Rice
Agriculture

Rice




Introduction 



Rice is a grain belonging to the grass family. It is related to other grass plants such as wheat, oats and barley which produce grain for food and are known as cereals. Rice refers to two species (Oryza sativa and Oryza glaberrima) of grass, native to tropical and subtropical southeastern Asia and to Africa, which together provide more than one-fifth of the calories consumed by humans. This plant needs both warmth and moisture to grow, measures 2-6 feet tall and has long, flat, pointy leaves and stalk-bearing flowers which produce the grain known as rice. Rice is rich in genetic diversity, with thousands of varieties grown throughout the world. 
Throughout history rice has been one of man's most important foods. Today, this unique grain helps sustain two-thirds of the world's population. It is life for thousands of millions of people. It is deeply embedded in the cultural heritage of their societies. About four-fifths of the world's rice is produced by small-scale farmers and is consumed locally. Rice cultivation is the principal activity and source of income for about 100 million households in Asia and Africa. India is an important center of rice cultivation. The rice harvesting area in India is the world's largest. 


Origin and History 


The two major rice varieties grown worldwide today are Oryza sativa indica and Oryza sativa japonica. According to research studies, they owe their origins to two independent events of domestication thousands of years ago. 

Historians believe that while the indica variety of rice was first domesticated in the area covering the foothills of the Eastern Himalayas (i.e. north-eastern India), stretching through Burma, Thailand, Laos, Vietnam and Southern China, the japonica variety was domesticated from wild rice in southern China which was introduced to India before the time of the Greeks. Rice plants have been traced back to 5000 BC, Most believe the roots of rice come from 3000 BC India, where natives discovered the plant growing in the wild and began to experiment with it. But the practice of rice growing is believed to have originated in areas of China, and southern and eastern Asia, in about 2000 BC.The earliest remains of cultivated rice in the sub-continent have been found in the north and west and date from around 2000 BC. 

O. sativa is a complex group composed of two forms, endemic to Africa but not cultivated, and a third from, O. rufipogon, having distinctive partitions into South Asian, Chinese, New Guinean, Australian, and American forms. The subdivision of O. sativa into these seven forms began long ago and came about largely as a result of major tectonic events and world wide climatic changes. It is postulated, based on measurements by electrophorosis, which the Australian form of O.sativa began to diverge from the main forms about 15 million years ago. 

At that time, during the Miocene, the Asian portion of Gondwanaland collided with the Australia/New Guinea portion, creating a land bridge across which O. sativa migrated. Once the blocks separated, the Australian form was free to follow an evolutionary path somewhat different from the O.sativa on the mainland. Divergence between the South Asian and Chinese forms, the ancestors that are commonly referred today as indica and japonica (or sinica) types, is believed to have commenced 2-3 million years ago. At that time, migration of fauna across the proto-Himalaya was still possible, and with the animals the wild rice was carried. 

The climate is suitable for rice even today in Central Asia and North China with almost ideal conditions. Botanical evidence concerning the distribution of cultivated species is based chiefly on the range and habitat of wold species that are believed to have contributed to the cultivated forms. 

The greatest variety of such rices is found in the zone of monsoonal rainfall extending from eastern India through Myanmar, Thailand, Laos, Northern Vietnam and into southern China. This diversity of species, including those considered by many have been involved in the original domestication process, lends support to the argument for mainland southeast Asia as the heartland of rice cultivation. The earliest and most convincing archeological evidence for domestication of rice is in Southeast Asia.. 

Piottery shards bearing the imprint of both grains and husks of O.Sativa were discovered at Non Nok tha in the Korat area of Thailand. These remains have been confirmed by 14C and thermoluminescence testing as dating from at least 4000 B.C. 

Perennial wild rices still grow in Assam and Nepal. It seems to have appeared around 1400 BC in southern India after its domestication in the northern plains. It then spread to all the fertile alluvial plains watered by rivers. Cultivation and cooking methods are thought to have spread to the west rapidly and by medieval times, southern Europe saw the introduction of rice as a hearty grain. Some says that the word rice is derived from the Tamil word arisi.There are many unproven mythological tales related to origin of rice, though historians hold little or no stock in any. Rice is first mentioned in the Yajur Veda (c. 1500-800 BC) and then is frequently referred to in Sanskrit texts. In India there is a saying that grains of rice should be like two brothers, close but not stuck together. Rice is often directly associated with prosperity and fertility, hence there is the custom of throwing rice at newlyweds. In India, rice is always the first food offered to the babies when they start eating solids or to husband by his new bride, to ensure they will have children.n the Middle East and Mediterranean Europe, it started around 800 BC. 



Geographic Distribution 


The earliest settlements might have been near the edge of the uplands, but on gently rolling topography and close to small rivers that provided a reliable water supply. The earliest agriculture had probably focused on plants that reproduced vegetatively, but the seeds of easily shattering varieties of world rice such as Oryzae fatua may have found their way to the gardens at an early date. Domestication most likely took place in the area of Korat or in some sheltered basin area of northern Thailand, one of the longitudinal valleys of Myanmar's Shan Upland, in southwestern China, or in Assam. 

Rice, an annual grass belongs to the genus Oryzae. There are about twenty three species out of which only two species have been known of their commercial value being used for cultivation. These two species are Oryzae sativa (Asian rice) and Oryzae glaberrima (African rice). 

The Oryzae sativa is the most commonly grown species through out the world today while Oryzae glaberrima is grown only in South Africa. In Asia Oryzae sativa is differentiated into three sub species based on geographical conditions viz., Indica, Japonica and Javanica. Indica refers to the tropical and sub tropical varieties grown throughout South and Southeast Asia and Southern China. The variety Japonica is grown in temperate areas of Japan, China and Korea, while Javanica varieties are grown along side of indicas in Indonesia . 

Rice cultivation is considered to have begun simultaneously in many countries over 6500 years ago. Rice has been cultivated in China since ancient times. Chinese records of rice cultivation go back 4000 yearsCultivation and cooking methods are thought to have spread to the west rapidly and by medieval times, southern Europe saw the introduction of rice as a hearty grain. In several Asian languages the words for rice and food are identical.

African rice has been cultivated for 3500 years.The crop was common in West Africa by the end of the 17th cent. Rice spread throughout Italy and then France, after the middle of the 15th century, later propagating to all the continents during the great age of European exploration. In 1694, rice arrived in South Carolina, probably originating from Madagascar. The Spanish brought rice to South America at the beginning of the 18th century. 


Rice cultivation has been carried into all regions having the necessary warmth and abundant moisture favorable to its growth, mainly subtropical rather than hot or cold. 

Spread of Rice
From an early beginning somewhere in the Asian arc, the process of diffusion has carried rice in all directions until today it is cultivated on every continent save Antarctica. In this early hearth area, rice was grown in forest clearing under a system of shifting cultivation. The crop was grown by direct seeding and without standing water. Rice was grown on "farms" under conditions only slightly different from those to which wild. A similar but independent pattern of the incorporation of wild rices into an agricultural system may well have taken place in one or more locations in Africa at approximately the same time. 

It was in china that the processes of puddling soil and transplanting seedlings were likely refined. Both operations became integral parts of rice farming and remain very widely practiced to this day. Transplanting, like puddling, provides the farmer with the ability to better accommodate the rice crop to a finite water supply by shortening the field duration (since seedlings are grown separately, and a higher density) and adjusting the planting calendar. With the development of puddling and transplanting, rice became truly domesticated. 

In China, the history of rice valleys and low-lying areas is longer that its history as a dryland crop. In southeast Asia, by contrast, rice was originally produced under dryland conditions in the uplands, and only recently did it come to occupy the vast river deltas. Migrant peoples from South china or perhaps northern Vietnam carried the traditions of wetland rice cultivation to the Philippines during the second millennium B.C. and deutero-Malays carried the practice to Indonesia about 1500 B.C. From china or Korea, the crop was introduced to Japan no later than 100 B.C. 

Movement to western India and to Sri Lanka was also accomplished very early. The crop may well have been introduced to Greece and neighboring areas of the Mediterranean by the returning members of Alexander the Great 's expedition to India ca. 344-324 B.C. From a centre in Greece and Sicily, rice spread gradually throughout the southern portions of Europe and to a few locations in North Africa. 

Medical geographers in the 16th century played an important role in limiting the adoption of rice as a major crop in the Mediterranean area. During the 16th and early 17th centuries, malaria was a major disease in southern Europe, and it was believed to be spread by the bad air (hence the origin of the name ) of swampy areas. Major drainage projects were undertaken in southern Italy, and wetland rice cultivation was discouraged in some regions. In fact, it was actually forbidden on the outskirts of a number of large towns. Such measures were a significant barrier to the diffusion of rice in Europe. 

Carbon dioxide has long been the prime suspect for the green house effect and warming up of earth , but it is now known that, methane traps 20 times more energy. Its agreed that methane concentrations are increasing at the rate of approximately 1% yr. A major methane source, perhaps even the largest of all, is flooded riceland. 

Not only do methane-producing bacteria thrive in such an environment, but rice plants themselves act as gas vents, putting greater-than-expected concentrations into the atmosphere. The problem is, of course, magnified by the extension of rice area, by the expansion of irrigation facilities, and especially by the enlargement of double-cropped rice areas. Rice fields are suspected of putting 115 million t of methane into the atmosphere each year. 

This is at least equal to the total production from all of the world's natural swamps and wetlands. Is it possible that agricultural intensification is hastening environmental degradation. As a result of Europe's great Age of Exploration, new lands to the west became available for exploitation. 

Rice cultivation was introduced to the New World by early European settlers. The Portugeuse carried it to Brazil, and the Spanish introduced its cultivation to several locations in Central and South America. The first record for North America dates from 168. The crop may well have been carried to that area by slaves brought from Madagascar. 

Early in the 18th century, rice spread to Louisiana, but not until the 20th century was it produced in California's Sacramento Valley. The introduction in the latter area corresponded almost exactly with the timing of the first successful crop in Australia's New South Wales. 

Taxonomy 
Kingdom: Plantae - Plants

Subkingdom: Tracheobionta - Vascular plants
Superdivision:Spermatophyta - Seed plants
Division: Magnoliophyta - Flowering plants
Class: Liliopsida - Monocotyledons
Subclass: Commelinidae
Order: Cyperales
Family: Poaceae - Grass family
Genus: Oryza L. ? rice 
Species: Oryza sativa - rice




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