IRRIGATION METHODS, SOIL-WATER-PLANT RELATIONSHIPS
Post on 15-Apr-2017
Slide 1NAMITHA M RID NO:2015664502M.TECH ,LWMEAEC&RI, KUMULURTNAUIRRIGATION METHODS, SOIL-WATER-PLANT RELATIONSHIPSIRRIGATIONArtificial application of water to arid land for growing cropsSupplementary to rainfall when it is either deficient or comes irregularly or at unreasonable timesIrrigation engineering: Multi-disciplinary science encompassing hydrology, agriculture, geology, climatology, river engineering, agronomy, forestry, social science, hydraulics, river soil mechanics, snow hydrology and groundwater hydrologyNEED FOR IRRIGATIONDeficient rainfall:Rainfall (cm)Irrigation requirement100Rainfall needs to be supplemented by irrigation100-50Rainfall is insufficient. Irrigation is essential.50-25Irrigation is essentially required.Less than 25No crop can be grown without irrigation.ContdNon- uniformity of rainfallAugmentation of crop yieldsExacting water requirementCash crops cultivationAssured water supplyOrchards and gardensADVANTAGES OF IRRIGATIONDirect benefitsIncrease in food output through higher yieldCultivation of cash cropsLand value appreciates manifoldProtection from famine irrigation makes agriculture and economy drought proofPrevention of damage through floodsHydel power generation at dam sites and canal fallsContdRise of subsoil water level in dry areasMeans of communication where navigation is possible in canalsRevenue from recreational facilitiesFish and wild life preservation and development of piscicultureLowers production risksMakes agriculture competitive and profitableReduced risks of crop failuresImprove the nutrition of peopleContdIndirect benefitsIncrease in GDPIncrease in revenue from sales tax on food grainsIncrease in employmentImprovement in groundwater storageIncrease in value of land propertyGeneral development of countryFarm laborers are benefited who get higher wagesRise to whole array of agro-based industriesDISADVANTAGES OF IRRIGATIONClimate becomes damp and cold, causing malarial diseasesOver-irrigation coupled with poor drainage in an area where water-table is high leads to water logging of the area, causes efflorescenceLow land revenue in certain cases Excessive seepage from unlined canals leads to water logging of lands adjacent to canalsSOIL-WATER PLANT RELATIONSHIPWater is the basic input influencing crop productionThe amount of water required for a given crop depends on:State of development of soilQuantity and type of fertilizer givenQuality of water usedClimatic conditionsContdSoil- water- plant relationship Process that requires to be regulated for maximization of yields with a given unit of water Understanding of Soil- Water- Plant relationship is essential in order that water management principles are applied to various climatic, soil and cropping regions of both rain fed and irrigated lands ContdSoil factors Infiltration:-Influences selection of irrigation methods, slope needed for the land, length of run, irrigation application time etc.Soil water parameters affecting infiltration rates:- Texture, Structure, Bulk Density, Sodium salts, Crop grown, Irrigation water, Temperature, Tillage and Water in soil ContdPermeability:- Depends on soil texture and structure, presence of plant roots and changes in temperature of water K= QL/A(H1-H2) where, Q= Discharge/ unit time A= Cross sectional area through which water flows H1-H2 = Hydraulic head L = Percolation path lengthContdSoilGravel (clean)Coarse sand (clean)Sand (mixture)Fine sandSilty sandSiltClay K1.0 or more1.0-0.01.01-.005.05-.0010.002-0.00010.0005-0.000010.00001 or lesserMeasured using Constant head permeameter and Variable head permeameterContdDrainability and Leachability:-Principal factors in predicting the drainability of a soil is its permeability and hydraulic gradientLeachability is directly related to drainabilityErodibilityContdPlant factorsRooting characteristics:-High water table limits the root growth due to lack of sufficient aerationEvapo-transpiration:-General rule is that 40,30,20 and 10 percent of the total ET is removed respectively from each successively deeper one-quarter of the rooting depth ContdEffect of soil water level on crop growth and yield:-Crop growth and transpiration generally decreases as the wilting point approachesThe point at which growth or transpiration of a plant is retarded for want of soil water, crop characteristics, low or high evaporative demand etc.ContdWater factorsWhen to irrigate:-Generally irrigation shall start when 50%, but not over 60% of the available moisture is used from the root zoneDesign frequency = (Field capacity of soil in effective crop root zone- moisture content of the same zone at the starting of irrigation)/ Moisture use of root of crop in peak periodContdHow much water to apply:-The amount of water to be replaced is usually 40-50% of the available water in the root zone of the soils having a uniform available water capacity with depthWater application method:-Influenced by quantity of available water supply, type of soil, topography and crops to be grownMethods include controlled surface flooding method, sprinkler method and drip method.METHODS OF IRRIGATIONA. Sub- surface irrigationWater applied beneath the ground by creating and maintaining an artificial water table30-75 cm below the ground surfaceConsists of main field ditches, laterals, laid 15-30m apartOpen ditches, mole drains or tile drainsAdvantages of sub-surface irrigationMinimum water requirement for raising crops and high yieldMinimum evaporation and deep percolation lossesMost economical method of irrigation and suitable for most cropsInvolves no wastage of landNo interference in free movement of farm machineryCultivation operations can be carried out without concern for the irrigation periodLittle field preparation and laborDisadvantages of sub-surface irrigationRequires a special combination of natural conditionsThere is danger of development of water loggingPossibility of choking of the pipe laid undergroundHigh costClassification of sub-surface irrigationNatural sub-irrigation:Applicable to low lying lands where the water table is highWater table is charged by seepage from irrigation canalsArtificial sub-irrigation:Very expensive methodWater under pressure provided to crops by capillarity through a network of buried perforated pipes B. Surface irrigationMost common type of irrigationWater is applied to the field in varied quantities at different timesFlow remains unsteadyDiverting a stream of water from the head of a field into furrows or borders and allows to flow downwardSupplemented with efficient water disposal systemAdvantages of surface irrigationAllows use of machinery for land preparation, cultivation and harvestingHelps to store the required amount of water in the capillary zone of the soil for supply to the root zone of plants Disadvantages of surface irrigationGreater loss of water by surface runoff and deep percolationLarger requirement of water per unit areaWater is lost in infiltration and deep percolationLow efficiency due to imperfect control over the water flowInferior quality crops with a low yieldWasteful use of waterCostly and time consuming land preparationClassification of surface irrigationFlooding method:Water is allowed to cover the surface of land in a continuous sheetThe flooding may be:Wild flooding (uncontrolled flooding) :Primitive and most inefficient methodWater is spread over the smooth or flat field without much control over the flow or prior preparationContdWater distribution is quite uneven Advantage: Low cost and does not interfere with tillage Suitable for all medium to fine texture soilsDisadvantage: Wasteful use of water Non-uniform distribution of water Excessive soil erosion on steeper slopes Require drainage arrangement to reduce pondingContdControlled flooding :Free flooding (ordinary flooding) : Land is divided into plots or kiaries of suitable size depending on porosity of soilWater is spread over the field from water courseSpreading may vary from less than 15m to more than 60mContdBorder flooding: Field is divided into narrow strips by low parallel ridges on the sidesWidth if strip: 5-15m ; Length of strip: 60-100m for sandy loam, 100-120 for medium loam, 150-300 for clay loamLongitudinal gradient: 0.02-0.05% for clay to clay loam, 0.20-0.40% for medium loam, 0.25-0.60% for sandy loam to sandy soilContdCheck flooding: Applying water to relatively level check basins enclosed by small bundsSize of check basin: 3*2m to 3*3m or even largeContour lateral method: Best suited to steeper terrain Dense network of contour laterals are laid with spacing 15-50m Adopted mostly in close growing crops on sloping landsContdZig zag method: Suitable for relatively level fieldsUnsuitable for mechanical farming operationsLand is divided into square or rectangular plots; each plot further sub divided with low bundsBasin flooding: Check method of flooding adapted to orchardsBasins are made around one or more trees depending on the soil condition and topographyadapted essentially to flat landsContdContour farming:Adapted to hilly areas with steep slopes and quick falling contoursLand is divided into longitudinal curved plots, the bunds of the plots following the contoursReduces runoff and soil lossContdFurrow method:Used for row cropsA furrow consists of a narrow ditch between the rows of cropsWater is applied in small streams between rows of crops, grown on ridges or in furrowsC. OVER HEAD IRRIGATION (SPRINKLER IRRIGATION)Simulates natural rainfall to spread water in the form of rain uniformly over the land surface Water is spread in uniform pattern and rate less than the infiltration rate of the soilNo land leveling is requiredSuitable for all types of soil and almost all cropsNot recommended for crops having high water requirement (eg. Rice, jute )ContdHelps to conserve water up to 50% Can irrigate 2 to 3 times the area compared to surface irrigationTried on large scale in Tamil Nadu, Karnataka, Haryana and PunjabFactors governing selection of sprinklerLand of undulating topography (sandy dunes)Land of steep slopes and easily erodible soils by surface irrigationLand with shallow soil cover, sandy soils or soils with high infiltration rateHighly porous or relatively impermeable soils unsuitable for proper water distribution by surface irrigation methodsContdLimited water supply and high cost of water as in lift irrigationNeed for light and frequent irrigationCostly and unreliable farm irrigationLands need to be brought into production quickly without waiting for land development and construction of channelsSprinkler irrigation systemWater pumped under pressure, carried through high pressure main line, let out through sprinkler nozzles placed at regular intervals on lateral lines forming a gentle rainConsiderations: Agro-climatic conditions, general land condition, maximum difference in elevation, cropping pattern, irrigation and cover crop requirements, matching pump and power unit, water supply source etc.ContdLayout:-Depends on the slope and size of the farm and location of water source Economical when source of water is at the centre of the area Distance between laterals= 12m Distance between 2 sprinklers= 12mContdWater application rate:-Less than the infiltration capacity of the soil to be irrigatedDepends on nature of soil, crop and topographyVaries from 0.25 cm/hr for clay to 5.5 cm/hr for very light soilsApplication rate= (Discharge(lps)* 282.6)/(spacing of sprinkler(m)* spacing of laterals(m))ContdWater application in each irrigation:-Determined by using not more than 50% available moisture in the soilArea to be irrigated depends on type & pattern of sprinkler and operating pressure adoptedSprinkler losses:-Depends on wind velocity, temperature, fineness of spray, humidity , soil texture and vegetation coverContdCapacity of the system:-To meet the peak demand of the area under crops during the hottest and driest periodsCapacity of pipe system depends on the rate of application of water and the area to be irrigated in one settingSystem capacity, Q= (A*D*27.8)/(I*H*E)QDischarge (lps) ; AArea(ha)DDepth of water application(cm)IInterval between successive irrigation (days); HOperating hours (hr/day) ; EField application efficiencyContdOperating pressure:-Size of droplets is limited by small nozzlesPressure: 2.75kg/cm2 for 3mm nozzle with additional 0.35 kg/cm2 pressure for each 0.75 mm increase in nozzle sizeWater pressure: 0.5 to 10 kg/cm2Sprinkler spacing and distribution pattern:-Properly maintained for adequate water distributionOverlap of sprinkler throw is adequateMaximum move interval =18mContdMain and lateral pipe sizes:-Determined by the maximum rate of flow and nature and length of pipes involvedVariation of pressure in the lateral, due to friction loss= 20% of operating head Pressure loss in main= 0.7kg/cm2Pumping unit:-Selection of the pumping set is made from the characteristic curve of the pump set supplied by the manufacturer ContdDischarge of sprinkler:-Discharge of a sprinkler, Q= (Sl*Sm*R)/360, lpsSl= Spacing (m) of sprinkler along lateralsSm= Spacing (m) of laterals along the mainsR= Optimum application rate (cm/hr)Discharge of sprinkler nozzle, q= Ca (2gh), m3/sa= Sectional area of the nozzle (m2)H= Pressure head of nozzle (m) ; C= Coefficient of dischargeContdWater spread of sprinkler, R= 1.35 (dh)R= Radius of the wetted area covered by sprinkler (m)d= Diameter of nozzle (m)H= Pressure head at nozzle (m)Types of sprinkler systemsBased on portability:Fully portable systemSemi-portable systemPermanent systemSemi- permanent sprinkler systemSprinkler hop systemPipe grid systemHose pull systemContd Based on spraying pattern:Rotary head or revolving systemPerforated sprinkler system (perfo-spray system)Based on arrangement of spraying:Fixed head typeRotary typeSprinkler losses and efficiencySprinkler Losses:Losses: Evaporation, some deep percolation, drift of spray due to wind, conveyance loss (negligible) etc.Evaporation loss is minimum at night and maximum at afternoonWindy and hot weather conditions increases lossesEfficiency: Varies according to climatic conditions60% on hot day, 70% in moderate and 80% in humid climateAdvantages of sprinkler irrigationSaves water, irrigates more landLow water lossEffective water managementSaving in landSaving in fertilizersLand leveling not necessarySoil conservedSoil condition is maintainedContdSoil is stabilizedBetter seed germinationFrost controlInstant irrigationUse of limited sourceUniform applicationControls climateSport grounds54ContdFree aeration of root zonePoor soils irrigatedDrainage problems eliminatedImproved soil fertility organismWeeds and pests controlledHigh crop yield and qualityReduced labor requirementPeoples participationLimitations of sprinkler irrigationHigh initial costPoor application efficiency in windy weather and high temperatureHigher evaporation losses in spraying waterNot suitable for jute or riceCannot be used with rotational supply systems of water distribution in canal irrigated areasWater supply free of solids and debris is neededContdAssured source of surface or groundwater supply is neededCannot be used in low infiltration rate soilsHigh power requirementUniformity coefficient is lowPoor distribution efficiencyUse of recycled water is restricted for health reasonsEquipment need careful handlingNozzles need screened water supplyD. BURIED IRRIGATIONSubstitute of canals by pipelinesWater is delivered by a canal from the source to the irrigation areaInside area is distributed by gravity pressure pipelinesWater supplied to field pipelines by pumping: 400m spacing between pipelines Field pipelines has hydrants, sprinklers or watering machinesContdField pipelines: HDPE pipes 10-30cm in diameter at 0.75-1.25m depthOperating under 6 atm pressureWater flows in pipelines due to the head created by the natural gradient (>0.003)Maximum velocity of flow is not to exceed 3.5 m/sNon silting velocity, V= (v2f)/( 0.0000232 u0.25 *8g) , kg/m3 v = current velocity of flow(m/s); u= fall velocity of sediment (mm/s)Advantages of buried irrigationIt is a reliable method of irrigation for the control of:Water losses from irrigation canalWater loggingSalinization of landsE. DRIP IRRIGATIONAlso known as Trickle irrigationWater is applied in the form of drops directly to the plants through drip nozzlesWater drops into the soil slowly and frequently to keep the soil moisture within the desired rangeParticularly suited for soils with very low and very high infiltration ratesMaximize the water savingContdInvolves lateral spread of water on the surface by conducting the water under pressure to a relatively closely spaced grid of outlets and discharging water at virtually zero pressureIrrigation is done through drippers fitted on small diameter lateral lines, delivers water to the crop root zoneWater is pre filtered for removing the suspended impurities Drip irrigation system-componentsHead tank: Water lifted is stored in head tank (3*3*3 m) resting on a raised platform to maintain a pressure head of 3-5mFunctions: Regulates the pressure and amount of water applied Filter the water Add nutrient materialContdMain lines: Plastic main lines deliver water to sub mains20-40mm diameter suitable for desired dischargeLaterals:Sub mains delivers water to laterals which I turn convey it to emitters10-20mm diameter, generally placed along plant rowPerforated at a distance equal to the plant spacing, usually 20cm for vegetables and cottonContdEmitter:Applies water to the root zoneVery low rate of flow, usually 1-9 lphChemical injection unit:To inject chemicals such as chlorineTo ensure fertigationMonitoring and control equipment:Includes controller, pressure gauges, tensiometers and a flow meter , valves etc.ContdFertilizer tank:Tank filled with concentrated nutrient solution connected to the head directly in front of filter unitNutrient solution is introduced into the water flowing to the trickle networkFertilizer dispenser injects fertilizers into the system at a predetermined rateDesign of drip irrigation systemIn plantations, trickle lines are 6m apart with 3 emitters at each pointDesign capacity should satisfy the peak irrigation water demand of each and all crops to be irrigated within the design areaContdIrrigation water requirement:Mainly influenced by the crop ET rate, irrigation interval and the water application uniformityEmitter discharge ratio:For point source emitters, the discharge is < 12lph for single outlet emittersFor line source emitters, it is
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