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Kinetics of molybdate and phosphate sorption by some Chilean Andisols
Erika Marina Vistoso G. 1 , Nanthi S. Bolan 2 , Benny K.G. Theng 3 , Maria de la Luz Mora 4
1 National Institute for Agricultural Research (INIA), Remehue Research Centre, Osorno, Chile
2 Centre for Environmental Risk Assessment, University of South Australia, SA 5095, Australia
3 Landcare Research, Private Bag 11052, Palmerston North 4442, New Zealand
4 Departamento de Ciencias Quimicas, Universidad de la Frontera, Temuco, Chile
The kinetics for the sorption of molybdate and phosphate by four Chilean Andisols have been
determined. About 55% of the molybdate and 61% of the phosphate was sorbed in the first 0.5 h, after
which sorption slowly increased, reaching 90% for molybdate and 97% for phosphate after 72 h. At
the same time, OH – ions were released into the external solution, raising its pH by 0.85 units for
molybdate and by 0.65 units in the case of phosphate. These observations indicated that both anions
were sorpbed by a ligand exchange mechanims. Among the five kinetic models examined (Table, 2),
the Elovich equation gave the best fit of the experimental data (R 2 = 0.93 to 0.97, standard error = 0.35
to 0.94). The sorption rate constant (α) for both anions was related to the organic matter (OM) content
of the soils, especially the content of Al- and Fe-humus complexes. The values for molybdate were
2.24x10 15 mmol kg –1 h –1 for the Vilcún soil (15% OM), 2.49 x10 12 mmol kg –1 h –1 for the Pemehue soil
(16% OM), 8.76x10 10 mmol kg –1 h –1 for the Osorno soil (20% OM), and 3.11x10 7 mmol kg –1 h –1 for
the Piedras Negras soil (24% OM). The corresponding values for phosphate were 3.89x10 7 , 5.21x10 10 ,
3.11x10 12 and 1.08x10 16 mmol kg –1 h –1 . The desorption rate constant (β) for the four soils (in the above
order) ranged from 0.47 to 0.28 for molybdate, and 0.22 to 0.39 mmol kg –1 h –1 for phosphate. The
results suggest that the mineralogical composition and organic matter content of the Andisols control
the kinetics for the sorption of both molybdate and phosphate. Molybdate appeared to have a high
affinity for Fe- and Al-oxides, while phosphate was largely sorbed to Fe-and Al-humus complexes.
Journal of Soil Science and Plant Nutrition 9: 55–68, 2009
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Effect of elevated CO2 on soil N dynamics in a temperate grassland soil
Christoph Müller a,b , Tobias Rütting c , M. Kaleem Abbasi b,d , Ronald J. Laughlin e ,
Claudia Kammann a,b , Tim J. Clough f , Robert R. Sherlock f , Jens Kattge g , Hans-Jürgen Jäger b ,
Catherine J. Watson e , R. James Stevens e
a School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland
b Department of Plant Ecology, Justus-Liebig University Giessen, Heinrich-Buff-Ring 26, 35392 Giessen, Germany
c Department of Plant and Environmental Sciences, University of Gothenburg, Box 461, 405 30 Gothenburg, Sweden
d
Faculty of Agriculture, University of Azad Jammu & Kashmir, Rawalakot, Azad Jammu & Kashmir, Pakistan
e
Agriculture, Food and Environmental Science Division, Agri-Food and Biosciences Institute, Newforge Lane, Belfast BT9
5PX, Northern Ireland
f
Agriculture & Life Sciences Division, Lincoln University, PO Box 84, Canterbury, New Zealand
The response of terrestrial ecosystems to elevated atmospheric CO 2 is related to the availability of
other nutrients and in particular to nitrogen (N). Here we present results on soil N transformation
dynamics from a N-limited temperate grassland that had been under Free Air CO 2 Enrichment (FACE)
for six years. A 15 N labelling laboratory study (i.e. in absence of plant N uptake) was carried out to
identify the effect of elevated CO 2 on gross soil N transformations. The simultaneous gross N
transformation rates in the soil were analyzed with a 15 N tracing model which considered
mineralization of two soil organic matter (SOM) pools, included nitrification from NH 4 + and from
organic-N to NO 3 - and analysed the rate of dissimilatory NO 3 - reduction to NH 4 + (DNRA). Results
indicate that the mineralization of labile organic-N became more important under elevated CO 2 . At the
same time the gross rate of NH 4 + immobilization increased by 20%, while NH 4 + oxidation to NO 3 - was
reduced by 25% under elevated CO 2 . The NO 3 - dynamics under elevated CO 2 were characterized by a
52% increase in NO 3 - immobilization and a 141% increase in the DNRA rate, while NO 3 - production
via heterotrophic nitrification was reduced to almost zero. The increased turnover of the NH 4 + pool,
combined with the increased DNRA rate provided an indication that the available N in the grassland
soil may gradually shift towards NH 4 + under elevated CO 2 . The advantage of such a shift is that NH 4
+
is less prone to N losses, which may increase the N retention and N use efficiency in the grassland
ecosystem under elevated CO 2 .
Soil Biology & Biochemistry 41 (2009) 1996–2001
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