Crop yields are limited primarily by unavailability of nutrients in agricultural soil. Adoption of reduced-tillage and no-tillage systems leads to stratification of nutrients in surface soil, so management of phosphorus (P) in these systems is a major issue. The objective of this research was to understand the influence of placement (broadcast vs. deep-placed P) and fertilizer source (granular vs. liquid P) on the reaction products of P under greenhouse conditions using soil columns. Phosphorus was added at a rate of 75 kg/ha to two soils: an acid soil from Manhattan, KS, and a slightly acid to neutral soil from Ottawa, KS. At 5 weeks after P application, soil pH, resin-extractable P, and speciation of P in soils were determined at different distances from the point of fertilizer application. Scanning electron microscope with energy-dispersive X-ray analysis and synchrotron-based X-ray absorption near-edge structure spectroscopy were used to understand P speciation. Results for P fertilizer sources and placement with respect to resin-extractable P showed no clear differences between the treatments except for granular broadcast and granular deep-placed treatments in the Ottawa soil. Reaction products formed after application of P in two soils showed some clear differences. The X-ray absorption near-edge structure speciation revealed that Fe-P-like forms dominated in the acidic soil, whereas adsorbed and Fe and Ca-P-like forms dominated in the neutral to slightly acid soil. No clear trends in reaction products were detected with respect to P source or the P placement method. Furthermore, scanning electron microscope with energy-dispersive X-ray analysis of incubated fertilizer granules extracted from soils at 5 weeks showed enrichment of Al, Fe, and Ca in the zones of remaining P in incubated granules, indirectly indicating that these cations enter and or remaining in the granules and begin to react with P before the granules dissolve completely.
1Department of Agronomy, Throckmorton Plant Sciences Center, Kansas State University, Manhattan, Kansas, USA.
2Department of Statistics, Dickens Hall, Kansas State University, Manhattan, Kansas, USA.
Address for correspondence: Dr. Ganga M. Hettiarachchi, Department of Agronomy, Throckmorton Plant Sciences Center, Kansas State University, Manhattan, KS 66506, USA. E-mail: firstname.lastname@example.org
Financial Disclosures/Conflicts of Interest: This is contribution number 12-304-J from the Kansas Agricultural Experiment Station. This project was funded by the Kansas State University Phosphorus Fellowship Consortium of International Plant Nutrition Institute; Mosaic, Agrium, Potash Corp.; and JR. Data were collected at the X-ray Operations and Research Beamline 9-BM-B at the Advanced Photon Source, Argonne National Laboratory. Use of the Advanced Photon Source, an Office of Science User Facilities operated for the US Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the US DOE under Contract No. DE-AC02-06CH11357.
Received August 9, 2013.
Accepted for publication May 2, 2014.