Soil CO2 evolution is driven by forage species, soil moisture, grazing pressure, poultry litter fertilization, and seasonality in silvopastures

Authors: Adams, Taylor; Ashworth, Amanda; Sauer, Thomas

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2021
Publication Date: 6/7/2021
Citation: Adams, T.C., Ashworth, A.J., Sauer, T.J. 2021. Soil CO2 evolution is driven by forage species, soil moisture, grazing pressure, poultry litter fertilization, and seasonality in silvopastures. Agrosystems, Geosciences & Environment. 4(2). Article e20179. https://doi.org/10.1002/agg2.20179.
DOI: https://doi.org/10.1002/agg2.20179

Interpretive Summary: Increased protein demands across the world has led to a need to characterize livestock production practices and their role in greenhouse gas emissions, such as CO2. Silvopastures, which combine tree and animal production in one area, may have the potential to store carbon dioxide that is generated by grazing livestock. Furthermore, management choices within these silvopastoral systems can affect a producer’s ability to sustain yields, while focusing on short- and long-term sustainability. An important aspect of the carbon cycle is carbon dioxide release from the soil via plant roots and microbial activity. In a silvopasture in Arkansas, carbon dioxide was measured in grazed and ungrazed, fertilized with poultry litter and unfertilized, and wet and dry environments for two different forage mixes. The greatest carbon dioxide was generated from the fertilized native mix of grasses, most likely due to greater microbial activity in the root zone of native grasses. Additionally, carbon dioxide release from fertilized and ungrazed areas was greater than fertilized grazed and all unfertilized areas. Carbon dioxide released was also related to soil temperature and moisture content. With these results, producers within this region will be better assisted in making sustainable management decisions.

Technical Abstract: Carbon cycling and soil gas exchange are complex yet important drivers of sustainability, especially in silvopastures, which have the ability to store large amounts of C. Although, it is largely unknown how site-specific variables, including edaphic factors, vegetation type, topography, and management affect soil CO2 flux in silvopastures. Therefore, this study aimed to elucidate CO2 flux differences in a silvopastoral system in Northwest Arkansas based on soil moisture (udic and aquic), forage species (native grass mix and orchardgrass [Dactylis glomerata L.], fertility (poultry litter and a control), and grazing pressure (grazed and an un-grazed). Temperature and volumetric water content (VWC) were measured simultaneous with flux measurements from 2018- 2019 during summer grazing. Averaged across years, fluxes were at least 20% greater (P = 0.05) in the native mix fertilized with poultry litter than under the unfertilized native mix and fertilized or unfertilized orchardgrass, likely owing to greater microbial diversity and overall activity in the rhizosphere of poultry litter amended native grass species. Across years, CO2 flux was 7% greater (P = 0.05) in the fertilized ungrazed areas, and 7% lower (P = 0.05) in the unfertilized ungrazed areas, compared to both the fertilized and unfertilized grazed areas. Carbon dioxide flux was correlated (P = 0.05) with sampling date, soil temperature, and VWC. Study results increase the understanding of C dynamics in diverse silvopasture systems and guide producers in their selection of forage species and nutrient sources when designing silvopastoral systems for enhanced regional sustainability.