Rapid decomposition of phytate applied to a calcareous soil demonstrated by a solution ³¹P NMR study

• Published in: European journal of soil science Vol. 61; no. 4; pp. 563 - 575
• Main Authors: Doolette, A.L, Smernik, R.J, Dougherty, W.J
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.08.2010; Blackwell Publishing Ltd; Blackwell
• Subjects: Abundance; Agronomy. Soil science and plant productions; Biological and medical sciences; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Soil science; Soils; Surficial geology; Triticum aestivum; Calcareous soils; phosphorus isotopes; solution; physical methods; Phytate; decomposition; Soil science; NMR spectrometry; Earth science; soils
• ISSN: 1351-0754; 1365-2389
• DOI: 10.1111/j.1365-2389.2010.01259.x

myo-Inositol hexakisphosphate (phytate) is widely regarded as an abundant form of soil organic phosphorus (P) in many soils. Its abundance is believed to be because of its resistance to microbial degradation. We examined the fate of phytate added to a calcareous soil as a solution at a concentration of 58 mg P kg⁻¹, with and without the addition of wheat straw. The soil was incubated for 13 weeks, with phytate concentrations determined at 0, 1, 4, 7 and 13 weeks using NaOH-EDTA soil extraction followed by ³¹P nuclear magnetic resonance (NMR) spectroscopy. The phytate concentration declined rapidly, with 18% (phytate + wheat straw) and 12% (phytate) of the initial phytate remaining after 13 weeks. This coincided with an increase in the proportion of orthophosphate relative to total NaOH-EDTA extractable P (from 65 to 81%) and a small increase in α- and β-glycerophosphate concentration, providing evidence for the microbial degradation of phytate. The decrease in phytate concentration was consistent with a first-order decay with a half-life for phytate of 4-5 weeks. This study demonstrates that in the calcareous soil examined, phytate was not highly stable, but a potentially biologically available form of P. In order to quantify the concentration of P species, we developed an improved method of spectral deconvolution. This method accounted for a broad signal (3.5-6.5 ppm) in the monoester region of the spectra that represented up to 23% of the total extractable P. We found that when this broad signal was not included, phytate concentrations were over-estimated by up to 54%.