1. Ainsworth, E. A., & Long, S. . (2005). What have we leared from 15 years of free-air CO2 enrichment (FACE)? A meta-analyic review of the responses of photosynthesis, canopy properties and plant production to rising CO2. New Phytologist, 165, 351–372.
2. Blanco-Canqui, H., Schlegel, A. J., & Heer, W. F. (2011). Soil-profile distribution of carbon and associated properties in no-till along a precipitation gradient in the central Great Plains. Agriculture, Ecosystems and Environment, 144(1), 107–116.
3. Classen, R., Carriazo, F., Cooper, J. C., Hellerstein, D., & Udea, K. (2011). Grassland to Cropland Conversion in the Northern Plains: The Role of Crop Insurance, Commodity, and Disaster Programs, ERR-120.
4. COGCC. (2012). Water Sources and Demand for the Hydraulic Fracturing of Oil and Gas Wells in Colorado from 2010 through 2015 (p. 9).
5. Croissant, R. L., Peterson, G. A., & Westfall, D. G. (2008). Dryland Cropping Systems: Fact Sheet No. 0.516. Colorado State University Extension Crop Series Factsheet No. 0.516 (pp. 11–13). Retrieved from http://www.ext.colostate.edu/pubs/crops/00516.pdf