Grazing and climate effects on soil organic carbon concentration and particle-size association in northern grasslands

Abstract

Grasslands cover more than 40% of the terrestrial surface of Earth and provide a range of ecological goods and services, including serving as one of the largest reservoirs for terrestrial carbon. An understanding of how livestock grazing, influences grassland soil organic carbon (SOC), including its concentration, vertical distribution and association among soil-particle sizes is unclear. We quantified SOC concentrations in the upper 30 cm of mineral soil, together with SOC particle-size association, within 108 pairs of long-term grazed and non-grazed grassland study sites spanning six distinct climate subregions across a 5.7 M ha area of Alberta, Canada. Moderate grazing enhanced SOC concentration by 12% in the upper 15 cm of soil. Moreover, SOC concentrations in mineral layers were associated with regional climate, such that SOC increased from dry to mesic subregions. Our results also indicate that C concentrations in each of 2000–250, 250–53, < 53 μm soil particle-size fractions were consistent with total SOC concentrations, increasing from semi-arid to more mesic subregions. We conclude that long-term livestock grazing may enhance SOC concentrations in shallow mineral soil and affirm that climate rather than grazing is the key modulator of soil C storage across northern grasslands.

Grassland Management Affects Delivery of Regulating and Supporting Ecosystem Services

“…In moist, warm climates and those populated by C 4 grasses, soil C increased for all grazing intensities, but in arid regions, only low or moderate intensities increased SOC, indicating site specificity in SOC response to grazing intensity. Greater soil C accumulation in higher rainfall environments has been cited by others (Chen et al, 2018;Hewins et al, 2018) and was attributed to greater species richness and belowground biomass in mesic than dry environments (Chen et al, 2018). A synthesis of 47 experimental contrasts in 17 studies showed that grazing effects were variable and highly context dependent, a function of climate, soil, forage species, and grazing intensity (McSherry and Ritchie, 2013).…”

“…A global review and meta-analysis of 83 studies of extensively managed grasslands found an interaction of grazing intensity and regional climate for soil C accumulation (Abdalla et al, 2018). Greater soil C accumulation in higher rainfall environments has been cited by others (Chen et al, 2018;Hewins et al, 2018) and was attributed to greater species richness and belowground biomass in mesic than dry environments (Chen et al, 2018). Greater soil C accumulation in higher rainfall environments has been cited by others (Chen et al, 2018;Hewins et al, 2018) and was attributed to greater species richness and belowground biomass in mesic than dry environments (Chen et al, 2018).…”

“…Differences were attributed to faster turnover of plant material, a higher proportion of nutrients cycling in excreta, and greater physical disruption of soil at the high stocking rate. Across a range of sites in Alberta, Canada, moderate grazing enhanced SOC concentration in the upper 15 cm of soil by 12% vs. nongrazing (Hewins et al, 2018). In subtropical Florida, the effects of cattle grazing and exclusion on net ecosystem CO 2 and CH 4 exchange were investigated using eddy covariance (Gomez-Casanovas et al, 2018).…”

Estimating soil organic carbon stocks under commercial forestry using topo-climate variables in KwaZulu-Natal, South Africa

“…14 Climatic variables such as rainfall and temperature can also be derived from WorldClim database (global climate layers) at a spatial resolution of about 1 km 2 . 23 The use of DEMs derived from satellite missions such as Light Detection and Ranging (LiDAR) and Shuttle Radar Topography Mission (SRTM) for terrain analysis has become particularly popular due to their relatively high resolutions. 24 Hence, the development of models with SRTM and LiDAR-derived topographic metrics in concert with selected bioclimatic variables could benefit studies characterised by limited observations and can be used to produce continuous SOC distribution.…”

Effects of Grazing Management on Spatio-Temporal Heterogeneity of Soil Carbon and Greenhouse Gas Emissions of Grasslands and Rangelands: Monitoring, Modelling and Upscaling

“…Jones et al [39] found that soil respiration from plots receiving manure was up to 1.6 times larger than CO2 release from control plots, and up to 1.7 times larger compared to inorganic treatments (p<0.05). Hewins et al [40] found that while climate had the largest impact on SOC concentrations, grazing increased C concentration more in mesic grazing lands of Alberta, Canada. Teague et al [41] indicated that grass cover under proper management is highly effective in reducing soil erosion and in increasing SOC stocks.…”