Kh. Dai et al., CHARACTERIZATION OF PHOSPHORUS IN A SPRUCE-FIR SPODOSOL BY P-31 NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY, Soil Science Society of America journal, 60(6), 1996, pp. 1943-1950
Factors affecting the distribution and biogeochemical cycling of soil
P are only partially understood. Many previous studies have focused on
P distribution within surface mineral soils and cycling of inorganic
P. Pew data are available on organic forms of P in forest Boor and min
eral horizons of forest soils. Therefore, we used P-31 nuclear magneti
c resonance (P-31-NMR) to characterize the P compounds in NaOH-ethylen
ediaminetetraacetic acid (EDTA) extracts of three Spodosol profiles. T
he NaOH-EDTA extracted most of the P in the three organic horizons (87
, 83, and 69% of total P in Oi, Oe, and Oa horizons, respectively) and
39 to 67% in the Bhs horizon. Major P species detected in all horizon
s were inorganic orthophosphate and orthophosphate monoesters and dies
ters that ranged from 11 to 53%, 12 to 52%, and 13 to 45% of total P e
xtracted, respectively. As is typical in Spodosol chemistry, considera
ble variation was found for organic P distribution in the organic hori
zons of the three profiles. However, on average, distribution patterns
of P forms with depth were observed, including a decrease in the prop
ortion of inorganic orthophosphate with greater decomposition in the f
orest floor (Oi > Oe > Ga), followed by an increase in the Bhs horizon
s. Pyrophosphate (5-19% of total P) and polyphosphates (5-13% of total
P) were found mainly in the forest Boor horizons, except for one prof
ile where pyrophosphate had evidently accumulated in the Bhs horizon.
Traces (approximate to 2%) of phosphonates occurred only in the Oa hor
izon. Results suggest that biological activity, extractable Fe concent
ration, structural characteristics of P compounds, and pH are probably
responsible for the distribution of P species hn these Spodosols.