Advance Desertification AGR 740AGR 740

Dr. Refaat AbohassanDr. Refaat Abohassan

Introduction to the courseIntroduction to the courseCourse content:Course content:o The concept of land degradationThe concept of land degradationo Coastal and terrestrial sand dunesCoastal and terrestrial sand duneso Winds affecting shapes of sand dunesWinds affecting shapes of sand duneso Classification of sand dunesClassification of sand duneso Sand dunes in Saudi ArabiaSand dunes in Saudi Arabiao Vegetation covering sand dunesVegetation covering sand duneso Sand dunes monitoring and assessmentSand dunes monitoring and assessmento Sand dunes fixationSand dunes fixation

Advance DesertificationAdvance Desertification AGR 740AGR 740

Lecture 1Lecture 1

The concept of land degradationThe concept of land degradation

• Land is the place in which Land is the place in which the biological system and the biological system and activities take place activities take place including soil, water and including soil, water and interactions with the interactions with the environment. environment.

• Land degradation: the reduction of the land Land degradation: the reduction of the land production capacity and failure to produce production capacity and failure to produce natural resources needed for the survival of natural resources needed for the survival of mankind (Desertification) mankind (Desertification)

•Ecological and economic Ecological and economic indicationsindications

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

Desert creep and Encroachment (Stebbing, 1937, Desert creep and Encroachment (Stebbing, 1937, 1938)1938)

The extension of the desert to areas beyond the The extension of the desert to areas beyond the natural boundaries natural boundaries

This is in direct relation to the movement of the This is in direct relation to the movement of the fine sand bodies from the desert to neighboring fine sand bodies from the desert to neighboring suburbs and invasion of agricultural lands and suburbs and invasion of agricultural lands and oasis. oasis.

1.1. Forest land utilization: deforestation and tree cutting.Forest land utilization: deforestation and tree cutting.

2.2. Grass land utilization: reduction in production, invasion Grass land utilization: reduction in production, invasion of foreign speciesof foreign species

3.3. Wet agricultural land utilization: soil erosion, loss of Wet agricultural land utilization: soil erosion, loss of organic matter, low nutrients, weed invasion, and organic matter, low nutrients, weed invasion, and formation of hardpan.formation of hardpan.

4.4. Utilization of irrigated lands: high water levels reaching Utilization of irrigated lands: high water levels reaching saturation point affecting soil chemical properties.saturation point affecting soil chemical properties.

The four land use systems governing land The four land use systems governing land degradation degradation

Anthropogenic causes of land degradationAnthropogenic causes of land degradation

1.1. The intensive use of land by mankind reached above the The intensive use of land by mankind reached above the natural production capacity.natural production capacity.

2.2. Population increase, conversion to commercial economy, Population increase, conversion to commercial economy, conversion of land toward crop production.conversion of land toward crop production.

3.3. Weakness of marginal ecological systems specially in the Weakness of marginal ecological systems specially in the arid and semi arid lands which is characterized by limited arid and semi arid lands which is characterized by limited water resources, low vegetative cover and low biomass water resources, low vegetative cover and low biomass production.production.

4.4. Weak soil characteristics: low precipitation and organic Weak soil characteristics: low precipitation and organic matter.matter.

Anthropogenic causes of land degradationAnthropogenic causes of land degradation

Soil degradation processSoil degradation process

1.1. Erosion: soil loss due to the mobilization of topsoil Erosion: soil loss due to the mobilization of topsoil by the forces of water and wind. Human activates by the forces of water and wind. Human activates would govern the severity of erosion (such as would govern the severity of erosion (such as agricultural practice, timber cutting, overgrazing and agricultural practice, timber cutting, overgrazing and land change)land change)

2.2. Desertification: non-desert area starts to exhibit the Desertification: non-desert area starts to exhibit the characteristics of a true desert, this is mainly due to characteristics of a true desert, this is mainly due to mismanagement of the land rather than drought.mismanagement of the land rather than drought.

Soil degradation processSoil degradation process

3.3. Salinization and Nutrient Loss: Salinization and Nutrient Loss:

- Soil salinization is the concentration of salts in the surface or near - Soil salinization is the concentration of salts in the surface or near surface of soils due to large-scale irrigation.surface of soils due to large-scale irrigation.

-Nutrient loss is an important problem in regions of low--Nutrient loss is an important problem in regions of low-input agriculture, such as in Africa. In such regions, when crops input agriculture, such as in Africa. In such regions, when crops are harvested, essential nutrients are taken away in the crop and are harvested, essential nutrients are taken away in the crop and not replaced. not replaced. 

  

Can degraded soils be restored to full function? Can degraded soils be restored to full function?

4.4. Recovery: is variable and depend on soil conditions:Recovery: is variable and depend on soil conditions:

- Lightly degraded soils: can be improved by crop Lightly degraded soils: can be improved by crop rotation, minimum tillage techniques, and other farm rotation, minimum tillage techniques, and other farm practices.practices.

- Moderately damaged land takes more resources than an - Moderately damaged land takes more resources than an average farmer has to restore. Changes in soil average farmer has to restore. Changes in soil conservation practices can slow land degradation, but conservation practices can slow land degradation, but not restore fertility often. National programs will be not restore fertility often. National programs will be needed for such lands, requiring major structural needed for such lands, requiring major structural change (e.g., draining, contour banks, etc.)change (e.g., draining, contour banks, etc.)

Can degraded soils be restored to full function? Can degraded soils be restored to full function?

- Severely eroded land generally is simply abandoned. - Severely eroded land generally is simply abandoned. Restoration efforts are simply beyond developing Restoration efforts are simply beyond developing countries - requiring deep ditches for drainage, countries - requiring deep ditches for drainage, terraces to hold the soil in place, mechanized deep terraces to hold the soil in place, mechanized deep plowing to remove compaction, reseeding programsplowing to remove compaction, reseeding programs