

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美国东南部饲草作物的水分利用效率

要使农业生产者应对不断变化的天气变化，特别是干旱，就需要对草料的用水效率（WUE）的潜力有更好的了解。改善农场抗旱能力的选择可能包括使用C ₄年度和多年生饲草，干旱期间的生产效率要高于常用的C ₃饲草。我们的目标是在（1）温室研究和（2）在田间放牧条件下通过光合作用和蒸腾作用的实时气体交换测量来测量WUE。在研究1的温室条件下，收集了以下物种的生长参数，瞬时水分利用效率（iWUE）和基于质量的WUE（mWUE）数据：马尾草（Digitaria sanguinalis简历。'Red River'），柳枝（（Panicum virgatum cv.'Alamo '），大蓝茎（Andropogon gerardii cv.'OZ-70'），Indiangrass（Sorghastum nutans cv.'Rumsey '），东部gamagrass（Tripsacum dactyloides cv。' Pete'），百慕大草（Cynodon dactylon cv.'Vaughn 's＃1'），高粱-sudangrass（Sorghum bicolor（L.）× Sorghum sudanese（P.）cv.'Greengrazer '）和高羊茅（Schedonorus arundinaceus（ ）Dumort）。研究2于2014年至2016年进行，并在田间条件下评估了马尾草，柳枝,、百慕大草，东部蒲甘草和大型蓝茎/印度草混合的iWUE。总体而言，马草，柳枝,、东部蒲苇和百慕大草的原位iWUE没有差异，而大蓝茎/印度草的iWUE则比柳枝and和马草的iWUE小，如果标准化降水指数降至零以下，则对这些物种来说是一个优势。在温室模拟干旱条件下，百慕大草，柳枝,、高粱-苏丹草，珍珠粟和印度草具有相当的mWUE值。这些结果将有助于为减少干旱和提高复原力而建议草料种类。