Evaluation of allelopathic potential of dominant herbaceous species in a coffee plantation.

Several shaded coffee plantations in Coatepec, Veracruz (Mexico) are characterized by a dense cover of herbaceous vegetation mainly dominated by species from the Commelinaceae which protect the soil from erosion and presumably contribute to regulating the abundance of other weeds. To detect their alleopathic potential, leachates from fresh, air-dried, or oven-dried plants and litter collected during different months of the year were tested uponBrassica campestris, Bidens pilosa, andRumex sp. seeds. Significant radicle growth inhibitions were obtained mainly from dried plants and litter collected during the rainy season (August). Drainage water collected from pots with fresh, chopped plants and litter produced no inhibitions until the third week of recycling the water. Concentrated soil extracts from chopped plants and litter collected after seven weeks of decomposition produced significant inhibitions on radicle growth ofRumex sp. Dry weight ofBidens pilosa was significantly reduced when grown in soils treated with fresh and chopped plants and litter exposed to natural field conditions for five weeks.