TREE-PLANTING and FERTLIZERS combat LAND DEGRADATION and DESERTIFICATION In the Sahel, some 650,000 square kilometers of AGRICULTURE LAND (an area equivalent to the country of France) have become desert over the past 50 years. Every year, an estimated 50,000 to 70.000 square kilometers of AGRICULTURE LAND is lost to the desert, because the soil itself is degraded to sand. This LAND DEGRADATION is worsened by periodic droughts, but only in part caused by drought and climatic change. Mismanagement of the land is probably the main cause of desertification. However, it is important to understand that the mismanagement has a lot to do with poverty. Poor peasants cut down the shelter belts because they need wood for cooking. Over-grazing is another main cause of desertification. As human populations have increased in the Sahel, so have the numbers of livestock. This has led to vegetation being stripped from rangelands. Over-grazing also changes the composition of plants in the rangelands. Useless and mildly poisonous plants such as Calotropis procera now infest vast areas of the Sudano-Sahelian belt because they no longer have competition from the nutritious grasses that used to make up the bulk of pasture plants. This phenomenon is typical for areas of over-grazing, worldwide. In addition, the increasing and unsustainable use of trees and brushwood for fuel, leading progressively to deforestation, has accelerated desertification over much of semi-arid Africa. All trees in the Sahel Region function as shelter belts against the hot air, coming from the Sahara, drying out the top soil. Moreover, desertification may happen quickly. During the Sahel drought of the early 1970s, nearly one million people were forced to leave Burkina Faso. 500,000 had to leave Mali. At present deforestation is proceeding 30 times faster than reforestation. The shortage of fuelwood and building materials has led to crop residues and animal manure being burned for fuel instead of being returned to the soil, adding to the quality of the soil. The lack of fertilizers, organic or inorganic, in most of Africa is a separate issue. More inorganic fertilizer on African fields will increase yields by several folds (100 - 500 %) and help to preserve farm land ! Hydrological conditions over much of Africa are being changed. When the vegetative cover partly disappear from the soil, there is a tendency for raindrops to cause soil-surface sealing. This phenomenon involves raindrops hitting the soil at velocities of about 30 km/h, instead of hitting the plants first. This direct hit causes the soil particles to be packed, effectively sealing the top layer of the soil against percolation (the slow motion) of water through the soil. Hence, less water sinks down to the roots of plants and to the water table, below. The water table is already being alarmingly depleted in Africa (as many other places), because of the drilling of wells. Paradoxically, less vegetation means less water stored in the soil, less water percolating down to the water table and less water absorbed by the remaining plants. On the other hand, less vegetation means increased amounts of fresh water pouring into the ocean, which also means more soil erosion. As a result, sediment loads in rivers are increasing, dams are filling with silt, hydro-electric schemes are being damaged, navigable waterways are being blocked and drinking-water quality is deteriorating. The inland fish catch is suffering in many areas. Part of the solution to the problem is tree-planting. Trees provides shelter for very hot and dry air from the desert, drying out the top soil, pulverizing it. Another part of the solution is the use of inorganic fertilizers in agriculture. If organic fertilizers exist, they can be used. Often, however, sufficient amounts of organic fertilizers are not available. By using fertilizers, crop yields can be increased by several folds. Some of the plant material (e.g. roots) will remain in the field after harvest, improving the quality of the soil by adding texture.
Posted on: Mon, 25 Nov 2013 06:54:10 +0000
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