REFLECTIONS ON YIELD GAPS IN RICE PRODUCTION: HOW TO NARROW THE GAPS - Mahmud Duwayri¹, Dat Van Tran², and Van Nguu Nguyen³

¹ Director, AGP, FAO, Rome, Italy; and Chairman of IRC Steering Committee.

² Senior Rice Agronomist, AGPC, FAO, Rome, Italy; and Executive Secretary, IRC.

³ Rice Agronomist, AGPC, FAO, Rome, Italy.

Rice is the world’s most important food. More than half of the world’s population depends on rice for food calories and protein, especially in developing countries. By the year 2025, the world will need about 760 million tons of paddy, or 35 percent more than the rice production in 1996, in order to meet the growing demand. However, arable lands are mostly 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 been substantially slowed down. Moreover, crop intensification during the Green Revolution has exerted tremendous pressures on natural resources and the environment. On the other hand, under the globalization of the world economy, rice producers are exposed to competition not only among themselves but also with the producers of other crops. The future increased rice production, therefore, requires improvement 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 its productivity. Also, in many countries, the gaps between yields obtained at research stations and farmers’ fields still exist. Narrowing of these gaps could improve not only the productivity but also the efficiency of rice production.

Some specialists, however, have expressed their concern about the economic gains of narrowing the yield gaps. They considered that economically there is very limited scope for further increasing rice yield by closing the gaps. Other specialists believe that the yield gaps are economically exploitable for increasing rice yield. In a number of countries, regardless of the initially high yield, national yields still significantly increased during the last 30 years thanks to integrated national efforts in promoting rice development programmes. In addition, it is well known that yields are different among farmers in the same location. Good farmers usually reap more benefits from improved technologies than mediocre farmers at the same place. The challenge for policy makers, scientists and developers is how these gaps can be effectively and economically narrowed at the rice grower level.

2. EVOLUTION OF RICE YIELDS AND PRODUCTIVITY

2.1 World

The annual growth rates of the world’s population and rice production, harvested area, and yield are shown in Table 1. The year 1961 was selected as base year for the analysis of the evolution of rice production since it was the earliest year when statistics on rice production were available in FAO databases (FAO, 1998).

Table 1: Annual Growth Rates (percent) of World Population and Rice Production, Harvested Area, and Yield.

Period	Population	Rice Production	Rice Harvested Area	Rice Yield
1960’s (starting 1961)	2.17	3.48	1.54	2.51
1970’s (1970-79)	2.03	2.71	0.80	1.76
1980’s (1981-89)	1.86	3.14	0.23	2.80
1990’s (ending 1996)	1.55	1.31	0.23	1.10

Note: Data on population, rice production, harvested area, and yield in FAOSTAT (1998) were transformed into 3-year-moving-average (3YMA) values. Growth rate was calculated based on the following formula:
	GR (percent) = ((B-A)/A) x 100)/N
	Where:	GR = Annual Growth Rate A = 3YMA values of the starting year of a period B = 3YMA value of the ending year of a period N = Number of years in a period

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

During the 1960’s the high annual growth rate of rice production was due to both a high yield growth and a moderate growth in rice area, whereas the rapid rice production growth during the 1980’s was due principally to improvement in rice productivity. The growth rate of rice yield was 2.5 percent per year during the 1960’s, 1.8 percent in the 1970’s, 2.8 percent in the 1980’s and only 1.1 percent in the first half of the 1990’s; while the annual growth rate of harvested rice area decreased from 1.6 percent during the 1960’s to 0.2 percent in the 1980’s (Table 1). The trend of evolution in growth of rice harvested areas indicates that future increase in rice production 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 cause for concern and it has been the topic of numerous reviews (Pingali and Rosegrant, 1994; Cassman and Pingali, 1995; and Pingali, et al., 1997). Regardless of food consumption trends, the slowdown in growth of rice yield is particularly serious considering the continuing population growth. The reversal of this trend and the bridging of yield gaps require urgent and concerted efforts of all concerned parties and political support from both national and international authorities.

2.2 Asia

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

Table 2. Annual Growth Rates (percent) of Population and Rice Production, Harvested Area, and Yield in Asia.

Period	Population	Rice Production	Rice Harvested Area	Rice Yield
1960’s (starting 1961)	2.64	4.35	1.34	2.70
1970’s	2.28	2.59	0.60	1.88
1980’s	2.05	3.24	0.31	2.86
1990’s (ending 1996)	2.05	1.25	0.10	1.06

Note: Please refer to note in Table 1, with regard to formula for calculating the growth rates.

It does not seem logical that the annual growth rate of rice yield observed during the 1970’s (1.9 percent per year) was lower than that which was observed during the 1960’s (2.7 percent per year), considering the fact that IR 8 was released for cultivation in 1966 and in China commercial hybrid rice cultivation started in 1976. This fact, however, is very valuable experience for all concerned with improvement in 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 it may take one decade or more from the successful development of new rice varieties/types before gains in productivity at farmer level are obtainable. The variety IR 8 and its parental variety Peta does not differ in yield very much if fertilizers and other improved cultural practices are not used. In Indonesia, although HYVs had been widely adopted in the early 1970’s, rapid increases in rice yield were obtained only after the implementation of coordinated extension and development programmes named INSUS from 1975 -1985 and SUPRA INSUS since 1985 (Dudung, 1990).

The increase in the annual growth rate of rice yield from 1.9 percent during the 1970’s to about 2.8 percent during the 1980’s could be attributable 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 agro-chemicals in rice production. It may also be due to the adoption of policies, which are favourable to rice production in a number of countries. Vietnam, for example, became a major rice exporter only in late 1980s after favourable policies were adopted.

Table 3. Estimated Areas Planted to HYVs and Hybrid Rice (percent of total rice areas) in Major Rice-Producing Countries in Asia in 1989

Country	1989		1997***
	HYVs*	Hybrid Rice**	HYVs	Hybrid Rice
Bangladesh	40.7	-	65	-
India	62	-	62	Neg
Indonesia	73	-	85	-
Myanmar	51.9	-	51.9	-
Philippines	88.5	-	93	-
Vietnam		-	85	Neg
China	-	50	45	50

* IRRI (1995) World Rice Statistics,

** Yuan (1996),

*** FAO estimates (Neg = Hybrid rice was planted to about 60,000 ha in India and about 120,000 ha in Vietnam)

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

2.3 South America

Rice production in South America has grown at about 3.7 percent per annum or faster, except during the 1980’s when it grew at only 1.6 percent per year. The growth rate of rice production in the Region was more than twice that of the population since 1990. The high growth rate of rice production during the 1960’s and 1970’s was due mainly to the expansion of rice area. The annual growth rates of harvested area during these periods were respectively 4.6 and 3.2 percent per year. However, improvement in the productivity of rice production was the main force behind the increase in rice production during the 1980’s and 1990’s. Rice yield increased at a rate of 4 percent per year during the 1980’s and of 3.5 percent per year since 1990 (Table 4).

Table 4. Annual Growth Rates (percent) of Population and Rice Production, Harvested Area, and Yield in South America.

Period	Population	Rice Production	Rice Harvested Area	Rice Yield
1960’s (starting 1961)	2.69	3.68	4.63	-0.67
1970’s	2.90	3.95	3.18	0.96
1980’s	1.91	1.57	-2.01	3.98
1990’s (ending 1996)	1.88	3.97	0.33	3.54

Note: Please refer to note in Table 1, with regard to formula for calculating the growth rates.

The Southern Horn of Latin America, such as southern Brazil, Uruguay, Paraguay and Argentina, which has a Mediterranean climate, still has yields of 5-6 t/ha. This yield is lower than the potential yield of 10t/ha and the yield gap reaches 3-4 t/ha.

2.4 Africa

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

Table 5. Annual Growth Rates (percent) of Population and Rice Production, Harvested Area, and Yield in Africa

Period	Population	Rice Production	Rice Harvested Area	Rice Yield
1960’s (starting 1961)	3.01	4.94	3.67	0.95
1970’s	3.05	1.58	2.37	-0.59
1980’s	3.25	5.16	2.85	1.84
1990’s (ending 1996)	2.88	3.38	2.09	1.02

Note: Please refer to note in Table 1, with regard to formula for calculating the growth rates.

The stagnation in yield potential of HYVs is of major concern to sustainable rice production in Egypt while socio-economic factors limit rice yield in irrigated schemes in Sub-Saharan Africa. However, there are still considerable land and water resources in the Region for future increase in rice production to meet consumer 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 due to the level of management and operation of large irrigation projects as well as farmers’ poor crop management practices (Table 6). The reversing of this trend and increased sustainable rice production and productivity are two major concerns in the Region.

Table 6. Rice Area, Yield and Production at the Mbarali Rice Farm in Tanzania, 1980/81-1988/89

Year	Area (ha)	Yield (t/ha)	Production (t)
1980/81	2,647	8.15	21,573
1981/82	2,897	7.90	22,886
1982/83	2,844	7.50	21,330
1983/84	2,881	7.00	20,167
1984/85	2,893	5.50	15,911
1985/86	2,690	4.00	10,625
1986/87	2,680	3.90	10,180
1987/88	2,786	3.50	8,915
1988/89	2,253	4.00	9,012
Potentials	2,800	6.0-7.1	16,800-20,000

Source: URT, Food Strategy Unit, 1989

3.1 Definitions of Yield Gaps

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

Rice cultivation extends from 50° N to 35° 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 temperature in countries under temperate and Mediterranean climates are favourable for high yields of rice. The highest rice yield recorded under tropical conditions was 10.3 tonnes/ha obtained from IR 8 planted at the experimental farm of IRRI, Philippines in the 1965 dry season (De Datta, 1981). The japonica rice variety Koshihikari planted in Yanco, NSW, 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 these exceptionally high yields.

Rice is cultivated under a wide range of agro-ecologies. Irrigated rice yields substantially improved during the Green Revolution, while in other ecologies, with the possible exception of the favourable rainfed lowland ecology, rice yields have not been substantially improved, due to a host of biotic and abiotic stresses. However, yields of irrigated rice in many developing countries are only around 4-5 t/ha. Substantial and exploitable yield gaps, therefore, are generally found only 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 which respectively account for the difference between actual and potential yields of 35, 20 and 15 percent (De Datta, 1981).

The gaps between research yields and actual farmers’ yields in a particular location and season, therefore, are better indicators of yield gaps.

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

Figure 1. Components of Yield Gaps (Adopted from De Datta, 1981)

The second component of yield gaps or Gap II in Figure 1, however, is mainly due to differences in management practices. This Gap II exists as farmers use sub-optimal doses of inputs and cultural practices. Herdt (1996) provided a similar description of the yield gaps and components. Gap II is manageable and can be narrowed by deploying more efforts in research and extension services as well as Governments’ appropriate intervention particularly on the institutional issues.

3.2 Views on the Potential of Narrowing Yield Gaps

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

Less Exploitable Yield Gaps: Pingali et al., (1997) argued that the yield gaps in favourable rice ecologies are not significant for exploitation for increasing rice yield and production. Under this situation further increase in yield is possible only with the deployment of new technologies, such as hybrid rice. Agronomic yield potential determined on experimental stations is the maximum achievable yield with no physical, biological and economic constraints to rice production (Gap I). Once these constraints are accounted for, the exploitable gap of rice is small and, in many cases, non-existent. Therefore, narrowing of the exploitable yield gap in Asia is of little profit, particularly in irrigated rice. The authors reported a reduction of the yield gaps in farms with favourable conditions in Nueva Ecija and Laguna, Philippines from nearly 2 t/ha to less than half a ton after a decade. They also reported that yield gaps in the remaining two-thirds of the same rice areas, remained around 2 t/ha, and were even widening. Thus, the narrowing of yield gaps is not profitable for farmers in these environments.

Exploitable Yield Gaps: Authors of this school of thought believe that large yield gaps of rice still exist in both favourable and less favourable conditions in many countries and they could still be exploitable for further improvement in productivity. This is due to poor crop management and problems of institutional support, especially input and farm credit supplies, in many developing countries. Table 7 shows that the estimated yield gaps in irrigated rice yield production vary from 0.8 t/ha in Bangladesh to 2.3 t/ha in India.

Table 7. Comparative National Average Yields, Irrigated Rice Yields, and Experimental Station Rice Yields, Asian Countries, 1991.

Countries	National Average Rice Yield (t/ha)	Irrigated Rice Yield (t/ha)	Average Potential Rice Yield (t/ha)
Bangladesh	2.6	4.6	5.4
China	5.7	5.9	7.6
India	2.6	3.6	5.9
Indonesia	4.4	5.3	6.4
Nepal	2.5	4.2	5.0
Myanmar	2.7	4.2	5.1
Philippines	2.8	3.4	6.3
Thailand	2.0	4.0	5.3
Vietnam	3.1	4.3	6.1

Sources: IRRI (1993)
Average potential yield data cited from Dey and Hossain (1995)

Table 8. Some Statistical Data on Rice Yields in 1995

Item	Value
World average yield	3,771 kg/ha
Number of records on national yield	118
Number of records on national yield whose values are less than 1,000 kg/ha	2
Number of records on national yield whose values are equal to or less than 2,000 kg/ha	37
Number of records on national yield whose values are less than world average yield	78

Adapted from FAOSTAT, 1998

3.3 Factors Causing Yield Gaps

Based on the data from experiments on yield constraints, fertilizer application rate and timing have been found to be the most limiting factors for high yields in dry seasons. In the wet seasons, insect control and fertilizer management have been found to be about equal in importance in contributing to high rice yields (IRRI, 1979). At farmer level, the management of inputs - fertilizer, insect control, weed control and seedling age - contributed little to explain the difference between the low- and the high-yield crops. However, the environmental parameters and a combination of weather-related factors and insects and diseases accounted for some 80 percent of the yield difference. In the dry season, the level of managed inputs used and their interaction with environmental factors accounted for 50-60 percent of yield differences among farmers (Herdt and Mandac, 1980). The observations at 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 fertilizer doses to obtain maximum production. The effort on narrowing the yield gap without considering the economic aspect may have a counter-productive effect. Closing the yield gap may actually decrease farmers’ income, particularly if rice prices are low. The ratio between price of rice and price of fertilizer could influence the rate of fertilizer applied by farmers and thus rice yield. Consequently, institutional factors, which increase the price of rice/price of fertilizer, could positively contribute to gap narrowing (De Datta, 1981).

In Southern India, the maximum rice yields obtained in experimental stations under irrigated conditions varied from 6.0 t/ha in Kerela to 8.6 t/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 estimates on yield losses provided by 120 rice scientists and an equal number of extension personnel in Southern India.

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

· Physical factors: problem soils, poor water management, drought, flash floods and temperature stresses.

· Biophysical factors: varieties, seeds, weeds, insect, diseases and other pests, due to inadequate crop management. Post-harvest losses, which vary from 10 to 30 percent, also contribute partly to yield gaps.

· Socio-economic factors: labour shortage, cost-benefit, farmers’ knowledge, skills and welfare conditions.

· Institutional factors: Governments’ policies, rice price, agricultural credit and input supply, land tenure, agricultural research and extension.

Table 9. Factors Contributing to Yield Losses (kg/ha of paddy) in Rice Production in South India

	A. Pradesh	T. Nadu	Karnataka	Kerala	South India
Scarcity of irrigation water	23	37	24	28	26
Drought	18	23	18	0	18
Cold temperature at anthesis	0	6	14	0	4
Lodging	28	28	17	28	26
Low light intensity	0	3	11	0	3
Soil salinity	23	22	22	27	23
Low fertility	17	29	18	18	20
Zinc deficiency	15	25	23	0	18
Acid soils	0	9	10	27	6
Alkalinity	0	9	10	27	6
Iron toxicity	0	6	0	0	2
Weeds	25	30	25	10	25
Imbalanced use of fertilizer	19	41	26	0	24
Aged seedlings	7	7	0	0	5
Varietal problems	0	0	26	28	7
Socio-economic circumstances	39	64	111	142	66

Adopted from Ramasamy, 1996

3.4 Selected Cases of Yield Gap Narrowing

Rice yields generally have been steadily increasing during the last three decades. The yield increases in China, Indonesia, and Vietnam in Asia and Egypt, Australia and USA, however, are very spectacular and the yield increases appear to be mainly due to concerted national efforts in narrowing the yield gaps. In the late 1960’s, rice yields in Vietnam and Indonesia were only about 1.8 to 1.9 t/ha; in China they were about 3.1 t/ha; in Egypt and USA 4.9-5.0 t/ha; and in Australia 7.3 t/ha (Table 10). Indonesia and Vietnam, therefore, represented countries where rice yields were still low; China represented countries where yields were medium; Egypt and USA represented countries where yields were high; and Australia where yields were extremely high. Rice yields during the 1995 to 1997 period were about 3.7, 4.4, 6.1, 6.7, 8.2 and 8.2 t/ha, respectively, in Vietnam, Indonesia, China, USA, Egypt and Australia. Consequently yield increases were about 0.9, 1.8, 1.9, 2.6, 3.1, and 3.3 t/ha, respectively, in Australia, USA, Vietnam, Indonesia, China, and Egypt. The yield increase in Australia indicates that even with very high yield (7.3 t/ha) further yield increase is possible through narrowing the yield gap. This observation is further strengthened with the impressive yield increases obtained in Egypt and China.

Table 10. Yield and Yield Growth Rate in Selected Countries, 1966-1997

Country	Growth Rate of Rice yield (percent)*			Average Yield (t/ha)**		Estimated N Rate (kg/ha)***
	1967-77	1977-87	1987-97	1966-68	1995-97	1980	After 1990
China	1.81	4.47	1.72	3.12	6.17	-	145 (1994)
Indonesia	4.91	4.32	1.03	1.89	4.42	68	90 (1993)
Vietnam	0.97	4.22	3.56	1.81	3.73	-	90 (1997)
Egypt	0.54	1.26	4.46	4.95	8.25	83	120 (1997)
USA	0.2	2.32	0.92	4.96	6.74	-	-
Australia	-2.41	1.69	3.06	7.33	8.23	-	32 (1996)

* Please refer to Table 1 for information on formula for calculation of the Growth Rate

** Source: FAOSTAT, 1998.

*** Estimated based on FAO/IFA/IFDC (1999) Database on fertilizer use by crop; for Vietnam based on Le (1998)

China: Rice production in China has steadily increased even though the rice area harvested has declined. This was possible due to substantial increases in rice yield which could be attributed to both the development and use of hybrid rice since 1974 (Yuan, 1996) and the improvement in crop management including increased fertilizer use (Singh, 1992). Rapid expansion of hybrid rice area took place in China after 1976. The area planted to hybrid rice attained about 15 million ha in the late 1980’s. During 1950-1979, crop management was improved with the transfer of integrated crop management packages such as “Seven Techniques”, which encompass improved varieties, growing strong/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 improved with the emphasis on improved land development, fertilization, cultivation and cropping systems, and use of improved seeds as well as integration of socio-economic factors such as prices. The annual growth rates for rice yield were only 1.8 percent during 1967-77 but increased to 4.9 percent during 1977-87. The stagnation of yield of 3-line hybrid rice varieties may be responsible for the decline in yield growth to about 1.7 percent during 1987-97.

Indonesia: The national rice yield increased considerably by about 4.9 percent per year during 1967-77 and 4.3 percent during 1977-87. The increase in rice production has enabled the country to attain self-sufficiency in rice. The country benefited from the Green Revolution during the period from 1977 to 1987 while the Government’s INSUS/SUPRA INSUS Rice Intensification Programmes have been effectively implemented since 1975. The successful IPM programme has also contributed to this high yield.

Vietnam: Vietnam had been a rice importing country and started exporting rice only in the late 1980’s, thanks to its adoption of new agricultural policies. The national rice yield grew only about 1.0 percent per year from 1967 to 1977, although about 850,000 ha of IRRI’s high yielding varieties were grown in South Vietnam in 1974. This was probably due to inadequate fertilizer use in this period. The annual growth rates of rice yield increased to about 4.2 percent annually during 1977-87 and about 3.6 percent annually during 1987-97 period. Increase in fertilizer application has played an important role in these increases in rice yields and narrowing of yield gaps. The use of fertilizers, especially urea, increased from 45 kg/ha in 1988 to 200 kg/ha in 1997 (Le, 1998).

Egypt: Egyptian rice yield increased from 5.8t/ha in 1987 to 8.5 t/ha in 1997, one of the highest yields in the world. The adoption of new HYVs (such as Giza 175, Giza 176, Giza 181, Giza 177, Giza 178, Sakha 101 and Sakha 102); the intensive demonstrations and training on crop management; and monitoring production constraints which were carried out under national coordinated programmes, namely Markbouk 4 and others (Badawi, 1998), have led to the successful narrowing of yield gaps.

Australia: The national rice yield declined by about 2.4 percent per year during 1967-77, moderately increased during the 1977-87 period, but then grew rapidly during the 1987-97 period. The Integrated Rice Crop Management Package called “Ricecheck” was developed in the mid-1980s and transfered to farmers since 1986 (Lacy, 1994). Cropping systems using legume-based pastures (Trifolium subterraneum) in rotation with the rice crop were another factor responsible for the impressive increase in rice yield. The main features of Ricecheck are shown in Annex 1. 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 exports.

U.S.A.: The annual growth rate of rice yield was high (2.3 percent) in 1977-87 but rather low (0.9 percent) in the last decade. Among the rice growing States, California has made considerable progress in yield increase, reaching around 9 t/ha, thanks to improvements in weed control, laser-based land preparation and modern rice varieties.

4. CHALLENGES IN NARROWING THE YIELD GAP

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

4.1 Concept

Narrowing the yield gaps aims not only to increase rice yield and production but also to improve the efficiency of land and labour use, to reduce the cost of production and to increase sustainability. Exploitable yield gaps of rice are often caused by various factors including physical, biological, socio-economic and institutional constraints, which can be effectively improved through participatory and holistic approach in action and attention of Goverments. An integrated programme approach is obligatorily required. The narrowing of the yield gap is not static but dynamic with the technological development in rice production, as the gaps tend to enlarge with the improvement of yield potential of rice varieties.

4.2. Policy Intervention

Rice policy should be well defined and formulated in a country, especially where major structural reforms were introduced. Most Sub-Saharan African and several Asian countries have experienced these reforms. Governments should address and find solutions for socio-economic and political questions before narrowing the agronomic gap between farmers’ fields and research stations (Hanson et al., 1982). The goodwill of Governments is also essential to initiate a yield gap narrowing programme and to make effective coordination and intervention, with the aim of providing appropriate solutions to actual problems. Sensitization of policy makers and Government officers is a very important activity in bridging yield gaps of rice. The pilot approach should be considered in selection of zone/s for intervention.

4.3. Survey and Classification of Yield Gaps

The first step to narrow the yield gap is to identify actual 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 agronomists, economists and statisticians should carry out this preliminary survey. Based on the results of the survey, for practical purposes, yield gaps should be classified into:

· Case 1: Unexploitable: Gaps due mainly to non-transferable factors (or Gap I in Figure 1).

· Case 2- Less exploitable gaps: These gaps can be closed, but with less economic gains, due to the yield ceiling and law of diminishing returns in a production function. This type of gap can be found when rice yields are equal or more than 6 t/ha under a tropical climate and 8 t/ha or more under a Mediterranean climate.

· Case 3- Exploitable gaps: Gaps are due mainly to sub-optimal crop management practices (or Gap II) in Figure 1. This type of yield gap occurs when:

· for irrigated rice under a tropical climate, yields are below 6 t/ha

· for irrigated rice under a Mediterranean climate, yields are less than 8 t/ha

· for favourable rainfed lowland rice, yields are less than 4 t/ha

· The introduction of emerging technologies, such as hybrid rice, New Plant Type is needed to increase yield ceilings in the first two cases, while the promotion of integrated crop management along with the improvement of socio-economic and institutional issues are relevant for narrowing of the exploitable gaps in case 3.

· Agronomic gaps: due mainly to biological and partly physical constraints

· Socio-economic gaps: due mainly to socio-economic constraints

· Institutional gaps: due manily to institutional constraints

· Mixed gaps: due to a combination of the above constraints. In this case and in the previous two cases, the socio-economic and institutional constraints should be solved before the agronomic gaps can be narrowed using improved technological packages.

Integrated crop management can narrow agronomic yield gaps and at the same time help farmers to reduce wasteful resource utilization due to poor management of inputs, natural resources and other cultural practices and increase rice yield and farmers’ incomes. Precision crop management practices can be realized with the use of advanced technologies. Precise application of fertilizers, for example, can be done with the use of computer-aided systems. However, most of the resource-poor farmers cannot afford such systems. The technique of using the chlorophyll meter and leaf colour chart for field-specific N management, which has been tested by IRRI, could be suitable for these farmers.

Narrowing the yield gaps by improvement of crop management practices of small farmers in developing countries is often not an easy task. Although there are several improved crop management practices, their dissemination has proven to be more complicated than that of seed-based technologies. Crop management practices are seldom static and often must be adjusted to environmental factors, knowledge and market forces. Interactions between crop varieties and environmental conditions and crop management practices are well known. Also, factors such as inputs and output prices and employment opportunities affect farmers’ decision on the level of inputs to be applied and the time spent in crop management. The influence of market factors on farmers’ decision with regard to crop management practices will be increased, as the market will be more and more open under the General Agreement on Tariffs and Trade (GATT).

It is essential, therefore, that crop management practices should not be applied in isolation but be holistically integrated in Integrated Crop Management Packages (ICMPs) with flexibility for adjustment to fit to prevailing environmental, socio-economic and market factors. The development of ICMPs, which are similar to the Australian Ricecheck package, and their transfer could effectively assist farmers in many countries to narrow the yield gaps as well as to reduce rural poverty. The ideal ICMP, however, must aim to improve farmers’ knowledge not only on crop production and protection but also on the conservation of natural resources and market dynamics. This requires substantial improvement to the system of collection and dissemination of information on rice, its production factors, and its technologies as well as the modification of the extension systems in many countries.

Suitable improved varieties and improved cultural practices including integrated pest management and integrated plant nutrition management are, of course, the main components of ICMPs. A number of innovative technologies identified by CREMNET (Crop and Resource Management Network), IRRI, may provide effective tools to partly narrow yield gaps in rice production for small farmers in developing countries. CREMNET works on the chlorophyll meter technique, leaf colour chart for field-specific N management, urea tablet deep placement, direct wet-seeding method, stripper-harvest, low-cost in-stored dryer, etc. (IRRI, 1997) and is appropriate for inclusion in integrated crop management packages to narrow gaps in rice production in developing countries.

4.5. Deployment of New Technologies

Yield can be raised either by lifting the actual yield closer to the ceiling by improving crop management or by raising the ceiling itself. It is probable that the theoretical maximum rice yield is not very much different from the maximum yield of wheat of 20 t/ha per crop (Hanson et al 1982). The highest yields obtained at research level are only about 17 tons/ha per crop for hybrid rice, 15 t/ha for japonica high yielding varieties planted under a sub-tropical climate, and 10 t/ha for indica high yielding varieties planted under a tropical climate (Fig. 2). Hybrid rice is presently available for increasing the yield ceiling by 15-20 percent. The New Plant Type of rice, which has been developed by IRRI, may raise the present yield potential by 25-30 percent (Khush, 1995). Rice biotechnology, which has recently made considerable progress, may also provide an opportunity to increase rice yield in a more effective and sustainable manner.

Figure 2. Yield ladders at research level (Adapted from Hanson et al., 1982).

20,000 kg/ha	Hanson et al (1982) reported that the theoretical maximum yield for wheat is 20,000 kg/ha
17, 113 kg/ha	Yuan (1998) reported this yield of a 2-line hybrid variety Pei’ai 64S/Teqing planted on 0.10 ha at Yongsheng, Yunnan, China in 1992	The Climate at Yunnan, China is Sub-Tropical
14,700 kg/ha	Horie et al. (1994) reported this yield of a japonica variety YRL sown in an experiment on 21 October 1991 and harvested on 24 April 1992 in Riverina, Australia. The crop received 320 kg N/ha.	The Climate at Riverina, Australia is Sub-Tropical
11,070 kg/ha	Badawi (1998) reported this average yield of a japonica variety Giza 178 from 17 demonstration fields planted in the Lower Nile River Valley, Egypt in 1997	The Climate at Lower Nile River Valley is Sub-tropical
10,300 kg/ha	De Datta (1981) reported this yield of an indica line IR 8-288-3 planted during the dry season of 1996 at the experimental farm of the International Rice Research Institute at Los Banos, Laguna, Philippines. IR8-288-3 was later named as IR 8 by IRRI	The Climate at Los Banos, Laguna, Philippines is Tropical

4.6. Adequate Input and Farm Credit Supplies

Fertilizers, especially nitrogen, play an important role in rice production and productivity. Farmers need adequate amounts of fertilizer at the right time for obtaining high yield in rice cultivation. The supply of fertilizers needs to be decentralized to village markets and the quality of fertilizers should be assured. Small farmers are usually unable to buy sufficient quantities on time for application; hence the provision of village credit could greatly help them. The Bangladesh Grameen Bank is an interesting example of providing rural credit to landless and resource-poor farmers for developing countries. The loan proposals are received by the bank only on a group basis (at least 5 persons), focusing on technology loan, housing loan, joint loan and general loan (Dadhich, 1995). The principle of the Grameen bank could be deployed in other developing countries, of course with some modification for adaptable local conditions. The problems of credit and input supplies cannot be quickly resolved unless there is strong Government intervention. The issues of village credit and input supplies are being tackled where FAO and Governments are implementing Special Programmes for Food Security.

4.7. Research and Extension

The support of research and extension ensures the effective bridging of a yield gap of rice. Farmers’ adoption of the above-mentioned improved technologies depends on the capability of national agricultural research centres and extension services, which need more Government resources allocation and training.

Research should understand well farmers’ constraints to high rice productivity and provide them with appropriate technological packages for specific locations to bridge the gap under participatory approaches. The extension service should ensure that farmers use correctly and systematically recommended technological packages (ICMPs) in the rice fields, through effective training and demonstrations. For example, only relevant application of nitrogen fertilizers from seeding to heading, in terms of quantity and timing, will make significant contributions to narrow the yield gap of rice while avoiding unnecessary losses of nitrogen, which increase cost of production and pollute the environment.

5. CONCLUSIONS

Sustainable increased rice production in the near future requires substantial improvement in productivity and efficiency. Rice yield and production have considerably been increased during the last 30 years. In a number of countries, yields of rice in favourable ecologies have reached the research yield potential of the present generation of high yielding varieties. The use of innovative genetic improvement including hybrid rice, New Plant Type and possibly transgenic rice can increase the yield ceiling, where yield gaps are nearly closed. These increases not only enhance rice productivity but also efficiency in production systems, resulting in high economic outputs as well as high income for farmers.

On the other hand, in many countries, the gaps between yields at research stations and in farmers fields are still substantially large due to a combination of lack of initiatives, resources and goodwill to narrow them. In these countries, the integrated crop management approaches including available location-specific technologies coupled with active institutional support from Governments, particularly for input and village credit supplies, stronger research and extension linkages, can expedite the bridging of yield gaps; thus, improving the productivity and efficiency of rice production.

The causes of yield gaps of rice differ widely from season to season, country to country and/or even from location to location within a country or region and province. It is essential, therefore, to promote closer collaboration between research, extension, local authorities, non-governmental organizations (NGOs) and private sectors in order to identify specific constraints to high yield and adopt appropriate technologies and solutions, and take concerted actions to bridge yield gaps of rice, through participatory approaches. This will depend mainly on the will of Governments to 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.

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ANNEX 1

The Eight Key Factors or Checks in “Ricecheck”
an Integrated Crop Management Package for Rice Production Technology transfer to farmers in New South Wales, Australia.

·	1. Develop a good field layout with a landformed, even grade between well constructed banks of a minimum height of 40 cm (measured at the lowest point).
·	2. Use the recommended sowing dates.
·	3. Obtain good or economic weed control.
·	4. Establish a seedling population of 150 to 300 plants/square meter.
·	5. Achieve an optimum crop growth level at panicle initiation of 500-1100 shoots/square meter and tissue nitrogen content (as measured by near-infra red NIR) of 1.2 percent to 2.2 percent depending on variety.
·	6. Topdress nitrogen based on shoot count & NIR tissue analysis using the NIR tissue test.
·	7. Achieve an early pollen microspore water depth of 20 to 25 cm on the high side of each bay for rice varieties Amaroo, Bogan, Jarrah, Illabong, YRL34 and for rice varieties Doongara and 25cm for Pelde, YRF9 and Goolarah.
·	8. Harvest as soon as possible after physiological maturity when the grain first reaches 22 percent moisture.