Land use effect on the distribution of soil physical and chemical properties under tropical rainforests of Puerto Rico

Relatively few studies have been focused on the land use effects on physical and chemical properties of soils. The authors' objectives were to examine the correlation between soil physical and chemical properties and to examine the distribution of selected soil physical and chemical properties under different land uses, landscape positions and soil depths. This study was conducted in three tropical rain forests in Puerto Rico: Luquillo (18/spl deg/ 18'N 65/spl deg/ 43'W), Guanica (17/spl deg/ 48'N 66/spl deg/ 53'W), and Ciales (18/spl deg/ 18'N 66/spl deg/ 30'W). Three types of land use were identified secondary forest, abandoned pasture, and active pasture. Three landscape positions (top, middle, and bottom) were delineated within each land use type. An Impedance Probe (IP) was used to measure volumetric water content (VWC) in the upper 6-cm soil depth within each land use and landscape positions. After the VWC measurement disturbed soil samples were collected from three landscape positions and three soil depths (0 to 5, 5 to 10, and 10 to 15-cm). Soil samples were air-dried and soil pH was measured using a pH meter. Exchangeable Ca, Mg, Al, and Fe were also determined using Inductively Coupled Plasma (ICP). The observed Coefficient of Variations (CVs) for the soil properties was in the order of Fe>Al>Mg>VWC>Ca>pH. Soil pH exhibited a significant positive correlation with Ca and Mg and a significant negative correlation with Fe and Al. A significant positive correlation was observed between VWC, pH, Fe, and Al and a significant negative correlation between VWC, Ca, and Mg. The Luquillo site had lower pH and higher exchangeable Al and Fe as compared to Ciales and Guanica. Land use practice also had significant influence on the spatial distribution of soil physical and chemical properties for all sites.