TITLE:
Variation in Speciation and Availability of Phosphorus in Paddy Soil
AUTHORS:
Shinji Sakurai, Yasuaki Nishiura, Haruhiko Horino, Takao Nakagiri
KEYWORDS:
Phosphorus, Availability, Chemical Form, Sequential Extraction, Incubation Experiment
JOURNAL NAME:
Open Journal of Soil Science,
Vol.8 No.9,
September
4,
2018
ABSTRACT: There is a global concern about the depletion in phosphorus (P) resources in
the near future. Some attempts for effective reuse of P, including recovery
from municipal wastes, have been conducted. However, a strong sorption of
P onto some minerals may result in low P availability for crops. Therefore, it
is necessary to understand the speciation of the chemical forms of P and to
elucidate the relationships between P availability and chemical forms of P in
soil. This study focuses on the variation in P speciation and the chemical
forms of available P in a paddy soil. Incubation experiments with/without
drainage, simulating the situation in a paddy field, were performed at a laboratory
scale to evaluate the variation in speciation and P availability in soil.
The speciation of P was analyzed according to Wilson’s sequential extraction
method and measured using Bray No. 2 and Truog methods. Two kinds of
chemical forms, i.e. , Fe and Mn (oxy)hydroxides (Fe-Mn-P) and organic and
biogenic P (Org-P) were predominant in the soil, and they were easily interconverted
by changing soil redox conditions. Available P using the Bray No. 2
method was increased in 21 days owing to the anaerobic condition; thereafter,
it reached a constant value by the end of both the incubation experiments.
However, a drastic decrease was detected in available P, using Truog-P. It
occurred owing to the drying of soil, which suggested that some chemical
form(s) of P other than Truog-P might be generated. A comparison between
the concentrations of available P and that of each chemical form showed that
available P included some Org-P, which might be less absorbed by plants
compared to the exchangeable and pore water fraction (Ex-P) and Fe-Mn-P.
We conclude that anaerobic soil conditions play an important role in the efficient
consumption of P.