In this article we will discuss about:- 1. Origin and Distribution of Wheat 2. Area and Production of Wheat 3. Importance 4. Harvesting 5. Tillage and Seeding.
Origin and Distribution of Wheat:
According to the well-known studies of Vavilov, the North Western parts of the Indian subcontinent together with contiguous region of Afghanistan were the centre of origin of bread wheat. Archaeological investigations at Mohenjodaro have shown that wheat was being grown in that region about 5000 years ago.
In fact, wheat was grown in India from prehistoric times. Although, as many as 25 species of wheat have been recognised in the world, only three species of wheat namely; T. aestivum/vulgare Linn (bread wheat), T. durum (macaroni wheat) and T. dicoccum (emmer wheat) are commercially grown in India.
Wheat is a very adaptable crop and is grown under a wide range of soil and climatic conditions. The crop is most successfully grown between latitudes of 30° and 60°N and between 27° and 40°S. It is grown from the borders of Arctic to near the Equator. In Soviet Union near Archangel, wheat is grown at latitude of 60°N and in the Peace River valley in Canada at about 50°N.
It is grown below sea level near the Dead Sea and in the Imperial Valley of California and at as high as 5000 m altitude of Tibet. In India, wheat is grown from 11° to 30°N and from sea level up to elevations of 3658 m in the Himalayas.
In India, it is grown mostly in the plains, where as in the hills it is cultivated in mountainous regions of north India and Nilgiri and Palani hills in south India. It is grown under a wide range of climatic conditions from Kashmir and other mountainous regions to semiarid regions with mild to severe winter.
Area and Production of Wheat:
Wheat is cultivated in about 122 countries of the world. Major wheat producing countries are China, India, USA, Russian Federation, Canada, Australia etc. China has emerged as the largest producer of wheat and accounted for 16 per cent share followed by India, which share 12.5 per cent in world production of wheat.
Although, India occupied largest area estimated at 12.25 per cent of total area under wheat in the world followed by China which occupied 11.25 per cent), the productivity of wheat in China, is appreciably higher at 4.5 t ha-1 compared to 2.6 t ha-1 in India.
World area, production and yield of wheat in major wheat producing countries is summarised in Table 2.1:
There are several countries like France, Netherlands, Sweden, Denmark, Belgium, west Germany, where the average yields range from 5 to 81 ha-1. However, their contribution to production is marginal due to limited area under wheat. As in the year 2003, India ranked first in area, second in production and 32 in productivity of wheat in the world.
India has made tremendous progress in production of wheat. During the year 1950-1951, its production was merely 6.46 M t, which increased to 78.60 M t in 2009-10. UP, Punjab, Haryana, Rajasthan, MP and Bihar together contributed about 93 per cent of production. The share of UP alone is 35 per cent of total production followed by Punjab, Haryana, MP, Rajasthan and Bihar with share around 22, 13, 9, 8 and 6 per cent respectively.
The area, production and yield of wheat in India are presented in Appendix 1.2. As per 2008-09 statistics, UP continues to be the highest producer (28.55 M t), followed by Punjab (15.73 M t) and Haryana (10.80 M t). Productivity is highest in Punjab (4462 kg ha-1) followed by Haryana (4390 kg ha-1) and Rajasthan (3175 kg ha-1).
India is expected to produce 109 M t by 2020 with annual rate of increase in production of about 2.2 per cent while present rate of annual increment is around 1.0 per cent. Recent yield plateau is a major concern in highly productive North-Western Plains Zone.
Importance of Wheat in India:
Importance of wheat worldwide as main food can be understood by use of stylised wheat spike as a symbol of FAO. Wheat is a major cereal in India after rice. Food grain production in India during the year 2009-2010 was around 220 M t and the share of wheat was 68 M t (about 35 per cent).
India has emerged as the second largest producer of wheat after China and accounted for 12.5 per cent share of total world production of wheat. Introduction of Mexican semi-dwarfs, followed by locally bred semi-dwarfs and development and adoption of management technologies resulted in dramatic increases in yield and total production.
Photo-insensitivity of the modern varieties had permitted diversification and intensification of wheat-based cropping systems. Experts point out that India has the potential to become the largest wheat producer in the world towards the year 2020.
Production of wheat in India, which was merely 4 M t during the year 1948 – 1949 increased spectacularly to 78.60 M t in 2009-10. The net per capita availability of wheat also increased from 65.7 g per day or 24.0 kg per annum in 1951 to 140 g or 51 kg in the year 2010.
The wheat revolution had, generally, bypassed the rainfed areas. Area under rainfed wheat has been declining and is currently about 25 per cent of the total wheat area and the yields are about one- third of that in the irrigated. The rice-wheat system is showing signs of fatigue and the growth factor productivity has decelerated.
All wheats, whether wild or cultivated, belong to the genus Triticum of the family Gramineae. The cultivated wheat Triticum aestivum is an allohexaploid (2n = 6x = 42) resulting from the combination of three genomes A, B and D.
It presents a classical case of evolution arising from natural hybridisation and genome building of grasses. Besides chromosome doubling, mutation and intercrossing of natural and human selections have helped in the development of different varieties.
Harvesting of Wheat Crops:
Wheat crop is harvested when the grain hardens and the straw turns light yellow, becomes dry and brittle at seed moisture content of 18-22 per cent. The rainfed (barani) crop reaches harvest stage much earlier than irrigated crop. The harvesting time varies from zone to zone.
Peninsular zone – Middle of February to first week of March
Central zone – February to March end
North eastern zone – Third week of March to mid April
North western zone – Third week of April to first week of May
Hill zone – May-June.
High temperature shortens the growing period. If the crop does not ripen before the onset of hot westerly winds, shrivelling of grain take place.
Most of the harvesting in India is with the sickle. Bullock drawn reapers are also used occasionally. In recent years, harvesting is done in Punjab, western Uttar Pradesh, Delhi and Haryana with combiners on custom service basis.
Harvesting, threshing and winnowing are completed in singe operation. Manually harvested crop is, generally, dried for 3-4 days and threshed by treading with cattle on threshing floor. Use of stoneroller, saw-thresher, tractor etc expedites the operation. Generally, winnowing is by winnowing baskets. Simple mechanical threshers have become popular in north eastern and north western zones.
The yield vanes with the duration of the variety and length of crop growing period besides several other management practices. The yields under rainfed conditions are generally low. It may be as lov* as 31-7 : – X) kg ha”1 in Peninsular and central zones. Under irrigated conditions, yields as high as 10 to 12 t ha’1 have been reported, where as in the National Demonstrations, yield up to 8.0 t ha–– u ere reported.
A grain yield of 4.0 to 5.0 t ha”1 of dwarf wheat has become a common feature i: farmer’s field in the major wheat zones. However, the national average during 1999 was 2.8 t ha”1.
Information gathered by wheat project indicates that Punjab has potential of 7.5 t ha–1 and north westen- plane zone around 7.01 ha–1 indicating a big gap between the potential and actual yield obtained by farmers. Results of Front-Line Demonstrations indicated yield gap of 1.0 t ha-1 in northeastern plane zone between front-line trials and experimental farms.
What straw is an important cattle feed in India. Generally, straw yield of rainfed wheat is about the same as that of grain, where as from irrigated crop it is about 1.5 to 2.0 times the grain yield. Straw yield of dwarf wheats is less than that from the traditional tall varieties.
Storage:
Wheat harvested at more than 12.5 ret cent grain moisture should be dried to less than 12.5 per cent within 3-5 days to prevent growth of molds and damage by storage pests. Heat must be added in areas of high humidity and airflow rate must be adjusted.
At 85 per cent relative humidity, wheat will equilibrate around 18.5 percent moisture but air alone at RH of 60 per cent will dry wheat to around 12 per cent moisture over time. Storage facilities depend on the economic factor. Easy and cost effective storage methods used by resource poor farmers include metallic bins, gunny bags and earthen pots.
Tillage and Seeding for Wheat Cultivation:
Land preparation for wheat cultivation varies widely based on geographic region, infrastructural facility and economics of crop production. Similarly, there is variation in time and method of seeding and seed rate and plant population. Tillage and seeding practices obviously affect wheat yield.
Tillage:
Wheat crop requires a well pulverised but compact seedbed for good and uniform germination. Traditional system of land preparation for wheat includes one deep ploughing followed by two to three harrowings. Two to three ploughings in summer, repeated harrowings in the rainy season followed by two to three cultivations and planking immediately before seeding produce an ideal firm seedbed for the dry crop on alluvial soils.
In black cotton soils, blade harrow is used instead of plough. One to two ploughings with an iron plough may some times precede use of blade harrow. For rainfed crop, soil moisture conservation is important for successful wheat crop. One deep chiselling once in three years should be done to break open hard pans. Two to three summer ploughings have been found adequate for soaking the rainwater into deep layers.
After cessation of monsoon, all the possible efforts should be made to conserve moisture. Field should be ploughed in the evening time and furrows kept open during night followed by planking after each ploughing every in the morning. Haveli or bundhia cultivation is adopted in northern and central India.
Main feature of these systems is bunding the field in sections to impound water. Crops are not grown during monsoon to allow water accumulation but drained at the end of monsoon. Furrows are opened with plough and wheat seeds sown as soon as soil is at optimum moisture content for ploughing.
When wheat follows sugarcane or pigeonpea, delay in seeding wheat leads to drastic reduction in yield. Presowing irrigation for wheat may be given in standing crop before its harvest, so that the field can be prepared immediately after the harvest of previous crop. Alternately, no-tillage system may be followed and wheat sown directly using zero-tillage seed drills.
This system has been practiced for over two decades in Panama state of Brazil. In India, zero-tillage seed drills have been recently developed and used in intensive cropping systems.
Time of Seeding:
As the environmental condition in the vegetative phase determines the plant morphology and the time of earing, dates of sowing wheat crop become important in the final yield. Venkataraman (1968) advocates selection of a 90 day period with the lowest mean air temperature to decide the time of sowing.
This would indicate that the optimum sowing dates would vary in different areas of the wheat belt. Optimum sowing time for traditional tall wheats (last week of October to first week of November) was not ideal for dwarf wheats. Hence, a large number of field experiments were conducted at several locations in different parts of the country.
Optimum sowing time for short duration thermosensitive varieties is second fortnight of November. When sown in first fortnight, they produce very few tillers, come to flowering very early and give low yields. However, for relatively less thermosensitive long duration varieties, optimum sowing time is first fortnight of November. Surprisingly, in spite of differences in the duration of wheat growing period in different wheat zones, the above recommendation holds good for all zones.
There was sharp reduction in yield in all the zones when wheat was sown after first fortnight of December. Long duration varieties were greatly benefited due to early sowings in first fortnight of November, especially in north western plain zone. There was progressive decrease in yield as the sowings were delayed. Delaying sowing from November 1 to 22, December 15 to January 7 resulted in 13, 23 and 49 per cent decrease in grain yield in Punjab.
In the north eastern plains, grain yield increased by 450 kg ha-1 when sowing date was advanced from third week of November to first week of November. In the Peninsular zone, November sowings up to 20 resulted in higher yields than December sowings.
From the results of experiments the following general conclusions can be drawn on optimum sowing time for wheat in different wheat zones:
In north eastern and north western wheat zones, sowing of wheat is often delayed owing to late harvest of rice, sugarcane or potato. Delayed wheat planting results in one per cent yield per day after first fortnight of November.
Wheat sowings beyond the third week of December are not profitable. The zero tillage-cum-fertiseed drill enables drilling of wheat within few days after rice harvest, avoiding the need to plough the field for sowing wheat.
When sugarcane or potato precedes wheat, sowing is considerably delayed. To gain the time for wheat sowing, it is necessary to irrigate the preceding crops before harvest such that the field can be prepared for wheat crop immediately after the harvest of preceding crop.
Depth and Method of Seeding:
The semi-dwarf varieties have shorter coleoptiles as compared with that of traditional tall varieties. Average coleoptile length of tall, single dwarf, double dwarf and triple dwarf wheats under laboratory conditions was 9, 5, 4 and 3 cm, respectively. Germination of all the categories was not affected when sown 6 cm deep.
However, at 8 cm depth of seeding, there was marked reduction in the germination of all the three types of dwarf wheats. Field studies at five places in mega wheat growing areas indicated that the average plant emergence in one meter row for 4, 6 and 8 cm depths were 45, 46 and 40, respectively. On the basis of field experiments, optimum depth of seeding is 5-6 cm for dwarf wheats.
Traditionally, wheat is sown by broadcast, kera method under irrigated conditions and by pora method under rainfed conditions. In kera method, wheat is sown behind the country plough. Quite a few seeds will be dropped at shallow depth in dry soil and germinate only after first irrigation. Consequently, the crop will not mature uniformly.
When the seed is dropped through a funnel attached to the country plough (pora method) the soil from furrow fall on the earlier made furrow in which the seed has been already dropped. Consequently, the seeding depth will be more than 8 cm leading to poor germination.
Hence, these two methods of seeding should be carefully conducted. The best method of sowing is with ferti -seed drill, which drops the fertiliser and seed at optimum depth for good germination and uniform crop maturity leading to high yield.
Under rainfed conditions, after sowing, the furrows are left open where as in the case of irrigated wheat, the furrows are covered with wooden plank. Transplanting of seedlings can be done when sowings are very much delayed under irrigated conditions.
Agrotechniques to reduce the losses due to delayed sowing indicated relatively higher yield due to closer row spacing of 15 cm with a seed rate of 125-150 kg ha-1. There was no response to increased rates of nitrogen application under late sown conditions.
Seed Rate and Spacing:
Optimum plant population is an essential prerequisite for high yield of wheat. Seed rate and row spacing vary with the variety, sowing time and other management practices. Generally, early maturing and poor tillering varieties needs closer spacing with higher seed rate compared with long duration and profusely tillering varieties. Likewise, late sown crop demands closer row spacing and higher seed rate to compensate for the lesser number of tillers and shorter growing period.
Studies on seed rate requirement for dwarf wheats indicated that, in general, seed rate of 100-125 kg ha-1 resulted in higher yields compared with 75 kg ha-1. A high seed rate of 125 kg ha-1 was needed for Sonalika, a very bold seeded variety. Other varieties did not show favourable response to seed rates higher than 100 kg ha-1.
The following recommendations could, therefore, be made:
All zones except Peninsular zone: 100 kg ha-1.
Peninsular zone: 120 kg ha-1.
Higher seed rate is necessary in Peninsular zone because of short growing season and poor tillering due to higher temperatures during the crop growing period.
Dwarf varieties did not show favourable response to different row spacings closer than 25 cm under irrigated conditions. Among the dwarf varieties, Sonalika responded to closer row spacing, especially under late sown conditions. Therefore, a row spacing of 20.0 to 22.5 cm, which is very convenient for adoption, is recommended.
Nigam (1977) from Delhi reported that 200 seedlings m-2 is the optimum plant population for irrigated wheat. Beyond this level, there was no increase in yield due to inverse relationship between ear number and grain weight per ear. For rainfed wheat (barani wheat), a row spacing of 20-25 cm has been found optimum if the soil moisture is adequate at sowing time. The row spacing should be 25-30 cm if the soil moisture is medium to low.