Abstract

Agricultural practices in the Great Plains have the potential to produce rapid changes in land-use across the region. The USDA Conservation Reserve Program (CRP) has active contracts on more than 2 million acres in the shortgrass prairie region of eastern Colorado alone and equally large, or larger, areas of CRP exist in the other Great Plains states. In the next few years many CRP contracts will come to an end and subsequent changes in management will likely alter vegetation structure and phenology in ways that will impact both the timing and intensity of short-term carbon, water and energy exchange and long-term carbon sequestration and hydrologic balance. The impacts of vegetation type on surface energy and water balance further impact atmospheric boundary layer processes, with consequent effects on weather systems and potential feedback on vegetation growth and biogeochemistry.

With funding from the National Institute for Climate Change Research (NICCR) (formerly NIGEC) we are carrying out an experiment in CRP land of eastern Colorado that is focused on the impact of land-use change (conversion of CRP land to grazing and minimal-till agriculture) on carbon, water and energy dynamics. Three eddy covariance systems, that measure gaseous exchanges above the vegetation, will be established in three adjacent, quarter-section (160 ac, for a total of 480 ac) parcels of CRP land that have been in the Program for approximately 10 years. After an initial comparison period (3-6 months), one parcel will be opened to cattle grazing at moderate intensity, a second parcel will be converted to minimum-till agriculture, while the third parcel will remain in CRP. The project will be closely linked to several existing research programs at the shortgrass steppe long-term ecological research (SGS-LTER) site and the adjacent Central Plains Experimental Range (CPER). In addition, we will make measurements of net primary production and long-term changes in carbon stocks in soils and vegetation in the CRP treatments. These measurements will be used to infer carbon sequestration and liberation rates by a mass balance approach. The combination of long-term flux measurements with comprehensive mass balance measurements will provide separate and independent measurements of sequestration rates and processes. The field measurement program will also be coupled with detailed biosphere-atmosphere exchange modeling to simulate vegetation dynamics and biogeochemistry, land surface-atmosphere interactions and atmospheric dynamics. The modeling component will provide a powerful tool for scenario testing to explore the impact of land-use changes on carbon and water dynamics in the coupled biosphere-atmosphere system of the Great Plains region.