Related Experiment Videos
Analysis of potentially mobile phosphorus in arable soils using solid state nuclear magnetic resonance
R W McDowell1, L M Condron, N Mahieu
1USDA-ARS Pasture Systems and Watershed Management Research Laboratory, University Park, PA 16802-3702, USA. richard.mcdowell@agresearch.co.nz
Journal of Environmental Quality
|April 5, 2002
Summary
Intensive agriculture increases soil phosphorus (P) and water pollution risk. Solid-state NMR revealed that above a threshold, mobile P in soil is mainly calcium-associated, indicating potential for targeted management.
Area of Science:
- Soil Science
- Environmental Chemistry
- Agricultural Science
Background:
- Long-term phosphorus (P) fertilization in intensive agroecosystems elevates soil P levels.
- High soil P concentrations increase the risk of P loss to surface waters, leading to eutrophication.
- Understanding the chemical forms of soil P is crucial for managing P mobility and environmental risk.
Purpose of the Study:
- To determine the chemical nature of potentially mobile phosphorus (P) associated with aluminum (Al) and calcium (Ca) in arable soils.
- To investigate the relationship between soil P concentrations, extraction methods, and specific P chemical forms.
- To assess the utility of solid-state nuclear magnetic resonance (NMR) spectroscopy for characterizing soil P species.
Main Methods:
- Utilized solid-state 31P nuclear magnetic resonance (NMR) spectroscopy, including high-power decoupling with magic angle spinning (HPDec-MAS) NMR and cross polarization with magic angle spinning (CP-MAS) NMR.
- Analyzed three soils from a long-term field experiment with varying Olsen P concentrations (40-102 mg P kg(-1)).
- Employed CaCl2 and water extractions to differentiate between Al-P and Ca-P forms.
Main Results:
- A soil P threshold of 59 mg Olsen P kg(-1) was identified, above which potentially mobile P increased significantly.
- CaCl2 and water extractions preferentially isolated Al-associated P and Ca-associated P, respectively.
- Above the threshold, potentially mobile P comprised soluble and loosely adsorbed Ca-P forms (e.g., monetite, dicalcium phosphate dihydrate) and some Al-P (e.g., wavellite).
Conclusions:
- Solid-state NMR spectroscopy provides accurate insights into the chemical forms of soil P species.
- Potentially mobile P in high-input agroecosystems is predominantly Ca-associated above a specific concentration threshold.
- Findings suggest that the chemical speciation of soil P influences its mobility and potential for environmental loss.