Assessment of Land Management and Environmental Factors on Soil Respiration

Agricultural fields are increasingly managed by heavy machinery, which can negatively impact soil health. In annual cropping systems, fields are often left bare over winter and are compacted during the growing season, with unknown effects on soil respiration. Within the footprint of a 30m eddy covariance tower at the USDA Dairy Forage Research Center in Prairie Du Sac, WI, we studied relationships among soil respiration and environmental factors, as well as land management intensity.

We measured soil respiration (CO₂ efflux) using an infrared gas analyzer (LI-COR 8100A) attached to a chamber fitted over 90 permanent PVC collars installed in both managed agricultural settings and natural ecosystems (forest, shrub, grass). Field crops included wheat, soybeans, alfalfa, and corn. We collected aboveground biomass samples associated with each soil respiration collar within the same week of soil respiration measurement. We evaluated the effects of volumetric water content, soil temperature, biomass, and management intensity on soil respiration for each vegetation type. Field activities included planting, applications of herbicide, manure and synthetic fertilizer, and harvesting.

In April when annual crop fields were bare, soil respiration rates were lower than natural sites, which already had considerable vegetation growth. In late May, respiration was significantly lower within alfalfa, wheat, and soy than in other fields. Management intensity (frequency of equipment passes) increased soil respiration within crop fields, however in natural ecosystems (grassland) it had no major effect. Manure application in pastures increased soil respiration, yet had no effect in corn fields. Pesticide application increased soil respiration in all treated fields (alfalfa, wheat, corn).

Soil respiration measurements are important for soil health assessments, and development of carbon budgets. These data could be used to inform farm management practices, improve methods to upscale eddy covariance flux data in agricultural fields, and develop resilient farming systems in the context of climate change.