RUNOFF DEVELOPMENT AND SOIL EROSION IN A WET TROPICAL MONTANE SETTING UNDER COFFEE CULTIVATION

The western interior portions of Puerto Rico offer optimal climatic conditions for coffee cultivation. However, land and water degradation result when abrupt topographic relief and high annual rainfall combine with forest conversion for coffee farming. Small-scale rainfall simulation experiments were conducted to quantify runoff and erosion from four land surface types (i.e., mulched, weed-covered, and bare soils under active cultivation, and unpaved roads) representative of coffee farms in Puerto Rico. Results show that mulch-covered soils had runoff coefficients similar to those from undisturbed forested conditions (similar to 4%), and that they eroded at rates about a quarter of those for bare cultivated soils. Weed-covered soils had surprisingly high runoff coefficients (similar to 70%), yet their erosion rates were only three-fourths of those for bare soils. Annualized erosion rates from unpaved roads were 65 Mg ha(-1) y(-1), or ten times greater than bare soils and about a hundred times higher than weed-or mulch-covered surfaces. Farm-scale sediment production estimates amount to similar to 11 Mg ha(-1) y(-1), about two-orders of magnitude higher than under forested conditions. At the farm-scale, only 2 - 8% of the total sediment is potentially attributable to cultivated hillslopes. In contrast, unpaved roads may account for over 90% of the sediment budget, even though they comprise only 15% of the farm surface area. Therefore, while providing mulch or a vegetative cover to bare cultivated soils should be part of effective soil management, mitigating the effects of coffee cultivation on downstream water resources must focus on the unpaved road network as the primary sediment source. Copyright (C) 2016 John Wiley & Sons, Ltd.