Diapositive 1

1
Effects of parent material and land use on soil
phosphorus forms in Southern Belgium
Renneson1 M., Dufey2 J., Bock1 L. and Colinet1 G.
1 University of Liege (Belgium) - Gembloux
Agro-Bio Tech Soil Science Unit. Passage
des Déportés, 2. B-5030 Gembloux -
Malorie.Renneson_at_ulg.ac.be 2 University of
Louvain-la-Neuve (Belgium) Soil Sciences Unit.
INTRODUCTION AND OBJECTIVES
Soil phosphorus faces both environmental and
agronomic issues because it is responsible for
eutrophication of surface waters and, at the same
time, it is an essential element for plants
growth. It is therefore important to deepen our
knowledge about the quantities and forms of P in
Walloon soils and the part of P content due to
the background characteristics.
MATERIALS AND METHODS
Twelve types of parent materials have been
selected in Walloon Region. For each one, 10
fields have been chosen (Fig. 1). Soil types were
observed by augering and soil samples were taken
in surface horizon (0-15 cm) and in the deep
100-120 cm horizon. They were located in 76 crop
fields, 15 temporary grasslands and 29 pastures,
chosen according to regional land use
distribution. Different parameters were
determined to characterize edaphic conditions
pHwater and pHKCl, total organic carbon (TOC),
cation exchange capacity (CEC) and particle size
distribution. Available phosphorus (Pav) (Lakanen
and Erviö, 1971) and total phosphorus (Ptot) (NF
X 31-147, 1996) were determined. Inorganic
phosphorus (Pinorg) was extracted by H2SO4 (140,
wv) while organic phosphorus (Porg) was
determined by difference of Ptot by Pinorg.
Fig. 1 Location of the parent materials in
Walloon Region.
The influence of parent materials can be seen in
deeper horizon but also in surface horizon.
Surface P content is also influenced by land use.
There is a large range of variation for studied
soil properties
On average, deep soil P amounts to half of
surface P. The ratio Porg/Pinorg is relatively
variable (from 7.9 to 74), with a mean of 30
close to values from Conesa Fardeau (1994).
Parameters Range of values
pH water 4.62 - 8.4
Clay content 6.2 - 67.2
TOC 0.42 - 9.71
CEC 2.5 - 71.2 cmol kg-1
Pav 15.5 - 241.5 mgP kg-1
P total 167 - 2294 mgP kg-1
Al total 7.5 - 77.7 g kg-1
Fe total 12 - 101.2 g kg-1
Influence of land use and parental material in
surface horizon
Fig. 2 Particle size distribution.
Influence of parent material on deeper horizon
The land use effect adds to parent material
influence on surface P con-tent. P availability,
however, depends mainly upon parent material
(Fig. 4). In sandy-loamy and loamy soils, the
higher P availability is attributed to weaker
sorption capacities. On ave-rage, Pav represented
9 of Ptot. The statistical analysis of land use
effect on P content should integer the influence
of parent materials. Other-wise, conclusions
might differ as can be seen in Fig. 5 and Fig.
6.
Statistical analyses have shown differences
between parent materials for Ptot, Pinorg and
Porg contents, Pinorg percentage but also for
edaphic properties. But, despite the diversity of
geological contexts , the Ptot differences are
relatively limited (Fig. 3), excepted for sandy
loamy soils which presented low Ptot and Porg
contents.
Fig. 5 Difference of total, inorganic and
organic P according to land use without
consideration of parent materials.
The difference between surface and deep P content
can be attributed to effects of biogeochemical
cycle and fertilization inputs. To determine the
geochemical effect, regression models for P
content in deep horizon can be applied to
surface. The difference or the ratio between
observed and predicted P contents permits to
estimate the importance of fertilization and
other inputs.
Fig. 4 P availability according to parent
materials.
Fig. 3 Difference of total P content according
to parent materials.
Fig. 6 Differences of Ptot, Pinorg and Porg
means between land use modalities and crops.
ANOVA.
Significant relationships have been found between
total P and total Fe and Al contents, which are
indicators of the quantity of P-adsorption sites.
But, on contrary of other studies, no
relationship has been observed with clay content
or Ca. Multiple linear regressions can be usefull
to predict soil P content from more easily
measurable or more available soil properties.
Ptot 453 25 Fetot - 20.7 clay 124 TOC (R²
64.6) Pinorg -174 0.657 Ptot 40.6 pHwater
- 5.68 CEC (R² 92.6) Porg 250 0.379 Ptot
2.28 clay - 48.9 pHwater (R² 80.8)
CONCLUSIONS
The fate of P in the soil is under the dependence
of soil characteristics and agronomic practices.
Parent materials have an influence on both
surface and deep horizons, explained by Fe and Al
contents mainly. In surface, land use also
influences P content and availability. So, the
management of phosphorus resources in cultivated
soils has to take into account the sub-regional
specificities of soil parent materials and land
use. Indeed, taking into account parent material
modifies conclusion concerning difference of P
content according to land use. Finally,
comparison between surface and deep P content
should allow to distinguish between P management
and geochemical influences.
Fardeau JC, Conesa AP (1994). Le phosphore In
Pédologie Tome 2. Constituants et propriétés du
sol. (Eds B Bonneau, M Souchier) pp. 649-658.
(Masson publishing Paris). Lakanen E, Erviö R
(1971). A comparison of eight extractants for the
determination of plant available micronutrients
in soils. Acta Agralia Fennica 123, 223-232.
This research has been financed by the  Fonds
pour la formation à la Recherche dans lIndustrie
et dans lAgriculture  (FRIA)
19th World Congress of Soil Science Brisbane
1-6 August 2010 Soil solutions for a changing
world