Molecular Speciation of Phosphorus in Dairy-

Manure Amended Soils in Idaho

Dan Strawn, Eva Weyers, Amber Moore, Leslie Baker

Derek Peak

Barbara Cade-Menun

Idaho dairies and manure

• 3rd largest dairy producer • 0.5M+ dairy cows

• One dairy farm with 1216 cows produces as much waste as the city of Boise1.

• Managing waste is imperative to protecting environmental quality

• Recycling nutrients from dairy manure is sustainable nutrient use.

Reference1U.S. EPA. (2004). August 27, 2012

Nutrients impact water quality

-P is the primary target

Phosphorus in Southern Idaho Soils

• So. Idaho soils are calcareous.• Ca reacts with P to form Ca-P

minerals.• Ca-P minerals have varying

solubility.• Other “sinks” for P in soils

exist.

Objectives and Methods• Determine speciation of P in manure-amended Idaho soils.

Long term manure-amended plots in Kimberly, Idaho Two amendment rates plus inorganic fertilizer Multiple methods of analysis

Sequential extraction Spectroscopic analysis (K-edge XAFS and NMR)

• Measure how manure affects P-Ca mineral formation. Create a manure extract Adsorb P on calcite in manure extract Measure adsorption kinetics Measure P speciation

XAFS Also NMR, electron microprobe, and L-edge XAFS

Not reported here

Selective Extraction Results

Control Fertilizer 17 Mg/ha 52 Mg/ha Control Fertilizer 17 Mg/ha 52 Mg/ha Control Fertilizer 17 Mg/ha 52 Mg/ha

2013 2014 2015

0

100

200

300

400

500

600

700

Extr

acte

d P

(mg

kg-1)

Labile Fe bound Ca bound

NMR Spectroscopy Results

K-edge XAFS data

Fitting XAFS data

2140 2145 2150 2155 2160 2165 2170 2175 2180-0.5

0

0.5

1

1.5

2

2.5

3

3.5

Soil Spectra Phytic AcidHy-drox-yapatite

energy

Nor

mal

ized

abs

orba

nce

Hydroxyapatite

Adsorbed P

Organic P

Fitting of All Soil P XAFS Spectra

Summary of P Speciation Results in Soils• XAFS spectroscopy

• P in the soils is primarily Ca-P minerals.• Some adsorbed P species and a small amount of organic P

species occur in soils.

• Sequential extraction • With increasing manure addition, P is adsorbing onto iron

oxides instead of forming Ca-P phases,

• Available P in manure is likely adsorbing on Fe oxides in preference to precipitation of Ca-P.

• Ca-P precipitation may be inhibited by slow processes especially in light of higher dissolved organic matter associated with manure…

P Adsorption on Calcite in Manure Extract

1% manure extract 10% manure extract

XAFS Speciation of P-calcite with manure extract

2150 2155 2160 21650

1

2

3

4

5

Nom

raliz

ed a

bsor

ptio

n

Energy (eV)

P addition 1% manure solution P addition 10% manure solution

2150 2155 2160 21650

1

2

3

4

Nor

mal

ized

Abs

orba

nce

Energy (eV)

1% manure extract Hydroxyapatite

Research Conclusions• Ca-P minerals do occur in Idaho calcareous soils• Organic matter in manure inhibits formation of highly

crystalline Ca-P phases such as hydroxyapatite• Other soil P phases, such adsorbed P, control P solubility

Dairy manure• P• Organic matter• Nutrients

Soil solution• Phosphate• DOM• Ca

Soil solid• P adsorbed on Fe-

oxides• Ca-P minerals

Leaching and runoff• Particulate P• Dissolved P

?

A Tale of Two Rivers

Snake River near Twin Falls ID

Salmon River near Riggins, ID

Acknowledgements

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2013-67020-21352.

• David Hilger (University of Saskatchewan), Corey Liu (Stanford University) and Owen Neill (Washington State University).

P availability from soils