PROCESSESSeven main groupsof land degradation processes are normally distinguished. Mass movement Mass movement is the movement of soil and/or rock downslope,under the influence of gravity, without necessarily being influenced by wateror ice. Nevertheless, water or ice may make mass movement even morecatastrophic. Mass movement classifications based on the material (mud, soil,earth, rock and debris), or movement type (falls, topples, slides, lateralspreads and flows)1.
Water erosion Water erosion is the removal of topsoil (up to 20 cm) due tothe action of water. It is divided into the following 3 types based onincreasing severity: Sheet erosion (water moves horizontally over a large area),rill erosion (small incisions take place as the water begins to collectalong parts of the land at lower elevation) and gully erosion (entire sectionsof the soil can be washed off)2. Wind erosionWind erosion occurs when strong winds blow overlight-textured soils that have been heavily grazed during periods of drought3.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 difficult the revegetation of the land, since there is a lack ofnutritious soil for the plants to be planted on.
SalinitySalinity in agricultural terms is theexcess of salts above the required plant level. Most often it poses constrainsin the growth and productivity of the plants and, therefore, it is a seriousconcern. Mingling with other environmental factors as precipitation,temperature, flooding, soil profile, water table exaggerates the catastrophe4. Chemical degradation Chemical degradation refers to the accumulation of toxicchemicals and chemical processes which impact on chemical properties that regulateslife processes in the soil5.? 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 to enable the flow and storage of water and air into it, to permit root growth and toanchor the plants. To be fertile a soil needs abundant and interconnected porespace. Pore space refers to the volume of soil voids that can be filled by water and/or air. Pore space generally depends on aggregatesof soil particles held together by soil organic matter. Unfortunately,intensive or inappropriate tillage practices have been a major contributor toland degradation. Soil tillage breaks down aggregates,decomposes soil organic matter, breaks pore continuity and forms hard panswhich restrict water and air movement and root growth.
On the soil surface, thepowdered soil is more prone to sealing, crusting and erosion. Improving soilphysical fertility involves reducing soil tillage toa minimum and increasing soil organic matter. Biological degradation Soil biological fertility refers to the quantity anddiversity of soil flora (all the plant life) and fauna (all the animal life) present in the soil6.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 and porecontinuity, and can help break down compacted layers. That means that aconstant food source is necessary to maintain soil fauna and flora.
A bare soilmeans low levels of biological activity. Tillage (we mention many of itsdisadvantages in the physical degradation) also disrupts the tunnels andhabitat of organisms. The best way to increase soil biological activity is toget as close as possible to a natural system. That means, stop soil tillage andleave plant residues as mulch on the surface.