Rice (Revised)

General Information and Agronomic Aspects

Introduction 

Oryza sativa (Rice) also known as the Asian rice is a species of annual grass in the grass family Poaceae and the genus oryza. The Oryza genus consists of more than 20 species, two of which are cultivated: common rice (O. sativa) and African rice (O. glaberrima).

Rice is believed to have originated in Asia, most likely in the region encompassing present-day China and India. From there, it spread across the continents through trade and agricultural practices. Today, it is cultivated in a wide range of climates, making it one of the most extensively distributed crops worldwide.
Rice thrives in warm, tropical and subtropical regions, where it can grow both in flooded fields (paddy or lowland rice) and on well-drained uplands (upland rice). It is a water-dependent crop, with paddy rice requiring standing water during parts of its growth cycle.
As a staple food, rice provides a major source of dietary energy for billions of people around the world. The grain is consumed in various forms, such as boiled rice, fried rice, rice cakes, and rice noodles, making it a versatile ingredient in countless dishes. Apart from its significance as a food crop, rice plays a vital role in cultural traditions, ceremonies, and rituals in many Asian societies. It is also used in traditional medicine and in the production of alcoholic beverages like sake in Japan.

Rice is primarily a source of carbohydrates, particularly starch, which provides a readily available source of energy. It is low in fat and contains essential nutrients, including protein, B-complex vitamins, and minerals such as iron and manganese. Brown rice, with its bran intact, is more nutritious, containing fiber and additional vitamins and minerals compared to polished white rice.

The rice industry has seen significant value addition over the years, with the production of processed rice products like rice flour, rice bran oil, and rice-based snacks becoming popular.
In the global market, key producers and exporters of rice include countries like China, India, Thailand, Vietnam, and the United States. Africa is also a significant player in the rice market, with countries like Nigeria, Egypt, and Senegal being major producers and consumers within the continent.
(Meertens, H.C.C., 2006, Rokni, 2013, OECD, 2004, OECD, 1999).

Uses

Rice is cultivated primarily for the grain, which is a main staple food in many countries, especially in Asia. In Kenya it is becoming increasingly popular, especially in urban centres. From 2010 to 2014, Kenya had a yearly production of about 119,000 metric tons (FAOSTAT, 2014).  Consumption of wheat has been on a steady increase from 410,000 metric tons in 2010 to 564,000 metric tons in 2014 (Economic Review of Agriculture, 2015). This increase in demand and the development of new upland varieties have created an opportunity for farmers to venture into rice growing. 

Rice will give the same or better yield as maize and fetch the double price on the market at harvest time. Grains are quite nutritious when not polished. Common or starchy types are used in various dishes, cakes, soups, pastries, breakfast foods, and starch pastes; glutinous types, containing a sugary material instead of starch, are used in the Orient for special purposes as sweetmeats. Grain is also used to make rice wine, "Saki", much consumed in Japan. Rice hulls are sometimes used in the production of purified alpha cellulose and furfural (an industrial chemical derived from a variety of agricultural by-products, and commonly used as a solvent). Rice straw is used as roofing and packing material, feed, fertiliser, and fuel. 

Species accounts

Oryza sativa is an annual or perennial  tufted grass typically growing to a height of 0.5 to 1.8 m high (up to 5 m in deep water species) with usually 4 to 5 tillers. Leaves: long, slender, and lance-shaped, with a prominent midrib. They are usually green but can vary in color depending on the specific variety. Inflorescence: a panicle, 50 cm long, bearing 50 to 500 spikelets. Spikelets contain 3 flowers, 2 of which are sterile. Fruit is a whitish to brownish grey, ovoid or ellipsoid caryopsis. Fruits: grain, commonly referred to as a rice kernel. These grains are what humans harvest and consume. They vary in size, shape, and color depending on the specific variety of rice.
Oryza sativa contains two main subspecies: 
•    Oryza sativa subsp. japonica (Japonica rice) - is mainly cultivated in temperate regions like Australia, northern China, Japan, and Europe. Variety if short-grained and when cooked, it has a moist and sticky texture. Japonica rice makes up 15% of the world's rice production and often achieves higher yields than indica rice.
•    Oryza sativa subsp. indica (Indica rice)- predominant variety, constitutes over 80% of worldwide rice cultivation. Typically cultivated in tropical and subtropical regions, Indica rice, when cooked, exhibits a distinct fluffy, dry, and separate texture, with grains typically being slimmer and longer compared to japonica rice.
Aromatic rice varieties, like basmati and jasmine, constitute a mere 1% of the world's rice production but are prized for their unique aroma, primarily due to the presence of 2-acetyl-1-pyrroline. The bulk of global rice production is comprised of glutinous rice varieties, encompassing both indica and japonica types.
(Merteens, 2006, Rokni, 2013, JungleDragon, n.d, OECD, 2004, Meertens, H.C.C., 2006,)

Oryza glaberrima (African rice) is an annual grass plant that grows to a height of 0.6-1.2 m (shorter than many O. sativa varieties). Dryland types have simple, smooth culms with root formation at lower nodes and simple branching to the panicle. Floating types can branch and root at upper nodes. Panicles are stiff and compact with self-fertilizing flowers, but some cross-pollination occurs. African rice resembles Asian rice from a distance, but has smaller ligules, less panicle branching, and lacks lawns on spikelets. It is completely annual and dies after seeding.
Despite lower yields than O. sativa, this species possesses valuable traits like resistance to rice yellow mottle virus, African gall midge, and nematodes. It's also tolerant to drought, acidity, iron toxicity, and competes well with weeds. This suggests potential for crossbreeding with O. sativa to combine beneficial traits

(National Academies of Sciences, 1996, Nair, 2019).).
Rice varieties
Examples of Rice varieties in Kenya
"Sindano", highly susceptible to Rice Yellow Mottle Virus (RYMV) and "Basmati 217" highly susceptible to blast have been grown since the 1960s. Since then alternative varieties of both irrigated rice and rain fed rice have been identified. 
Varieties of irrigated rice and their characteristics:

The upland "NERICA" rice varieties were developed at the Africa Rice Center (AfricaRice) ex-WARDA. They are resistant to blast, RYMV stemborers and leafminers and are high yielding and doing well from West Africa to Uganda. They are now also being promoted by NIB (National Irrigation Board), Kenya, KALRO and JICA. In Kenya they have great potential for medium altitudes with high rainfall or possibility for irrigation. "NERICA" can be planted as other small grains, but do need irrigation especially during flowering, and fertilization. 

Some characteristics of the NERICA varieties (KEPHIS).

Varieties in Tanzania
•    "Supa". Optimal production altitude: 0-400 m; grain yield: 1.5-3.5 t/ha; moderately resistant to RYMV and sheath rot.
•    "IR 54". Optimal production altitude: 400-600 m; grain yield: 4.0-7.0 t/ha; moderately resistant to bacterial blight and sheath rot
•    "IR 22". Optimal production altitude: 400-1000 m; grain yield: 6.6-8.0 t/ha; days to maturity: 120-13"5; resistant to bacterial blight.
•    "Katrin". Optimal production altitude: 400-1000 m; grain yield: 6.6-8.0 t/ha; very low panicle shattering.
•    "Dakawa". Optimal production altitude: 400-1000 m; grain yield: 3.5-5.2 t/ha; none-photoperiod sensitive; resistant to lodging except under high N levels; easy to thresh.
•    "TXD 85". Optimal production altitude: 0-400 m; grain yield: 4.8-7.0 t/ha; moderately resistant to sheath rot, blast and RYMV.
•    "TXD 88". Optimal production altitude: 0-400 m; grain yield: 2.8-6.5 t/ha; moderately resistant to sheath rot, blast and RYMV.
•    "SARO 5". Optimal production altitude: 0-600 m; grain yield: 4.0-6.5 t/ha; susceptible to RYMV and sheath rot. Adapted to rain-fed lowlands and irrigated ecosystems.
•    "Kalalu". Grain yield: 2-3 t/ha; resistant to RYMV and blast.
"Mwangaza". Grain yield: 2-3 t/ha; resistant to RYMV and blast.Ecological conditions 

Ecological conditions

Rice thrives on land that is water saturated or even submerged during part or all of its growth. Optimal temperatures for rice growing are 20 to 37.7degC, and no growth occurs below 10oC. Optimal pH is between 5 and 7, though rice has been grown in fields with pH between 3 and 10. Rice will grow in altitudes ranging from 0 to 2500 m above sea level, but worldwide is mostly grown on the humid coastal lowlands and deltas. Aquatic rice may require a dependable supply of fresh, slowly moving water, at temperature of 21 to 29degC. Rain fed rice requires an average of 800 to 2000 mm of rainfall well distributed over the growing season. If rainfall is less than 1250 mm annually, irrigation is used to make up deficit. The crop is salt tolerant at some stages of growth; during germination but not seedling stages and has even been grown to reclaim salty soils. Terrain should be level enough to permit flooding, yet sloped enough to drain readily. The soils on which rice can grow are as varied as the climatic regime it tolerates, but ideally it prefers a friable loam overlying heavy clay, as in many coastal and delta areas. 

Agronomic aspects

Seedling production.

Steps for producing healthy seedlings: 
1. Seed selection. Select plump and healthy seeds. 
2. Seed pretreatment. This is practiced in order to secure better germination of seeds and better growth of seedlings. It involves:
•    Seed disinfection. Hot water treatment is effective in destroying the nematode Aphelenchoides besseyi, which causes the white tip disease. For more information on hot-water treatment click here
•    Seed soaking. To supply the required moisture for germination, to shorten germination period and reduce seed rotting. During the soaking period change water to remove poisonous substances and allow entry of fresh air.
•    Pre-sprouting. The seeds are drained and covered with grass for 24 to 48 hours. This ensures uniform seed germination, avoids over sprouting and allows air circulation for germination.
3. Sowing: 
•    Sowing 80 to 100 g/m2 is normal practice.
•    Broadcast seed uniformly.
•    Do not submerge the nursery bed after sowing.
•    Use a seed rate of about 20 kg/acre (50 kg/ha).
4. Seed bed preparation (nursery): 
•    Plough at least 2 weeks before sowing and flooding.
•    Puddle 1 week before sowing and prepare raised nursery bed
•    Drain the nursery bed the day before sowing to stabilize the surface of the soil
•    If the soil covering the nursery bed is too soft, sown grains are buried into the soil resulting in poor establishment.
•    For 1 ha of transplanted rice, a nursery of about 350 m2 is required
•    Irrigate a few days after sowing so that the surface is kept moist, and as the seedlings emerge keep submerged conditions with water controlled at 1 to 3 cm according to growth of seedling.
•    Raise the water level to 10 cm one day before uprooting to ease washing off of soil that sticks to roots. This will make transplanting easy.
Main land preparation
a) Under irrigation: Land preparation is carried out by flooding the fields to a depth of 10 cm and then cultivating by use of tractor (40 to 75 hp) equipped with rotavators. Good timing and quality of land preparation will influence the growth of rice. Poor and untimely land preparation will cause serious weed problems and expose plants to harmful substances such as carbon dioxide and butyric acid, released by decaying organic matter in the soil.
It is recommended that land should be tilled and immediately flooded at least 15 days before transplanting or direct sowing. The purposes of this are:
•    To save the seedling from the effect of high concentration of harmful substances generated by decomposing organic matter rotated into flooded soils.
•    To prevent loss of nitrogen released by decomposing organic matter through denitrification. The ammonia released during decomposing of organic matter is conserved because ammonia is not converted to nitrate due to the absence of oxygen in the soil. This ammonia is later utilised by the rice plant.
b) Under rainfed situation: Land should be ploughed twice and harrowed once.

Transplanting
It is important to transplant from the nursery as soon as the seedlings are big enough. Seedlings are said to be ready for transplanting after a period of between 3 to 4 weeks depending on daylight, temperatures and the variety. "Basmati 217" will be ready for transplanting 25 days after sowing (4.5 to 5 leaf stage); "BW 196" and others at 28 to 30 days after sowing (5 to 5.5 leaf number).

Planting depth:

Practise shallow planting of about three cm depth for vigorous initial growth and will result in good rooting and tillering. Deep transplanting delays and reduces tillering resulting in a non-uniform crop growth and ripening, consequently resulting in yield losses. Seedlings should be transplanted in an upright position to allow correct tillering and rooting.

Direct sowing method: Trials have been done on direct sowing and have showed that the same level of yields performance as those of transplanting system can be obtained. This method saves substantially on labour input. However it has some disadvantages such as uneven germination rate and more weeding work in the paddy field. 

Planting under rainfed conditions:

Planting should be done before the onset of the long rains. Farmers are advised to use certified seed and appropriate variety for the region. Drill seed in rows at the rate of 50 kg/ha with a spacing of 25 cm for short varieties and 35 cm for tall varieties. In case of broadcasting, 75 kg/ha is often used. 

Main field water management 

Water is applied to the rice field for the use of the rice plant and also for suppressing weed growth. For this reason, it is important to practise appropriate water management throughout the growing period of a rice crop. 
In lowland rice fields, water comes from rainfall and irrigation. Water is lost by transpiration, evaporation, seepage and percolation. Prevent water loss by: 

• Repairing levees to minimise seepage.
• Removal of weeds to avoid competition with rice plants for water.
• Increasing the height of levees to prevent surface run-off water.

Critical stages when water is required in large quantities are:

• For a period of 3 to 7 days after transplanting cover the crop up to 80% of its height. This reduces transpiration and gives the plants a chance to re-establish their roots to be able to take up enough water from the soil
• From the stage of booting to 14 days after heading, more water is required because the shedding of pollen and the process of fertilsation requires very high moisture content in the air. Low moisture content in the air leads to sterile spikelets.

Seven to 10 days before harvesting, drain the field to harden the soil for good harvesting and also to hasten the drying and ripening of the rice grains.

Harvest, post-harvest practices and markets

Harvest
Time from planting to harvesting varies between 4 to 6 months. The crop should be ready to harvest when 80% of the panicles are straw dust coloured and the grain in the lower portion are in the hard dough stage. In a well-grown crop, the grain matures evenly and can be harvested in one operation. In the tropics it is essential to harvest the crop on time, otherwise grain losses may result from feeding by rats, birds, insects and from shattering and lodging. When harvesting rice with a sickle or knife, cut the rice straw about 4-5 cm above the ground to minimize what's left standing. This prevents stem-borer worms and adults from completing their life cycle. 
Post-harvest
After cutting the rice stems, they are bundled for transportation to the next stage.
•    Drying: Rice grains typically contain a high moisture content of about 25% after harvest, which can result in discoloration and pest problems. To mitigate this, it's essential to reduce the moisture content to around 13-14%. This is achieved through either traditional sun drying or mechanical drying using specialized dryers. It is crucial to complete the drying process within 24 hours of harvesting to maintain grain quality.
•    Threshing: Following drying, the next step is threshing, where the rice grains are separated from the husks. This can be done manually by hand or foot, involving swinging and beating actions against a frame, or with the help of winnowing machines.
•    Cleaning: Once threshing is complete, the rice undergoes a cleaning process to remove any remaining impurities such as rice straw, chaff, foreign objects, and immature grains from the paddy. This meticulous cleaning ensures rice quality and reduces the risk of contaminants, thereby minimizing transportation and milling costs for growers. Additionally, it lowers machine wear and spoilage costs for rice mill operators.
•    Milling: Rice milling is a critical post-harvest step where mechanical processes are employed to remove the outer layers of the rice grain, revealing the edible white kernel. By-products like the germ and bran can be repurposed for livestock feed.
•    Final Drying: Before rice is stored, it undergoes a final drying process to reach a moisture content of approximately 12%. This step is essential to preserve the grain quality for storage and consumption.
•    Storage: After completing these preparatory steps, the rice is ready for storage. Proper storage is crucial to maintain the quality and prevent deterioration. Rice should be stored in clean, airtight containers or silos to protect it from moisture, pests, and contaminants. Maintaining a consistent temperature and humidity level in the storage area is also vital to prevent spoilage and maintain rice quality over time(Wikifarmer, 2022a, JICA, 2004).
Markets
Rice is cultivated primarily for the grain, which is a main staple food in many countries, especially in Asia. In Kenya it is becoming increasingly popular, especially in urban centres. From 2010 to 2014, Kenya had a yearly production of about 119,000 metric tons (FAOSTAT, 2014).  Consumption of wheat has been on a steady increase from 410,000 metric tons in 2010 to 564,000 metric tons in 2014 This increase in demand and the development of new upland varieties have created an opportunity for farmers to venture into rice growing. (Economic Review of Agriculture, 2015).

Nutritional value and recipes

White and brown rice are two of the most widely consumed rice types. The brown type is essentially the whole rice grain, comprising the bran, which is rich in fiber, the germ, packed with nutrients, and the endosperm, a source of carbohydrates. In contrast, white rice is produced by removing the bran and germ, leaving just the endosperm. It is then processed to enhance flavor, prolong shelf life, and improve its cooking characteristics.
Rice primarily is a source of carbohydrates, offering a quick and easily digestible energy source. Brown rice, in particular, is rich in dietary fiber, aiding digestion and promoting a feeling of fullness. Rice contains moderate amounts of protein, contributing to daily protein intake, although it is not as protein-rich as some other foods. It is also low in fat and cholesterol-free, making it a heart-healthy choice.
Rice provides essential vitamins and minerals, including B vitamins and minerals like magnesium, phosphorus, and selenium, which are crucial for metabolism and overall health. Additionally, rice, such as red and black varieties, can contain antioxidants like anthocyanins and flavonoids, offering potential health benefits and reducing the risk of chronic diseases.
Being gluten-free, rice is suitable for individuals with celiac disease or gluten sensitivity. Its versatility allows for easy incorporation into various cuisines and diets, and it holds cultural significance in many societies. Brown rice, with its higher fiber content and added nutrients, is generally considered a healthier option compared to white rice.
Note:  White rice has a high glycemic index, causing notable blood sugar spikes after meals, which could elevate the risk of type 2 diabetes. To manage this risk, it's recommended to consume white rice in moderation. Combining it with fiber-rich foods, vegetables, and lean proteins can offset its glycemic impact and promote better blood sugar control.
(Healthline n.d, Medicalnewstoday)
Table 1: Proximate nutritional value of 100g of rice

Source (Nutrient data): FAO/Government of Kenya. 2018. Kenya Food Composition Tables. Nairobi, 254 pp. http://www.fao.org/3/I9120EN/i9120en.pdf

RE=retinol equivalents.

RAE =Retinol activity equivalents. A RAE is defined as 1μg all-trans-retinol, 12μg beta-carotene, or 24μg α-carotene or β-cryptoxanthin.

^a Lewis, J. 2019. Codex nutrient reference values. Rome. FAO and WHO

^b NHS (refers to saturated fat)

^c https://www.hsph.harvard.edu/nutritionsource/water/

^d British Heart Foundation

^e FDA

^f NIH

^g Mayo Clinic

Nutritive Value per 100 g of edible Portion

*Percent Daily Values (DV) are based on a 2000 calorie diet. Your daily values may be higher or lower, depending on your calorie needs.

Recipes
1.    Couscous 
West Africa 
Note: Couscous is a steamed granulated product made from cereal flour)

Ingredients
10 cups hungry rice flour 
1 heaped teaspoon dry baobab leaf or dry okro powder
Water for mixing and steaming

Procedure 
Sieve flour with 1mm sieve to ensure an adequately fine starter product
Pour flour in a bowl and sprinkle with about 2 cups cold water, mix and rub wetted flour between both palms to form sand-like aggregates
Prepare the steamer for steaming
Sieve the granulated product with a 1.5 mm mesh sieve
Put the sieved cereal granules on the top part of the double boiler (steamer/ couscoussier) and steam for 15 minutes
Take out the steamed granules which should now form a single mass, put into a convenient bowl and break it up into particles again
Put the granules back into the steamer and steam for another 15 minutes
Take out again the formed mass and break up into aggregates, sieve the resulting particles with a 2.5 mm sieve
If for later consumption (storage), sun dry the sieved cereal granules until grains are no longer moist to touch, then store in a tight lidded container
For immediate consumption, sprinkle sieved granules with 3½ to 4 cups water and mix thoroughly with the fingers, add one heaped teaspoon of baobab* leaf powder or dry okro powder, mix thoroughly again
Put mixture back in the steamer and steam again for 15 minutes
Cool cooked couscous slowly and serve warm with peanut soup or couscous sauce
Yields 8 servings
Remarks
*Powdered dry baobab leaf (Adansonia digitata or dry okro powder is used locally used to prevent the cereal granules from sticking together during the final steaming process. Where these are not available, a teaspoon of peanut oil or any light cooking oil, or a blob of margarine will produce the same effect. 
Millet, sorghum and maize can be a substitute for Hungry rice

2. District and region: Coast

Food name (in local language and other languages)
Pea pilau

Ingredients (with quantities and/or proportions):
2 cups of rice
1 cup of garden peas
2 medium sized Irish potatoes
2 medium sized onions
½ cup of ghee
2 cloves
Crushed garlic
2 pieces of cinnamon
½ tsp turmeric powder
1 cardamom
1 tsp cumin seeds

Procedure (step by step explanation with time):
•    Pick the rice and wash it and peel the potatoes
•    Pound the cinnamon, cardamom and cumin together in a mortar
•    Heat the fat and fry the onions until light brown
•    Add all the spices and cook for 10 minutes 
•    Stir well; add Irish potatoes, peas and salt. Continue frying for a while
•    Add the rice and fry lightly for 5 minutes
•    Pour in 4 cups of water, cover and simmer until rice is cooked
•    Serve warm  
Served with: Kachumbari