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.

Influence of Height‐Based Management on Forage Nutritive Value of Four Warm‐Season Forage Grasses

“…The corresponding regression equations could be used to estimate nutritive value from herbage samples without costly laboratory analysis. These results correspond to the findings of Gelley et al (2016).…”

“…In most cases, nutritive value decreased from first to last cut. These findings correspond to the patterns observed in many warm‐ and cool‐season grass studies where nutritive value is highest in young herbage regrowth and declines with maturity (Perry and Baltensperger, 1979; Bosworth et al, 1980; Belesky et al, 1991; Iptas and Brohi, 2003; Nave et al, 2013; Gelley et al, 2016). Correlations between morphological components and nutritive value variables indicated a positive relationship between proportion of lamina and CP content for all species ranging from 0.6967 to 0.8829, which allows us to tie morphology to a key component in determining forage nutritive value.…”

“…Results presented by Gelley et al (2016) documented the influence of using the calendar year to dictate harvest and the influence of that management system on forage nutritive value and herbage mass for these species using similar methods. Treatments were a single cut made on varying dates to the sward without a reoccurring harvest, after which changes in nutritive value and herbage mass accumulation (HMA) were mapped to detect predictable patterns of change.…”

“…This study was conducted at the Plateau AgResearch and Education Center in Crossville, TN (36° 0′ N, 85° 7′ W, 580‐m elevation) from June to September 2013 to 2015 (simultaneously with the study of Gelley et al, 2016). Experimental units were 9.8‐ × 14.8‐ft plots arranged in a randomized complete block design with four replications.…”

“…In all species, the observed ranges of CP, ADF, NDF, and NDFD were comparable to those recorded in other experiments (Bosworth et al, 1980; Griffin and Jung, 1983; Vona et al, 1984; Teutsch et al, 2005; Starks et. al., 2006; Beck et al, 2015 Burns and Fisher, 2008; Temu et al, 2014; Gelley et al, 2016). It was expected that nutritive value would differ among cuts of each species, with earlier cuts producing herbage with higher nutritive value than later cuts when the samples were compared at similar stages of maturity (weeks postcutting) (Tables 2, 3, 4, and 5).…”