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Phosphorus fractionation chemistry across the Great Plains




Kelly, E. F., author
Blecker, S. W., author
Ippolito, J. A., author
Freeman, C. L., author
SGS-LTER, Colorado State University, publisher

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Phosphorus is one of the three important plant nutrients found in soils and has been used with great success as an index for soil and ecosystem development (Aguilar et al., 1988; Honeycutt et al., 1990; Vitousek et al., 2004). In general, phosphorus is has minimal solubility in soil because it participates in a number of secondary reactions after release from primary minerals as a result of weathering. Studies of the biogeochemical cycling of P in humid ecosystems has led to important insights about soil and ecosystem development. Arid and semi-arid ecosystems have largely been ignored under the assumption that chemical transformations are minimal. We conducted research on the biogeochemistry of P along a bioclimatic gradient in grassland ecosystems of the Great Plains. The overall goal of our research is to use a systematic approach to characterize and further quantify the P transformations in biogeographically diverse grassland ecosystems. Identifying P quantities originally contained in central Great Plains soil will allow us to assess 1) the relative importance of P in the biogeochemical behavior of grassland soils, 2) help us quantify the degree of chemical weathering in semi-arid-humid grassland ecosystems, and 3) elucidate cultural use and potential productivity of these ecosystems prior to use of commercial fertilizers. We sampled soils along a bioclimatic gradient that represent three grassland ecosystems, namely, the shortgrass steppe, the mixed-grass prairie, and the tallgrass prairie in eastern Kansas. The soils were collected from sites studied within the Long-Term Ecological Research Program in areas that had not been used for agricultural practices other than grazing. We conducted a sequential extraction procedure to identify the following P fractions: soluble, Al-bound, Fe-bound, occluded, and Ca-bound. Our results suggest that soluble P is generally below detection limits at these sites, illustrating the high turnover rate of available P in these undisturbed systems. The Al-bound fraction was variable across all sites. The Fe-bound P contributed to the total P fraction only from the mixed grass and tall grass prairies. The occluded P fraction was greatest in the shortgrass steppe, decreased dramatically as mean annual and primary production increase from west to east.


The SGS-LTER research site was established in 1980 by researchers at Colorado State University as part of a network of long-term research sites within the US LTER Network, supported by the National Science Foundation. Scientists within the Natural Resource Ecology Lab, Department of Forest and Rangeland Stewardship, Department of Soil and Crop Sciences, and Biology Department at CSU, California State Fullerton, USDA Agricultural Research Service, University of Northern Colorado, and the University of Wyoming, among others, have contributed to our understanding of the structure and functions of the shortgrass steppe and other diverse ecosystems across the network while maintaining a common mission and sharing expertise, data and infrastructure.
Colorado State University. Natural Resource Ecology Laboratory; Colorado State University. Department of Forest and Rangeland Stewardship; Colorado State University. Department of Soil and Crop Sciences; Colorado State University. Department of Biology; California State University, Fullerton; United States. Agricultural Research Service; University of Northern Colorado.

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shortgrass steppe
Central Plains Experimental Range
Pawnee National Grassland
grassland ecology
long term ecological research


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