BRIDGING THE RICE YIELD GAP IN CHINA - Zhu Defeng^*

^* China National Rice Research Institute, Hangzhou 310006, China.

Rice is the main staple food in China. About 60 percent of the population live on rice. Over the recent decade, rice has accounted for less than 30 percent of the grain area, but has contributed more than 40 percent of grain production with the highest yield in all grain crops and nearly 40 percent of calorie intake. Rice in China is an important component of rice in the world. Since 1980, the rice planting area in China has accounted for 23 percent of the world’s rice area, and contributed 37 percent of the world’s rice production. Therefore, rice production in China plays an important role for the Chinese people and also affects the world rice market.

Table 1 Rice Ecological Zone in China (Min. 1989)

Rice Ecological Zone	Proportion of Rice Area (%)	Proportion of Rice Production (%)	Accumulated Annual Temperature (>10°C)	Precipitation (mm)	Cropping System
1. South China, double rice cropping region	17.7	15.7	5800-9300	1200-2500	Three maturing, 73.5% of double rice.
2. Central China, double and single rice cropping region	68.1	69.9	4500-6500	800-2000	Two or three maturing, 40% of double rice and 60% of single rice.
3. Southwestern plateau region of single and double rice cropping	7.8	7.6	2900-3000	800-1400	Two maturing, 93% of single rice and 7% of double rice.
4. North China, single rice cropping region	3.3	3.4	4000-5000	580-1000	One or two maturing, single rice.
5. Northeast China, early maturing and single rice cropping region	2.6	2.9	2000-3700	350-1100	One maturing, single rice
6. Northwest China, single rice cropping region in dry areas	0.5	0.5	2000-4250	50-600	One maturing, single rice

Since much of China lies within the East Asia Monsoon zone, natural conditions such as sunshine, temperature and moisture suit the cultivation of rice. Wherever rainfall is abundant or irrigation facilities are available, there is rice production. It extends from 18° to 53° north latitudes. The main rice growing areas, with more than 90 percent of the total rice area and production, are south of the Qinling Mountains and the Huai River. Rice production areas in China are classified into six ecological zones according to natural environmental factors such as rainfall, temperature and cropping system (Table 1).

2. STATUS OF RICE CULTIVATION IN DIFFERENT ECO-SYSTEMS

2.1 Area, Production and Yield Trends in Different Ecologies

Over recent decades, the rice planting area has varied within a relatively small range. In comparison with the 1949 rice area, the rice cultivated area in 1976, which was the largest, only increased by 4.1 percent. However, yield and production of rice in China varied over a larger range. Highest yield in 1997 increased by 234 percent over the yield in 1949. Production in 1997 increased by 313 percent over 1949 (Figure 1).

Figure 1. Change in Rice Planting Area, Yield and Production in China (Ministry of Agriculture, 1949-1998)

In this period, rice production is related to yield (Figure 1 and Table 2). However, the rice area has been decreasing from the 1970’s. Average annual increase rate of rice yield and production decreased from the 1960’s to 1990’s (Table 2) due to environmental, technical and socio-economic constraints. This indicates there is difficulty in raising yield and production over the level of high yield obtained at present.

Table 2. Rice Area, Yield and Production and Average Annual Increase Rate of Yield and Production during the Period of 1960’s-1990’s.

Year	Area kg/ha	Yield kg/ha	Production kg/t	Average Annual Increase Rate of Yield (%)	Average Annual Increase Rate of Production (%)
60’s	29125.4	2769	79920	3.3	3.7
70’s	34865.0	3571	124437	3.3	4.4
80’s	32763.8	5073	166103	2.9	2.6
90’s	31523.5	5949	187503	1.5	1.2

Among the contributions of the increase of area and yield to production, 60-85 percent of the increase of production is due to the increase in yield (Zhu, 1997). With the decrease in rice producing area, which resulted from the basic construction and the adjustment of agricultural production infrastructure, and limited area for expansion, increase of yield has assumed the important role in maintaining and raising rice production in China.

Variation of area is related to the reform and adjustment of rice cropping systems. In the 1950’s, rice cropping systems were reformed into multiple cropping systems, which changed single rice to double rice, intercropped rice to continuous rice and Indica to Japonica in late rice in the south of China. At the same time, irrigation systems were improved. This made it possible for some upland to be converted to rice lands. These activities stimulated the rice area to expand to 33m ha in 1956 (Zhu, 1982). At the end of the 1950’s, the rice area decreased through the adjustment of unsuitable double rice areas. In the 1960’s, however, the double rice area developed gradually but in the 1970’s, the double rice area expanded rapidly with the popularization of short growth duration varieties. In 1976, the double rice area occupied 71.3 percent of the total national rice planting area. From the end of the 1970’s to current times, the double rice area has shrunk and single the rice area has increased, mainly due to economic constraints and the development of diversified cropping systems (Table 3).

Table 3. Yield of Various Rice Monoculture Production and Rice Cropping Systems in China

Year	Percentage of Area to Various Rice Seasons (%)			Yield (t/ha)
	Early Rice	Single Rice	Late Rice	Early Rice	Single Rice	Late Rice
1964	27	49	24	2.67	3.15	2.27
1978	38	25	37	4.17	4.66	3.24
1985	32	35	33	5.10	5.96	4.65
1990	28	42	30	5.49	6.50	5.18
1995	27	41	33	5.15	6.74	5.87
1997	26	46	28	5.61	7.17	5.58

Popularization of dwarf varieties at the end of the 1950’s in farmers’ fields and commercial use of hybrid rice at the end of the 1970’s resulted in a quantum jump of yield, which is called as the ‘two-time breakthrough’ in rice yield in the history of rice production, making the greatest contribution to rice production in China.

In China, irrigated rice is the primary rice ecosystem occupying 93 percent of the total rice area and 96.5 percent of total rice production. Rainfed lowland rice and upland rice stand at 5 and 2 percent of total rice area, respectively and 2.6 and 0.9 percent of total production due to low yields (Table 4).

Table 4. Rice Area, Yield and Production by Ecosystem in 1991

Ecosystem	Area ha	Yield kg/ha	Production kg/ha
Irrigated rice	30783	5.9	180830
Rainfed lowland rice	1655	3.0	4965
Upland rice	662	2.5	1655
Flood-prone rice	0	0	0
Total	33100	5.7	187450

Upland rice is mainly scattered in the mountain regions, such as Yunnan, Guizhou, Guangxi, Jiangxi, etc. Rainfed lowland rice is mainly distributed in the water limited areas, such as Hebei, Henan, Shangdong, Shaaxi, Liaoning, Jinlin, Heilongjiang, etc.

Yunnan is one of the main areas where upland rice is planted. In the recent decade the upland rice area in Yunnan province is static due to the limitation of low yield (Table 5).

Table 5. Area and Yield of Upland Rice in Yunnan Province (Jiang, 1994)

Year	Area kg/ha	Yield t/ha
1953 1963 1982 1983	37.2 82.5 165.9 180.2	0.80 1.44 1.81 1.81

2.2 Production Constraints in Different Ecologies

Lin (1996) analyzed yield gap between actual farmer yield and potential farmer yield under favourable conditions based on the information obtained from the prefectural agricultural bureau survey. In analyzing factors contributing to yield difference, varieties are taken as indicators. Yield difference can be explained by socio-economic and technical constraints. In the analysis technical constraints were classified into four categories: adverse soils, adverse weather, pests and others. Percentage of contribution of constraints to yield difference from survey data is summarized in Table 6.

Table 6. Percentage of Contributions of Constraints to Yield Difference (%)

		Early Rice	Late Rice	Single Rice
Yield difference		100.0	100.0	100.0
Technical constraints		44.9	40.7	43.1
	Soils	22.7	20.0	18.7
	Pests	4.2	3.4	5.3
	Weather	15.7	15.0	16.4
	Other	2.3	2.3	2.7
Unexplained		55.1	59.3	56.9

Average losses in the nation as a whole attributed to those identified constraints are 44.9 percent of yield difference for early rice, 40.7 percent for late rice and 43.1 percent for single rice. The balance of yield difference is caused by factors not listed, such as seed impurity, seed regression, bad management, poor extension services, etc.

Among yield losses, the soil-related, weather-related, and pest constraints can be subdivided into more detailed factors.

Table 7 lists the estimated percentages of yield losses at the national level from 20 major individual technical constraints. For early rice, adverse soil, adverse weather and pests contributed 48.8, 28.8 and 8.4 percent, respectively; for late rice, adverse soil, adverse weather and pests contributed 47.4, 32.3 and 6.5 percent, respectively; and for single rice, adverse soil, adverse weather and pests contributed 40.7, 34.5 and 8.5 percent, respectively.

From Table 7, it is evident that the more important technical constraints are deficiencies in nitrogen, phosphorus, potassium, soil organic matter content and trace elements. This reflects that in the long history of intensive cropping of rice, soil fertility has been depleted and cannot be recovered by natural processes. The highly fertilizer responsive varieties give high yield by increasing the fertilizer application, but the efficiency of the increase of yield by the application of fertilizer in farmers’ fields decreased.

The second most important factor of yield losses is related to weather, including drought, submergence, cold and heat. Lodging caused by wind and storm is also important. Among the various pests, sheath blight, weeds, striped stem borer and blast are listed.

Table 7. The Top 20 Constraints at the National Level and Percentage of Yield Losses Contributed by them

Early Rice	Yield Loss (%)	Late Rice	Yield Loss (%)	Single Rice	Yield Loss (%)
Potassium deficiency	12.6	Potassium deficiency	14.9	Organic matter deficiency	7.5
Phosphorus deficiency	7.8	Cold at flowering period	8.3	Cold waterlogged soil	7.2
Nitrogen deficiency	6.3	Nitrogen deficiency	7.1	Nitrogen deficiency	7.1
Cold waterlogged soil	6.0	Drought at flowering period	6.8	Phosphorus deficiency	6.8
Organic matter deficiency	5.9	Phosphorus deficiency	6.4	Potassium deficiency	6.5
Cold at seedling period	5.5	Organic matter deficiency	6.2	Flood	6.2
Flood	4.3	Drought at vegetative period	5.1	Drought at flowering period	5.6
Acidity	4.1	Cold waterlogged soil	4.5	Drought at vegetative period	4.8
Trace elements deficiency	3.6	Flood	4.4	Trace elements deficiency	3.7
Drought at flowering period	3.3	Acidity	3.5	Cold at flowering period	3.5
Sheath blight	3.2	Trace elements deficiency	3.5	Submergence at flowering period	2.9
Heat at flowering period	3.1	Sheath blight	2.2	Rain at harvest	2.7
Lodging from wind and storm	3.0	Weeds	1.8	Drought at seedling period	2.7
Submergence at flowering period	2.8	Lodging from wind and storm	2.4	Sheath blight	2.7
Drought at vegetative period	2.7	Submergence at vegetative period	1.5	Weeds	2.6
Swamp soil	2.5	Swamp soil	1.4	Cold at seedling period	2.1
Cold at vegetative period	2.2	Submergence at seedling period	1.3	Acidity	1.9
Rain at harvest	2.0	Submergence at flowering period	1.3	Rats	1.7
Rice blast	1.6	Drought at seedling period	1.2	Striped stemborer	1.6
Weeds	1.6	Rats	1.2	Lodging from wind and storm	1.5
Other	16.0	Other	15.0	Other	18.9
Total	100.0		100.0		100.0

Rainfed lowland and upland rice

Few research institutes are involved in upland and rainfed lowland rice research. Most varieties used in those rice ecosystems are improved varieties and varieties introduced from other countries. Yield of upland and rainfed rice varies with the available water. Therefore water is a main constraint to yield. New varieties with high yield, resistance to disease, especially blast, to drought and good quality are needed.

Most upland rice fields are located in the hilly and mountain areas. Low soil fertility influences the growth and yield. Serious soil erosion makes the soils poor for rice.

Blast is one of the main diseases. Due to the low water level in rice fields, weed control is a problem.

2.2.2 Irrigated rice

Low economic efficiency and transfer of labour

Low profit from rice production affects the enthusiasm of farmers engaged in rice production. Labour cost occupies about 50 percent of cost of production. Due to the high input of labour for transplanting rice, farmers are willing to select a planting method that uses less labour, such as seedling broadcasting and direct rice seeding (Table 8).

Table 8. Cost and profit of different planting methods in rice production in Zhejiang, 1995

Season	Planting method	Cost Yuan/ha	Output Yuan/ha	Profit Yuan/ha
Early rice	Transplanting by hand	5475	9225	3750
	Seedling broadcasting	4410	9825	5415
	Direct seeded	4605	10095	5490
Late rice	Transplanting by hand	5675	11304	5630
	Seedling broadcasting	5067	12296	7229

Rural labour has been transferred from agriculture to rural industry, construction and urban activities. Input of labour to rice growing has decreased gradually over the recent decade. The share of rural labour engaged in agriculture decreased from 91.6 percent in 1980 to 70.6 percent in 1997. In some regions, women carry out most of the work in rice production.

Insufficient investment

The Chinese government has made great efforts to increase investment in agriculture. However, it is still far from the actual demand. Low yielding fields that comprise about 25 percent of the total are difficult to improve due to the limited investment.

Due to low profit in rice production, farmers in some regions are unwilling to invest in rice production.

Small-scale farmer structure

The agriculture sector in China has small-scale farms with an average farm size of 0.5-1.0 ha. In the south, where more than 90 percent of rice is produced, farm sizes are smaller. In Zhejiang province where rice area and production occupy 85 percent and 92 percent of provincial grain area and production, there were only 60 thousand farms that averaged more than 0.67 ha of land in 1995. Those farms only account for 6.1 percent of the provincial arable area. The study indicates that when the size of farm is lower than 2 ha, with the increase in farm size, production costs decrease and profits tend to increase.

Climate

Due to heavy population pressure land unsuitable for cropping has been exploited for grain production in many areas. This damages the ecological equilibrium. Floods often occur with uneven distribution of rainfall in the main rice producing areas which cause serious yield losses. In the coastal area typhoons cause lodging of rice, which also result in yield losses. In the ripening period of early rice in the south, continuous rain results in the germination of seed on the panicles in the field which affects yield and quality.

In the south, low temperature at the seedling stage causes the death of seedlings and reduction in spikelet fertility during the flowering period.

In regions with poor irrigation systems drought affects rice growth. If drought occurs at the time of panicle initiation, damage to yield is serious.

Soil

Deficiency in nitrogen, potassium, phosphorus, trace elements and organic matter can be found in rice fields. In recent decades less manure has been used in rice production. Heavy chemical fertilizer application was used in most areas in the main rice producing regions. This has affected negatively the soil structure and fertility, and resulted in rice yield decline in some locations, especially in areas with continuous rice cropping systems.

In low yielding fields, low temperature in soil water, waterlogged soils, acid soils, saline and alkaline soils are critical problems.

Pests

Sheath blight, blast and leaf blight are major diseases. Stem borer, plant hopper and striped stemborer are economically important insects in rice production.

Weeds still reduce yield due to poor weed control and misuse of herbicides.

2.3 Yield potential of released varieties/hybrids in different ecologies

Many varieties and hybrids with high yield, good quality and resistance to diseases and insects are released at the national, provincial and district level. Some of the varieties can be popularized on a large scale and some will disappear at the farmer level due to problems of yield, quality, resistance to pests and adaptation to cropping systems. Rice varieties and hybrids released at the national level in 1998 are listed in Table 9. Most of varieties give more than 5 percent of yield increase over the local check. On an average, new varieties give yield increases in excess of 7.1 percent.

In the southern region testing programme of new bred varieties, some elite varieties and hybrids give yield increases of 3.4 to 21.3 percent over local checks.

Table 9. Rice Varieties and Hybrids Released for Irrigated Ecosystems by the Ministry of Agriculture in 1998

Variety	Type	Yield kg/ha	Percentage of Increase in Yield Over Local Check (%)
Zhongyouzao 5	Early indica	5830-6176	5.6
Yujing 6	Japonica	9482	13.6
Zhongzuo 93	Japonica	6630-7475	3.2
Liaongyan 283	Japonica
Shanyou 77	Indica hybrid	7559	8.0
Zhongzao 1	Early indica	600-6750
Zhongsi 2	Early indica	5700	7.3
Kyou 402	Indica hybrid	7593	10.4
Gongyou 22	Indica hybrid	8807	6.3
Shanyouduoxi 1	Indica hybrid	8723	3.5
Xieyou 57	Indica hybrid	8474	5.8

2.3 Evidence of yield gaps in different ecologies

According to the work done at IRRI and China (IRRI, 1977, De Datta, 1978 and Lin, 1996), the yield gap can been divided into two parts. Yield Gap 1 is the difference between an attainable yield and actual farmer yield that is listed in the statistics. Yield Gap 2 is the difference between an experimental maximum yield that is obtained in the high yielding experiments carried out under the advice and support of rice specialists and scientists (Huang, 1996, Li, 1995, Tan, 1989, Xu, 1994 and Xu, 1996), and an attainable yield under the adaptive trials and good management in farmers’ fields. Attainable yield is from an average yield of high yielding varieties in new bred variety tests in the multi-location trials in the different regions. National maximum yield is calculated from farmer yield multiplied by the average increase rate of provincial maximum yield compared to provincial farmer yield in the main rice producing regions. National attainable yield is calculated through farmer yield multiplied by the average increase rate of provincial attainable yield to provincial farmer yield in the main rice producing regions.

The attainable yield is 6,967 kg/ha for early season, 8,653 kg/ha for single season and 7,653 kg/ha for late rice. The maximum yield is 9,830 kg/ha for early season, 11,555 kg/ha for single season and 9,498 kg/ha for late rice. Yield of single season rice is usually higher than early and late rice due to long growth duration and suitable temperature and sunshine (Table 3).

Yield Gap 1 and Yield Gap 2 for nation as a whole is listed in Table 10. Yield Gap 1 is 1,358 kg/ha for early rice, 1,487 kg/ha for single rice, and 2,074 kg/ha for late rice; while Yield Gap 2 is 2,863 kg/ha for early rice, 2,903 kg/ha for single rice, and 1,845 kg/ha for late rice. From the comparison of Yield Gap 1 and Yield Gap 2, the transferable Yield Gap 1 is much larger than non-transferable Yield Gap 2 for early rice and single rice. Yield Gap 1 is caused by technological and sociological constraints. Yield Gap 2 arises from differences in the varieties and production environment, which cannot be easily managed or eliminated.

Table 10. Farmer Yield, Attainable Yield, Maximum Yield (kg/ha) and Yield Gap in Various Seasons

Yield	Early rice	Single rice	Late rice
Farmer yield	5609	7166	5579
Attainable yield	6967	8653	7653
Maximum yield	9830	11555	9498
Yield Gap 1	1358	1487	2074
Yield Gap 2	2863	2903	1845

In the last two decades, rice yield in China increased from 4.25 t/ha in 1979 to 6.32 t/ha in 1997. However, coefficient of variation for yield among provinces decreased from 1979 (Figure 2). This indicates that the yield gap among provinces has shrunk in recent years.

Figure 2. Change of rice average yield and coefficient of variation of yield among province.

3. PROGRAMME FOR NARROWING THE YIELD GAPS

3.1 Historical Perspective

After the People’s Republic was founded, land reform was carried out throughout China. By 1956, agricultural cooperatives were set up all over the country, boosting the development of agriculture, including rice production. However, the excessively large scale of the agricultural production units and un-enlightened management affected the development of agricultural production adversely. In 1979 a series of reforms were carried on a system of contracted household responsibility that links remuneration to output based on the collective economy, thus greatly arousing the enthusiasm of farmers. This has greatly contributed to a sharp and sustained increase in rice production since the 1980’s.

The state has helped farmers improve conditions for production by investing in capital construction works in farmlands. As a result of decades of work, the national area under effective irrigation has expanded from 18.5 percent of the total cultivated area in 1952 to 45.5 percent, with all rice fields having irrigation facilities. The level of farm mechanization rose sharply during the same period. All these played an important role in guaranteeing a steady increasing yield for rice production.

The development of the chemical industry has increased the application of chemical fertilizers in rice production. The average per hectare application of chemical fertilizer for 1983 was 65.5 kg in terms of pure nutrients.

Efforts have been made to reform cropping systems and raise the multiple cropping index. In expanding the multiple cropping area, much effort was made to popularize rice varieties with different growth duration and introduce a series of relevant management technologies such as close planting and scientific application of fertilizer. Thus, the steady increase of rice yield was assured. At this time, a national network for rice breeding, testing, producing and disseminating semi-dwarf rice varieties was set up. Those varieties have fertilizer-responsive and lodging-resistant characteristics and show high yield potential.

The successful application and popularization of hybrid rice at the end of the 1970’s marked another important breakthrough in China’s rice production. In 1976 hybrid rice was popularized in rice production in the farmers’ fields. Hybrid rice normally yields 15 percent more than inbred. Subsequently, the area sown to hybrid rice expanded rapidly until it occupied 54 percent of the total rice planting area in 1997 (Table 11).

Table 11. Area and Yield of Hybrid in China

Year	Percentage of area sown to hybrid (%)	Yield (t/ha)
1976	0.4
1978	12.6
1982	17.0	5.90
1986	27.9	6.60
1990	41.2	6.68
1997	54.5	7.03

3.2 Activities and results of programmes to narrow yield gaps during the last two decades.

· Poverty relief by deployment of science and technology innovations

China has set up a programme to organize scientists to help undeveloped regions improve rice production. In undeveloped regions there are one or more factors that limit rice growth, including poor technology of rice cultivation and lack of information. Rice yield is usually substantially lower than in developed regions. Through the programme, high yielding varieties and new technologies on rice cultivation are popularized. Local extension workers and farmers are trained, while the rice yield potential in the area is exploited.

From 1987 to 1989, one group of rice scientists was sent to the rice growing areas of Hunan, Sichuan and Guizhou (Wulin region) to popularize new varieties and cultivation technologies. Through the popularization of new hybrids, improvement in seedling raising, adjustment of transplanting spacing, improvement in fertilizer application, and water management and pest control, the rice yield was increased by more than 30 percent in these areas.

· Agricultural bumper harvests

This programme bridges research and production, and stimulates the popularization of research achievements. Since 1986, many grain crop varieties and new technologies, including rice varieties and cultivation technologies have been popularized. At the same time the extension system has been strengthened and farmers have been trained. From 1986 to 1996, the grain increased by more than 30 billion kg through the realization of the programme activities.

· Basic agricultural construction and integrated agricultural development

The Chinese government has focused on agricultural infrastructure development and soil conservation. Since the 1950’s, irrigation and drainage systems in rice production areas have been improved. That makes possible the expansion of the rice area and the realization of a stable and high yield in areas under various environments. In recent years, high yielding rice producing areas have been developed which transformed some mediocre yielding rice fields into more productive farms.

· Agricultural jump

The 1998 plan on agricultural jump aims to integrate the suitable varieties and technology in rice production, and to formulate and popularize the package technology. The programme will accelerate the popularization of new varieties and new technology on rice production.

· Scientific research programme

A series of varieties and hybrids were bred in support of this programme. New bred varieties and hybrids gave higher yield potential. At the same time, a package of cultivation practices for new varieties and hybrids made it possible to achieve the yield potential of these varieties and hybrids at farm level.

3.3 Issues and Challenges in Narrowing the Rice Yield Gap in the Country

· Soil problems in the low and medium yielding area

There are several soil problems in the low yielding and medium yielding areas. In comparison with high yielding fields, fertility is slightly low in the medium yielding fields. Rice yield in these farms can be raised through the application of improved technologies such as selection of a suitable variety, a rational cropping system, and improved management and the increase of inputs. However, in the low yielding fields, some soil problems such as waterlogging, drought, cold water, acidity and low fertility, etc. need improvement. In such fields, rice yields can be raised through the improvement of soil structure and irrigation and drainage systems in combination with cultivation technologies.

· Farmer interest and technology

Low efficiency in rice production affects farmer’s enthusiasm towards rice production. Transfer of rural labour has increased from agriculture to rural industry and cities in recent years. Due to low input of labour in rice production, management of rice fields is poor and consequently results in poor yields. The new generation of rice farmers lack the necessary technology for rice production. Training on rice production is therefore necessary for the new generation of farmers.

· Direction of scientific research

In recent years most of the funds for scientific research on rice flows to biotechnology. Less funds to support research on agronomy affects adversely the role of agronomy in rice production. Research on agronomy has lagged behind farmers’ needs. Some practical problems in rice production that concern farmers need to be solved through agronomic research.

· Environmental protection

In recent years, heavy use of chemical fertilizers and pesticides in rice fields is polluting the environment in the field and water systems. Remaining herbicide in rice fields restrains rice growth and emergence of tillers in the early stage. Heavy use of chemical fertilizer destroys soil structure. Efficiency of the increase of yield through nitrogen application decreases in rice production and endangers the environment through leaching and volatilization.

4. CONCLUSIONS AND RECOMMENDATIONS

The average annual growth rate of rice production from 1961 to 1997 was 3.5 percent. Rice planting area decreased from 1976. Increase of rice production is related to yield increase. The main source of increase in rice production has been yield increase, which was made possible through use of modern varieties, cultivation technologies and use of more inputs.

Irrigated rice is the main type of rice ecosystem, accounting for 93 percent of the rice area and 95.5 percent of rice production. There are a few areas of rainfed rice in the limited water environments and upland rice in the mountain and hilly areas.

Low profit from rice production, which is partly caused by the small-scale farms, affects the enthusiasm of farmers who engage in rice production. Deficiency in nitrogen, phosphorus, potassium, trace elements and organic matter content in the soil are the main constraints. Low and high temperature during the various growth phases, flooding, lodging caused by wind and storm, and drought often threaten rice production. Sheath blight and blast are major diseases contributing to yield loss. Striped stemborer, plant hopper and stemborer are major insect pests.

The yield gap between actual farmer yield and attainable yield is 1,358 kg/ha for early rice, 1,487 kg/ha for single rice and 2,074 kg/ha for late rice. Compared with actual farmer yield, attainable yield increased by 24 percent for early rice, 21 percent for single rice and 37 percent for late rice. New varieties and hybrids released can explain about 7.1 percent of yield difference. The improved cultivation technologies contributed 14 to 30 percent of yield difference between actual farmer yield and attainable yield.

To narrow the yield gap between actual farmer yield and attainable yield it is important that new varieties and hybrids and improved cultivation technologies are popularized in farmers’ fields. In the execution of the programme to narrow the yield gap, extension workers and farmers were trained, and information and technologies were transferred to rice growing areas. Scientific research programme will bridge the yield gap between attainable yield and maximum yield through the creation of a new generation of varieties and cultivation technologies.

To further narrow the yield gap between actual farmer yield and attainable yield, low yielding and medium yielding fields should be improved through research, use of suitable technologies and/or on-farm infrastructure improvements. Varieties and cultivation technologies to adapt to various biotic and abiotic stresses should be developed and popularized. Training should be emphasized on extension workers and farmers. International and domestic cooperation needs strengthening to exchange experience and technologies.

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