Fertilizers - a benefit or a hazard to agriculture?

R J Olembo Professor R J Olembo Is a Kenyan geneticist currently serving at the United Nations Environment Programme as Deputy Assistant Executive Director. Before joining UNEP, he held academic positions at Makerere University, Uganda and the University of Nairobi where he was Professor of Botany. Current data indicate that the world population will reach over 6.5 billion by the year 2000 and that the Increase will be greatest In the developing countries. So, to feed the growing population adequately, food production needs to be approximately doubled from the 1980 output. Can this be achieved without increased use of fertilizers? And if fertilizers are necessary, what about the risks now widely associated with fertilizer use In the mind of the public In Europe and North America? Experience in countries with highly developed agricultural systems over the last 100 years or so has shown that 60% and more of increased yields are due to the use of mineral fertilizers and to some extent manures, where these are readily available. In addition to increased yields inorganic and organic fertilizers have done much to improve the quality of food and have provided the preconditions for agricultural development in the broadest sense. An efficient use of fertilizers has proved to be highly advantageous to the economies of the various countries no less than to the individual farmer. Where developing countries are concerned, it should be realized that agriculture must come first in the path to national prosperity and in their plans for food self-sufficiency. Establishment of a heavy industry base first will not meet the nutritional needs of the people manning the machines. It is further necessary that the entire agricultural enterprise be profit motivated to provide incentive to the farmers concerned. Introduction of fertilizer has perhaps greater immediate impact than any other input for effecting the latter objective in most farming situations of the developing world. While there is demonstrable evidence in industrialized countries that excessive fertilizer use may cause hazards to human health and to the environment, the case in the developing world is that more could be used beneficially. That is providing it is always used in an efficient and judicious manner. In general, most soils in humid regions of the world, especially those in subtropical and tropical areas where a majority of the people live are poor in nutrients. Inherent nutrient supplies commonly will allow only 2-3 years economic cropping followed by 20-30 years bush fallow. Some proponents of the so-called sustainable agriculture think that the situation can be corrected simply on the basis of different types of organic manures and mulches. But quantities of manure required would not be available, nor would it be possible to grow sufficient amounts of legumes without extensive soil amendments. What about the productivity of soils which have been subjected to long periods of fertilizer treatment? Is the structure of the soils destroyed? It has been said that the Broadbalk plots of Rothamsted Experimental Station in the UK, on which chemical fertilizers have been applied since 1843, are more productive today than at any time in the recorded past. The aggregated action from enhanced root proliferation and greater amount of decaying residues from well fertilized crops have been reported to help make soils more friable, tillable and receptive to water. The type of farming practiced in the highly developed countries of the world would be quite impossible today without fertilizers. More than 20 years ago, it was established that, depending on soil conditions and type of crop, the yield foregone would range from modest to severe even in the first year fertilizer was excluded. Productivity foregone by totally excluding. fertilizer use would have to be made up by bringing more land under the plough, land that should never be cultivated because, using it in this fashion would add to environmental damage. A well fertilized soil supporting a thriftily growing crop is much less prone to erosion in sloping positions than a corresponding soil supporting a poor crop. The greater surface canopy and the greater binding action of a more prolific root system accompanying the crop that enjoys adequate nutrition provide protection against adverse water and wind action. The residual effects of the greater organic production are significant, too, in the improved soil aggregation imparted by the larger quantity of fresh organic return. Physiologists stress the role of living plants in air purification, absorbing CO2 from the atmosphere for use in the photosynthesis of carbohydrates and releasing O2. One source has estimated that some 18.5 short tonnes of CO2 is removed from the atmosphere over a maize field producing 6300kg grain/ha as approximately 15 tonnes of oxygen is realized, enough oxygen for about 30 people for a year. Stimulated vegetative production with the aid of fertilizers clearly means a real bonus as we take inventory of the increasing amounts of CO2 that man's activities are releasing into the atmosphere. How serious is the impact of widespread fertilizer use on the environment? The most commonly cited hazards are the eutrophication of surface waters the toxicity potentials of high NO3 levels in the ground and surface waters, crop damage, and damage to soils by destruction of the natural N cycle. If fertilizers are used judiciously, these risks are negligible while the potential benefits are considerable. The views expressed are those of the author and do not necessarily reflect those of CTA.R J Olembo Professor R J Olembo Is a Kenyan geneticist currently serving at the United Nations Environment Programme as Deputy Assistant Executive Director. Before joining UNEP, he held academic positions at Makerere University, Uganda and the..