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Lesson Note

Subject: Agricultural Science
Topic: Production of Rice (Oryza sativa)
Lesson: At the end of the lesson, learners should be able to:

  1. Explain the processes involved in rice production,
  2. State the different types of rice grown,
  3. Explain with diagrams, the stages of rice growth.

Lesson Discussions

Rice is a cereal grain of the grass family. It is botanically known as Oryza glaberima or Oryza sativa. Rice being a staple food for the world growing population, it is largely cultivated worldwide.

Scientific Classification

Origin: Rice is a native of South East Asia from India to Japan. The production of rice has outweighed that of any other cereal. Unfortunately, it’s supply to the world market has been limited by local consumption. Rice could be grown as:
(a) Upland rice (Dry land paddy): where rice is grown as a rain fed crop.
(b) Low land (Swamp) rice: where rice is grown on irrigated or flooded river plains.
(c) Floating rice: where there is deep flooding up to a few metres.

Varieties:Two types of rice are mostly grown – Oryza sativa and Oryza glaberimaThe Oryza sativa has two major classification, viz:
(a) Oryza sativa variety Japonica: This has grains that appear fat, roundish and has soft starch that is made up mostly of amylopectin. It is produced around Japan and constitutes the bulk of international Rice Research Institute (IRRI) series such as IRRI -40 and IRRI-120.

(b) Oryza sativa variety Indica: This is long and slim grained and has hard starch that is made up of amylose and amylopectin. Examples include Mass-2401 and GEB-24. These are more sensitive to soil moisture regime than the Japonica type. Rice is not an aquatic plant, though it grows in waterlogged areas. It’s ability to grow in waterlogged conditions is related to three characteristics of the plant, namely;
i. Possession of air channels in the leaf sheath which go down into the root.
ii. Existence of respiratory roots which extend to the upper layer of the mud and above water level.
iii. Existence of enzyme system which enables rice tissues to respire anaerobically. Since it is not an aquatic plant, it uses the products of anaerobic situation e.g, ethylene

Uses: Rice serves as a staple human food and as a livestock feed. It is used in the industries for the production of beer, wine, spirits, wax, soap, anti-corrossives etc.
Geographical conditions: Rice grows in many soil types ranging from sandy loam to clayey soils provided that enough water from either natural rains or irrigation is guaranteed.
However, heavy alluvial soils which permit padding are preferable to lighter soils. The optimum pH for rice is 7.0 – 7.2 on flooded lands and 5.5 – 6.5 when the soil is dry. Rice requires long period of sunshine for high yields especially from inflorescence initiation to harvesting. It requires an annual rainfall and/or irrigation of 1500 – 2000mm to produce a good crop. Although, many countries depend on rainfall alone to provide the water requirements, rice is best grown under irrigation.

Nursery Preparation: Rice seedlings may be raised in nurseries. The nursery is prepared to control weeds and then condition the soil to favour aeration. Select a nursery site close to the rice field. The size of the nursery is dependent on the area of land to be planted.
Till the nursery soil to a depth of 10 – 12cm, apply well decomposed organic manure and work it in. The nursery soil should not be flooded but must be level and fertile. Water the nursery to field capacity in the evening preceeding sowing. Soak the seed in water to remove light (immature and incompletely filled) seeds before sowing. Broadcast seeds lightly walking backwards.
Rake after planting to cover the seeds with a thin layer of soil.
The nursery may be shaded with palm fronds. Raking and Sha protect rice seeds from bird attack and excessive direct sun rays. Remove shade after germination to avoid etiolation.

Life Cycle of Rice

Stages Of Rice Growth

This is made up of three stages, namely;
i. Juvenile stage: This is from generation to early tillering. It takes 7 – 9 weeks and requires just enough water. Nitrogen fertilizers should best be applied at the end of the juvenile stage.
ii. Reproductive/Adult stage: This is the accelerative stage of growth and is marked by inflorescence initiation. A lot of water is needed here. Inadequate water prevents filling up. This stage takes about 8 – 10 weeks. It ends with the dough stage. At the dough stage, the grains are solid. Too much water at this stage leads to loss of grains. This stage demands effective control of birds.
iii. Maturation/Ripening stage: This is the stage at which the grains mature and dry out. It takes 2 – 3 weeks and is after the dough stage.

Stages Of Rice Growth: mdpi.com

Method of sowing: Rice is seed propagated.

Time of planting: In Nigeria, rice season coincides with the rainy season and in the Southern Nigeria and Ghana it begins with the early regular rains of April-May for the early crop while the second crop is planted in August and September. In the Northern Nigeria, Ghana, Gambia and Sierra Leone, rice is planted between June and July.

Spacing: Spacing varies with cultivars and availability of water. Where there is enough water the recommended spacing is 10 – 15cm and 20 – 25cm for short term and long term cultivars respectively. The closer spacing gives a higher yield.

Seed Rate: The recommended seed rate is 60 – 80kg/ha

Land Preparation: Select a very gently sloping land. This is because the irrigation water must be slow moving so as to be attending the soil and eliminate pests/pathogens. Bunding and levelling may be required to supply and control water in the rice field. Land preparation involves deep ploughing and pudding. Pudding is a repeated ploughing operation to bring the soil into a soft puddle or slurry. Puddling is aimed at:

  • Maintaining a uniform water level.
  • Aerating the land.
  • Providing the soil with a fairly impervious subsoil.
  • Burying all kinds of weeds and surface trash.
  • Offering seedlings the right conditions for vigorous growth.

Transplanting: Transplanting permits more effective weed control, requires less number of seeds, leads to higher yield, reduces damages by birds, and has a higher survival percentage. Water the nursery in the evening preceding the day of transplanting to loosen the soil and reduce shock on the seedling. The seedlings are ready for transplanting at 4 – 6 weeks after sowing. Pull up the seedlings in bunches and prune off the top portions of leaves and even roots to;

  • Reduce transpiration and
  • Offer rigidity to the seedling when planted. Hold a bunch of seedlings in the left hand and using the right hand, thrust 2 – 3 seedlings into the mud. Transplanters move backwards while planting to avoid trampling on the planted seedlings. At the end of the planting day, the remaining seedlings are put under shade in a clay slurry.

Fertilizer application: Rice responds readily to Nitrogen but not always to phosphorus and potassium. This Nitrogen fertilizer application e.g Ammonium sulphate, is best done at the time of inflorescence initiation. It is recommended that the fertilizer be put in the anaerobic depth of the soil to reduce volatilization and denitrification.

Weeding: Rice does not stand weed competition in the nursery and field, and the most critical stage is between jointing and initiation of inflorescence primordia. Weeding is done generally and manually with hoes. However, the use of pre-emergence herbicides such as 2,4-D; 2,4,5-T and Dalapon is now on the increase.

Harvesting: Rice matures in 3 – 6 months. The time of harvesting depends on the cultivar and is usually between 4 – 6 weeks when the moisture content is in the range of 16 – 25%. At the time of harvest, a bite cuts the grain sharply and the husk goes off easily when the grain is rubbed on the grain. Harvesting is done by cutting the culm, collecting the panicles and tying them into bundles called sheaves. When harvesting is mechanized, it is done by combine harvesters.

Threshing: This is the separation of the paddy from the stalk and is done by beating the panicles against a hard surface. The moisture content of the paddy is further reduced to about 13% by controlled drying especially if the rice is for planting and storage.

Milling: This is the detachment of the glumes from the actual grain. If only the glume is removed, the rice is brown, (unpolished rice) which is rich in vitamin B. Rice is usually parboiled before milling. Partial boiling (parboiling) has the following advantages;
i. It gelatinizes and hardens the rice so that it stands storage longer.
ii. It reduces breakage percentages.
iii. There is diffusion of minerals and nutrients into the endosperm at parboiling.
iv. Parboiled rice is more resistant to weevils.
Parboiling is initiated by washing the rice to remove dirtiness, stones and incompletely filled grains and is done in two stages;

  • Soaking: Cold soaking produces odour and leads to fermentation and should therefore be avoided. Hot water soaking involves pouring hot water (about 70°C) to rice paddy in cut drums and covering it with sacks for about 4 hours.
  • Steaming: Transfer the paddy into another cut drunk and add very small amount of water and apply heat. Remove heat source when heat comes out and then dry the grains on mats. These dried great are then fed into the mill or are stored in bags until required for milling.

Storage: Rice paddy cab be stored in bags until required for milling and milled rice may be stored in dry air-tight and insect free containers.
Marketing: Paddy and milled rice are sold in local markets in Nigeria.

Pests: Birds, stem borers, rodents, rice gall midge, fish, crabs, weevils and grasshoppers are the pests of rice.

Diseases: Rice diseases are blast, smut, brown spot, leaf blight, stem rot and foot rot.

Problems That Militate Against Rice Production

i. Lack of effective water control. This leads to poor weed control, incomplete filling up of grains and poor pests and disease control.
ii. Lack of good cultuvation especially puddling.
iii. Indiscriminate use of planting materials such as incompletely filled seeds.
iv. Inadequate use of fertilizers.
v. High labour intensiveness especially in the area of weeding, transplanting and control of pests (birds).

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  1. Explain the processes involved in rice production.
  2. State the different types of rice grown.
  3. Explain with diagrams, the stages of rice growth.

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