Crop residues decomposition dynamics in farms practising conservation agriculture in the Grand Est region, France

Reduced tillage of farms practicing conservation agriculture leads to leaving crop residues on the soil surface after harvesting, but few references are available on their in situ field decomposition. This study aimed to determine residues decomposition through their dry matter, carbon (C) and nitrogen (N) dynamics in reduced tillage and direct sowing cropping systems, to improve their management and N contribution over time to the following crops. Maize, sunflower, rapeseed, winter wheat and winter barley residues decomposition were recorded in four farms in the Grand Est region (France) from 2009 to 2011. Monitoring was done by sampling and analysis of residual biomass, during one to two years after harvest. The expression of time, based on normalized days at 15 degrees C, permitted to compare crop residue dynamics for the different sites and the three years. Decomposition was rapid in all situations, with almost all residues disappearing after 700 normalized days at 15 degrees C. The kinetics of biomass, C and N followed a common mathematical relationship as a function of normalized time, regardless of species, location and year. These kinetics can be predicted by a single nonlinear equation, statistically very highly significant. This indicates that, under the explored agricultural and climatic conditions of the Grand Est region, temperature was the main factor determining the kinetics of crop residue decomposition, making it relatively simple to estimate net N input from crop residues in N budgets for subsequent crops-soil sequences