Impact of residue quality and location in soil on the C and N mineralisation of residues from cropping systems from Cerrados, Brazil

Impact of biochemical characteristics and initial location of crop residues was experimentally measured in laboratory incubations. Nitrogen and carbon dynamics were followed during the decomposition of four sub-tropical species and one temperate species buried in the soil or laid down on the surface. Proximate analysis and measures of C, N and polyphenols realised on the different organs of the residues permitted to point out high polyphenol content of the leaves and high lignin-like content of the roots. C mineralisation of roots was significantly lower than for the other organs mineralisation. In those optimal conditions, no differences were observed depending on the initial location. Use of different linear relationships models from literature linking C and N mineralisation to biochemical residue characteristics were not able to simulate our data. A dynamic model based on the C:N ratio allowed to predict leaves and stems C mineralisation but failed at predicting C mineralisation of roots and N dynamics in soil. This study particularly put the stress on the interest to consider separately the different organs of plant when studying decomposition and on the need to develop other methods of characterisation of residue quality to improve prediction of residue decomposition. (Résumé d'auteur