Effects of crop residue incorporation and properties on combined soil gaseous N2_{2}O, NO, and NH3_{3} emissions—A laboratory-based measurement approach

Crop residues may serve as a significant source of soil emissions of N$_{2}$O and other trace gases. According to the emission factors (EFs) set by the Intergovernmental Panel on Climate Change (IPCC), N$_{2}$O emission is proportional to the amount of N added by residues to the soil. However, the effects of crop residues on the source and sink strength of agroecosystems for trace gases are regulated by their properties, such as the C and N content; C/N ratio; lignin, cellulose, and soluble fractions; and residue humidity. In the present study, an automated dynamic chamber method was used in combination with soil mesocosms to simultaneously measure the effects of nine different crop residues (oilseed rape, winter wheat, field pea, maize, potato, mustard, red clover, sugar beet, and ryegrass) on soil respiration (CO$_{2}$) and reactive N fluxes (N$_{2}$O, NO, and NH$_{3}$) at a high temporal resolution. Specifically, crop residues were incorporated in the 0–4 cm topsoil layer and incubated for 60 days at a constant temperature (15 °C) and water-filled pore space (60% WFPS). Residue incorporation immediately and sharply increased soil N$_{2}$O and CO$_{2}$ emissions, but these were short-lived and returned to background levels within respectively 10 and 30 days. The magnitude of increase in soil NO flux following residue incorporation was lower than that in CO$_{2}$ and N$_{2}$O fluxes, with peak emissions observed around day 20. Overall, the N content or C/N ratio of the applied residue could not sufficiently explain the variation in soil N2O and NO emissions. The range of the calculated N$_{2}$O EFs over a 60-day period was −0.17 to +4.5, being wider than that proposed by the IPCC (+0.01 to +1.1). Therefore, the residue maturity stage may be used as a simple proxy to estimate the N$_{2}$O + NO emissions from incorporated residue

Soil organic carbon models need independent time-series validation for reliable prediction

Numerical models are crucial to understand and/or predict past and future soil organic carbon dynamics. For those models aiming at prediction, validation is a critical step to gain confidence in projections. With a comprehensive review of ~250 models, we assess how models are validated depending on their objectives and features, discuss how validation of predictive models can be improved. We find a critical lack of independent validation using observed time series. Conducting such validations should be a priority to improve the model reliability. Approximately 60% of the models we analysed are not designed for predictions, but rather for conceptual understanding of soil processes. These models provide important insights by identifying key processes and alternative formalisms that can be relevant for predictive models. We argue that combining independent validation based on observed time series and improved information flow between predictive and conceptual models will increase reliability in predictions

Challenges of accounting nitrous oxide emissions from agricultural crop residues

Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N$_2$O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N$_2$O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N$_2$O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N$_2$O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N$_2$O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N$_2$O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N$_2$O emissions

Challenges of accounting nitrous oxide emissions from agricultural crop residues

Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N2O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N2O emissions

Challenges of accounting nitrous oxide emissions from agricultural crop residues

Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N2O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N2O emissions

Évolution des polluants organiques au cours du compostage de déchets organiques : approche expérimentale et modélisation

The levels and availability of organic pollutants (OPs) are criteria for compost quality that determine their environmental impacts. In this work, we characterized the evolution of OP speciation during the composting of organic wastes in order to estimate OP availability in final composts. Four 14 C-labeled OPs were studied during the composting of sewage sludge with green waste: a polycyclic aromatic hydrocarbon (fluoranthene), two surfactants (4-n-nonylphenol, NP, and sodium linear alkylbenzene sulfonate, LAS) and a herbicide (glyphosate). An experimental set-up including six small-scale composting pilots was built. It was used to simulate the composting process with a good reproducibility. Organic pollutant sorption and mineralization capacities were analyzed during composting. Simple molecules were mainly degraded during the active composting phases and complex molecules during the maturation. Sorption decreased as compost maturity increased, except for glyphosate. The evolution of OP speciation during composting showed that the dissipation of LAS was largely due to mineralization, those of fluoranthene to the formation of non-extractable residues. Both mineralization and formation of non-extractable residues contributed to the dissipation of NP and glyphosate. The direct availability of OP in final compost was low. A model (COP-Compost) simulating the evolution of organic matter and OPs during composting was proposed. Hypotheses, specifying that the OP biodegradation and formation of non-extractable residues would be dependent of the overall microbial activity driven by organic matter decomposition, were validated.La qualité des composts dépend de leurs teneurs en polluants organiques (OPs). L'objectif était de caractériser l'évolution de la spéciation des OPs au cours du compostage afin d'évaluer leur disponibilité dans les composts finaux. Quatre OPs marqués au 14 C ont été étudiés lors du compostage d'une boue d'épuration mélangée à des déchets verts : un HAP (fluoranthène), deux surfactants (4-n-nonylphénol - NP et un alkylbenzène sulfonate linéaire - LAS) et un herbicide (glyphosate). Un dispositif de compostage comprenant six mini-pilotes et permettant un compostage réaliste et reproductible a été conçu. Les propriétés de sorption et de minéralisation des OPs ont été suivies au cours du compostage. Les molécules simples ont été principalement dégradées lors des phases actives et les molécules complexes lors de la maturation. Les capacités de sorption ont diminué au cours du compostage, sauf pour le glyphosate. L'évolution de la spéciation des OPs a montré que la dissipation du LAS a été largement provoquée par sa minéralisation, celle du fluoranthène par la formation de résidus non-extractibles. La minéralisation et la formation de résidus non-extractibles ont contribué de façon équivalente à la dissipation du NP et du glyphosate. La disponibilité directe des OPs en fin de compostage était faible. Un modèle (COP-Compost) simulant l'évolution de la matière organique et des OPs au cours du compostage a été proposé. Des hypothèses selon lesquelles la biodégradation des OPs et la formation de résidus non-extractibles sont influencées par l'évolution de la taille de la biomasse microbienne, elle-même dépendante de la décomposition de la matière organique, ont pu être validées

Couplages et contrôles des cycles du carbone et de l’azote par les communautés microbiennes dans les sols cultivés

National audienceLe couplage des cycles du carbone et de l’azote dans les sols est sous le contrôle des communautés microbiennes hétérotrophes, pour lesquelles les matières organiques entrantes (litières végétales aériennes et souterraines, effluents et produits organiques) sont les ressources trophiques. Ce chapitre aborde comment la diversité et l’activité de ces communautés, ainsi que les proportions des éléments majeurs (carbone, azote, soufre, phosphore) des matières organiques vivantes et mortes, déterminent la partition entre le carbone qui est minéralisé, assimilé par les microorganismes, stocké dans les sols, et les flux de nutriments associés. En retour, la nature des couverts végétaux des agrosystèmes, leurs mélanges éventuels, et les ressources en nutriments disponibles, notamment la richesse en azote du sol, structurent les communautés microbiennes du sol et influencent leurs activités. Sur la base de ces connaissances récentes, est illustré comment l’objectif de réduire l’utilisation des fertilisants de synthèse et de limiter les excédents d’azote minéral dans les agrosystèmes, peut être envisagé en favorisant le couplage des cycles biogéochimiques dans les sols grâce à des systèmes de culture basés sur l’utilisation d’espèces cultivées plus diversifiées

Évolution des polluants organiques au cours du compostage de déchets organiques (approche expérimentale et modélisation)

La qualité des composts dépend de leurs teneurs en polluants organiques (OPs). L'objectif était de caractériser l'évolution de la spéciation des OPs au cours du compostage afin d'évaluer leur disponibilité dans les composts finaux. Quatre OPs marqués au 14 C ont été étudiés lors du compostage d'une boue d'épuration mélangée à des déchets verts : un HAP (fluoranthène), deux surfactants (4-n-nonylphénol - NP et un alkylbenzène sulfonate linéaire - LAS) et un herbicide (glyphosate). Un dispositif de compostage comprenant six mini-pilotes et permettant un compostage réaliste et reproductible a été conçu. Les propriétés de sorption et de minéralisation des OPs ont été suivies au cours du compostage. Les molécules simples ont été principalement dégradées lors des phases actives et les molécules complexes lors de la maturation. Les capacités de sorption ont diminué au cours du compostage, sauf pour le glyphosate. L'évolution de la spéciation des OPs a montré que la dissipation du LAS a été largement provoquée par sa minéralisation, celle du fluoranthène par la formation de résidus non-extractibles. La minéralisation et la formation de résidus non-extractibles ont contribué de façon équivalente à la dissipation du NP et du glyphosate. La disponibilité directe des OPs en fin de compostage était faible. Un modèle (COP-Compost) simulant l'évolution de la matière organique et des OPs au cours du compostage a été proposé. Des hypothèses selon lesquelles la biodégradation des OPs et la formation de résidus non-extractibles sont influencées par l'évolution de la taille de la biomasse microbienne, elle-même dépendante de la décomposition de la matière organique, ont pu être validéesThe levels and availability of organic pollutants (OPs) are criteria for compost quality that determine their environmental impacts. In this work, we characterized the evolution of OP speciation during the composting of organic wastes in order to estimate OP availability in final composts. Four 14 C-labeled OPs were studied during the composting of sewage sludge with green waste: a polycyclic aromatic hydrocarbon (fluoranthene), two surfactants (4-n-nonylphenol, NP, and sodium linear alkylbenzene sulfonate, LAS) and a herbicide (glyphosate). An experimental set-up including six small-scale composting pilots was built. It was used to simulate the composting process with a good reproducibility. Organic pollutant sorption and mineralization capacities were analyzed during composting. Simple molecules were mainly degraded during the active composting phases and complex molecules during the maturation. Sorption decreased as compost maturity increased, except for glyphosate. The evolution of OP speciation during composting showed that the dissipation of LAS was largely due to mineralization, those of fluoranthene to the formation of non-extractable residues. Both mineralization and formation of non-extractable residues contributed to the dissipation of NP and glyphosate. The direct availability of OP in final compost was low. A model (COP-Compost) simulating the evolution of organic matter and OPs during composting was proposed. Hypotheses, specifying that the OP biodegradation and formation of non-extractable residues would be dependent of the overall microbial activity driven by organic matter decomposition, were validatedPARIS-AgroParisTech Centre Paris (751052302) / SudocSudocFranceF

Hemp harvest time impacts on the dynamics of microbial colonization and hemp stems degradation during dew retting

Dew retting, a selective microbial degradation of industrial hemp (Cannabis sativa L.) stems occurring after harvest under local climatic conditions, is an important field process for plant fibre uses. We investigated how the crop harvest time, which depends on the hemp valorization strategy envisaged by the farmer, affected the initial stem quality and the subsequent microbial degradation dynamics of retting. We used simulated rains and dews to carry out retting under laboratory conditions for 42 days at 15 °C with hemp stems harvested at different times (flowering and seed maturity stage). The microbial colonization and changes in the bast tissue architecture were tracked from day 0 to day 42 using colorimetry, surface infrared spectroscopy, chemical analysis, and scanning electron microscopy. The early changes in the microbial colonization and color of the stem surface and the degradation of the bast tissue parenchyma followed the same pattern during retting for the two stem qualities. However, the kinetic of these processes was 7–14 days faster for the flowering stems, which had higher initial soluble and lower lignin contents than the mature stems. The results suggest a promising potential use of colorimetry and surface infrared spectroscopy data as candidate indicators for the dew retting progress in the field. Besides the results of this study indicate that differences in hemp stem chemical composition due to different crop harvest time significantly impacted microbial colonization, biofilm formation and eventually dew retting duration