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2. Food production versus land degradation
Population pressures increase
Extent
of soil erosion
Lower
productivity forecast
Hillside
forests destroyed
Overgrazing
is critical
Salinization threatens production
Extent
of sediment damage
Efficient shifting cultivation declines
Deserts are spreading
FAO studies indicate that agricultural production will have to increase by an estimated 60 percent by the year 2000 if the world's population is going to be fed. For this goal to be met, three things will have to happen. First, agriculture will have to be intensified on lands already being cultivated. In the 1970s, one hectare of arable land supported about 2.6 persons; by 2000, one hectare will have to support 4 persons.
Second, the area of cultivated land will have to be expanded by some 200 million hectares, or about 14 percent. It appears, however, that this amount of land - even if it can be found and developed will only just compensate for the amount of soil productivity lost over the same period, if erosion continues at present rates.
The third requisite, therefore, is that the continuing degradation of the world's soils be reversed and soils managed for sustained production. Meeting all three requisites will require a new sense of commitment on the part of the developing countries as well as the more developed ones.
There is no doubt that the number of people in the world is growing rapidly. Under even the most conservative projections, world population will increase from 4 billion in 1975 to an estimated 6.35 billion in the year 2000. Most of that population growth is expected to occur in those countries with the least capacity to feed themselves. The population of Asia and Oceania would increase 60 percent; that of Latin America, nearly 100 percent, and that of Africa, more than 100 percent.
World food production, of course, is also expected to increase, but most of that increase will occur in countries that already have relatively high per capita food consumption. For many in developing countries, per capita consumption will decline. These are a few of the disturbing predictions contained in The Global 2000 Report, published in the USA in 1980.
It is not necessary, of course, to look into the future to find hunger and misery. Despite major technological advances in agricultural production, millions of people in the world today are undernourished or starving. This paradox stems from a number of causes, of which the most alarming is the rate at which the productive capacity of the land is being degraded by mismanagement of agricultural and forest resources.
Agriculturists living and working in developing countries and travellers on business or holiday do not require statistical evidence to convince them that land degradation is widespread and serious and that it is encouraged by the pressures of a growing population.
For those who prefer observations substantiated with numbers, a joint FAO/UNEP assessment of land degradation around the world has come up with the following findings:
Assessments provided by countries attending an FAO consultation on degradation also reveal serious resource damage. Of India's total area of 328 million hectares, 90 million are affected by water erosion and 50 million by wind erosion. The erosion is accelerated by the floods that visit the country every year, causing untold misery and affecting an average area of 20 million hectares. In Argentina, 13 percent of the cropland is affected by erosion from water and 16 percent from severe wind erosion.
In the USA, which has had an active soil conservation programme for nearly 50 years, the average annual loss of topsoil from all cropland today is about 12 tons per hectare - and it is higher still in many important farming areas. In Iowa, one of the country's leading maize producers, two cubic metres of soil are lost for every cubic metre of maize produced. The impact on production of such serious soil losses has been masked by other inputs, including mineral fertilizers and improved crop varieties, but the long-term effect will be to push crop yields downward, with inevitable increases in food prices.
What do these soil losses mean in terms of the world's future capacity for growing food? Provisional results of a new FAO/UNFPA project on "land resources for populations of the future", which forecasts probable farm output in the year 2000, predict that if soil losses continue unchecked in Africa, the potential rainfed crop production will decline about 15 percent during the next two decades. In Southeast Asia, production will fall about 19 percent, and in Southwest Asia, more than 41 percent.
From 10 to 22 percent of the rainfed cropland in these regions would become too degraded to use for crops at all but it could be used for grazing livestock. Even so, the study predicts that the land's "potential population carrying capacities" will decline by 8 to 12 percent, which means that these regions will be able to feed fewer people, not more, by the year 2000.
The Global 2000 Report takes a pessimistic view, predicting that land under cultivation will increase only L percent by the year 2000 because most of the good land is already under cultivation. Whether or not this estimate proves correct, an all-out effort to expand world cropland will be necessary, although reclamation could be expensive, and much more research on managing tropical soils will have to be conducted and applied before farming can be carried out safely and productively, especially on lands already degraded. Some relocation of people might also prove necessary, since the densest populations in developing countries do not always coincide with locations of the best agricultural soils.
Part of the accelerated land degradation around the world is caused by the continued destruction of forests. In developing countries, where firewood is the chief fuel for cooking and heating, demand is fast outstripping the growth of new trees. Villagers in some countries are forced to burn dried cow dung for fuel, a practice that deprives local soils of needed organic matter and nutrients.
Deforestation of slopes also causes soil erosion and destructive floods. The 1974 floods in Bangladesh, which brought about severe famine by reducing the rice harvest, were caused in part by deforestation in Nepal and eastern India. In just 5 years, between 1975 and 1980, some 37 million hectares of tropical forests were destroyed in Africa, 12.2 million in Asia, and 18.4 million in Central and South America.
Forests need to be conserved and managed much more carefully than they have been in the past. One way to conserve them is to make eroding cropland more productive, so that people are not driven to cut trees and destroy watersheds to clear new land for farming.
Some 23 percent of the world's land is used for grazing livestock, and soil erosion caused by overgrazing is one of the most important environmental problems in the developing world. Some observers report that, on average, rangeland in developing countries is a third more crowded with livestock than rangeland in the developed world.
The destruction of grazing land follows an all too familiar sequence of events. Overgrazing by cattle reduces plant cover, eliminating the most desirable forage species first. This opens up the land to undesirable weeds, brush, and trees and leads to increasing soil erosion and lower soil fertility. The land becomes less and less productive.
With less nutritious forage available, some graziers respond by actually increasing the size of their cattle herds to compensate for losses in weight. In other instances, sheep replace cattle as forage deteriorates, and eventually sheep are replaced by goats, who will eat just about anything, including young trees. The end result is barren land, windstorms, erosion and floods.
Salinization threatens production
Waterlogging and salinity are reducing agricultural production in many of the irrigated areas of the world today - in the Near East and North Africa, in Argentina and Peru, in China, in the Soviet Union, and in the United States of America and northern Mexico. irrigated farming takes place today on more than 200 million hectares of the world's land and, according to published UN estimates, some 40 million hectares are either waterlogged or plagued by excessive salinity, or both.
While some land is literally sterilized by salts and must be abandoned, most symptoms of salinization are not so obvious. It is difficult to assess exact losses in productivity, since the symptoms are not always visible. Top growth may be reduced more than root growth, and grain yields for maize and rice may be reduced appreciably without affecting straw yields. Average losses in yields in different countries have been estimated as high as 20 percent on saline and waterlogged land and at 10 percent in the San Joaquin Valley of California, where annual loss of farm income from salinization is estimated at $31.2 million.
Rehabilitation of waterlogged and saline soils, however, is expensive and time-consuming and usually beyond the reach even of wealthy land users. Reclamation costs in one large area were estimated by the UN at $650 per hectare. A great deal of salinization research has been directed at finding more salt-tolerant plant species.
Sedimentation is a by-product of soil erosion. When erosion is reduced, so is sedimentation; when erosion goes unchecked, sedimentation damage also increases. When eroded soil flows into a stream with runoff water, a portion of it is transported in suspension until it reaches larger and larger rivers. The size of a sediment load can be truly amazing and is a fairly good index of the amount of erosion in the watershed.
The river that carries the largest amount of sediment in the world is the Yellow River in China with an average annual load in suspension of nearly 1.9 billion metric tons. It is followed closely by the Ganges, with nearly 1.5 billion tons of sediment a year. Next in line are the Brahmaputra, Yangtze, Indus, Ching, Amazon, and the Mississippi. The amount of sediment carried is not proportionate to the size of the watershed. The basin of the Yellow River is 673 000 square kilometres; the basin of the Amazon, which carries only a fifth as much sediment as the Yellow River, is more than 8 times as large.
Sediment causes damage in several ways. Firstly, channel sedimentation of navigable rivers means costly dredging bills to keep channels open for barge traffic. Secondly, the still waters of reservoirs placed in the path of streams or rivers cause silt to drop out, reducing the water storage capacity and the useful life of the impoundment. Thirdly, sedimentation of bottomland, which occasionally proves beneficial, can also be harmful if flooding rivers deposit deep layers of sand over fertile bottomland. In such cases, either the land is lost to production or large amounts of money are spent to remove the sediment.
Efficient shifting cultivation declines
Practice
met local needs
Fallow
is shorten
Two problems that are particularly threatening in developing countries are a decline in efficiency of traditional shifting cultivation and an increase in desert encroachment on what were once agricultural lands. Both problems require special attention.
Shifting cultivation is a traditional method of farming that works well where the ratio of land to people is high. It is a system, common throughout the tropics today, of cutting trees and shrubs and tall grasses, burning the litter, growing crops for 2 to 5 years on the cleared land, and then allowing the natural cover to return to regenerate the soil. Where the system is practiced successfully, the fallow period may last any time from 5 to 15 years, depending on the soil and type of vegetation. The important thing is that the land be left fallow long enough for the tired soil to regain its former fertility.
From the point of view of the conservationist, shifting cultivation can be the cause of excessive soil erosion. immediately after land is cleared and before a crop grows enough to provide some protection from rainstorms, the soil is extremely susceptible to washing. Erosion losses can be alarming.
Shifting cultivation, in one form or another, is carried out in many places, on a wide range of soils, and with a variety of crops. It was once practised in northern Europe. Today some 30 percent of the world's arable soils are under shifting cultivation in Africa, Latin America, Oceania, and Southeast Asia.
The system does not require the use of machinery to be successful. Clearing is accomplished with axes, cutlasses, machetes, and fire. The cropland thus wrested by hand from forest and savanna is then cultivated with hoes or other hand tools, or with animal drawn implements, resulting in little disturbance of the surface soil.
When, after a few years, declining crop yields dictate abandonment of the land, new cropland is cleared elsewhere.
For many years, shifting cultivation proved a satisfactory farming system - as long as there was plenty of land and populations did not become excessively high. While it was hard work to clear the land, local experience and tradition directed the farmer to the most fertile soils, the easiest to cultivate, and those best suited to each particular crop. Many African farmers had (and still have) names for the soils and rated the fertility of a piece of land and its suitability for various crops by the vegetation that covered it. They understood their farming system and knew how to make the most of it.
Forest fallow in particular is known to have a beneficial effect on soil structure. Structure is not nearly as good under savanna and cultivated crops. The forest does a better job of protecting soil against erosion than does savanna, and forest soils contain much more organic matter. Further, studies in East Africa showed that water was available in forest soil at all levels throughout the year. On grassland and in cultivated fields, upper layers of soil dried out rapidly after rain.
The chief problem with shifting cultivation today is that increasing populations and the need for higher production to feed them are pressuring many farmers to shorten or even eliminate the fallow. Without the full period of regeneration, the land does not recover from the loss of nutrients, soil erosion, and deterioration of the soil structure that took place during cropping by the next time the land is cleared. As a consequence of shortening the fallow, yields are lower and soil damage greater. The result can be permanent destruction of the soil and a disintegration of the village system.
So far, the problem of shifting cultivation has not been solved, although there are many ideas on how to approach the problem. They range from the opinion that nothing at all should be done, to the opposite extreme of completely replacing shifting cultivation by new systems of continuous cultivation. In between these extremes, various proposals aim at a gradual improvement of the productivity of the present system. Much more research and field testing will be needed, however, before some of these approaches can be applied with assurance of success.
Legacy
is desert
Potential for deserts is widespread
A second problem demanding special attention is "desertification", a relatively new term for the creation of desert-like conditions in what was once agricultural land. Desertification is not a process of land degradation like soil erosion and overgrazing, but is an end product. It occurs in arid and semi-arid zones and results from a combination of drought and mismanagement of resources, sometimes from ignorance but just as often from necessity. If soil erosion is a sickness of the land, then desertification is a land's death.
There is evidence that desertification is as old as civilization, but today it appears to be accelerating. What focused international attention on desertification was the 5 years of drought that began in 1968 in the Sahel, the southern margin of the Sahara that encompasses several countries. While drought was not new to this region, the plight of the people in past years had gone unnoticed by the rest of the world. In the early 1970s, however, communication media made the vast migrations, the refugee camps, and the hunger and starvation in the Sahel familiar to every newspaper reader and television viewer.
The seriousness of the disaster was not exaggerated. By 1973, the fifth year of drought, Lake Chad had shrunk to a third of its normal size and was no longer a single body of water. Failure of the Niger and Senegal rivers to flood left much of the best cropland in five countries unwatered and barren. Shrubs and trees died and, as grazing became restricted, livestock concentrated around watering places, where they destroyed what little vegetation remained and compacted the soil. Those graziers who fled south found only more people and herds similarly stricken. Estimates of deaths in the Sahel during the drought years ranged from 100 000 to 250 000, while the number of drought-induced diseases, including epidemics of measles and spinal meningitis among children, was impossible to calculate. Livestock losses were also high.
The drought ended in 1974, but returned after a few years. Its continuing legacy is the intensification of desert-like conditions in the Sahel and an extension of true desert into land that once supported people and their livestock. There is convincing evidence of this. Following the drought, in 1975, aerial surveys were made of the Sudan's desert margins. The photographs were compared with aerial maps made in 1958 of the same region. Studying the line where scrub vegetation tapers off into barren desert, it was concluded that the boundary of the Sahara had shifted southward by from 90 to 100 kilometres during the 17 years between surveys .
Ground observations support this conclusion. Dense concentrations of Acacia trees, which are useful for firewood and forage, were common around Khartoum as recently as 1955; by 1972, the nearest stands of Acacia were located 90 kilometres south of the city.
Desertification is also evident elsewhere, including the Americas. Journals and maps of the first Spanish settlers in northern Chile indicate that the Atacama Desert was once dense jungle. Many believe that overcutting of forests and overgrazing by livestock were responsible for turning the area into a wasteland.
Potential for deserts is widespread
The territories of half of the countries of the world are located in arid or semiarid zones susceptible to land degradation and eventual desertification. Much of this land, which currently contains about 14 percent of the world's population, is gradually losing its capacity to support life .
A United Nations Conference on Desertification in Nairobi focused attention on the problem in 1977 and developed a broad plan of action "to achieve zero desertification by the year 2000". Recommendations of the conference covered a variety of activities.
Although the conference acknowledged the role of natural calamities, like changes in climate, in extending the range of deserts, it considered the actions of man the more critical. Of the causes of desertification identified at the meeting, only 13 percent involved natural changes in the environment. The other 87 percent were attributed to human mismanagement of resources, including overgrazing, overcultivation, cutting too many trees for firewood, and inefficient and destructive irrigation practices.
One cause of trouble identified was the response of farmers and graziers to fluctuations in rainfall between good years and drought years. In dryland grazing areas, large numbers of cattle and sheep tend to build up during years of normal rainfall, too many to be supported during years of drought. When the inevitable drought arrives, graziers are naturally reluctant to cut back on herds after a single dry year. When it becomes apparent that the drought will be prolonged and serious, many ranges are already overgrazed.
Dryland farmers also tend to extend croplands into more marginal lands during good years, pushing back graziers in the process. When drought begins, the new cropland lacks defences and the soil may emerge from the drought too degraded even for livestock.