Programa e Resumos - I Congresso Ibérico de Ciência do Solo 2004

I Congresso Ibérico da Ciência do Solo – 15 a 18 de Junho de 2004, Bragança, Portugal
Evaluation of three soil test extractants for copper and iron availability in
agricultural alkaline soils
M.I. Rico, J. Novillo, A. Obrador, L.M. Lopez-Valdivia & J.M. Alvarez
Departamento de Química y Análisis Agrícola, Escuela Técnica Superior de Ingenieros
Agrónomos, Universidad Politécnica de Madrid, Ciudad Universitaria, s/n, 28040 Madrid, Spain
Tel: (34) 913 365 650 – Fax: (34) 913 365 639 – E-mail: mirico@qaa.etsia.upm.es
Abstract
Communication: Poster
A variety of soil test extractants are used for the evaluation of micronutrient availability
in soils. The nutrient concentrations measured by a specific extractant are a function of
both the chemical composition of the extractant and the particular properties of the soil
tested. Consequently, the nutrient concentrations measured by two different extractants
in the same soil may be very different. The fact that the results obtained by different
methods differ quantitatively does not imply that they do not provide the same
interpretation, thereby leading to identical nutrient recommendations.
The copper (Cu) and iron (Fe) availability in typical uncontaminated soils of Central
Spain characterised by their medium or high calcium carbonate content was evaluated
by sampling and analyzing twenty-eight representative soils, and greenhouse cropping
six of them with spring barley (Hordeum vulgare, L.). Three commonly used chemical
extractants (DTPA, EDTA and 0.1 M HCl) for soil fertility evaluation were selected to
measure the available metal concentration in soils. The correlation coefficients (r)
between metals extracted by each extractant and the amounts removed by plants were
determined.
With regard to the removal of metals from the soil samples, extractants followed the
order: Cu, EDTA > DTPA > 0.1 M HCl and Fe, EDTA > HCl > DTPA. Significant
linear relationships suitable for use as conversion equations were obtained between the
soil tests applied. Both Cu and Fe phytoavailability for barley in the greenhouse study
could not be predicted significantly by using empirical models with only the quantities
extracted by one of the extractants, but the inclusion of adequate soil properties (e.g.
soil free carbonate and clay contents) in the regression models improved such
predictions. R2 values of the obtained models ranged from 36.2 to 75.0.
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