Book review: Environmental Management in Tropical Agriculture by Robert J. A. Goodland, Catherine Watson and George Ledec. Westview Press, Boulder, Colorado. 1984.
Published in The Ecologist Vol. 14 No. 5-6, June-July 1984.
This is a very comprehensive, yet concise, study by a group of people who have obviously had considerable experience in the field of tropical agriculture. All three authors work in the Office of Environmental Affairs of the World Bank in Washington, DC. Robert Goodland is a tropical ecologist of note, having held professorships at several universities (including McGill) and having published widely on ecological issues mainly in South and Central America. His highly authoritative ecological impact assessments of large scale water projects in Brazil and elsewhere, are already well known. Catherine Watson, the second author, is a researcher and George Ledec is a research assistant.
The book is divided into four parts, plus an epilogue. The first part discusses the environmental problems associated with such food crops as rice, maize, sorghum and cassava. The second section deals with the ecological impact of growing cash crops, including coffee, tea, cocoa, sugar cane, tobacco and forest trees. The third section considers large and small livestock schemes, and fresh water and marine fisheries. The fourth section is devoted to such issues as the use of biocides, the benefits of integrated pest management, the problem of tsetse fly control in livestock projects, the environmental hazards of perennial irrigation, the use of energy, the problems of Weed control, the need to preserve genetic diversity and the problems of soil erosion.
Intercropping for nitrogen
Each chapter contains valuable information, much of which may be new even to those readers with some knowledge of tropical agriculture. We learn, for instance that for economic reasons no artificial fertiliser is available in the developing world for the cultivation of maize, sorghum and millet – this in spite of the fact that these crops “feed directly millions of people”.
The authors show us how the yields of millet can be increased dramatically through fertiliser use. In trials in the south of the Sahara, nitrogen increased millet yields from 100 kilogrammes per hectare (kg/ha.) to 1,500 kg/ha, when combined with potassium and phosphorous. In ideal conditions, NPK can still further increase yields to 2,000 kg/ha, so long as there is 125 mm of soil moisture in the growing season.
In fact, the lack of artificial fertiliser is not the disaster it might at first appear. Traditional farmers introduce the nitrogen they require in their soils by intercropping with legumes.
“Thus, in Colombia, 98 percent of the bean crop is grown in association with maize: in tropical Latin America as a whole, 60 percent of the maize is associated with other crops, usually legumes.”
In addition, the authors report,
“the yields of four successive maize plantings intercropped with a legume but without nitrogenous fertiliser were comparable with yields from maize grown with nitrogenous fertiliser. . . Experiments In Africa, India, Thailand, and the Philippines show that, especially on low nitrogen soils, yields from millet-legume and sorghum-legume mixtures are regularly 20 to 60 percent greater than those obtained from comparable pure strands.”
Unfortunately, the use of biocides on maize and even on sorghum is increasing. This is a very undesirable trend. As the authors point out,
Back to top
“The global area under maize, sorghum, and millet cultivation is so vast when compared, for example, with the area under biocide-intensive cotton cultivation, that the amounts of chemicals involved in even moderate biocide applications on these crops will become enormous if these trends continue.”
Cassava – an invaluable crop
The chapter on Cassava and other root crops is of considerable interest. Cassava or Manihot (Manihot esculenta) is one of the world’s major staple foods. In 1976, 100 million metric tons were harvested. It is particularly valuable in that it can “withstand drought, brief periods of flooding, generally low soil fertility, and light management”. In addition,
“in terms of calories produced per unit area per unit time, cassava is one of the most productive of all crops. Yields of 10-20 tons per hectare (t/ha) per harvest are commonly reported under field conditions, whereas yields of 77 t/ha per harvest or about 211 kg/ha/day are possible under experimental conditions. This is more than one third greater than calorie production from rice grown under optimal conditions.”
The cassava root tuber is mainly digestible starch with 0.5-1.5 percent protein, which is quite low. However
“if the starchy root is mixed with yeasts and ptyalin (as in human saliva), the partially digested gruel product contains improved levels of vitamins and amino acids.”
Significantly, in many traditional societies people have taken advantage of this culinary fact and consume much of their cassava as fermented gruel which is referred to in Nigeria as gari and In Guyana as cassiri. In addition cassava foliage has a very high protein content and is often eaten by traditional people.Back to top
Sugar cane and energy
A wide variety of chemicals, which are currently obtained from petroleum, can be obtained from sugar cane. But growing sugar cane as a substitute for petroleum brings numerous problems. As the authors point out:
Back to top
“Where sugar is required for food or the land is needed for other food crops, human nutritional tradeoffs have to be addressed. Under current practices, the social impact is severe. Large cane growers in Brazil, for example, purchase land from small food growers. This increases the price of agricultural land and forces small farmers to more marginal and distant land. The result can be higher food prices and inflation. Furthermore, the amount of useful ethanol energy produced only slightly exceeds the amount of energy consumed in production. In a large (50 million gallons per year) modern factory, about 70,000 BTU are required to produce one gallon of ethanol containing only 76,000 BTU. If a new technology can remove the 8 percent ethanol from the 92 percent water, only then will real progress be made.”
Tobacco: a deadly crop
The chapter on tobacco is also of great interest. The adverse health effects of smoking tobacco are well known: however it is not generally realised how damaging the cultivation of tobacco is to the soil on which it is grown. Tobacco deprives the soil of nitrogen and other nutrients more rapidly than almost any other crop. In addition it is one of the crops on which biocides are used most heavily.
As the authors note:
“Vast quantities of biocides are applied to tobacco crops virtually throughout its seven to eight month growing season. Most of these biocides are toxic: some are carcinogenic. Besides being hazardous to users, these chemicals can contaminate village water supplies. Although most western governments either ban or severely restrict the use of obsolete persistent organochlorine biocides, their use in developing countries continues. For example, Aldrin is widely supplied by the international tobacco monopoly in Kenya. Warnings are printed in two of Kenya’s 15 languages (Swahili and English). Even if the user can read and understand the warnings, it is not easy to ‘avoid contaminating rivers’, nor to ‘wash with soap and water after use’. Most users have never seen a physician, and certainly are not able to consult one ‘immediately’ as advised on the label.”
But this is not all. Tobacco has to be cured and this usually involves using large amounts of wood.
Back to top
“On a global scale, the fuelwood requirements for producing flue-cured tobacco contribute substantially to the serious and growing problem of deforestation in developing countries. Of the estimated 5.66 million tons of tobacco produced each year, at least 2.5 million tons are flue-cured, using fuelwood. About 55 cubic meters of stacked wood are needed to cure each ton of flue-cured tobacco, and some 82.5 million cubic meters per year of roundwood are harvested for this purpose. Since most wood for tobacco curing is harvested from the wild (rather than from sustained-yield fuelwood plantations), it is reasonable to conclude that worldwide, the equivalent of some 1.2 million hectares of open forest each year is stripped of wood for tobacco curing. WHO estimates that 12 percent of the trees cut down each year worldwide are used for tobacco curing. This harvest is far in excess of rates of natural forest regrowth. For every 300 cigarettes made in the developing world, one tree is burned.”
Cotton: maximising yields, maximising destruction
The pressure to increase cotton yields – in some areas, it is only economic to grow cotton if yields of 1000 kg/ha can be obtained, which is twice the average yield in the United States – has caused severe ecological problems in the tropics. To obtain such yields, perennial irrigation is required – and that not only favours the transmission of such water-borne diseases as malaria and schistosomiasis but also invariably leads to waterlogging and salinisation. Moreover, heavy applications of nitrogen are necessary which, under irrigation, can lead to serious contamination of groundwaters. The authors note,
“On well-drained heavily fertilised soils, large quantities of nutrients (especially nitrates) leach downward and enter local water bodies. Assuming a soil absorption rate of 50 percent for the applied nitrogen and an application rate of 220 kg N/ha, perhaps as much as 100 Kg of nitrogen is lost into the drainage from each hectare. Similarly high levels of nutrient runoff into watercourses have resulted in eutrophication and, when combined with biocide residues, the destruction of fisheries.”
Cotton also depletes the soil of its nutrients very quickly. In addition, like tobacco, it requires the use of massive amounts of biocides. In fact,
“More biocides are used in cotton production than in any other crop. Cotton cultivation receives by far the bulk of biocides used in developing countries. Even in the United States, cotton absorbs 47 percent of all insecticides used. The frequent and heavy application of biocides on intensively cultivated cotton and the resulting serious major health and environmental effects are well described in the literature. Since the early 1970s, of the many Central Americans who have been poisoned by biocides, hundreds have died and thousands more suffer from sub-clinical intoxication.”
Significantly, cotton can be successfully grown
Back to top
“using traditional methods under rainfed conditions with only about 1 metre of rain per crop. Yields are low, averaging 300 kg/ha in Northern Nigeria. However, since little fertiliser and biocide is used, there is little pollution of the drainage water or human health hazard.”
Fisheries – the value of mangrove swamps
The authors start off their chapter on marine fisheries by noting the destruction wrought by modern fishing techniques.
“As a result of today’s highly sophisticated fish-harvesting technology, industrial fishing fleets are now increasingly able to upset the marine food chain, deplete fish populations, and overwhelm traditional fishing industries.”
The destruction is all the more tragic when one considers that nearly one-third of the fish harvested is fed to livestock.
The section on mangrove swamps is particularly interesting. The authors tell us that research carried out in West Bengal indicates that potential shrimp yields of 1000 tons per annum could be obtained from 44,000 hectares of tidal mangrove swamps. In addition, mangrove swamps are very effective in preventing salt water intrusion – a problem in many coastal areas. The authors argue that
Back to top
“Investment in mangrove reforestation and protection would not only benefit certain marine populations but also would provide such functions as shore stabilisation, flood control, and the sustained production of wood and other products for domestic and commercial uses”.
A salutary warning
In the epilogue, the authors point to the limitation of their study. All they claim to have done is to outline “various relatively minor options for environmental improvement that make little fundamental change in the prevailing conventional style of tropical agriculture”. They hope that “these realistic options will be found useful to designers wanting to reduce any environmental problems”. They are being very modest. This book could not be of greater value; indeed, it must be regarded as a handbook for environmental management in tropical agriculture.
The authors end up by pointing to “the growing and, to us, compelling body of opinion that major changes in agricultural development strategies are essential and overdue”. Such changes, they acknowledge, “will be politically difficult and cannot be accomplished overnight. However, they appear inevitable if large-scale disaster is to be avoided”. A salutary warning indeed, coming as it does from such an experienced team. Let us hope that those responsible for funding today’s development projects read this book – and act on it.
·Ω·Back to top