ALUMINUM AND HEAVY-METAL PARTITIONING IN A HORIZONS OF - SOILS IN COSTA-RICAN COFFEE PLANTATIONS

The objective of this study was to provide a contribution to a databas e on the heavy metal status of tropical soils. We assessed the partiti oning of Al, Cd, Cu, Fe, Mn, Pb, and Zn in A horizons of Costa Rican s oils used for coffee cultivation. These soils are subject to heavy met al inputs as a result of the regular use of fungicides and fertilizers and, possibly, because of atmospheric depositions as well. A horizons of 16 soils in coffee plantations and two under natural forest (eight Oxisols, six Andisols, two Mollisols, two Alfisols) were sampled and analyzed for pH, ECEC, BS, C-org, N-tot, oxalate-extractable Al and Fe (Al-o, Fe-o) dithionite-citrate-extractable Fe (Fe-d), and texture. A l, Cd, Cu, Fe, Mn, Pb, and Zn were extracted with a seven-step sequent ial extraction procedure. Because of advanced desilication, total Al a nd Fe concentrations were high in Mollisols, Alfisols, and particularl y in Oxisols (45-134 and 21-115 g kg(-1), respectively). In Andisols, total Al concentrations were high as a result of the occurrence of all ophanes (up to 76 g kg(-1)). Cd, Pb, and Zn concentrations in all soil s were low or comparable to background concentrations in temperate soi ls (Cd: 0.03-0.33; Pb: 4-57; Zn: 31-141 mg kg(-1)). Mn concentrations were highly variable (Mn: 156-4965 mg kg(-1)). Total Cu concentrations were high (generally 100-330 mg kg(-1)). Average metal partitioning w as element-specific, and in Mollisols, Alfisols, and Oxisols it was si milar to that in temperate soils, but it was markedly different in And isols, which contained high EDTA- and oxalate-extractable proportions and low metal proportions that are extractable only with strong acids.