Brazilian soils, especially in the Cerrado region, are highly weathered and poor in some cationic micronutrients in the soil solution. Diffusion is the main transport mechanism to the root surface. The adoption of management practices such as the use of green manures might favor the diffusive flux (DF) and availability of micronutrients to plants. The present experiment aimed to evaluate the effect of incorporation of two distinct green manures into a clayey Red Latosol (LV, Typic Haplustox) on the DF of the micronutrients Zn, Cu, Fe and Mn. For this purpose, two widely cultivated green manures: guandu bean (Cajanus cajan) or millet (Pennisetum americanum) were incorporated into the soil for different periods (0, 15, 25, 35, 45, and 55 days) and at variable doses (0, 9, 18, and 36 t ha-1, dry matter basis) before starting the evaluation of the DF. To evaluate the DF, two ion-exchange membranes (a positively-charged anionic and a negatively-charged cationic exchange resin) were incubated with the soil in diffusion chambers for 15 days. The obtained results demonstrated that there was an increment in the Cu and Fe DF with the increase in the doses of plant residues, particularly in the beginning of the incubation period. The results also showed a higher DF of these two micronutrients to the anionic resin compared with the cationic resin. This probably occurred because the Cu and Fe transport in the soil depends on the formation of organometallic complexes with net negative charge. The DF of Zn and Mn to occurred mainly toward the cationic resin. A longer incubation time favored the DF of Mn and Zn and reduced that of Cu and Fe.
organic carbon; ion-exchange membranes; nutrient transport; organometallic complexes
