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Hubert-2007-Geoderma.doc - Pore morphology changes under...

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Pore morphology changes under tillage and no-tillage practices HUBERT Fabien 1* , HALLAIRE Vincent 2 , SARDINI Paul 1 , CANER Laurent 1 , HEDDADJ Djilali 3 Accepted version : Geoderma , 2007, 142 , (1-2), 226-236 1 CNRS UMR 6532 Hydrogéologie, Argiles, Sols et Altérations. Université de Poitiers, 40 avenue du Recteur Pineau, 86022 Poitiers cedex, France. 2 UMR Sol Agronomie Spatialisation, Agrocampus-INRA. 65 rue de Saint-Brieuc, CS 84215, 35042 Rennes cedex, France. 3 Chambre d'agriculture de Bretagne. Avenue du Général Borgnis Desbordes, BP 398, 56009 Vannes cedex, France. * Corresponding author: mail. [email protected] , tel. +33 5 49 45 38 67, fax: +33 5 49 45 42 41. Abstract The relative influence of biological and mechanical processes on the structure of cultivated soils was estimated by investigating the macroporosity of the surface layers of a silty soil during a maize growing season. The soil was subjected to different cultivation techniques (conventional tillage, moderate tillage, and no tillage) and fertilization modes (mineral or organic) for five years. A typological model was developed (i) to identify the macropores by 2D image analysis in undisturbed soil samples, and (ii) to characterize their morphology with two shape parameters (elongation and regularity indexes). Based on the three usual pore categories (tubular, planar and packing pores), five groups were defined with an additional distinction within the packing pore category (discrete, continuous and planar packing). This typology, as based on a set of images that reached the representative elementary area (REA), proved appropriate to describe the structural modifications linked to the crop management practices. It was shown that mechanical soil working produces ‘continuous packing pores’ 1
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whereas the absence of work induces ‘discrete packing pores’. The study of the intra-annual structural dynamics enabled the identification of the processes responsible for those modifications. With conventional tillage, the progressive substitution of continuous packing pores with discrete packing pores can be interpreted as the resumption of biological fragmentation after mechanical fragmentation (harrowing). Without management, the soil is only subjected to biological fragmentation, so neither quantitative nor morphological evolution of the macroporosity was observed during the growing season, with the soil structure depending more on spatial heterogeneity than on seasonal changes. Key words : no tillage, reduced tillage, image analysis, pattern recognition, representative elementary area. 2
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Introduction Soil quality is closely related to soil structure and can be directly influenced by environnemental damage in intensive arable lands, such as erosion, desertification or susceptibility to compaction (Pagliai et al., 2004). Results from field experiments usually recommend adoption of reduced tillage practices to prevent soil structural degradation and reveal beneficial long-term effects on physical, chemical and biological soil properties (Unger et al., 1991; Hubbard et al., 1994; Karlen et al., 1994). According to different authors, reduced
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