Organic and inorganic phosphorus in Mollisol soil
under different tillage practices
E.C. Zamuner
*
, L.I. Picone, H.E. Echeverria
Unidad Integrada EEA INTA Balcarce – Facultad de Ciencias Agrarias (UNMP), CC 276, 7620 Balcarce, Argentina
Received 27 February 2007; received in revised form 28 November 2007; accepted 11 December 2007
Abstract
The distribution of soil phosphorus (P) between different organic and inorganic forms depends on, among other factors, the
tillage systems. The evaluation of soil P fractions is essential to determine if they are related to available P. The objective was to
characterize the P forms from a soil under no tillage (NT) and conventional tillage (CT). Soil samples were taken at 0–5, 5–10 and
10–20 cm depth from a fine, mixed, thermic Petrocalcic Paleoudoll, after 8 years under NT and CT. Inorganic and organic P was
measured in the anion exchange membrane (AEM), NaHCO
3
, NaOH, NaOH after sonication, HCl and residual fractions extracted
sequentially. Microbial P was determined by fumigating with chloroform after P extraction with AEM. The tillage systems did not
affect the total P content but the distribution of P among fractions changed between NT and CT. No tillage system had significantly
higher microbial P at all soil depths and ranged from 34 mg P kg
À1
at 0–5 cm to 10 mg P kg
À1
at 10–20 cm. In the upper 10 cm of
soil, NT tended to have higher AEM-Pi and NaHCO
3
-Pi comparing to CT system. The increase in AEM-Pi was closely related to
organic carbon increases and pH decreases. The was a consistently higher concentration of NaOH-Po but the increase was
significant al 5–10 and 10–20 cm, and represented on average about 35% of total P. The residual P which was considered mostly
organic was also an important pool in both NT and CT, and accounted for about 30% of total P. Therefore, P availability is mainly
controlled by organic P which makes up a larger proportion of total P.
# 2008 Published by Elsevier B.V.
Keywords: Phosphorus fractions; No tillage; Tiessen fractionation
1. Introduction
Soil phosphorus (P) is described kinetically as
soluble, labile, and non-labile P, where the equilibrium
between labile and non-labile P is slower than the
equilibrium between soluble and labile P (Larsen,
1967). This suggests that there is a continuum among
different forms of soil P; however the fractionation
procedures that use chemical sequential extractions can
separate the continuum in different P fractions but
without identifying the type of P compounds. The
fractionation method developed by Hedley et al. (1982)
has been widely used to characterize the organic and
inorganic forms of P that differ in availability to plants
and microorganisms. The fractionation procedure
allows examining the P fractions that participate in
short and long-term transformations in soil. This
procedure also helps to carry out a complete balance
of different forms of P and to evaluate the availability of
organic P for plant used.
The distribution of P between inorganic and organic
fractions depends in part, among other factors, on tillage
systems (Selles et al., 1999; Essington and Howard,
2000; Daroub et al., 2000). The widespread adoption of
www.elsevier.com/locate/still
Available online at www.sciencedirect.com
Soil & Tillage Research 99 (2008) 131–138
* Corresponding author.
E-mail address: lpicone@balcarce.inta.gov.ar (E.C. Zamuner).
0167-1987/$ – see front matter # 2008 Published by Elsevier B.V.
doi:10.1016/j.still.2007.12.006