Sinergias y trade-offs del secuestro de carbono con otros servicios de los agroecosistemas: una síntesis de literatura global

Comunicación oral presentada en: XVI Congreso Nacional de la Asociación Española de Ecología Terrestre. La Ecología en una biosfera humanizada. Almería, España. 16-20 octubre (2023)Las prácticas de manejo agrícola que incrementan el secuestro de carbono (C) promueven otros servicios de los agroecosistemas, como el mantenimiento de la estructura y la fertilidad del suelo o de la biodiversidad edáfica. Sin embargo, pueden incrementar la emisión de gases de efecto invernadero (GEIs) y la pérdida de nutrientes. Con el objetivo de revisar si las prácticas de secuestro de C muestran sinergias con la estructura y la biota edáficas, pero generan trade-offs en términos de emisión de CO2 y N2O o pérdidas de N y P, realizamos una síntesis de literatura global. Realizamos búsquedas sistemáticas de literatura para detectar artículos que evaluaran experimentalmente el efecto de minimizar la perturbación del suelo, diversificar los agroecosistemas y/o incrementar los aportes de materia orgánica frente a la utilización de prácticas convencionales. Detectamos 771 publicaciones, de las cuales incluimos 234 que analizaban 572 efectos en 228 sitios de 38 países. Las prácticas de manejo sostenible incrementaron el C en el suelo sin comprometer el rendimiento de los cultivos. El secuestro de C tuvo efectos positivos sobre la biota del suelo, más evidentes en términos de biomasa que de biodiversidad, así como sobre la agregación, porosidad, retención de agua y reducción de la compactación. Los efectos negativos del secuestro de C fueron en términos de emisión de CO2 y pérdida potencial de N. Discutiremos cómo estos efectos variaron entre prácticas de manejo, en el tiempo y el espacio, y revisaremos los principales vacíos de conocimiento detectados en la literatura

Trade-offs and synergies of carbon sequestration in global agricultural soils: a literature synthesis

Comunicación oral presentada en: EGU General Assembly 2023. Viena, Austria, 23-28 abril (2023)Agricultural management practices aimed at sequestering carbon (C) in soils can have synergies with many agroecosystem services, but may come at the cost of increased greenhouse gas (GHG) emissions and nutrient losses. We performed a systematic literature synthesis to review whether C sequestration practices show synergies with soil structure and soil biota, but generate trade-offs in terms of CO2 and N2O emissions or N and P losses worldwide. We also assessed whether the magnitude of trade-offs and synergies vary across climatic regions and over time. We performed systematic literature searches in the Web of Science for articles that: 1. experimentally assess the effect of minimising soil disturbance, diversifying agroecosystems, and/or increasing organic matter inputs versus standard practices, and 2. include measurements of C sequestration and at least another response variable related to synergies or trade-offs. We retrieved 771 publications, 537 of which were excluded based on i) the type of article (review, opinion papers), ii) a focus on non-soil habitats, forests or organic soils, or iii) experimental designs not matching our criteria. We included 234 studies that report 572 effects of sustainable practices on 228 sites located in 38 countries. Experiments averaged 10 years of monitoring and the majority reported effects of increasing organic matter inputs and minimising soil disturbance (88%) in temperate and continental climates (75%). Soil organic C increased without compromising crop yields considering all management practices together, i.e. positive effects of sustainable versus standard practices on C sequestration were more frequent than expected by chance. As expected, C sequestration promoted soil biota, but effects were more evident on biomass than on diversity. We also detected synergistic effects on soil aggregation, porosity, water retention and compaction. Negative effects of C retention practices were significant when considering GHG emissions and nutrient losses, particularly for CO2 emissions and mineral N accumulation. However, the magnitude of these trade-offs varied significantly depending on the metrics used to measure them, e.g. field versus lab GHG fluxes. We discuss how these effects vary across management practices, time and space, and review main knowledge gaps detected in the literature

Laboratory estimates obscure the patterns of GHG emissions from agricultural soils

Comunicación oral presentada en: EJP Soil Annual Science Days 2023. Riga, Letonia 12-14 junio 2023Agricultural management practices aimed at sequestering carbon (C) in soils show synergies with many agroecosystem services, but may come at the cost of increased greenhouse gas (GHG) emissions. We performed a systematic literature synthesis, followed by a meta-analysis and experimental measurements, to analyse whether C sequestration practices generate trade-offs in terms of CO2 and N2O emissions. We performed systematic literature searches in the Web of Science to look for articles published worldwide that experimentally assess the effect of: 1. minimising soil disturbance (reduced or no tillage), 2. diversifying agroecosystems (crop rotations, cover crops, intercropping), and/or 3. increasing organic matter inputs (crop residue retention, organic amendments) versus standard practices. We only included studies that quantified C sequestration and at least another response variable related to the synergies or trade-offs of C sequestration. We retrieved 771 publications, 537 of which were excluded based on the type of article, a focus on non-soil habitats, forests or organic soils, or experimental designs not matching our criteria. We included 234 studies that report 572 effects of sustainable practices on 228 sites located in 38 countries. Experiments averaged 10 years of monitoring and the majority reported effects of increasing organic matter inputs and minimising soil disturbance (88%) in temperate and continental climates (75%). Sustainable practices effectively sequestered more C than standard practices considering all studies together. In total, we detected 353 effects related to CO2 and N2O emissions, 51% of which were measured as field fluxes and 43% as laboratory fluxes. Taking both types of measurements, C sequestration increased GHG emissions, particularly CO2. However, the response of CO2 and N2O emissions (increase, neutral, decrease) of sustainable versus standard agricultural practices varied significantly depending on how emissions were measured (field or laboratory fluxes). This result was confirmed in a subsequent meta-analysis, including 71 articles that report 123 independent experiments: CO2 and N2O emissions increased significantly when using agricultural practices that sequester C, but the magnitude of this trade-off depended on the use of field or laboratory measurements. This pattern was remarkable for CO2, where lab fluxes (N=48) yielded significantly larger responses than field fluxes (N=50). Finally, we quantified CO2 emissions, both as field and laboratory fluxes, in a long-term (27 year) experiment in central Spain, comparing standard tillage (mouldboard plough 30 cm), reduced tillage (chisel plough, 15 cm) and no tillage (direct seeding). Field fluxes measured weekly for a month were significantly lower under no tillage compared to standard tillage, while laboratory fluxes under controlled conditions yielded the opposite result. Independent methodological approaches indicate that the use of laboratory fluxes, particularly to measure CO2, might overestimate the magnitude of the trade-offs of C sequestration in terms of climate regulation services

Effects of different tillage regimes on soil structural characteristics along a pedoclimatic gradient

International audienceIntensive tillage regimes may cause detrimental effects on soil pore characteristics and structural stability. Conservation tillage has been suggested as an effective measure to avoid such adverse effects as well as to increase soil organic matter in soil surface layers. However, the accumulation of soil organic matter may also promote nitrous oxide emissions and nutrient losses through strong links between the carbon and nitrogen cycles. The TRACE-Soils project aims to identify mechanismsunderpinning trade-offs and synergies of soil carbon sequestration, greenhouse gas emissions and nutrient losses in agricultural soils across Europe.Soil structure is a driving factor in the transport of water and gas through soil, and influences, among others, the prevalence of oxic and anoxic soil processes. While it is common knowledge that soil structure is highly responsive to soil management practices, knowledge on the effects of different tillage strategies on soil structure in relation to trade-offs and synergies of soil carbon sequestration is still lacking. We conducted a range of laboratory measurements on intact soil cores (100-cm3) taken from seven long-term agricultural experiments (12 years or longer) with a common experimental setup located along a pedoclimatic gradient in Europe.We measured oxygen diffusivity and air permeability at -100 hPa matric potential and deducted airfilled and water-filled pore space at -100, -60 and -30 hPa matric potential as well as dry bulk density from balance-measurements. The soil samples were taken from two depths – 0–0.1 m and 0.1–0.2 m – after harvest, prior to any further field operations. We tested for differences (p <.05) in tillage regime (inversion tillage, reduced tillage, no tillage), depth and their interaction across the long-term experiments, as well as for confounded location-effects.Location and soil depth generally had the strongest effect on the assessed soil characteristics, while the effect of tillage practice and the interaction between tillage and depth often was much smaller or not significant. The effect of tillage practice was pronounced but generally interacted with depth. For77 instance, a higher water-filled pore space at -100 hPa was found for no tillage (63%) compared to inversion tillage (58%) at 0–0.1 m depth (across locations). The effect of depth and/or treatment could not be generalised to all individual long-term experiments assessed. We observed strong interaction effects between depth and experimental location. Moreover, we observed an interaction between tillage practice and experimental location on pore conductivity characteristics, except for oxygen diffusivity.These results show that the effects of location and sampling depth generally overshadowed the longterm effect of tillage on soil structural characteristics in the topsoil when soil was sampled after thegrowing season. Stronger effects of tillage may have occurred if samples had been taken closer to thetime of tillage

Laboratory estimates obscure the patterns of GHG emissions from agricultural soils

International audienceAgricultural management practices aimed at sequestering carbon (C) in soils show synergies with many agroecosystem services, but may come at the cost of increased greenhouse gas (GHG) emissions. We performed a systematic literature synthesis, followed by a meta-analysis and experimental measurements, to analyse whether C sequestration practices generate trade-offs in terms of CO2 and N2O emissions. We performed systematic literature searches in the Web of Science to look for articles published worldwide that experimentally assess the effect of: 1. minimising soil disturbance (reduced or no tillage), 2. diversifying agroecosystems (crop rotations, cover crops,intercropping), and/or 3. increasing organic matter inputs (crop residue retention, organic amendments) versus standard practices. We only included studies that quantified C sequestration and at least another response variable related to the synergies or trade-offs of C sequestration. We retrieved 771 publications, 537 of which were excluded based on the type of article, a focus on nonsoil habitats, forests or organic soils, or experimental designs not matching our criteria. We included 234 studies that report 572 effects of sustainable practices on 228 sites located in 38 countries.Experiments averaged 10 years of monitoring and the majority reported effects of increasing organic matter inputs and minimising soil disturbance (88%) in temperate and continental climates (75%).Sustainable practices effectively sequestered more C than standard practices considering all studies together. In total, we detected 353 effects related to CO2 and N2O emissions, 51% of which were measured as field fluxes and 43% as laboratory fluxes. Taking both types of measurements, C sequestration increased GHG emissions, particularly CO2. However, the response of CO2 and N2O63 emissions (increase, neutral, decrease) of sustainable versus standard agricultural practices varied significantly depending on how emissions were measured (field or laboratory fluxes). This result was confirmed in a subsequent meta-analysis, including 71 articles that report 123 independentexperiments: CO2 and N2O emissions increased significantly when using agricultural practices that sequester C, but the magnitude of this trade-off depended on the use of field or laboratory measurements. This pattern was remarkable for CO2, where lab fluxes (N=48) yielded significantlylarger responses than field fluxes (N=50). Finally, we quantified CO2 emissions, both as field and laboratory fluxes, in a long-term (27 year) experiment in central Spain, comparing standard tillage (mouldboard plough 30 cm), reduced tillage (chisel plough, 15 cm) and no tillage (direct seeding). Fieldfluxes measured weekly for a month were significantly lower under no tillage compared to standard tillage, while laboratory fluxes under controlled conditions yielded the opposite result. Independent methodological approaches indicate that the use of laboratory fluxes, particularly to measure CO2, might overestimate the magnitude of the trade-offs of C sequestration in terms of climate regulation services