Influence of vegetation and land use on functional soil conditions and soil erosion in the western coastal plain of El Salvador

Abstract

Soil conditions have critical effects in the function of ecosystems, and consequently, in human society. Vegetation affects soil through important feedbacks, and both vegetation and soil can be altered by human activities. In El Salvador, and in many countries worldwide, agricultural land use and management are major activities affecting vegetation, water resources and soil conditions. Hence, in order to better understand how soil quality and water availability can be improved through changes in vegetation, land use and in agricultural practices, this research aims to answer what is the influence of vegetation and land use on functional soil conditions: infiltration capacity, stability, degree of erosion, organic matter availability and moisture content; by comparing the main land uses in the western coastal plain of El Salvador: forest, resting lands, pastures, corn croplands, plantain croplands and sugar cane croplands.

The Landscape Functional Analysis (LFA) indicator methodology was used to assess soil conditions. Vegetation structure variables and soil condition indicators were collected in five sampling transects per land use, accounting for 30 samples in total, each containing six subsampling points along the transect. Three LFA indexes were also generated and compared: Nutrient Cyling/Organic Matter, Stability and Infiltration Capacity. Information to characterize the main management practices was collected directly from the field and from interviews with the local farmers.

Significant differences were found between land uses for all functional soil conditions assessed. Differences were generally higher between managed (croplands and pastures) and unmanaged (forest and resting lands) lands. For soil organic matter and the Nutrient Cycling Index the most influential variables were litter cover and management practices and the lowest values were found in sugar cane croplands; for soil stability, the former two variables and permanent vegetation cover were important, the three croplands presented lower values. In the same three land uses erosion was observed, influenced by management practices and soil cover. Sugar cane had the lowest infiltration value due to a combination of variables. Pastures also presented low infiltration values and the lowest moisture at the root level, mostly as a result of soil compaction and reduced above ground vegetation cover.

Both vegetation and management were proved to have a substantial effect on soil condition differences between the selected land uses. In order to improve soil conditions, both vegetation and management should be improved. Regarding vegetation, perennial vegetation, canopy cover and litter are particularly important. Regarding management, intensive tillage, land burning, herbicides, inadequate irrigation and intense cattle presence were identified as negatively affecting soil conditions.