WEED CONTROL EFFECTS ON SOIL CHEMICAL CHARACTERISTICS

The weed control procedures are known to affect the soil physical attributes and the nutrient amount taken up by weed roots. This work hypothesis is that weed control methods might also affect soil chemical attributes. Four experiments were carried out, three with maize (E-1, E-2 and E-3) and one with cotton (E-4), in randomized complete blocks design arranged in split-plots, with five replications. In E-1 experiment, the plots consisted of two weed control treatments: no-weed control and weed shovel-digging at 20 and 40 days after sowing; and the subplots consisted of six maize cultivars. In the three other experiments, the plots consisted of plant cultivars: four maize cultivars (E-2 and E-3) and four cotton cultivars (E-4). And, the subplots consisted of three weed control treatments: (1) no-weed control; (2) weed shovel-digging at 20 and 40 days after sowing; and (3) intercropping with cowpea (E-2) or Gliricidia sepium (Jacq.) Walp. (E-3 and E-4). In all experiments, after harvest, eight soil samples were collected from each subplot (0-20 cm depth) and composed in one sample. Soil chemical analysis results indicated that the weed control by shovel-digging or intercropping may increase or decrease some soil element concentrations and the alterations depend on the element and experiment considered. In E-2, the weed shovel-dug plots showed intermediate soil pH, lower S (sum of bases) values and higher soil P concentrations than the other plots. In E-4, soil K and Na concentrations in plots without weed control did not differ from plots with intercropping, and in both, K and Na values were higher than in weed shovel-dug plots. Maize and cotton cultivars did not affect soil chemical characteristics.