Root decomposition in silvopastures is influenced by grazing, fertility, and grass species

Authors: Ashworth, Amanda; ADAMS, TAYLOR - University Of Arkansas; Kharel, Tulsi; PHILIPP, DIRK - University Of Arkansas; Owens, Phillip; Sauer, Thomas

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2021
Publication Date: 7/12/2021
Publication URL: https://handle.nal.usda.gov/10113/7709343
Citation: Ashworth, A.J., Adams, T., Kharel, T.P., Philipp, D., Owens, P.R., Sauer, T.J. 2021. Root decomposition in silvopastures is influenced by grazing, fertility, and grass species. Agrosystems, Geosciences & Environment. 4(3). Article e20190. https://doi.org/10.1002/agg2.20190.
DOI: https://doi.org/10.1002/agg2.20190

Interpretive Summary: Decomposition of roots are a major source of fixed carbon in terrestrial ecosystems and are important aspects of ecosystem function, although decomposition rates are largely unknown, especially in silvopastoral systems. Silvopasture is the intentional combination of agroforestry and animals (either through grazing or hay management) and such systems can be a mechanism to mitigate risk by diversifying markets. To improve the current understanding of root turnover in silvopastures, researchers evaluated decomposition rates based on forage species (native and non-native), fertility (poultry litter and a control), soil moisture (wet and dry), and pasture management (grazed and an un-grazed control). This study found that here was greater root decomposition with native grass species and poultry litter applications, however, soil moisture affected root turnover to a lesser extent. This study contributes to the current understanding of complex interactions of grass species, soil moisture, fertility, and grazing, which controls productivity in silvopastoral systems.

Technical Abstract: Grass root production and subsequent decomposition is a major source of carbon (C) entering soils, although rates are largely unknown based on edaphic and management factors. Therefore, study objectives were to evaluate four explanatory variables including forage species (native and non-native), fertility (poultry litter and a control), soil moisture (udic and aquic) and pasture management (grazed and an un-grazed control) in order to evaluate driving mechanisms for root turnover and subsequent soil organic matter formation in silvopastoral systems. This study was conducted on a 4.25-ha silvopastoral system located in Fayetteville, AR from 2017-2018 using the root litter bag technique. Results indicate native grass root decomposition is accelerated relative to the non-native forage after 48 days of incubation based on root mass balance (initial vs. remaining), as well as the exponential decay function. This was likely owing to greater (P=0.05) 5 and 6 C sugars and more digestible root tissues of the native grass mix (10% and 11% greater hemicellulose and neutral detergent fiber, respectively), suggesting more favorable microbial food sources, which culminate in faster decomposition and potentially greater microbially derived organic matter. Overall, there was greater root sloughing and subsequent soil humus formation potential with native grass species and poultry litter applications, with soil moisture regimes affecting root sloughing to a lesser extent. This study contributes to the current understanding of complex interactions of grass species, soil moisture, fertility, and grazing, which controls primary productivity, as well as nutrient cycling and C sequestration in silvopastoral systems.