Evaluation of phosphorus indices in recently acidified soil of the Columbia basin, Washington State
Bair, K. E. 2012. Washington State
Abstract
Continual application of ammoniacal sources of nitrogen fertilizer can result in
decreased bulk soil pH in Columbia Basin (CB) soils. This change in pH may result in
altered phosphorus (P) chemistry and oppugns the validity of using certain P extraction
methods. The purpose of this dissertation is: 1) identify species of P that exist in
acidified CB soils, 2) determine differences in P sorption and availability extraction occur
across a range of soil pH's and 3) evaluate plant uptake and production differences in
soils that have become acidified.
Several CB soils were collected representing a range of soil pH (5.2-8.4) and soil
test P (3-331 mg P kg-1, Olsen P extraction, 0.5M NaHCO3, OP). Samples were analyzed
by sequential extraction and 31P NMR to determine predominant P species. Phosphorus
sorption isotherms compared P sorption and binding energies. Further, fertilizer
additions were made and incubated soils were extracted to determine the effectiveness of
several P availability indices. Lastly, a greenhouse study with various fertilizer
treatments sought to compare plant P uptake and biomass production for soils with
varying pH values.
Soil P speciation revealed that even at very low soil pH (5.2), the form of P that
predominated was as calcium (Ca)-P (60% or more). 31P NMR spectroscopy was less useful for making this determination than the sequential P extraction method for these
samples. Comparison of extraction methods following incubation with fertilizer showed
that variability was least with the OP method. Differences in sorption maximum and
binding energy existed, in limited instances, suggesting CB soils changed little in these
two parameters due to acidification.
Similarly, results from the greenhouse suggest that while some differences in the
measured greenhouse parameters occurred, generally one can expect that soils at low pH
will react similarly to high pH soils following fertilizer application in terms of biomass
production and P uptake.
We conclude that differences in P speciation, sorption, extraction indices, and
plant growth are not large enough to merit changing extraction methods from current
preference. The OP test and fertilizer recommendations presently made using OP can be
utilized on acidified CB soils reliably.
Key Words
Soil sciences, Agronomy, Fertilizer, Olsen Phosphorus, Phosphorus, Soil Analysis, Soil pH
