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Water, carbon and nitrogen dynamics in soil - Influence of crop residue location and quality

Abstract : At present, the mechanisms for carbon sequestration in soil are not well identified and there is still a great deal of uncertainty about its quantification. In particular, little information is available on the impact of modifications in tillage practice (e.g. conversion from conventional tillage towards no-tillage) or changes in land use on carbon stocks and fluxes in soil. Land use and management are principal factors affecting the transformation of organic matter, determining the mineralization of carbon and nitrogen or their retention in soil. In addition, different ecosystems (e.g. arable land, pasture and forest) offer a large variety of vegetation types and likewise plant residues of different nature and quality.
The main objective of this work was to identify the physical and biological processes that are affected by plant residue location in soil, in interaction with residue quality. The initial location of plant residues acts directly on some soil physical properties: thewater dynamics, solute transport and soil temperature. The biochemical quality of crop residues influences the soil (micro-)biological processes: biotransformations of carbon and nitrogen, and the activity and composition of the soil microbial biomass. These soil physical and biological changes may interact, modify the soil structure (e.g. by aggregation) and in turn influence the decomposition of soil organic matter.
In a first part, the influence of residue quality and soil type on C and Nmineralization was investigated with ‘optimal' soil-residue contact, i.e. with homogenous incorporation of finely chopped plant material. It has been demonstrated that, under controlled and non-limiting N conditions, the quality of the substrate added was the first factor determining the residue decomposition rate and that soil type had little or no effect on the short-term dynamics of residue decomposition. However on a longer term, carbon mineralization was slightly influenced by soil type, which was probably due to differences in the capacity to stabilize soluble carbon and/or microbial derived carbon.
In a second part, the effect of plant residue location on C and N mineralization was examined for oilseed rape residues in a silt loam soil. Soil columns were constructed with incorporated or surface applied residues and periodically placed under a rainfall simulator to simulate field conditions. Soil evaporation was reduced with surface placed residues, resulting in a larger soilwater content than with residue incorporation. At the same time, fast desiccation of the residue mulch was observed. Mulch-derived C and N were concentrated near the soil surface, while residue-C and -N were distributed more deeply in the soil profile with residue incorporation. Microbial activity was closely related to soluble carbon concentrations in the soil profile. Differences in water and nutrient availability resulted in a slower decomposition rate of residues left at the soil surface than when incorporated in soil. Net nitrogen mineralization was larger in soil under mulch than with residue incorporation.
Further, the influence of crop residue location on the fate of C and N in soil and soil aggregates was investigated to elucidate the mechanisms controlling carbon storage in soil. On the short term, a large fraction of particulate organic matter (POM) was left at the soil surface, while almost all of the POM had disappeared with residue incorporation. Residue addition increased the aggregate mean weight diameter (MWD) compared to the control soil, and a larger MWD was obtained in the 0-5 cm soil layer under mulch than with residue incorporation. The total amount of residue-C recovered in the aggregate fractions did not significantly differ between treatments. However, this carbon was mostly located in the upper soil layer with mulch, while it was almost equally distributed over the two soil layers with residue incorporation. Despite the different way for new C toenter the soil, the relative distribution of residue-C in the various aggregate fractions did not differ between the two treatments on the longer term - probably because in both treatments residue-C mainly entered the aggregate fractions as soluble C.
Finally, the interaction of crop residue location with residue quality regarding C and N mineralization was examined. Residue mulch significantly reduced soil water evaporation, the extent of reduction depended on physical properties of the mulch layer. Changes in mulch water content, assumed as the main factor controlling surface residue decomposition, also depended on (physical) residue quality. When incorporated, C mineralization rates were mainly influenced by the biochemical residue quality, e.g. C:N ratio and soluble compounds. The strongest interactions between residue location and quality were observed in the N dynamics: net N mineralization was determined by the interaction between soil water content (depending on residue location) and N availability (depending on residue quality). Our results contributed to the development and calibration of a submodule of the PASTIS model (Garnier et al., 2003), describing the decomposition of mulched residues. Modelling with PASTISmulch allowed to access gross N fluxes, to estimate nitrate transport and potential leaching in the soil profile and to quantify the impact of residue location and quality on C and N mineralization in soil.

Keywords: carbon, nitrogen, decomposition, crop residue location and quality, modelling
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Theses
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https://tel.archives-ouvertes.fr/tel-00121922
Contributor : Filip Coppens <>
Submitted on : Friday, December 22, 2006 - 2:51:39 PM
Last modification on : Saturday, June 6, 2020 - 9:11:34 PM
Long-term archiving on: : Tuesday, April 6, 2010 - 9:29:55 PM

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  • HAL Id : tel-00121922, version 1
  • PRODINRA : 252080

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Filip Coppens. Water, carbon and nitrogen dynamics in soil - Influence of crop residue location and quality. Earth Sciences. Institut national agronomique paris-grignon - INA P-G; Université Catholique de Louvain, 2005. English. ⟨tel-00121922⟩

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