Soil Respiration: Influence of Agricultural Management

Soil respiration represents the sum of CO₂ produced by root respiration and by heterotrophic decomposition of root exudates, soil organic matter, and plant litter. It is commonly estimated as the flux of CO₂ emitted from the soil surface. The influence of CO₂ fixation by autotrophic soil microorganisms, as well as non-biological reactions such as the chemical oxidation of organic molecules and the precipitation or dissolution of soil carbonates, is small in most situations. Root respiration is largely regulated by the root biomass and the rate of photosynthate transfer from plant leaves and often exhibits a strong diurnal pattern. It may represent 10 to 90% of soil respiration. Decomposition processes are the result of complex interactions among soil fauna, fungi, actinomycetes, and bacteria. These organisms break down complex molecules such as cellulose, hemi-cellulose, proteins and lignin into low-molecular-weight substances, which are then oxidised to CO₂ to produce energy or used to provide C for cell growth. The rate of decomposition is determined by the quantity and quality of organic substrates, the efficiency and population dynamics of various decomposer groups, and the soil's physico-chemical environment including moisture, temperature, oxygen, acidity, and redox potential. Most if not all of these factors are influenced by farming practices such as crop selection, harvesting of crop residues, fertilization and soil tillage. Consequently, agricultural management impacts on the magnitude and on the spatial and temporal variation of respiration in agricultural soils. In this presentation, general concepts will be presented and CO₂ flux data under field conditions will be used to provide specific examples of soil respiration responses to agricultural management.