Soil carbon stocks and nitrous oxide emissions of pasture systems in Orinoquía region of Colombia: Potential for developing land-based greenhouse gas removal projects

Abstract

Improving grassland conditions under grazing has the potential not only to accumulate carbon in soils, but also to reduce nitrous oxide (N2O) emissions from animal urine deposition. However, measurements in developing countries are still scarce. In the Orinoquia region, permanent grasslands (PG; this unimproved, native pasture is considered as at some state of degradation) based on unimproved grasses are found due to extensive, inefficient grazing combined with annual burning of pastures. We hypothesized that, compared to PG, improved grasslands (IG) managed through rotational grazing of introduced, productive and deep-rooted pasture grass species promote soil organic carbon (SOC) accumulation and reduce N2O emission from urine deposited by grazing cattle. We determined SOC and N2O emissions from urine deposited on soils in an area of PG and in a 6.5 year-old IG area of Urochloa (Syn. Brachiaria) humidicola grass pasture in a beef cattle ranch in Orinoquía region (Colombia). In both areas, we sampled soil for chemical/physical analysis, and measured N2O emissions by simulating urine deposition over 21 days. We applied two-way analysis of variance considering pasture type and soil depth as fixed factors. Estimated SOC stocks (0–100 cm) were in the range of 224.8 Mg C ha−1 for the PG and 259.0 Mg C ha−1 for the IG, with a significant (p < 0.05) average accumulation of 2.0 Mg C ha−1 y−1 (0–20 cm) in the IG area. N2O emissions were 10 times lower in the IG compared to the PG. The introduction of U. humidicola grass influenced SOC accumulation probably through its more abundant root system and greater turnover together with higher (14%) forage dry matter production compared to PG. The reduced N2O emissions observed from urine patches in IG were attributed to biological nitrification inhibition ability and greater nitrogen uptake of U. humidicola grass. Compared to the reference default value of IPCC for, the SOC stock found in PG was almost 40% higher, whereas the N2O emission factor (5%) was within the uncertainty range (0.7–6%). The Orinoquía region shows significant potential for SOC storage and reduced N2O emissions in improved pastures with deep root systems. Thus, scaling the implementation of land-based SOC storage practices/projects could significantly contribute to reducing net emissions from beef production from this region.

A dynamic simulation model to assess farm-level effects of pasture intensification strategies on beef herd outputs and carbon footprints in acid soil savannas of Eastern Colombia

“…The values of SOC accumulation to GHG emissions ratio that are higher than 1.0 in all 3 pasture systems from both sub-ecosystems with the assumption of continuous SOC accumulation over 20 years period indicate that the gradual intensification of pasture systems at the farm level can lead to net SOC accumulation over time. These results are similar to several published reports that showed an increase in SOC stocks that can reduce the overall C footprints from well-managed, long-term tropical pastures under grazing (Fisher et al, 1994;Qian and Follett, 2002;Follett and Schuman, 2005;Viglizzo et al, 2019;Ramírez-Restrepo et al, 2020;Baptistella et al, 2020;Durrer et al, 2021;Stoner et al, 2021;de Campos Bernardi et al, 2021;Costa et al, 2022).…”

Soil carbon storage potential of acid soils of Colombia's Eastern High Plains

“…The decreased SOC at 0-80 cm depth in the native savanna, B. humidicola and B. humidicola + A. pintoi (54, 58, and 48%) after 1994, when the management was reduced to a minimum, emphasizes the importance of continuous pasture management for increasing and sustaining SOC storage potential. Indeed, other recent research in the Eastern High Plains has confirmed high SOC accumulation under proper pasture management (Costa et al, 2022).…”

“…Increasing the herd size and fertilized areas not only has an impact on CO 2 emissions but also in CH 4 and N 2 O emissions. Costa et al (2022) showed N 2 O emission reductions with improved B. humidicola grass in a recent study in silty clay loam soils of the Eastern High Plains. Ramírez-Restrepo et al (2020) predicted CH 4 emissions, animal-environmental metrics and C footprint over the productive lifetime of the tropical beef cattle herds grazed on B. decumbens pastures and reported that under well-managed conditions, these pastures contribute to net C gain through SOC accumulation.…”

“…While we need more research on in CH 4 and N 2 O, there is clear potential to reduce emissions per unit product (meat and milk) following well-adjusted mitigation options (Peters et al, 2012;Havlík et al, 2014;Lerner et al, 2017;Ramírez-Restrepo et al, 2023;Vera-Infanzón et al, 2023). Improved Brachiaria based pastures could also reduce N 2 O emissions through biological nitrification inhibition (Byrnes et al, 2017;Costa et al, 2022).…”

The carbon footprint of beef production from cull cows finished on sown pastures in the savannas of the Colombian Orinoquía

“…The aboveground and belowground C stocks and SOC accumulation rates from improved pastures were estimated for the three contrasting SCEs to reflect differences that are not usually captured by animal performance variables and static characteristics. Values on SOC accumulation derived from contemporaneous experiments at CRC and nearby to the current study area were used (Fisher et al, 1994;Rao, 1998;Trujillo et al, 2006;Costa et al, 2022;Hyman et al, 2022). The methods used to determine SOC stocks in different pastures were described by Fisher et al (1994).…”