URBAN ROADSIDE TOPSOIL–SUBSOIL NUTRIENTS UNDER THE CANOPY OF TERMINALIA MANTALY: RELATIONSHIPS AMONG TREE GROWTH, BIOMASS, AND SOIL QUALITY INDICATORS

The study examined urban roadside topsoil–subsoil nutrients under the canopy of Terminalia mantaly, as well as the relationships among tree growth, biomass, and soil quality indicators. Using a transect line approach, soil samples were collected under the canopy of each tree at a horizontal distance of 1 m from the tree base in the topsoil and subsoil. The soil nutrients were subsequently analyzed in the laboratory. Diameter at breast height, tree height, and canopy were measured using standard procedures, while aboveground and belowground biomass was estimated using allometric equations. Data were statistically analyzed using both descriptive and inferential statistics (Student’s t-test and Pearson’s product–moment correlation). The study revealed that higher values of sand, silt, total porosity, pH, cation exchange capacity, soil organic matter (SOM), total organic carbon (TOC), total nitrogen, available phosphorus, calcium (Ca), magnesium (Mg), and potassium were observed in the topsoil, while clay, bulk density, and sodium were higher in the subsoil. Significant differences between the two soil depths were detected only for sand, clay, SOM, TOC, Ca, and Mg. Significant relationships were observed among tree growth, biomass, and soil quality indicators at both soil depths. The findings further revealed that tree growth and biomass are more strongly related to subsoil properties than to topsoil properties. The study concluded that the differences in soil quality indicators’ levels between the soil depths are attributed to the effects of anthropogenic activities along the roadside and the canopy, and that the subsoil plays a stronger role in the tree species’ growth and development