In this method, the irrigation water is conveyed from the source to the field, usually through earthen channels and in the field, water is allowed to flow on the soil surface. This method is simple, cheap and easy to adopt. But a major portion of the water is lost both during conveyance and application. There are different methods of surface irrigation which are described below:
This type of irrigation is adopted generally for the crop planted in flat system. In this method, the irrigation water is not regulated in the field and allowed to flow uncontrolled. The irrigation water requirement per irrigation in this method often exceeds 100 mm. As the water stagnates in the field, a lot of the water percolates down beyond the root zone resulting in the wastage of precious irrigation water. Besides the root zone soil remains saturated for a few days every time it is irrigated which affects the soil aeration and consequently the growth of the crop. The only advantage of this system is that it is easy to adopt when the availability of irrigation water is plenty or unlimited. But this results in poor water use efficiency and poor water application uniformity, in addition to potential water logging and salinity problems.
This is the most common irrigation method adopted for sugarcane. Water from the irrigation channel is diverted into small furrows along the slope in between small ridges or broad beds. Water in furrows moves both laterally and vertically to moisten the ridges and sub soil. This is a cheap and easy method but there is some application loss. The method could be improved by adopting a proper irrigation schedule based on soil moisture deficit approach or climatological approach or the depth-interval-yield approach and by regulating the quantity of water per irrigation based on the available moisture holding capacity of the soil.
Skip furrow irrigation
It is a modification over furrow irrigation wherein alternate furrows are skipped by bringing two rows in a common furrow, if necessary by suitable adjustment of spaces between the rows. The crop population remains the same whereas the number of furrows irrigated gets reduced. There are reports which show that there could be a saving of 30 to 36 % in the quantity of irrigation water by adopting skip furrow method of irrigation. However, a reduction of 14 % in the cane yield has also been reported.
Alternate furrow irrigation
Alternate furrow irrigation is another modification of furrow irrigation wherein irrigations are given in cycles to the odd and even numbered furrows. It has been reported that there is a saving of 41 per cent in the quantity of irrigation water by adopting this method. But there was a reduction in the cane yield to the extent of 26 per cent. This method could be adopted during periods of irrigation water scarcity and the normal furrow irrigation could be readopted when the availability of irrigation water improves. Ved Singh (2002) reported the highest water saving of 33% when alternate furrow irrigation was adopted.
In this method, water is transported through easily dismantleable, surface laid pipes under pressure and sprinkled over the canopy by rotating type of nozzles. There are different sizes in sprinklers. The medium sized ones could sprinkle water to a radius of 10 to 15 metres and could be arranged in the field in such a way that sprinkling of water is more or less uniform all over the field. There are larger sized ones known as rain guns which could sprinkle water to a radius of over 30 metres. These could be fixed and operated in semi circles also.
Just one rain gun can cover over 0.1 ha at a time. Here the conveyance and application losses are lower and it is easy to regulate the quantity of water to be applied. This is a useful and feasible method when the crop is young. But at later stages, when the height of the crop canopy goes up, shifting of the pipes and sprinklers in the field from one place to the other becomes very difficult and poses practical problems in its adoption. This system of irrigation limits the root system to the surface layer of the soil which leads to the lodging of the cane.
As the water is sprinkled over the canopy, it wets the canopy, trash and cane before reaching the soil surface. In this process, a small quantity of water is wasted. Sometimes it may induce aerial rooting of the cane which affects the quality. The distribution of water is also not uniform all over the field. The initial cost of the system is very high and the energy required for operation of the system is also very high. Of the different sprinkler type systems available, only permanent systems have proved practical in the long run. In clayey soils, sprinkler systems have proved very useful for better germination of the crop and to economise irrigation water as it wets only the surface soil.
The term “micro-irrigation” describes a family of irrigation systems that apply water through small devices. These include mini sprinklers, micro sprinklers, bubbler irrigation and drip irrigation. These devices deliver water onto the soil surface very near the plant or below the soil surface directly into the plant root zone facilitating precision water application. Micro-irrigation systems are immensely popular in arid as well as subhumid and humid zones where water supplies are limited or water is expensive. In irrigated agriculture, micro irrigation is used extensively for row crops, mulched crops, orchards, gardens, greenhouses and nurseries. Of the different micro-irrigation systems, drip irrigation is gradually becoming popular in India mainly in wide spaced horticultural crops and also in sugarcane.
Drip / Trickle Irrigation
Drip irrigation was introduced in the 1970s in Hawaii, Australia and Mauritius. The main advantage of drip system is that the irrigation water is transported from the source to the root zone of the crop through a net work of tubing without any conveyance loss. Besides the quantity of irrigation water can be easily regulated in the drip irrigation system to the actual requirement of the crop. Through drip irrigation, the moisture in the root zone of the crop can be maintained near field capacity almost continuously. As the conveyance loss is practically eliminated and the irrigation water is directly fed into the root zone of the crop at the levels required by the crop, it results in the saving in the quantity of irrigation water.
Types of drip irrigation systems
There are two types of drip irrigation systems viz. surface and sub-surface systems. A drip system, whether surface or sub-surface, essentially consists of a pump, sand filter, screen filter, venturi, back water arrangement, pressure gauge, water meter, control valves, mains and sub-mains, laterals and drippers/emitters. In the surface system, the laterals are laid on the surface and drippers are fixed at desired intervals on the laterals. This type of drippers is known as online drippers.
In this type, again there are ordinary drippers and self-flushing and pressure compensating drippers. The drippers are available at varying capacities, say 2, 4, 6 or 8 litres per hour. The distance between the laterals, the distance between the drippers and the capacity of the drippers can be varied depending upon the need of the crop and soil characteristics. Here the water drips at the soil surface and there is a chance for the loss of water through surface evaporation.
In the subsurface system, the laterals are buried in the soil at desired depth along the crop rows. These laterals have emitters fixed inside and are known as inline drippers. They are fixed at desired intervals which emit the water right in the root zone of the crop and only a little quantity of this water comes to the surface. Hence, in this system, the chance for the loss of water through surface evaporation is very less. Different types of sub-surface laterals with emitters are available commercially. Biwall and Typhoon are some of them. Field layout of the drip system: The field layout depends on the area of the field, shape of the field, distance between the water source and the field, and the capacity of the pump available.
In most cases, the drip system can be directly connected with the existing pump in the farm. But when the operating pump pressure is too less or very high than that required by the drip system, a new pump has to be installed for the drip system. To facilitate drip irrigation in sugarcane, the planting method needs to be changed to wide row or paired row or trench or pit system. The spacing between the laterals can be from 1.5 to 2.4 m depending upon the planting system and geometry. The drip system is designed for the specific fields by the manufacturers/dealers in consultation with the farmers. The manufacturers/dealers also do the installation as per the requirement of the farmers taking the local conditions into account.
Scheduling of drip irrigation
Irrigation water economy could be achieved in drip irrigation only when the actual water requirement is computed on a daily or once in two days basis and only the computed quantity is applied. At planting, the drip system is run continuously so as to bring the moisture in the root zone of the crop to field capacity. Thereafter, the quantity of irrigation water has to be computed based on the crop coefficient (Kc value) and the evaporative demand of the climate (pan evaporation).The Kc values for sugarcane at different ages for a location with moderate humidity and wind velocity are given below. The quantity of water to be irrigated on a given day can be computed using the formula given below in table 4.
|Crop age (months)||Kc value|
Q = A x Kc x PE
Q = Quantity of water to be irrigated on a given day in litres
A = Area of the field in m2
Kc = Crop coefficient value depending on the age of the crop
PE = Pan evaporation for the day in mm
It may be difficult to obtain the pan evaporation data daily. As discussed earlier, the average monthly PE values of the district or the nearest agricultural research station can be used. A chart can be prepared to indicate the duration for which the system should be operated every day right from planting up to the harvest. Whenever there is rain, the farmer has to use his judgment and can withhold irrigation for a few days. Similarly, there may be situations
wherein the farmer may not be in a position to give irrigation on certain days due to reasons like power shut down. Running the system for more time in the subsequent days can compensate this. Hence, at the farmers’ level, the system can be used with some flexibility.
Fertigation can be a more efficient means of applying crop nutrients, particularly N and K, so that nutrient application rates could be reduced. However, only information limited is available on the extent of the possible reduction in N application rate for fertigated sugarcane. Thorburn et al. (2003) studied the response of cane and sugar production to different N rates (0 – 240 kg/ha/year) applied through drip fertigation to one plant and three ratoon crops in Australia. The results indicated that the high soil water contents maintained with daily application of irrigation water through the trickle system promoted mineralisation of soil organic matter and stressed the need to avoid over-application of N in fertigated sugarcane.
Raskar and Bhoi (2001) in their studies on the effect of sources and levels of fertigation on yield and quality of sugarcane found that the yield obtained due to the application of 75 % and 100 % of the RDF was on par indicating 25 % saving in fertilizer. Cane yield obtained with the use of water soluble fertilizers was on par with that obtained with urea, DAP and MOP.
Economics of drip system
Assuming that the drip laterals are spaced at 1.8 m and drippers are spaced at 0.6 m along the laterals, about 5600 m length of laterals and 9400 drippers are required to install drip irrigation system for one hectare of sugarcane. These along with other components costs at present between Rs. 70,000 and Rs. 100,000 per hectare depending upon the type of system and size of fields. By replacing the laterals in 6th year, the system could be used for about 10 years. The cost of replacement in the 6th year will be about Rs. 30,000 to Rs. 50,000 per hectare.
Therefore, the total investment on drip irrigation system for 10 years ranges from Rs. 100,000 to Rs. 150,000 per hectare. Even assuming that there is about 30 per cent saving in irrigation water and about 15 per cent increase in cane yield, the cost is very much prohibitive. Narayanamoorthy (2002) assessed the impact of drip irrigation for sugarcane in India and estimated that drip irrigation resulted in 44 % energy saving, 23 % increase in productivity and a saving of 1059 kWh of electricity per hectare and was found to be economically viable even without the subsidy.
Advantages of drip irrigation
- Irrigation water is transported from the source to the root zone of the crop without much conveyance and application losses which result in economy of irrigation water.
- The quantity of irrigation water can be regulated so as to wet only the root zone of the crop.
- Soil moisture in the root zone of the crop could be maintained near field capacity throughout the crop duration which leads to better crop growth and higher cane yield.
- Costly inputs like fertilizers and pesticides could be applied through irrigation water and the dose of such inputs could be reduced increasing their efficiency.
- Under situations of acute water shortage, the irrigation interval gets widened beyond the critical limit and the crop often dries up. With drip irrigation it is possible to evenly apply the available irrigation water over the entire cropped area, thereby keeping it alive so that it can be rejuvenated later.
- With drip irrigation as separate space is not allotted for irrigation channels etc., the effective cropped area is more producing additional cane yield.
- It reduces the drudgery of the irrigation labour as well as labour cost.
Constraints in adoption of drip irrigation in sugarcane
- The high cost of the system.
- Operational problems like non-availability of electricity, spare parts, good quality components, trained man power etc.
- Clogging of drippers particularly when poor quality irrigation water is used.
- Shallow rooting is a common feature which results in severe lodging affecting yield and quality.
- Filter maintenance
- Root intrusion
- Damage from farm implements and animals
- Difficulties in designing and installation of the drip irrigation system because of the small size of the holdings.
- The planting geometry of the crop needs to be modified from the conventional uniform rows to paired rows for adoption of drip irrigation
- Components like pressure gauges, filter screens and water meters become non-functional quite often due to salt deposition necessitating replacements or repairs which add to the maintenance cost.
- The power consumption is more compared to conventional irrigation
- There are different grades of drip irrigation system components with wide variation in quality and longevity, which cannot be easily distinguished, and there are chances for the farmers to lose on account of poor quality.
- Once a drip irrigation system is installed for Sugarcane, one plant and one or two ratoon crops can be successfully taken. After that, most often the system is not suitable for crops coming in rotation like rice, groundnut etc,
- Sugarcane Breeding Institute