«Dissertation Zur Erlangung des akademischen Grades Doctor rerum agriculturarum (Dr. rer. agr) eingereicht an der Landwirtschaftlich-Gärtnerischen ...»
Soil Fertility: Because of intensive agricultural activities and poor replenishment of plant nutrients, soils sometimes become infertile and decline in their production capacity. The loss of productive surface soil through erosion also reduces the biological activities of soil, and the loss of organic matter ultimately affects soil fertility. Soil slope, texture, and surface and subsurface features play important roles in soil reclamation and the rehabilitation of degraded lands. Some aspects of land degradation are easily reversible, and some are difficult to return back to their original capacity. For example, the removal of the total top soil cover through wind or water erosion is irreversible, whereas a shortage of some nutrients can be recovered (Coxhead and Oygard 2007: 2).
Waterlogging: When the ground water Table becomes so high that excess water stagnates on the surface of land or in the roots of the plants, this is known as waterlogging. This occurs in those areas where water cannot penetrate deeply because of an excess amount of subsurface water or the presence of some hard subsurface layer (clay pan, hardpan) that restricts downward water movement. Waterlogging is evident in low lying areas where hydrological flow causes water logging in depressions and ponds are created, or in those areas that are prone to intermittent floods. Waterlogged conditions are not conducive for agricultural activities and are deadly for plants. According to the strategic plan 2007-16 of Forum of Agriculture Research in Africa (FARA) most of the large scale irrigation systems established to enhance the productivity of the agriculture sector have failed to give the required results;
they are even contributing some serious natural hazards such as waterlogging and are the cause of the damage of agricultural land.
Salinity: This is a measure of the concentration of all the soluble salts in soil or water. Arid and semi-arid zones receive inadequate and irregular precipitation to accomplish the leaching of salts originally present in the soil profile. Normally, when the precipitation is more than 1000 mm per annum, salinity should not develop. This is not the case in arid zones; therefore, salts accumulate in soils. Salts building up in concentrations detrimental to plant growth is a constant threat in irrigated crop production. In arid and semi-arid regions, evapotranspiration is higher than the total annual rainfall. Therefore, rainfall contributes insignificantly to groundwater recharge, and hence, there is general shortage of fresh quality water to offset the total agriculture water demand in these countries. The shortage of fresh water necessitates the use of marginal quality ground water, such as brackish and saline water, for irrigation purposes. This is highly demanded in water-scarce regions. The improper use of saline/brackish water in irrigated agriculture often introduces salinity and sodicity problems, and the soil, if not properly managed, can reach a condition in which it cannot be exploited to its full production capacity. Under such conditions, irrigated agriculture has faced the challenge of sustaining its productivity for centuries; in particular, soil and water salinity, poor irrigation, and drainage management continue to plague agriculture, especially in arid and semi-arid regions (Tanji1996). If soil becomes saline and sodic, its quality becomes poor creating plant- and soil-related problems, with many plants either failing to grow in saline soils or their growth being retarded significantly; therefore, soil salinity often restricts options for cropping in a given area. Australia suffers from this kind of degradation as sixty eight percent of its total land is affected by this white plague (WMO 2005: 8).
Sodicity: This is a measure of sodium ions in soil or water relative to calcium and magnesium ions (Richards 1954). It is expressed either as the Sodium Absorption Ratio (SAR) or as the Exchangeable Sodium Percentage (ESP). If SAR of the soil is equal to or greater than thirteen or ESP is equal to or greater than fifteen, the soil is termed sodic (Richards 1954: 4).
Accumulation of excess Sodium on the soil exchange complex causes adverse effects on soil structure and enhances concentration of Hydrogen ion in soil (pH) and soil erosion. High ESP also affects plant growth because of imbalances in plant nutrition, causing Na-induced nutrient deficiencies of several nutrients (Qadir and Schubert 2002: 276). Soil sodicity is a major constraint to Pakistani agriculture where sixty per cent of the salt-affected soils are affected by various levels of soil sodicity. The reclamation of sodic soils is a laborious, time consuming, and costly task. In Pakistan, the reclamation of sodic soils is usually performed with gypsum as a supplement. The gypsum on dissolution introduces calcium, which replaces Sodium from the soil exchange complex and reduces ESP levels. India has severe problem of soil sodicity. Morocco, in the southern Mediterranean region, has limited growth of vegetation and crop yield attribuTable to this natural problem in its agricultural land, mainly because of the over-utilization of ground water and land for more agricultural output (Bannari et al.
Soil Burial: In some countries in which floods are common, fertile soils are covered by new sediment brought by the floods; however, in many cases, these sediments bring good quality material, such as clay and silt, which improve soil structure and nutrient holding capacity. In sandy desert conditions, wind also plays a role in the burial of soil, and sand can deluge grazing land (UN/FAO 1994).
Impact of climate change (CC) on land degradation and agriculture: Climate change will affect rainfall amounts, frequency, patterns, and duration (rainfall becomes less reliable) leading to increased floods, hurricanes, storms, and drought (leading to water and food shortages). The green-house effect (GHE) will increase evapotranspiration, and thus crop water demand will definitely increase, leading ultimately to changes in cropping patterns and declines in yields. Immediate impacts will be on dryland farming in Africa, specifically in Ethiopia where less than one per cent of the total cultivated lands are irrigated, and the rest is rain-fed; therefore, the dry areas are likely to become even drier and will be too hot for certain crops. By 2020, yields from rain-fed agriculture in some African countries are projected to decline up to fifty percent, thereby increasing food insecurity and hunger. Seventy five to two hundred and fifty million people are predicted to be exposed to water stress attribuTable to climate change. In sub-Sahara Africa, the combination of historical crop production and weather data into a panel analysis has predicted a decline in the yield of maize, sorghum, millet, groundnut, and cassava by 22, 17, 17, 18, and 8 percent, respectively, by 2050 (Burke et al. 2009: 4).
2.3.2 Land Degradation as Anthropogenic Factor To a large extent, land degradation is a natural process; however, it is also enhanced by human involvement. Increased human activities lead to drastic changes in the land response and cause an irreversible decline of its natural safeguard function (FAO/World Bank, 2004).
For instance, to achieve greater output from the land, over-cropping is a common problem all over the World and causes deficiency in the micronutrients of the soil (World Bank/GFE Support Effort 2008, Environment Assessments of Nepal 2005).
In the recent past, land use had been considered a local environmental issue, but now it is recognized as a global problem (Foley et al. 2005). Land-use change at the World level, from forest to farm land and from farm land to housing in recent decades, has been observed to provide food, fiber, and shelter to more than six billion people. Because of this change, natural resources such as land have lost their productivity. The main causes of land degradation via anthropogenic influences are of two types, a) disturbance in cultivation and pastoral activities and b) effect on natural ecosystem (Sherbinin 2002).
Over-cultivation of land: The use of lands in excess of their capacities leads to a decline in soil quality through the loss of most of its minerals nutrients. This is common in areas where human demands for food have increased because of uncontrolled population growth (Saleh 2007: 4). A continuous decrease in the amount of arable land per person of the world population means more output is needed from the same quantity of land. This is required to fulfill the demand for food and industrial raw material for the population (World Development Indicator), which is growing day by day and will indeed double in about fifty years (Blaikie and Brookfield 1991: 28).
Monocropping: The repeated monoculture, for example, of rice-wheat together with intensive agriculture has created a number of ecological and hydrological problems. The cropping pattern demands sustainability, as the soil is consistently becoming deficient of all the micro- and macronutrients. This calls for pragmatic soil-use planning in terms of crop diversification by identifying the soil pockets suitable for particular crops coupled with favorable policy measures, making alternative crops more remunerative through building strong research bases and various economic incentives in terms of, for example, technical support, efficient marketing, and assured prices.
Overgrazing: Overgrazing reduces native vegetation cover, and also soil becomes loose because of animal movement. Thus, soils become prone to wind erosion, whereby the top surface layer is lost through the combined affect of wind and water erosion. This type of degradation is also known as loss of vegetation and is observed when there is pressure to feed more animals on the same rangeland (FAO 1993b). Hardin (1968) explains this problem of vegetation in case of open excess and excludability. He has found that if users increase their number of cattle on specific rangeland and do not care for its production, then the land suffers with a loss of vegetation. In Bhutan state, the ministry of the environment reported, in 2001, the presence of about 0.3 million cattle and described it as a huge load on limited rangeland.
Similarly, World Wildlife Foundation has been reported in 2007 that in Australia, thirteen percent of its vegetation has been removed because of clearing activity for agriculture (WWF 2007: 2).
Deforestation: Forests are the habitats of seventy percent of animal and plant species on the Earth. Deforestation represents the loss of their environment and the natural source of air filtration that can control air pollution (National geographic). The conversion of forests into farmland is a phenomenon in which most small farmers are settled near the roads and clear some part of the forest for agricultural production. After some time, when that plot of land has become unproductive, they move to another. In the New World, new pressures, the heavy burden of cattle rearing, urbanization, mining, and industrial development, and the need for firewood are increasing forest degradation (Lang 2009: 2). In Australia, the clearing of forests to use land for agriculture causes severe soil salinization attribuTable to imbalance in water cycles.
Desertification: The degradation of land in arid, semi-arid, and dry areas is caused by climatic variations (insufficient water amount) and human activities, i.e., improper practices of plowing, deforestation, overgrazing, and loss of fertility. United Nations Convention to Combat Desertification (UNCCD) negates the impression that this occurs in dryland areas with water scarcity, low rain fall, and maximum evaporation leading to the expansion of existing deserts is wrong (Zelaya 2008: 2). Together with other causes of degradation pursuant to human activities such as the cultivation of inappropriate areas, overgrazing, deforestation, and inadequate irrigation practices, the intensification of these activities reduces the chances of the resilience in land ecosystems (Enne & Zucca 2000). Shahid (2004: 15) has characterized desertification as the reverse of soil development or formation.