In highly weathered tropical soils the diffusive flux is the main transport mechanism of Zn, Cu, Fe, and Mn to the root surface of plants. Management practices such as liming and the presence of plant residues can alter the diffusive flux of these cationic micronutrients. The aim of the present study was to evaluate the diffusive flux in anionic and cationic forms and bioavaiability of cationic micronutrients Zn, Cu, Fe and Mn in Oxisols with distinct textures as influenced by liming doses, in the absence and presence of plant residues. Two plant materials widely used as green manure - guandu bean and millet - were incorporated into two Oxisols (a loamy-sand Red Yellow Latosol - LVA and a clayey Red Latosol - LV). The diffusive flux was evaluated using a positively charged anion exchange resin membrane and a negatively charged cation exchange resin membrane. The membranes were incubated with the soils for 15 days. Results showed that liming reduced the diffusive flux of the cationic micronutrients. The presence of green manures attenuated this negative effect of liming on Zn, Cu, Fe and Mn transport. Cu and Fe were transported predominantly in the anionic form, whereas Zn and Mn did mainly in the cationic form. The addition of green manure also raised the soil pH, and improved the absorption of cationic micronutrient by corn plants, especially when millet was incorporated into the LVA and guandu bean into the LV.
guandu bean; millet; transport; green manures; ionic resin
