INFLUENCE OF WEEDS CONTROL, MANAGEMENT IN COFFEE PLANTATION ON EXCHANGEABLE CATIONS AND CATION-EXCHANGE CAPACITY OF SOIL WITH VARIABLE CHARGE

Field experiment was conducted during 1976 to 1986 in a coffee plantation to evaluate the following cultural practices for weeds central: manual clean weeding, mechanical rotary tiller, herbicides, slash weeding (weeds cut just above ground level)and green manuring. Soil samples were collected in 1986 for chemical analysis of pH, exchangeable Ca, Mg, K, and Al, total cation exchange capacity at pH7 (CEC-pH7) and variable cation exchange capacity (CEC(V)). The contribution of clay and organic matter to CEC(V) was evaluated. The only treatment that consistently changed soil chemical properties was dash weeding. The following changes were observed: decreased acidity and Al, increased Ca, Mg, K, organic carbon, CEC-pH7, and CEC(V). Organic matter showed the biggest contribution to CEC(V). The CEC-organic matter varied from 432.8 to 470.3 meq/100g and CEC-clay from 7.8 to 8.0 meg/100.