Physico-Chemical Properties of Soil in the High Forest Zone of Ghana Associated with Logged Forest and with Areas Converted to Teak (Tectona grandis Linn. F)

Abstract

Salifu, K. F. 1997. Physico-chemical properties of soils associated with logged forest and areas converted to teak (Tectona grandis Linn. F). M.Sc.F thesis, Faculty of Forestry, Lakehead University, Thunder Bay. 104 pp. Major advisor Dr. W. L. Meyer. Keywords: Tectona grandis Linn. F, logged forest, physico-chemical properties, total nutrients, nutrient concentration, regression analysis. The rapid and extensive introduction of teak to satisfy a predicted wood shortage in Ghana has given rise to the question of the short/long-term effects that management of teak plantations might have on soil properties. No research data is currently available to answer this question. Physico-chemical properties of soils were compared under two distinct forest covers (logged native forest, and teak plantations) at three different forest reserves (Bosomoa, Tain II and Yaya) located in the Kintampo, Dormaa - Ahenkro, and Sunyani Forest Districts, respectively in The High Forest zone of Ghana. One-Way analyses of variance (ANOVA) was used for the comparisons. Ages of the plantations used for the study ranged from 15 to 29 years. A total of 28 [20m x 20m] random sample plots representing 14 teak/logged forest pairs were included in the study. Three hundred fifty (350) soil samples were collected in June, 1997 and analyzed for their physico-chemical properties. Within the Bosomoa and Yaya locations, nitrogen (N), and magnesiumn (Mg) concentrations and organic matter (OM) contents in the surface soil horizons were significantly higher under logged forest than under teak plantations. Also phosphorus (P) and potassium (K) concentrations were significantly higher under logged forest at Bosomoa. Similarly, total nutrients were generally higher in soils under adjacent logged forest compared to teak plantations in the Bosomoa and the Yaya locations. Higher nutrient concentrations and contents in soils under logged forest was due to more undergrowth, litter and organic matter under logged forest. Higher nutrients under logged forest may also be due to a lesser demand for these nutrients by tree species in logged forest. Lower soil macro-nutrient concentration and contents in soils under teak was due to lower organic matter content under teak cover. Lower nutrients in soils under teak plantations may also be associated with higher nutrient demand, and nutrient immobilization by teak. At the Tain II sites, there were no significant differences among soil nutrient concentrations and contents under teak and native logged forest. Soil exposure due to bush fires at Bosomoa sites resulted in higher surface soil horizon bulk densities (Db’s) under teak plantation (1.33 g cm'5). In contrast, surface soil horizon Db’s under teak plantation were lower at Tain II (1.23 g cm ’) and at Yaya sites (1.10 g cm'3). There were no significant differences in Db’s between vegetation types within locations. Regression models were developed for Db of soils under teak cover, using easily measurable soil variables such as OM, Clay, silt, volume of coarse fragments and soil pH. Equations relating Db of soils under teak cover to these soil variables are presented for Bosomoa and Tain II. The models can be used to explain Db at the study locations and on comparable sites.