50 Years of contrasted residue management in an agricultural crop: Impacts on the soil carbon budget and on soil heterotrophic respiration.

Within the context of Climate Change, crop management exerts a strong influence on the soil carbon (C) balance. This study aims (1) to estimate the C loss by soil heterotrophic respiration (SHR) in different residue management treatments through the establishment of their soil C budgets and (2) to compare these estimations with field SHR measurements.

Three contrasted treatments were considered: Residue Export (RE), Farm Yard Manure addition (FYM) and Residue Restitution after harvest (RR). They were established in 1959 and continuously applied since then at an experimental field located in the Hesbaye region in Belgium. The soil C budget was calculated for each treatment on the basis of total soil organic C content measurements and C input data compiled since the beginning of the experiment. This allowed estimating the C loss by SHR in the different treatments. SHR measurements were performed in 2010 and 2011 to compare them with the budget-based estimations and to assess SHR sensitivity to temperature in the different treatments.

The soil C budgets showed that the soil under the RR treatment was likely to undergo the largest C loss by SHR since the beginning of the experiment. The comparison between the results from the C budget and the SHR field measurements, performed 50 years after the experiment had begun, did however show that the treatment that received the largest amount of crop residues (RR) did not necessarily sequestrate the most C or produce the largest CO2 fluxes (FYM). Besides, no significant difference between treatments was observed in the field measurements in terms of SHR sensitivity to temperature.

Laboratory investigations (microbial biomass, basal respiration, metabolic diversity and soil fractionation) will later be performed to better understand the effects of long-term residue management on soil C dynamics.