Ground cover and weed control of selected cover crops in acidic soil of Colombia.

Ground cover and weed control of eight leguminous species (Cajanus cajan, Calopogonium mucunoides, Canavalia brasiliensis, Crotalaria juncea, Mucuna pruriens var. utilis, Pueraria phaseoloides, Vigna unguiculata and Stylosanthes guianensis) was observed in Mondomo (Colombia). Plots, arranged in a split-splot block design with four replicates, were hand weeded or unweeded (control) and 80 kg ha-1 as triple superphosphate or poultry manure were distributed. The low pH and the high Al saturation influenced both emergence and developing of the species. With the exception of M. pruriens and V. unguiculata, the emergence was low (30% by mean) and the maximum ground cover of most the selected species was reached at 130-140 days after sowing (DAS). In contrast, P. phaseoloides and C. cajan, species characterized by low emergence, showed a rapid increase of canopy starting from 150 DAS. M. pruriens, C. juncea and P. phaseoloides were the species with the best competition towards weeds keeping their ground cover by a mean of 35-40%. Yet, P. phaseoloides showed a slow development that caused a high canopy of weeds at 180 DAS. A satisfactory weed control during all the experiment was recorded with C. juncea. From this study it can be concluded that the effectiveness of cover crops in acidic soils is strictly related to the choice of the species tolerant to low pH and high Al saturation as well as a fast emergence and development.