Kinetics of added organic matter decomposition in a Mediterranean sandy soil

Carbon mineralization kinetics of 17 organic materials were studied in a Me diterranean sandy soil. These added organic matters (AOM) used in the organ ic fertilizer industry differed in their origin and composition: plant resi dues from the agri-food industry, animal wastes, manures (plant and animal origin), composts at different composting times and organic fertilizers. Th e mixtures AOM-soils were incubated under aerobic conditions at 28 degreesC during 6 months. Soil moisture was maintained at 75% water holding capacit y and respired-CO2 was regularly trapped into alkali media in closed chambe rs, then checked by HCl titration. Analyses of CO2 were performed in tripli cate at 17 sampling occasions. The mineralized AOM fraction (MAOMF) varied according to the AOM origin: from 12-33% of added C for composts, to 65-90% for animal-originated AOM, with many intermediate patterns for plant-origi nated AOM. Seven decomposition models from the literature were fitted to ac tual MAOMF: (a) three consecutive models with two 1st-order-kinetic compart ments and three parameters (ml. humification: m2, exchange: m3, decompositi on), (b) three parallel models (m4. with two compartments and three paramet ers: m8. a i st-order plus 0-order model with three parameters; m4. a three -compartment model with four parameters). and (c) m7, a model with one 2nd- order-kinetic compartment and two parameters. Additionally, m6. a simplifie d version of m5 was proposed. Models m2 and m7 did not match with actual da ta or gave a poor fit. By the correlation parameters, the most simple model m4 was chosen instead of the consecutive models rn 1 and rn3. Residual sum s of squares were always greater-but not significantly -in m8 than in m4 wh ich confirmed the superiority of the models with two Ist-order compartments against 1 st-order plus 0-order models for incubation times higher than 10 0 days. Model m5 (most of its parameters being not correlated) gave the bes t predictions of our data. The proposed m6 version gave e predictions with similar precision as m4 and appeared powerful with only two parameters (ver y labile and stable ii actions of the AOM). A compromise between the precis ion of the predictions and the simplicity of the formulae allowed the recom mendation of the well-known m4 model, and above all the simpler m6 model. ( C) 2001 Elsevier Science Ltd. All rights reserved.