1. conservation agriculture
Journée des doctorants de l’ABIES – 14 et 15 avril 2016
Increasing soil organic carbon storage with alternative cropping systems: results from a 16-year field experiment
Contact: Bénédicte Autret,
Bénédicte Autret1, Bruno Mary1 , Claire Chenu2 , May Balabane3 , Cyril Girardin3 , Michel Bertrand2 , Gilles Grandeau2 , Nicolas Beaudoin1
1 INRA, UR 1158 AgroImpact, Site de Laon, F Barenton-Bugny, 2 INRA, UMR Agronomie, AgroParisTech, Université Paris-Saclay, F Thiverval-Grignon,
3 INRA, UR Ecosys, AgroParisTech, Université Paris-Saclay, F Versailles
Introduction
Alternative cropping systems are expected to decrease negative impacts of agriculture on the environment through sequestration of soil organic carbon (SOC) and mitigation of greenhouse gas emissions.
We studied SOC dynamics in the long term field experiment of “La Cage” (Versailles, France) which compares four arable cropping systems free from manure application.
Materials and methods
Field experiment of “La Cage”:
Measurements between 1998 and 2014:
Crops yields
Carbon inputs via crop residues
SOC content SOC stocks at equivalent soil
Bulk densities mass over the 0-30 cm depth
4 cropping systems
1998
627 mm
11.3°C
AMG model:
CON
conventional LI
low input CA
conservation agriculture
ORG
organic
ploughing
each year
every year
no till
kg N ha-1 yr-1
143
114
104 10
Temperature, humidity
Humified organic matter
Crop residues
Ca active SOC
Cs stable SOC
CO2 h k m
Objectives
To compare SOC stocks in alternative cropping systems
To predict the dynamics of SOC stocks with AMG model
To understand the drivers of C storage with modelling
cover crop
(fescue or alfalfa)
m : annual aerial and belowground carbon inputs (t C ha-1 yr-1 )
h : humification coefficient of crop residues
Ca and Cs : active and stable carbon content (t C ha-1 )
k : mineraliszation rate of active carbon (yr-1)
catch crop
Modelling SOC stocks evolution:
With default parameters (S0)
With optimized m and k for each or all of the cropping systems (S3 and S6)
main crop
auxiliary crop
Figure 1. Cumulative frequencies of occurrence of main and auxiliary crops, tillage and nitrogen fertilization between 1998 and 2014.
Results
Carbon inputs:
Soil organic carbon contents:
C content (g kg-1)
Depth (cm)
Figure 3. Mean annual C inputs from crop residues over the period
Figure 4. Distribution of carbon concentration in the soil profile in 1998 and The depths correspond to fixed equivalent soil masses. Asterisks indicate significant evolution between 1998 and 2014 (* p<0.05; ** p<0.01; *** p<0.001).
In short
Carbon inputs ranked as (t C ha-1 yr-1): CA (5.41) > CON (4.09 ) > LI (3.81 )
> ORG (2.87)
Evolution of SOC stocks between and 2014: +24% in CA, +12% in ORG, +3% in CON and +1% in LI
Simulations were optimized with a common k of yr-1 and a higher alfalfa and fescue belowground inputs.
Soil organic carbon stocks evolution and modelling:
Figure 5. Evolution of SOC stocks in the 0-30 cm layer from 1998 to 2014 in block 2: observed (symbols) and simulated values (lines). S0 = simulation with original parameters; S6 = simulation with 6 parameters optimized; S3 = simulation with 3 parameters optimized.
Conclusion
Outlook
The assessment of the environmental impacts of these cropping systems is not achieved regarding greenhouse gas emissions. Further research will address the N budget, including N2O emission.
A high SOC storage was observed only in CA and was slighter in ORG
Modelling SOC stocks evolution was possible with a single mineralization rate for the 4 cropping systems
High carbon inputs derived from alfalfa and auxiliary crops belowground residues explained SOC storage, rather than a reduced soil diturbance
Acknowledgements
“La Cage” experiment is coordinated by INRA Versailles. We acknowledge P. Saulas, D. Le Floch and C. Montagnier for managing the experiment, J.P. Pétraud, F. Mahu and E. Venet for their technical assistance, C. Dominiarczyk and A. Teixeira for processing samples and O. Delfosse for carbon analyses.
Reference
Saffih-Hdadi, K., Mary, B., Modeling consequences of straw residues export on soil organic carbon. Soil Biol. Biochem. 40, 594–607. doi: /j.soilbio