Nitrate leaching through volcanic soils in the Central Valley, Costa Rica

A pilot experiment is being conducted to evaluate water and nitrate transport processes through Andisols planted with coffee under intensive and traditional management systems in the Central Valley, Costa Rica. The region has high precipitation rates (>2000 mm), permeable soils and rocks, and high concentrations of nitrate are available in the soil, derived mainly from intensive N fertilizer applications. It has been suggested that significant amounts of nitrate form fertilizers may be leading through the soils and contributing to aquifer contamination. Tritiated water and potassium nitrate in solution were injected as tracers at a depth of 45 cm in plots in two adjacent plantations under different management systems. The preliminary results indicate that, contrary to what has been observed in temperate soils, nitrate movement is slower than that of water. It is evident that water cannot be used as a nitrate tracer in soils of a variable charge that are potentially able to adsorb anions and even to retard nitrate leaching. Different rates of nitrate transport in the two plots and lower recovery in the shaded coffee plantation suggest that large overstory trees with well developed root systems may be competing successfully with coffee bushes for nitrate and water uptake. (author). 19 refs, 2 figs, 1 tab