Fjölrit RALA - 15.06.2004, Side 145

Solute and water fluxes in andisol fertilized with pig manure:
soil columns experimentation
Frédéric Feder1 and Antoine Findeling2
1 CIRAD - RELIERA team - station de La Bretagne, F-97 408 Saint Denis messag. CEDEX 9 - France
2 CIRAD - REUERA team, TA 40/01 - F-34 398 Montpellier CEDEX 5 - France
Introduction
Waste production is dramatically increasing in Réunion island and valorisation becomes an
important scientific, technologic and economic challenge for the future. Among different
recycling techniques, spreading is suitable for many wastes (especially for organic wastes)
and permits to enhance soil fertility and to use soil purification power. In contrast, with the
rich literature found for temperate conditions, few studies tackle risk estimation and
management of waste spreading under tropical conditions with specific climatic and agro-
pedologic features. This work aims at studying the physical and chemical transformations and
the solutes transfer related to pig manure spreading on a volcanic andisol of Réunion island.
Materials and methods
The experimental layout was based on three columns of disturbed soil (Cl, C2 and C3) of one
meter height and forty centimetres diameter (figure 1). Spreading was carried out on C1 and
C2 whereas C3 was used as the reference. Columns were kept at 25°C and supplied with
calibrated amounts of water corresponding to measured rainfall. Each soil layer (0-20, 20-40
and 40-100 cm) was equipped with a TDR probe to follow water regime and a pH electrode
and redox electrode to monitorate chemical properties. A limnigraph stored the water flow at
the outler of the columns. All these sensors were connected to a datalogger operating at a ten
minutes time step. Micro-samplers were inserted at the same levels and at 7.5 cm to analyze
the changes in soil solution chemical composition.
Results and discussion
The chemical composition of the pig manure used in this study is reported in table 1. By
comparing the two replications (C1 and C2) with reference column (C3), we observed several
agronomical consequences of pig manure spreading:
1/ Nitrification of the pig manure (i. e. the conversion in the soil of ammonium into nitrate
with the release of H+ ions: NH4+ + 2 O2 NO3" + 2 H+ + H2O). In the soil solution, at
7.5 cm depth, nitrate production was correlated with ammonium disparition. After one month
and 500 mm of cumulated water amounts, nitrification was over and corresponding nitrate
was leached. At 15 cm depth, we never observed ammonium from the pig manure and
leaching of the nitrate, all coming from nitrification in the upper part of the soil, was
completed after 750 mm of cumulated water amounts. Acidification of the soil solution was
measured at 7.5 and 15 cm depth. At 15 cm depth, the acidification could not result from
nitrification because no ammonium was observed at this depth. However, it may come from
the leaching of H+ ions from above.
2/ Vertical transfer of major chemical elements. We observed similar results for calcium,
magnesium, sodium and nitrate: the maximum concentration of elution peak was measured
after 600 mm of cumulated water amounts at 35 cm depth, and after 1200 mm of cumulated
water amounts at the column outlet.
3/ Saturation ofsoil exchange complex by potassium. Conversely, potassium concentration in
soil solution did not reveal the high concentration of the pig manure. A large part of
potassium ions probably participated to the saturation of soil exchange complex.
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