4.5 Fertilizers and plant protection agents

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Fertilizers

Typical fertilizer response ratios (kilograms of additional crop produced per kilogram of additional plant nutrient applied) in countries with low to middle level yields and areas not subject to severe water constraints, range from 8 to 12 for cereals, 4 to 8 for oil crops and 30 to 50 for roots and tubers (FAO, 1989c). Such high physical response ratios do not always translate into economic incentives for fertilizer use when its costs are high, product prices low and marketing opportunities limited. About one-third of the fertilizer used in developing countries is imported and shortages of foreign exchange affect costs and availability. Likewise, inefficient distribution systems and infrastructure constraints within countries raise the cost to the farmer and limit availability.

Estimates on fertilizer use by crop (FAO/IFA/IFDC, 1992) suggest that for developing countries as a whole (excluding China), about 60 percent of fertilizer is allocated to cereals, with rice alone accounting for one-third of total use and wheat for one-sixth. The allocation of fertilizer to cereals roughly corresponds to the share of cereals in total harvested area (55 percent), though some of the coarse grains, especially sorghum and millet, use little fertilizer. The share of non-food crops and of fruits and vegetables in total fertilizer use is large relative to the share of these crops in harvested area. Sugarcane and cotton are also major consumers accounting for 9 percent and 4 percent respectively of total fertilizer use. Roots and tubers and in particular pulses receive little fertilizer relative to their shares in harvested area.

Table 4.13 shows the present and projected fertilizer use per hectare in the different developing regions. The projections have been derived by applying crop-specific fertilizer use coefficients to the projected harvested areas presented earlier. The coefficients vary with land class and yield level for each crop (see Appendix 2). The fertilizer use per hectare is highest in the Near East/North Africa region and it is projected to remain so. It is likely that by 2010 the region's use per hectare, and to a smaller extent also Asia's, will exceed today's average use of the developed countries, though it would still be well below current use rates in the EC. At the other extreme, sub-Saharan Africa's use will continue to be very low and probably not sufficient for the sustainability of its agriculture (see below), even if it doubled (to 21 kg/ha) from the current extremely low levels.

The projections imply that total fertilizer consumption in the developing countries will grow at a lower rate compared with the past (Table 4.14). This would be a continuation of the longer term trend for consumption to grow at a decelerating rate. In part, this is explained by the relatively high levels of per hectare fertilizer use already attained, particularly in Asia and in the Near East/ North Africa, where dressings appear to be reaching their ceilings in some countries and crops. In addition, the growth rate of agricultural production will be lower than in the past. Only sub-Saharan Africa may experience a sharp acceleration in the growth of fertilizer use, given its very low levels per hectare and the need to increase production faster than in the past. Still, fertilizer consumption in the developing countries will probably continue to grow faster than in the developed countries and therefore their share in world consumption will continue to grow from the level of 43 percent of 1990 (it was only 20 percent in 1970 and 32 percent in 1980).

Many countries with high levels of fertilizer use are experiencing the environmental problems associated with intensive use of fertilizers. Sub-Saharan Africa however suffers from the opposite problem, namely too little use. Only few countries in sub-Saharan Africa have average dressings of more than 20 kg/ha (FAO/IFA/IFDC, 1992). Such low levels of fertilizer use when fallow periods become shorter represent a serious threat to sustainability. Crops "mine" the soil of its nutrients unless they are replaced with plant residues, manures or fertilizers. Soil nutrient deficiencies limit potential yields in many developing countries, especially in sub-Saharan Africa and Latin America/ Caribbean (see earlier discussion on the soil constraints in these regions). Smaling (1993) holds that soil nutrient mining occurs in almost all countries in sub-Saharan Africa. Soil mining, if left unchecked, will lead to significant soil degradation and declining crop yields (see Chapter 11 for a further discussion of soil nutrient mining).

Some developing countries are encountering difficulties in increasing yields in spite of increasing doses of fertilizers. The efficiency of fertilizer use is often quite low as a result of incorrect timing and poor application methods or failure to maintain the balance between the main nutrients (nitrogen, phosphate and potassium), secondary nutrients and micronutrients. Soil toxicity caused by salinity, alkalinity, strong acidity, iron toxicity and excess organic matter, also prevents the full benefits of fertilizer from being expressed. Evidence suggests that in the long term manufactured fertilizers need to be complemented by organic matter in the soil. Crop and nutrient management at plot, farm and village level will have to become increasingly sophisticated to ensure that the lack of one component does not invalidate the use of the entire package of all nutrients. The optimal use of all possible sources of plant nutrients is advocated under the Integrated Plant Nutrition Systems (IPNS discussed in Chapter 12) approach to fertilization. IPNS uses sources of organic manure, biological fixation as well as mineral fertilizers in an integrated manner to improve or maintain soil fertility in cropping systems.

Plant protection and pesticides

The increasing intensification of agriculture has led to an increased susceptibility of crop production to pests. Agricultural practices such as multiple crops per growing season, shortening fallow periods and monocultures all have helped to create conditions for pest outbreaks and to reduce natural checks on such events. Also some of the earlier modern varieties of the green revolution were often more susceptible to pest damage than the traditional varieties. Byerlee (1994), however, states that the later editions of such varieties are often superior in pest resistance compared with traditional varieties.

It is well known that pests may become resistant to pesticides, resulting in increased but less effective usage of pesticides. New pesticides therefore need to be developed continuously. Inappropriate choices of insecticides may disrupt the pest-natural enemy balance by being more deadly for the natural enemy than for the pests themselves, thus upsetting natural control mechanisms. The perception by farmers and extension services of yield losses due to pests are often higher than actual losses. This, together with the desire to reduce risks, induces the farmer to use large quantities of pesticides that have only marginal or no benefits in terms of yield gains or may even induce pest outbreaks. Also, in many countries, the overuse of pesticides was and still is encouraged by pesticide subsidies.

Table 4.13 Fertilizer use per hectare in developing countries (excluding China)

* Manufactured fertilizer in kg of nutrient content (N, P₂O₅, K₂O).

Pesticide use in the developing countries grew rapidly in the late 1960s and 1970s in the wake of rapidly spreading agricultural modernization. There is, however, substantial variation in the type of pesticides used and in the intensity of use, depending on the farming system and crop. In general, the demand for chemical pesticides increases with increasing land scarcity and market access (see Pingali and Rola, 1994). Traditional plant protection methods however remain important. Practices such as tillage (ploughing and hoeing), flooding and burning contribute to reduce all types of pests. Cultural control measures such as crop rotations and disposal of plant material also help to reduce losses due to pests. As noted above, with increasing agricultural intensification, pest pressure also increases due to increased spatial and temporal carryover. Together with increased market orientation, often the opportunity costs of labour increase also, leading to higher use of herbicides. Pesticide consumption varies widely by crop. Pesticide use is high on deciduous fruits, vegetables, cotton and cereals, and more moderate on citrus fruits, tropical fruits, cocoa, coffee and tea.

In the mid-1980s, developing countries accounted for about one-fifth of global consumption of pesticides. Their share in world use of insecticides is relatively high at 50 percent, while this share is 20 percent for fungicides and 10 percent for herbicides. East Asia (including China) accounts for 38 percent of developing countries' use of pesticides, Latin America for 30 percent, Near East/North Africa for 15 percent, South Asia for 13 percent, and sub-Saharan Africa for only 4 percent. About half of the pesticides used in developing countries are insecticides, with herbicides accounting for a minor part of total consumption. The opposite pattern is seen in the developed countries. This difference can be explained by both ecological and economic factors. In humid tropical countries, pest generations may follow each other without being reduced by low temperatures or aridity. Under these conditions damage from insect pests can be particularly severe and also the pressure from fungal infections is strong. Insect pests are also a severe threat in semi-arid areas and insecticides are widely used to control migratory pests such as locusts. Fungal diseases are often less important in such areas. On the other hand, low labour costs prevailing in many developing countries can make manual weed control more economical than herbicide use.

Table 4.14 Total fertilizer consumption in the developing countries (excluding China)

Pesticide consumption in the developing countries in 1985 was about 530 000 tonnes (in terms of active ingredients), down from some 620 000 tonnes in 1980. Pesticide consumption increased again by about I percent per year in the second half of the decade. This is about the same growth rate as in developed countries. Since 1990, however, worldwide use of pesticides has been declining. Future growth of pesticide consumption is likely to be influenced by a great number of factors such as economic profitability (which in turn is determined by such things as pesticide price, product price, price of alternative plant protection means, opportunity cost of labour, etc.), concern about environmental damage and direct damage to the health of persons handling pesticides, the effectiveness of pesticides, pest resistance of plants, the development of substitutes for chemical pesticides, etc. Overall and for the reasons set out below, a reasonable estimate seems to be that pesticide consumption in developing countries will continue to increase but at a slower pace than in the past. Most of the growth is likely to be in South and East Asia and in Latin America.

The damaging effects of indiscriminate pesticide use on the environment and human health (through exposure to pesticides and indirectly through residues in food commodities and drinking water) are well documented and have led to increasing concern and consequently to a number of national and international regulations regarding the production, trade and use of pesticides (see Chapter 11 for a discussion of the environmental issues related to pesticides use). One of the consequences has been that the development costs of new pesticides have strongly increased and that the number of companies willing and able to invest in product research and development has been reduced significantly.

Older compounds (off-patent pesticides) dominate the market in developing countries as they are far lower priced than new ones. However, strict regulations, bans and severe restrictions in developed countries will gradually also reduce their availability in developing countries, while new, less toxic and more environmentally friendly compounds may remain too expensive for many applications.

The increased awareness of the negative aspects of pesticides has resulted in new emphasis given to reduce dependence on chemical control and to develop and employ non-chemical means of pest control. Integrated Pest Management (IPM, see Chapter 12), which considers both crops and pests as part of an ecological system and combines natural factors that limit pest outbreaks while using pesticides as a last resort, is now considered as the preferred method of pest control.

Public and private research on biological control and biotechnological solutions to plant protection problems are increasing substantially. This includes the development of microbiological pesticides, the mass production of natural enemies and the development of transgenic plants with pest resistances. A particular example is the mass production of sterile male Mediterranean fruitflies to eradicate or suppress fruitfly populations. There is also increased attention to other non-chemical mechanisms like cultural control. Results of such programmes become gradually available and these techniques will gain in importance in future plant protection programmes especially as use of pesticides may become less acceptable. A drawback remains that in general the use of biological control tends to be information- and knowledge-intensive and poses high demands on management skills of farmers.

Pest control methodologies are expected to change substantially in developed countries but pesticides will remain a major tool. Pesticide reduction programmes are in place or considered in a number of countries, to decrease excessive use of and reliance on pesticides. In developing countries, there is substantial scope for a similar decrease of pesticide use in certain crops like cotton, vegetables and rice. However, as noted before, there may be an increase in herbicide use in countries where labour is becoming scarce, while intensification may make insecticide and fungicide use economically viable. On the other hand, older, cheap, off-patent pesticides will gradually disappear, increasing the price of pesticides but reducing their hazard. In the longer term, non-chemical control methods are expected to gain strongly in importance in both developed and developing countries (Zadoks, 1992).

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