PROCESSESSevenmain groups of land degradation processes are normally distinguished. Mass movement Mass movement is the movement of soil and/or rock downslope, under theinfluence of gravity, without necessarily being influenced by water or ice.Nevertheless, water or ice may make mass movement even more catastrophic. Massmovement classifications based on the material (mud, soil, earth, rock anddebris), or movement type (falls, topples, slides, lateral spreads and flows)1.
Water erosion Water erosion is the removal of topsoil (up to 20 cm) due to the action ofwater. It is divided into the following 3 types based on increasing severity: Sheeterosion (water moves horizontally over a large area), rill erosion (smallincisions take place as the water begins to collect along parts of the land atlower elevation) and gully erosion (entire sections of the soil can be washedoff)2.Wind erosionWind erosion occurs when strong winds blow over light-textured soils thathave been heavily grazed during periods of drought1.
Wind erosion has many impacts. Firstly, fertility is reduced since the majority of the plantnutrients are concentrated on the soil that is blown away. This reduces thesoils capacity to support productive pastures and sustain biodiversity. Secondly,it makes revegetation of the land difficult since there is a lack of nutritioussoil for the plants to be planted on. SalinitySalinity in agricultural terms is the excess of salts above the required plantlevel. Most often it poses constrains in the growth and productivity of theplants and, therefore, it is a serious concern.
Mingling with other environmentalfactors as precipitation, temperature, flooding, soil profile, water tableexaggerates the catastrophe2. Chemical degradation Chemical degradation refers to the accumulation of toxic chemicals and chemicalprocesses which impact on chemical properties that regulates life processes inthe soil3.? change in one or more of these soil chemical properties has a direct andindirect adverse effect on the chemical fertility of soils. Chemically degradedsoils have the presence of large amounts of toxic chemicals interfering withactivities of soil life processes. These toxic chemicals may also interferewith nutrient availability. Chemical soil degradation is hard to spot and thusmay be overlooked. Physical degradation Physical soil fertility is the ability of the soil toenable the flow and storage of water and air into it,to permit root growth and to anchor the plants.
To befertile a soil needs abundant and interconnected pore space. Pore space refers to the volume of soil voids that can be filled bywater and/or air. Pore space generally depends on aggregates of soil particlesheld together by soil organic matter. Unfortunately, intensive or inappropriatetillage practices have been a major contributor toland degradation. Soil tillage breaks down aggregates, decomposes soil organicmatter, breaks pore continuity and forms hard pans which restrict water and airmovement and root growth. On the soil surface, the powdered soil is more proneto sealing, crusting and erosion.
Improving soilphysical fertility involves reducing soil tillage to a minimum and increasingsoil organic matter. Biological degradation Soil biological fertility refers to the quantityand diversity of soil flora (all the plant life) and fauna (all the animal life) present in the soil4.Biological activity is necessary to break down crop residues (roots, etc.) into humus (the organic component of soil). Soil fauna (including earthworms, termites, insects,etc.) also transfer crop residues into the soil, increase soil porosity andpore continuity, and can help break down compacted layers. That means that aconstant food source is necessary to maintain soil fauna and flora. A bare soil means low levels of biologicalactivity.
Tillage (we mention many of its disadvantages in the physicaldegradation) also disrupts the tunnels and habitat of organisms. The best wayto increase soil biological activity is to get as close as possible to anatural system. That means, stop soil tillage and leave plant residues as mulchon the surface. CAUSESThereare five main causes of land degradation1.
DeforestationDeforestationis taking place at a faster rate due to increasing demands of timber, fuel andforest products which results into degradation of land resources. OvergrazingOvergrazingrefers to excessive eating of grasses and other green plants by cattle. Itresults into reduced growth of vegetation, reduced diversity of plant species,excessive growth of unwanted plant species, soil erosion, and degradation ofland due to cattle movement.
Agricultural practices Themodern agricultural practices, excessive use of fertilizers and pesticides hasadversely degraded the natural quality and fertility of the cultivation land.