Advance Desertification AGR 740 Advance Desertification AGR 740 Dr. Refaat Abohassan

Introduction to the course Course content: o The concept of land degradation o Coastal and terrestrial sand dunes o Winds affecting shapes of sand dunes o Classification of sand dunes o Sand dunes in Saudi Arabia o Vegetation covering sand dunes o Sand dunes monitoring and assessment o Sand dunes fixation Advance Desertification AGR 740 Advance Desertification AGR 740

Lecture 1 The concept of land degradation

Land is the place in which the biological system and activities take place including soil, water and interactions with the environment. Land is the place in which the biological system and activities take place including soil, water and interactions with the environment. Land degradation: the reduction of the land production capacity and failure to produce natural resources needed for the survival of mankind (Desertification) Land degradation: the reduction of the land production capacity and failure to produce natural resources needed for the survival of mankind (Desertification)

Ecological and economic indications Ecological and economic indications Prosopis juliflora (mesquite) and Prosopis spp. ( الغاف ) are 2 examples of economic indicators that results in the reduction of grass growth (used to feed cattle) and thus the increase in fodder prices. Prosopis juliflora (mesquite) and Prosopis spp. ( الغاف ) are 2 examples of economic indicators that results in the reduction of grass growth (used to feed cattle) and thus the increase in fodder prices.

Desert creep and Encroachment (Stebbing, 1937, 1938) The extension of the desert to areas beyond the natural boundaries The extension of the desert to areas beyond the natural boundaries This is in direct relation to the movement of the fine sand bodies from the desert to neighboring suburbs and invasion of agricultural lands and oasis. This is in direct relation to the movement of the fine sand bodies from the desert to neighboring suburbs and invasion of agricultural lands and oasis.

1. Forest land utilization: deforestation and tree cutting. 2. Grass land utilization: reduction in production, invasion of foreign species 3. Wet agricultural land utilization: soil erosion, loss of organic matter, low nutrients, weed invasion, and formation of hardpan. 4. Utilization of irrigated lands: high water levels reaching saturation point affecting soil chemical properties. The four land use systems governing land degradation

Anthropogenic causes of land degradation 1. The intensive use of land by mankind reached above the natural production capacity. 2. Population increase, conversion to commercial economy, conversion of land toward crop production. 3. Weakness of marginal ecological systems specially in the arid and semi arid lands which is characterized by limited water resources, low vegetative cover and low biomass production. 4. Weak soil characteristics: low precipitation and organic matter.

Anthropogenic causes of land degradation

Soil degradation process 1. Erosion: soil loss due to the mobilization of topsoil by the forces of water and wind. Human activates would govern the severity of erosion (such as agricultural practice, timber cutting, overgrazing and land change) 2. Desertification: non-desert area starts to exhibit the characteristics of a true desert, this is mainly due to mismanagement of the land rather than drought.

Soil degradation process 3. Salinization and Nutrient Loss: - Soil salinization is the concentration of salts in the surface or near surface of soils due to large-scale irrigation. -Nutrient loss is an important problem in regions of low- input agriculture, such as in Africa. In such regions, when crops are harvested, essential nutrients are taken away in the crop and not replaced. -Nutrient loss is an important problem in regions of low- input agriculture, such as in Africa. In such regions, when crops are harvested, essential nutrients are taken away in the crop and not replaced.

Can degraded soils be restored to full function? 4. Recovery: is variable and depend on soil conditions: - Lightly degraded soils: can be improved by crop rotation, minimum tillage techniques, and other farm practices. - Moderately damaged land takes more resources than an average farmer has to restore. Changes in soil conservation practices can slow land degradation, but not restore fertility often. National programs will be needed for such lands, requiring major structural change (e.g., draining, contour banks, etc.)

Can degraded soils be restored to full function? - Severely eroded land generally is simply abandoned. Restoration efforts are simply beyond developing countries - requiring deep ditches for drainage, terraces to hold the soil in place, mechanized deep plowing to remove compaction, reseeding programs