Effets de fertilisants organiques sur les propriétés d'un sol sableux maraîcher. Modélisation de leur cinétique de minéralisation et conséquences sur la rationalisation de leurs procédés de fabrication industrielle

*INRA UMR Science du Sol de Montpellier Diffusion du document : INRA UMR Science du Sol de Montpellier Diplôme : Dr. Ing

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-N AOM ratios ([êta]AOM) ranged from 1.1 to 27.1. Sequential fibre analyses gave C-to-N ratios of soluble ([êta]Sol), holocellulosic ([êta]Hol) and ligneous compounds ([êta]Lig) 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. The Transformation 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 Pl 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 kremim). 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) [êta]L, [êta]R, [êta]S (C-to-N of L, R and S) [êta]Sol, [êta]Hol, [êta]Lig, respectively, (ii) [êta]L = [êta]R = [êta]S = [êta]AOM. 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. (Résumé d'auteur

Does the methoxyl group content of the humic acid-like fraction of composts provide a criterion to evaluate their maturity ?

To be considered beneficial, nutrient-rich, and be applied safely to soil, a batch of compost should be assessed for its maturity. We tested a new method to follow the time course of maturation on a compost consisting of sheep manure, grape and coffee by-products. This method was based upon the content of the humic acid-like compost fraction in methoxyl (-OCH3) groups, functional groups characteristic of lignin structural units. It involved the conversion of OCH3 groups to the corresponding alkyl iodide (ICH3) groups by treatment with boiling hydriodic acid, before gas chromatography determination. Among the various characteristics studied (ash, organic C, N, lignin), the OCH3 content appeared to be a good tracer of compost maturity. (c) 2006 Elsevier Ltd. All rights reserved

Influences of organic fertilization and solarization in a greenhouse on particle-size fractions of a Mediterranean sandy soil

Abstract The effects of a composted organic amendment and solarization on the organic matter (OM) of a sandy soil were determined by means of particle-size fractionation and analysis of carbon and nitrogen contents. After 2 years, total soil carbon increased under organic fertilization but did not significantly change with solarization. As a consequence of the climatic conditions in the greenhouse, the carbon concentrations (g kg -1 fraction) of the particle-size fractions were lower than those found for temperate soils and closer to those for tropical soils. The carbon amounts (g kg -1 soil) and carbon:nitrogen ratios, which were highest in fractions 1 200 mm, reflected the short-term influence of the industrially processed organic amendment, rich in composted coarse plant debris. In contrast, the characteristics of the OM associated with each fraction were not significantly affected by solarization. In comparison with other coarse-textured temperate or tropical soils, carbon concentrations in fine silt (2-20 mm) and clay (0-2 mm) fractions were very low. This suggests a "greenhouse effect", together with a high rate of carbon mineralization affecting fine silt and clay fractions

Use of NIRS to predict organic matter characteristics and RothC model pools of exogenous organic matter

NJF Report Vol 5 No 1absen

Biochemical composition and mineralization kinetics of organic inputs in a sandy soil

The carbon mineralization of added organic materials (AOM) in soil was assessed by combining laboratory and modeling approaches. The AOM used in the organic fertilizer industry included: plant residues from agri-food origin, animal wastes, manures, composts, and organic ferfilizers. They were fractionated by sequential analyses of fibers and analyzed for C, N and ash contents. A previous kinetic study permitted to select two predictive models for AOM C mineralization in a sandy soil. These models, m4 and m6, were respectively defined by (i) two compartments (labile L and very resistant R) with three parameters: PL (proportion of L), and kmL, kmR (kinetic constants of L and R); (ii) three compartments (very labile L', resistant R' and stable S), with two parameters: P'L and Ps (proportions of L' and S) with fixed kinetic constants at 28°C, 75% WHC. We tested for the best prediction of the above parameters with the analytical data. These predictions were significant for the whole AOM set, but to a lesser degree for the C mineralization of AOM with contrasted characteristics. A Principal Component Analysis (PCA) was used to classify the AOM according to their biochemical contents into two groups: (+) ligneous ones with relatively high C and low N contents (mostly plant-originated AOM), and (-) more nitrogenous ones, poorer in organic C and ligno-cellulosic fibers (mostly animal-originated or partially composted AOM). The classification improved the predictive equations, which use one to three biochemical variables in agreement with the conceptual definition of the parameters. P'L, PL and Ps were more accurately estimated than kmL and kmR. For most of the AOM, m6 gave better simulations than m4. From m6 equations, the conceptual compartments L', R' (with P'R = 1 - P'L - PS) and S appeared to correspond to (i) parts of soluble, nitrogenous and hemicellulosic compounds, (ii) cellulose and the remaining fraction of hemicelluloses, (iii) the ligneous fraction, respectively. (Résumé d'auteur