Soil C in agriculture: the big uncertainty Franco Miglietta IBIMET-CNR, Firenze, Italy

Climate variability, extreme events increasing atmospheric greenhouse gas concentrations Forest soils Peatland Permafrost Agricultural soils Land Use & Management Terrestrial carbon storage, exchange flows and soil carbon dynamics The climate feedback +

Uncertainty on Anthropogenic Carbon Emissions Up to 250 ppm IPCC SRES 2000; Friedlingstein et al Vulnerability of the Carbon Cycle in the 21 st century Up to 200 ppm Uncertainty of the Biospheric-Carbon-Climate Feedback Slide courtesy of Pep Canadell, GCP

EU25: Utilised agricultural area = ha; Land under permanent crops = ha; Land under cereals (excluding rice) = ha; Permanent grassland = ha; Arable land = ha Forest area ~ ha

Ploughed out grassland. Highfield, Rothamsted, UK C-content of agricultural soils is sensitive to management

100 years 20 years Micro's aggregates type 0mMM B B A B B A g C kg –1 sand free micro’s 100 agricultural use 20 years afforestation AFN AFN Source: II° Università di Napoli, Caserta – Università di Udine Del Galdo et al. Global Change Biology (2003) Assolari et al., Soil Biology and Biochemistry (2003) +3% per year-1.3% per year

Davidson & Jansseens, Nature Vol.440, March 2006 Giardina, C.P. & Ryan, M.G. (2000) Evidence that decomposition rates of organic carbon in mineral soil do not vary with temperature. Nature, 404, Fang, C., Smith, P., Moncrieff, J.B. & Smith, J.U. (2005) Similar response of labile and resistant soil organic matter pools to changes in temperature. Nature, 433, Knorr, W., Prentice, I.C., House, J.I. & Holland, E.A. (2005) Long-term sensitivity of soil carbon turnover to warming. Nature, 433, C-content of agricultural soils sensitive to climate ?

Reductionist’s approach Temperature sensitivity of decomposition Irrigation Ploughing Fertilization

Relating fractions to the pools used in models

Experimentalist’s approach Manipulation experiments: Temperature + Precipitation/Irrigation+ Elevated CO2 + Crop management = Model validation datasets Short-term: Flux changes Long-term: stock changes

OTC Pro: Relatively easy to make Con: Unavoidable decoupling between crop/soil-atmosphere Free Air CO2 Enrichment (FACE) Pro: Realistic Con: Very-high CO2 demand, Difficult to sustain in the long-term Manipulation strategies I: (CO2)

Automated Rain Shelters Pro: Excellent control / manipulation Con: Expensive, major infrastructure Throughfall displacement Pro: Simple installation, low cost Con: Soil shadowing Manipulation strategies II: (Water)

Soil warming Pro: Relatively easy to make Con: Unrealistic, due to the decoupling crop/soil processess Free Air Thermal Enhancement (FATE) Pro: Very Realistic Con: High energy demand, Temp & Vpd, difficult to sustain in the long-term Monolith transplanting Pro: Very realistic, easy to make Con: Requires proper and extended networking, long-term complications, potential confounding effects Manipulation strategies III: (Temperature) Passive heating Pro: Relatively easy to make Con: Not very realistic, sometimes small effects

CONCLUSIONS OF DOE(USA) ON FATE A plot 10 m wide with vegetation 0.5 m tall and an average wind speed of 1 m s-1. A volume of 18,000 m3 hr-1 would have to be heated. If the heat treatment was set at 4°C above ambient this would require 1,448 kWh. For a 24-hr operation, and at US$ 0.1/kWh, this would cost US$ 108,000

Lateral-view Heaters/Blowers °C +2°C

Top-view: surface 30cm above ground °C +2°C

Courtesy of Wayne Polley USDA-ARS, TX

European Soil Monolith Exchange Network

EuroSOMNET + Monolith Exchange

+2°C Model validation Fluxes Stock change Further manipulation (Water / CO2 / Management)

CONCLUSION - We can’t predict climate change effects on soil C in croplands. The big uncertainty. New knowledge on thermal response of decompositoin of SOM fractions is required. - Experimental manipulations are necessary to learn more about such response. Networking should be a priority, linking observations and modelling -Detailed measurements (sensu Zimmermann et al. 2007) are also required to constrain our models. Towards standard fractions/pools protocols?

Very large C-sequestration in agricultural soils