Rice Cultivation
Among the food grains cultivated in India rice ranks first both in terms of area as well as production. Rice occupied roughly 40 m ha of area with a record production of 72.8 million tonnes during 1989-90. Though rice is a native crop of India, its average yield per hectare is only 16.40 quintals. The average yield of rice in China is 32-33 quintal per hectare, Japan 58 q/ha, Republic of Korea 62 q/ha, Spain and Australia 60 q/ha and world average is 27 q/ha. Among different states of India, Punjab tops with an average yield 0f 32 q/ ha followed by Haryana (27 q/ha), Orissa, U.P. with 11 q/ha and M.P. with only 8.86 q/ha
Climate
Rice is indigenous to the humid areas of tropical and subtropical regions of Asia. The climatic factors that influence rice production are temperature, day-length and humidity. They are known to cumulatively influence the total production and area of rice in the world.
Rainfall
Rainfall and its duration is very important for rice cultivation. It is the highest in the north eastern part of the country where precipitation of 508 cm is recorded. In eastern region, the rainfall is about 125-150 cm. On the west coast, average rainfall is around 40-60 cm per year. During winter months, Tamil Nadu and Andhra Pradesh also get showers.
Rice is more suited to high rainfall regions because it requires abundant moisture either through rainfall or irrigation to keep the soil under saturation throughout its life period. Therefore, the practice of rice cultivation is mostly dependent on the rainfall conditions. It is the dominant crop in North eastern part comprising Assam, West Bengal and South Bihar where precipitation is high. In the Peninsular India, it is concentrated in the east and west coastal areas of Tamil Nadu and Kerala. In the northern and central India, rice is grown where rainfall conditions are favourable.
Temperature
Proper growth and high production of rice crop is conditioned by temperature parameter at different growth stages. During flowering, it should range between 16 to 20 degree C, whereas during maturity 28 to 32 degree C temperature is optimum. The temperature beyond 35 degree C affects grain filling. During panicle initiation, 20-22 degree C temperature is ideal. The temperature below or above this range will adversely affect the trop growth and yield.
Light period
Light period is also called photoperiodism. Late maturing varieties are very sensitive to the day length and can be grown only during a specific season, while early maturing varieties can be grown at any time of the year but mostly during summer and kharif season. Generally, rice plant requires about 14 hours of daylight every day during its growth period. When the rice plant is subjected to day length shorter than 12 hours, it will come to flowering. So, when rice is subjected to lower temperature and short duration of sunshine, its vegetative phase will be reduced considerably. Too long or too short vegetative phase adversely affects the reproductive phase. In general, longer hours of sunshine with a temperature varying from 20-35 degree C and abundant moisture supply are the ideal conditions for rice plant.
Soil
Rice is grown in almost all types of soils in India. The soils most suited for the cultivation of rice are clay, loam and dry soils. Such soils are capable of holding water for long period. The groups of soil under which rice can be successfully grown in India are alluvial, red soils, laterite, lateritic, and black soils.
System of Rice Cultivation
There are three main systems of rice cultivation viz. (a) low land or wet, (b) dry or upland, and (c) semi-dry system. In low land cultivation, transplanting is done, whereas in other systems direct seeding is done. Generally low land rice refers to rice grown on low lying areas where water can be collected and retained by artificial irrigation, rainfall or a flooded river to keep the soil constantly submerged at the appropriate growing period of the crop. On the other hand, upland rice refers to the rice crop grown on higher land, hill tops, hillside or areas where neither irrigation nor any water retaining device is available. It grows and matures with rain just like other dry land crops. In semi-dry condition rice is grown under low lying conditions but mostly depends on rain. The rain water is collected, field is puddled and then germinated seeds are broadcast. This is also called "Lehi cultivation of rice".
The different cultivation practices for different systems of rice cultivation are given below. As in most parts of India rice seedlings are transplanted in fields, the method of nursery raising is given first.
Nursery Raising
The general practice in India is to go in for wet nurseries. Another system of nursery raising is known as the Dapog method which had been suggested for areas where seedlings are to be obtained within a fortnight for immediate transplanting. The nursery area should be ]/20th part of the field where rice has to be transplanted.
Wet nursery bed
Following is the stepwise procedure for preparing the nursery under wet method.
1. Determine the area required for the nursery: One-twenteeth part (i.e. 500 sq. metre per hectare) of the field will be enough.
2. Plough the area, harrow it thrice and level it.
3. Divide the field into beds of 1-1.25 meter width and of any convenient length with bunds of 10-15 cm height. Provide irrigation and drainage channels between the beds. The beds should be 1-1.5 meter wide. Length can be up to 20 meter or more according to the space available. Width is kept proper as mentioned above because, in nursery a man can cover about 1.5 meter area by his hands without getting inside the bed. By moving inside the bed, the young seedling can be trampled under the feet of workers. Between two beds, 40-50 cm path is kept for easy movement and other nursery operations.
4. Flood the beds, puddle them thoroughly and level them. Then they are left undisturbed for about a week or more. When the water dries up, allow the weeds to germinate and grow.
5. When the weeds have germinated, puddle the plots again and incorporate all the organic manures.
6. Weigh out the amount of seeds required for the field. The seed rate depends on the variety of rice to be grown. Small grained varieties require less quantity of seeds by weight and vice versa. About 35-45 kg seed is required for transplanting a hectare of land.
7. The rice seed meant for sowing should be true to type, viable, healthy and free from the pathogens of seed-borne diseases. Preferably, it should be certified seed purchased from the registered and authentic seed store.
8. A large number of diseases viz. fungal, bacterial, viral and insect pests are carried or introduced through the seeds. Therefore, seed treatment is a necessary practice in rice cultivation. Rice is mainly affected by blast, Helminthosporium, stern rot, sheath blight, brown leaf spot. bunt, false smut, leaf smut, bacterial blight and bacterial leaf streak diseases. Treatment of seed by soaking it for 12 hours in a mixture of Streptocycline (0.015%) and wettable Ceresan (0.035%), fol- lowed by hot water treatment at 52-54 degree C for 30 minutes can control most of the diseases. Seed can also be treated by Agrosan GN or Ceresan, or Thirarn. The dust of these chemicals can be mixed with the seeds @ 2.5 g/kg of seed and sown in the field. This treatment is for all the diseases except two bacterial diseases i.e. bacterial blight and bacterial leaf streak.
9. Prepare a solution of salt in water at the rate of 1:40 in a convenient vessel and immerse the seed in it. The light seeds will float, remove them. This will help in separating damaged seeds and spores of pathogens of various diseases.
10. Remove the seeds from salt water and soak them in fresh water for 24 hours in a convenient container.
11. After soaking, take out the seeds and dry them by keeping in gunny bags or by heaping in a convenient place and pressing the sides gently but firmly to make it compact. The heap should be covered with gunny bags or broad leaves.
12. Drying of seed is done for 36 to 48 hours, in a warm and shady place. Sprinkle some water on the 2nd day of incubation. On the 3rd day of incubation the seeds will germinate.
13, Before sowing, puddle the beds and Ievel them. Incorporate all the chemical fertilizers into the beds if the soil is found to be of poor fertility. Incorporate 1 kg of N, 0.5 kg of P2O5 and 0.5 kg of K2O for every 100 sq metre nursery bed.
14. Sow the germinated seed uniformly in the beds. To ensure uniform sowing, divide the quantity of seed according to the number of beds. Sow the seed by broadcasting or in lines.
15. After sowing, allow the water to sink into the soil and keep the water level to the minimum. However, the soil should be kept at saturation point till the needle like seedlings grow to provide a greenish patch like appearance in the beds. A well puddled soil will not have problems in maintaining the saturation point. Thereafter the level of water should be raised gradually up to 4-5 cm of standing water.
16. The beds should be free from weeds. Weeding should be done as and when required.
17. The seedlings should be protected from diseases by spraying proper insecticides and fungicides once in 10.,15 days.
18. Reduce the level of water occasionally (once a week) for a day or two to encourage the production of healthy seedlings. Too much flooding provides weak and tall seedlings which do not recover easily after transplanting.
19. In areas where zinc deficiency is observed, give two sprays of a mixture of zinc sulphate and lime @ 500 gm zinc sulphate and 200 gm lime in 10 litres of water is sufficient for the nursery grown for one hectare transplanting. The spraying should be done at 10 days and 20 days after sowing of the seeds.
20. If there is any infestation of insects in seedlings any of the following insecticides can be sprayed Methyl parathion (50%) 100 ml or Phosphomedon 25-30 ml or Dimethoate (30%) 100 ml or Monocrotophos (36 EX) 75 mi. The above dose of the insecticide is sufficient for the nursery required for one hectare transplanting.
If seedlings are infected by blast disease, spray of Banlet 50% W.p. @ 50 gm or Hinosan 50 EC @ 60 ml or Dvitagin 30 ml is required. These plant protection measures are generally applied on 10th and 17th days after sowing.
21. The seedlings are ready in 21 days in case of short duration and 30-35 days in the case of long duration varieties.
22. Water in the nursery bed is drained out a few days before the removal of seedlings to harden them.
Dry nursery bed
This method is adopted when there is high rainfall and danger of washing away of the seed. The procedure of dry method of raising seedlings is similar to that of the wet method.
1. About one tenth of the cultivated area is demarcated for nursery raising. This area is ploughed and harrowed properly to get a good tilth.
2. The area is divided into beds of 1-1.5 metre width and suitable length by making channels of 40-45 cm width between the beds with bunds all around.
3. Well rotten organic manure or compost should be incorporated 3-4 weeks before the sowing of seed.
4. Chemical fertilizers are added on the day of sowing as it is done in the case of wet. seed bed i.e. 1 kg of N, 0.5 kg of P2O5 and 0.5 kg of K20 for every 100 sq metre area.
5. Similarly, the amount of seed required is 35 to 45 kg for transplanting in one hectare field.
6. immerse the seed in salt-water solution (1:40 ratio) as in the wet method and remove the floating seeds.
7. The seed is immediately sown in the nursery beds uniformly as mentioned above. The sowing is done either in close lines or by broadcasting. Later, sown beds are covered with a thin layer of compost.
8. Irrigate the beds through the irrigation channels or by using a sprinkler to keep the beds wet. Irrigate carefully so that the water does not wash away the seeds.
9. Care of the seedlings against weeds, pests, diseases, etc. is in the manner adopted for the wet method.
10. The seedlings are ready for transplantation in 21 days in the case of short duration varieties and 30 days in the case of long duration varieties.
11. Irrigation is given on the day of removal of seedlings to facilitate easy removal of the seedlings.
Dapog method
In this method, rice seedlings can be raised within two weeks without affecting their quality. By this method only 30-40 sq. metres of space is required for transplanting one hectare as against 300 to 500 sq metres in case of wet nursery method. Dapog method is described below.
The preparation of land, if needed, is done essentially in the same way as in the case of wet-bed method. Raised seed beds are prepared after final levelling and are packed, levelled and covered with polythene sheets. It can be raised on concrete platform of 12- 15 cm height. Instead of polythene, banana leaves with their midribs removed or paddy husk ( 5 cm thick layer) or fine sand or empty gunny bags can also be used to prepare the nursery bed. The objective is that the roots of the seedlings do not penetrate into the soil. This will help separating the seedlings at the time of transplant- ing. Pre-germinated seeds should be sown on top of these sheets at the rate of 1 kg of seed per sq meter of the nursery. The germinating seeds are sprinkled with water and pressed down gently with hand or with a flat wooden board twice a day for the first 3-6 days. This helps the roots of the seedlings to remain in contact with water retained on the surface and prevents drying. After 6 days, the seed bed could be irrigated up to a depth of 1-2 cm of water. The seedlings raised by using the Dapog method are then divided into convenient sizes and rolled like a mat with roots outward. It is necessary to control the water level in the main field transplanted with Dapog seedlings as they are too small Iand are liable to be damaged very easily by letting in too much of standing water. The leveling of the fields is very essential to avoid the stagnation of water and the mortality of the seedlings. Generally, 6-8 seedlings are placed in a hill. This method of nursery is also useful for raising post flood rice crop in Assam and West Bengal.
Modified dapog method
In the modified Dapog method, the seeds are sown on polythene sheets on which 2.5 cm of sand is spread. After the germinated seeds are sown in the beds as described earlier, the beds are covered with gunny bags for 3 days. After 3 days, water is maintained in the nursery for the rest of the period with mud. Watering should be done every day in the morning and evening carefully to avoid shifting of the seedlings. From the eighth day after sowing, ammonium sulphate dissolved in water at the rate of 28 gm for 4 litres per 3 sq meter area of nursery bed should be supplied to the seedling on alternate days upto 16th day or till the time of transplanting.
Land Preparation
Make a first furrow with the plough across the whole length of the field. At the end of the field turn, make a second furrow along side the first. The Second strip of ploughed field joins the first. After that keep turnig around the double strip of ploughed field. If the field is ploughed only in one direction, the land is likely to become sloppy after 5 to 10 years. There fore cross ploughing is recommended i.e. the field once ploughed in east-west direction, next ploughing should be in north-south direction so that field remains levelled for longer time. Mould board ploughing i.e. soil turning should be avoided because it causes more loss of moisture. If there are clods in the field, they should be broken either by harrowing or by planking.
In the land preparation for dry system of cultivation, the field is ploughed and harrowed in summer for achieving the required tilth. Farmyard manure is uniformly distributed 2-3 weeks before sowing. In case of transplanted rice the field is ploughed thoroughly, harrowed 2-3 times and puddled at a week's interval and leveled well. Puddling can be done with 3-5 cm of standing water in field. The optimum depth of puddling is found to be around 10 cm in the clay and clay loam soils. The primary objective of puddling is to obtain a soft seed bed for the seedlings to establish faster, to minimize the leaching losses of nutrients and thereby increasing the availability of plant nutrients, to incorporate the weeds and stubbles into the soil, and to minimize the weed problem. Puddling can be done with ploughs, tillers or tractors, depending upon their availability and soil conditions. Proper bunds are made around the field and organic manures and composts are added into the soil 3-4 weeks before transplanting. Just before transplanting, the field is puddled again and the chemical fertilizers are incorporated. The land is leveled after puddling to facilitate a uniform distribution of water and fertilizers. Puddling of the rice field has the following advantages.
1. A good leveling of the land is ensured.
2. The weeds are buried at the time of puddling and the weed problem is reduced.
3. The population of plants becomes more uniform.
4. The availability of most of the plant nutrients, such as, nitrogen, phosphorus, iron and potassium, is increased and con- served better.
5. The seedlings transplanted in a soft puddle are able to establish themselves faster and start early tillering and growth.
Spacing
The yield of crop is directly related to the optimum spacing. It has been scientifically proved if we keep appropriate plant population in the field, we can double the rice production in comparison to the un maintained one. The spacing is affected by various factors and according to soil type, nutrient status and moisture availability, size of seed germination percentage, duration of crop, sowing time, etc. Following points are considered while determining the planting distance or spacing of rice crop:
1. low fertile soil: wider spacing,
2. high fertile soil: closer spacing,
3. low moisture content: spacing is closer,
4. irrigated conditions: wider spacing,
5. late sowing: closer spacing,
6. early sowing: normal spacing, and
7. inter cropping: spacing is widened as in sole crop but plant population is same by adopting paired row or skip row planting method.
In rice, spacing is near about equal for both wet and dry rice cultivation i.e. 15x15 cm in general. For medium and late varieties, it is 20 x 15 cm. For late sowing, spacing should be 15 x 10 cm.
Sowing
Time and method of sowing are the two important factors considered for healthy cultivation of rice. These are described briefly.
Time of sowing
Uncertainty of monsoon and unavailability of irrigation water makes it difficult to recommend the sowing time. However, it will be worth saying that the crop must be sown after monsoon has set in and about 15-20 cm deep soil layer has become wet. If the sowing is delayed, the crop has to suffer a great deal of loss because of soil and atmospheric drought due to aberrant weather condition during the grain filling stage which results in shrivelling of grains and the grains of much inferior quality are obtained.
Rice growing season also depends very much on prevailing temperature. In parts of eastern region and Peninsular India the mean temperatures throughout the year are favourable for rice cultivation and hence two or three crops of rice are taken in a year. In northern and western parts of the country where Winter temperatures are fairly low, only one crop of rice is taken during kharif season. There are three seasons for growing rice in India as given below (Table 1).
Different sowing seasons of rice in India
Sl.No.
|
Crop season
|
Local name
|
Sowing time
|
Harvesting time
|
1
|
Kharif
|
|
May-June
|
Sept-Oct
|
2
|
Rabi
|
Aman or Aghani
|
June-July
|
Nov-Dec
|
3
|
Summer or Spring
|
Dalua 9Orissa)
|
Nove-Dec
|
March-April
|
Method of sowing
The common methods used for sowing crops are as follows:
Broadcasting
Broadcasting is the scattering of seeds on the field surface. Soon after broadcasting, seeds are covered by manipulating the soil and planking it over. Slightly higher seed rate is required for sowing , by this method. Adopting this method does not ensure uniform plant population in the whole field, and therefore, thinning and gap filling are also required in large scale.
Dibbling
Dibbling method consists of placing 2 or more seeds in each hole made in soil either by hand tools or by some implement. Dibbling of seed is done only for small plots. The seed rate in this method is reduced to 1/5th or even less.
Seeding behind the plough
Seeding behind the plough in the furrow is widely adaptable and well accepted method. It is used for cereals and other larger seeds since the depth of seeding is very little. It is generally observed that seed rates are increased and the moisture content of the soil is kept slightly higher. An indigenous plough is employed to open a furrow in which a person following the plough drops the seed by hand. When the next furrow is opened, the previous gets partially covered.
Drilling
Drilling means dropping the seeds in the furrow through seed tubes. Drilling of seeds may either be done manually or mechanically. Some of mechanically operated seed drills gave a very high accuracy in metering. The number of rows planted at a time may be one or more. In this method, accuracy of proper depth, spacing and amount of seed sown is much higher than the other methods. The area covered per day is also more. The only disadvantage with this method is that mechanical seed drills may damage the seed and are likely to get clogged during operations. This may not result in uniform germination of the crop.
In the hill dropping method, the seeds are sown in lines as in drilling and the seed dropping in line is also controlled. Unlike drilling the seeds are dropped at a fixed spacing, not in a continuous stream. Thus the spacing between the plants in a row is constant. But the spacing between rows is not the same as that between the plants in a row.
Check-rowing is the method in which spacing between tows is the same as between the plants. This method makes it possible to do interculture operations from both directions.
Transplanting
In transplanting, the seedlings are first raised in nursery beds. These seedlings are uprooted from the nursery bed at the optimum age and transplanted in the main field. In wet or low land cultivation of rice, transplanting is advantageous for the following reasons:
1. it enables the cultivator to have optimum plant population at desired spacing in the field;
2. it enables the cultivator to have an opportunity to give a thorough cultivation and puddling operation which brings down the weed population; and
3. since the nursery occupies only a small area of the field, the control of diseases and insect pests, irrigation, manuring, etc. of the young crop are easier and cheaper than a broadcast or direct sown crop.
In the case of dry and semi-dry method of sowing rice, the land is ploughed and harrowed till a good tilth is attained. After applying fertilizer, soaked or un-soaked seeds of rice are sown in the field after first shower of monsoon. Any of the following methods may be used in dry or semi dry sowing.
1. Broadcasting the seeds at random and then covering the seeds by harrowing.
2. Sowing seeds in lines using seed drills either locally made or industrially manufactured.
3. Sowing seeds in line behind a plough either by hand or using a funnel and tube attached to a plough.
In wet method or in semi-dry method germinated seeds are also sown. The field is puddled, as in the case of transplanted rice and the sprouted seeds are broadcast evenly. This sowing method is better than dry sowing because in wet sowing the plants get all the advantages of puddling and the weed infestation is less as compared to dry method. In this method bunds are made around the field for collecting the rain water. When sufficient water is collected, field is puddled and sprouted seeds are spread by broadcasting. This method is used in western V.P., Punjab, etc.
Different steps in transplanting seedlings to main field
1. Removing seedlings
Seedlings are taken out from nursery 21 days after sowing. The seedlings should not be left in the nursery for more than 30 days. If they are not uprooted in time, they will not grow properly later in the field. If seedlings are too young, they will be damaged while uprooting. Seedlings should be taken out when they have 3 or 4 leaves. To get seedlings out without damaging them, water the nursery in order to facilitate their removal.
2. Sorting out seedlings
It is very important to sort out seedlings before transplanting them. Throw away any seedlings broken at the crown, seedlings that have no root and seedlings that are too small. If seedlings are sorted out properly, all those seedlings which are transplanted will grow better. Seedlings are then tied together in small bundles to help easy transportation. Seedlings are tied into convenient bundles of 5 to 8 cm diameter with soft material such as banana twine and root portions are submerged in water.
3. Preparing seedlings
Next step is to prepare the seedlings by cutting off the tips of the leaves to enable them to stay straight and they will not touch the ground. The transplanted seedlings will grow better. Do not wait longer than 2 or 3 days between taking out the seedlings and transplanting them.
4. Seedling treatment
Seedlings affected by gall midge are sorted out. Before trans- planting, roots of seedlings are dipped in Dresban or Carbofuron (0.02% solution) for 12 to 15 hours. Seedlings are also dipped in a solution of Dresban (0.02%) and urea (1 %) to protect them from insect attacks in establishment stage. The latter treatment is especially more useful when the transplanting is delayed till July last or first week of August.
To reduce the field incidence of brown spot, root dipping in zinc oxide (1 % solution) is recommended. Dissolve 500 gm of zinc oxide in 50 litres of water and dip the seedlings in this solution for one hour before transplanting.
If white tip nematode is a problem, dip the seedlings in Phosphamidon (0.02% solution) for 20 minutes prior to planting.
Planting in rows and holes
Leave about 20 cm distance between rows and about 15 cm distance between each plant. Place 2 or 3 seedlings in each hill or seed hole. But if transplanting is delayed and seedlings are more than 30 days old, place 4 or 5 seedlings in each hill. Take the lowermost portion of the seedlings between fingers and push fingers 2 or 3 cm deep into the soil so that the roots will be at the right depth in the earth. Various specifications of transplanting are given in table 2.
Number of seedlings per hill for different conditions
Sl. No.
|
Specifications
|
Medium & low fertility
|
High fertility
|
Short duration
|
Medium duration
|
Long duration
|
Short duration
|
Medium duration
|
Long duration
|
1
|
No. of seedlings/hill
|
2-3
|
2
|
2
|
2-3
|
2
|
2
|
2
|
Depth of planting (cm)
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
Spacing (cm)
|
15x10
|
20x10
|
20x15
|
20x10
|
20x10
|
20x10
|
4
|
No. of hills per square meter
|
66
|
50
|
33
|
50
|
33
|
|
Intercultural Operations
Regular intercultural operations should be performed to make all the plants survive and grow fast
Gap filling
It is carried out about to 10 days after transplanting. Take some healthy seedlings out of the nursery and plant them in the places where they have not grown successfully or died because of other reasons.
Improved Biasi operation in dry sown rice
In dry sown rice when first hoeing is done 20-2.5 days after sowing, the plant population remains only 100-125 per sq metre, whereas for optimum yield seedlings must be 300-400 per sq metre. For maintaining this population, three times more seed rate i.e. 30 gm/sq metre is used in field for sowing in about 1/20th area of cultivable land. During Biasi operation these extra plants are up- rooted and transplanted in the places where plant population is not up to standard.
Weed Control
Weeds compete with rice plant for water and nutrients. They also act as alternative host plants for different insect pests. Therefore, destruction of weeds from rice crop is of paramount importance. Generally, the weed infestation is more serious in dry sown I rice than in flooded or transplanted rice.
In India, the yield reduction in rice due to weeds alone is estimated to be around 15-20% for transplanted rice, 30-35% for direct seeded rice under puddle conditions and over 50% for upland rice. The potential loss In production of rice In India due to weed infestation is estimated at 15 million tonnes per annum. The losses are more under direct seeded conditions, mainly because of lack of precise water control and poor land preparation.
There are mainly three types of weeds found in the rice fields:
A. In upland rice
1. Grasses
Grasses are monocotyledenous plants having long, narrow, two ranked flat leaves with parallel venation and round hollow stems. Eg. Echinochloa colanum, Dactyloctenium aegypticum. Setaria glauca, Eleusine indica. Saccharum munja, Ergrostis aspera, Ergrostis interrupta, Elytrophorus arteculata. Digitaria longifolia. Cynodon dactylon, etc.
2. Sedges
They are similar to grasses but have three ranked leaves and triangular solid stems. They frequently have the modified rhizomes adapted for storage and propagation, e.g. Cyperus rotandus, Mu- radinia nudiflora, Cyperus iria. etc.
3. Broad leaved weeds
These plants have dicotyledenous leaves and are easy to identify. Eg. Mollugo pentaphylla. Eclypta alba, Ageratum- co- nyzoides, etc.
B. In low land rice
1. Grasses
Echinochloa colonum. Echinochloa crusagalli. Leersia hescandra. Paspalum scrobictatum. Panicum spp., Sirpus erectus, etc 2. Sedges
Cyperus iria, Cyperus haspan. Cyperus rotandus, Fimbristylis miliacea. etc.
3. Broad leaves
Monochoria vaginal is. Altemalthere sessiles. Ludwickia parv~flora, Commelina bengalensis.etc.
Aquatic weeds like water hyacinth and Salvinia molesta (S. auriculata) are also posing major problems in rice culture.
C. Weed control measures
1. Prepare the land thoroughly
A thoroughly prepared land before planting or sowing helps the crop in two ways. First, the weeds are greatly reduced by repeated cultivation. Secondly, it gives the crop a good start by ensuring regular germination and vigorous growth and enables it to compete with weeds on more favourable terms.
2. Practice straight row planting
Straight row planting or sowing costs a little more than a random one but it is more effective to operate rotary weeder or wheel hoe in between two rows of crops. Rotary weeder can effectively operate only in soft mud. So before operation excess water from the field should be drained out. On the other hand, wheel hoe is smoothly drawn on the upland soil with proper moisture conditions. But it is not very effective due to the fact that weeds near the crop plants escape destruction. Deep hoeing too near the crop rows injures the root system of the crop.
In the absence of a rotary weeder or wheel. hoe, employ hand weeding. Pull the weeds by hand and incorporate them deep in the mud or throw them out of the field. This practice can easily be done in line sown crop.
3. Flooding rice at effective water depth
Proper water management controls germination and growth of weeds. This method is useful and effective only when plenty of water is available either through irrigation or through heavy rains to completely submerge the weeds for 6-8 weeks. However, aquatic weeds or broad leaved weeds are not affected by this treatment.
Under continuous soil saturation (1 cm water upto the late dough stage), more sedges grow than broad leaved weeds and grasses. Submerging the field to 15 cm four days after transplanting to the late dough stage practically suppresses most of the grasses and sedges.
Flooding the rice to control grasses and sedges includes the following stages.
a. Flood the field 5 to 10 cm. deep starting on the 5th to 7th day after transplanting. The water must be deep enough to cover the weeds but not the rice seedlings.
b. Keep the field flooded for 14 days until about 3 weeks after transplanting.
Flooding, however, has its own drawbacks. Heavy expenditure and great efforts are involved in constructing high bunds or embankments around the fields to confine the water in a particular area. Furthermore, as these bunds cannot be cu!tivated, weeds growing on them serve as a source of weed Infection and provide shelter to pests and pathogens.
Most weed seeds require much longer submergence than the growing plants. For these reasons, flooding, unless properly carried out, is usually unsuccessful in eliminating weeds.
D. Control of weeds in upland rice
The problem of weed competition in direct sown rice under rainfed and upland conditions is quite severe as compared to that in low land rice. The failure of germination due to moisture stress, uneven stand and poor growth rate of rice offer better opportunities for the weeds to grow profusely and more vigorously than the rice crop. Even by repeated weedings, it is difficult to maintain a weed i free situation in upland rice. The perennial weeds such as Cyperus rotundus are very difficult to be controlled because of their extensive underground system of corms (basal bulbs) and their apical dominance.
Since upland farmers are marginal farmers practising the subsistence level of farming, they give very little attention to weeding by any means. But without weeding, the yield is miserably low. Following are some chemical measures to check weed menace in upland rice.
1. Pre-emergence
Spray uniformly Nitrofen (Tok E-25) solution of 2.0 kg a.i. dissolved in 400-600 litres of water. This spray should be done immediately after one or two days of transplanting.
2. Post emergence
Spray Propanil 3 kg a.i. (i.e. 8.5 I of Stam F-34 in 600 litre of water) at 3 to 4 leaf stage of grassy weed i.e. 18-25 days after sowing. In the case of infestation of both grasses and broad leaved weeds, a combination of Propanil and 2,4-D may be applied one month after sowing in 600 litres of water. In that case, dose of Propanil will be 21itres and that of 2,4-D (sodium saIt) will be 800 g /ha.
E. Control of weeds in low land rice
The problem of weeds in transplanted rice is not very severe as compared to that in direct sown crop.
Broadcasting of 1-1.5 kg /ha of Butachlor (i.e. 20-30 kg of Machele 15%) 4-6 days after transplanting.
Or
Nitrofen @ 1.5-2 Kg a.i./ ha 4-6 days after transplanting.
Or
Benthiocarb @ 1.5 Kg a.i./ha 6 days after transplanting.
When broad leaved weeds are dominant, spray 800 gm to I kg a.i of 2,4- D/ha one month after transplanting/sowing in 600 litres of water.
Irrigation Scheduling
In order to produce a higher yield, the rice must constantly stand in water. But it is wrong to flood the field always to the same depth of water. For the first 6 to 8 days after transplanting, leave the soil as a liquid mud. If the soil becomes dry, let in only a little water. About a week after transplanting, when the rice has begun to grow, flood the field with 2 to 3 cm of water and leave for 45 days. But, twice during these 45 days, drain the field in order to apply fertilizers.. After 45 days, increase the depth of water to 10 cm.
When the panicles have formed and are turning yellow, the rice field must always be well flooded. It should have about 20 cm of water. Afterwards, gradually make the water less deep. About 10 days before harvesting, drain all the water away.
A. Irrigation requirement
1. Aus paddy
It requires a total of 100 ha centimeter (40 acre inches) of water.
a. Seed bed -25 ha cm. It means 25cm standing water in one hectare field.
b. Transplanting-15 ha cm. It means 15cm standing water in one ha field.
c. Transplanting to ripening time -60 ha cm water.
2. Amon paddy
It requires 90 ha cm (36 a'cre inches) of water.
a. For raising seedlings -25 ha cm.
b. Puddling -15 ha cm.
c. From transplanting to the grain formation period - 40 ha cm.
d. Ear emergence to ripening -10 ha cm.
3. Summer paddy
It requires 150 ha cm (60 acre inches) of water.
a. For raising seedlings -25 ha cm.
b. For puddling 15 ha cm.
c. From transplanting to grain formation -110 hacm.
Harvesting
Usually farmers harvest rice crops at maturity to minimise field losses resulting from shedding of grains. Sometimes farmers are forced to delay harvesting mainly due to unfavourable weather and lack of labour, especially during critical period of harvesting i.e. October- November. The delay of harvesting beyond optimum date, increases shattering of grains and over drying results in poor milling recovery.
The harvesting of early and medium rice varieties can be done 25-30 days after flowering. In the case of late maturing varieties harvesting can be done 3540 days after flowering.
In India, rice is harvested manually with the help of sickle. It takes about 170 to 200 man hours to harvest one hectare of crop. Due to high labour demand at the time of harvesting. the entire operation continues for weeks together resulting in over drying in the field itself. This will gradually cause 5 to 15% grain loss in subsequent operations.
After harvesting, harvested stalks are either laid loosely on the ground for field drying or the crop is. left in the field for whole day and night. Later collect it in the bundles. The direct drying under the sun leads to an increased breakage of the grains during milling. Gradual drying in the shade is essential for better recovery in rice grains.
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