FAO Regional Office for Asia and the
Pacific
FAO, Bangkok, Thailand
The FAO Expert Consultation on Technological Evolution and Impact for Sustainable Rice Production in Asia and the Pacific was held at the FAO Regional Office for Asia and the Pacific, Bangkok, Thailand, from 29 to 31 October 1996. Participants included experts from Bangladesh, Cambodia, China, India, Indonesia, Laos, Malaysia, Thailand and Viet Nam as well as representatives of the Asia and Pacific Seed Association (APSA), the International Rice Research Institute (IRRI) and FAO. The objectives of the consultation were:
Rice is not only a major cereal crop in Asia but also a way of life. It contributes about 40 to 70 percent of the population's total calorie intake. Therefore, sustained production and increased productivity of rice is critical for food and nutritional security in Asia.
World demand for rice by the year 2025 is estimated to be about 765 million tonnes as compared with the present production of around 556 million tonnes. On the other hand, it is estimated that, in 25 years, the balance of uncropped land will be halved in South Asia and sliced by one-third in East Asia. Meanwhile, prime farmland in the whole of Asia has been shrinking owing to non-agricultural use while water and wind erosion, respectively, are also estimated to affect another 317 million and 90 million ha of agricultural land in Asia. Another 41 million and 6 million ha are subject to chemical and physical degradation.
The green revolution success story of 1970s and early 1980s took place in high-potential irrigated areas, in which high-yielding varieties (HYVs) of rice and wheat were introduced. However, this success carried with it certain economic and environmental penalties, such as the dependency on a steady supply of expensive fertilizer, fuel and pesticides. Moreover, many of the development projects undertaken in the high-potential irrigated areas have not been environmentally sound, leading to water logging and salinization as well as to micronutrient deficiencies and organic matter depletion.
Therefore, given the fact that there is negligible scope for area expansion, the growth rate of rice production must not only be sustained but even accelerated to meet the demand.
The task of increasing yield levels will be much more challenging than in the past. With the increasing cost of investment of new irrigation systems, attention should be given to less favourable rice-growing areas, areas which have benefited less from research and technology development and where productivity remains low and unstable, thus exacerbating poverty and inequity problems.
The research and technology development strategy to increase and sustain future rice productivity should encompass: i) yield potential increases of irrigated and favourable rainfed lowland rice; ii) productivity increases in less favourable rice-growing areas; iii) problem-solving research in national programmes and the development of location-specific management practices; and iv) the use of modern biotechnology to incorporate resistance to biotic and abiotic stresses in conventional approaches, increase biological nitrogen fixation, enhance overall physiological efficiency, tailor the new plant type and strengthen hybrid rice approaches.
In Asia rice yields increased rapidly from 1970 to 1985, moderately from 1985 to 1990 and slowly (sometimes stagnant) from 1991 to the present. The increasing trend has contributed to the region's increased rice production in the last 30 years. Several Asian countries still have a low average yield, mainly owing to the large share of rainfed rice production. Water control and crop management improvement could rapidly increase their rice yield and production. In irrigated rice fields, the yield of modern rice has reached a plateau and yield gaps between farmers' fields and research stations still exist. The closing of these gaps requires the concerted effort of governments to ensure adequate support for increased rice production. The Australian "Ricecheck" method, which was cited as an example, was considered the blueprint to help farmers to obtain 10 tonnes/ha of rice yield.
The phenomenon of yield decline of modern rice in intensive rice cropping systems has been reported at IRRI's rice stations, but its occurrence in farmers' fields is still questioned. However, numerous cases of farmers' low incomes and stagnant or decreasing yields and productivity were reported. In Asia, the annual growth rate of yields was 2.46 percent in 1965-75, 3.28 percent in 1975-85 and only 1.63 percent in 1985-95. This means that it was more difficult to improve modern rice yields after the green revolution. Meanwhile, arable lands are under pressure from intensive competition between agriculture, urbanization and industrialization. In view of this, considerable efforts in research, development and effective extension should be made to break the trend of stagnant yields, close the rice yield gaps and sustain farmers' increased rice production.
Following are the summary reports of case studies on yield trends of modern rice varieties in intensive farming systems in Bangladesh, China, India, Indonesia and Viet Nam.
Yield trials consisting of three and two rice crops per year with three fertilizer treatments, i.e. of zero fertilizer application, N+P+K and N+P+K+S or N+P+K+S+Zn+N, showed yield declines for each treatment over a period of ten years (1984-1995). However, the inclusion of organic fertilizer with the chemical fertilizers tended to reduce the rate of decline although it did not arrest it. Overall country rice production and average rice yields increased from 1970 to 1995, but the yield of HYVs declined.
Higher cropping intensities caused nutrient deficiencies, especially of sulphur (S) and zinc (Zn), and the depletion of organic matter by about 19 to 45 percent from 1970 to 1990. A nutrient balance sheet for three rice crops per year over a period of eight years (1984-1991) showed a negative balance for all nutrients on a net basis, but a positive balance for nitrogen (N), phosphorus (P), Calcium (Ca) and S on a gross basis.
Increased irrigation caused a fall in the water table in the dry season in some areas, but there was no sign of water or soil pollution resulting from less fertilizer and pesticide use. The adoption of HYVs contributed to poverty alleviation at the household level.
To meet the future demand for rice, the area under irrigation should be expanded while the area under HYVs and the cropping intensity should be increased. However, a comprehensive study needs to be undertaken on recommended inputs and management practices at representative intensive rice cropping sites so as to determine the exact nature and cause of yield declines.
China produced 182.5 millions tonnes of rice from about 30.82 million ha of land in 1995. The improved HYVs and intensive production systems have been considered very important factors in increasing rice yields in mixed systems of rice-winter crops (wheat, barley, rape or green manure) as well as in rice-rice-winter crops. Recent trends in rice yield and productivity declines in intensive irrigated rice systems have been reported.
To determine whether the decline of rice productivity has really taken place on farmers' land, 20 farmers' fields at two representative sites in Longyou and Xiaoshan counties, Zhejiang province, were surveyed. The survey showed that the grain yield of double cropping of rice in red soil in Longyou was higher than that in alluvial soil in Xiaoshan. But the coefficient of variation (CV) of grain yield and the decrease in rice production was higher in Longyou than Xiaoshan. The decline in grain yield of the early rice (first rice) was more significant than that of the late rice (second rice) at the two selected sites. The average annual grain yield decreased by 1.3 to 2 percent from 1989 to 1992 and 1993 to 1995 at the two sites, except the late rice at Xiaoshan. Further, the average annual ratio of output to input prices decreased by 1 percent to 12.4 percent from 1989-92 to 1993-95 at the two sites. In addition, the average annual rice grain yield per kg of N fertilizer applied decreased by 3.1 percent to 17.3 percent during the same period. The above results indicate a decline in grain yield and productivity growth of rice in intensive irrigated cropping systems in farmers' fields in central China. This is possibly due to the decrease in rice prices, less use of organic matter, varieties that are less resistant to biotic and abiotic stresses and other socio-economic factors.
The country's rice productivity increased from 2.21 tonnes/ha in 1985 to 2.93 tonnes/ha in 1994/95, recording a maximum growth rate of 2.77 percent during this period. The increase has been ascribed to the progressive increase in the contribution from all over the country, in general, and from eastern India, in particular. The compound growth rate of the northern region (Punjab, Haryana and western Uttar Pradesh), which was 6.46 and 4.24 percent, respectively, in the two preceding decades before 1985, decreased to 2.57 percent throughout the period 1985-1995, while in the southern region it has been more or less static. Eastern India, which accounts for more than 60 percent of the country's rice area, registered an impressive rate of 2.82 percent in the period 1985-1995, compared with 0.83 percent during the preceding decade. However, analyses of the rice productivity at the state and district levels and according to season in high-productivity areas indicate rice yield declines, stagnation and deceleration.
Of the seven intensively cropped and highly productive rice states studied, Andhra Pradesh, Tamil Nadu and Karnataka represent irrigated rice-rice areas, Punjab and Haryana represent rice-wheat systems, while Orissa and West Bengal grow rainfed rice during kharif followed by dry season rice (borg system). There was an increase in productivity throughout the 1983-1994 study period in Andhra Pradesh, Karnataka, Tamil Nadu, Punjab and Haryana of 2.51, 3.65, 4.01, 0.94 and 1.17 percent, respectively. Compared with the preceding decade, growth rates were found to decelerate marginally in Andhra Pradesh, and drastically in Punjab and Haryana. Main causes of deceleration in Andhra Pradesh were: i) frequent weather vagaries such as cyclones in its coastal areas; ii) newly emerging pest and disease problems; iii) nutritional imbalances owing to the removal of subsidies on phosphatic fertilizers; and iv) yield plateaus. In Punjab the main causes of deceleration were: i) genetic plateaus; ii) soil health problems; and iii) nutrient mining together with nutritional imbalances. As Orissa and West Bengal have picked up modern technologies, the yields in these states have been steadily increasing since 1985.
Productivity trend curves of all those districts, particularly of Haryana, Punjab, Andhra Pradesh, Tamil Nadu and Karnataka during the dry season, clearly indicate yield plateauing and stagnation especially during the last five to seven years; this suggests a need to develop rice varieties with a higher yield ceiling for those areas.
Decelerating and declining trends in rice productivity in the irrigated ecosystems are a matter of great concern since, with 45 percent of the rice area, these ecosystems contribute 61 percent of the national rice production. To maintain the present level of sustainability and to be able to produce the targeted 140 million tonnes of grain paddy by the year 2000, efforts should be made to identify the endangered areas of these ecosystems as well as the causes for such disturbing trends. Related problems could then be addressed jointly by FAO, IRRI and the national agricultural research system (NARS).
An increase in rice production through intensification in lowland rice-growing areas has been Indonesia's main agricultural development policy for the past three decades. Lowland rice production increased from 12.3 million tonnes in 1969 to 46.3 million tonnes of dry grain in 1994. This increase was mainly due to an increase in rice productivity through the adoption of modern technology, consisting of high-yielding varieties, fertilizer, irrigation and water management, pest and disease control and other improved cultural practices.
The growth of rice yields contributed significantly to the rice production growth in the 1970s. However, the yield growth decreased drastically in the 1980s and was accompanied by a lower growth in rice production until the early 1990s. A national farm cost survey indicated that rates of N and P use in many areas of Java, Bali and parts of Sumatra are far higher than recommended. Also, a soil fertility study showed that 82 percent of the 5.4 million ha of the lowlands have a medium to high P status, with no expected response to applied P fertilizer.
A preliminary survey on alleged decline in yield and factor productivity of HYVs in farmers' fields indicated differences in rice yield trends. A common phenomenon was an increased yield growth until a certain stage, followed by a period of levelling-off. The total factor productivity (TFP) fluctuated very slightly; in only one case was there a declining trend in the TFP. Data collected from many areas for the 1971-1991 period showed an increase of aggregate input as well as of rice yield over a period of time. However, the increase in TFP occurred only until about 1977, followed by a declining trend until 1991. This situation may be viewed as "overintensification", a symptom of inefficiencies in rice farming leading to a decrease in farm income. Concerted efforts, therefore, need to be made in order to find ways to improve rice farming in a sustainable manner, with the aim of increasing rice production and farm income while conserving natural resources.
Since HYVs were first introduced into Viet Nam (1968), many Vietnamese farmers have been trying to modify their traditional practices and adapt the new technology in order to increase their production. However, the degree of success with HYVs has varied from place to place and from year to year.
In response to the alleged yield decline of HYVs in intensified farming, a preliminary investigation was carried out in four provinces (An Giang, Dong Thap, Vinh Long and Tien Giang) of the Mekong Delta. The results of the study on the yield trends showed mostly stable yields. There was an increased yield on some sites owing to the increase in fertilizer application. Some decrease in yield was recorded when the water level was unusually high. The yield of the DX (October-November planting) crop was always higher than that of the HT (May-June planting) crop, and the yields in An Giang and Dong Thap provinces were higher than in others. Based on the results obtained and the indigenous knowledge of the surveyed farmers, it was recommended that for sustainable rice production in intensive irrigated rice areas of the Mekong Delta, attention should be given to: i) using high-quality seed of appropriate rice varieties that are non-photosensitive, of short duration (901 to 910 days), pest-resistant and of good eating quality; ii) applying appropriate soil management techniques during the fallow period between two succeeding rice crops (dry fallow, flood fallow, total drying of the soil, growing an upland legume crop and applying compost); and iii) making use of profitable integrated crop-livestock farming systems.
The Consultation expressed concern that the growth rates in aggregate rice output and yields had declined from 2.6 percent in the 1960s and 1970s to 1.5 percent in the last decade, which is below the growth rate of population in Asia. Recognizing that future food security in the region will continue to depend heavily on rice security and that the annual growth rate of rice production is below the desired level, the Consultation strongly advocates that the declining yield trend of the past decade be reversed and that rice production in the region be increased annually by 2.5 percent as against the current rate of less than 1.5 percent.
Based on the case studies presented and other reports, the Consultation noted that there are indications of decelerating yield growth in farmers' fields in intensive rice systems in certain areas of some countries. Often, occasional yield decreases owing to known reasons are confused with steady yield decline. Further, considering that the important indicator of average yield trends is affected by technological and policy changes, it is advised that other indicators such as TFP, which is a ratio of total output value to the total input costs, are more reliable and should be used along with yield indicators.
Recognizing the very serious consequences of the downward yield trend and its implications on future research and technology development priorities and policies, the Consultation recommends that the different countries should undertake systematic studies on the actual and potential downward yield trends (deceleration, stagnation and decline), quantify these processes and delineate the affected areas as accurately as possible. The Consultation also suggests that the balance between inputs plus soil nutrient supply and crop uptake plus losses should provide measures to quantify decline, deceleration and decrease. Noting that the various terms are not being used uniformly and correctly, the Consultation proposes the following definitions:
The Consultation recognized that the problem of deceleration and decline is acute in intensive rice ecosystems, especially when encountered in low-yield regimes. In order to define intensive systems, the Consultation recommends that such a system should have a minimum on-farm yield of 8 tonnes/ha of rice equivalent per year, which could be achieved by a cropping intensity of 100 percent or more. The use of various inputs such as fertilizer, water, agrochemicals, seed and energy (mechanization) should be quantified in order to monitor the productivity growth.
Analysing the causes behind deceleration and decline in rice yield trends, the Consultation found that technologies for achieving and maintaining the desired yield and productivity growth rates are generally available for most rice production systems and areas in the region, especially where average on-farm yields are below 6 tonnes/ha. The gaps in desired yield levels in farmers' fields or deceleration, stagnation and decline in yield growth are thus mostly due to gaps in technology assessment, adaptation, transfer and adoption. The Consultation therefore recommends that, while maintenance research should continue to receive attention, national programmes should assign much higher priority to identification, transfer and adoption of available recommended technologies.
The Consultation noted that there is generally a high correlation between intensification and inefficiency in the use of recommended inputs. It further noted that, with the adoption of knowledge-intensive technologies, such as the use of a chlorophyll meter for N management and integrated pest management (IPM) in rice, the quantities and costs of inputs could be significantly reduced, as could environmental costs, without sacrificing yield. In other words, knowledge could considerably substitute for monetary (and often polluting) inputs. In this context, the Consultation recommends that greater attention should be paid to the transfer and adoption of information- and knowledge-intensive technologies (KIT) for promoting enhanced productivity, profitability and sustainability. There is urgent need to identify and address farmer adoption constraints (suitability of technologies, inputs and technology delivery systems, infrastructure and institutional support, policy directives and interventions). It is important to reorient extension and technology delivery systems and to train the extension and development staff to handle the delivery of KIT effectively. A new paradigm should be established to strengthen research-extension-farmer linkages to deliver information and technology packages, based on participatory and freely communicative approaches. This calls for judicious collaboration among NARS, FAO, IRRI, non-governmental organizations (NGOs) and the private sector. Farmers have to be trained and educated to receive and process information, knowledge and technologies in order to tackle their rice production constraints.
The Consultation observed that, especially in high-yield environments, there is a negligible gap in transferable technology, and often yield ceilings have been reached. In order to raise yields further in such ecosystems, the Consultation recommends that new technologies such as hybrid rice, new plant types, transgenic rice for management of biotic and abiotic stresses, simulation modelling and systems approach should be developed. New mechanisms for assessment and transfer of such technologies will also be urgently needed.
The Consultation emphasized that the synergistic interaction among wider use of improved varieties, expansion of irrigation and increased use of fertilizers was responsible for the impressive gains in cereal production during the past three decades or so. This synergism is essential for future increases in production by raising yield ceilings, especially under irrigated conditions. However, the plateauing and declining yield trends, deteriorating soil quality and increasing agrochemical toxicity in intensive systems call for the improved management of resources with the aim of alleviating these problems and ensuring greater sustainability. The Consultation recommends that an integrated approach is required for managing soil fertility and nutrients, water, seed, chemical inputs and pests and diseases. Countries should focus on both existing and emerging technologies from different sources to promote integrated nutrient management in intensive rice cropping (e.g. fallow period management; rotation with upland crops, preferably legumes, if possible; crop-livestock systems; use of organic manures, crop residues and biofertilizers).
The consultation strongly felt that it is important to develop a networking system of Asian NARS to exchange information, knowledge, technologies, and experiences. It noted that IRRI operates the Integrated Rice Research Consortium for research and development of new technologies, and the Crop and Resource Management Network (CREMNET) to facilitate the exchange and evaluation of knowledge-intensive technologies (KITs) among primarily Asian NARS. The Consultation therefore advocates that collaboration between national and international organizations (FAO, IRRI, CIMMYT, UNDP, NARS, etc.) should be strengthened to avoid duplication of efforts and to promote the use of sound practices and technologies in intensive rice cropping systems. In addition, the consultation recommends that the existing networks of NARS should be strengthened to facilitate the exchange and evaluation of promising KITs, and to freely share information, knowledge and experiences in promoting KITs for intensive and sustainable rice production.
The consultation recognized the need for developing suitable indicators of intensification and sustainability to monitor the performance of intensive rice systems. In order to plan and monitor the development, use and impact of various technologies, the Consultation recommends that FAO, IRRI and NARS should jointly formulate effective indicators for the intensification and sustainability of target rice systems. Such indicators should be pilot tested in different settings and wide use made of those that are standardized. The information thus generated should be consolidated, value added and widely disseminated by FAO.
The participants noted the importance of using quality rice seed to improve and maintain rice yields in intensive farming. The Consultation therefore advocates that Asian countries should create increased awareness among farmers about the advantage of using good-quality seed, strengthen their national seed production and distribution systems (in public, private and NGO sectors) and meet the demand for quality seeds by farmers.
Governments' policies on intensive rice cropping systems should be well defined, coordinated and implemented to improve rice productivity and farmers' incomes, ensure the sustainability of food security systems and minimize rice farming-related pollution of the environment. The Consultation recognized that the protection of the environment, especially in developing Asian countries, is closely linked to adequacy of food production through the intensification of rice farming. The Consultation therefore recommends the adoption of appropriate policies to effect socio-economic adjustments in terms of input-output pricing, institutional support and attention to the needs of small farmers, who constitute the bulk of rice farmers, as a complement to technological advancement.
The consultation recognized the seriousness of yield decline and deceleration and the associated problems of food, economic, environmental and ecological security. Thus, there is an urgent need to develop an FAO/IRRI/NARS joint programme to identify the causes of and arrest the downward yield trends. The Consultation recommend that FAO, in close collaboration with IRRI and NARS, should prepare a regional programme of action to enhance and sustain rice production and to attain durable food security and environmental protection in the Asia and Pacific region. UNDP and other donors are urged to provide the necessary funding in support of this priority programme.
1Excerpt from a report of the Expert Consultation on Technological Evolution and Impact for Sustainable Rice Production in Asia and the Pacific, 29-31 October 1996, Bangkok, Thailand.
Le texte ci-apr�s est tir� d'un rapport de la Consultation d'experts sur l'�volution technologique et son impact sur la production durable de la riziculture en Asie et dans le Pacifique, qui s'est tenue du 29 au 31 octobre 1996, � Bangkok (Tha�lande).
Le succ�s remport� par la r�volution verte pendant les ann�es 70 et au d�but des ann�es 80 a concern� des zones irrigu�es offrant un grand potentiel dans lesquelles on a introduit des vari�t�s de riz et de bl� � haut rendement. Toutefois, certaines p�nalit�s �conomiques et �cologiques ont accompagn� cette r�ussite: d�pendance des cultivateurs � l'�gard d'un approvisionnement continu en engrais, carburants et pesticides co�teux et endommagement des sols par la saturation en eau, la salinisation, l'insuffisance de micronutriments et l'�puisement de la mati�re organique. En Asie, le taux annuel de rendement, qui avait progress� de 2,46 pour cent dans la p�riode 1965-1975 et de 3,28 pour cent en 1975-1985, n'a augment� que de 1,63 pour cent dans la p�riode 1985-1995. Cela signifie qu'il a �t� plus difficile d'am�liorer le rendement du riz moderne apr�s la r�volution verte. Entre-temps, la concurrence intensive que se font l'agriculture, l'urbanisation et l'industrialisation a �puis� les terres arables. Par cons�quent, la strat�gie de d�veloppement de la recherche et de la technologie visant � accro�tre et � soutenir la productivit� future de la riziculture devrait avoir pour but
Le ph�nom�ne de la baisse de rendement de la riziculture moderne intensive a �t� signal� dans les stations de l'IRRI, mais il est toujours contest� pour ce qui est des champs des planteurs. On a toutefois signal� nombre de cas o� le revenu des cultivateurs stagnait ou baissait et o� la croissance du rendement et de la productivit� s'infl�chissait. Se fondant sur des �tudes de cas r�alis�es au Bangladesh, en Chine, en Inde, en Indon�sie et au Viet Nam et sur d'autres rapports et �tudes, la Consultation a relev� que certains indices signalent le ralentissement de la croissance du rendement des rizi�res cultiv�es de mani�re intensive dans certaines r�gions de quelques pays. Souvent, on confond la diminution occasionnelle de rendement imputable � des raisons connues avec un ralentissement continu. Relevant que les diff�rentes expressions ne sont pas utilis�es uniform�ment et correctement, la Consultation propose les d�finitions suivantes:
La Consultation a reconnu la gravit� de la baisse/du ralentissement du rendement ainsi que des probl�mes connexes sur le plan de l'alimentation, de l'�conomie, de l'environnement et de la s�curit� �cologique. Il faut donc �laborer d'urgence un programme commun FAO-IRRI-SNRA (Syst�me national de recherche agricole) afin d'identifier les causes de la tendance � la baisse des rendements et d'y mettre fin.
Este es un extracto del informe de la Consulta de Expertos sobre Evoluci�n y Efectos de la Tecnolog�a para la Producci�n Sostenible de Arroz en Asia y el Pac�fico, que se celebr� en Bangkok (Tailandia) del 29 al 31 de octubre de 1996.
Los logros de la revoluci�n verde en el decenio de 1970 y principios del de 1980 tuvieron lugar en zonas de regad�o de alto potencial, en las que se hab�an introducido variedades de arroz y trigo de alto rendimiento. Sin embargo, estos �xitos llevaron consigo ciertos problemas econ�micos y ambientales, como la dependencia de un suministro constante de fertilizantes, combustible y plaguicidas costosos, as� como algunos efectos negativos, en particular el anegamiento, la salinizaci�n, las carencias de micronutrientes y la disminuci�n de la materia org�nica. En Asia, la tasa de crecimiento anual de los rendimientos fue del 2,46 por ciento en 1965-75, del 3,28 por ciento en 1975-85 y s�lo del 1,63 por ciento en 1985-95. Esto significa que despu�s de la revoluci�n verde fue m�s dif�cil mejorar el rendimiento de las variedades modernas de arroz. Mientras tanto, las tierras de labranza se han agotado con la competencia intensiva entre la agricultura, el desarrollo urbano y la industrializaci�n. Por consiguiente, la estrategia de investigaci�n y desarrollo de tecnolog�as para aumentar y mantener la productividad del arroz en el futuro deber� abarcar los siguientes aspectos: aumento del rendimiento potencial del arroz de regad�o y, en condiciones favorables, de secano en tierras bajas; aumento de la productividad en zonas de cultivo menos favorables; inicio de investigaciones para resolver los problemas en el marco de programas nacionales y promoci�n de pr�cticas de gesti�n espec�ficas para cada lugar; y utilizaci�n de la biotecnolog�a moderna como instrumento para un enfoque convencional, con el fin de mejorar la resistencia a las presiones bi�ticas y abi�ticas, aumentar la fijaci�n biol�gica de nitr�geno, potenciar la eficiencia fisiol�gica en general, adaptar los nuevos tipos de plantas y perfeccionar los criterios aplicados al arroz h�brido.
El fen�meno del descenso de los rendimientos de las variedades modernas de arroz en los sistemas de producci�n intensiva se ha se�alado en las estaciones del IRRI, pero se sigue poniendo en duda su presencia en los campos de los agricultores, aunque se han notificado numerosos casos de estabilizaci�n o reducci�n de los ingresos de los agricultores o de desaceleraci�n de sus rendimientos y su productividad. Tomando como base las monograf�as presentadas sobre Bangladesh, China, India, Indonesia y Viet Nam y otros informes y estudios, la Consulta observ� que hab�a indicios de una desaceleraci�n del crecimiento de los rendimientos de los sistemas de cultivo intensivo de arroz en los campos de los agricultures en ciertas zonas de algunos pa�ses. Disminuciones ocasionales, por razones desconocidas, de los rendimientos se suelen confundir con un descenso constante de �stos. La Consulta tom� nota de que los diversos t�rminos no se utilizaban de modo uniforme y correcto, por lo que propuso las definiciones siguientes:
La Consulta reconoci� la gravedad del descenso y desaceleraci�n del rendimiento, con los consiguientes problemas alimentarios, econ�mi-cos, ambientales y de seguridad ecol�gica. Por ello, es necesario elaborar urgentemente un programa conjunto FAO/IRRI/SNIA para determinar las causas e invertir la tendencia descendente del rendimiento.
