Document: MAR-3-60-4

Changes in soil phosphorus pools along substrate gradients at Niwot Ridge, Colorado: Methods and results.

LEFER, M.E.*, A.R.TOWNSEND and B.CONSTANCE

University of Colorado, Boulder, CO 80309-0450 USA ¹

Abstract:
The sequential soil P extraction method first described by Hedley and later modified by Tiessen and Moir has proven useful in separating biological and geochemical forms of P, and for analyzing changes in soil P dynamics along ecosystem gradients. We used a modification of this method to analyze changes in soil P pools with soil development along a substrate age gradient created by different glaciation periods at the Niwot Ridge LTER site in Colorado. We found that even in this cold climate, soils were developed enough to demonstrate a significant shift in phosphorus pools. Primary forms of mineral phosphorus decreased with soil age while organic and occluded pools increased. Previous work on the older soils has indicated a P limitation of plant growth. If anthropogenic nitrogen fertilization continues in this region, these relatively P-deficient older soils may be especially sensitive to N saturation. Finally, the Murphy-Riley method used in the modified Hedley technique is sensitive to sample acidity, making it necessary to neutralize samples prior to analysis. We have developed a new procedure for measuring extracted soil P in temperate and tropical soils that makes hand-titrations unnecessary, allowing for rapid determination using an automated spectrophotometer. Adjusting the pH of the color reagent to compensate for the sample's acidity allowed us to eliminate labor intensive hand-titrations and increase sample throughput.

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This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.