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

Abstract

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 31 P 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%.

Solution Phosphorus-31 Nuclear Magnetic Resonance Spectroscopy of Soils from 2005 to 2013: A Review of Sample Preparation and Experimental Parameters

“…The majority of studies used air-dried soils (e.g., Lehmann et al, 2005;Smith et al, 2006;Cade-Menun et al, 2010;Soinne et al, 2011;Turner and Blackwell, 2013). A few studies used soils that were oven dried at various temperatures (e.g., Turner 2006;Bol et al, 2006), while others extracted fieldmoist soils (Briceño et al, 2006;Turner, 2008;Hill and CadeMenun, 2009;Doolette et al, 2010Doolette et al, , 2011bRedel et al, 2011). Wetland soils were extracted field moist (Sundareshwar et al, 2009) or after oven drying at various temperatures (El-Rifai et al, 2008;Cheesman et al, 2010b;Hamdan et al, 2012), air drying , or after freezing and freeze-drying (Turner et al, 2006a).…”

“…In a study of a tropical soil, Turner (2008) observed that increasing the soil/extractant ratio (i.e., less soil, more extractant) increased MRP but not MUP and also increased the OH − concentration; however, these samples were not examined with 31 P NMR so the effects on spectra are unknown. For low-P soils, Doolette et al (2010) reported that a ratio of 1:10 improved P recovery and the spectral S/N ratio compared with a 1:20 ratio. They did not indicate, however, if recovery of both organic P and Young et al (2013) NaOH-EDTA no no 4 1:15 no yes † Pretreatment of sample before main extractant.…”

Spectroscopic quantification of soil phosphorus forms by 31p-nmr after nine years of organic or mineral fertilization

“…Therefore, inositol phosphates could be used as tracers of organic fertilizer. On the other hand, Doolette et al (2010Doolette et al ( , 2011 demonstrated that myo-inositol hexakisphosphate can be mineralized quickly in some soils. However, as the fertilizers were applied repeatedly over nine years in the current experiment, we assume that the high concentration of inositol phosphates in the cattle, poultry and swine manure treatments occurred because these slowly degradable compounds were present in the annually reapplied manures, permitting Po accumulation as inositol phosphates.…”

The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and <i>Aspergillus niger</i> phytase

“…There it can be stabilized on particles by sorption mechanisms (Ognalaga et al, 1994) and can comprise up to 50 % of organic phosphorus (Dalal, 1977;Anderson, 1988), becoming in some instances the dominant form of organic phosphorus (Turner, 2007). In other cases, however, IP 6 can be rapidly mineralized after its introduction in a soil (Doolette et al, 2010).…”