In this article we will discuss about:- 1. Introduction to Rice 2. Origin and History of Rice 3. Geographic Distribution 4. The Rice Plant 5. Types 6. Growth Stages 7. Growth Phases 8. Growing Regions 9. Constraints and Opportunities of Production 10. Strategies to Step-Up Productivity.
Contents:
- Introduction to Rice
- Origin and History of Rice
- Geographic Distribution of Rice
- The Rice Plant
- Types of Rice
- Growth Stages of Rice
- Growth Phases of Rice
- Rice Growing Regions
- Constraints and Opportunities of Rice Production in India
- Strategies to Step-Up Rice Productivity
1. Introduction to Rice:
Rice is primarily a high-energy food. It is a primary grain crop for more than 50% of the world’s population. Rice is an important food crop of India as it has the world’s largest area covering 41.9 million hectares with a total production of 83.13 million tonnes annually. Its area is about 37% of the total area under food grains as against 20% under wheat, another important food crop of India. However, globally it stands next to wheat in harvested area. In fact, about 65% of the people consume rice as part of their diet in India.
On an average, an Asian consumer eats about 150 kg of rice per year as compared to a European who consumes only 5 kg of rice in a year. It is grown in diversified soil types, topographical and hydrological situations varying from sloppy uplands to deep water conditions of above 1 m depth. It can be grown in hot and cool areas to adverse soil conditions such as salinity, alkalinity and acidity. Each and every part of the plant has various uses in society.
It is staple food of about 2/3rd population of world. In caloric and food value it is in no way inferior to wheat and other cereal grains. The rice grains contains many carbohydrates, chiefly starch (up to 75%), but rather little protein (about 7.5%), as much as 2.2% fat, 0.8% cellulose and 5.9% ash. Rice is also low in fat, salt and cholesterol, and thus helps in keeping the heart healthy.
Rice grain contains as much B group vitamins as wheat. The digestibility and assimilability of rice starch and protein (95.5%) is higher than other cereal grains. Rice grains are easily and rapidly cooked and store well in tropical conditions. Mostly it is cooked with water. Rice water is valuable medical remedy. Rice grain can also be ground into flour and fermented to produce sake, an alcoholic beverage. Other edible use includes rice flakes and puffed rice, rice wafers and canned rice.
The rice grain is, as a rule, not processed for flour because it does not contain any gluten and is not suited for bread (chapatti) making. In some cases rice flour is added to wheat flour for bread making. Rice is also used in starch and brewing industries. The by-products of rice milling are used for variety of purposes. Rice bran is the most valuable byproduct of rice milling industry. It is obtained from the outer layers of the brown rice.
Generally, rice bran consists of pericarp, aleuronic layer, germ and a part of endosperm. Bran removal amounts to 4 to 9% of the weight of paddy milled and is abundant in oil. Raw rice bran contains about 18-20% oil whereas parboiled rice bran contains about 22-25% oil of which about 15 % is recoverable. Of the total oil in grain, about 75% is present in bran itself. The de-oiled bran, which is rich source of protein (about 17%) and vitamins (vitamins A and E), is used as cattle and poultry feed.
2. Origin and History
of Rice:
The origin and history of rice probably dates back to the antiquity. The earliest forms of rice were grown in China around 5000 years back. In fact, the rice paddy was first invented by the Chinese farmers cultivated grains and is regarded as a first cultivated crop of Asia. It was raised in India 2000 years B.C. From India, it spread to the east, China, Japan, Indonesia, and also to the west, to Iran and Mesopotamia. De Candolle (1886) and Watt (1892) thought that South India was the place where cultivated rice originated.
According to D. Chatterjee (1948), there are altogether 23 species of genus Oryza. Tateoka (1964) recognized 22 species of Oryza to be valid, of only two viz. Oryza sativa and Oryza glaberrima are cultivated. Oryza sativa is raised in all rice producing areas, but Oryza glaberrima is confined to West Africa. It seems plausible, therefore to assume that there might have been two centres of our cultivated rice, South-Eastern Asia and West Africa.
Paddy grains found during excavation at Hastinapur (UP) around 1000-750 B.C. considered as a oldest sample in the world. Vavilov (1926) concluded that South-west Himalayas has various types and varieties and indicated probable centre of origin.
3. Geographic Distribution
of Rice:
Most of the world’s rice is grown in tropics which include countries of South and South East Asia, West Africa, Central and South America. About 90% of the world crop lands and production of this crop is concentrated in Asia, about 3% of the areas under rice are in Africa (2.2% of world rice grain production), 6% in America (6% of world production). Only 1% of world rice crop land is found in Europe. The average productivity of rice is the highest in Egypt i.e., 9.84 t/ha as against world’s average of 4.05 t/ha.
Among the various rice growing countries of the world, India has the largest area under rice and in case of production it stands next to China. In India, rice is the most important and extensively grown food crop, occupying about 43 million ha of land. However, productivity of India (2.22 tonnes/ha) is lower than the world average yields (4.05 t/ha) and is much behind than the rice productivity of Egypt, Japan, China, Vietnam, USA and Indonesia. Rice contributes 42 % of total food grains production and 45 % of the total cereal production in the country.
The major rice growing states in India are West Bengal, Uttar Pradesh, Orissa, Chhattisgarh, Andhra Pradesh, Bihar, Assam, Punjab, Tamil Nadu, M.P. and Maharashtra. West Bengal ranked first in total rice production. Among the different states of India there are regional imbalances with regard to average yield. In north-west India (Punjab) and southern India (Tamil Nadu and Andhra Pradesh), the yield levels are fairly higher than the national average because of assured irrigation and better technology adoption.
In general the yield levels in eastern states of India (except West Bengal), are not only poor but remained stagnating since several years. The reasons are quite obvious. More than 70 % of rice area is rainfed, depends on the marcey of rains. Less fertilizer use, adoption of traditional varieties, drought, floods, insect and disease problems besides socio-economic constraints are responsible for limiting rice yields in these states.
But with the adoption of high yielding insect-pests resistance varieties and hybrids and appropriate agro-techniques available for different agro- climatic situations including balance fertilization and plant protection measures, there is an ample scope to enhance the yield levels of rice in these states.
4. The Rice Plant
:
Rice is only grain adapted to moisture-induced anaerobic conditions and is typically grown in flooded conditions. The stem and root contain large air spaces that allow for air diffusion throughout the plant. Rice leaves are able to float on water because of the air spaces. The root system is fibrous. The rice caryopsis germinates with one embryonic root which is very important for supplying the plant with nutrients and water before it begins tillering.
Adventitious roots develop at the base of the first 4-6 leaves. The root system is found to develop best under flooding. Most of rice roots are 30 to 40 cm long. As the rice plant grows, its roots structurally acquire features pertinent to the aquatic plants. This is due to the parenchyma, a developed air conducting tissue present in the roots, leaves and culms through which the above-ground parts of the plant supply air oxygen to the roots and consequently to the soil.
In this way, the plant maintains essential oxygen concentrations after it has formed 2-3 true (foliage) leaves, and grows comfortably under submergence. It can also grow under dryland or upland conditions, but it is most productive when grown submerged in water or frequently irrigated.
The stem (Culm) is hollow straw filled with parenchyma only in its upper part. The stem varies in length from 50 to 200 cm. The straw decreases in thickness from bottom to top. The stem nodes divide the straw into internodes. The shortest internodes are at the base of the straw, they have buds and meristematic tissue giving birth to roots and sprouts. This is the so- called tillering node. Tillering is the process when the underground buds of the stem nodes form sprouts.
The leaves are linear, long composed of sheath, leaf blade, ligule and two auricles. The leaf blades are up to 35 cm long and 1.5 to 2.0 cm wide. The upper leaf is called the flag. It is shorter and broader than the other leaves. The rice leaf is similar to that of wheat, but is usually distinguishable from it by the length of the ligule, sometimes known as a rain-guard, a scale-like structure that appears as a continuation of the sheath, and at tine junction of the blade or the lamina and the sheath.
In the rice plant this structure is very prominent and is bigger than in any other cereal. Rice leaves formed at different stages of vegetation clearly differ in their quality. The first four leaves do not take any active part in the formation of panicle. The products of photosynthesis of these leaves are utilized for the development of the root system.
The leaves of the middle layer are the most important for differentiating the vegetative cone and forming the panicle. When cultivated, the productivity of rice largely depends on the activity of the middle-layer leaves. The leaves of the upper layer (10-12th) supply the products of photosynthesis to the generative organs, i.e., the caryopses and the spikelet’s.
The inflorescence is a panicle (tassel). The spikelets that make up the panicle are one- flowered and laterally compressed. The rice tassels are compact (dense) or loose, depending on the number of spikelets. The tassels vary in length from 15 to 25 cm, each having from 80 to 300 spikelets.
The lemma and palea (palet) are similar in size, but the former is five nerved whereas the latter is only three-nerved. Either may or may not possess awns. The lemma and the palea together are known as the ‘ hull’, and rice enclosed in the hull is known as ‘ paddy’. The rice flower contains six functioning stamens, which distinguish it from the other cereals.
The flower is bisexual, with two paleas the inner and outer ones. Rice is usually self- pollinated, though natural cross-pollination occurs to a limited extent. The rice grain is caryopsis 4 to 6 mm long, up to 3.5 mm wide. The caryopsis consists of a germ and endosperm.
The germ comprises about 2.0-3.5% of the weight of the caryopsis and includes a plumule, embryonic root and a corymb. The external layer of the endosperm adjacent to the seed coat is composed of rich-in-protein aleurone grains beneath which there are cells filled with starch grains.
5. Types of Rice
:
The most basic parameter on which rice can be classified is according to its length. According to these criteria, one can find three types of rice.
These are:
(i) Long Grain Rice/Basmati Rice:
It belongs to the category of ‘Indica Rice’ or long grained rice. The grain of the rice is long, and is about 5 times longer than its width. The long grain rice is known as a ‘rough’ or ‘paddy’ rice at the time of its harvesting. Its grains, when cooked, are light in weight as well as soft in texture.
Due to its full-bodied flavor and versatility, the long grain rice is also known as an ‘all-purpose rice’ or ‘ basmati rice’, and is an ideal choice for an everyday meal. Basmati rice is mainly cultivated in climates that are warm, like those in India, Pakistan and Thailand. The long grain rice is further classified as ‘ Long Grain Brown Rice’ and ‘ Long Grain White Rice’.
(ii) Medium Grain Rice:
This type of rice has a creamy color and a slightly chewy texture. The kernels of this kind of rice are shorter and wider as compared to that of long grain rice and also do not always remain fluffy. It is an ideal form to be used in desserts, breads, etc. The grains of the medium grain rice are 2-3 times longer than the width, which is about 5 mm in length. It can also be further classified as ‘ Medium Grain Brown Rice’ and ‘ Medium Grain White Rice’.
(iii) Short Grain Rice:
Belonging to the ‘Japonica’ (round grained) category of rice, the grains of this type of rice have short and plump kernels. This rice is identified as having a smooth, creamy texture, ideal for making rice pudding and other sweet dishes involving the use of rice. The length of the grains is 4 mm while its width is around 2.5 mm. It is mainly grown in cold weather areas, such as Japan, Korea and China. This type of rice can also be further classified as ‘Short Grain Brown Rice’ and ‘Short Grain White Rice’.
6. Growth Stages of Rice
:
Rice vegetates from 90 to 200 days, depending on the varieties and agro-ecological situations. There are six phonological phases of rice reflecting the basic quantitative and qualitative changes in the plant.
(i) Germination:
It includes swelling, the growth of the germ, the formation of the sprout and embryonic root. At this stage first three leaves are formed, the coleoptile, the first leaf without a blade, and the first true leaf. Rice seeds germinate in the absence of oxygen because the coleoptile is a facultative anaerobe capable of growing in oxygen free media. Rice requires oxygen later, when the embryonic root and leaves begins to grow out.
(ii) Sprouting:
The second stage begins when the buds and meristematic tissues in the leaf axils are formed and lasts about 20 days. During this period the leaves of the middle layer and the adventitious roots are formed.
(iii) Tillering:
It begins with appearance of the 3rd – 4th leaf and ends after 8-9 leaves are formed. Lateral sprouts develop very intensively and the vegetative cone grows. When tillering is fading, the phase of leaf tube formation begins, the vegetative cone is differentiated and transformed into a rudimentary tassel. Tillering lasts for about 45 and more days, depending on the vegetation period in the rice plant.
(iv) Leaf Tube Formation:
It coincides with the formation of 8-9th leaf. The upper internodes of the stem grow, terminal leaves are produced, and the rudimentary tassel begins branching. Formation of spikelets, paleas, pistil and ovule, as well as lodicules takes place. All organs of the pistil complete formation, i.e. the ovary, style, and two pinnate stigma. This stage also shows the intensive growth of the panicle (tassel) and all organs of the spikelet increase 3 to 5 times in size.
(v) Flowering (Blossoming):
This is the stage of tasseling, flowering and fertilization. Blossoms in the rice can open and closed, and lasts up to 7 days. During this period the anthers, ovary and stigma ripen, the filaments elongate and fertilization takes place.
(vi) Ripening (Maturation):
This stage denotes the formation of the embryo and the endosperm. The embryo develops within 10-15 days after fertilization. It also indicates that the endosperm is filled with starch grains and that the aleurone layer is formed. Ripening (maturation) of the caryopsis (milky, waxy, complete ripeness) which means that dry matter is accumulated and the water content is diminished. The period of ripening lasts for 30-35 days after flowering.
7. Growth Phases of Rice
:
The growth of the rice plant is divided into three phases:
(i) Vegetative (germination to panicle initiation);
(ii) Reproductive (panicle initiation to flowering); and
(iii) Ripening (flowering to mature grain).
In the tropics, the reproductive phase is about 35 days and the ripening phase is about 30 days. The differences in growth duration are determined by changes in the length of the vegetative phase. For example, IR64 which matures in 110 days has a 45-day vegetative phase, whereas IR8 which matures in 130 days has a 65-day vegetative phase.
Yoshida (1981) outlined the following physiological requirements for high yields of rice:
i. Varieties should possess a short and stiff stem.
ii. Leaf arrangement should be such that erect upper leaves graduate down to droopy leaves at low canopy levels.
iii. Leaf area index of 5-6 is necessary for achieving maximum photosynthesis during reproductive stage.
iv. Maintenance of as many active leaves as possible until crop maturity.
v. Planting time should be chosen so that the crop is exposed to high solar radiation during reproductive phase.
vi. All the essential nutrients must be supplied to meet the crops requirement in time.
vii. Nitrogen absorption after heading assumes importance when high yields are expected by increasing the harvest index.
8. Rice Growing Regions
:
Rice is grown under so diverse soil and climatic conditions that it is said that there is hardly any type of soil in which it cannot be grown including alkaline and acidic soils. Rice crop has also got wide physical adaptability. Therefore, it is grown from below sea-level (Kuttanad area of Kerala) upto an elevation of 2000 metres in Jammu & Kashmir, hills of Uttaranchal, Himachal Pradesh and North-Eastern Hills (NEH) areas.
The rice growing areas in the country can be broadly grouped into five regions as discussed below:
i. North-Eastern Region:
This region comprises of Assam and North eastern states. In Assam rice is grown in the basins of Brahmaputra River. This region receives very heavy rainfall and rice is grown under rain fed condition.
ii. Eastern Region:
This region comprises of Bihar, Chhattisgarh, Madhya Pradesh, Orissa, Eastern Uttar Pradesh and West Bengal. In this region rice is grown in the basins of Ganga and Mahanadi rivers and has the highest intensity of rice cultivation in the country. This region receives heavy rainfall and rice is grown mainly under rain fed conditions.
iii. Northern Region:
This region comprises of Haryana, Punjab, Western Uttar Pradesh, Uttaranchal, Himachal Pradesh and Jammu & Kashmir. The region experiences low winter temperature and single crop of rice from May-July to September-December is grown.
iv. Western Region:
This region comprises of Gujarat, Maharashtra and Rajasthan. Rice is largely grown under rain fed condition during June-August to October-December.
v. Southern Region:
This region comprises of Andhra Pradesh, Karnataka, Kerala and Tamil Nadu. Rice is mainly grown in deltaic tracts of Godavari, Krishna and Cauvery Rivers and the non-deltaic rain fed area of Tamil Nadu and Andhra Pradesh. Rice is grown under irrigated condition in deltaic tracts.
9. Constraints and Opportunities of Rice Production in India:
The problems/constraints in rice production in India differ from state to state and location to location. The major rice growing areas are concentrated in Eastern region, which often experiences high rainfall and severe flood almost every year. The loss to the rice crop is considerably very high. Besides, in upland areas the crop gets setback either from high rainfall or drought condition.
Certain categories of soils do not give the desired yield response to the balanced application of N.P.K. fertilizers due to some inherent characters of the soil. All these problems/constraints are affecting the productivity of the rice crops in different growing zones. In certain area, the availability of suitable high yielding varieties and quality seeds are also a problem.
The major problems/constraints of rice production are follows:
1. Majority of the rice farmers (about 78%) are small and marginal in the country and they are poor in resource. They could not afford to use optimum quantity of inputs in their crops which are essential for increasing the productivity.
2. Rice crop often suffers with soil moisture stress due to erratic and inadequate rainfall. In upland soils rain water flows down quickly as runoff and farmers are unable to conserve the soil moisture. There is also no way for life saving irrigation particularly in upland and rainfed lowland areas.
3. Intermittent soil moisture stress, Hue to low and erratic rainfall and poor soil problems are experienced in Chhattisgarh, Madhya Pradesh, Orissa and some parts of Uttar Pradesh. The problems of floods, water logging/submergence due to poor drainage, low-lying physiography and high rainfall in submergence prone lowlands are in Assam, West Bengal, North Bihar and Eastern Uttar Pradesh. Accumulation of toxic substances in poor drained soils and soil iron toxicity in Assam are problems of low production of rice.
4. Use of traditional varieties due to the non-availability of seeds and lack of awareness about high yielding varieties (Upland, rainfed lowland and deep water areas).
5. Low soil fertility due to soil erosion resulting in loss of plant nutrients and moisture.
6. Low and imbalanced use of fertilizers, low use efficiency of applied fertilizers particularly in the North-Eastern and Eastern States.
7. Heavy infestation of weeds and insects/pests such as blast and brown spot and poor attention for their timely control (upland and rainfed lowland).
8. Inadequate plant population in case of broadcast/Biyasi sowing method under upland and direct seeded lowland situation. Delay in monsoon onset often results in delayed and prolong transplanting and sub-optimum plant population (Mostly in rainfed lowlands).
9. Poor adoption of improved crop production technology due to socio-economic constraints of the upland and lowlands farmers.
10. Un-availability of bullock drawn or power drawn transplanter for timely transplanting of rice crop.
11. Upland rainfed situation the growth and development of rice crop is greatly affected by the vagaries of the monsoon. In the years of uneven distribution of rainfall, the crop fails owing to drought and in the years of heavy rainfall, particularly during flowering, there is poor grain setting and also the matured grains germinate on the panicles.
12. In the high-rainfall region, the rain-water is lost rapidly through deep percolation, because of the upland location and loose texture of the soil. In these soils the plant nutrients applied through fertilizers are also lost rapidly and investment on fertilizers becomes risky. Further, low water retention capacity by the soil due to high permeability brings in moisture stress condition quickly after the cessation of rains.
13. In the low-rainfall regions, the crop suffers from iron and zinc deficiency in some soils, in the high-rainfall regions, diseases break out particularly Helminthosporium possibly due to unbalanced nutrient availability in the soils.
14. Generally, upland rice crop becomes ready for harvesting earlier in the season, there is much damage due to birds and rodents.
15. In acid, red laterite and lateritic soils, the following problems are encountered:
i. Moderate to high acidity
ii. Deficiency of nutrients, because of their soils are low in C, N and available nutrients.
iii. Toxicity due to iron and in some soils due to aluminum and manganese.
iv. P- deficiency and high P-fixing capacity which necessitate higher rates of application of P-fertilizers.
v. Impeded drainage in certain areas.
16. The acid sulphate soils have been reported to occur on the west coast of Kerala. These soils are locally known as Kari, Karapadam, Kole, Pokkali and Swamp soils, depending upon their location. The presence of substantial amounts of organic matter in these soil results in the accumulation of large amounts of ammonical nitrogen, particularly in the “Pokkali” and “Swamp” soils, which might also prove toxic for the growth of rice plant. These soils contain low amount of phosphate and are likely to show up phosphate deficiency.
17. Saline and alkali soils mostly occur in the coastal districts of West Bengal, Orissa, Andhra Pradesh, Tamil Nadu, Kerala, Karnataka, Maharashtra and Gujarat.
The problems of saline and alkali soils are given below:
i. Osmotic effect due to high concentration of salts in the saline and saline-alkali soils.
ii. Difficulty in removal of salts by flushing from these lands in the coastal region because of heavy texture of the soil, lack of freshwater source, particularly in the north-western India, recharge of the salt from sub-surface to the surface soil due to capillary rise and periodic inundation with sea water.
iii. Toxicity due to high pH and due to the presence of sodium either as carbonate or as bicarbonate in the alkali or saline-alkali soils.
iv. Highly dispersed soil under alkaline or saline-alkali situation, where drainage becomes a problem.
10. Strategies to Step-Up Rice Productivity:
The scope for expansion of area under rice cultivation has almost been exhausted, the only way to sustain production for meeting the increasing demand, is to increase the productivity per unit of area including intensive use of land by increasing the cropping intensity.
The following strategies may be adopted to increase the productivity of rice in various states:
1. Emphasis may be given on a cropping system approach rather than a single crop development approach.
2. Dissemination of location specific crop production technologies in different agro- climatic zones through demonstrations on farmers field and organizing trainings for farmers including women in improved crop production technology.
3. Replacement of traditional old varieties (susceptible to insects-pests and diseases) by new high yielding varieties/hybrids.
4. Adoption of rain water harvesting suited to the conditions of individual farm holding as well as watershed as a whole, motivating the farmers to provide lifesaving irrigation to the crop wherever possible during long dry spells.
5. Improving soil fertility by inclusion of leguminous crops in the crop rotations or as mixed crop.
6. Encouraging the use of soil ameliorants for improving saline, alkaline and acidic soils.
7. Emphasis on balanced use of plant nutrients along with the popularization of integrated plant management system, use of zinc sulphate in zinc deficient areas and method of applying required nutrients in standing water e.g., neem cake coated urea, fertilizer mud balls, deep placement of super granules urea by the applicator.
8. Use of bio-fertilizer such as Blue-Green Algae, Azosprillum, Azotobacter and Azolla may be encouraged for supply of nitrogen to the crop and also phospho-bacteria may be used for solubilizing non available phosphorus to available form easy uptake by the crop plants.
9. Popularization of line sowing in upland rice areas through suitable seeding devices establishment of desired level of plant population, easy in weed control and the application of other management techniques.
10. Encouraging the use of machines as well as bullock drawn and hand operated implements.
11. Promoting the Integrated Pest Management Approach for effective control of pests and diseases by emphasizing the need based application of pesticides.
12. More emphasis on the adoption of non-monetary inputs like timely sowing/planting, maintaining optimum plant population, timely irrigation, efficient use of fertilizers, need based plant protection measures and timely harvesting of crop.