SYSTEMS OF SOIL PREPARATION AND THE CONTROL OF PERENNIAL WEEDS IN BRACHIARIA-DECUMBENS

The aim of this work was to study the influence of some soil preparati on systems on weed population and vigor, and on the formation of the B rachiaria decumbens pasture. The treatments consisted of various combi nations of disc ploughs, harrows (24 '') and levelling harrows. The be st results for weed control and pasture establishment were those that reached the deeper soil layers, corresponding to the following impleme nt combinations: ploughs + levelling harrows, ploughs + harrows, harro ws + harrows, harrows + levelling harrows, or only harrows. Among the systems of deeper soil preparation, those that involved the use of the plough were slightly more efficient than the rest. The systems of sup erficial soil preparation with levelling harrow, or without soil prepa ration (no tillage) were not efficient in either weed control or pastu re establishment. Differences among the results due to the soil prepar ation systems were evident for both weed species. Generally, B, bongar dii was more sensitive to deeper soil preparation than R. martiana. Th e economic analysis of the soil preparation systems followed by one he rbicide treatment showed that the systems which included at least one deep operation are more economic.