Alterações nos atributos químicos de um latossolo pelo manejo de plantas invasoras em cafeeiros

Abstract

Weed control is one of the most intensive management practices in coffee plantations resulting in changes in soil chemical properties. The objectives of this study were: a) to assess the effects of weed management in a coffee plantation on the chemical properties of a Dystroferric Red Latosol (Oxisol) compared to soil under native forest; b) to verify the relationship between soil organic carbon content (COS) and the effective cation exchange capacity (effective CEC) and the cation exchange capacity at pH 7. This study was carried out on an experimental farm of the Agricultural Research Company of Minas Gerais (EPAMIG) at the São Sebastião do Paraíso County, of Minas Gerais State. In the experimental area, coffee was planted and the experiment was installed in randomized blocks with three replications. The following weed plant managements were evaluated: without weed control (SCAP); hand weeding (CAPM); post-emergence herbicide (HPOS); mechanized mower (ROÇA); rotary tiller (ENRT); coffee tandem disc harrow (GRAD) and pre- emergence herbicide (HPRE). Each one of these weed control systems had been performed in the preceding 30 years in three inter-rows (length 36 m). Five soil samples were collected in three layers (0-3, 10-13 and 25-28 cm) per plot between coffee rows, in December 2007. The following soil chemical analyses were performed: pH-water, exchangeable cations (Ca, Mg, K and Al), cation exchange capacity at natural pH (effective CEC) and cation exchange capacity at pH 7.0 (CEC potential. The results showed that the maintenance of weed plants between coffee rows in the treatment no weed control (SCAP) had positive effects on the chemical properties (exchangeable Ca, effective CEC and CEC at pH 7.0 in the three layers). Furthermore, the total soil organic carbon content at 0-3 cm depth increased and may contribute to the increase and maintenance of carbon stocks in coffee plantations. Thus, no weed control (SCAP) between coffee rows can be adopted for the improvement and maintenance of the chemical properties in coffee plantations. On the other hand, the constant long term-use (30 years) with HPRE management decreases the pH-water values in the layers 10-13 and 25-28 cm and the exchangeable Ca, Mg and effective CEC in the three layers studied in relation to other weed plant managements. The effective CEC of the soil was related with organic carbon content in 59, 60 and 47 % of the cases and CEC at pH 7 in 65, 55 and 46 % in the layers 0-3, 10-13 and 25-28 cm.