Drip irrigation in sugarcane is a relatively new innovative technology that can conserve water, energy and increase profits. Thus, drip irrigation may help solve three of the most important problems of irrigated sugarcane - water scarcity, rising pumping (energy) costs and depressed farm profits.
Whether or not drip will be successful depends on a host of agronomic, engineering and economic factors. "Drip irrigation is defined as the precise, slow and frequent application of water through point or line source emitters on or below the soil surface at a small operating pressure (20-200 kPa) and at a low discharge rate (0.6 to 20 LPH), resulting in partial wetting of the soil surface.
In the literature, "trickle" is used interchangeably with "drip". Most popular drip versions used in sugarcane are surface and subsurface drip.
- Surface Drip: The application of water to the soil surface as drops or a tiny stream through emitters placed at predetermined distance along the drip lateral is termed as surface drip irrigation. It can be of two types - online or integral type surface drip system. Integral dripline is recommended for sugarcane.
- Subsurface Drip (SDI):The application of water below the soil surface through emitters molded on the inner wall of the dripline, with discharge rates (1.0 - 3.0 LPH) generally in the same range as integral surface drip irrigation. This method of water application is different from and not to be confused with the method where the root zone is irrigated by water table control, herein referred to as subirrigation. The integral dripline (thin or thick-walled) is installed at some predetermined depth in the soil depending on the soil type and crop requirements. There are two main types of SDI - "one crop" and "multicrop".Agronomic Advantages of Drip Over Sprinkler & Furrow IrrigationAdoption of drip irrigation (surface or subsurface) system in sugarcane cultivation is technically feasible, economically viable and beneficial in many ways:
- Deceased energy costs due to reduced pumping time to irrigate a given design area
- Saving in water up to 45 to 50% contributing to higher water use efficiency
Effective drip technology requires a more intense application of crop, soil, climatic, engineering, and economic factors than is usually present with furrow irrigation. New management perspectives and skills are required t planting configuration, land preparation, drip design features, irrigation scheduling, fertigation, operation & maintenance of the system.The new management practices induced with drip technology seem to have significantly helped increase cane and sugar yields. Planting configuration and drip design features will be dealt in this section while others will dealt in different sections.Widely followed sugarcane planting systems are viz., ridge and furrow system in tropical region and flat system in sub-tropical region. The spacing of crop rows ranges from 0.60 m to 1.5 m. The most common spacing followed is 0.90 m in ridge and furrow system as shown in Fig, because it facilitates easy irrigation and solid support when proper earthing up is done.However, when the crop is raised under drip method of irrigation modifying the conventional ridge and furrow planting system to a paired-row or dual row system without sacrificing the plant population per unit area proved to be physiologically efficient and cost effective.The spacing of paired-rows is dependent upon the soil type and planting season. Wider spacing is advisable in fine textured soils under high fertility conditions and for long duration crop (> 13 to 16 months) and high tillering varieties. While in coarse textured soils with poor soil fertility status, short season crop (10-12 months) and shy tillering varieties narrow spacing is desirable.The paired-row planting pattern and associated spacing requirements both under surface and subsurface drip irrigation are depicted in the picture.These planting patterns are for guidance only. If necessary, adjustments in planting patterns may have to be made depending upon the variety, planting season, and fertility status and soil textural conditions of the region.The summary of drip guidelines recommended for sugarcane in different countries based on varietal characteristics, soil type, management, cost-effectiveness, and a local condition is given in Table 3.Table 3. Sugarcane: Drip Design GuidelinesPlanting patternDrip systemDistance (m)Dripline installation depth (cm)Emitter distance(m)Discharge(LPH)Two rows of a pairTwo paired rows / two rowsTwo driplinesSingle rowSurface---1.2 to 1.51.2 to 1.5---0.4 to 0.61.0 to 3.0Paired rowSurface0.4 to 1.01.4 to 2.01.8 to 2.5---0.4 to 0.61.0 to 3.0Paired rowSDI0.4 to 1.01.4 to 2.01.8 to 2.50.15 to 0.300.4 to 0.61.0 to 2.3Drip irrigation offers the grower the potential for increasing cane yields & quality; and opportunity for improving irrigation & energy efficiencies in irrigated sugarcane. However, to realize this potential and opportunity, drip irrigation schemes must be designed, installed and managed correctly.Design FactorsThe main technical factors that should be considered when designing a drip irrigation scheme for sugarcane are as follows:
- Less weed growth and saving in labour due fewer weed control, fertigation & plant protection operations
- Less pest & disease incidence due to better field sanitation
- Optimum soil water air relations contributing to better germination, uniform field emergence and maintenance of optimum plant population
- Early harvesting and more ratoons
- Day/Night irrigation scheduling is possible
- Facilitates growing of crop on marginal soils due to frequent irrigations and fertigation
- High frequency irrigation, micro-leaching and higher soil water potential enables use of saline water for irrigation
- Higher cane and sugar yields
the pictures shows the main components of a drip irrigation system.Drip irrigation system must have a design capacity adequate to satisfy the peak crop water requirement of the crop to be irrigated within the design area. The capacity shall include an allowance for water losses that may occur during application periods. The system shall have the capacity to apply a stated amount of water in the design area in a specified net operation period. The system should have a minimum design capacity sufficient to deliver the peak daily crop water requirements in about 90% of the time available or not more than 22 h of operation or not more than the power availability period per day.The design operating pressure shall be in accordance with the recommendations of the manufacturer. The system operating pressure must compensate for pressure losses through system components and field elevation effects.The control head station includes facilities for water measurement, filtration & treatment, injection of fertilizers & chemicals, flow and pressure control, timing of application and backflow prevention.Filtration system is the assembly of independently controlled physical components used to remove suspended solids from irrigation water. Filtration of irrigation water is vital for drip irrigation schemes in order to avoid blockage of emitters as the internal passages of emitters are very small.The choice of filter depends mainly on the kind of impurities contained in the water and the degree of filtration required on the emitter. It is recommended that Netafim expert advise is sought on water quality analysis for pH, suspended solids, dissolved solids and bacterial population. Filtration system design recommendations should include location, size, specification of allowable suspended material sizes, types of filters, and maintenance requirements.Location: A primary filter shall be located after the pump and fertigation unit to remove both large and fine particles from the flow. Secondary filters may be used downstream from the primary filter to remove any particles, which may pass through the primary filter during normal or cleaning operations. When secondary filters are used, the size of the openings is usually larger than that of the primary filter to minimize needed attention.Size: Filter flow openings shall be sufficiently small to prevent the passage of unwanted particles into the system. The filter size should be based on the diameter of the emitter opening or the type and size of contaminants to be filtered. The capacity of the filter should be sufficiently large to permit the rated flow without frequent cleaning. Filters that are to be cleaned by hand should not require more than daily maintenance. The size should be the most economical with the lowest friction losses ranging from 0.3 to 0.5 bars.Types: Filtration may be accomplished through the use of different types of filters viz., screen (for inorganic impurities and moderate quality water or following a primary filtration with sand or disc filters) disc (for removal of impurities of organic and inorganic origin, algae included), hydrocyclones (for separation of sand or silt from well or river water) and media or sand filters (for open wells, open reservoirs, streams etc).Drip irrigation systems provide a convenient method of applying fertilizers and chemicals with the irrigation water using special fertigation devices. The fertigation devices include pressure differential systems (fertilizer tank), suction produced by a venturi principle (venturi injectors) and pumps (diaphragm or piston or electrically operated). The fertilizer unit is an integral part of control head.The important considerations are injection method & rate, concentration, storage tank capacity, contamination of water supply, reliability and accuracy of operation, warranty and service, automation suitability, field performance, price including acquisition and maintenance cost, life expectancy etcThe design objective of supply lines, main lines and submains is to deliver the required, pressurized quantity of water to the laterals (driplines) as efficiently as possible. The cane grower should attempt to minimize the total cost of the supply lines and mainlines needed to meet the engineering specifications.Sub-main pipe should be based upon capacity requirement, maintenance cost, investment cost and pressure uniformity. Buried pipelines are less subject to damage than surface lines and do not require special handling during the crop season. Appropriate risers and valves exist for each kind of pipe. Supply lines, main lines and submains generally account for 20-35% of total investment cost/ha.Riser AssemblyConnected to the water carrier system and located at each field block is a riser assembly. Typically, this will consist of a control valve, a disc filter, a pressure relief valve and pressure regulator, a water pressure test point, and an air release valve.The volume of water applied to each field block is controlled by the opening and closing of valves. These can be simple gate valves, semi-automatic volumetric valves or automatic solenoid valves connected back to a central controller. Although semi-automatic and automatic systems reduce labour running costs and facilitate night-time irrigation, they are more expensive. It is recommended, wherever possible, that cane growers choose the simplest control systems and systems that are easy to use and easy to maintain.The air relief valve, which may also act as a water pressure test point, is necessary to prevent water hammers whenever air is escaping from the water carrier system. The discharge of driplines other than those with pressure compensating emitters is dependent on the water pressure in the dripline.The pressure regulator at the riser is used to maintain water pressure in the driplines at the level recommended by the Netafim design engineer. It should be noted that riser assemblies should be protected from damage through vandalism, cane fires and infield operations such as mechanical harvesting, loading etc. A concrete box with a metal door usually provides sufficient protection.In most sugarcane drip irrigated systems water is conducted from the riser assembly into a sub-main into which the driplines are connected. Although there are many different types of Netafim driplines that are used in sugarcane, they are all designed to distribute water uniformly over the entire design area of a given field block. A variation in discharge rate from dripline emitters that is acceptable is of the order of
- Peak crop water requirements
- Area of fields to be irrigated
- Availability of irrigation water and power
- Irrigation water quality
- Soil characteristics
- Land topography
± 8-10%.Driplines vary in emitter design, quality, uniformity of discharge and cost. From the outside, most integral driplines look alike. Yet there are major differences between products, particularly emitters. Consistent and superior performance of an integral dripline lies in the quality of its emitter. Several years of experience has shown that the following factors should be considered when selecting a dripline that is to remain either on surface or buried throughout a complete life cycle of a plant cane and 2 to 8 ratoons.
- Precision-molded emitters for uniform and constant low discharge of water & nutrients
- Wider and deeper flow path cross section for clog free discharge of water
- Sharp teeth for increased turbulence, flow control & flushing the emitter
- Seamless pipe construction for maintaining greater tensile and burst strength facilitating higher operation pressures for longer runs
- Raised filter inlet emitter for drawing clean water from the pipe center to prevent clogging
- Emitters with filters to prevent plugging, less maintenance & longer life.
- Flexible emitter spacing and choice of flow rates to suit different sugarcane varieties, planting patterns, soil types etc.
- Low emitter exponent and manufacturing coefficient of variation
- Flow rate insensitive to temperature differences
- Insect resistance, resistance to sunlight, no moving parts and anticipated life
- Driplines come in a range of wall thicknesses. Construction and wall thickness of the dripline should be sufficient to reduce the risk of the pipe being crushed or pinched by cane stools or roots or by in-field traffic such as mechanical loaders, farm machinery etc. Recommended successful driplines are given in Table 4:
- Flap mechanism to prevent the risk of sucking of fine soil material into the dripline emitters leading to plugging
- Nominal diameters are 16 mm and 22mm. A larger diameter will allow the supply of water to a greater length of dripline before pressure drops below design requirements. This results in saving in the cost of submains.
- Availability of machinery to recover the driplines at the end of the crop cycle and used for a second crop cycle if possible after refurbishment
Crop type34 mil (0.8 mm) - 47 mil(1.2 mm)Thickwalled &PC or Non PCFor surface and subsurface drip, rougher soil conditions and where insect damage is expected. Lasts 10+ years with proper operation and maintenance techniques12 mil (0.3 mm) - 25 mil(0.63 mm)Thinwalled &PC or Non PCFor subsurface drip and good soil conditions. Lasts for 3-5 years.
The area wetted as a percent of the total crop area i.e., wetting patterns that are obtained under drip irrigation depend on a number of factors which include the soil hydraulic properties, emitter spacing, dripline placement with respect to the cane rows, emitter discharge rate, planting configuration, crop evapotranspiration and irrigation regime. The following information concerning wetting patterns has been obtained by Netafim Agronomists & Design Engineers from several years of experimentation and experience under diverse agro-ecological conditions:
- Both surface and subsurface drip irrigation system were technically feasible in sugarcane under diverse conditions
- Availability of dripline types for application in sugarcane viz., thick-walled for surface drip irrigated cane, thin-walled for subsurface drip irrigated cane, non-pressure compensated driplines for leveled land, pressure compensated driplines for undulated topography etc
- Subsurface drip irrigation was superior over surface drip in terms of water availability, uniformity, water use, water use efficiency, cane yield and quality, management etc
- Paired row or dual row or pineapple planting configuration with variable spacings depending upon the soil texture with one dripline for every two rows was found to be technically feasible, economically viable and potentially profitable in comparison to rectangular single row planting configuration with dripline for every crop row.
- Driplines can be successfully buried before planting cane with out waiting for planting and germination of cane.
- Cane germination and field emergence was adequate to give satisfactory plant stand both under surface and SDI systems with out any supplementary use of surface furrow or overhead sprinkler system for germination irrigation
- Emitter Spacings: Spacings of 0.3 to 0.75 m and discharge rates of 1.0 to 3 LPH were acceptable to most soil types on which sugarcane is grown in different countries today. It is recommended, however, that the lower discharge rates and closer emitter spacings are used on light textured sandy, loamy sands, sandy loams, which have low water retention capacities. Conversely higher discharge rates and wider emitter spacings are recommended for medium to heavy textured soils viz., loamy, silty clay, clay loams and clays. Emitter discharge rate should not create runoff within the immediate application area. In fields with varying soil types, this criterion shall apply to the soil with the lowest infiltration rate unless it is less than 15% of the area irrigated. It should be noted that wider the spacing between emitters the more difficult it is to achieve uniform wetted strip and in turn uniform cane germination and field emergence.
- Wetted Area: The area wetted as a percent of the total cane cropped area ranged from a low of 28% in widely spaced paired-row planting configuration with dripline for every two rows (placed midway in between two rows) to a high of 60% in single-row rectangular planting configuration with dripline for each row.
Soil texturePlacement depth below groundRemarksLoamy sand & Sandy loam15 to 20 cmThese soils benefit from short & frequent irrigations. Irrigate to refill the soil profile to effective rooting depth only. Note that drip irrigation wets only a narrow band under the dripline in these soils and the storage capacity of the soil is small.Silty loam & Clay loam20 to 25 cmLess frequent irrigations, larger volume of irrigation water application can be allowed since water spreads laterally more into the root zone. Water storage capacity of the soils is high.Clay soil25 to 30 cmLess frequent, longer irrigation cycles and larger volume of irrigation water application can be allowed since water spreads laterally more into the root zone. Water storage capacity of the soils is very high. However, watch for ill-drained conditions and waterlogging in the crop root zone.
- Depth of Placement: Subsurface dripline placement is the most popular technique used in cane. Driplines buried underground are protected from mechanical damage. Depth of placement is critical to optimize the potential for drip irrigation. Soil type and topography dictates depth of placement. Light textured soils (sandy, loamy sand and sandy loam) require shallow depth of dripline placement so that water is not lost by deep percolation. Medium to heavy textured soils (loamy, silty loam, clay loam & clay) which will wet-up laterally (larger wetted diameter) can have deeper placement.
This is an advantage in minimizing damage to dripline from insects and rats and intrusion of roots; it also allows planting over the top of the dripline. In sloping blocks dripline placement can be offset to the uphill side of the sett so that water will gravity drain to the root zone but care must be taken to avoid damage during cultivation. The overall aim when considering dripline placement is to maintain the most efficient supply of water to the effective root zone of the plant under the conditions of soil type, soil depth, topography and any other limiting conditions (Table 5).
Shallow depth can cause crushing of driplines by mechanical loaders and cane fires. Shallow depth of installation of driplines may also lead to irrigation water being lost to direct soil evaporation as a result of puddles formed above the driplines during irrigation. Try not to allow water to reach the soil surface as it will allow germination of weed seeds. In dry conditions it will be beneficial to wet-up to the surface after harvest to assist in ratooning.
The main managerial and economic factors that should be considered when designing a SDI for sugarcane are as follows:
- Potential yield and CCS increment
- Cost of subsurface drip irrigation system
- Cost of installation and interest rate
- Operation and maintenance costs
- Availability and cost of water
- Availability and cost of trained skilled staff to operate the drip scheme
- Price of sugar
- Water - Source, availability and quality evaluation for determining filtration system type, maintenance of irrigation system, crop management and selection of fertilizers
- Soil evaluation for fertility status, clay content, CEC, bulk density etc for determining the fertigation programme
- Determination of moisture holding properties and evaporative demand of the atmosphere for irrigation scheduling
- Contour survey for selection of dripline type (pressure compensating or non-pressure compensating), to determine dripline length and sub-main spacing
- Soil characteristics for determining appropriate emitter spacing and depth of dripline placement
Driplines and emitters, for both surface and subsurface systems, are subject to plugging and breaking with passing time. Microbial and inorganic deposits are the two principal causes of emitter plugging. Algae and bacterial slimes are of particular concern when water is pumped directly from an irrigation ditch, reservoir, open well, or natural channel. Even with sand media filters, microorganisms may grow in the lines and become a major problem.Maintaining a pH of 6.5-6.8 with periodical acid injection reduces precipitation of inorganic compounds (phosphates, calcium, bicarbonates) and discourages algae growth. Chlorine, also, may be used to treat algae. Shock treatments, with acids (sulphuric, hydrochloric and phosphoric), which periodically reduce pH to 2-3 also kill algae and eliminate some inorganic plugging.Acidified fertilizers are used or are being developed to deal with emitter plugging.Rodents, rabbits, and coyotes may chew holes in driplines, roots may clog subsurface emitters, or lines may be mechanically damaged. For the most part, drip irrigated cane growers world over have nor found these to be major problems. Broken or damaged lines (from all causes) have affected less than 4% of the total system. Broken lines are usually easily and inexpensively repaired.Chemicals (like Trifluralin) help keep roots from clogging emitters under SDI. And subsurface driplines are better protected from mechanical as well as rodent damage with deeper line placement and more careful machinery operation in the field.
- It is essential that high quality installation and maintenance is adopted for dripline which is installed below ground. The following points are important when installing a system:Follow the Netafim Design Engineer instructions scrupulously, for example when glueing PVC pipes, installing mains & submains as pipe sizes will have been dimensioned to enable specified flow rates and pressure throughout the system.
- After installation, check each part of the system carefully for leaks as these will cause pressure problems at the tail end of the scheme
- Check every dripline being injected for correct placement, orientation and depth and to ensure there is no crimping of the riser, which connects dripline to the submain.
- Bury mains and submains to ensure that rocks in the back fill do not damage pipes.
- After hook-up, partially backfill portions of submains and pressure test before completely backfilling trenches.
- Flush out the water carrier system to remove extraneous material before riser assemblies and driplines are connected.
- Check water pressure at the risers and dripline flow rates: if these are not according to the specification there has been a problem at either the design or the installation stage.