Soil greenhouse gas emissions as impacted by soil moisture and temperature under continuous and holistic planned grazing in native tallgrass prairie

Abstract

Adaptive multi-paddock (AMP) grazing has demonstrated the potential to substantially improve ecosystems service outcomes relative to the most commonly used grazing management of moderate (MC) and heavy continuous (HC) grazing. We hypothesize that AMP grazing would decrease net soil emissions of CO2, CH4 and N2O exchange between the soil surface and the atmosphere relative to continuous grazing and the management practice options of prescribed fire (AMP-burn), and production of hay (AMP-hay) both managed using AMP grazing. Soil temperature was lower (P < 0.009) and soil moisture higher (P < 0.01) with AMP grazing than with HC and MC grazing. As CO2, CH4 and N2O emissions are less with lower temperatures and increasing soil moisture, they should have declined with AMP grazing. However, AMP grazing had the highest and HC the lowest CO2 emissions, indicating higher levels of soil respiration, an index of soil microbial activity, with AMP. Emissions of N2O were consistent with previous research, being higher under anaerobic conditions and very low under aerobic conditions. AMP, AMP-burn and AMP-hay treatments on average had lower N2O emissions than HC and MC (P ≤ 0.002). Methane (CH4) emissions were negative for most sample dates but were dwarfed by the occasional periods when soils were saturated. These elevations in CH4 emissions occurred on 8 of the 35 dates sampled (rate >0; P ≤ 0.05), 7 times for HC, 4 times for MC, and 3 times for AMP. On the remaining dates sampled (27 of 35), AMP was the strongest CH4 sink ahead of AMP-burn (P = 0.0335), AMP-hay (P = 0.0232) and HC, but was similar to MC (P = 0.17). MC was a stronger sink than HC (P = 0.057). The emissions of CO2 and N2O were decreased with removal of green canopy material at sampling, indicating positive responses could be achieved by adjusting grazing management. Adaptive multi-paddock grazing, but not continuous grazing, can be adjusted to maintain higher proportions of green material, and as this would also benefit energy capture by photosynthesis and livestock diet quality, multiple benefits could accrue from implementing such management. Removal of green material had no influence on CH4 oxidation, which was greatest with AMP grazing. These results are consistent with AMP grazing having a lower intensity ecological impact than continuous grazing.