Agency for International Development. Search Fusion Enter the terms you wish to search for. Inside this Issue About FrontLines. Sowing Seeds of Stability in Micronesia. No Rain? Raising Childhood Immunization Rates in Madagascar. By Gina Althoff. After harvesting her maize field outside Liwonde Forest Reserve, Edna Ndalama adheres to conservation agriculture practice and keeps the maize stalks in the field instead of the traditional practice of burning them.
Chisomo Mdalla. Techniques to conserve water while improving soil fertility and crop yields are making believers out of skeptical smallholders. Edna Ndalama stands with her healthy and high-yielding drought tolerant maize. Ramzy Kanaan.
Throughout the world's continents water tables are falling, and it has been estimated that by more than half the world's population will be living in regions suffering from a shortage of water Rockstrom, The combination of falling groundwater and greater runoff will reduce the base flows of rivers and streams, and will greatly increase peak flows and the incidence of floods. High runoff often affects the quality of surface water by its load of eroded soil sediments, may make the water unsuitable for drinking, and may increase the costs of water treatment.
High sediment loads in the reservoirs of hydroelectric schemes will reduce the life span of dam sites and increase turbine maintenance costs. The recommended amount of water needed for one person per day for cooking, drinking and washing is about 50 litres, but the amount of water needed every day for a crop to transpire and produce sufficient grain for one person is some 10 to 20 times larger. Therefore, water shortages will have most effect on food production, rather than on the availability of water for domestic use.
The following are simple visual indicators of deteriorating quantity and quality of water supplies FAO, a. Increased possibilities for safe and sustainable intensification of production can be identified if the nature of soil productivity and the process and the effects of soil erosion are examined. Fertility is the inherent capacity of a soil to supply nutrients in adequate amounts and suitable proportions, whereas soil productivity is a wider term referring to the ability of a soil to yield crops Brady, The chief factors in soil productivity are soil organic matter including microbial biomass , soil texture, structure, depth, nutrient content, water-storage capacity, reaction and absence of toxic elements.
A brief description would indicate that soil productivity depends on physical, hydric, chemical and biologic characteristics and their interaction. Much can be known about the above-ground growth and development of plants by observing and measuring them and their functions. We know much less of what goes on beneath the surface in the soil ecosystem, where plants' roots are important constituents.
In order to function unimpeded through cycles of growth to maturity, land plants require water to pass through them from soil to atmosphere. Plate 28 shows the length of roots relative to the above-ground parts. The smaller roots and their root hairs also constitute a large part of any root system, but are not easily visible. Root systems are of astonishing dimensions, as illustrated by comparative figures from the same-sized samples of soil Table 7. Root hairs Total number Total lengths Total surface area. The relative proportions of solids, liquid and gases in the rooting environment are as important as the manner in which they are arranged.
In this respect, the biotic content of soil is also important because together with plant roots it contributes to restructuring soil and the improvement of porosity after damage by compaction, pulverization or structural collapse. Without good conditions for roots very high-yielding crops will be unable to express their full potentials. The key role of soil porosity is shown in Figure Soil structure and its impact on soil processes and agricultural sustainability Lal, Many degraded soil situations have arisen because of mould-board or disk plough-based farming practices, which have resulted in:.
Each of these four factors negatively affects soil as a habitat for plant roots. The view that such conventional tillage methods limit the development of an optimum habitat for rooting is borne out by the experience of alternative agriculture systems.
Land of No Rain by Amjad Nasser
The amount of moisture in the soil depends on how much rainfalls and enters the soil. Under rainfed agriculture, the amount of water entering the soil depends on what percentage is diverted above the surface as runoff. It may not always be possible to prevent all runoff, but improvement of soil physical conditions will help to reduce it to the unavoidable minimum. A thin surface crust or subsurface compaction can be enough to reduce the rainwater infiltration rate, to provoke runoff and to cause loss of water, soil and consequently potential soil moisture Plates 29 and However, when the soil is covered with litter, more water enters and the soil surface is protected from the force of raindrops Figure Where the soil is not crusted and is protected by litter from the force of raindrops more water enters the soil than where the surface is bare Lilongwe, Malawi [T.
Infiltration and availability of water to plants depends on how the water is held between, firstly, individual particles of the soil e. If the majority of pore spaces is very small, whether because of the inherent properties of the soil such as in a very clayey Vertisol, or because the soil has been compacted, the water may be held so tightly that plants cannot extract much of it.
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On the other hand if the soil has a predominance of large spaces, such as in coarse-textured sandy soils, much or all of the rainfall may enter the soil and pass easily and rapidly down through the profile without much of it being retained. A wide range of pore sizes is therefore desirable for enabling both retention and transmission of rainwater. PLATE A thin surface crust caused by raindrop impact on a bare soil of poor structure Tabatinga, Brazil. Crusting and subsurface compaction can result in serious losses of water and soil Khobotle, Lesotho. Reduction of pore space may be at least as important as losing soil particles with respect to yield.
It affects water movement and the soil's tenacity of water retention, root expansion and gas exchange of O 2 and CO 2 with the atmosphere. Field observations in Malawi, Zambia and Tanzania indicate that repeated tillage to the same depth with hand hoes can cause subsurface pans of compacted soil at the base of the tillage layer.
After a few years, they may become so dense that neither roots nor water can penetrate them easily.
This increases surface runoff, severely limits soil depth and causes stunting of roots Plate With root access to soil moisture restricted to the shallow soil layer above the compacted layer, plants are prone to suffer water stress after only a few days of dry weather. Much of the blame for this damage to soils can be attributed to inappropriate tillage practices. Such problems are found not only in tropical areas but also are now widely seen as well in temperate zones across North and South America, Europe, Asia, Australia and New Zealand.
In temperate zones damage is due to compaction by machines. In tropical regions much damage is also done by high-intensity rainfall on unprotected soils.
Physical degradation of the soil is the precursor of excessive runoff, reduced soil moisture and root restriction, and is a primary limitation to crop growth. There are already widespread and serious problems in soils as rooting environments, characterized not so much by erosion as by unexpectedly poor performance of crops in large parts of the world, in both rainfed and irrigated areas. Runoff and erosion occur because soil porosity has been damaged, whether at or below the surface of the soil.
They are the consequences, not primary causes of land degradation. In many instances tillage aimed at loosening the soil to let in more rainwater can also result in soil collapse, which then leads to increased erosion and loss of potential soil moisture through runoff. It is sometimes assumed that yield reductions following soil erosion can be directly related to the quantities of soil materials lost.
This may not always be the case, for example where erosion removes a similar quantity and quality of material from three soils with different subsoils, yields may be different from each other and equal, lower or higher than before the erosion Figure Where a subsurface layer is of better quality for rooting than that which overlays it, erosion could be followed by higher, not lower, yields though such situations are not common.
Land of No Rain
The differences in yields are related to the differences in the characteristics of the subsurface habitats in which the roots will grow before and after the erosion i. Erosive loss of the pale surface soil would expose the dark soil layer whose characteristics might provide a completely different quality of potential seed bed Thabana Morena, Lesotho. Yield after erosion is related to the quality of soil remaining, not to quantity and quality of soil removed Shaxson, a.
Differences in soil surface porosity affect water infiltration rates. Compaction of the soil by trampling or machinery has the same effect, changing the hydraulic conditions of the soil. Loss of porosity in the soil increases surface runoff, increasing infiltration increases soil moisture. A failure to understand this relationship has often led to inappropriate actions to stop erosion, such as construction of physical works or overuse of fertilizers Box 2.
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In the Philippines, investigations were made of loss of soil productivity associated with erosion. This problem is widely recognized by small farmers who have observed natural terraces forming between contoured buffer strips on agricultural land with percent slopes. They noted that crop performance on the upslope side of these terraces was not as good as that on the lower side. Water availability can make a pronounced difference to agricultural output and standard of living. Areas fed by canals fare better than those that rely on rains. Today, farmers in rain-dependent areas are being pushed against a wall.
The Green Revolution was designed around growing high-yielding varieties of wheat and rice, which needed plenty of water and chemical inputs.
Over time, even farmers in unirrigated areas cobbled together their own water supply — mostly through groundwater — and switched to the green revolution framework. But now, as groundwater levels collapse, agricultural soils weaken and rainfall gets erratic, the green revolution seems to have run its course in these unirrigated areas.
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The Green Revolution Comprising arid and semi-arid ecosystems, drylands stretch from Gujarat in the west till Eastern Madhya Pradesh; and from Rajasthan till the southern tip of India. To reduce their vulnerability to rains, farmers here used to grow jowar, bajra and pulses. While low-yielding, such crops were less affected by variations in rainfall. Farmers invested little in their fields. Why invest if returns are uncertain? In the same field, they planted multiple crops. For instance, Jowar or pulses, both drought-resistant, would be planted alongside wheat, which gave high yields in normal rains.