Partitioning of Forage Mass and Nutritive Value in Sunn Hemp Leaf and Stem Components

Abstract

Sunn hemp (SH; Crotalaria juncea L.) is a fast-growing, annual, warm-season tropical legume that could complement less productive cool-season forages such as tall fescue during summer. Little is known about seasonal forage mass and nutritive value partitioning in SH plant components when SH is managed for forage. We determined partitioning of forage mass and nutritive value (crude protein (CP), in vitro true digestibility (IVTD), neutral detergent fiber (NDF), acid detergent fiber (ADF), and neutral detergent fiber digestibility (NDFD)) concentrations in SH leaves and stems harvested 35, 45, and 55 days after planting (DAP) at Bradford Research Center, Columbia, MO, in a 2-year field study. Leaf and stem mass increased with increasing DAP and was greatest ( P ≤ 0.05 ) at 55 DAP followed by 45 and 35 DAP. Stems contributed most to the total forage mass beyond 45 DAP. Across years, CP was greatest ( P ≤ 0.05 ) in leaves (281 g kg−1 DM) and lowest for stems (81 g kg−1 DM) at 55 DAP. The lowest NDF ( P ≤ 0.05 ) was observed in leaves (251 g kg−1 DM) and stems (585 g kg−1 DM) at 35 DAP. Acid detergent fiber was lowest ( P ≤ 0.05 ) for SH leaves (178 g kg−1 DM) and stems (484 g kg−1 DM) at 35 DAP. Digestibility of leaves was greater than that of stems and generally decreased with maturity. The nutritive value of leaves was consistently greater than that of stems and decreased with maturity, except for CP of leaves, which was maintained throughout the season. Results suggested that SH leaves can maintain forage mass and greater quality than its stem throughout the growing season.

Identifying optimal early‐season harvest timing in annual fall forages

“…In contrast, SP concentrations in sunn hemp were greatest at the first harvest and declined with successive harvesting. These results are congruent with previous research, as sunn hemp has previously been shown to have CP concentrations >20% (Eberle & Shortnacy, 2021; Lepcha & Naumann, 2021). Sunn hemp's decline in SP was likely related to a decrease in leaf/stem ratio as the plants grew, as reported by Lepcha et al.…”

Characterization of Green Manure Sunn Hemp Crop Silage Prepared with Additives: Aerobic Instability, Nitrogen Value, and In Vitro Rumen Methane Production

“…Studies of the chemical compositions, N fractions, and in vitro digestibility have been recommended to elucidate the nutritive values of forage for ruminant feeding regimes [34,35]. The analyzed CP, NDF, and ADF levels for the GMSH crop were consistent with those for SH plant materials reported by Lepcha et al [36]. The present study was the first report of N fractions determined in GMSH crop.…”

“…When applying fertilizers, SH can be cut after 35 days of planning for receiving CP crop [36]. For late cuts, the results show a very high ADL (95 g/kg DM), which probably suppresses fiber utilization in livestock production.…”

Seeding and Harvesting Times and Climate Conditions Are Important for Improving Nitrogen and Fiber Contents of Green Manure Sunn Hemp

“…Additionally, they reported that the proportion of stems in the DMY had increased from around half at 6 weeks to over two-thirds at 9 weeks after planting. Lepcha and Naumann [28] reconfirmed these differences in ADF and NDF between the leaves and stems. They pointed out that the fiber concentration variation because of the cumulative degree days is associated with the proportions of structural tissues, e.g., xylem and sclerenchyma.…”

“…The whole plant TN concentration depends on the leaf/stem ratio in some legumes due to the concentrations of TN in leaves and stems differing [26]. Mansoer et al [27] and Lepcha and Naumann [28] also reported differences in sunn hemp TN concentrations between leaves and stems. In addition, Mansoer et al [27] reported a significant TN decrease from 3 to 6 weeks after planting and a slight TN decrease from 6 to 9 weeks after planting in both leaves and stems.…”