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Organic matter contribution to aggregate stability in silty loam cultivated soils. carbon input effects.

Abstract : Soil aggregate stability is a key property for soil functioning. However, there are still no tools to predict its temporal variations or to determine cultural practices to improve it. The subject is particularly important in regard to the effect of C inputs to fragile soils (silty cultivated soils). The general aim of this work is to improve the knowledge in factors determining short-time aggregate stability variations caused by C inputs and soil water contents variations. To establish quantitative relationships among aggregate microbial agents, elementary physical properties that determine aggregate stability (porosity, hydrophobicity and soil cohesion) and aggregate stability we varied the organic matter added rate (maize residue) and wetting-drying cycles in soil controlled conditions. We used three aggregate stability tests that distinguish different soil breakdown mechanisms (slaking, microcracking and mechanical breakdown) to analyze the relationships from a mechanistic point of view. In our conditions, C inputs stimulated linearly microbial activity and by-products to all doses of C inputs used. Aggregate microbial agents measured (microbial biomass-C, ergosterol content (biomarquer of fungi), and hot water extractable polysaccharides (surrogate of extracellular polysaccharides)), had an important dynamic pattern and there were all correlated to aggregate stability. No hierarchic order among biological variables could be established. Aggregate stability to slaking, microcracking and mechanical breakdown had a similar dynamic pattern after C input. A linear semi-mechanistic model predicting aggregate stability variations based on coupling an soil C and N dynamic model (CANTIS) and multiple linear regressions linking microbial biomass-C and respired CO2 after a C input and aggregate stability was proposed. C input has also strongly modified the elementary physical properties that determine aggregate stability. The aggregates increased porosity, hydrophobicity and Interparticle cohesion with C input rate. Giving the impact of microbial activity in hydrophobicity, emphasis was given in determining hydrophobicity and three methods were applied and evaluated. Diversity of microbial activity effects on soil physical aggregate properties suggests that is still pertinent to consider aggregate stability as an integrative and sensitive property to organic matter input effects in soil. Climatic conditions as wetting-drying cycles have shown to modulate the effect of C inputs on aggregate stability, particularly changing the relative impact of the organic matter in breakdown mechanisms of aggregate stability.
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Submitted on : Wednesday, February 11, 2009 - 8:00:00 AM
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Diego Julian Cosentino. Organic matter contribution to aggregate stability in silty loam cultivated soils. carbon input effects.. Sciences of the Universe [physics]. AgroParisTech, 2006. English. ⟨NNT : 2006INAP0041⟩. ⟨pastel-00004754⟩

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