Soil carbon budget of a 50-year residue management experiment in a Belgian cropland.

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 biggest C loss by SHR since the beginning of the experiment. The SHR field measurements, performed 50 years after the experiment had begun, did however not show any significant difference between the SHR rates in the three treatments.
Laboratory investigations (microbial biomass, basal respiration, metabolic diversity and soil fractionation) will be performed to better understand the effects of long-term residue management on soil C dynamics.