Transcript C content of managed grasslands under Mediterranean

Carbon content of managed grasslands:
implications for carbon sequestration
Justine J.
*
Owen
and Whendee L. Silver
Dept. of Environmental Science, Policy & Management, University of California, Berkeley, *[email protected]
INTRODUCTION
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Grassland soils typically have considerable carbon (C) storage
potential, but C storage or loss is sensitive to management.
In California, C content in grassland soils spans almost an order of
magnitude and is not correlated to climate or soil type (Silver et al.,
2010), suggesting a dominant role for management.
The effects of management practices on soil C storage and loss are
not well constrained in these ecosystems.
Manure application to grazed fields is a common practice which we
predicted would increase soil C storage.
RESULT 1: Soil C spanned a wide range,
independent of manure application treatments.
RESULT 3: Soil C content was not correlated to clay
content in most of the profile.
• Range of 61-223 Mg C/ha (0-50 cm
depth), slightly higher than C content
in CA grasslands compiled by Silver et
al (2010)
 Dairy management practices may
increase soil C in grasslands.
• Differences within dairies are
comparable to differences between
dairies
 Variations in local climates and
geology did not significantly affect
the results
 Does long-term dairy land management affect soil C?
SITE SELECTION
• We focused on grazing systems on dairies as they are the most
important land use type for rangelands in California
• Soils sampled from 2 to 4 fields at 8 pasture-based dairies (A-H) in
Marin and Sonoma counties, CA.
• Management practices sampled: manure application, plowing,
aeration, seeding, irrigation, and grazing intensity.
• Management practices have been in use for >30 years.
0-5
Depth (cm)
5-10 10-20 20-30 30-50
• Suggests C content at depth is associated with clays, whereas C content
near the surface is not. May reflect different types of C fractions at
different depths.
RESULT 4: Soil C content decreased with bulk
density in most of the soil profile.
no manure
solid manure
liquid manure
both
± standard error
RESULT 2: Liquid manure addition led to greater
soil C content than solid manure addition
• Mean soil C content was
the same for manured and
non-manured fields
25 km
SAMPLE COLLECTION AND ANALYSIS
1. Sample field
0-5 cm
5-10 cm
10-20 cm
20-30 cm
30-50 cm
40 m
Field surface
± standard error
Soil core
2. Soil preparation
Sieved (<2 mm)
Organic matter
fragments removed
3. Soil analysis
C and N by CN analyzer
Particle size by hydrometer
pH by 1:1 soil-water slurry
• Soil C in fields with liquid
manure was significantly
higher than in fields with
solid manure
ACKNOWLEDGEMENTS
We thank Zoe Statman-Weil and Julia Cosgrove for help with soil sampling, and Andrew McDowell, Melissa
Juedemann, Kristine Grace, Ryan Salladay, Nicola Overstreet for help processing samples. We also thank
Becca Ryals and Marcia DeLonge for their guidance and discussion. Special thanks go to all the farmers who
allowed us onto their dairies. This work was funded by a USDA NRCS Conservation Innovation Grant to the
Environmental Defense Fund and the 11th Hour Project.
REFERENCES
Silver, W.L., Ryals, R., and Eviner, V. 2010. Soil Carbon Pools in California’s Annual Grassland Ecosystems.
Rangeland Ecology & Management 63: 128-136.
• Greater bulk density may limit the transport of C into the soil
• Mixing of the soil surface (0-5 cm) by trampling, plowing, and aerating
causes C content to be insensitive to bulk density
IMPLICATIONS AND FUTURE WORK
• Long-term manuring of dairy pastures under Mediterranean climates does
not consistently increase C storage in soil
• Manure type may affect how much C is stored in the soil
• More data are required to determine how soil C is affected by irrigation,
aeration, and grazing (no significant correlations were observed at our
sites)
Unanswered questions:
• Are these fields C saturated?
• Are there specific strategies for consistently increasing soil C in these soils?
Future work: Model dairy pastures with Century, analyze soil C fractions