Kinetics of C and N mineralization, N immobilization and N volatilization of organic inputs in soil

C and N mineralization data for 17 different added organic materials (AOM) in a sandy soil were collected from an incubation experiment conducted under controlled laboratory conditions. The AOM originated from plants, animal wastes, manures, composts, and organic fertilizers. The C-to-NAOM ratios (ηAOM) ranged from 1.1 to 27.1. Sequential fibre analyses gave C-to-N ratios of soluble (ηSol), holocellulosic (ηHol) and ligneous compounds (ηLig) ranging from 1.1 to 57.2, 0.8 to 65.2, and 3.5 to 25.3, respectively. Very different patterns of net AOM-N mineralization were observed: (i) immobilization for four plant AOM; (ii) moderate mineralization (4–15% AOM-N) for composts; (iii) marked mineralization (11–27% AOM-N) for 1 animal AOM, 1 manure and 2 organic fertilizers; and (iv) high rates of transformations with possible gaseous losses for some N-rich AOM. ansformation of Added Organics (TAO) model proposed here, described AOM-C mineralization (28 °C, 75% WHC) from three labile (L′), resistant (R) and stable (S) compartments with the sole parameters P′L and PS=fractions of very labile and stable compounds of AOM, respectively. Dividing the C-compartments by their C-to-N estimates supplied the remaining NAOM fraction (RAONF). A Pim parameter split the TAO nitrogen fraction (TAONF=added N-RAONF) into two compartments, immobilized (imN) and inorganic (inorgN) N. A Pim>0 value meant that all the TAONF plus a fraction (Pim−1) of native soil inorganic N was immobilized. Additional N mineralization was predicted when necessary from imN by first order kinetics (constant kremin). The TAO version with two parameters Pim and kremin allowed us to predict very different patterns of N mineralization and N immobilization. In a few cases, a further first order kinetic law (constant kv) was added to predict N volatilization from inorgN. Two hypotheses were tested: (i) ηL′, ηR, ηS (C-to-N of L′, R and S)=ηSol, ηHol, ηLig, respectively, (ii) ηL′=ηR=ηS=ηAOM. The first hypothesis was validated by these data, and the second was a good approximation of the former one. In all the cases, predictions were in good agreement with measured values.