In this essay we will discuss about the irrigation practices used for growing cereals and millets in India.
Essay Contents:
- Essay on the Irrigation Practices Used for Growing Rice
- Essay on the Irrigation Practices Used for Growing Wheat
- Essay on the Irrigation Practices Used for Growing Millets
Essay # 1. Irrigation Practices Used for Growing Rice:
Irrigated rice is largely cultivated under conditions of land submergence all through the country except in the states of West Bengal, Assam, Kerala and parts of Orissa, Madhya Pradesh and Uttar Pradesh where it is grown as a rainfed crop. Lowland (irrigated) rice requires more water than other crops of similar duration due to land submergence.
Depending on the environment in which the crop is cultivated, 50 to 70 per cent of the applied water is lost in deep percolation and about 200 mm of water is necessary for land preparation (Table 11.1).
TABLE 11.1: Water Requirement of irrigated lowland rice
The amount of water used at field level is 20,000 m3 t-1 with poor water management and 3,000 m3 t-1 with good management. Irrigation agencies, generally, take only “laissez faire” approach to measurement and control of water in canal command areas where rice is the major crop. A large proportion of the water making up the current system water requirements (Fig 11.1) is used in lieu of added control and management.
Most irrigation systems of rice producing nations in Asia are operating at the left hand side of abscissa where the system water requirement is much higher than the actual requirement. It is desirable to incur added (incremental) costs in control and management to save added (incremental) units of water (ha-cm) until last unit of water saved has a cost equal to the cost of a replacement (alternative or new) source of water.
It has been reported that about 5000 l of water is required to produce 1.0 kg rice. Average production of grain (kg ha-mm-1 of water) is 3.7 for rice, as against 13.4 for fingermillet, 12.6 for wheat, 9.0 for sorghum, 9.2 for maize and 8.0 for pearlmillet. It is often said and agreed that seasonal water requirement for rice varies from 750 to 1500 mm day-1 with an average of 1200 mm.
If irrigation period is assumed to be 120 days, the average requirement will be 10 mm day-1, which appears to be reasonable on the condition that land submergence is the usual practice with a minimum of 2 mm day-1 percolation and seepage losses.
As per Kung (1971), the total water loss from rice fields ranges from 5.6 to 20.4 mm day-1. However, most observed losses range from 6 to 10 mm day-1. On an average, a total of 1,240 mm is the water requirement of rice (Table 11.1).
Rice crop has been found to perform better under the conditions of land submergence due to:
1. Relatively weed free environment leading to efficient use of inputs by the rice crop
2. Increased availability of nutrients, especially phosphorus, potassium, calcium, silicon and iron
3. Reduced loss of nitrogen from rhizosphere placed ammonium fertilisers due to reduced soil conditions
4. Fixation of atmospheric nitrogen by blue-green algae and other microbes due to favourable environment
5. Regulation of soil temperature within the range, ideal for optimum growth and development of the crop.
Weed free environment due to continuous land submergence appears to be the major reason for the preferred land submergence. With increasing scarcity for irrigation water, there is need for a look back on the practice of continuous land submergence for sustainable rice production.
Extensive field studies to quantify the irrigation requirement of rice with continuous land submergence during kharif indicated large variations in different regions (Table 11.2). It was lowest in eastern region and highest in northern region. Such differences in irrigation requirements have been attributed largely to soil type and seasonal rainfall.
TABLE 11.2: Irrigation requirement of rice with continuous land submergence
In order to bring down the huge irrigation requirement under continuous land submergence, the approach of intermittent land submergence (irrigation after 1 to 5 days after the disappearance of ponded water) was tested in all the regions (Table 11.3). Irrigation 3 days after disappearance of ponded water appears to be reasonable in most locations.
This schedule resulted in saving of 23 to 60 per cent irrigation water compared with continuous land submergence, without significant reduction in grain yield. If the water table is high, as at Madhepura, irrigation could be 5 days after the disappearance of ponded water. Even one day period considerably saved the irrigation water. Intermittent land submergence enables efficient use of rainfall and enables irrigating larger area with a limited water supply.
TABLE 11.3: Effect of intermittent irrigation on rice yield
i. Recommended Irrigation Practices:
Great economy in irrigation water could be achieved if suitable measures are adopted to minimise the deep percolation losses.
Some of the recommended practices to economy in irrigation water use in rice cultivation are:
1. Rice cultivation on heavy soils with percolation below 5 mm day-1
2. Since the seepage is proportional to perimeter of the area, rice should be grown in large blocks instead of in isolated plots
3. Puddling to reduce soil permeability
4. Subsoil compaction to minimise deep percolation losses
5. Addition of bitumen, asphalt etc to the soil
6. Application of tank silt to light soils
7. Scrupulous land leveling.
ii. Rice Nursery:
1. Water should be drained next day after sowing
2. Allow enough water to saturate the soil from 3rd to 5th day
3. Protect the seeds from tilting due to rain
4. Maintain wet condition to avoid cracks and development of long roots
5. From 5th day onwards, raise water level from 1.5 to 2.5 cm according to the height of the seedlings.
iii. Main Field:
Adequate irrigation water availability to meet the crop needs:
If irrigation water in not a limiting factor for rice cultivation, continuous shallow land submergence with 5 cm water could be ideal to achieve the benefits of land submergence in kharif, rabi and summer seasons.
Limited irrigation water availability:
Under the conditions of limited supplies, the following phasic land submergence could be optimum both for kharif and rabi crops:
1. Maintain not more than 2 cm water depth at transplanting
2. Up to 3 days after planting (establishment period), 5 cm land submergence is necessary
3. Maintain 2 cm depth of land submergence from 3 days after planting to panicle primordial initiation
4. From panicle primordial initiation to 21 days after heading, maintenance of 5 cm
5. From 21 days after heading to harvest, gradual withholding of irrigation.
If the irrigation water is not adequate to meet the above recommended schedule, the following intermittent land submergence could be followed during kharif and rabi:
1. From transplanting to panicle initiation, irrigations could be 3 days after the disappearance of ponded water
2. From panicle initiation to 21 days after heading, irrigation should be 2 days after the disappearance of ponded water
3. From 21 days after heading to a week before harvest, irrigations may be given 5 days after the disappearance of the ponded water.
Limited irrigation water availability for summer rice crop:
A short duration rice crop is transplanted around mid-April under well-irrigation, especially in south India to meet the family needs. The recharging capacity of wells, generally, goes down from April onwards, thus subjecting the crop to soil moisture stress around heading and grain development stages.
The following irrigation practices are suggested under such situations:
1. Since there is no scope to apply around 5 cm depth of water every day to the entire rice crop, about 2 cm of water may be applied every day to cover the entire area or irrigation may be given on alternate days to cover the entire area.
2. If the above practice could not serve the purpose, the crop may be irrigated 2 or 3 days after the disappearance of the applied water depending on the recharging capacity of the well
3. If the above practices could not serve the purpose, the only alternate to save the standing crop is to irrigate the crop by following check-flooding method of irrigation.
There is no scope for dividing the rice field into beds and channels using machinery or other farm equipment, without causing damage to standing rice crop, for check flooding. An alternative is to use sand to demarcate plots and forming channels for irrigation. This practice can minimise the deep percolation losses relative to wild flooding method of irrigation and aids in irrigating larger area than that with wild flooding.
Irrigation practices for rice crop on saline soils:
If irrigation water is not a limiting factor, rice is usually a crop of saline soils.
Recommended management practices for rice crop on such soils are:
1. Aged seedlings, which can better withstand salinity, may be transplanted in 5 cm standing water
2. Deep land submergence (around 8 cm) may be maintained during seedling establishment
3. Periodical change of water to minimise salt accumulation
4. Mid-season drainage at tillering
5. Since flowering period is more sensitive to salinity, deep submergence (up to two- third plant height) should be practiced during flowering phase
6. Flowing irrigation (flowing water from field to field) minimises accumulation of soluble salts.
The dwindling water resources suggest irrigated-dry crops during rabi and summer seasons instead of a rice crop as at present. Such a shift in cropping system leads to efficient use of scarce irrigation water to meet the increasing food needs of the country.
iv. Micro-Watershed System for Uplands:
In semiarid and humid rainfed areas where rice is also grown on uplands, micro- watershed system of rainwater management for rice based pair-cropping system appears to be advantageous. Upper part of the field is put to crops such as maize, groundnut, sesame, pigeonpea and soybean that have lower water requirements and the lower part of the field in the toposequence is put to rice.
This is to allow runoff of excess rainwater from upper part for harvest in the lower part for use of rice crop. Rice crop, thus, gets additional water besides the rainfall that helps it to grow successfully particularly in uplands. Field is shared by rice and another crop, in a specified ratio. Land share ratios (LR) between rice and the associated crop ranges from 1:1.6 to 1:2.0. This system leads to higher economic returns than growing only rice depending rainfall (Table 11.4).
v. Water Management for SRI:
1. SRI method does not require continuous flooding
2. Irrigation is given to maintain soil moisture near saturation initially and water is let in when surface soil develops hairline cracks
3. Irrigation intervals, however, vary with soil texture. Soils having low water holding capacity require frequent irrigation
4. At the time of weeding operation, field should be irrigated to have 2-3 cm of water
5. After completion of weeding, water should not be let out of the field for a day or two
6. After the panicle initiation stage until maturity, 2 cm of water should be maintained in the field until maturity
7. Water can be drained after 70 per cent of the grains in the panicle get hardened.
Essay # 2. Irrigation Practices Used for Growing Wheat:
Wheat season commences after withdrawal of monsoon either as rainfed crop on stored soil moisture or as an irrigated crop. Studies on irrigation requirements of wheat are based on depletion of available soil moisture (DASM), critical growth stages for irrigation and climatological approaches.
On sandy loam soils of Hisar, four irrigations, one each at crown root initiation (CRI), flowering, milking and dough stages produced highest yield as against one irrigation at CRI. At Morena, on the other hand, five irrigations resulted in highest yield (Table 11.5).
TABLE 11.5: Wheat yield (t ha-1) in relation to Irrigation at Different Growth Stages
Importance of physiological crop growth stages for irrigation in case of water scarcity may be considered in the order of CRI – flowering – dough stage – late tillering – milk stage and late jointing stage.
In general, irrigation at different stages may be timed between 20 and 25 days (CRI), 40 and 45 days (late tillering), 100 and 115 days (milk stage) and 125 and 135 days (dough stage) after sowing, These stages, however, vary with crop duration in different wheat zones.
The IW/CPE approach has been effectively employed for scheduling irrigation to wheat crop. Grain yield of 4.6 t ha-1 at Navsari and 4.1 t ha-1 at Rahuri was obtained by scheduling irrigation at IW/CPE ratio of 1.05, which required 7 and 5 irrigations of 6 cm deep, respectively (Table 11.6).
TABLE 11.6: Wheat yield and irrigation needs at optimum IW/CPE ratio
On light soils, grain yield around 4 t ha-1 was obtained at IW/CPE ratios varying from 0.6 to 1.05. On sandy loam soils of Bikramganj and Bilasapur, grain yield of 2.64 and 4.011 ha-1 were obtained at 0.9 ratio, requiring 3 irrigations. Several other studies at different places indicated necessity for irrigation at CRI, CRI and tillering, CRI, tillering and flowering, depending on the availability of irrigation water, for realising optimum wheat yield.
Studies under Coordinated Project for Research on Water Management showed that wheat yields were optimum at several locations when the crop was irrigated at 50 per cent soil water availability, while irrigation at 25 per cent depletion was ideal at Indore and Bikramganj, Irrigation at 0.5 atm was ideal at Delhi.
Depending on soil type, crop characteristics, cropping season, agronomic practices, irrigation schedules etc., wheat crop water requirements vary from 450 to 650 mm. Water requirements as low as 250 mm also have been reported.
i. Recommended Irrigation Practices:
Based on the results of experiments, the following general conclusions can be drawn on irrigation practices for wheat:
Critical stages approach:
In general, 4 to 6 irrigations are needed for optimum yield under different soil and weather conditions as indicated in Table 11.7.
Climatololgical Approach:
As indicated already, this approach has been tested extensively under different conditions.
1. Scheduling irrigation at IW/CPE ratios of 0.9 to 1.05 with 6.0 cm depth is ideal for optimum yield. Depending on the climatic conditions, 4 to 6 irrigations may be necessary during the season.
2. When the available irrigation water cannot meet the above schedule, irrigation may be scheduled at 0.9 ratio at CRI and at 0.6 during other stages for highest water use efficiency.
3. Under situations of acute water shortage, IW/CPE ratio of 0.6 requiring 3 irrigations at critical stages (CRI, boot and milk stages) appears to be the minimum requirement for reasonably good yield.
Depletion of available soil moisture approach:
This approach is still the usual approach for scheduling irrigation.
1. When irrigation water is not a limiting factor, scheduling irrigation at 25 per cent DASM in the case of light soils and at 40 per cent DASM in the case of heavy soils could be ideal for high yield.
2. Under the conditions of limited irrigation water availability, scheduling irrigation at 40 and 60 per cent DASM could be adopted for the crops on light and heavy soils respectively
3. The other alternative is to irrigate the crop around 50 per cent DASM at CRI and at 75 DASM during other critical stages.
Essay # 3. Irrigation Practices Used for Growing Millets:
Among the millets, maize is grown as irrigated crop throughout the country, especially during winter and summer seasons. Sorghum, fingermillet and pearlmillet are occasionally grown as irrigated crops during rabi and summer seasons, especially in southern parts of the country. As such, work on irrigation needs of millets, except maize, is limited.
Maize:
For maximum production, a medium maturity grain crop requires 500 to 800 mm of water, depending on climate. Maize crop is sensitive to both moisture stress and excessive moisture, hence regulate irrigation according to the requirement at different growth stages (Table 11.8).
Growth stages of maize:
Vegetative phase: 15 to 39 days
Flowering phase: 40 to 65 days
Maturity phase: 66 to 95 days
i. Frequency and Depth of Irrigation:
1. Maize appears relatively tolerant to water deficits during the vegetative (1) and ripening (4) periods
2. Greatest decrease in grain yields is caused by water deficits during the flowering period (2) including tasselling and silking and pollination, due mainly to reduction in grain number per cob
3. Severe water deficits during flowering period (2), particularly at the time of silking and pollination, may result in little or no grain yield due to silk drying. Water deficits during the yield formation period (3) may lead to reduced yield due to reduction in grain size.
4. Water deficit during the ripening period (4) has little effect on grain yield.
Where water supply is limited, it may therefore be advantageous to meet, as far as possible, full water requirements so as to achieve near maximum yield from a limited acreage rather than to spread the limited water over a larger acreage.
Maize flourishes on well-drained soils and waterlogging should be avoided, particularly during the flowering (2) and yield formation (3) periods. Waterlogging during flowering (2) can reduce grain yields by 50 per cent or more.
ii. Irrigation Scheduling:
1. Taking into account the level of ETm, to meet full water requirements, water depletion level is about 40 per cent in the establishment period (0), between 55 and 65 per cent during periods 1, 2 and 3 and up to 80 per cent during the ripening period (4).
2. Where irrigation water supply is restricted, irrigation scheduling should be based on avoiding water deficits during the flowering period (2) followed by yield formation period (3).
3. When a severe water deficit during flowering period (2) is unavoidable, water may be saved by reducing supply during vegetative period (1) as well as during yield formation period (3) without incurring additional yield losses.
4. Under conditions of limited irrigation water supply, number of possible irrigation applications may vary between 2 and 5 as indicated in Table 11.9.
Sorghum:
This crop is mainly a rainy season crop on light soils or a post-rainy season crop on stored soil moisture of deep black soils. Very rarely it is grown as an irrigated crop during rabi and summer seasons.
Seedling, primordial and flowering stages are the critical stages for soil moisture stress. At Siruguppa (Karnataka), one irrigation at 75 per cent DASM was adequate for kharif crop on heavy soils. However, summer crop gave highest grain yield when irrigations were scheduled at 50 per cent DASM, requiring 550 mm water in 9 irrigations.
Optimum IW/CPE ratio and number of irrigations to sorghum crop varied widely from region to region. Only one irrigation scheduled at 0.4 ratio produced highest grain yield (4.02 t ha-1) of kharif sorghum at Parbhani (Maharastra). On sandy loam soils of Bhavanisagar, grain yield was 3.01 t ha-1 at 0.4 ratio, requiring 5 irrigations.
The following general conclusions may serve as a guide for irrigation water management of sorghum under different soil and climatic conditions:
1. If irrigation water is adequate, irrigation schedules at 50 per cent DASM or at IW/CPE ratio 0.75, all through the crop period, could be ideal for high grain and fodder yield of sorghum during rabi and summer seasons. Depending on soil type and climate, 7 to 9 irrigations may be necessary
2. During years of deficit supplies, irrigation schedules at 50 per cent DASM or at IW/CPE ratio 0.75 at seedling, primordial and flowering stages and at 75 per cent DASM or at 0.4 IW/CPE ratio at other stages could be ideal for optimum grain and fodder yield during rabi and summer seasons. About 4 irrigations could be adequate with this irrigation schedule.
The following water management practices could also serve the same purpose as that of the above:
1. If water supply is adequate for only one irrigation, it should be applied at primordial stage
2. If water supply is adequate for two irrigations, they should be applied at seedling and primordial stages
3. If water supply is adequate for three irrigations, they should be applied at seedling, primordial and flowering stages
4. Four irrigations, one each at seedling, primordial, flowering and grain development stages leads to optimum yield.
Pearlmillet:
Area of pearlmillet, both under rainfed and irrigated conditions, has progressively decreased during the last fifteen years due to introduction of more remunerative crops. Still, considerable area exists under irrigation, especially in southern parts of the country during summer season (April-June) as transplanted crop.
Much attention has not been paid for irrigation management of the crop. Scheduling irrigation at IW/CPE ratio of 0.75/0.80 required three irrigations for an yield of 2.81 ha-1 during kharif at Kota in Rajasthan (Table 11.6). At Hyderabad (AP), rabi pearlmillet could produce 2.2 t ha-1 with 10 irrigations.
Flowering and grain development stages are most sensitive for soil moisture stress. Scheduling irrigation at 50 per cent DASM during moisture sensitive stages and at 75 per cent DASM during other stages appears to be optimum under several situations.
Based on the available information, the following conclusions can be drawn on irrigation practices for pearlmillet:
1. Under conditions of adequate irrigation water availability, scheduling irrigation at 50 per cent DASM all through the crop period, requiring 5 to 7 irrigations could be ideal for high grain yield of transplanted crop during rabi and summer seasons. If scheduling is based on IW/CPE ratio, 0.75 ratio all through the crop period could be as good as the above for optimum grain yield
2. At times of deficit water supplies, scheduling irrigations at 50 per cent DASM during moisture sensitive stages and at 75 DASM during other stages or scheduling irrigations at IW/CPE ratio of 0.75 during moisture sensitive stages and at 0.4 ratio during other stages could serve the purpose without significant reduction in grain yield
3. For transplanted summer pearlmillet, 6 irrigations, one each at planting, a week after planting, three weeks after planting, panicle initiation, flowering and grain development are ideal, if water supply is not a limiting factor
4. Under conditions of deficit supplies, three irrigations (planting, tillering and flowering) can optimise the grain yield during summer season.
Fingermillet:
Among the small millets, fingermillet is the only crop grown under irrigation to a considerable extent during rabi and summer seasons, especially in south India. During rainy season, one or two supplemental irrigations, at times of drought spells, can double the yield of fingermillet. Tillering, panicle initiation and grain development stages are sensitive to soil moisture stress.
The following irrigation schedules may serve as a guide for irrigation water management of fingermillet under different situations:
1. If irrigation water is not a limiting factor, 7 irrigations (8 cm) at 10 days interval during rabi and 9 irrigations at 8 days interval during summer can meet the crop needs for high grain yield
2. Under conditions of limited water supply, a minimum of 3 irrigations with 5 cm depth (tillering, panicle initiation and grain development) are necessary for economic crop production during rabi and summer seasons
3. Under conditions of adequate irrigation water availability, scheduling irrigation at 50 per cent DASM all through the crop period could be ideal for high grain yield of transplanted crop during rabi and summer seasons. If scheduling is based on IW/CPE ratio, 0.75 ratio all through the crop period could be as good as the above for optimum grain yield
4. At times of deficit water supplies, scheduling irrigations at 50 per cent DASM during moisture sensitive stages and at 75 DASM during other stages or scheduling irrigations at IW/CPE ratio of 0.75 during moisture sensitive stages and at 0.4 ratio during other stages could serve the purpose without significant reduction in grain yield.
Barley:
It is a rabi cereal crop, preferred to wheat in low rainfall areas where wheat can not be successfully grown. Its water requirement varies from 400 to 550 mm, depending on the duration of the cultivar, cultural practices and weather conditions during the crop season.
Several studies indicated necessity for a minimum of two irrigations, one at 30 DAS and the other at pre-flowering phase for optimum grain yield. However, more number of irrigations appears necessary for a crop on sandy and sandy loam soils of Rajasthan. At Jobner, irrigation at 30 to 50 per cent depletion of available soil moisture, requiring 5 to 6 irrigations, was ideal for optimum grain yield. When water is available for two irrigations, they should be scheduled on 30 and 60 DAS.
At Jobner, barley gave highest grain yield when irrigation was scheduled at 0.8 IW/CPE ratio. At Ludhiana, barley gave highest yield with two irrigations applied at CRI and flowering phases at an IW/CPE ratio of 0.9.
Based on results of several studies at different environments, the following irrigation schedule can be recommended to barley crop:
1. Under conditions of adequate water availability, irrigations may be scheduled at 30-40 per cent DASM all through the crop growth, requiring 4-6 irrigations. Based on IW/CPE ratio, optimum irrigation schedule is around 0.75 ratio all through the crop period. Based on physiological growth stages, irrigations at tillering (30 DAS), jointing (60 DAS), flowering (80 DAS) and milk stage (95 DAS) equally optimum for normal grain yield
2. Under conditions of limited irrigation water, irrigations may be scheduled at 50 per cent DASM at critical stages and at 75 per cent DASM during other stages, requiring 3-4 irrigations, IW/CPE ratio of 0.75 during critical stages and 0.5 at other stages is equally effective
3. If irrigation water is available for only two irrigations, it should be applied at critical stages of CRI and flowering for high water use efficiency.