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Contrasting nitrate adsorption in Andisols of two coffee plantations in Costa Rica

by Ryan, M.C; Graham, G.R; Rudolph, D.L.
Publisher: 2001ISSN: 0047-2425.Subject(s): COFFEA | COFFEA ARABICA | ADSORCION | MINERALES DE ARCILLA | ALUMINIO | ANDOSOLES | ANIONES | CAPACIDAD DE CAMBIO IONICO | CAFE | EUTROFIZACION | NITRATOS | SILICIO | PH DEL SUELO | TIPOS DE SUELOS | CALIDAD DEL AGUA | COFFEA | COFFEA ARABICA | ADSORPTION | CLAY MINERALS | ALUMINIUM | ANDOSOLS | ANIONS | ION EXCHANGE CAPACITY | COFFEE | EUTROPHICATION | NITRATES | SILICON | SOIL PH | SOIL TYPES | WATER QUALITY | COFFEA | COFFEA ARABICA | ADSORPTION | MINERAL ARGILEUX | ALUMINIUM | ANDOSOL | ANION | CAPACITE D'ECHANGE IONIQUE | CAFE | EUTROPHISATION | NITRATE | SILICIUM | PH DU SOL | TYPE DE SOL | QUALITE DE L'EAU In: Journal of Environmental Quality (EUA) v. 30(5) p. 1848-1852Summary: Fertilizer use in coffee plantations is a suspected cause of rising ground water nitrate concentrations in the ground water-dependent Central Valley of Costa Rica. Nitrate adsorption was evaluated beneath two coffee (Coffea arabica L.) plantations in the Central Valley. Previous work at one site had identified unsaturated zone nitrate retardation relative to a tritium tracer. Differences in nitrate adsorption were assessed in cores to 4 m depth in Andisols at this and one other plantation using differences in KCl- and water-extractable nitrate as an index. Significant adsorption was confirmed at the site of the previous tracer test, but not at the second site. Anion exchange capacity, X-ray diffraction data, extractable Al and Si, and soil pH in NaFcorroborated that differences in adsorption characteristics were related to subtle differences in clay mineralogy. Soils at the site with significant nitrate adsorption showed an Al-rich allophane clay content compared with a more weathered, Si-rich allophane and halloysite clay mineral content at the site with negligible adsorption. At the site with significant nitrate adsorption, nitrate occupied less than 10Summary: of the total anion adsorption capacity, suggesting that adsorption may provide long-term potential for mitigation or delay of nitrate leaching. Evaluation of nitrate sorption potential of soil at local and landscape scales would be useful in development of nitrogen management practices to reduce nitrate leaching to ground water.
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Fertilizer use in coffee plantations is a suspected cause of rising ground water nitrate concentrations in the ground water-dependent Central Valley of Costa Rica. Nitrate adsorption was evaluated beneath two coffee (Coffea arabica L.) plantations in the Central Valley. Previous work at one site had identified unsaturated zone nitrate retardation relative to a tritium tracer. Differences in nitrate adsorption were assessed in cores to 4 m depth in Andisols at this and one other plantation using differences in KCl- and water-extractable nitrate as an index. Significant adsorption was confirmed at the site of the previous tracer test, but not at the second site. Anion exchange capacity, X-ray diffraction data, extractable Al and Si, and soil pH in NaFcorroborated that differences in adsorption characteristics were related to subtle differences in clay mineralogy. Soils at the site with significant nitrate adsorption showed an Al-rich allophane clay content compared with a more weathered, Si-rich allophane and halloysite clay mineral content at the site with negligible adsorption. At the site with significant nitrate adsorption, nitrate occupied less than 10

of the total anion adsorption capacity, suggesting that adsorption may provide long-term potential for mitigation or delay of nitrate leaching. Evaluation of nitrate sorption potential of soil at local and landscape scales would be useful in development of nitrogen management practices to reduce nitrate leaching to ground water.

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