Soil degradation

The increased and extended human activities by growing pressure on land resources resulted in soil quality degradation, particularly linked to land use and land use change (MEA, 2005). The FAO report on the status of world's soil resources (FAO, 2017) demonstrates that the majority of soils are in fair, poor, or very poor conditions.

Soil degradation is defined as a change in the soil health status resulting in a diminished capacity of the ecosystem to provide goods and services for its beneficiaries (FAO, 2017). Soil degradation caused by human activities, has been a major global issue during the 20th century and will remain high on the international agenda in the 21^st century.

37 The importance of soil degradation among global issues is enhanced because of its impact on world food security and quality of the environment. Human induced soil degradation can be defined by the type of soil degradation (the process that causes degradation) and by the degree of degradation (the present state of the degradation process) (Oldeman et al., 1994).

The types of soil degradation are physical degradation (erosion, compaction, sealing), chemical degradation (humus degradation, acidification, salinization, sodification, nutrient depletion, microelement depletion, contamination) and biological, ecological degradation (reduced biodiversity and ecological function) (Gruiz, 2016).

 Erosion is the loss of soil. When raindrops reach the soil, they detach soil particles. The detached soil particles are subsequently transported by overland water flow. Some particles fill up soil voids, sealing the soil surface. Erosion occurs when the precipitation rate exceeds the infiltration rate of the soil (Gruiz, 2014).

 Compaction takes place when pressure is applied to the soil surface. Pores become disconnected and gas and water movement through soil is impeded, leading to reduced availability of water and oxygen (Gruiz, 2014).

 Soil sealing is the covering of the soil surface with impervious materials as a result of urban development and infrastructure construction (Gruiz, 2014).

 Acidification of soil is a process by which the pH of the soil continuously decreases. The direct cause of acidification is the dominance of H⁺ ions on the negatively charged binding sites in soil. Protons are derived from proton-donor compounds such as the ammonium ion from nitrogen fertilizers (Gruiz, 2014).

 Salinization is the accumulation of water-soluble salts in the soil specifically those containing the ions K⁺, Ca²⁺, Cl^–, SO42-, CO32-, HCO3– and Na⁺. Salts are dissolved and transported by water. When water evaporates, salts precipitate in a crystalline form. The accumulation of sodium in soil is also called sodification (Gruiz, 2014).

 Organic matter decline in soil is caused by the unbalance of three properties of soil: organic matter input, the activity of degrading, mineralizing organisms and the rate of humus formation (Gruiz, 2014).

The degree to which the soil is presently degraded is related in a qualitative manner to the agricultural suitability of the soil, to its declined productivity, to its possibilities for restoration to full productivity and in relation to its original biotic functions. The following four degrees of soil degradation were specified (Oldeman et al., 1994):

38 1. Light. The terrain has a somewhat reduced agricultural suitability, but is suitable in local

farming systems. Restoration to full productivity is possible by modifications of the management. Original biotic functions are largely intact.

2. Moderate. The terrain has a greatly reduced productivity, but is still suitable for use in local farming systems. Major improvements are required to restore the terrain to full productivity. Original biotic functions are partially destroyed.

3. Strong. The terrain has virtually lost its productive capacity and is not suitable for use in local farming systems.

Major investments and/or engineering works are required to rehabilitate the terrain, which are often beyond the means of national governments in developing countries. Original biotic functions are largely destroyed.

4. Extreme. The terrain is unreclaimable and beyond restoration. It has become human-induced wasteland. Original biotic functions are fully destroyed.

The concept of human-induced soil degradation implies by definition a social problem and distinguishes the following types of causative factors: deforestation or removal of the natural vegetation; overgrazing; agricultural activities e.g. insufficient or excessive use of fertilizers, use of poor quality irrigation water, improperly timed use of heavy machinery, absence of anti-erosion measures on land susceptible to water and wind erosion; overexploitation of the vegetation for domestic use e.g. for fuel needs, fencing; bio-industrial and industrial activities (Oldeman et al., 1994).

UNEP's (United Nations Environment Programme) project 'Global Assessment of Soil Degradation (GLASOD)' was implemented to produce a scientifically credible global assessment of soil degradation in 1987–1990. In 1990, the world map of the status of human-induced soil degradation was published (Fig. 2.11) (Oldeman et al., 1990). The GLASOD assessment includes all the types of soil degradation. Two categories of soil degradation processes are recognized. The first group relates to displacement of soil material. The two major soil degradation types in this category are soil erosion by water forces or by wind forces. The second group deals with soil deterioration in situ. This can either be a chemical or physical soil degradation process (Oldeman et al., 1994).

39 Figure 2.11 Human-induced soil degradation around the world (Source:

http://www.fao.org/docrep/003/w2612e/w2612eMap12-e.pdf)

Extensive information on soil types and characteristics in Hungary are available in thematic soil maps as a result of long-term observations, various soil surveys, analyses and mapping activities during the last seventy years. Figure 2.12 shows land degradation types in Hungary. The most important degradation types are: physical degradation (large-scale soil erosion) and chemical degradation.

Figure 2.12 Land degradation map of Hungary (Source:

http://www.mtafki.hu/konyvtar/HIM/fejezet8.pdf)

40 Soil amelioration is the process of modifying soils to provide what the native or existing soils do not naturally provide. The amelioration required can vary depending upon the existing soil and the traits of the soil that require alteration e.g. increasing the nutrient holding capacity of a highly sandy soil.

One option is using wastes as soil amendments because wastes able to amend soil texture will increase soil quality and prevent low stability, compaction, or erodability. Most wastes contain large amounts of nutrient, which has no benefit or is even disadvantageous at the wrong place (i.e., in surface waters), but beneficial if streamed to agricultural land. Some wastes provide meso- and micronutrients satisfying special plant needs (Gruiz and Klebercz, 2014). Therefore, an overview of waste utilization in soil will be provided in the next part of the thesis.