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Assessing the Impact of the Conservation Reserve Program (CRP) and Prairie Restoration on Soil Carbon Sequestration in Southern Wisconsin

a project by Chris Kucharik

The threat of global climate change has prompted policy-makers to consider how to offset greenhouse gas emissions through “carbon sequestration projects”, which help remove CO2 from the atmosphere. One strategy for CO2 sequestration in Wisconsin is to increase the amount of land planted in grasslands and prairies, which dominated the southern WI landscape two centuries ago. Agricultural soils are among the planet’s largest reservoirs of carbon. Unfortunately, several uncertainties exist: (1) we have no formal “blueprint” for maximizing soil carbon (C) accumulation across the WI landscape and (2) a statistically defensible standard measurement protocol to verify soil carbon sequestration in soils does not exist. Therefore, we do not have a proven scientific database to help utilities and policy makers plan for the future.

SAGE is currently examining how the federal Conservation Reserve Program (CRP) and other prairie restorations have affected soil carbon replenishment as a function of plant species across southern Wisconsin. A paired-site experimental approach (restored grassland vs. cropped land) is used to estimate current rates of C sequestration, and sites are geo-referenced with a handheld GPS system to allow for future re-sampling in 5 to 10 years. These data will either support or discount the notion that soil carbon sequestration projects should be relied upon in the future by utilities to help offset emissions, and whether the measurement technique is statistically robust.

The current situation and fundamental needs for this research are because:

• Wisconsin landowners currently rehabilitate agricultural landscapes to grassland to help prevent erosion and increase biodiversity but are not aware of the growing need for sequestered carbon and biofuels that could result from their efforts.

• Scientists cannot yet offer “blueprints” to maximize soil carbon sequestration across larger geographic regions.

• A standardized approach to quantify and verify changes in soil carbon stocks has not been developed.

• The energy sector does not have the necessary data on statewide carbon offsets to help guide future decision-making for electrical power generation.

Adjacent cropped land (maize) and CRP land (prairie restoration) near Stoughton, WI in June, 2001.

SAGE scientist Chris Kucharik collects soil samples in a soybean field adjacent to a CRP prairie restoration near Mt. Vernon (Dane County) WI in June, 2001.

SAGE scientist Chris Kucharik separates soil samples as a function of depth in a restored CRP grassland near Springfield Corners (Dane County) WI in August, 2001.

CRP land restored to prairie in 1987 (foreground) adjacent to cropped fields (background – corn and soybean) near Springfield Corners (Dane County) WI in August, 2001.

A CRP restored prairie near Blue Mounds, WI in February, 2003.

Soil carbon storage differences between paired CRP and cropland sites. The data is split into two data sets (a) results for 10 year old CRP sites for the 0-5 and 5-10 cm soil layers and (b) younger, 4 year old CRP sites.

Reference

Location

0– to 5-cm C Sequestration Rate

0- to 10-cm C Sequestration Rate

Follett et al., 2001

US Great Plains

570 kg ha-1 yr-1

740 kg ha-1 yr-1

Kucharik et al., 2003 (8+ yr old CRP)

Dane Co. WI

247 kg ha-1 yr-1

Not Significant

Roth, 2002 (4 & 5 yr old CRP)

Dane Co. WI

875 kg ha-1 yr-1

Not Significant

Significant coordination has taken place with the Wisconsin USDA Natural Resource Conservation Service (NRCS) and Farm Service Agency (FSA) in Dane County. This research is support by the UW-Madison College of Agricultural and Life Sciences Barker Fund, and Madison Gas and Electric Corporation.

Switchgrass on CRP land: Potential Future Biofuel?

As a tandem benefit to carbon sequestration in restored grasslands, one of the native grasses (e.g., switchgrass) used in grassland restorations has great potential as a biofuel source for future electrical power generation. Because switchgrass is a C4 grass species, it fixes carbon via several metabolic pathways, and will produce 30% more biomass per unit of water than other C3 grass species typically used in prairie and grassland restorations. This, coupled with a characteristically high root density, offers encouraging potential not only for a biofuel source but also for erosion control and belowground soil carbon accumulation. Based on previous studies, typical biomass yields are between 17 to 35 Mg dry matter ha-1 yr-1. Current estimated production costs for switchgrass range from $22 to $110 Mg-1, and transportation of $5 to $8 Mg-1 for 40 km.

While there is great potential for integrating bioenergy sources into the electrical power generation process, we have little current understanding of how this may eventually function for Wisconsin utilities. For example the following questions need to be addressed:

- What is the future potential in Wisconsin for total biomass production via switchgrass through programs such as the CRP?

- Will supply be able to meet a potential growing demand from local utilities in the near future?

• How does grass productivity respond to changing environmental stresses (e.g., nitrogen, water, and temperature) and soil type across Wisconsin

In SAGE, we are using a combination of field measurements and ecosystem modeling to help address the above questions. Realistic large-scale estimates of total productivity can only be accomplished using numerical modeling that considers many environmental factors simultaneously. As part of the current study we are:

• Collecting data on aboveground productivity at multiple switchgrass sites

• Measuring switchgrass photosynthetic response to temperature, light, and CO2 using a LI-COR 6400 portable photosynthesis system

• Using our state-of-the-art terrestrial ecosystem model called IBIS (or the Integrated BIosphere Simulator) to scale up field-based measurements of total productivity to a landscape level across the region.

We are working closely with Madison Gas and Electric (MG&E) Corp., to help provide estimates of available carbon credits and availability of grasses that could be co-fired with coal at local power plants. The MGE corp. pledged $180,000 over three years to support this research under the direction of Dr. Chris Kucharik.

This research was featured in several news stories:

Should We Buy Biomass? Dr. Chris Kucharik talks about biomass, switchgrass, and Carbon cycling (The Why Files Science Behind the News, UW-Madison, Aug 2002)

Switchgrass: Is this simple prairie grass a panacea for the world? Wisconsin State Journal (Aug 2002) 11.4 MB pdf

Related literature

Brye, K.R., and C.J. Kucharik (2003). Carbon sequestration in two prairie topochronosequences on contrasting soils in southern Wisconsin. American Midland Naturalist 149, 90-103.

Kucharik, C.J., J.A. Roth, and R.T. Nabielski (2003). Statistical assessment of a paired-site approach for verification of C and N sequestration on Wisconsin Conservation Reserve Program (CRP) land. Journal of Soil and Water Conservation, 58, 58-67.

Follett, R.F., S.E. Samson-Liebig, J.M. Kimble, E.G. Preussner, and S.W. Waltman. 2001. Carbon sequestration under the CRP in the historic grassland soils of the USA, p. 27-49, In R. Lal and K. McSweeney, eds. Soil management for enhancing carbon sequestration, Spec. Publ. 57 ed. SSSA, Madison, WI.

Roth, J., 2002. Carbon Sequestration in Dane County: An Analysis of the Scientific and Economic Feasibility of Grasslands to Offset Power Plant Emissions. M.S. Thesis, UW-Madison.