Physicochemical properties of soil under two different depths in a tropical forest of international institute of tropical agriculture, Abeokuta, Ibadan , Nigeria.

Abstract

The variations in the physicochemical properties of soil at two different depths in a tropical secondary forest of International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria was investigated. Soil samples were collected at three random points each from twenty-four sampling plots at predetermined depths of 0-15cm and 15-30cm with soil auger. Soil particle size was determined the using pipet method, Soil pH was determined in a water suspension at 2:5 soil/water ratio. Exchangeable Ca, Mg, K, Al, and available P were extracted by the Mehlich-3 procedure. Cations were determined by atomic absorption spectrophotometry and P by the Malachite green colometric procedure. Organic C was determined by chromic acid and digestion and spectrophotometry, Total N was determined using the Kjeldahl method for digestion and ammonium electrode determination. Analysis of variance was conducted using the General Linear Model (GLM) procedure of SAS. Statistical comparisons of the all the plots were performed by analysis of variance. The data for the various soil depths were grossly analyzed. The variation in the values of sand, clay and silt content among the soil depth is minimal. Sand (89.448^a), clay (5.925^a) and silt (9.525^a) contents are significantly different (P>0.05) in (0-15 cm) soil depth than in (15-30 cm). Irrespective of depth, sand content was significantly high in plot 84 (91.90^a), clay in plot 14 (9.900^a) and silt in plot 49 (12.600^a) at (P>0.05) (Table 2). The effect of depth was significant in 0-15 cm depth (table 1) in Ca (4.007^a), K (0.827^a), Mg (5.065^a), Na (1.102^a) and CEC (10.945^a). On the effect of depth, OM and OC content were significant in 0-15 cm depth (6.591^a and 3.854^a) respectively at (P>0.05). High soil fertility status in plots 6 and 69 that are Chromolaena odorata fallows could be due to the fact that, it is herbaceous, covers well the soil surface and does not immobilize plant nutrients. It is concluded that forest regeneration support improved soil nutrient status.