COFFEE SEEDLING RESPONSES TO EXCHANGEABLE CATION EQUILIBRIUM IN A VARIABLE CHARGE SOIL

A greenhouse experiment was conducted with a high pH dependent charge soil to evaluate the effects of the basic cation saturation of the CEC of the soil on coffee seedling growth and nutrition. The treatment va riables for effective soil CEC were 2.3, 4.6, and 7.1 meq/100g corresp onding pH 4.0, 4.8 and 6.1 respectively and for percent Ca/Mg/K satura tion ratios of each CEC were 45/45/10, 65/25/10, 8/10/10 and 10/80/10. Increasing soil pH increased effective CEC and decreased pH dependent CEC with no change in total CEC. Coffee growth increased with increas ing CEC values and the percent of Ca saturation of CEC. Coffee growth decreased with increasing percent Mg of CEC. Leaf-Ca was better correl ated with Log(10) Ca/Mg ratio than with Ca/Mg ratio of KCI exchangeabl e Ca. The results suggested that both concepts basic cation saturation and sufficiency levels of available nutrients are important tool for interpreting soil test results for coffee growth in a variable charge soil.