SEALING INDEX AND HYDRO-PHYSICAL PROPERTIES OF SHALE AND COASTAL PLAIN SAND UNDER MANAGED FOREST....

The research was carried out in two forest ecosystems in southern Nigeria to assess the variability in soil sealing, water retention, and structural features of Shale and Coastal Plain Sand (CPS) soils under Gmelina and rubber land use. Particle-size distribution (PSD), pore-size distribution (through a water desorption process), and related hydro-physical characteristics were measured in soil samples obtained at 0-20 and 20-40 cm depths. The silt + clay-size proportion in Shale (>75%) was significantly greater (P=0.05) than in CPS (35%), according to the findings. At 0-20 cm topsoil, there was a low risk of soil sealing (6.1-6.4 percent), but a high risk (1.4 percent) at 20-40 cm depth. Because of the large difference in PSD between Shale and CPS, there was no significant change in sealing index. Water retention was minimal in CPS at high potentials (-10 to -1500 kPa), owing to the broad inter-particle pore spaces of CPS. At both 0-20 and 20-40 cm depths, Shale had significantly more accessible water (AW), usable available water (UAW), and rapidly available water (RAW) than CPS (P=0.05). Between saturation (0 kPa) and field capacity, approximately 24.42 percent and 53.7 percent of soil water were released in Shale and CPS, respectively (-10 kPa). In Shale, stable aggregates > 0.25 mm dominated the aggregate ratio (AR). The mean weight diameter (MWD) had a positive association relationship with AW (r = 0.486, P=0.05), UAW (r = 0.524, P=0.05), and EAW (r = 0.0635, P=.01). As a result, organic litter from Gmelina and rubber trees can minimise the danger of soil sealing, but microporosity dominates in Shale and controls water retention measurements.

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