1. Reduced tillage and cover crops as a strategy for mitigating atmospheric CO2 increase through soil organic carbon sequestration in dry Mediterranean agroecosystems
María Almagro, Noelia Garcia-Franco, Joris de Vente, Carolina Boix-Fayos, Elvira Díaz, María Martínez-Mena
Soil and Water Conservation Research Group
Centre for Applied Soil Science and Biology of the Segura
Spanish National Research Council

2. Soil physical properties
Background
Soil physical properties
Soil C cycle
↓ Soil loss by erosion
Yield Productivity
Runoff control
& ↑ SWC
↑ C inputs
SUSTAINABLE MANAGEMENT PRACTICES
Prevent land degradation
Biodiversity
& Ecosystem services
CC mitigation & adaptation
No Tillage (NT)
Reduced Tillage (RT)
Green Manure (RTG)

3. Study areas & Experimental design
RTG RT RT CT
RTG CT RT
370 mm
16 ºC
284 mm 15 ºC 3

4. General soil characteristics of the study areas
Soil properties
“Burete” farm
“Alhagüeces” farm
Soil depth (cm)
0-30
0-45
Clay (%)
15.5 ± 4. 2
17.76 ± 3.7
Silt (%)
41.5 ± 9.0
48.9 ± 11.5
Sand (%)
43.0 ± 12.0
33.2 ± 14.8
SOC (%)
1.2 ± 0.3
2.30 ± 0.6
Total N (%)
0.12 ± 0.04
0.20 ± 0.04
Polsen (ppm)
15.60 ± 5.8
41.8 ± 18.7
CaCO3 (%)
54. 2 ± 11.5
44 ± 9.2
pH (water, 1:25)
8.7 ± 0.2
8.8 ± 0.14
EC (siems cm-1)
168.3 ± 23.3
90.8 ± 14.7

5. Implemented SLM practices
No tillage (NT)
Conventional tillage (CT)
chisel ploughing (3-5 times yr-1)
15 cm depth
No tillage (NT)
Reduced tillage (RT)
chisel ploughing (2 times yr-1)
15 cm depth
Reduced tillage+green manure (RTG)
chisel ploughing (2 times yr-1) at 15 cm depth
Avena sativa & Vicia sativa 1:3 at 150 kg ha-1
Reduced tillage (RT)
chisel ploughing (2 times yr-1)
15 cm depth 5

6. Green manure: wet vs. dry growing season (Nov-May)
2009 (P=345 mm)
2011 (P=230 mm)
‘Alhagüeces’ & ‘Burete’ farms
Vicia sativa + Avena sativa (3:1) at 150 kg ha-1
Vicia sativa + barley (3:1) at 150 kg ha-1

7. Monitoring soil CO2 efflux and OC sequestration

8. Monitoring soil CO2 efflux and OC sequestration
Monthly measurements of soil CO2, T & WC
Soil sampling (0-15 cm; autumn 2012)
Carbon inputs derived from plant residues
Water-stable soil aggregates and OC
↑ C inputs

9. Results: Soil CO2 efflux dynamics and after tillage
61%
58%
P <0.05
P >0.05
82%
53%
P >0.05
Almagro et al (2009)
P <0.05

10. Results: Annual balance of soil CO2 emissions
20%
11%
P >0.05
Annual soil CO2 emissions were not significantly increased by tillage!
The slight increase in annual soil CO2 emissions at RT & RTG compared to CT was off-set by increments in the SOC stocks driven by plant biomass incorporation to the soil.
Tillage suppression decreased annual soil CO2 emissions but did not increased the SOC stock.
162 g m-2
138 g m-2
183 g m-2
114 g m-2
182 g m-2 CT RT
RTG NT

11. Results: Soil aggregation and carbon sequestration
SLM & soil aggregates size distribution at Alhagüeces (left) and Burete (right) farms
+ 74% %
↑ C inputs
soil aggregates formation!

12. Results: Soil aggregation and carbon sequestration
Organic C in soil aggregate sizes at Alhagüeces (left) and Burete (right) farms
Garcia-Franco et al (2015)
~60%
~35%
+44%
+32%
+24%
+36%
~130%
+125%
+112% CT RT
RTG NT

13. Conclusions
Reducing tillage frequency and incorporating plant residues promoted soil aggregation and the physico-chemical OC protection without increasing soil CO2 emissions to the atmosphere.
Suppressing tillage slightly reduced soil CO2 emissions but did not increase the amount of carbon stored in the soil.
↑ C inputs
Longer term results and studies at larger spatial scales are needed to fully understand the mitigation capacity of SLM practices in dry agroecosystems under climate change.

14. Thank you very much!