Soil Physical Variability: A Field Assessment to Identify the Major Factors of Soil Component Variation in Akwa Ibom State, Southeastern Nigeria

Nowadays, gully erosion is a major process of land degradation in arid and semi-arid areas of the world. Researchers have shown that the causes of gully erosion initiation in different climates can be different. The menace of gully erosion is quite alarming on the soils of the coastal plain sands of Southeastern Nigeria. Consequent upon this, a study was conducted to determine the effect of Gully Categories, gully slope position and soil depth affect soil properties on coastal plain sand, Akwa Ibom State, Southeastern Nigeria. The study was conducted in nine (9) gully erosion sites. The gullies were grouped into three broad categories based on their dynamics namely, Active gullies, Meta stable gullies and Stabilized/Old gullies at three Gully slope positions of upper slope, middle slope and Lower Slope with a control site. Samples were collected with a spade at 0-20cm and 20-50cm depths. Data generated were fitted into a 3 x 3 x 2 factorial design and were assessed with the use of analysis of variance. Significant differences were tested at a probability level of 5%. The result revealed that under the gully category, there was no significant effect of gully category on the content of Fs, Cs, Ts, Silt and Clay but sand fraction dominated other soil particle fractions also, SoG > MsG >AcG soil in saturated hydraulic conductivity and was affected by gully category. The result of bulk density affected by the gully slope position obtained shows the lowest bulk density in CT soil (1.38 mgm-3), followed by LS soil (1.39 mgm-3) and US (1.44 mgm-3) soils, which were statistically equal. Total porosity was significantly affected by the Gully category as well. Effect of depth shows that 0.20cm depth, Fs, Cs, Ts, silt and clay had mean values of 256, 525, 780, 50 and 169 gkg-1, respectively, while 20-50cm depth, FsCs, Ts, Silt and Clay recorded mean values of 262, 523, 784, 52 and 164 gkg-1, respectively. The permanent wilting point was also significantly affected by the interaction of Gully Category, Gully Slope position and soil depth. The combination of SoG and subsoil showed high PWP at the CT, US and Ms when compared to other combinations (AcG and MsG) with exceptions in AcG x US x Subsoil and MsG x US x Topsoil and MsG x US x topsoil and Subsoil, which were at the same level with the earlier mentioned combinations involving SoG. It was concluded that factors influencing soil physical variability and gully erosion the most in the area are those that aided in cementing soil particles together into aggregates. The study recommended that relevant governmental institutions should, as a matter of urgency embark upon engineering intervention works on gully to reduce continuous cutting, collapse and soil degradation. It was recommended that a high premium should be placed on improving soil organic matter and soil structural stability.