Evaluation of soil nutrient status in three forest stands of Sao Hill Forest plantation in Iringa, Tanzania

Abstract

We investigated soil physical and chemical properties between natural vegetation, first, and second-rotation Pinus patula stands. The study provides valuable information for plantation management and a database for soil nutrient status in Sao Hill forest plantation. Soil samples from 120 plots established on three forest stands analyzed for physical and chemical properties. Analysis of variance applied to ascertain nutrients variations between stand types and soil depth. Topsoils have sandy loam and subsoil clay loam textural classes. Soil bulk density on topsoil were 1.18, 1.34, 1.28 g cm-3 and subsoil 1.23, 1.28 and 1.25 g cm-3 for three forest stands respectively and differed significantly (p < 0.05). Soil pH was higher in natural vegetation stand (5.23) than in first (4.96) and second (4.61) rotations Pinus patula stands and differed significantly (p<0.05) between forest stands and depth. Organic carbon, Total Nitrogen, Phosphorus, and Potassium were higher in topsoil of three forest stands and decrease with depth. Calcium (1.2 Cmol(+)/kg), magnesium (0.98 Cmol(+)/kg ) and Sulphur (19.72 mg/kg) were higher in topsoil (0 - 40 cm) of natural vegetation stand and differed significant (p<0.05) with that of Pinus patula stands. Zinc, and Manganese differed significantly (p<0.0001) across forest stand and soil depth. Planting Pinus patula first and second rotations in the same area led to decrease in soil pH, Nitrogen, Phosphorus, Sulphur, CN ratio, Zinc and Manganese but cause increase in soil organic carbon and exchangeable Al3+. Bioassay experiment is needed to get exactly levels of nutrients to apply as supplement.