Mineralogy and forms of potassium in red yellow latosol of a guava (Psidium guajava) tree orchard

A trial was conducted during 1994-95 to study the effect of potassium ferti lization on a guava (Psidium guajava L.) culture for 3 years. The control p lots (without K) showed fruit production and potassium exportation that did not agree with the levels obtained by chemical analysis of the soil. Physi cal, chemical, mineralogic and morphologic analyses were performed on the r ed yellow latosol to identify minerals able to supply potassium, with empha sis on the fact that guava trees have a considerably widespread root system . The results obtained confirmed the presence of minerals in this soil that can supply potassium to the trees through weathering. Feldspars were ident ified in the silt fraction and micas in the clay fraction by X-ray diffract ometry. The determination of total potassium revealed that the silt fractio n of the soil had the largest absolute amounts of potassium, followed by cl ay. However, in view of its greater content, clay was the fraction that con tributed most to the total amounts of potassium detected.