Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2011
Publication Date: 9/12/2011
Citation: Ohno, T., Hiradate, S., He, Z. 2011. Phosphorus solubility of agricultural soils: a surface charge and phosphorus-31 NMR speciation study. Soil Science Society of America Journal. 75:1704-1711. Interpretive Summary: In agricultural systems the low efficiency of phosphorus (P) fertilizer is due to P sorption and precipitation onto soil surfaces. Sensitivity analysis of plant P uptake models have shown that water-soluble P (WSP) concentration is the most important factor in P uptake by plants. Understanding how the level of WSP is controlled in soils is dependent on a thorough understanding soil P speciation which can only be obtained with spectroscopic studies. A set of ten soils from six states across the United States was used to examine soil surface charge and soil P speciation. P speciation by 31P NMR and traditional chemical extraction methodologies were related to WSP concentrations and P desorption capacity of the soils. This study demonstrated the important role of surface charge in determining the concentration of WSP in soils. Observations in this study provided detailed chemical information on soil P processes which are of vital importance to the environmental and economic sustainability of agricultural systems.
Technical Abstract: We investigated ten soils from six states in United States to determine the relationship between potentiometric titration derived soil surface charge and Phosphorus-31 (P) nuclear magnetic resonance (NMR) speciation with the concentration of water-extractable P (WEP). The surface charge value at the native soil pH was correlated to the WEP concentration indicating that electrostatic interactions are involved in determining soil P solubility. The titration curves were fit to a two-site Langmuir model and analysis showed that the native pH surface charge was accounted by the low pH Type 1 (S-OH2+) attributed to be positively charged metal (oxy)hydroxides. The P-13 NMR data indicated that 98% of the inorganic form of P was the monomeric phosphate species and 95% of the organic P was the phosphorus monoester class compounds. The inorganic form of P was directly related to the total soil P content suggesting that external fertilizer inputs control the level of this form of soil P. In contrast, phosphate monoesters was not related to total soil P content suggesting that organic soil P is controlled by P cycling independent of the external P inputs. The 31P NMR speciation data indicated the inorganic monomeric phosphate, pyrophosphate, DNA phosphorus, and phosphate monoesters concentrations in the soils were significantly associated with oxalate-extractable Al + Fe concentrations which further demonstrates that the metal (oxy)hydroxide component are the surfaces where P species are interacting with in soils.