Water-Use Efficiency of Forage Crops in the Southeastern United States

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. &lsquo
Red River&rsquo
), switchgrass (Panicum virgatum cv. &lsquo
Alamo&rsquo
), big bluestem (Andropogon gerardii cv. &lsquo
OZ-70&rsquo
), indiangrass (Sorghastum nutans cv. &lsquo
Rumsey&rsquo
), eastern gamagrass (Tripsacum dactyloides cv. &lsquo
Pete&rsquo
), bermudagrass (Cynodon dactylon cv. &lsquo
Vaughn&rsquo
s #1&rsquo
), sorghum-sudangrass (Sorghum bicolor (L.) &times
Sorghum sudanese (P.) cv. &lsquo
Greengrazer&rsquo
), 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.