**8. Anthropogenic influence**

reliable properties in explaining, quantifying or predicting soil erosion and other soil prob‐

Again other soil properties encourage structural failure, sliding and mass movement of soils. These soil factors are the mineralogy of the clay and even the soil chemical properties. The sta‐ bility of the soil mass is therefore depended on the clay minerals present. Illite and smectite more readily form aggregates but the more open lattice structure of these minerals and the greater swelling and shrinkage which occur on wetting and drying render the aggregates less stable than those formed from kaolinite. Soils in which either kaolinite or illite clay predomi‐ nates but contains small amounts of smectite are easily dispersive. Smectitic soils are more erodible than the soils that contain only small amount of smectite. Conversely, soils that do not

contain smectite are more stable, less erodible and less susceptible to seal formation.

The sodium dithionite extractable Fe oxide is a soil chemical property which relates signifi‐ cantly with erodibility of the soil. This particular property affects the soil structure and the soil fabric, often being responsible for the formation of soil aggregates and cementation with other major soil components [26, 27]. The mechanism of aggregation of soils in southeastern Nigeria in the presence of Fe (Hydr) oxide has been demonstrated [8, 26, 27]. The presence of OH-Al polymers may lead to a reduction in the swelling and expansion of clay particles by bonding adjacent silica sheets together and by displacing interlayer cations of high hy‐ dration power and thus promoting aggregation. Well crystallized aluminium hydroxide may also be able to act as cementing agent in acid soils such as in southeastern Nigeria but its magnitude may be negligible as compared with non-crystalline materials. Iron oxides

lems such as crusting and sealing.

164 Research on Soil Erosion Soil Erosion

**Figure 4.** Gully site in association with interill and rill erosion

An important factor which contributes significantly to soil erosion problem in southern Ni‐ geria is anthopogenic influence arising from misuse of land. Poor farming systems have con‐ tributed to collapse of soil structure and thus encouraging accelerated runoff and soil loss due to erosion. In the event of uncontrollable grazing caused by the nomads has resulted in deforestation of the landscape while indiscriminate foot paths created on the landscape has helped the incipient channels on the landscape to form. These channels eventually metamor‐ phose to gullies especially when they are not checked at inception. Road constructions in‐ cluding uncontrolled infrastructural developments have contributed significantly in gully developments. Some road networks under construction have been abandoned in the region due to gully formation.

**Figure 5.** Gully about cutting an asphalt surfaced road
