Soil Carbon and Agricultural Land Management in Semi-Arid Central Spain Darcy Boellstorff Assistant Professor, Bridgewater State College, Massachusetts

Economic and societal benefits –Food source stability –Biodiversity Soil carbon and soil restoration determined by site-specific processes –Land use –Climate Overview: soil restoration and soil carbon

Soil organic carbon (SOC) –Physical – controls aggregate stability, aeration, water storage –Chemical – allows soil to hold nutrients for plant growth –Biological – energy source for microbes SOC level determined by balance between interrelated factors –Vegetation decomposition rates –Temperature and moisture regimes –Land management Where SOC is low, land management that increases SOC is linked to restoration of degraded soil (Parshotam and Hewitt 1995, Lal 2003, Kong et al. 2005) Soil restoration and soil carbon

Rates of carbon cycling, SOC pools –Fast turnover Plant matter Biomass –Slow turnover Humus Positive correlation between humus and aggregate stability (Drogovoz 1994, Hernanz et al. 2002, Sevink et al. 2005) SOC aggregate stability Modified from Hernanz et al AS = 1.67SOC r 2 = 0.62 Soil restoration and soil carbon

Soil type - Alfisols Arkose pedisediment Well-drained Topsoil –SOC stored in upper horizon –Varying texture, clay content image source: CSIC-CCMA

Chemical –mining of soil fertility and loss of nutrients Biological –decline of soil microbes Physical –lowered aggregate stability from tillage –crusting and redistribution of topsoil Soil degradation Lower image source: CSIC-CCMA

T C ha -1 percent pasture rotated T C ha -1 percent pasture rotated7.80.7

Soil carbon cycling models Models –SOCRATES: southern Australia (P. Grace) –RothC: northeast United Kingdom (D. Jenkinson, K. Coleman) Applied in range of ecosystems –Semi-arid systems in U.S., Europe and Australia –Range of SOC values Benefits –Calculate changes for different SOC pools over long time scales –Can be used to predict outcome of land use and climate change –Crop yields (SOCRATES)

SOCRATES r 2 = :1 line

Scenario comparison: SOCRATES CP: Continuous pasture T: Traditional cereal rotation P5: 5 year pasture, 5 year cereal rotations P10: 10 year pasture, 5 year cereal rotations

Scenario comparison: SOC

Scenario comparison: Humus

Scenario comparison: Grain yields TCPP5P10 Years pasture Years cereal Years fallow Average annual yield (kg/ha)2,638--2,9942,976 Total yield (kg/ha)89, ,82562,513

Longer pasture rotation positively correlated with: –Improved humus conditions –Increased aggregate stability –Crop yields Longer pasture could present policy-makers with win-win scenarios –Restoration of soil –Maintained crop output Conclusions and application

Bridgewater State College Center and the Advancement of Teaching and Research. Senior research scientists Dr. Gerardo Benito and Dr. Gonzalo Almendros and Carlos LaCasta, manager of La Higuerela experimental farm The Centro de Ciencias Medioambientales, part of the Consejo Superior de Investigaciones Cientificas in Madrid, Spain for sharing their data sources. Acknowledgements