Effects of weed control with paraquat and glyphosate on erosion and soil nutrient losses in coffee. A trial was conducted during 2002-2003 at Alajuela, Costa Rica to determine weed control, weed dynamics, soil erosion and nutrient losses due to successive applications of paraquat and glyphosate. Two plots of 900 m2 were treated with paraquat and two more plots were treated with glyphosate. During 2003 one plot of each treatment was ammended with calcium carbonate and organic mater (shell of coffee berry). Run-off water and sediments from a 2 x 7 m plot were collected into a 200 l drum. The amount of nutrient lost from each plot was determined. The first year both treatments provided 90-100% of weed control but tolerant weeds were selected. A mechanical control and an increase of the herbicides application rate were necessary to keep these weeds under control. During 2002 soil losses from glyphosate treatments were double (3.956 MT/ha) compared to that occurred from the paraquat treated areas (1.936 MT/ha). During 2003 at the amended plots again areas treated with paraquat had less erosion (0,231 MT/ha) vs 0,329 MT/ha from glyphosate sprayed plots. Soil losses from the amended plots were 0,170 MT/ha and 0,187MT/ha, respectively. Sediment analysis indicates that Ca, Mg & K losses were similar in both treatments. In 2003 the estimated yield was similar in both areas.