In this essay we will discuss about irrigation practices used for growing commercial crops.
Essay Contents:
- Essay on the Irrigation Practices Used for Growing Sugarcane
- Essay on the Irrigation Practices Used for Growing Cotton
- Essay on the Irrigation Practices Used for Growing Tobacco
Essay # 1. Irrigation Practices Used for Growing Sugarcane:
Water requirement per year is around 20,000 to 30,000 m3 for a good crop of sugarcane. This is equal to 2000 to 3000 mm. Total water requirement depends on various factors such as soil type, climate, agronomic practices, crop duration etc.
Approximate water requirement of 12 month sugarcane at each growth phase is indicated below:
1. Germination (0 – 45 days): 300 mm
2. Tillering phase (45 – 120 days): 550 mm
3. Grand growth phase (120 – 270 days): 1000 mm
Germination:
During germination phase, general principle is light irrigation at frequent intervals, so that the soil is kept just moist, not dry or over moist. When the soil is dry due to under irrigation, buds dry leading to a lower and delayed germination. Excess water application leads to bud rotting due to fungal attack, lack of aeration and soil dampness.
Tillering:
Crucial phase of tillering needs optimum water supply. Any shortage would reduce tillering, increase tiller mortality and thus ultimately the stalk population.
Grand growth:
Shortage of water in grand growth phase leads to shortening of internodes and thus cane length and reduced cane weight. Tillering and grand growth phases mostly coincide with hot weather period and atmospheric demand for water is greater.
Ripening phase:
Require mild moisture stress for sugar accumulation. Plentiful supply of water leads to continued vegetative growth thus hampering sugar accumulation. Soil should not be allowed to crack, as the minute cracks would damage the root system. If the old crop is subjected to stress, there could be serious cane weight loss, cane breakage, pith formation, increase in fiber per cent and deterioration in juice quality.
Water use efficiency of sugarcane under field conditions is low (0.4 to 0.6 t ha-cm-1). It can be increased to 1.0 t cane ha-cm-1 of water with appropriate water management practices. Studies on critical stages of sugarcane of water at IISR, Lucknow indicated that tillering, grand period of growth and early ripening stages are most critical for irrigation.
Irrigating February planted cane crop at 25 per cent DASM requires 10 irrigations and at 50 per cent, 7 irrigations. Irrigation at 80 per cent leaf sheath moisture content produced highest cane yield at Caddalore. Scheduling irrigation at IW/CPE ratio of 0.7 was optimum for high cane yield. Numerous studies conclusively proved beneficial effect of trash mulch in minimising the irrigation needs of sugarcane.
Studies on drip irrigation during late 1980s at Rahuri indicated saving of 64 per cent irrigation water compared to furrow method and produced 12 per cent higher cane yield (Table 11.11).
TABLE 11.11: Relative efficiency of drip and surface irrigation at Rahuri
Irrigation interval of one day with drip method is better than daily irrigation or two to three day’s interval. Even three days interval gave higher yield than surface irrigation. Cane yield with paired row planting in drip method was better than all surface treatments, indicating scope for minimising cost for drip system with paired row system. Paired row planting required 26 per cent less water without significant yield reduction. In spite of marginal yield advantage, pit method requires substantial labour and hence not economical.
Suggested irrigation practices are:
1. Premonsoon is the crucial period for irrigation in tropical and subtropical regions
2. Tillering, grand growth period and early ripening period are more sensitive to soil moisture stress. At times of deficit water supplies, irrigation must be provided at least during these stages
3. If irrigation water is not a limiting factor, sugarcane needs 8 to 12 irrigations during rainy season and 8 to 14 during postrainy period in tropical regions. In subtropical regions, irrigation is not necessary during monsoon period, while 2 to 3 irrigations are needed during postrainy period
4. In general, scheduling irrigation at 50 per cent DASM or at IW/CPE ratio of 0.75 is ideal, if there is no scarcity for irrigation water
5. Generally, a drying off period of 4 to 6 weeks prior to harvest has to be allowed
6. Alternate day drip irrigation increase the cane yield and decrease the irrigation needs by more than 50 per cent compared with surface irrigation. Paired row planting considerably bring down the cost of drip equipment and reduce the irrigation needs by about 25 per cent compared with surface irrigation.
Essay # 2. Irrigation Practices Used for Growing Cotton:
More than 75 per cent of the area under cotton in India is entirely depending on rainfall during monsoon period, while supplemental irrigation is available for about 25 per cent. Supplemental irrigation is, generally, given for American and hybrid cottons, depending on the availability of irrigation water.
Cotton has a taproot that grows quickly reaching 20-25 cm depth before the seedling emerges from the soil. Root depth may reach 90 to 150 cm when the plant is 20 to 25 cm tall. The main root reaches about 200 cm. Depending upon the climate and crop growing period, water requirement of cotton varies from 700 to 1200 mm. Water requirement is low during the first 60-70 days after sowing and highest during flowering and boll development stages.
Optimum yield of fiber depends on maintenance of a proper balance between leaf production and boll (fruit) production. A planned moisture regime that will restrain vegetative growth without adversely affecting yield is essential. It is desirable that the plant completes most of its vegetative growth before flowers appear and this is best achieved by moisture regime that promotes regular and rapid but not excessive development of young plant. During early part of the season, less water is used by plant and more water is lost by evaporation than transpiration.
Depending on climate and length of the total growing period, cotton needs around 700 to 1300 mm to meet its water requirements. In the early vegetative period, crop water requirements are low (10 % of total). They are high during flowering period when leaf area is at its maximum (50 to 60%). Later in the growing period, the requirements decline. Growth stages of cotton are shown in Fig 11.2.
Irrigation Scheduling:
1. To enhance root development, adequate water should be available in the soil at the time of sowing and pre-irrigation is required when stored soil-water from preseason rainfall is not available
2. In the vegetative period (1), irrigation may be scheduled when around 60 per cent of the available soil-water over the first 0.75 m has been taken up by the crop
3. During flowering (2), depletion of some 70 per cent of available soil-water will in general check vegetative growth without impairing yields; delayed irrigation during this period may cause considerable flower and bud shedding
4. During yield formation (boll idling) (3) and ripening (4), the soil-water depletion may increase from 60 per cent to higher values as the season progresses and depending on climate and depth of stored soil-water, irrigation can be terminated 4 to 5 weeks before final picking
5. When grown under conditions of high groundwater tables, even for short duration, and when soils are wet for long periods, yield decrease may be up to 50 per cent, not-withstanding unrestricted water use. This may be due to inadequate soil aeration. The same phenomenon has been noticed under very frequent irrigations.
Regulate irrigation according to the following growth phases of cotton as indicated in Table 11.12.
Methods of Irrigation:
Skip furrow irrigation:
Suited to heavy soils like clay and loam. Alternate furrows should be skipped and may be converted to ridges having a wide bed formation. Short term crops like pulses may be raised in wider bed without exclusive irrigation. Water saving is 50% when compared to control.
Alternate furrow irrigation:
During any one run of irrigation, a particular set of alternate furrows is irrigated.
Interval of irrigation should be shortened when compared to the conventional furrows. During the next run, the left over furrows be irrigated. Suited to heavy soils.
Essay # 3. Irrigation Practices Used for Growing Tobacco:
It has been observed that tobacco cannot tolerate waterlogging at any stage of growth but at the same time the plants may not withstand drought. Therefore, a compromising situation would be to give light and frequent irrigations to the crop. However, the interval and number of irrigations depends upon soil type, weather, cultivation practices and type of tobacco grown.
Field should be irrigated when the soil moisture falls to about 25 per cent field capacity. Irrigation at 50 per cent depletion of available soil moisture is adequate for different cultivars under several situations. Crop water requirement varies from 450 to 550 mm. Hard water (saline) from wells should not contain more than 30 ppm (maximum limit 50 ppm) of chloride, otherwise the leaves have poor burning quality.
Water needs of tobacco may be considered in phases. In the first 2-5 weeks after planting, water needs are small and the plant is sensitive to excessive soil moisture. After the plant has been watered at planting, water should be withheld for 4-5 weeks. The second phase covers rest of the development phase (emergence and expansion of remaining leaves).
During this phase, crop water needs are highest and needs frequent rainfall, irrigation or adequate stored moisture in the soil. The third phase extends over the reminder of the maturation phase when water needs decline due to removal of leaves and the crop ages.
Such a soil moisture regime during the crop growth leads to high yield with acceptable leaf quality. A crop with frequent irrigations or adequate available soil moisture gives high yield, however, at the cost of leaf quality. Critical stage for irrigation is knee-height stage.
Based on the results of experiments conducted at different environments in the country, the following general conclusions can be drawn on optimum irrigation schedules to FCV and Non-FCV tobaccos:
FCV on Black Soils of AP (Guntur and Prakasam Districts):
Pot watering at planting may be necessary if the weather is dry. During continuous dry spells, one life saving irrigation can be given if water of good quality is available (less than 50 ppm chlorides). Adequate care should be taken to avoid excessive soil moisture or waterlogging.
FCV on Light Soils:
Water from canals, tanks, wells and deep bore wells can be used but the chloride content should not exceed 50 ppm. Total irrigation water required, including rainfall, has to be applied in 6-8 irrigations.
Irrigation through all furrows requires more irrigation water. Alternate/skip furrow irrigation checks wastage of irrigation water. It improves the leaf quality and gives 10-20 per cent higher yield than all furrow irrigation.
Recommended irrigation schedule:
At planting in plough furrow: 15 mm
I irrigation – 15-20 days after planting by surface irrigation, if needed: 20 mm
II irrigation – 30-35 days after planting as surface irrigation: 24 mm
III irrigation – 40-45 days after planting by furrow irrigation immediately after ridge formation: 48 mm
IV irrigation – 50-55 days after planting by furrow irrigation: 48 mm
V irrigation – 65-70 days after planting by alternate skip furrow method: 24 mm
VI irrigation – 80-85 days after planting by alternate skip furrow method: 24 mm
VII irrigation – 95-100 days after planting by alternate skip furrow method: 24 mm
VIII irrigation – 115-120 days after planting by alternate skip furrow method: 24 mm
In alternate/skip furrow method, in subsequent irrigation, avoid first irrigated furrows and irrigate the un-irrigated furrows. Follow the same fashion in consecutive irrigations.
The following IW/CPE ratio climatological approach can also be followed if agromet observatory is available in the vicinity of the crop area:
Irrigation Schedule for Non-FCV Tobaccos:
Cigar and cherrot tobaccos of Tamil Nadu and chewing tobacco of Bihar are, generally, grown under irrigated conditions.
1. Following transplanting, light irrigations should be given for the first 4-5 days
2. Subsequent irrigations are necessary at 6-7 days interval
3. In all, 16-20 irrigations necessary for optimum yield and quality.
Bidi tobacco of Karnataka, Maharashtra and hookah and chewing tobaccos of West Bengal are, generally, grown as rainfed crops, but under drought, one or two irrigations are desirable for economic yield.
The hookah and chewing tobaccos of UP are, generally, grown under irrigated conditions and need 12-15 irrigations.
For optimum yield and quality, tobacco should not be subjected to severe soil moisture stress:
1. Between establishment stage and knee-high stage, a little moisture stress is not harmful and it may improve yield and quality
2. Low soil moisture at this stage encourages deeper root development which is beneficial during grand growth period
3. Between knee-high stages to early bloom stage (grand growth period) moisture is extremely important
4. Around 50 per cent soil moisture depletion level ensures good leaf spread, rapid growth, high yield and quality
5. During the harvest period, occasionally, it may be desirable to irrigate tobacco. This should be done only during extreme drought
6. A slight moisture stress during harvest period reduces brown spot, slows down harvest rate which helps in improving yield and quality.
It has been observed that tobacco leaf ripens faster (false ripening) after heavy rains or heavy irrigation. This faster ripening may be due to leaching loss of nitrogen from root zone, anaerobic conditions in the root zone or physiological reaction within the leaf due to high moisture. If tobacco does not show any signs of wilting before 11.00 AM, irrigation is not necessary.