Soil C pools and aggregate stability

Towards climate-smart sustainable management of agricultural soils AGROECOlogical strategies for an efficient functioning of plant ‐ soil biota interactions to increase SOC sequestration AGROECOseqC Deliverable D6.1.3 Soil C pools and aggregate stability Due date of deliverable: M49 Actual submission date: 31.05.2024 Deliverable D6.1.3 Soil C pools and aggregate stability This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 862695 2 GENERAL DATA Grant Agreement: 862695 Project acronym: EJP SOIL Programme title: Towards climate-smart sustainable management of agricultural soils Programme website: www.ejpsoil.eu Project title: AGROECOlogical strategies for an efficient functioning of plant ‐ soil biota interactions to increase SOC sequestration Project website: https://ejpsoil.eu/soil-research/agroecoseqc Start date of the project: February 1st, 2020 Project duration: 60 months Name of lead contractor: INRAE Funding source: H2020-SFS-2018-2020 / H2020-SFS-2019-1 Type of action: European Joint Project COFUND DELIVERABLE NUMBER: D6.1.3 DELIVERABLE TITLE: Soil C pools and aggregate stability DELIVERABLE TYPE: Report WORK PACKAGE N: WP6 WORK PACKAGE TITLE: Soil C retainment through stable aggregates and microbial biomass activity DELIVERABLE LEADER: Skaidrė Supronienė (LAMMC) AUTHOR: DOI: S. Supronienė, G. Kadžienė, A. Šlepetienė, A. Skersienė, S. Pranaitienė, M. Doyeni, A. Shamshitov, A. Trinchera 10.5281/zenodo.14145251 DISSEMINATION LEVEL: CO Deliverable D6.1.3 Soil C pools and aggregate stability This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 862695 3 ABSTRACT Continuous agricultural activities lead to soil organic carbon (SOC) depletion, and agroecological intensification practices (i.e., reduced soil disturbance and crop diversification) have been suggested as strategies to increase SOC storage. The study aims to assess the effect of the agroecological intensification, introduced in different EU agricultural cropping systems, on soil carbon (C) pool and aggregate stability. The C-stock, soil microbial biomass carbon (SMB-C), SOC, water extractable organic carbon (WEOC) in bulk soil, fine and coarse soil aggregates, and water-stable aggregates (WSA) were measured during maximum nutrient uptake in plants under diversified agroecological practices across different environmental conditions (core sites: Italy (CS1), France (CS2), Denmark (CS4), Spain (CS5), Netherlands (CS6), Lithuania (CS7), Turkey (CS8), and Belgium (CS9)). The percentage of WSA (1-0.25 mm) varied among sites (countries) and treatments (p < 0.001). At sites CS7 and CS9, WSA was higher in T1 and T2 compared to the control, similar trend was observed at other sites, except CS1. The highest amount of C-stock in bulk soil (on average 92.9 t ha-1) was determined at site CS6 (Netherlands), lowest (on average 15.9 t ha-1) - at site CS2 (France). The only significant difference among treatments was found site CS2 (France), with higher C-stock in T2 compared to T1. Positive correlations were detected among all variables tested with strong correlations (r>0.5**l) of SMB-C with WSA, SOC, and WEOC in bulk soil. This study demonstrates the significance of agroecological practices in improving soil carbon stock and optimizing plant-soil-microbe interactions. Deliverable D6.1.3 Soil C pools and aggregate stability This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 862695 4 Table of Contents List of Tables ............................................................................................................................................ 4 List of Figures ........................................................................................................................................... 4 List of acronyms and abbreviations ......................................................................................................... 4 1. Introduction ..................................................................................................................................... 5 2. Materials and methods ................................................................................................................... 5 3. Main results ..................................................................................................................................... 7 List of references ................................................................................................................................... 10 List of Tables Table 1. Core-sites and treatments selected. ......................................................................................... 6 Table 2. Pearson's correlation analysis between the WSA, SOC, WEOC, C-stock, and SMB-C data. ...... 9 List of Figures Figure 1. Selected sites are represented as i) local-scale and ii) European-scale gradients of agroecological intensification.................................................................................................................. 7 Figure 2. Amount of water stable aggregates (%) within 0.25-1 mm soil fractions, under diversified agroecological practices and different environmental conditions in tested sites. The sites are arranged according to European-scale gradients of ecological intensification (Figure 1). ..................... 8 Figure 3. The C-stock (t ha-1) in bulk soil, under diversified agroecological practices and different environmental conditions at experimental sites. The sites are arranged according to European-scale gradients of ecological intensification (Figure 1). ................................................................................... 8 List of acronyms and abbreviations WP Work Package EU European Union SOC Soil organic carbon SMB-C Microbial biomass carbon WEOC Water extractable organic carbon WSA Water stable aggregates Deliverable D6.1.3 Soil C pools and aggregate stability This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 862695 5 1. Introduction The interest in soil health is increasing globally due to its active role in sustainable agriculture, enhanced biodiversity, and ecosystem services. As soil biodiversity and resilience are susceptible to anthropogenic disturbances and climate change impacts, implementing effective agricultural management and conservation strategies becomes imperative. The challenges of climate change to agriculture are changing and daunting. Implementing and validating sustainable agroecological practices is essential to ensure agricultural soil's long-term productivity and resilience. Considering the interlinked multiple factors affecting soil aggregate formation and distribution, there are questions about how to measure the effects of agroecological intensification on soil carbon cycling across varied EU pedoclimatic conditions. There is a need to identify the relevant and most sensitive drivers that can describe and enhance the productivity of agroecosystems in different cropping systems concerning soil carbon dynamics and aggregate stability. Hence, it was opined that agricultural intensification could shape soil structure and carbon cycling while promoting nutrient supply-plant demand synchrony and SOC persistence in soil. The aim of this study was to assess the effect of the agroecological intensification, introduced in different EU agricultural cropping systems, on soil carbon (C) pool and aggregate stability. We hypothesized that the reduction of soil disturbance and the increased plant diversity in field may improve soil C retainment and soil aggregate stability. 2. Materials and Methods In each experimental site, the following parameters were measured under diversified agroecological practices across different environmental conditions at all the nine experimental sites: - C-stock (t ha-1) in bulk soil, - soil microbial carbon C (SMB-C) (μg g-1) in bulk soil, - soil organic carbon (SOC, %) in bulk soil and in different soil aggregates (fine: 0.25-1 mm and coarse: >2 mm), - water extractable organic carbon (WEOC, g kg-1) in bulk soil and in different soil aggregates (fine: 0.25-1 mm and coarse: >2 mm), - water stable aggregates (%) (within 0.25-1 mm soil aggregates). Sampling was carried out at plant growth, when soil functions as “C source” (MAX nutrient plant demand) (Table 1). The selected sites are representative of two crossed gradients of agroecological intensification: i) a local-scale gradient and ii) a European-scale gradient built in the frame of this project. Considering the local-scale gradient, three treatments per core-site were selected. Several criteria were considered for selection: i) introduction of crop diversity (cover crops, intercropping, agroforestry); ii) reduction of soil disturbance (reduced tillage, no tillage) iii) organic inputs (plant residues, animal manure, composts, bioinoculants). Based on agroecological intensity, the first treatment (T1) was selected as lower intensification level, second (T2) – as higher intensification level. Each core site includes a “control” treatment (T3), where agroecological intensification was not applied (tillage, monocropping, no service crop introduction, no organic inputs). Each treatment was replicated in n.4 blocks, while in CS3 (agroforestry), in n.3 blocks only. European-scale gradient of agroecological intensification includes the sites starting from conventional agricultural practices (using tillage, monocropping, pesticide, etc.) to organic agricultural practices (using no-tillage, agroforestry, intercropping, etc.) (Fig. 1). Soil samples from CS1, CS2, CS4, CS5, CS6, CS7, CS8 and CS9 were received for this analysis. It was impossible to collect undisturbed soil samples, 20 cm deep and 5 cm thick using a flat shovel, for this analysis in CS3, as their Mediterranean soil is super hard, like stone, for most of the year, therefore Deliverable D6.1.3 Soil C pools and aggregate stability This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 862695 6 this CS was excluded from further T6.1 activity. Soil samples were collected from four blocks in three treatments: T1 - 1st agroecological intensification level, T2 - 2nd agroecological intensification level and T3 - control. Undisturbed soil samples (0-20 cm in depth) were taken for the aggregate stability analysis, following the protocol reported in AGROECOseqC handbook (see: Chapter “Schemes for soil/biomass/root sampling”, pp. 14-16; Chapter “Soil C retainment through stable aggregates and microbial biomass activity, pp. 565-61). Core-sites Codes Treatments CS1 (CREA), Italy T1 INC - compost, no tillage, spontaneous cover T2 ICC - compost, tillage, mixed cover crops T3 BAU -tillage, organic fertilizer, no CC (Control) CS2 (INRAE - CF), France T1 GLN - grasses, legumes - new system T2 WGLN - spring wheat, grasses, legumes - new system T3 WN - spring wheat - new system (Control) CS3 (INRAE -MP) - T2 TSG - Tree strip + perennial grass T3 TSR - Crop rotation in agroforestry alley (Control) CS4 (AU), Denmark T1 LP + TR - Lolium perenne and white clover T2 MS6 - Six-species mixture T3 LP - Lolium perenne (Control) CS5 (CSIC-INIA), Spain T1 No tillage, monocrop T2 No tillage, rotation T3 Minimum tillage, monocrop (Control) CS6 (WUR), Netherlands T1 VO - Vetch + Oat T2 VOR - Vetch + Oat + Radish T3 F - Fallow (Control) CS7 (LAMMC), Lithuania T1 NT - No tillage without cover crops T2 NT + CC - No tillage + cover crops T3 CT - Conventional tillage without cover crops (Control) CS8 (TAGEM), Turkey T1 NFC - No fungi inoculum with cover crop T2 FC - Fungi inoculum with cover crop T3 NFNC - No fungi inoculum without cover crop (Control) CS9 (CRAW), Belgium T1 SBWBFYM - Sugar beet, wheat, barley, farmyard manure T2 SBWBCR - Sugar beet, wheat, barley, crop res. restitution and cover crop T3 SBWB - Sugar beet, wheat, barley, residue exportation (Control) Table 1. Core-sites and treatments selected. Dry sieving was performed by Retch sieve shaker: mesh sizes 8.0, 5.6, 4.0, 2.0, 1.0, 0.5, and 0.25mm and soil aggregates of 0.25-1 mm and >2mm were subjected to SOC and WEOC analysis. Aggregates from 1 mm sieve were wet sieved by Ejkelkamp apparatus (Velykis, Satkus, 2018). Bulk soil samples for the SOC and WEOC analysis were sieved through a 2 mm sieve. The content of SOC was determined according to the Nikitin-modified Tyurin method (Nikitin, 1999), WEOC - by the IR detection method after UV-catalyzed persulphate oxidation, SMBC - by the chloroform fumigation extraction method (Vance et al., 1987). Data were not normally distributed, therefore aligned rank transformation (ART) ANOVA was used. The post hoc test was done to compare the difference within each country. To determine relationship between the C-stock, SMB-C, WSA, SOC, and WEOC data, Pearson's correlation analysis was performed. Deliverable D6.1.3 Soil C pools and aggregate stability This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 862695 7 Figure 1. Selected sites are represented as i) local-scale and ii) European-scale gradients of agroecological intensification. 4. Main results The percentage of WSA (1-0.25 mm) varied among sites (countries) and treatments (p < 0.001) (Fig. 2). The distribution of data between sites was closely related to the European-scale gradient of agroecological intensification. The lowest WSA was determined at site CS5 (Spain), the highest at sites CS2 (France), CS4 (Denmark) and CS1 (Italy), the average - at sites CS7 (Lithuania), CS6 (Netherlands), CS9 (Belgium) and CS8 (Turkey). Significant differences among treatments were found at sites CS7 (Lithuania) and CS8 (Turkey), with the lowest WSA in the control group. In contrast, WSA at the CS1(Italy, organically managed system) site was greater during the control treatment, where minimum tillage (0-10 cm) was applied, compared to T1 and T2 (no tilled). The highest amount of C-stock in bulk soil (on average 92.9 t ha-1) was determined at site CS6 (Netherlands), following CS4 (Denmark) and CS1 (Italy) (Fig. 3). The lowest C-stock (on average 15.9 t ha-1) was found at site CS2 (France) and average at sites CS5 (Spain), CS7 (Lithuania), CS9 (Belgium) and CS8 (Turkey). The only significant difference among treatments was found site CS2 (France), with higher C-stock in T2 compared to T1. Pearson's correlation analysis showed positive correlation between the WSA (%) and all C pool sources tested (SMB-C (μg g-1), SOC (%) and WEOC (g kg-1) in >2 mm and 1-0.25 mm soil aggregates) except C-stock in bulk soil (Table 2). C-stock in bulk soil (t ha-1) positively correlated with SMB-C (μg g1) and WEOC (g kg-1) in 1-0.25 mm soil aggregates. Soil microbial biomass carbon also corelated with SOC (%) in bulk soil and both fractions, and WEOC (g kg-1) in bulk soil. SOC (%) in >2 mm soil aggregates corelated with SOC (%) in 1-0.25 mm soil aggregates and bulk soil, and with WEOC (g kg-1) in bulk soil. WEOC (g kg-1) in >2 mm soil aggregates corelated with WEOC (g kg-1) and SOC (%) in 1-0.25 mm soil aggregates. Deliverable D6.1.3 Soil C pools and aggregate stability This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 862695 8 Figure 2. Amount of water stable aggregates (%) within 0.25-1 mm soil fractions, under diversified agroecological practices and different environmental conditions in tested sites. The sites are arranged according to European-scale gradients of ecological intensification (Figure1). Figure 3. The C-stock (t ha-1) in bulk soil, under diversified agroecological practices and different environmental conditions at experimental sites. The sites are arranged according to European-scale gradients of ecological intensification (Figure1). Deliverable D6.1.3 Soil C pools and aggregate stability This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 862695 9 WSA, % (1-0.25 mm) SOC, % (>2 mm) WEOC, g kg-1 (>2mm) SOC, % (1-0.25 mm) WEOC, g kg-1 (10.25 mm) SOC, % in bulk soil WEOC, g kg-1 in bulk soil C-stock in bulk soil SMB-C, (μg g-1) 0.48**l 0.63**l 0.192 n 0.365**l 0.049 n 0.711**l 0.558**l 0.483**l WSA, % (1-0.25 mm) 0.4**l 0.404**l 0.662**l 0.396**l 0.335**l 0.386**l 0.034 n SOC, % (2-1 mm) 0.067 n 0.304**l -0.083 n 0.582**l 0.324**l 0.382**l WEOC, g kg-1 (2-1 mm) 0.377**l 0.672**l 0.107 n 0.189 n -0.003 n SOC, % (1-0.25 mm) 0.645**l -0.059 n 0.548**l -0.341**l WEOC, g kg-1 (1-0.25 mm) -0.166 n 0.284**l -0.281**l SOC, % in bulk soil 0.334**l 0.903**l WEOC, g kg-1 in bulk soil 0.066 n Table 2. Pearson's correlation analysis between the WSA, SOC, WEOC, C-stock, and SMB-C data. Conclusions This study emphasizes the complex relationship between soil structure, microbial activity, and carbon cycling across diverse environmental conditions and agricultural practices. The strong correlations observed among SMB-C, SOC, WEOC, and WSA highlight the pivotal role of soil aggregate stability in regulating soil carbon processes. Integrated agricultural management strategies are essential for improving soil carbon dynamics in response to these findings.