Reflections on yield gaps in rice production

M. Duwayri, D.V. Tran and V.N. Nguyen

Plant Production and Protection Division, FAO

INTRODUCTION

Rice is the world's most important food. More than half of the world's population depends on rice for calories and protein, especially in developing countries and, by the year 2025, about 760 million tonnes of paddy, which is 35 percent more than the rice produced in 1996, will be needed to meet the growing demand. However, most arable land is already exploited, especially in Asia, where 90 percent of the world's rice is produced and consumed.

Rice production had steadily increased during the green revolution, but recently its growth has slowed down substantially. Moreover, crop intensification during the green revolution has exerted tremendous pressure on natural resources and the environment. Nevertheless, under globalization of the world economy, rice producers are exposed to competition, not only among themselves but also with the producers of other crops. Future rice production therefore requires improvements in productivity and efficiency. Innovative technologies such as hybrid rice, new plant types and, possibly, transgenic rice can play an important role in raising the yield ceiling in rice production, thus increasing productivity. In addition, in many countries there are still gaps between the yields obtained at research stations and those from farmers' fields. Narrowing these gaps could improve not only the productivity but also the efficiency of rice production.

Some specialists, however, have expressed concern regarding the economic value of narrowing yield gaps and consider that it has very limited potential for increasing rice yields. Other specialists believe that yield gaps could be economically exploited to increase rice yields. In a number of countries, in spite of initially high yields, national yields have continued to increase significantly over the last 30 years, thanks to integrated national efforts to promote rice development programmes. Furthermore, it is well known that yields vary among farmers in the same area. Good farmers usually reap more benefits from improved technologies than mediocre farmers in the same zone. The challenge for policy-makers, scientists and developers is to narrow these gaps effectively and economically at the rice-grower level.

EVOLUTION OF RICE YIELDS AND PRODUCTIVITY

World

The worldwide annual growth rates of population and rice production, harvested area and yield are shown in Table 1. The year 1961 was selected as the base year for analysis of the evolution of rice production since it is the first year for which statistics on rice production are available on FAO databases (FAO, 1998).

Table 1 shows that world rice production has increased continuously since 1961, but at varying growth rates. The annual growth rate was about 3.5 percent during the 1960s, 2.7 percent in the 1970s, 3.1 percent in the 1980s, and 1.3 percent in the first half of the 1990s. A comparison between the growth rates of rice production and population since 1961 shows that, for the first time since 1990, rice production has grown more slowly than population.

During the 1960s, the high annual growth rate of rice production was caused by both a high increase in yield and a moderate increase in rice area, whereas the rapid growth in rice production during the 1980s was owing, principally, to improvements in rice productivity. The annual growth rate of rice yield was 2.5 percent during the 1960s, 1.8 percent in the 1970s, 2.8 percent in the 1980s, and only 1.1 percent in the first half of the 1990s; while the annual growth rate of harvested rice area decreased from 1.6 percent during the 1960s to 0.2 percent in the 1980s (Table 1). The trend of reduced growth of rice harvested areas indicates that future rice production increases will come mainly from improvement in productivity, unless major development activities are undertaken to bring more land under rice cultivation.

The very low annual growth rate of rice yield observed since 1990, therefore, is a cause for concern and it has been the topic of numerous reviews (Pingali and Rosegrant, 1996; Cassman and Pingali, 1995; and Pingali, Hossain and Gerpacio, 1997). Regardless of food consumption trends, the slowdown in growth of rice yield is particularly serious considering the continuing growth of population. The reversal of this trend and the bridging of yield gaps require the urgent concerted efforts of all concerned parties and political support from both national and international authorities.

Asia

Asia accounts for over 90 percent of world production. The evolution of rice production, area and yield in Asia is, therefore, similar to that observed at the global level, but more pronounced. The annual growth rate of rice production in Asia was about 4.4 percent during the 1960s, decreased to about 2.6 percent during the 1970s, and then increased to about 3.2 percent during the 1980s. During the first half of the 1990s rice production grew by only 1.3 percent per year (Table 2). Growth in rice production in the region was faster than population growth during the 1960s, 1970s and 1980s, but slower than population growth during the 1990s. The growth rate of rice production has become about half that of the population since 1990.

Increases in rice production have been caused mainly by improvements in productivity per hectare. The harvested rice area has grown at a decreasing rate since 1961; from about 1.3 percent per year during the 1960s to only 0.3 percent in the 1980s and 0.1 percent since 1990. At the same time, the annual growth rate of rice yield was 2.7 percent during the 1960s, 1.9 percent in the 1970s, 2.8 percent in the 1980s, and only 1.1 percent since 1990 (Table 2).

It is extremely surprising that the annual growth rate of rice yield observed during the 1970s (1.9 percent per year) was lower than that observed during the 1960s (2.7 percent per year), considering that IR8 was released for cultivation in 1966 and, in China, commercial hybrid rice cultivation started in 1976. This decline in the rice yield growth rate is, however, a very valuable experience for all concerned with improving rice production, as it indicates that the adoption of new rice varieties alone does not necessarily result in higher rice yield. It also shows that, after the successful development of new rice varieties and types, it may take a decade or more for gains in productivity to be obtainable in farmers' fields. The IR8 variety, and its parental variety Peta, do not improve yield very much if fertilizers and other improved cultural practices are not used. In Indonesia, although high-yielding varieties (HYVs) had been widely adopted in the early 1970s, rapid increases in rice yield were obtained only after the implementation of coordinated extension and development programmes, called INSUS from 1975 to 1985 and SUPRA INSUS since 1985 (Dudung, 1990).

The increase in the annual growth rate of rice yield from 1.9 percent during the 1970s to about 2.8 percent during the 1980s could be attributed to the wide adoption of a new generation of rice varieties (Table 3), the improvement of farmers' crop management practices and the increased use of irrigation, fertilizer and other agrochemicals in rice production. It may also be owing to the adoption of policies that are favourable to rice production in a number of countries. Viet Nam, for example, became a major rice exporter only in the late 1980s after favourable policies were adopted.

Several factors may be responsible for the drastic decrease in growth rate of rice yield since 1990. These need to be examined in detail so that the current trends of rice yield and rice production can be reversed and food security for the region's population, as well as the conservation of natural resources and socio-economic stability, can be achieved.

Future increases in rice production in Asia will continue to depend on improvements in the productivity of irrigated rice production, which in 1995 occupied about 57 percent of the region's rice harvested area, as it is in this ecology that the application of hybrid rice and other genetic improvements of rice plants are most feasible. In the long term, regional increases in rice production depend on improvements in the productivity of rice production in rainfed ecologies, because the land and water resources in irrigated ecologies are under increasing competition from other crops, urbanization, industrialization and environmental protection.

South America

Rice production in South America has been growing at a rate of about 3.7 percent per annum or more, except during the 1980s when it grew at only 1.6 percent per year. Since 1990, the growth rate of rice production in the region was more than twice that of the population. The high growth rate of rice production during the 1960s and 1970s was mainly the result of expansion of the rice area. The annual growth rates of harvested area during these periods were respectively 4.6 and 3.2 percent. However, improvement in the productivity of rice was the main force behind the increase in rice production during the 1980s and 1990s. Rice yield increased at a rate of 3.98 percent per year during the 1980s and 3.54 percent per year since 1990 (Table 4).

The high growth rate of yield in South America during the 1980s can mainly be attributed to a significant reduction in the area devoted to low-yielding upland rice in Central America and central Brazil. The rapid spread of HYVs and the recent expansion of irrigated rice areas in southern Brazil, Argentina and Uruguay also contributed to high annual growth rates during the 1980s and the first half of the 1990s. Nevertheless, upland rice production in South America has become increasingly unsustainable owing to its low productivity.

The Southern Horn of Latin America, including southern Brazil, Uruguay, Paraguay and Argentina, has a Mediterranean climate and rice yields of 5 to 6 tonnes/ha. This yield is lower than the potential yield of 10 tonnes/ha - the yield gap being in the region of 3 to 4 tonnes/ha.

Africa

The annual growth rate of rice production in Africa was about 4.9 percent during the 1960s. It decreased to about 1.6 percent during the 1970s, then increased to about 5.2 percent during the 1980s. Growth in rice production in the region has slowed since 1990, but the current rate (3.4 percent per year) is still respectable and higher than the population growth rate (Table 5). The growth in production has not been sufficient to satisfy the greater demand, however, resulting in increased importation of rice into sub-Saharan Africa.

Most of the production increase can be attributed to an expansion in rice area. The growth rate of harvested rice area was always more than 2.1 percent per year, while that of yield was below 1.1 percent, except during the 1980s when it was 1.8 percent. All rice production in North Africa is under irrigation. Yields in Egypt are among the world's highest, increasing by nearly 50 percent over the last decade. In contrast, in sub-Saharan Africa upland rice production is dominant and average yields in most countries are still less than 2.5 tonnes/ha. Upland rice production in sub-Saharan Africa is generally practised under shifting cultivation and there is much concern about this type of cultivation in Africa, owing to widespread ecological damage such as soil erosion, deforestation and losses in soil fertility.

The stagnation in yield potential of HYVs and a shortage of irrigation water are of major concern to sustainable rice production in Egypt, while socio-economic factors limit rice yields from irrigated schemes in sub-Saharan Africa. However, there are still considerable land and water resources in the region and these could be exploited so that future rice production increases to meet the population's demand. In sub-Saharan Africa, most of the inland swamps and hydromorphic lands are still untapped. In addition, in many irrigated rice schemes, rice yield is decreasing after a few years of exploitation, mainly owing to inadequate overall management and operation as well as to farmers' poor crop management (Table 6). The reversing of this trend and increasing sustainable rice production and productivity are two major concerns in the region.

ANALYSIS OF CURRENT YIELD GAPS

Definitions of yield gaps

The national rice yield is the average yield of rice planted in different agro-ecologies and locations across a country. The exploitable yield gap is not, therefore, merely the difference between the national yield and the yield of research stations. National yields may, however, be used as indicators for monitoring the evolution of rice productivity in a country and, in general, analysis of the evolution of world rice yield shows that national average yields have increased; suggesting that yield gaps have narrowed, although at a slow rate.

Rice cultivation extends from 50^o N to 35^o S and, generally, yields of rice planted in tropical climates (or in areas between the Tropic of Cancer and the Tropic of Capricorn) are lower than those for rice planted in temperate and/or Mediterranean climates. The high solar radiation, long summer days and low night temperatures in countries with temperate and Mediterranean climates are favourable to high rice yields. The highest rice yield recorded under tropical conditions was 10.3 tonnes/ha, obtained from IR8 planted at IRRI's experimental farm in the Philippines during the 1965 dry season (De Datta, 1981), while the japonica rice variety Koshihikari planted in Yanco, New South Wales, Australia, was reported to give 13 tonnes/ha (Horie et al., 1994). It is, however, very rare, not only for farmers but also for researchers, to obtain such exceptionally high yields.

Rice is cultivated under a wide range of agro-ecologies. In irrigated and favourable rainfed lowland ecologies, rice yields have been substantially improved during the green revolution, while in other ecologies this has not been the case, owing to a host of biotic and abiotic stresses. Yields of irrigated rice in many developing countries are still only about 4 to 5 tonnes/ha, while substantial and exploitable yield gaps are generally found in irrigated and, to a lesser extent, in favourable rainfed ecologies. In the Philippines, it was reported that water control, seasonal factors (solar radiation) and economic factors are the yield constraints that account for differences between actual and potential yields of 35, 20 and 15 percent, respectively (De Datta, 1981). The gaps between research yields and actual farmers' yields in a particular location and season are, therefore, better indicators of yield gaps.

The yield gaps have at least two components. The first of these is mainly owing to factors that are generally not transferable, such as the environmental conditions and some of the built-in technologies that are available at research stations. This component of the gaps (Gap I in Figure 1) cannot, therefore, be narrowed and is not exploitable.

The second component of yield gaps (Gap II in Figure 1) is mainly the result of differences in management practices. Gap II arises when farmers use suboptimal doses of inputs and cultural practices. Herdt (1996) provided a similar description of yield gaps and their components. Gap II is manageable and can be narrowed by deploying more efforts in research and extension services as well as by appropriate government intervention, particularly on institutional issues.

FIGURE 1: Components of yield gaps

Source: adapted from De Datta, 1981.

Views on narrowing yield gaps

Owing to its complexity, there are different views with regard to the possibility of narrowing yield gaps as a tool for increasing rice production.

Less exploitable yield gaps: Pingali, Hossain and Gerpacio (1997) argued that, in favourable rice ecologies, exploiting the yield gaps would not increase rice yield and production. In this situation, further growth in yield is possible only when new technologies, such as hybrid rice, are utilized. Agronomic yield potential, determined on experimental stations, is the maximum achievable yield when there are no physical, biological or economic constraints to rice production (Gap I). When such constraints are accounted for on the farm, the exploitable yield gap of rice is small or, in many cases, non-existent. Narrowing the exploitable yield gap in Asia, for example, is therefore of little profit, particularly in irrigated rice. The authors reported a reduction in yield gaps on farms with favourable conditions in Nueva Ecija and Laguna, the Philippines, where gaps were reduced from nearly 2 tonnes/ha to less than half a tonne, after a decade. However, they also reported that yield gaps in the remaining two-thirds of the same rice areas remained at about 2 tonnes/ha, or even widened. Thus, the narrowing of yield gaps is not profitable for farmers in these environments.

Exploitable yield gaps. Authors in this school of thought believe that there are large yield gaps in rice, in both favourable and less favourable conditions, in many countries and that these gaps could be exploited to bring about further improvement in productivity. Such gaps are caused by poor crop management and problems with institutional support, especially input and farm credit supplies, in many developing countries. Table 7 shows that the estimated yield gaps in irrigated rice production vary from 0.8 tonnes/ha in Bangladesh to 2.3 tonnes/ha in India.

In 1995, national average yields of rice in many developing countries were still low - in about 78 countries they were less than the world average yield of 3.77 tonnes/ha (Table 8) - hence, yield gaps obviously exist in many developing countries.

Yield gaps at specific locations in each growing season, however, need further study. Yield differences among farmers in the same area are frequently observed because of farmers' different skill levels for crop management and environmental variations.
Progressive farmers usually obtain higher yields and more profits than less progressive farmers.

Causes of yield gaps

Based on data from experiments on yield constraints, fertilizer application rate and timing have been found to be the most significant factors for high yields in dry seasons. In wet seasons, insect control and fertilizer management were found to have the same importance in contributing to high rice yields (IRRI, 1979). At the farmer level, the management of inputs (e.g. fertilizer, insect control, weed control and seedling age) contributed little to explaining the difference between low- and high-yielding crops. In dry seasons, the level of managed inputs used and their interaction with environmental factors accounted for 50 to 60 percent of yield differences among farmers (Herdt and Mandac, 1980). Observation at the farmer level suggests that potentially exploitable yield gaps are more prevalent under favourable environmental conditions.

Yield gaps may be caused by technical deficiencies, but also by economic considerations. For example, farmers who seek maximum profit may not apply the correct fertilizer doses for maximum production. Efforts to narrow the yield gap without considering the economic aspects may be counterproductive; closing the yield gap may actually decrease farmers' incomes, particularly if rice prices are low. The ratio of the price of rice to the price of fertilizer could influence the amount of fertilizer applied by farmers and, thus, the rice yield. Consequently, institutional factors that increase the ratio of rice price to fertilizer price could positively contribute to narrowing the gap (De Datta, 1981).

In southern India, the maximum rice yields obtained in experimental stations under irrigated conditions varied from 6.0 tonnes/ha in Kerala to 8.6 tonnes/ha in Tamil Nadu and Andhra Pradesh. The average yields in farmers' fields are less than half of these amounts (Ramasamy, 1996). Table 9 summarizes the estimated yield losses caused by several different factors. Figures were provided by 120 rice scientists and 120 extension workers in southern India.

Table 9 indicates that yield gaps are actually present, owing to such factors as:

• physical factors: problem soils, poor water management, drought, flash floods and temperature stress;
• biophysical factors: varieties, seeds, weeds, insects, diseases and other pests, caused by inadequate crop management - post-harvest losses, which vary from 10 to 30 percent, also contribute;
• socio-economic factors: labour shortage, cost-benefit, farmers' knowledge, skills and welfare conditions;
• institutional factors: government policies, rice price, agricultural credit and input supply, land tenure, agricultural research and extension.

In many developing countries, socio-economic and institutional factors at the farm level often constrain efforts to narrow the yield gap. Most modern rice technologies are resource- or input-intensive and put small-scale farmers at a disadvantage.

Cases of yield gap narrowing

Rice yields, generally, have been increasing steadily during the last three decades. The yield increases in China, Indonesia, Viet Nam, Egypt, Australia and the United States, however, are very spectacular and appear to be caused mainly by concerted national efforts in narrowing yield gaps. In the late 1960s, rice yields in Viet Nam and Indonesia were only about 1.8 to 1.9 tonnes/ha; in China they were about 3.1 tonnes/ha; in Egypt and the United States 4.9 to 5.0 tonnes/ha; and in Australia 7.3 tonnes/ha (Table 10). Indonesia and Viet Nam, therefore, represented countries where rice yields were still low; China represented countries where yields were medium-sized; Egypt and the United States represented countries where yields were high; and Australia represented countries where yields were extremely high. Rice yields during the 1995-97 period were about 3.7, 4.4, 6.1, 6.7, 8.2 and 8.2 tonnes/ha, respectively, in Viet Nam, Indonesia, China, the United States, Egypt and Australia. Consequently, yield increases were about 0.9, 1.8, 1.9, 2.6, 3.1 and 3.3 tonnes/ha, respectively, in Australia, the United States, Viet Nam, Indonesia, China and Egypt. The yield increase in Australia indicates that, even with a very high yield (7.3 tonnes/ha) increases are possible through narrowing yield gaps. This observation is backed up by the impressive yield increases obtained in Egypt and China.

The factors responsible for rapid increases in rice yield vary from country to country.

China. Rice production in China has steadily increased even though the rice area harvested has declined. This has been the result of substantial increases in rice yield which could be attributed both to the development and use of hybrid rice since 1974 (Yuan, 1996) and to improvements in crop management, including increased use of fertilizer (Singh, 1992). Rapid expansion of the hybrid rice area took place in China after 1976. The area planted to hybrid rice reached about 15 million ha in the late 1980s. Between 1950 and 1979, crop management was improved by the transfer of integrated crop management packages (ICMPs) as the "Seven Techniques", which encompassed improved varieties, the planting of strong and healthy seedlings, intensive cultivation, proper plant population, balanced fertilizer application, rational irrigation, and control of pests and diseases. After 1980, the crop management package was further improved by emphasizing improved land development, fertilization, cultivation and cropping systems and using improved seeds, as well as by the integration of socio-economic factors such as prices. The annual growth rates for rice yield were only 1.8 percent in 1967-1977 but increased to 4.9 percent in 1977-1987. The stagnation in yields of three-line hybrid rice varieties may be responsible for the decline in yield growth to about 1.7 percent in the 1987-1997 period.

Indonesia. The national rice yield increased considerably by about 4.9 percent per year from 1967 to 1977 and 4.3 percent per year in 1977-1987. The increase in rice production has enabled the country to attain self-sufficiency in rice. Indonesia benefited from the green revolution during the 1977-1987 period, while the Government's INSUS/SUPRA INSUS rice intensification programmes have been effectively implemented since 1975. A successful integrated pest management (IPM) programme has also contributed to this high yield.

Viet Nam. Viet Nam had been a rice-importing country and started to export rice only in the late 1980s, as a result of its adoption of new agricultural policies. The national rice yield grew by only about 1 percent per year from 1967 to 1977, although about 850 000 ha of IRRI's HYVs were grown in south Viet Nam in 1974. This low growth rate was probably caused by inadequate use of fertilizer throughout the period. The annual growth rates of rice yield increased to about 4.2 percent annually in 1977-1987, decreasing slightly to about 3.6 percent per year during the 1987-1997 period. Increase in fertilizer application played an important role in these increases in rice yields and in narrowing yield gaps. The quantity of urea applied to rice increased from 45 kg/ha in 1988 to 200 kg/ha in 1997 (Le, 1998).

Egypt. Egyptian rice yields increased from 5.8 tonnes/ha in 1987 to 8.5 tonnes/ha in 1997, one of the highest yields in the world. Yield gaps have been narrowed as a result of: adoption of new HYVs (such as Giza 175, Giza 176, Giza 181, Giza 177, Giza 178, Sakha 101 and Sakha 102); intensive demonstrations and training on crop management; and monitoring of production constraints - all of which were carried out under national coordinated programmes, including Markbouk 4 among others (Badawi, 1998).

Australia. The national rice yield declined by about 2.4 percent per year from 1967 to 1977, moderately increased during the 1977-1987 period, and then grew rapidly in 1987-1997. The Integrated Rice Crop Management Package (Ricecheck) was developed in the mid-1980s and transferred to farmers since 1986 (Lacy, 1994). The main features of Ricecheck are shown in the Box. Cropping systems using legume-based pastures (Trifolium subterraneum) in rotation with rice crops were another factor responsible for the impressive increase in rice yield. The increase in rice yield has made rice production in Australia a profitable business for farmers and enabled the country to earn substantial foreign exchange from export.

United States. The annual growth rate of rice yield was high (2.3 percent) in 1977-1987, but rather lower (0.9 percent) from 1987 to 1997. Among the rice-growing states, California has made considerable progress in yield increase, reaching about 9 tonnes/ha, thanks to improvements in weed control, laser-based land preparation and modern rice varieties.

It is worth noting that national yields in some Mediterranean countries, mainly Italy, Spain, France and Turkey, have been stagnant at about 5 to 6 tonnes/ha since the 1960s, while the rice yield in Egypt reached 8.5 tonnes/ha in 1997. The difference in national yields between these countries in the Mediterranean and Egypt is difficult to explain. Greece has also made great progress in narrowing yield gaps, with a national yield reaching 7.6 tonnes/ha in 1996.

CHALLENGES IN NARROWING THE RICE YIELD GAP

The narrowing of the rice yield gap, as shown in the above cases, requires integrated and holistic approaches, including appropriate concepts, policy intervention, an understanding of farmers' constraints to high yields, deployment of new technologies, promotion of IPM, adequate supplies of inputs and farm credit, and strengthening of research, extension and the linkages among them. If one of these components is missing or weak the yield gap in a particular rice production area cannot be narrowed effectively (Tran, 1997).

Concept

Narrowing the yield gaps aims not only at increasing rice yield and production, but also at improving the efficiency of land and labour use, reducing the cost of production and maintaining sustainability. Exploitable yield gaps of rice are caused by various factors including physical, biological, socio-economic and institutional constraints, which can be improved through a participatory and holistic approach to interventions and governments' attention. An integrated programme approach is essential. The narrowing of the yield gap is a dynamic process that needs to keep up with technological developments in rice production - gaps tend to increase as the yield potential of rice varieties is improved.

Policy intervention

Rice policy should be well defined and formulated in each country, especially when major structural reforms have been introduced. Most countries in sub-Saharan Africa, and several in Asia, have undergone such reforms. Governments should address and find solutions to socio-economic and political issues before narrowing the yield gap between farmers' fields and research stations (Hanson, Borlaug and Anderson, 1982). Governments also need to be willing to intitiate a yield gap narrowing programme, to coordinate it and to intervene when specific problems arise. The sensitization of policy-makers and government officers is a very important activity in bridging yield gaps of rice, and pilot trials should be set up in selected zones.

Survey and classification of yield gaps

The first step in narrowing the yield gap is to identify the existing and potential constraints to rice production in a particular area. The major constraints to high yield may vary from one place to another and should be well understood. A group of at least one agronomist, one economist and one statistician should carry out a preliminary survey and, based on the results of the survey, yield gaps should be classified into:

• Case 1: Unexploitable - gaps caused mainly by non-transferable factors (or Gap I in Figure 1);
• Case 2: Less exploitable gaps - gaps that can be closed, but with fewer economic gains because of the yield ceiling and the law of diminishing returns in a production function. This type of gap arises when rice yields are equal to or more than 6 tonnes/ha in tropical climates and 8 tonnes/ha in Mediterranean conditions;
• Case 3: Exploitable gaps - gaps caused mainly by less than optimal crop management practices (or Gap II in Figure 1). This type of yield gap occurs when:

- irrigated rice under tropical climates has yields of less than 6 tonnes/ha;

- irrigated rice under Mediterranean climates has yields of less than 8 tonnes/ha;

- favourable rainfed lowland rice has yields of less than 4 tonnes/ha.

In the first two cases, yield ceilings are increased by the introduction of emerging technologies, such as hybrid rice and new plant varieties, while the promotion of integrated crop management, along with the improvement of socio-economic and institutional conditions are relevant for narrowing the exploitable gaps in case 3.

Yield gaps can also be classified according to the following constraints:

• agronomic gaps, owing mainly to biological and, partly, physical constraints;
• socio-economic gaps, owing mainly to socio-economic constraints;
• institutional gaps, owing mainly to institutional constraints;
• mixed gaps, owing to a mixture of the above constraints.

In the last three of these, the socio-economic and institutional constraints need to be solved before the agronomic gaps can be narrowed by using improved technological packages.

Promotion of integrated crop management

Integrated crop management can narrow agronomic yield gaps and, at the same time, help farmers to reduce wasteful resource utilization and increase rice yield and incomes. Precision crop management practices can be followed with the use of advanced technologies; for example, precise application of fertilizers can be achieved through the use of computer-aided systems. Most resource-poor farmers cannot afford such systems, however. The technique of chlorophyll meters and leaf colour charts for field-specific nitrogen (N) management (which has been tested by IRRI) could be suitable for these farmers.

Narrowing the yield gaps by improving the crop management practices of small farmers in developing countries is not an easy task. Although several improved crop management practices have been developed, their dissemination has proved to be more complicated than that of seed-based technologies. Crop management practices are seldom static and must often be adjusted to environmental factors, knowledge and market forces. Interactions among crop varieties, environmental conditions and crop management practices are well known, but additional factors such as input and output prices and employment opportunities also affect farmers' decisions on the level of inputs to be applied and the time spent in crop management. The influence of market factors on farmers' decisions regarding crop management practices will increase as the market opens up under the General Agreement on Tariffs and Trade (GATT).

It is essential, therefore, that crop management practices should not be applied in isolation but as part of an ICMP that can be adjusted to fit the prevailing environmental, socio-economic and market factors. The development of ICMPs, which are similar to the Australian Ricecheck package, and their transfer could assist farmers in many countries to narrow the yield gaps and reduce rural poverty. The ideal ICMP should aim at improving farmers' knowledge, not only of crop production and protection, but also of natural resources conservation and market dynamics. This requires substantial improvements in the system of collection and dissemination of information on rice, its production factors and its technologies, as well as modification of the extension systems in many countries.

Suitable improved varieties and improved cultural practices, including IPM and integrated plant nutrition management, are the main components of ICMPs. A number of innovative technologies identified by IRRI's Crop and Resource Management Network (CREMNET) may provide effective tools in the partial narrowing of yield gaps in rice production on small farmers in developing countries. CREMNET uses the chlorophyll meter and leaf colour chart technique for field-specific N management, deep placement of urea tablets, the direct wet-seeding method, stripper-harvesting, low-cost in-storage dryers, etc. (IRRI, 1997), all of which are appropriate for inclusion in ICMPs aimed at narrowing gaps in rice yields in developing countries.

Deployment of new technologies

Yields can be raised by lifting the actual yield closer to the ceiling through improved crop management, or by raising the ceiling itself. It is probable that the theoretical maximum rice yield is not very different from the maximum yield of wheat, i.e. 20 tonnes/ha per crop (Hanson, Borlaug and Anderson, 1982). The highest yields obtained at research stations are only about 17 tonnes/ha per crop for hybrid rice, 15 tonnes/ha for japonica HYVs planted in subtropical climates, and 10 tonnes/ha for indica HYVs planted in tropical climates (Figure 2).

FIGURE 2: Yield ladders at research level

Hybrid rice is currently available for increasing the yield ceiling by 15 to 20 percent. The new plant type of rice, which has been developed by IRRI, may raise the present yield potential by 25 to 30 percent (Khush, 1995). Rice biotechnology, which has recently made considerable progress, may also provide an opportunity for increasing rice yield in a more effective and sustainable manner.

Adequate input and farm credit supplies

Fertilizers, especially N, play an important role in rice production and productivity. Farmers need an adequate amount of fertilizer at the right time to obtain high yields in rice cultivation. The supply of fertilizers should be decentralized to village markets, and the quality of fertilizers should be assured. Small farmers are usually unable to buy sufficient quantities in time for application; the provision of village credit could, therefore, greatly help them. The Bangladesh Grameen Bank is an interesting example of how to provide rural credit to landless and resource-poor farmers in developing countries. Loan proposals are received by the bank on a group basis only (groups of at least five people), focusing on technology loans, housing loans, joint loans and general loans (Dadhich, 1995). The principle of the Grameen Bank could be deployed in other developing countries, with some modifications to adapt it to local conditions. The problems of credit and input supplies cannot be resolved quickly without strong government intervention. The issues of village credit and input supplies are being tackled in countries where FAO and governments are implementing the Special Programmes for Food Security (SPFS).

Research and extension

The support of research and extension ensures the effective bridging of the rice yield gap. Farmers' adoption of improved technologies depends on the capability of national agricultural research centres and extension services, which need more government resources and training.

Research should take account of farmers' constraints to high rice productivity and should provide them with technological packages, appropriate to specific locations, that bridge the gap in participatory approaches. The extension service should provide effective training and demonstrations to ensure that farmers use recommended technological packages (ICMPs) correctly and systematically in rice fields. For example, N fertilizers should be appropriately applied, in terms of quantity and timing, from seeding to heading so that the yield gap of rice can be narrowed while avoiding unnecessary losses of N, which would increase production costs and pollute the environment.

CONCLUSION

Sustainable increased rice production in the near future will require substantial improvements in productivity and efficiency. Rice yield and production have been increased considerably during the last 30 years - in some countries, yields of rice in favourable ecologies have reached the research yield potential of the present generation of HYVs. The use of innovative genetic improvements, including hybrid rice, new plant types and, possibly, transgenic rice, can increase the yield ceiling when yield gaps are very narrow. This increases not only rice productivity but also the efficiency of production systems, resulting in high economic outputs and high income for farmers.

On the other hand, in many other countries, the gaps between yields at research stations and in farmers' fields are still substantially large, owing to a combined lack of initiatives, resources and support for narrowing them. In these countries, yield gaps can be bridged by integrated crop management approaches, including location-specific technologies, coupled with active institutional support from governments (particularly for input and village credit supplies, stronger research and extension linkages), which improve the productivity and efficiency of rice production.

The causes of yield gaps of rice vary widely from season to season, country to country and even from area to area within a country, region or province. It is essential, therefore, to promote close collaboration among research, extension, local authorities, non-governmental organizations (NGOs) and the private sector in order to identify specific constraints to high yields and appropriate technologies and solutions. A concerted effort is needed to bridge rice yield gaps through participatory approaches, and it is essential that governments support, coordinate and monitor such integrated and holistic programmes. International support to government initiatives in this direction could speed up sustainable increased rice production and the conservation of natural resources and the environment for future generations.

REFERENCES

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Quelques réflexions sur les écarts de rendement

Pour augmenter durablement la production de riz dans les années à venir, il conviendra d'améliorer sensiblement la productivité et l'efficacité. Des technologies novatrices telles que le riz hybride, les nouveaux types de plant, voire le riz transgénique, peuvent contribuer sensiblement à relever le plafond des rendements du riz dans les zones où les rendements des agriculteurs sont désormais proches de ceux de la recherche. Toutefois, dans de nombreux pays, il existe encore des écarts entre les rendements constatés aux stations de recherche et ceux obtenus dans les champs des agriculteurs. La réduction de ces écarts pourrait améliorer non seulement la productivité, mais aussi l'efficacité de la production rizicole. Certains spécialistes, toutefois, expriment une certaine inquiétude quant aux gains économiques liés à la réduction des écarts de rendement. D'autres spécialistes estiment que les écarts de rendement peuvent être exploitables d'un point de vue économique pour accroître les rendements du riz. Les causes de ces écarts diffèrent considérablement d'une campagne à l'autre, d'un pays à l'autre, voire d'un endroit à l'autre au sein d'un même pays, d'une même région ou d'une même province. La réduction de l'écart de rendement exige des approches intégrées, incluant une réflexion appropriée, une intervention politique, la compréhension des difficultés réelles des agriculteurs pour obtenir des rendements élevés, le déploiement de nouvelles technologies et la promotion de la gestion intégrée des cultures, l'apport d'intrants et la disponibilité de crédits, ainsi que le renforcement de la recherche, de la vulgarisation et des liens entre les facteurs. Tout, ou presque, dépendra de la volonté des gouvernements d'appuyer, de coordonner et de suivre ces programmes intégrés. Un soutien international aux initiatives gouvernementales permettrait d'accélérer les progrès en matière de production durable de riz et de conservation des ressources naturelles et de l'environnement au profit des générations à venir.

Consideraciones sobre las disparidades de rendimiento en la producción arrocera

Para un aumento sostenible de la producción de arroz en un próximo futuro se requiere una mejora sustancial de la productividad y la eficacia. Las tecnologías innovadoras como el arroz híbrido, los nuevos tipos de plantas y posiblemente el arroz transgénico, pueden contribuir a elevar el techo de rendimiento de la producción de arroz en zonas en que el rendimiento en los campos de los agricultores se ha aproximado al de los centros de investigación. Sin embargo, en muchos países perduran las diferencias entre el rendimiento obtenido en éstos y en los terrenos de los agricultores. La reducción de esos desajustes podría contribuir a mejorar no sólo la productividad sino también la eficacia de la producción arrocera.

No obstante ha habido especialistas que manifestaron su preocupación por los beneficios económicos que se derivarían al reducir las diferencias del rendimiento. Otros han estimado que esas diferencias podrían aprovecharse para aumentar el rendimiento del arroz. Las causas de las diferencias de rendimiento del arroz varían ampliamente de una temporada a otra, de un país a otro e incluso de uno a otro lugar dentro de un país, región o provincia. La reducción de esas diferencias de rendimiento del arroz exige aplicar enfoques integrados y globales, en particular una noción adecuada, intervenciones a nivel de políticas, comprensión por parte de los agricultores de las limitaciones reales para un alto rendimiento, despliegue de nuevas tecnologías y fomento de un manejo agrícola integrado, así como un suministro suficiente de insumos y de crédito agrario y el reforzamiento de la investigación y extensión y de las vinculaciones existentes entre los distintos factores. Esto dependerá en gran parte de la voluntad de los gobiernos por apoyar, coordinar y seguir de cerca esos programas integrados y globales. El apoyo internacional a las iniciativas de los gobiernos en este sentido podría acelerar un aumento sostenible de la producción de arroz, así como la conservación de los recursos naturales y el medio ambiente para las generaciones futuras.