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• <br />geochemical evolution <br />13 ' <br />As N7u ttaker and Woodwell (1972) state: <br />" ... in terrestrial ecosystems the inventory of nutrients <br />retained in the system increases as succession progresses." <br />Since geochemical segregation in a soil column occurs at rates that are a <br />function of temperature and moisture content, soil formation in the northern <br />plains nrr~~rc dominantly during favorable times of high summer moisture <br />when temperatures are warm enough for chemical breakdown and seasonal down- <br />ward percolation of soil water can segregate iaeathering products and dis- <br />solved salts. <br />Successful reclamation must recognize that northern high plains soils are <br />in the process of geochemical segregation today. It mut also recognize <br />that life supporting fimctions o£ the soils are a function of maintenance <br />of the biogeochemical systems, and that such systems are insufficiently <br />well understood to be able to be manufactured or reconstructed from randomly <br />stockpiled soil materials. For instance, mixing alkaline carbonate-rich <br />lower soil horizons from depths of 15 to 40 an with the organic rich <br />neutral to slightly acid surface horizons will tend to cause reactions in <br />stockpiled or redistributed materials that will kill off soil microorganisms <br />and limit soil productivity. Similarly, raising clay minerals from depths <br />of greater than 15 cm to the surface will cause release of exchangeable <br />cations stored upon those mineral storage structures, thus increasing site <br />productivity temporarily by opening the previously closed nutrient loop, <br />