SRC Users' Meeting - Synchrotron Radiation Center - University of ...

THE RELATIONSHIP BETWEEN PHOSPHATE SPECIATION IN SOILS
AND BIOSOLIDS/MANURE MANAGEMENT PRACTICES: A P K-EDGE
XANES SPECTROSCOPIC STUDY
Derek Peak,Gurpal Toor, and James T Sims
1 Dept. of Soil Science, 51 Campus Dr, Univ. of Saskatchewan. Saskatoon SK S7N 5A8
2 Dept Plant and Soil Sciences, Univ. Delaware. 149 Townsend Hall Newark DE 19717
The long-term application of animal manures and biosolids has resulted in serious
environmental issues in many locations throughout the world. For example, the state of
Delaware has a large amount of farmland characterized as having “excessive P levels” due to
heavy application of poultry waste for the last three decades. These soils serve as a significant
source for phosphate movement into waters, including the Chesapeake Bay. Elevated phosphate
levels in natural waters are a serious concern because it is typically the limiting nutrient for algae
and other photosynthetic organisms. Increased phosphate can therefore result in algal blooms
and ultimately fish kills and eutrophication.
The tendency of phosphorus to move from a soil to surface waters is highly dependent
upon its chemical form. In soils, phosphate has a tendency to form insoluble metal phosphate
solids and to form strong sorption complexes with iron and aluminum oxides. These reactions
result in phosphate typically being held very strongly by soils. In biosolids and manures,
however, high levels of soluble phosphate and readily degradable organic phosphates are found
along with more stable organic phosphates and calcium phosphate minerals. To attempt to
reduce the environmental risk of manure applications, scientists have proposed that (a) the
manures be chemically amended prior to application to reduce P availability or (b) the diet of the
animals be modified to reduce P in manures. The presented research will perform direct
chemical samples from a variety of animal types, diets, and chemical amendments using P K-
Edge XANES spectroscopy coupled with linear combination fitting. This allows us to directly
assess the success of different strategies to reduce manage phosphorus.
We found that changes in animal diet do indeed play a large role in the resulting
phosphate speciation. Adding supplemental P often served to increase the fraction of calcium
phosphate minerals present. Take for example the samples in Figure 1. The DM01 sample on
the left is a dairy manure sample from an animal with 29%P in its diet. The sample on the right
is a dairy manure sample from an animal fed 58% P. There is a marked increase in calcium
phosphate precipitation in the higher P diets, which can affect the solubility of P compared to
organic and aqueous forms. XANES has similarly been useful in determining the chemistry of
phosphate in manures amended with aluminum coagulants.
This research was supported by an NSERC Discovery grant and the Saskatchewan
Synchrotron Institute.