Variation of Surface and Subsurface Soil Organic Carbon within the Haiti Cul-De-Sac Pilot Area.

A pilot soil survey (1:24,000) was conducted on 3000 ha within the Haiti Plaine de Cul-de-Sac using a combination of digital and traditional mapping techniques as part of the USAID/USDA capacity building effort to develop a soil information system to inform conservation planning, agricultural productivity, land use planning, environmental and climate change mitigation. Preliminary soil maps were developed from slope, curvature, and a topographic wetness index using clustering algorithms and inference rule-based fuzzy logic. Using Latin Hypercube observation sites for delineating soil map units based on general drainage patterns; bedrock and parent material depositions; and native or cultivated plants were determined. Traditional methods included characterization of soil profiles; soil color, texture, kind and amount of rock fragments, pH, size and shape of soil aggregates, distribution of plant roots, and other features needed to assign taxonomic classes (units) complimented by comprehensive laboratory soil analyses needed for soil interpretations. Eleven soil types and map units were identified in the study area. Approximately 60% of the area was dominated by flood plains, while foothills, hills and dissected alluvial fans made up the remaining 40%. Dominant parent materials were marine sediments and limestone bedrock. The wide diversity of landforms, landscapes, climatic conditions, management and vegetation resulted in high variability of the surface and subsurface organic carbon distribution. The modal surface SOC content of about 2%, ranged from a high of about 7-8% in the Sha Sha-Delman (15-45% slope) and Sha Sha-Haut Boën (15-35% slope) complexes to lows of about 1.3% in the Bas-Boën alluvial plains. Surface variability in SOC was mostly management dependent. Difference between surface and sub-surface varied on average from 3.1 to 1.1 % SOC. Depending on the soil type the range was wider and varied from 8.1 to 0.1 % SOC resulting in diverse soils with different properties, land use capabilities.