Rice cropping

Rice panicles with ripening grainRice is the staple food for more than half the world. In Asia alone, more than two billion people obtain over 60% of their calories from rice. It is the most rapidly growing source of food in Africa and is critical to food security. Rice-based production systems and the operations processing the grain for food employ nearly one billion people in rural areas of developing countries. About 80% of the world's rice is grown by smallholders in these places. In Asia, women are often left to conduct many of the rice farming tasks as men have moved to work in the cities. Efficient and productive rice-based production systems are essential for economic development and for improved quality of life for much of the world's population. For thousands of years, cultivating rice has meant that people have had to work together, and the need for standing water in rice farming has shaped the landscape. Festivals are dedicated to rice and the crop was considered divine by many ancient Asian emperors and kings. Even today, the Japanese refer to rice as their ‘mother’ and regard rice farmers as the guardians of their culture and countryside. The UN Food and Agriculture Organisation declared 2004 as the International Year of Rice. There were nine themes running through the activities in the International Year of Rice: culture, nutrition, agro-biodiversity


The variety of life in all its forms, levels and combinations. Includes ecosystem diversity, species diversity, and genetic diversity (IUCN, UNEP and WWF, 1991).

Authoritative On-line References and Resources

http://earthtrends.wri.org/ EarthTrends is a comprehensive online database, maintained by the World Resources Institute, that focuses on environmental, social, and economic trends. Statistics on biodiversity indicators are available.
, environment, livelihood, post-harvest processing, gender, science and economics.
Science has provided improved technologies which enable farmers to grow more rice on limited land with less water, labor and inputs, thereby reducing damage to the environment. Improved plant breeding, weed and pest control, water management and fertilization increase productivity and reduce costs of production. Protecting rice from weeds, pests and diseases is essential to avoiding heavy losses in yield and quality of grain. Weed control is usually most important. Paraquat is a non-selective


A chemical product used for eliminating all types of weeds (annual and perennial grasses and broadleaved weeds).

Authoritative On-line References and Resources

http://www.weeds.iastate.edu/ An invaluable source of contemporary information about herbicides and weeds from Iowa State University.
herbicide which, by its use in integrated weed management


A decision support system for crop protection which focuses on long-term prevention or suppression of pest problems with minimum impact on human health, the environment, and non-target organisms. IPM takes into consideration all available pest control techniques and tactics (cultural, mechanical, biological, chemical). IPM emphasizes the growth of healthy crops for better productivity with the least possible disruption to agroecosystems.

Authoritative On-line References and Resources

http://www.ipmcenters.org "The USDA's National Site for the Regional IPM Centers' Information System provides information about US commodities, pests and pest management practices, people and issues."
systems, can provide solutions to these weed control issues.

Paraquat is an essential tool for rice farmers

Paraquat is used to prepare the land for cultivating rice and on the bunds (levies) which surround paddy fields to retain the flood water. Paraquat is a broad spectrum, non-selective herbicide because its mode of action is to inhibit photosynthesis. This process is essential to plants and means that paraquat destroys all green tissue. A video showing paraquat’s unsurpassed speed of action can be viewed here. However, paraquat is immobilised and deactivated on contact with the soil meaning that there are no leaching


The natural process by which water soluble substances are carried downward through the soil into groundwater.
or root uptake problems to restrict its use. It can be sprayed to burndown weeds before planting a rice crop without risking damage to that crop or indeed subsequent crops in the rotation.
You can read more about paraquat’s unique soil properties here.

CASE STUDY: Long-Term Paddy Rice Trials in Japan

  Officially monitored long-term research in Japan has showed that paraquat does not enter crops and does not continually accumulate in the soil with repeated applications. The Japanese Association of PhytoRegulators (JAPR) oversaw field experiments with paraquat in Japan on three typical types of rice growing soil, lasting for up to 30 years. A normal rate of paraquat was applied every year to control weeds before planting rice and compared with traditional methods of mechanical weed control. After ten years the paraquat treatment in half of the treated area was stopped so that effects on soil residues could be monitored. No paraquat was taken up in to the rice crops and yields were the same regardless of weed control method. After paraquat application stopped, residues of the chemical in the soil declined significantly, showing that paraquat is degraded even under the anaerobic conditions in paddy soils for much of the growing season.
Before the introduction of paraquat, weed control in rice depended on plowing to bury weeds. In some regions this is still the case and the several rounds of plowing needed, with intervals between them, are time consuming, costly and labor intensive. As a broad spectrum herbicide, paraquat allowed the development of no-tillage (‘no-till’) systems. These systems do not rely on plowing to control weeds. Not disturbing the soil helps prevent erosion and maintains a healthy soil. Recent work suggests that the production of methane (a greenhouse gas more damaging than carbon dioxide) from plant material decaying in anaerobic conditions after burial is significantly reduced under no-till. Glyphosate is the main alternative non-selective herbicide, but its intensive use has caused new weed problems as species less well controlled have ‘shifted’ to become more dominant and troublesome. Some species have evolved biotypes which are resistant to glyphosate. Using paraquat as an alternative non-selective herbicide, with a different mode of action, in integrated weed management systems is helping to avoid problems of weed shifts


A change in the weed community within a field i.e. relative abundance or type of weeds. This can be the result of a management practice like herbicide use or any other phenomenon that brings about a change in weed species composition. Species or biotypes adapted to current weed management practices increase, whereas weeds susceptible to those practices decrease.

Authoritative On-line References and Resources

http://www.weeds.iastate.edu/mgmt/qtr00-1/popdyn.htm A classic article on weed population dynamics on the Iowa State University Weed Science website.
and resistance


The inherited ability of a plant/weed to survive a dose of a herbicide normally lethal to that species.

Authoritative On-line References and Resources

http://www.weedscience.org/in.asp The International Survey of Herbicide Resistant Weeds monitors the evolution of resistant species and assesses their impact. All confirmed instances of new cases are listed.
The importance of paraquat in fighting weed resistance to glyphosate and maintaining farmers’ options to use conservation tillage


Any tillage and planting system that covers 30 percent or more of the soil surface with crop residue after planting to reduce soil erosion by water.

Authoritative On-line References and Resources

Purdue University-based Conservation Technology Information Centre.
systems is discussed here.
Further details of paraquat’s safety to the environment, spray operators and consumers can be found by referring to the Paraquat Fact Sheet. You can read more about the benefits of using paraquat here

What is Rice?

Paddy riceRice is an annual grass typically growing 1-1.8 m tall. Shorter, higher yielding ‘semi-dwarf’ varieties were introduced during the ‘Green Revolution’ in the 1960s. The main species of cultivated rice is Oryza sativa. It is one of 23 species in the genus Oryza. Plants in this genus are tolerant to desert, hot, humid, flooded, dry and cool conditions, and grow in saline, alkaline and acidic soils. Oryza sativa originated in the humid tropics of Asia. One other member of the genus Oryza glaberrima, from West Africa, is the only other cultivated rice species. Asian rice has evolved into three eco-geographic races - indica, japonica and javanica. Within each of these races are distinctive varieties of rice which can be classified by their grain shape and texture. Long grain rices are typically of the indica race and include the fragrant Jasmine rice from Thailand and Basmati rice from India. Short grain rice, typically japonica, is usually more sticky than long grain and is favoured in Japan. Saki rice is grown in Japan to make rice wine, and in Indonesia there are red and black grained varieties. ‘Golden Rice’ is a new type of variety being developed which is genetically modified to produce more beta carotene which is needed in the diet as a precursor to viatmin A. In some regions of SE Asia and Africa vitamin A deficiency is a serious problem, responsible for over a million deaths and half a million cases of blindness each year, particularly in children and pregnant women.

Where is Rice Grown?

Rice:  Area harvested 2013 (FAO)Rice is one of the world’s top three most widely grown crops. At 165 million ha harvested in 2013, it is third to wheat (218 million ha) and maize (184 million ha) in area. In terms of grain production, at 746 million tonnes it exeeds wheat (713 million tonnes) and follows only maize (1016 million tonnes). Rice is grown in warm, wet climates, or ones with rainy seasons, all around the world, but the vast majority is grown in Asia. India and China grow far more hectares of rice than any other countries. Areas under rice have been growing fastest in SE Asia. Some harvest data for main producing countries are shown below.  The area of rice harvested in the world over the past decade has increased by 11%.  However, global production in 2013 was 27% more than in 1999 as the average yield of rice over the world increased by 29%.


Table 1. Rice production in leading countries in 2013 (FAO data).

  Area Harvested
(million ha)
Annual Production
(million t)
Average Yield
1 India  43.5 China  205.0 USA  8.6
2 China  30.2 India  159.2 S. Korea  6.8
3 Indonesia  13.8 Indonesia    71.3 China  6.7
4 Thailand  12.4 Bangladesh    51.5 Japan  6.7
5 Bangladesh   11 8 Vietnam    44.0 Vietnam  5.6
6 Vietnam    7.9 Thailand     38.8 Indonesia  5.2
7 Myanmar     7.5 Myanmar     28.0 Bangladesh  4.4
8 Philippines    4.7 Philippines    18.4 Philippines  3.9
9 Pakistan    2.8 Brazil    11.8 Sri Lanka  3.9
10 Brazil    2.3 Japan    10.8 Myanmar  3.7

How is rice grown?

Transplanting rice in IndonesiaThe systems used for growing rice are perhaps more diverse than for any other crop. Some more sophisticated systems, such as in Japan where growing is technologically advanced, but on a small scale by part-time farmers, are quite complex. In more temperate areas, only one crop can be grown each year, being planted in the spring and harvested in early autumn. In tropical regions, two or more crops can be grown every year. For example, in the Mekong Delta in Vietnam, three crops are grown and in China four harvests have been gathered. Two main systems are based on whether the crop is submerged in a flooded field, or paddy, or grown like other cereals on dry land. The latter is often known as upland rice and confined to less developed regions, especially in Africa and Latin America. Paddy rice accounts for over 85% of the area grown and over 95% of rice production. Flooded rice depends on rain or irrigation. Soils are usually clays and often compacted to retain water. In some systems the soil is cultivated when wet, in others the fields are not flooded until the rice is well established. In Bangladesh, deep water rice is grown where the ears, or panicles, float on the top of stems which may be up to 5 m long. Rice is adapted to grow submerged by having a specialised tissue which allows air to reach the roots. Flooded rice is higher yielding because the crop transpires a lot of water in hot climates; because the pH of a flooded soil makes some mineral nutrients more available; and because many weeds are controlled by flooding. Aquatic weeds, however, can be problematic. Another key difference between growing systems is how the crop is established. In most of Asia, rice seedlings are transplanted in to paddies when they have two or three leaves. The transplants are raised from seed in nurseries. In larger scale systems, the crop is direct seeded by drilling as any other cereal into dry land before flooding; or seed, often pre-germinated, is scattered on to the flooded paddy. In California, for example, flooded fields are seeded by air. On smaller scales in the Eastern Hemisphere, preparing rice paddies is very labor intensive. Fields have to be cultivated to kill weeds and ensure the soil will allow water to percolate only slowly; the levies, or bunds, bordering the fields to retain the water have to be maintained; and the fields have to be irrigated and the rice transplanted. Often paddies are flooded and drained several times before a final draining before harvest. This is to manage the growth of the crop, eg to encourage tillering or discourage excessive stem elongation.

Protecting Rice Crops

Rice crops need protecting from weeds, pests and diseases to produce the best yields and quality of grain.


Insect pests of rice

  • Defoliators lay eggs on rice leaves which are eaten by larvae when they hatch. Various flies (Diptera) and butterflies and moths (Lepidoptera) are defoliators. Later in development, adults and nymphs of beetles (Coleoptera) and thrips (Thysanoptera) feed on leaves. Grasshoppers (Orthoptera) can also be a problem.
  • Sap feeders have needle-like mouth parts which they use to suck sap from rice shoots. Leafhoppers and planthoppers (Hemiptera) are widespread pests.
  • Stem borers are the destructive larvae of otherwise harmless butterflies and moths. They burrow in stems causing ‘dead heart’ symptoms in younger shoots and ‘whiteheads’ in older plants in which the ears have failed to fill with grain.
  • Root feeders live in the soil and include crickets (Orthoptera) and beetles.
A vast number of insect pests can cause enormous damage to rice crops if not controlled. The general types are described here, but for further details visit the International Rice Research Institute (IRRI) webpages: Nematodes can also be significant pests. These includes species of Meloidogyne, Aphelenchoides and Ditylenchus


Growing in warm and wet environments, rice is very susceptible to diseases caused by many fungi, bacteria and viruses. A useful source of diagnostic information to identify rice diseases can be found at the IRRI Rice Doctor webpages Major fungal diseases are the blasts and blights. Leaf blast is caused by Pyricularia oryzae; seedling and sheath blights are caused by Rhizoctonia solani amongst other species. An important bacterial disease is the blight caused by Xanthomonas oryzae pv. oryzae. Perhaps the most infamous viral disease is tungro which causes severe stunting, reduced tillering and poorly filled grains.

Weeds and Integrated Weed Management

Weeds can reduce the yield and quality of rice by competing with the crop for light, nutrients and space; and their seeds can contaminate the harvested grain. Numerous species of grasses


The leaves are "narrow" as opposed to the "broad" leaves of broadleaved weeds. Also called 'monocots' having one seed leaf opposed to 'dicots' having two seed leaves.

Authoritative On-line References and Resources

The International Weed Science Society represents individual associations around the world. 
, broadleaved weeds


The leaves are "broad" as opposed to the "narrow" leaves of grasses. Also called 'dicots' having two seed leaves, while grasses are 'monocots' having one seed leaf.

Authoritative On-line References and Resources

http://www.iwss.info The International Weed Science Society.
and sedges need to be controlled. Some of the most widespread and aggressive weeds are the Echinochloa species (barnyardgrass). Infestations of only ten of these weeds per square metre have been recorded to reduce yields by 25%. Also difficult to control is red rice which is the same species as commercial varieties. Cyperus rotundus is a sedge which has been called ‘the world’s worst weed’
Controlling weeds can cost a lot of money, time and effort, often all in scarce supply. Competitive weeds must not be permitted to set seed as this will contaminate the land for years to come. Apart from directly affecting the crop, weeds can block irrigation channels making water management difficult. Allowing weeds to grow unchecked in and around rice fields (ie on paddy bunds) can attract insect pests and rodents, and act as hosts for diseases. However, a managed vegetative cover is important to give structure and stability to the soil, helping to prevent erosion, and providing a habitat for beneficial flora and fauna. In developing countries, weeds are controlled typically by cultural methods including ploughing and flooding the paddies. In upland rice, crops are weeded by hand and hoeing. Herbicides are used in more advanced cropping systems. They are applied in relation to the state of weeds, crop and paddy: pre- or post-emergence of the weeds or direct seeded crop; pre- or post-transplanting; and pre- or post-flooding. This is according to their mode of action, properties in soil and water, and selectivity to rice. Paddy riceChemical methods of weed control are best used in a system of integrated weed management in which cultural methods are also important. Weeds are most competitive when the crop is small. So, controlling weeds when preparing the land for a rice crop is essential. Weed seed should be allowed to germinate and then killed before flooding or drilling the crop. Plowing is traditionally used to bury weeds, but this is laborious and costly. Non-selective herbicides


A chemical product used for eliminating certain types of weeds only (ie either grasses or broadleaved weeds) and not affecting specified crops.

Authoritative On-line References and Resources

http://www.weeds.iastate.edu/ An invaluable source of contemporary information about herbicides and weeds from Iowa State University.
which control a broad spectrum of weeds can be used.
Herbicides like paraquat and glyphosate have no residual activity in the soil and do not affect the rice crop. Glyphosate gives good control of perennial weeds


Weeds that return year after year. Some die back in the winter but their roots remain alive and shoots reappear in spring; some don't die back and grow in size and stature the next season.

Authoritative On-line References and Resources

The International Weed Science Society represents individual associations around the world.
, but its intensive use can lead to adverse changes in the weed flora towards more aggressive broadleaved weeds, and even cases of weed resistance to glyphosate are arising. Paraquat can provide the alternative means of effective and sustainable weed control.
Water management is also an effective method of weed control. A permanent flood of at least 5 cm depth is best maintained between transplanting and when a full crop canopy has developed to smother out any weeds.  

CASE STUDY: Paraquat and Tidal Rice in Indonesia

Using paraquat to control weeds in tidal rice areas of Indonesia is enabling improvements in rice yields by saving time and making family labour go further. Read more … 

CASE STUDY: Paraquat in West Bengal

Using paraquat to control weeds between rice crops in West Bengal saves the need and cost of ploughing paddies several times, and makes time to grow a third crop. Read more

CASE STUDY: Paraquat Helps ‘Revolutionary’ Rice Technique Take Hold in West Bengal

Paraquat has helped the development of a simple, yet effective planting technique which when all are combined in a no-till system have benefits throughout the rotation. Read more … 

CASE STUDY: Chinese Villagers Sing the Praises of Paraquat in No-Till

Using paraquat for weed control in Sichuan province has enabled farmers to increase the yield and profitability of rice grown in the rainy season. Read more  

References & Resources

International Rice Research Institute (IRRI) UN FAO Year of Rice United Nations Food and Agriculture Organisation FAOSTAT International Rice Research Institute’s Rice Knowledge Bank: US National Information System for the Regional IPM Centers