Long-term effects of soil conservation barriers on crop yield on a tropical steepland in Haiti
In this research, we wanted to know how alley cropping between tree barriers compared to the more traditional conservation barriers used in Haiti in terms of long-term crop yields. Our hypothesis was that alley cropping (between leucaena barriers), which is a system designed to sustain crop yields through recycling of plant nutrients and additions of organic matter and N, would sustain crop yields at a higher level than rock walls, contour canals, or grass rows. Secondly, we hypothesized that addition of a modest fertilizer would result in additional benefits. In seasons when drought stress conditions were severe, none of the soil conservation practices without fertilizer substantially increased maize yield on a total area basis compared to the no-barrier control. In seasons where drought stress was less limiting, tree barriers (alley cropping) without fertilizer provided 40% higher yield than no barrier, whereas rock walls and contour canals provided 20% and 17% higher yield, respectively. In addition to higher yields, alley cropping was the only practice that sustained crop yields over time. It also sustained soil N and organic C at higher levels than did other conservation practices. Thus, for low resource farmers, contour alley cropping is the best alternative among those tested for soil conservation on tropical steeplands, because it sustains soil organic matter and N at a higher level and thus sustains crop yields over time, while also reducing runoff and soil erosion. However, to sustain yields at higher than subsistence levels will require application of fertilizers to correct nutrient deficiencies.