Wheat – Origin, climate, soils, crop rotations, field preparation, varieties, cultivation, insect-pests-diseases and post-harvest operations.

Wheat is the second most important food crop of the country, which contributes nearly one-third of the total foodgrains production. This contribution has increased over years and was less than 10% in the early fifties. It is consumed mostly in the form of unleavened pan-backed bread, called chapati. Wheat straw is used for feeding the cattle.

The crop is mostly grown under irrigated conditions in sugarcane-wheat rotation. It has a very high degree of heat tolerance and can be sown as late as December and January without much fear of heat damage during grain filling, even in the southern zone. It is preferred for several south Indian dishes which use granular form of wheat.

Wheat

The area under wheat has steadily gone up since the start of the Wheat Revolution in 1967 and its production and productivity have increased tremendously.The Wheat area has risen from 12.8 million ha in 1966-77 to 28.15 million ha in 2007-08. During the same period production has increased from 11.4 to 78.4 million tonnes and the productivity has gone up from 887 kg/ha to 2,785 kg/ha.

Wheat

Another major change that has occurred in wheat cultivation since Independence is that the proportion of area under irrigated wheat has increased greatly. It has gone up from 34% in 1967 to 51% in 1970 and more than 89.6% in 2006. Thus the crop has how become largely irrigated as compared to being primarily rainfed earlier.

India, in terms of production and area, now occupies the second place among the comity of wheat-growing countries of the world. The total world wheat production is estimated at 605.9 million tonnes from 216.6 million ha during 2005-06, to which India contributed 11.4%.

Scientific classification

 Kingdom  Plantae
 Family  Poaceae
 Subfamily  Pooideae
Genus  Triticum L.
 Famous Spices  T. aestivum
 Scientific Name Triticum aestivum

In the past there were 4 species, viz. Triticum aestivum, Tdurum, T dicoccum and T sphaerococcum, under cultivation in India. T. sphaerococcum has now practically gone out of cultivation because of its low productivity and high susceptibility to diseases. Throughout the country only spring-type wheat varieties are grown, though these are raised in winter.

The common bread wheat, T.aestivum, is the most important species, occupying more than 90% of the total wheat area in the country. It is grown all over India from the sea-level up to an elevation of 3,500 m in the Himalayas. The macaroni wheat, Triticum durum, is the second most important species, occupying nearly 10% of the wheat area. Earlier its cultivation was primarily confined to the central and southern India, with very small area in Punjab and West Bengal. Its cultivation was most common under rainfed conditions only, on account of high susceptibility to rusts. In recent years with the development of high-yielding semidwarf types, a large area has come up in Punjab under irrigated conditions, where it was popularized to contain Karnal bunt disease. Now efforts are on to export it to earn foreign exchange.

The T dicoccum cultivated emmer, is grown on a very restricted scale in Gujarat, Maharashtra, Karnataka, Andhra Pradesh and Tamil Nadu, where it is known as popatiya, khapli, ravva, godhumalu, samba etc. On account of a high fibre and protein content it is now being popularised as health food. A large pocket of several thousands hectares of this species exists in Belgaum district of Kamataka along the river Krishna.

Climate

In India, “wheat” is a winter (rabi) crop. The sowing is done in autumn and harvesting in summer. The high temperatures at both ends of the crop season determine the duration available for wheat cultivation, which ranges from 100 days in down south to more than 145 days in north-western plains and 180 days in the hills. High temperatures in October do not permit early seeding of the main crop. Early seeding increases the incidence of root rot and seeding-blight fungi and severely restricts tillering capability, crop duration and yield potential of most varieties. Very hot temperature during the grain-ripening period can result in grain shrivelling.

The annual rainfall in the wheat-growing regions of India ranges from 12.5 to 100 cm, but most of it is received in summer during the monsoon. In winter, when wheat is in the field, the rainfall ranges between 3 and 7 cm only. As such to achieve high yield, irrigation is essential, which enables the application and utilization of required inputs. However, availability of irrigation facilities varies widely in different regions. The proportion of irrigated wheat in Punjab, Haryana and Rajasthan is more than 97%, whereas in Himachal Pradesh and Karnataka it is only 19.6 and 51.6% respectively. In Bihar it is 90.7% and in Uttar Pradesh it is 97.5% while in Madhya Pradesh it is 78.3% only. Prevalence of several wheat diseases, viz. rusts, loose smut, Karnal bunt etc., is another important component of wheat cultivation in India.

Agroclimatic zones

Based on climatic conditions and disease prevalence, particularly rusts, the country is broadly divided into 5 main wheat zones and a small southern hills region.

North-western plains zone: It comprises Punjab, Haryana, Rajasthan (except the south-eastern portion), western Uttar Pradesh, and the foothills of Jammu and Kashmir, Himachal Pradesh and Uttarakhand. This is the most important among the 5 zones and accounts for around 40% of area and 55% of wheat production in the country.

This zone has the longest and the coolest winter in the plains region of India and the duration of the timely sown crop may extend up to more than 145 days, making it potentially the most productive region. In this zone most of the wheat crop is irrigated (98%) and the optimum sowing period is mid-November. The rainfed wheat is sown early towards the end of October. Harvesting is generally carried out in April/May. Leaf rust, stripe rust, loose smut and Karnal bunt are the most important diseases. T. aestivum was exclusively grown in this zone till recently, but now some area has come under T durum, particularly in Punjab.

North-eastern plains zone: It comprises eastern Uttar Pradesh, Bihar, Jharkhand, West Bengal, Asom and Orissa. The other north-eastern states, viz. Manipur, Tripura, Nagaland, Meghalaya and Mizoram, which grow very little wheat, are also included in this zone. It has shorter winter and the crop duration is around 125 days. This is also an exclusively T. aestivum region and productivity is relatively low. It is the second largest zone of the country accounting for nearly 30% of area and 25% of production.

Most of the wheat crop is preceded by paddy. Delayed harvesting of paddy delays the sowing of wheat towards the end of November to December. Harvesting is done in March-April.

The most important diseases in the zone are leaf rust and foliar blight. Karnal bunt incident is prevalent in some pockets.

Central zone: It comprises Madhya Pradesh, Chhattisgarh, Gujarat, south-eastern Rajasthan (Kota and Udaipur Divisions) and the Bundelkhand and Jhansi regions of Uttar Pradesh. This is the third most important wheat zone of the country, which accounts for more than 20% of area and 15% of production. Crop duration is relatively shorter and is around 125 days. Both bread and durum wheat varieties are grown in the zone. T. dicoccum is also grown in a few pockets in Gujarat. The region is famous for quality wheat grain production. The best-quality durum wheat is produced in this zone.

A large part of the wheat area (around 25%) is rainfed. Under these conditions the sowing of wheat depends on the moisture conserved in the soil from the preceding monsoon. The sowing of rainfed wheat is done in October. Irrigated wheat is seeded after mid-November. Harvesting of rainfed wheat commences in the beginning of March, while the irrigated crop is harvested later.

Important diseases of the zone are leaf and stem rusts and root rot. Incidence of Karnal bunt has been recorded only sporadically and has been attributed to source of seed.

Peninsular zone: It comprises states of Maharashtra, Karnataka, Andhra Pradesh and Tamil Nadu. It contributes less than 500 of the area and about 200 of wheat production. All the 3 species mentioned above, viz. T. aestivum, T. durum and T. dicoccum, are grown in this zone. Triticum durum is the most important species under rainfed conditions. On account of a short and warmer cool season, the crop duration is the shortest and is only around 110 days.

Area under irrigated wheat is around 66% in Maharashtra but only 51% in Karnataka. However, assured water supply is limited, but wherever it is available, a good crop of wheat comparable with that of northern-western India can be raised. The sowing under rainfed conditions is practically over in October and the irrigated crop is sown in the first half of November. Most of the harvesting of the rainfed crop is over by the second half of February, while the irrigated crop is harvested in the first fortnight of March.

The important diseases are leaf and stem rusts and root rot. Incidence of Kamal bunt has not been recorded from any region.

Northern hills zone: It comprises the hilly areas of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, West Bengal, Arunachal Pradesh and Sikkim. Wheat is grown up to an elevation of 3,500 m above mean sea-level. Triticum aestivum is the only species grown. The zone contributes only about 2% of the wheat area and 1% of production. Most of the crop is grown under rainfed conditions. Irrigated wheat crop is restricted to valley regions, which accounts for less than 20% of area.

In this zone, the rainfed crop is sown in October and is harvested in May-June. The irrigated crop is sown in November. The wheat plants remain slow growing from December to February when the temperature is very low. After this the crop starts growing rapidly with the increase in temperature. In very high mountain ranges (above 2,500 msl) irrigated wheat is grown during summer (April october) instead of the winter when the area remains under snow. Here, the sowing is done in April-May after the snow melts and the crop is harvested in September-October.

The most important diseases of the region are stripe, leaf and stem rusts, loose smut, powdery mildew and hill bunt.

Southern hills zone: It comprises Nilgiri and Palni hills of Tamil Nadu and Kerala. It has only a few hundred hectares under wheat, but the region is extremely important on account of its crucial role in perpetuation of rusts since all 3 rusts (i.e. stripe, leaf and stem) survive here round the year and spread to plains under suitable environments, thus posing a threat to the crop in plains. Wheat can be grown all around the year, but mainly 2 crops of wheat are raised. The first crop is grown between October and April and the second between May and September.

Soils

Well-drained loams and clayey loams are considered the best for growing wheat. However, good crop of Wheat can be raised in sandy loams and the black soils also. Durum Wheat is considered more suitable for cultivation in heavy and black soils, whereas aestivum wheat is grown in all types of soils. The durum types when grown in light soils tend to express high yellow berry problem, resulting in poor-quality grains.

Crop rotations

Till the advent of high-yielding, semi-dwarf, fertilizer-responsive, photo-insensitive varieties, most of the irrigated crop was grown after the harvest of maize, sorghum, pearl millet, cotton, etc. grown during khari . Sometimes, green-manure crops, viz. sunnhemp (Crotalaria juncea), greengram, clusterbean, cowpea etc. are sown to enrich the soil prior to wheat sowing.

With the increased emphasis on intensive cropping and high yields, the rotation patterns have undergone drastic changes all across the country, particularly in Punjab, Haryana, western Uttar Pradesh where rice is now extensively grown in kharif and is followed by wheat. Similarly, wheat is now extensively cultivated after rice in eastern Uttar Pradesh and Bihar. Hence the rice-wheat rotation has become extremely important, although the sequence has several problems associated with it for which extensive research is in progress. Since this region is the major wheat area of the country, more than 10 million ha are estimated to be under this rotation. This represents more than 40% of the wheat grown in the country.

The sugarcane-wheat and cotton-wheat rotations are also common in several parts in northern India under irrigated conditions. Soybean~wheat has become important rotation in Madhya Pradesh and Maharashtra.Wherever more irrigation water is available, a legume crop is grown between 2 cereal crops to enrich the soil as well as to get the needed pulses. Bajra (pearl millet)–wheat, jowar (sorghum)-wheat and jute-Wheat are other rotations followed in some parts of the country. Development of short-duration varieties of pigeonpea has made the growing of wheat feasible after harvest of this crop.

Very intensive cropping sequences involving the raising of 3 crops within 1 year are also followed by a limited number of farmers. This may involve the raising of a short-duration variety of kharif crops, viz. rice, bajra, maize, legume etc., followed by growing of toria, potato or vegetable pea in September to December and than seeding of wheat in December to January. Such late sowing of wheat is also carried out after harvest of sugarcane in end December/January.

In north-westem India and in the foot-hill (tarai) areas of Uttar Pradesh, irrigated wheat is also grown as a companion crop between rows of sugarcane and potato. Up to 3 tonnes of wheat can be harvested as bonus in such a companion cropping without affecting the yield or quality of sugarcane.

Earlier most rainfed wheat in northern and central India was grown in a monocrop sequence in fields that were left fallow during kharif and kept open by deep ploughing to conserve moisture from the rainy season. Now such area has been greatly reduced with the development of irrigation facilities. In the black soils of central and peninsular India, dryland wheat is rotated with sorghum, pearl millet or cotton in kharif in alternate year. The growing of quick-maturing crops, viz. greengram, gingelly, onion, coriander and even groundnut or early sown maize as catch crops before wheat are fairly common.

All over India, the growing of rainfed wheat mixed with gram, lentil, mustard, linseed, barley and safflower is quite common. Even under irrigated conditions a row of mustard for every 8 to 12 rows of wheat is a common practice. This mixed cropping meets the farmer family requirement for cereals, pulses and oil and also gives some insurance against pests, diseases and other natural clamities, which might destroy the pure crop of oilseed and pulse.

Field preparation

Wheat crop requires a well-pulverized but compact seedbed for good and uniform germination. The 3 to 4 ploughings, repeated harrowing, cultivation and planking, involving 10 -15 field operations, before sowing to produce firm seedbed are considered desirable for raising a good crop of wheat. Very timely cultivation to conserve moisture in the soil is essential under rainfed condition. In the black cotton soil, blade harrow (bhakar) is used instead of the plough. The l to 3 ploughings with an iron plough may sometimes precede the use of bhakar.

For the irrigated cop, the land is given a pre-sowing irrigation (palewa or rauni), followed by cultivation and planking to prepare a fine well-pulverised seedbed. Recently zero-tillage and minimal tillage sowing practices using a specially designed zero-till seeding-cum-fertilizer drill have been recommended to save the time required to prepare proper seedbed under the rice-wheat rotation, particularly when medium-long and long-duration varieties of rice (or basmati types) are grown and the fields get vacated very late in November and December. Such practices can be followed even for timely sown wheat since it enables savings on diesel costs (around 60 litres diesel), labour (15-20 working hours) and time (15-20 days) which helps to reduce cost of wheat production. However, these are successful when weeds are not a serious problem or when these are controlled with the use of weedicides. Owing to the cost and time saving advantages, the zero-tillage seeding technology has been widely adopted by the farmers in north-western plains in recent years. Large number of farmers are using this seed drill for sowng in fields partially prepared involving minimal tillage operations to save fuel costs. In recent years use of rotovators for yield preparation is becoming popular. This equipment makes field ready for seeding with only one/two operations.

Varieties

For getting the maximum yield, under good management and optimum input conditions, the choice of appropriate variety plays a very important role. In the absence of a right variety, proper production technology cannot be applied effectively. Appropriate plant height, maturity duration, disease resistance, fertilizer responsiveness, lodging and heat tolerance during grain-filling period as well as shattering tolerance are some of the important features for a variety suitable for cultivation under irrigated conditions. Under rainfed conditions, the ability to withstand soil and atmospheric drought during various growth stages and high temperature at sowing time are most important characteristics.

Before the Green Revolution in 1967, all the wheat varieties grown in India were of tall type. Some of the old varieties were outstanding for grain quality, wide adaptability and performance under low-input condiitions. Such types included PbC 518, PbC 591, NP 165, NP 824, NP 839, NP 846, NP 852, C 273, C 306, K 65, K 68, Narbada 4, RS 31-1 etc. These types were very suitable for lowand medium-yielding environments and had a yield potential of 2.5 to 3 tonnes/ha under well-managed conditions. However, when the fertilizer dose was increased beyond 40 to 60 kg/ha of N and more intensive production practices were followed to achieve higher yields, these varieties generally showed high lodging and yield realization was reduced. Since farmers feed the straw to the cattle, they preferred the tall types and the breeders of the time had to keep this requirement in View while deve10ping the new varieties. Tall varieties are still popularly grown under the rainfed conditions.

With the introduction of semi-dwarf varieties in the later half of sixties and the establishment of their high-yield potential at all levels of fertility, the emphasis was shifted to development of such varieties, particularly for areas where irrigation is available. These varieties were able to produce around 4.5 tonnes/ha and could withstand fertilization of up to 120 kg N/ha. The currently available full duration varieties are capable of producing up to 6.5 tonnes ha under well-managed conditions.

Now semi-dwarf varieties have been developed for most irrigated cultural environments, viz. early-sown, late-sown and very late-sown situations. Varieties have also been developed for salt-affected soils. Experience has shown that semi-dwarf varieties can perform very well under favourable rainfed conditions, and these have been recommended for cultivation in the north-western, north-eastern and hilly regions of the country where soil moisture levels remain favourable for longer duration. Recently semi-dwarf Triticum dicoccum varieties have also been developed and released for cultivation in southern part of the country.

Development of improved wheat varieties is a continuously ongoing process, since most varieties in due course of time become susceptible to new forms of the prevalent wheat diseases particularly rusts, which undergo a corresponding change in theif virulence pattern after release and wide-scale cultivation of resistant varieties. This change in virulence pattern is highly dependent on the extent of area coverage under a variety. Varieties that become extremely popular and cover more extensive area fall prey to new rust virulences more rapidly.

Therefore coverage of very large area undef one variety in a region is discouraged and more than one variety is always available for general cultivation. However, since farmer’s cannot be prevented from growing any particular variety, vast area gets covered with the same variety, reducing its useful life. Under such a situation the only solution is to develop new resistant varieties as vigorously as possible and replace the older varieties continuously on sustained basis.

Most of the older high-yielding varieties that were popular earlier in various parts of the country, such as Sonalika and Kalyansona, WL 711, WG 377, HD 2285, HD 2329, Lok 1, WH 147, UP 215, UP 310, Sharbati Sonora, Chhoti Lerma, Shera, Heera, Moti, Janak, Partap, N15439, HD 2278, VL 421, Girija etc., have become highly susceptible to rusts and hence unsuitable for general cultivation. Only a few of the old varieties, viz. HD 2009, UP 262 and HD 2189, continue to maintain a high degree of rust resistance, but have lost popularity since higher yielding replacements have become available. Sonalika, WH 147 and Lok 1 in spite of having become susceptible to rusts continue to be grown in some parts of the country in view of their very special adaptability to certain environments.

Cultivation

Sowing time

Normally wheat is sown when the average daily temperatures fall to around 22°C-23°C which happens only in November in most wheat-growing areas. Sowing ‘wheat‘ while the temperatures are high (around 25°C) results in poor germination, reduced tillering and early onset of flowering, thereby exposing the floral parts to cold damage.

All these factors depress the crop yields. Only few varieties, viz. C 306, K 8027, N 15439, are suitable for sowing prior to end of October which makes these suitable for rainfed conditions where seeding is done early.

Under irrigated conditions, the first fortnight of November is considered the optimum time for sowing the medium and long-duration varieties, which are capable of giving the highest possible yield. Such varieties include PBW 343, WH 542, CPAN 3004, PDW 233, K 88, HUW 468, HD 2336, Raj 1555, GW 190, MACS 2486, DWR 162 in the zone of their recommendation.

Wheat

In eastern India, where long-duration varieties of rice are grown as also in a northwestern parts, where Basmati types are cultivated in the rice-wheat rotation, the sowing of wheat is often delayed, and may go up to the third week of December for which short-duration wheat varieties are suitable. In several parts of India, wheat is sown after harvesting sugarcane, toria, short-duration pigeonpea, potato and some vegetables, viz. peas, where it is sown beyond the third week of December and even early January. Such sowing requires extreme care in crop management to achieve reasonable yields, since the crop has to mature within a very short duration and under very high temperatures. Special set of varieties have been recommended for such sowings. However, very late sowing is not normally recommended, because it requires extreme care to get reasonable yield.

Under rainfed conditions the sowing is done relatively early before the moisture built up from the monsoon rains recedes deeper. The second half of October is the optimum time. Since the temperature at this time is still relatively high, the choice of right type of varieties is extremely important to overcome some ofthe losses caused by yield depressing factors (as listed earlier). Varieties recommended for rainfed sowing possess heatand drought-tolerance features to varying degree. The success of rainfed wheat depends highly upon the amount of moisture conserved in the soil from monsoon rains.

Seed rate

The seed used for sowing should be well developed, healthy, with good germination capacity, free from seed-borne diseases and weed seeds. It is advisable to sow certified seed. For varieties with the medium-sized grains (38 g for 1,000 seeds) a seed rate of 100 kg/ha is recommended. For bold-seeded varieties (around 45 g/1,000 seeds) a seed rate of 125 kg/ha is optimum. For late-sown wheat, seed rate of 125-150 kg/ha is recommended.

Under rainfed conditions a reduced seed rate of 75-80 kg/ha is recommended. Most of the improved varieties are susceptible to loose smut disease, and the seed used should be given either solar or hot-water treatment or should be treated with appropriate fungicide before sowing.

Sowing method

For proper germination the seed must be placed in moist soil. Sowing is done by drilling or broadcasting of seeds. Sowing with seed-drills, whether tractor-drawn or bullock-drawn, deposits the seed at a uniform depth, gives a more uniform stand and leads to early emergence of vigorous seedlings. In many places the seed is sown by hand in furrows behind the plough, drawn by bullocks by the kera method. The seed of semi-dwarf varieties should not be placed below 4 to 5 cm depth, since they have a short coleoptile, but that of the tall types can be placed up to a depth of 6 to 7 cm.

For irrigated timely sown wheat, a spacing of 22.5 cm between the rows is considered optimum. For irrigated late-sown conditions, the row spacing is reduced to 15-18 cm. After seeding the furrows are covered by running a wooden plank (sohaga). Under rainfed conditions seed is required to be placed deeper, and after sowing, the furrows are left open. Deeper sowing is also practised in rough, dry and light soils, whereas comparatively shallow sowing is done in moist soils. Rainfed wheat is sown at relatively wide spacing of about 25 to 30 cm between the rows.

Other methods of sowing include seeding wheat in untilled soils using a specially designed zero-till seed drill. It is specially recommended for areas where wheat sowings get delayed due to late harvest of long-duration rice varieties grown in Eastern Uttar Pradesh and Bihar. However the method has become quite popular in Punjab and Haryana owing to economy in cultivation. Another method of sowing recommended for seeding wheat is bed-planting where wheat is seeded on top of 65 to 70 cm wide beds with 30 cm channel betwen two beds using a specialy designed bed planter. This helps in saving water (25-40%), seed (25%) and fertilizers (25%) without any adverse effect on yield.

Some farmers sow the crop by broadcasting seeds in the well-prepared fields followed by harrowing. Good plant stand be achieved only when top soil layer has adequate moisture, higher seed rate is used and operation is performed by experienced worker. However, this is an undesirable practice since seed cannot be spread uniformly, and get placed at variable depths resulting in erratic crop stand and mechanical weeders cannot be used. In case this method has to be adopted under certain constraints then seed rate should be increased by 25% and moisture availability ensured in top-soil level.

Irrigation

Wheat” sown under irrigated conditions requires 4 to 6 irrigations, depending on the soil and weather conditions. Heavy deep soils with good water-holding capacity may require only 3 to 4 heavy (7 to 9 cm) irrigators whereas 6 to 8 lighter (5 to 6 cm) may be required in sandy soils. Higher temperatures during any of the crop growth phases may necessitate additional irrigation. Adjustments need to be made for rainfall during crop season.

There are several methods to decide when to apply irrigation. These include soil moisture level determination, consumptive water use and physiological crop stage. The last method is the easiest to follow since no specific measurements and estimates are required and can be readily followed by farmers. In this method the first irrigation is given at the crown-root initiation (CRI) stage, i.e.20–25 days after sowing, followed by irrigation at late tillering, late jointing, flowering, milk and dough stages. Among these, crown-root-initiation stage is the most critical for irrigation since the crown roots are formed at around 2 cm of soil depth, irrespective of depth of seed placement and this is the level which is subject of fastest drying. Under dry-soil conditions roots fail to grow and subsequently result in yield loss. Irrigation during grain falling is also extremely important since inadequate moisture can lead to grain shrivelling.

Two or three extra irrigations may be required where the soils are very light or sandy and in the central and peninsula zones where temperatures are relatively higher. lrrigation should be avoided at the stage during which sufficient (rainfall of more than 1 cm) has occurred, as also during the windy weather particularly post-flowering stage to prevent lodging of the crop.

Under limited water supply the number of irrigations depends on the quantum of its availability, i.e. (a) if water is available for only 1 irrigation, it should be applied at the crown-root-initiation stage (CR1); (b) if water is available for 2 irrigations, the first irrigation should be applied at the crown-root initiation and the second at bootleaf stage, i.e. 7 to 8 weeks after the first irrigation; and (c) if water is available for 3 irrigations, the first irrigation should be given at the crown-root-initiation stage, followed by boot and milk stages.

Weed control

Keeping weeds under controls is very crucial for achieving high yield levels. Maximum damage is caused by weeds during early growth stages. Several methods are available for their control including hand-held equipment, power driven implements and chemical weedicides. Hoeing or interculturing a few days after the first and second irrigations or rain will break the crust and also help remove the weeds. On a smallscale hand-held equipment, Viz. khurpi, hand hoe, etc. are used. Several power-drawn implement, Viz. cultivators, are also used.

Use of chemical weedicides has become quite prevalent in several parts of the country, since it is economical, effective and enables timely control of weeds. For controlling non-graminaceous broad-leaf weeds, a spray of 2, 4-D sodium salt @ 625 g a.i/ha in 750 litres water 4 to 6 weeks after sowing is effective. Spraying before or after this specific period will be harmful to the wheat crop. If graminaceous weeds, e.g. Phalaris minor (foxtail weed) and wild oats (Avena ludoviciana), are present, use of Isoproturon @ 1.0 kg a.i/ha or pre-emergence weedicides, Viz. Pendimethalin @ 1.0 kg a.i/ha 2-3 days after sowing, is quite effective. Widespread use of same weedicides (Isoproturon) over several years in Haryana and Punjab has resulted in development of resistant forms of Phalaris. In such situations use of Sulfosulfuron @ 45 g a.i./ha is recommended. Other recommended weedicides include Metribuzin, Clodinafop, Fenoxoprop ethyl, Metsulfuron methyl for specific situations.

Fertilization

To achieve high productivity levels use of synthetic fertilizers is very essential. It Should be remembered that large quantities of plant nutrients are removed from the soil along with the harvest of grain and straw. The nutrients removed from the soil include large quantities of N, P and K along with small amounts of several other elements. Average quantities of nutrients removal for each tonne of grain harvest along with 2 tonnes of straw amount 25 kg N, 2 kg P2O5 and 38 kg K along with 5 to 6 kg of each of S, Mg and Ca and small quantities of elements like Fe, Mn, Zn, B, Cu etc. Unless these nutrients are replaced through considered application sustaining high productivity over time is not possible.

Use of organic manures is highly effective to achieve and sustain reasonable yield levels since these contain small amounts of all plant nutrients. Organic manures are also essential to maintain biological processes and soil physical properties. However, to achieve higher levels of productivity use of synthetic fertilizers is essential. Therefore integrated nutrients management involving balanced use of synthetic fertilizers and organic manures is essential to sustain high productivity levels.

Use of farmyard manure @ 5-10 tonnes/ha is recommended for cultivation of wheat both under rainfed and irrigated conditions which should be applied 5 to 6 weeks before wheat sowing.

Normaly farmers do not apply synthetic fertilizers to the rainfed wheat in the majority of cases but farmyard manure or some other organic matter is frequently used. The rainfed wheat is greatly benefited, if 40 kg N/ha and 20 kg P2O5/ha are applied. It should be applied 10 cm deep (3-4 cm below the seed) at or before sowing.

The fertilizer dose recommended for the timely sown irrigated wheat is 80-150 kg/ ha nitrogen (N) (depending upon soil-fertility status), 40-60 kg/ha phosphorus (P2O5) and 40 kg/ha potassium (K2O) (based on soil-test results). The indicated lower levels are commended for high fertility status soils or wheat sown after harvest of legume crOps. Where a green-manure crOp precedes wheat, the farmer should give all the phosphorus that is subsequently used by the wheat crop. In a cropping system involving the rice-wheat rotation, all the potassium needed under this system should be given to the rice crop and all the phosphorus to the wheat crop, and nitrogen to both the crops.

For the late-sown irrigated wheat crop, the recommended dose of fertilizer is 60-80 kg N/ha, 30-40 kg/P2O5 ha and 25-30 kg/K2O ha.

Total quantities of phosphorus and potassium and half of nitrogen should be placed 5 cm below the seed at the sowing. The remaining quantity of nitrogen should be applied at the first irrigation at crownroot initiation. In lighter/sandy soils it should be applied in two splits, i.e. one-fourth at first and the remaining at second irrigation. Indian soils are generally not deficient in potassium, but its application should be adjusted according to the soil-test results.

Zinc, manganese, sulphur and boron deficiencies are becoming important in some areas with light soils under high intensity cultivation. Zn, Mn and S deficiency has been reported from Punjab, parts of Haryana, western Uttar Pradesh and Delhi. While B deficiency has been reported from West Bengal, Bihar and Eastern Uttar Pradesh. If Zn deficiency is acute, a dose of 50 kg zinc sulphate/ha is recommended. In moderately deficient soils 25 kg/ha of this chemical is sufficient. S deficiency can be removed by the use of fertilizers containing sulfur such as ammonium sulfate, single

superphosphate etc. Spray of 0.5% solution of MnSOagainst Mn deficiency and solubor against B deficiency if symptoms are noticed in growing crops is recommended.

Insect-pests and diseases

Diseases

Three rusts, viz. leaf or brown (caused by Puccinia recondita), stripe or yellow (caused by P. striiformis) and stem or black (caused by P. graminitritici), are the most important diseases of wheat in India. The best strategy is to grow rust-resistant varieties. All improved wheat varieties at the time of release are resistant to the rust types prevalent in the zone for which recommendations are made. Later in due course of time these may become susceptible to the new races of these rusts, which also undergo changes by various mechanisms. It is therefore very important to grow the latest released varieties and discard the older types.

Loose smut (caused by Ustilago tritici) is also an important disease of wheat, whose expression is most serious in north-western parts and hilly regions of the country. Most of the improved varieties are susceptible to this disease. Hence it is important that in the disease-prone areas before sowing the seed is treated with systemic fungicides, viz. Carboxin or Carbendazim @ 2.5 g/kg seed. Solar treatment can also be used to control the disease.

Since the disease is strictly internally seed borne, if adequate precautions are taken at the seed production stages and the disease infection is not allowed to occur at flowering through rigid disease-control measures in the seed production plot, there may be little need to treat the seed for commercial sowing.

Kamal bunt (caused by Neovossia indica) is another disease of wheat that can pose serious threat to wheat crop in same areas. It is an important disease for the north-western plains of the country. The best strategy is to grow resistant or tolerant varieties in disease-prone areas. Timely sowing and avoiding irrigation at flower-emergence stage helps reduce its incidence. Among the other wheat diseases, foliar blights (caused by Helminthosporium spp. and Alternaria spp.) are extremely important in the north-eastern region.

Powdery mildew (caused by Erysiphe graminis tritici) is quite important in the Northern hills zone and Northern plains zone. Karnal bunt, foliar blight and powdery mildew can be controlled by spray of 0.1% Propiconazole at appropriate stage. Hill bunt (caused by Tilletia foetida and T. carries), flag smut (caused by Urocystis agropyri), and foot-rot (caused by Helminthosporium spp., Sclerotium spp., Fusarium spp. and Pythium spp.) are of sporadic occurrence in various parts of the country and can be controlled by the use of appropriate fungicides.

Among the diseases caused by nematodes ear-cockle or tundu (caused by Anguina tritici and Clavibacter tritici) and molya (caused by Heterodera avenae) are of sporadic occurrence in various parts of the country. Ear-cockle can be easily controlled by the removal of nematode galls from the seed before sowing or flotation in 2% common salt solution. Molya disease is important in Raj asthan and Haryana. It can be controlled by repeated summer ploughing, rotation with non-host crops, Viz. gram, carrot, radish and marigold, or growing resistant varieties of barley for 1-2 years.

Insect-pests

These are not very serious in general but termites, shoot-fly, aphids, brown wheat mite, cut worms and borers can pose problems. Among these, termites are the most serious and can be controlled by treatment of seed with Chlorpyriphos or Endosulfan. These insecticides can also be used for soil treatment if the termite damage is noticed after sowing the crop.

Aphids are another insect-pests which have started becoming important in several parts of the country. These can be controlled by the spray of Dimethoate, Oxydemeton methyl or Monocrotophos.

Post-harvest operations

The crop is harvested when the grains harden and the straw becomes dry and brittle. Harvesting of the crop when plants turn yellow / white before complete drying is recommended to reduce losses due to shattering. At this stage grains have already become hard and break rather then crush when pressed under teeth. The harvesting time varies from zone to zone and also depends on the rainfed or irrigated condition of the crop. The rainfed crop sown early reaches the harvest stage much earlier than the irrigated crop.

Wheat

In peninsular zone, harvesting starts in the latter half of February and most of it is over by the end of this month or in the beginning of March. In the central zone, the . crop starts ripening by the end of February, and the peak of harvesting season is March. In eastern zone, it starts in the latter part of March and is generally over by mid-April. In north-western zone, the crop ripens in the mid-April and the latter half of April is the peak harvesting time. In hills the crop is harvested in May-June, depending on altitude. The same wheat variety behaves differently in respect of maturity in different zones. For example, variety Sonalika matures by the end of February in the peninsular zone, while it matures by May in the hill zone in spite of it sowing in November in both the zones. High temperatures in the south shorten its growing period whereas in the hills the low temperatures lengthen its life cycle.

Most of the harvesting in India is done with the sickle. Only in recent years, the combines are being used for harvesting in Punjab, western Uttar Pradesh, Haryana, Rajasthan and Madhya Pradesh. These are generally operated on customhire basis.

Simple mechanical threshers, have become the most widely used implements for threshing and winnowing of wheat’ all across the country. These machines thresh and winnow in one go. Most of these threshers are locally made or obtained from Punjab, Haryana and western Uttar Pradesh, where these are manufactured on a large scale.

The traditional method of threshing by treading of cattle and winnowing has become obsolete, and is followed only in very backward or tribal areas.

Yields

The yield under rainfed conditions is generally low. It may be as low as 0.3 to 0.4 tonne/ha under very harsh conditions and may be over 1.8 to 2 tonnes/ha under favourable situations.

Under irrigated conditions, the yield may vary from 2.5 to 6.5 tonnes/ha depending on the management practices followed and the level of inputs used. Some progressive farmers are regularly harvesting 6.5-7.5 tonnes/ha. Under the National Demonstrations and Front-line demonstrations, yield up to 8 tonnes/ha has been recorded. There was a notion that the best wheat yields can be obtained only in north-westem India. However, recent experience with high-yielding varietites indicates that similar yields can be obtained in eastern, central and peninsular parts of the country provided the farmers grow the suitable variety, apply all the needed inputs, follow the appropriate production technology and perform all the operations as per time schedule which are very critical factors for the relatively shorter growth period available in eastern, central and peninsular India.

The wheat straw is an important cattle feed in India. Generally, the yield of straw from rainfed or barani crops is about the same as that of grain, whereas from the irrigated crop it is about 1.5-2-fold the grain yield.

storage

Before storage the grains must be thoroughly dried. Successful storage of the grain depends mainly on its moisture content. Grains with less than 10% moisture store well. This level of moisture can be easily achieved by sun drying during May-June in most parts of India. However, in eastern India there is problem due to high humidity and special care is needed for drying and storage of grains. Retention of good viability of the grain for sowing of the next crop is a serious problem in this region.

Wheat

A large number of insect species attack the wheat grain in storage. The most important are Khapra beetle (Trogoderma granarium), lesser grain-borer (Rhizopertha dominica), rice weevil (Sitophilus oryzae), flour beetle (Tribolium castaneum), and grain moth (Sitotroga cerealella). The storage bins or godowns must be moisture-proof and should be fumigated to keep down storage-grain insect-pests. Proper care must also be taken to keep the grain safe from rat damage and moisture.

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