HAL (Le Centre pour la Communication Scientifique Directe), Oct 5, 2014
Though it is of crucial importance in order to better understand carbon stabilization in soils, t... more Though it is of crucial importance in order to better understand carbon stabilization in soils, the chemical nature of stable soil organic matter (SOM) is poorly characterized. This is explained by two major difficulties: (1) there is sti ll no successful experimental way to isolate the pool of SOM that has a pluri - decennial residence time and (2) SOM with high residence time is often associated to minerals, which complicates its characterization. In this work, we overcame these two major d ifficulties by characterizing samples from long term bare fallow (LTBF) experiments using the state - of - the - art synchrotron - based NEXAFS spectroscopy (Canadian Light Source, Saskatoon, Canada). Firstly, LTBF experiments offer a unique opportunity to study s table SOM, as without carbon inputs and with continuing biodegradation and mineralization, SOM becomes progressively enriched in its most stable components. Secondly, NEXAFS technique allows the characterization of Carbon speciation with no sample pre - trea tments and no noise induced by the mineral part of the samples. In this work, the fluorescence emission spectra at the Carbon K - edge threshold (280 eV) were measured for samples taken up at the initiation of 5 different european LTBF experiments and severa l decades later. Results show that differences in chemical composition between di ff erent dates are subtle but signi fi cant and spectra are highly reproducible between fi eld replicates. More advanced data treatment is ongoing and will be presented at SOM6
<p&amp... more <p><span>The conventional soil organic matter (SOM) decay paradigm considers SOM quality as the dominant decay limitation, and it is modelled with simple first-order decay kinetics. This view and modelling approach is criticized for being too simplistic and unreliable for predictive purposes. It is still under debate if first-order models can correctly capture the variability in temporal SOM decay observed between different environments. The hypothesis needs to be tested statistically, but this implies the use of a dynamic model with multiple degrees of freedom to describe the observations. Since we want to test the general validity of the SOC decay theory the test must also include multiple sites, and rises the problem of how to describe the unavoidable local variability. This defines a multivariate space where the hypothesis must be tested which, considering also the known problem of an equifinality “by design” in biogeochemical models, generate difficulties.</span></p> <p><span>To address this issue, we calibrated a first-order model (Q) on six long-term bare fallow field experiments across Europe within a Bayesian framework assuming some general and some local parameters. Following conventional SOM decay theory, we assumed that parameters directly describing SOC decay (rate of SOM quality change and decomposer metabolism) are thermodynamically constrained, therefore valid for all sites. Initial litter input quality and edaphic interactions (both local by definition) and microbial efficiency (possibly affected by nutrient stoichiometry) were instead assumed to be site-specific. Initial litter input quality explained most observed kinetics variability, and the model predicted a convergence toward a common kinetics over time, while site-specific variables played no detectable role. All these characteristics could be represented with posterior probability distributions and their comparison provided the hypothesis testing.</span></p> <p><span>According to our analysis the decay of decades-old SOM seemed mostly influenced by OM chemistry and was well described by first order kinetics and a single set of general kinetics parameters.</span></p>
ABSTRACT Determining the relative stability of soil organic carbon (SOC) is a critical step to be... more ABSTRACT Determining the relative stability of soil organic carbon (SOC) is a critical step to better understanding its vulnerability to global change. The absence of convincing physical or chemical procedures to define, characterize or isolate relatively labile versus stable pools of SOC makes it difficult to study. Long-term bare fallow (LTBF) experiments, in which C inputs have been stopped for several decades, provide a unique opportunity to study stable SOC without the inherent artefacts induced by extraction procedures, the hypothesis being that SOC is gradually enriched in stable C with time as labile components decompose. We determined the evolution of energetic and chemical characteristics of bulk SOC in five LTBF experiments across Europe: Askov (DK), Grignon (FR), Rothamsted (UK), Ultuna (SW) and Versailles (FR), using simultaneous thermal analysis (i.e., thermogravimetry (TG), differential scanning calorimetry (DSC) and evolved CO2 gas analysis (CO2-EGA)) and diffuse reflectance Fourier transformed mid-infrared spectroscopy (DRIFT-MIRS). Results of TG analyses showed that the temperature needed to combust the first half of the SOC (i.e., TG-T50) increased with bare fallow duration at all sites. Conversely, the energy density (in mJ mg-1 C) decreased with bare fallow duration. Combined together, these results provide a means to contrast the stable, mineral-associated SOC pool from any potential pyrogenic C, which would have much greater energy density. DRIFT-MIRS results showed that the "carboxylation index" (the ratio of C=O bonds peak area over (C=C + C=O) bonds peak areas) decreased with bare fallow duration, that aromaticity (C=C bond peak area over C content) increased with bare-fallow duration, and that the "reticulation index" (CH3 peak area over CH2 peak area) decreased with increasing bare fallow duration at Rothamsted, Versailles and Ultuna. These trends were less clear or not observed at Grignon due to the presence of carbonates or at Askov due to greater variability, thus precluding unequivocal conclusions. Our results showed that in spite of the heterogeneity of the soils at the LTBF sites, generalized energetic and chemical pathways exist for SOC stabilization. The DRIFT-MIRS indices demonstrate that SOC stabilization is accompanied by a consistent evolution of its bulk chemical composition across most sites, over decades (ca. 50 years). The general decarboxylation of SOC observed in bare fallow challenges the current view of SOM decomposition, raising questions about the oxidative state of the stable C pool. The increased burning temperature and lower energy density of stable SOC suggest that decomposition of the stable C pool may be more temperature sensitive and thus vulnerable to increased temperature. Conversely, decreasing energy density suggests that priming might be the only means available for the microbial community to decompose this pool of SOC, and that SOC stability may be a function of low potential energy gain from decomposition of this material. Finally, this study illustrates the enormous value of such long-term field experiments, and a potential multi-faceted approach to quantify SOC stability as an ecosystem property.
Стабильность почвенного органического вещества является главным источником неопределен- ности про... more Стабильность почвенного органического вещества является главным источником неопределен- ности прогноза концентрации CO2 в атмосфере в XXI веке. Разделение между стабильными и лабильными пулами углерода в почвах является важнейшей задачей, решение которой поможет понять механизмы стабилизации почвенного углерода
. Litter decomposition is an important factor affecting local and global C cycles. It is known th... more . Litter decomposition is an important factor affecting local and global C cycles. It is known that decomposition through soil microbial activity in ecosystems is mainly influenced by soil type and climatic conditions. However, for agroecosystems, there remains a need for a better understanding how management practices influence litter decomposition. This study examined the effect of different management practices on decomposition at 29 sites with long-term (mean duration of 38 years) field experiments (LTEs) using the Tea Bag Index (TBI) protocol with standard litter (Rooibos and Green tea) developed by Keuskamp et al. (2013). The objective was to determine if the TBI decomposition rate (k) and stabilization factor (S) are sensitive enough to detect differences in litter decomposition between management practices, and how they interact with edaphic factors, crop type and local climatic conditions. Tea bags were buried and collected after ~60 and 90 days in 16 Austrian and 13 Swedish sites. The treatments at Austrian LTEs focused on mineral and organic fertilization, tillage systems and crop residues management, whereas the Swedish LTEs addressed cropping systems, mineral fertilization and tillage systems. The results showed that in Austria, decomposition differed more between sites than between treatments for the same experiment category. Incorporation of crop residues and high N fertilization increased k. Minimum tillage had significantly higher k compared to reduced and conventional tillage. In Sweden, litter decomposition differed more between treatments than between sites. Fertilized plots showed higher S than non-fertilized and high N fertilization had the highest k. Growing spring cereal lead to higher k than forage. Random Forest regressions showed that k and S were mainly governed by climatic conditions, which explained more than 70 % of their variation. However, under similar climatic conditions, management practices strongly influenced decomposition dynamics. Thus, the TBI approach may be suitable to apply in a more large-scale network on LTEs for evaluating decomposition dynamics more precisely.
Soil compaction (SC) is a major threat for agriculture in Europe that affects many ecosystem func... more Soil compaction (SC) is a major threat for agriculture in Europe that affects many ecosystem functions, such as water and air circulation in soils, root growth, and crop production. Our objective was to present the results from five short-term (<5 years) case studies located along the north–south and east–west gradients and conducted within the SoilCare project using soil-improving cropping systems (SICSs) for mitigating topsoil and subsoil SC. Two study sites (SSs) focused on natural subsoil (˃25 cm) compaction using subsoiling tillage treatments to depths of 35 cm (Sweden) and 60 cm (Romania). The other SSs addressed both topsoil and subsoil SC (˃25 cm, Norway and United Kingdom; ˃30 cm, Italy) using deep-rooted bio-drilling crops and different tillage types or a combination of both. Each SS evaluated the effectiveness of the SICSs by measuring the soil physical properties, and we calculated SC indices. The SICSs showed promising results—for example, alfalfa in Norway showed go...
Predicting bi-decadal organic carbon mineralization in northwestern European soils with Rock-Eval... more Predicting bi-decadal organic carbon mineralization in northwestern European soils with Rock-Eval pyrolysis. EGU 2017, European Geophysical Union General Assembly 2017
In the context of climate change, one mitigation technique currently investigated is the use of p... more In the context of climate change, one mitigation technique currently investigated is the use of pyrogenic organic carbon (PyOC) -which is biomass turned into charcoal- to sequester carbon in soils with the hypothesis that PyOC is persistent and will not be biodegraded (or mineralized). In this study, we use the unique opportunity offered by five long term bare fallow (LTBF) experiments across Europe (Askov in Denmark, Grignon and Versailles in France, Ultuna in Sweden and Rothamsted in the United Kingdom) to compare the dynamics of PyOC and soil organic carbon (SOC) in the same plots at the decadal time scale (from 25 to 80 years of bare fallow depending on the site). Bare fallow plots were regularly sampled throughout the bare fallow duration and these samples were carefully archived. In bare fallow plots, with negligible external carbon input and with continuing biodegradation, SOC is depleting. Using the Benzene Polycarboxylic Acid (BPCA) technique to estimate the PyOC quantity a...
Mitigation and Adaptation Strategies for Global Change, 2020
International initiatives are emphasizing the capture of atmospheric CO2 in soil organic C (SOC) ... more International initiatives are emphasizing the capture of atmospheric CO2 in soil organic C (SOC) to reduce the climatic footprint from agroecosystems. One approach to quantify the contribution of management practices towards that goal is through analysis of long-term experiments (LTEs). Our objectives were to analyze knowledge gained in literature reviews on SOC changes in LTEs, to evaluate the results regarding interactions with pedo-climatological factors, and to discuss disparities among reviews in data selection criteria. We summarized mean response ratios (RRs) and stock change rate (SCR) effect size indices from twenty reviews using paired comparisons (N). The highest RRs were found with manure applications (30%, N = 418), followed by aboveground crop residue retention and the use of cover crops (9–10%, N = 995 and 129), while the effect of nitrogen fertilization was lowest (6%, N = 846). SCR for nitrogen fertilization exceeded that for aboveground crop residue retention (233 ...
HAL (Le Centre pour la Communication Scientifique Directe), Oct 5, 2014
Though it is of crucial importance in order to better understand carbon stabilization in soils, t... more Though it is of crucial importance in order to better understand carbon stabilization in soils, the chemical nature of stable soil organic matter (SOM) is poorly characterized. This is explained by two major difficulties: (1) there is sti ll no successful experimental way to isolate the pool of SOM that has a pluri - decennial residence time and (2) SOM with high residence time is often associated to minerals, which complicates its characterization. In this work, we overcame these two major d ifficulties by characterizing samples from long term bare fallow (LTBF) experiments using the state - of - the - art synchrotron - based NEXAFS spectroscopy (Canadian Light Source, Saskatoon, Canada). Firstly, LTBF experiments offer a unique opportunity to study s table SOM, as without carbon inputs and with continuing biodegradation and mineralization, SOM becomes progressively enriched in its most stable components. Secondly, NEXAFS technique allows the characterization of Carbon speciation with no sample pre - trea tments and no noise induced by the mineral part of the samples. In this work, the fluorescence emission spectra at the Carbon K - edge threshold (280 eV) were measured for samples taken up at the initiation of 5 different european LTBF experiments and severa l decades later. Results show that differences in chemical composition between di ff erent dates are subtle but signi fi cant and spectra are highly reproducible between fi eld replicates. More advanced data treatment is ongoing and will be presented at SOM6
&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp... more &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;The conventional soil organic matter (SOM) decay paradigm considers SOM quality as the dominant decay limitation, and it is modelled with simple first-order decay kinetics. This view and modelling approach is criticized for being too simplistic and unreliable for predictive purposes. It is still under debate if first-order models can correctly capture the variability in temporal SOM decay observed between different environments. The hypothesis needs to be tested statistically, but this implies the use of a dynamic model with multiple degrees of freedom to describe the observations. Since we want to test the general validity of the SOC decay theory the test must also include multiple sites, and rises the problem of how to describe the unavoidable local variability. This defines a multivariate space where the hypothesis must be tested which, considering also the known problem of an equifinality &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#8220;by design&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#8221; in biogeochemical models, generate difficulties.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;To address this issue, we calibrated a first-order model (Q) on six long-term bare fallow field experiments across Europe within a Bayesian framework assuming some general and some local parameters. Following conventional SOM decay theory, we assumed that parameters directly describing SOC decay (rate of SOM quality change and decomposer metabolism) are thermodynamically constrained, therefore valid for all sites. Initial litter input quality and edaphic interactions (both local by definition) and microbial efficiency (possibly affected by nutrient stoichiometry) were instead assumed to be site-specific. Initial litter input quality explained most observed kinetics variability, and the model predicted a convergence toward a common kinetics over time, while site-specific variables played no detectable role. All these characteristics could be represented with posterior probability distributions and their comparison provided the hypothesis testing.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;According to our analysis the decay of decades-old SOM seemed mostly influenced by OM chemistry and was well described by first order kinetics and a single set of general kinetics parameters.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;
ABSTRACT Determining the relative stability of soil organic carbon (SOC) is a critical step to be... more ABSTRACT Determining the relative stability of soil organic carbon (SOC) is a critical step to better understanding its vulnerability to global change. The absence of convincing physical or chemical procedures to define, characterize or isolate relatively labile versus stable pools of SOC makes it difficult to study. Long-term bare fallow (LTBF) experiments, in which C inputs have been stopped for several decades, provide a unique opportunity to study stable SOC without the inherent artefacts induced by extraction procedures, the hypothesis being that SOC is gradually enriched in stable C with time as labile components decompose. We determined the evolution of energetic and chemical characteristics of bulk SOC in five LTBF experiments across Europe: Askov (DK), Grignon (FR), Rothamsted (UK), Ultuna (SW) and Versailles (FR), using simultaneous thermal analysis (i.e., thermogravimetry (TG), differential scanning calorimetry (DSC) and evolved CO2 gas analysis (CO2-EGA)) and diffuse reflectance Fourier transformed mid-infrared spectroscopy (DRIFT-MIRS). Results of TG analyses showed that the temperature needed to combust the first half of the SOC (i.e., TG-T50) increased with bare fallow duration at all sites. Conversely, the energy density (in mJ mg-1 C) decreased with bare fallow duration. Combined together, these results provide a means to contrast the stable, mineral-associated SOC pool from any potential pyrogenic C, which would have much greater energy density. DRIFT-MIRS results showed that the &quot;carboxylation index&quot; (the ratio of C=O bonds peak area over (C=C + C=O) bonds peak areas) decreased with bare fallow duration, that aromaticity (C=C bond peak area over C content) increased with bare-fallow duration, and that the &quot;reticulation index&quot; (CH3 peak area over CH2 peak area) decreased with increasing bare fallow duration at Rothamsted, Versailles and Ultuna. These trends were less clear or not observed at Grignon due to the presence of carbonates or at Askov due to greater variability, thus precluding unequivocal conclusions. Our results showed that in spite of the heterogeneity of the soils at the LTBF sites, generalized energetic and chemical pathways exist for SOC stabilization. The DRIFT-MIRS indices demonstrate that SOC stabilization is accompanied by a consistent evolution of its bulk chemical composition across most sites, over decades (ca. 50 years). The general decarboxylation of SOC observed in bare fallow challenges the current view of SOM decomposition, raising questions about the oxidative state of the stable C pool. The increased burning temperature and lower energy density of stable SOC suggest that decomposition of the stable C pool may be more temperature sensitive and thus vulnerable to increased temperature. Conversely, decreasing energy density suggests that priming might be the only means available for the microbial community to decompose this pool of SOC, and that SOC stability may be a function of low potential energy gain from decomposition of this material. Finally, this study illustrates the enormous value of such long-term field experiments, and a potential multi-faceted approach to quantify SOC stability as an ecosystem property.
Стабильность почвенного органического вещества является главным источником неопределен- ности про... more Стабильность почвенного органического вещества является главным источником неопределен- ности прогноза концентрации CO2 в атмосфере в XXI веке. Разделение между стабильными и лабильными пулами углерода в почвах является важнейшей задачей, решение которой поможет понять механизмы стабилизации почвенного углерода
. Litter decomposition is an important factor affecting local and global C cycles. It is known th... more . Litter decomposition is an important factor affecting local and global C cycles. It is known that decomposition through soil microbial activity in ecosystems is mainly influenced by soil type and climatic conditions. However, for agroecosystems, there remains a need for a better understanding how management practices influence litter decomposition. This study examined the effect of different management practices on decomposition at 29 sites with long-term (mean duration of 38 years) field experiments (LTEs) using the Tea Bag Index (TBI) protocol with standard litter (Rooibos and Green tea) developed by Keuskamp et al. (2013). The objective was to determine if the TBI decomposition rate (k) and stabilization factor (S) are sensitive enough to detect differences in litter decomposition between management practices, and how they interact with edaphic factors, crop type and local climatic conditions. Tea bags were buried and collected after ~60 and 90 days in 16 Austrian and 13 Swedish sites. The treatments at Austrian LTEs focused on mineral and organic fertilization, tillage systems and crop residues management, whereas the Swedish LTEs addressed cropping systems, mineral fertilization and tillage systems. The results showed that in Austria, decomposition differed more between sites than between treatments for the same experiment category. Incorporation of crop residues and high N fertilization increased k. Minimum tillage had significantly higher k compared to reduced and conventional tillage. In Sweden, litter decomposition differed more between treatments than between sites. Fertilized plots showed higher S than non-fertilized and high N fertilization had the highest k. Growing spring cereal lead to higher k than forage. Random Forest regressions showed that k and S were mainly governed by climatic conditions, which explained more than 70 % of their variation. However, under similar climatic conditions, management practices strongly influenced decomposition dynamics. Thus, the TBI approach may be suitable to apply in a more large-scale network on LTEs for evaluating decomposition dynamics more precisely.
Soil compaction (SC) is a major threat for agriculture in Europe that affects many ecosystem func... more Soil compaction (SC) is a major threat for agriculture in Europe that affects many ecosystem functions, such as water and air circulation in soils, root growth, and crop production. Our objective was to present the results from five short-term (<5 years) case studies located along the north–south and east–west gradients and conducted within the SoilCare project using soil-improving cropping systems (SICSs) for mitigating topsoil and subsoil SC. Two study sites (SSs) focused on natural subsoil (˃25 cm) compaction using subsoiling tillage treatments to depths of 35 cm (Sweden) and 60 cm (Romania). The other SSs addressed both topsoil and subsoil SC (˃25 cm, Norway and United Kingdom; ˃30 cm, Italy) using deep-rooted bio-drilling crops and different tillage types or a combination of both. Each SS evaluated the effectiveness of the SICSs by measuring the soil physical properties, and we calculated SC indices. The SICSs showed promising results—for example, alfalfa in Norway showed go...
Predicting bi-decadal organic carbon mineralization in northwestern European soils with Rock-Eval... more Predicting bi-decadal organic carbon mineralization in northwestern European soils with Rock-Eval pyrolysis. EGU 2017, European Geophysical Union General Assembly 2017
In the context of climate change, one mitigation technique currently investigated is the use of p... more In the context of climate change, one mitigation technique currently investigated is the use of pyrogenic organic carbon (PyOC) -which is biomass turned into charcoal- to sequester carbon in soils with the hypothesis that PyOC is persistent and will not be biodegraded (or mineralized). In this study, we use the unique opportunity offered by five long term bare fallow (LTBF) experiments across Europe (Askov in Denmark, Grignon and Versailles in France, Ultuna in Sweden and Rothamsted in the United Kingdom) to compare the dynamics of PyOC and soil organic carbon (SOC) in the same plots at the decadal time scale (from 25 to 80 years of bare fallow depending on the site). Bare fallow plots were regularly sampled throughout the bare fallow duration and these samples were carefully archived. In bare fallow plots, with negligible external carbon input and with continuing biodegradation, SOC is depleting. Using the Benzene Polycarboxylic Acid (BPCA) technique to estimate the PyOC quantity a...
Mitigation and Adaptation Strategies for Global Change, 2020
International initiatives are emphasizing the capture of atmospheric CO2 in soil organic C (SOC) ... more International initiatives are emphasizing the capture of atmospheric CO2 in soil organic C (SOC) to reduce the climatic footprint from agroecosystems. One approach to quantify the contribution of management practices towards that goal is through analysis of long-term experiments (LTEs). Our objectives were to analyze knowledge gained in literature reviews on SOC changes in LTEs, to evaluate the results regarding interactions with pedo-climatological factors, and to discuss disparities among reviews in data selection criteria. We summarized mean response ratios (RRs) and stock change rate (SCR) effect size indices from twenty reviews using paired comparisons (N). The highest RRs were found with manure applications (30%, N = 418), followed by aboveground crop residue retention and the use of cover crops (9–10%, N = 995 and 129), while the effect of nitrogen fertilization was lowest (6%, N = 846). SCR for nitrogen fertilization exceeded that for aboveground crop residue retention (233 ...
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