Forage Nutritive Value and Herbage Mass Relationship of Four Warm‐Season Grasses

Abstract

To provide animals with high quality forage, practical methods are needed to estimate nutritive value to optimize harvest timing. The objective of this study was to develop such models to estimate warm‐season forage nutritive value in the southeastern United States. The experiment was conducted at the University of Tennessee Plateau AgResearch and Education Center in Crossville, TN, from 2013 to 2015. Four warm‐season forages were evaluated separately, each in a randomized complete block design and, each for 2 yr: switchgrass [Panicum virgatum (L.) ‘Alamo’‐ a lowland variety from Texas with high forage quality and biomass production], sorghum–sudangrass [Sorghum bicolor (L.) Moench ×Sorghum sudanese (P.) Stapf, ‘FSG208BMR’‐ a vigorous, drought tolerant variety with improved digestibility], bermudagrass [Cynodon dactylon (L.) Pers. ‘Vaughn's # 1’‐ a cold tolerant, upright variety] and crabgrass [Digitaria sanguinalis (L.) ‘Quick‐N‐Big’‐ a fast germinating variety with a quick growth rate]. Monthly initiations were established based on cutting timing, in which a single cut was made at the beginning of the assigned month with nutritive value and herbage mass (HM) of the regrowth observed in the following weeks. Results determined that HM was influential on crude protein (CP) and neutral detergent fiber digestibility (NDFD) for all species tested, except crabgrass. Based on differences in nutritive value and morphological composition by maturity, as well as the successful prediction of CP and NDFD from HM through linear regression, it was determined that June and July initiations are preferred for switchgrass and bermudagrass, while July initiation is preferable for sorghum–sudangrass. Nutritive value was analyzed over time for four warm‐season forage grasses. Herbage mass accumulation was estimated for each management strategy. Nutritive value can be predicted from herbage mass for most species. Early initiation cuts are preferable to produce forage of high value in all cases.