Factors affecting sugar accumulation and fluxes in warm- and cool-season forages grown in a silvopastoral system

Authors: NIYIGENA, VALENS - University Of Arkansas; Ashworth, Amanda; Nieman, Christine; ACHARYA, MOHAN - University Of Arkansas; COFFEY, KENNETH - University Of Arkansas; PHILLIPP, DIRK - University Of Arkansas; MEADORS, LILLIAN - University Of Arkansas; Sauer, Thomas

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2021
Publication Date: 2/16/2021
Citation: Niyigena, V., Ashworth, A.J., Nieman, C.C., Acharya, M., Coffey, K.P., Phillipp, D., Meadors, L., Sauer, T.J. 2021. Factors affecting sugar accumulation and fluxes in warm- and cool-season forages grown in a silvopastoral system. Agronomy. https://doi.org/10.3390/agronomy11020354.
DOI: https://doi.org/10.3390/agronomy11020354

Interpretive Summary: Forages, or grasses in pastures, constitute a large part of ruminant diets throughout the world. Forage management, fertility in particular, is important for increasing forage yield and quality. Environmental conditions can also affect forage quality, especially the accumulation of water-soluble carbohydrates, or forage sugar content. Integrating cool and warm season grasses in an agroforestry system is advantageous to farmers due to their contrast in seasonal changes and different adaptability to a wide range of temperature and shade conditions. Typically, important carbohydrates, including forage sugars, are not measured in grazing experiments because methods are time-consuming and costly, but can help explain animal grazing preference. Thus, there is little information on variation in seasonal and daily forage sugar accumulation in cool-season and warm-season forages, particularly with or without poultry litter fertilization. Therefore, a group of scientists conducted a study to evaluate i) differences in sugar accumulation between forage species and how fertility (poultry litter) changes throughout the day, impact forage sugar content; and, ii) assess linkages between forage nutrient quality parameters and sugar concentration. The results indicated that cool-season accumulated more sugar than warm-season forages, and harvesting forage in late hours of the day increased sugar levels compared to the morning (8:00 am). Therefore, harvesting forages for hay or bailage late in the day may improve palatability and quality. Forage sugar content was linked to digestibility and nutrient content and these estimates may be used as a proxy for this time-consuming analysis. This study contributes to further understand of factors affecting sugar and nutrients content in forage and different strategies to improve the productivity in integrated agroforestry and animal production systems.

Technical Abstract: Forage management and environmental conditions affect water soluble carbohydrate (WSC) storage, and, in turn, influence ruminant forage utilization in agroforestry systems. The objective was to determine effects of four dependent variables: forage species {(non-native, C3 [orchardgrass (Dactylis glomerata L.)] and native C4 mix [8:1:1 big bluestem (Andropogon gerardii Vitman), little bluestem (Schizachyrium scoparium Michx. Nash) and indiangrass (Sorghastrum nutans L.)]}; fertility (poultry litter and a control); forage sampling date (mid-May, late-May, early-June, mid-June, and late-June); and, hour of day (0800, 1100, 1400, and 1700), on forage WSC accumulation and quality in a silvopasture system from May to July, 2018 and 2019. Overall, concentrations of WSC (g kg DM-1) were greater (P < 0.01) in C3 compared to C4 forages, with poultry litter not impacting WSC accumulation. In relation to sampling date and hour of day, WSC was greatest (P = 0.05) mid-June, with the lowest (P = 0.05) WSC concentration observed at 0800 compared to 1100, 1400, and 1700, regardless of photosynthetic pathway. Therefore, harvesting forage later in the day resulted in greater WSC in both forage groups. There were positive correlations (P = 0.05; R = 0.52) between WSC and forage nutrient concentrations (K, Mn, P), yield, ash, and hour of day. A stepwise regression model indicated acid detergent fiber, ash, and forage P content were best predictors (R2= 0.85, P = 0.05) of forage WSC. These results may be useful in future studies aimed at explaining diurnal cattle grazing preference and optimum forage harvest timing in silvopastoral systems.