Abstract
Adaptive multi-paddock (AMP) grazing is a form of rotational grazing in which small paddocks are grazed with high densities of livestock for short periods, with long recovery periods prior to regrazing. We compared the fluxes of greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), from soils of AMP-grazed grasslands to paired neighboring non-AMP-grazed grasslands across a climatic gradient in Alberta, Canada. We further tested GHG responses to changes in temperature (5 °C vs. 25 °C) and moisture levels (permanent wilting point (PWP), 40% of field capacity (0.4FC), or field capacity (FC)) in a 102-day laboratory incubation experiment. Extracellular enzyme activities (EEA), microbial biomass C (MBC) and N (MBN), and available-N were also measured on days 1, 13, and 102 of the incubation to evaluate biological associations with GHGs. The 102-day cumulative fluxes of CO2, N2O, and CH4 were affected by both temperature and moisture content (p < 0.001). While cumulative fluxes of N2O were independent of the grazing system, CH4 uptake was 1.5 times greater in soils from AMP-grazed than non-AMP-grazed grasslands (p < 0.001). There was an interaction of the grazing system by temperature (p < 0.05) on CO2 flux, with AMP soils emitting 17% more CO2 than non-AMP soils at 5 °C, but 18% less at 25 °C. The temperature sensitivity (Q10) of CO2 fluxes increased with soil moisture level (i.e., PWP < 0.4FC ≤ FC). Structural equation modelling indicated that the grazing system had no direct effect on CO2 or N2O fluxes, but had an effect on CH4 fluxes on days 1 and 13, indicating that CH4 uptake increased in association with AMP grazing. Increasing soil moisture level increased fluxes of GHGs—directly and indirectly—by influencing EEAs. Irrespective of the grazing system, the MBC was an indirect driver of CO2 emissions and CH4 uptake through its effects on soil EEAs. The relationships of N-acetyl-β glucosaminidase and β-glucosidase to N2O fluxes were subtle on day 1, and independent thereafter. AMP grazing indirectly affected N2O fluxes by influencing N-acetyl-β glucosaminidase on day 13. We conclude that AMP grazing has the potential to mitigate the impact of a warmer soil on GHG emissions by consuming more CH4 compared to non-AMP grazing in northern temperate grasslands, presumably by altering biogeochemical properties and processes.
Generated Summary
This study investigated the effects of Adaptive Multi-Paddock (AMP) grazing on greenhouse gas (GHG) emissions from grassland soils compared to conventional grazing (non-AMP). The research employed a laboratory incubation experiment, manipulating soil temperature and moisture to assess their impact on GHG fluxes. Extracellular enzyme activities (EEAs), microbial biomass, and available-N were measured to evaluate biological associations with GHGs. The study aimed to determine how AMP grazing alters GHG emissions and whether it modifies the sensitivity of these emissions to changes in soil temperature and moisture. The paired design included 11 pairs of ranches across south-central Alberta, Canada. The study specifically examined the influence of grazing system on GHG emissions, soil microbial activity, and the role of EEAs in regulating GHG fluxes. The study tested GHG responses to changes in temperature and moisture levels.
Key Findings & Statistics
- The cumulative fluxes of CO2, N2O, and CH4 were affected by both temperature and moisture content (p < 0.001).
- Cumulative fluxes of N2O were independent of the grazing system.
- CH4 uptake was 1.5 times greater in soils from AMP-grazed than non-AMP-grazed grasslands (p < 0.001).
- An interaction of the grazing system by temperature was observed on CO2 flux (p < 0.05).
- AMP soils emitted 17% more CO2 than non-AMP soils at 5 °C, but 18% less at 25 °C.
- The temperature sensitivity (Q10) of CO2 fluxes increased with soil moisture level (i.e., PWP < 0.4FC ≤ FC).
- Overall, CH4 uptake was 2.6-fold greater in AMP soils (52.4 ± 6.4 µg CH4-C kg−¹) in comparison to non-AMP soils (20.4 ± 2.5 µg CH4-C kg−¹).
- Soils at 25 °C had 2.9-fold greater uptake of CH4 compared to soils incubated at 5 °C.
- Soils at FC emitted 3.1 and 3.7 times more net GHGs (p < 0.05) in comparison to soils at either PWP or 0.4FC.
- Net GHG emissions were 15% lower in non-AMP than in AMP systems at 5 °C, but were 22% higher in non-AMP soils at 25 °C compared to the AMP soils.
- The temperature sensitivity (Q10) of CO2 flux within these grassland soils differed between the AMP and non-AMP grazing systems, and were consistently greater (p < 0.001) from non-AMP soils (2.76 ± 0.11) compared to AMP soils (2.13 ± 0.08).
- At 5 °C, the proportion of SOC mineralized as CO2-C was <0.5%, but at 25 °C reached as high as 2.9%.
- Within the AMP soils, SOC mineralization was 3.7 times greater at 25 °C than at 5 °C, while in non-AMP soils this increase was 5.6 times.
- Increasing soil moisture and soil temperature both increased the proportion of SOC mineralized.
Other Important Findings
- Structural equation modelling indicated that the grazing system had no direct effect on CO2 or N2O fluxes, but had an effect on CH4 fluxes, indicating that CH4 uptake increased in association with AMP grazing.
- Increasing soil moisture level increased fluxes of GHGs—directly and indirectly—by influencing EEAs.
- The relationships of N-acetyl-β glucosaminidase and β-glucosidase to N2O fluxes were subtle on day 1, and independent thereafter.
- AMP grazing indirectly affected N2O fluxes by influencing N-acetyl-β glucosaminidase on day 13.
- The net GHG emissions were also affected by soil moisture and the interaction of grazing with temperature.
- The temperature sensitivity (Q10) of CO2 flux increased with soil moisture.
- The proportion of soil organic carbon (SOC) mineralized as CO2-C was affected by the interaction of grazing, temperature, and moisture.
- The use of Structural Equation Modeling (SEM) revealed marked differences among GHGs and the sampling times.
- Emissions of CO2 from soil were consistently positively influenced by increasing soil moisture, and even more so by greater soil temperatures.
- In contrast, the grazing system had no impact on CO2 emissions.
- Soil EEAs had a strong positive response to both increasing MBC and higher soil moisture, particularly on day 13, but also on day 102, and to a lesser extent on day 1.
- Unlike CO2, CH4 fluxes directly declined (i.e., uptake increased) in response to higher soil temperature during the first two sampling periods, and also decreased more within soils subject to AMP rather than non-AMP grazing at these times.
- By the end of the incubation period, however, no direct grazing effect remained, while CH4 flux increased at that point with soil temperature and declined with greater moisture.
- CH4 fluxes were also closely coupled with MBC, but only via the indirect influence of MBC on EEA.
- Fluxes of N2O were not affected by the grazing regime either directly or indirectly, with the lone effect of grazing being an increase in NAG EEA in soil arising from AMP grazing.
Limitations Noted in the Document
- The study was conducted within an incubation environment, which may not fully represent the complexities of field conditions.
- The simplified categorical differentiation between grazing systems as either AMP or non-AMP might be inadequate to test for grazing induced responses.
- Variations in management metrics within non-AMP ranches may influence results.
- The study did not test for factors that affect CH4 oxidation, such as the type of methanotrophs.
- The lack of a relationship between grazing systems and either MBC or EEAs could be due to simplified categorical differentiation between grazing systems.
- The study did not examine the effects of litter and light levels.
Conclusion
The study’s findings suggest that AMP grazing has the potential to mitigate the impact of warmer soils on GHG emissions by enhancing CH4 consumption. The results demonstrate that the grazing system, soil temperature, and moisture significantly influence GHG fluxes in grassland soils. Notably, the uptake of CH4 was significantly higher in AMP-grazed soils, especially under warmer and more humid conditions, underscoring the potential of AMP grazing to act as a sink for CH4. However, the study also found that the flux of CO2 and N2O increased with rising temperatures and soil moisture, regardless of the grazing system. The temperature sensitivity of CO2 flux was higher in non-AMP soils, suggesting a greater risk of carbon loss under conventional grazing practices.The research highlights the importance of maintaining cool soil temperatures and the retention of ample litter in grasslands to mitigate GHG emissions. The study’s findings underscore the need for grazing management practices that consider both temperature and moisture to minimize GHG emissions. Overall, the research reinforces the idea that AMP grazing can be a valuable tool in sustainable grassland management, especially in the face of climate change. The study suggests the importance of accounting for the role of grazing management in GHG dynamics. It offers insights into how grazing practices can influence the balance between GHG emissions and uptake in grasslands. The study’s findings may contribute to the development of more effective grazing strategies aimed at reducing the overall GHG footprint of grassland ecosystems. Furthermore, these findings stress the importance of soil moisture management in grazing practices as soil moisture plays a crucial role in the decomposition of grassland SOM.