Microirrigation design

Soil-Water-Plant RelationshipNatural Resources Conservation ServiceNRCSUnited States Department of Agriculture1SoilsCheck the followingTextureStructureIntakeSaltWater holding capacity***Lateral movement

2Soil Components

Water

Soil Particles

VgVw

Vp = Vg + VwVsVV = Soil VolumeVg = Volume of airVw = Volume of waterVs = Volume of Soil ParticlesVp = Volume of Soil PoresAir3

Gravitational Water, rapid drainageHydroscopic Water, essentially no drainageCapillary Water, very slow drainageOven DrySaturationTAWMADPermanent Wilting PointField CapacitySoil Water4Available Water CapacityAvailable water capacity - the amount of water that a soil can store that is available for use by plants.

Field capacity amount of water left after free water has drained because of gravity. ~1/3 bar potential

Permanent wilting point soil water content at which most plants cannot obtain sufficient water to prevent tissue damage. ~15 bars potential 5Available Soil water

6Available Water Holding CapacityLimits the amount of water that can be applied at any one irrigation .

For a given crop determines frequency of irrigations7ReviewGiven: Root zone = 3.5 ft, WHC = 1.6/ft, MAD = 40%, Pw =50%

Find: Available water8SolutionAW =RZ * WHC * MAD * Pw = 3.5*1.6*.4 *.5= 1.2 inches

9SalinityAll irrigation waters have saltsThree potential problemsSalt can accumulate in the soilCertain types of salt cause surface sealing and poor infiltrationSpecific types of salts are highly toxic to plants even in low concentrationsSoil and water chemistry should always be examined before doing an irrigation design10Salt distribution -Surface drip irrigation

11CropECe (mmhos/cm)CropECe (mmhos/cm)MinMaxMinMaxField crops Alfalfa Barley Cotton Sugarbeet Wheat Sorghum2.08.07.77.06.06.82827242018 Corn Flax Broadbean Cowpea Bean1.71.71.64.91.01010128.56.5Fruit and nut crops Date palm Fig, olive Pomegranate Grapefruit Orange Lemon Apple, pear Walnut Peach4.02.72.71.81.71.71.71.71.7321414888886.5 Apricot Grape Almond Plum Blackberry Boysenberry Avocado Raspberry Strawberry1.61.51.51.51.51.51.31.01.5612776665.54Vegetable crops Beets Broccoli Tomato Cucumber Cantaloupe Spinach Cabbage Potato4.02.80.91.12.23.21.01.71513.512.51016151210 Sweet corn Sweet potato Pepper Lettuce Radish Onion Carrot Bean1.72.51.71.72.01.21.01.01010.58.5997.586.512Lateral movementWhat affect lateral movement:

Varying soil textures throughout a field (e.g., sand vs. loam vs. clay).

Varying installation depths of the tape.

Varying soil compaction or stratification.

Different soil chemistry conditions

Beginning soil moisture

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Silt Loam soil

Clay Loam Soil

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19Surface(DI) vs. buried(SDI)

Percent Wetted AreaPw is the average horizontal area wetted in the top 6 to 12 inches of the root zone as a percentage of the total crop area. (NEH 623, Ch. 7)For a lone tree Pw=Aw/ArzAwArzEmitterTree trunkSurface area wettedActual area wettedRoot zone21Percent Wetted Area and emitter spacinge = # of emitters/treeSeSpSwSrSe = emitter spacingSp = plant spacingSr = row spacingSw = diameter of the circular area wetted by a single emitter22Wetted Area

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Desired wetted areaFor widely spaced crops such as vines, bushes, and trees, a reasonable design objective is to wet at least one-third and up to one-half of the horizontal cross-sectional area of the root system.smaller Pw is favored for economic reasons.rows spaced less than 6 ft. (1.83 m) apart, the Pw may approach 100 %.25Soil wetted areaKind of soil layersSoilDepthAnd TextureHomogeneousVarying layers,GenerallyLow densityVarying layers,GenerallyMedium densitySe x Sw = Aw (ft2)Se x Sw = Aw (ft2)Se x Sw = Aw (ft2)Depth 2.5 ft2.5 ft2.5 ft Coarse1.2 x 1.5 = 1.82.0 x 2.5 = 5.02.8 x 3.5 = 9.8 Medium2.4 x 3.0 = 7.23.2 x 4.0 = 12.84.0 x 5.0 = 20.0 Fine2.8 x 3.5 = 9.84.0 x 5.0 = 204.8 x 6.0 = 28.8Depth 5 ft5 ft5 ft Coarse2.0 x 2.5 = 5.03.6 x 4.5 = 16.24.8 x 6.0 = 28.8 Medium3.2 x 4.0=12.85.6 x 7.2 = 39.27.2 x 9.0 = 64.8 Fine4.0 x 5.0=20.05.2 x 6.5 = 33.86.4 x 8.0 = 51.21 Based on an emitter flow rate of 1 gph (3.785 L), the estimated Aw is given as a rectangle with the wetted width (Sw) equal to the maximum expected diameter of the wetted circle and the optimum emitter spacing (Se) equal to 80 percent of that diameter.26Factors affecting wetted areaLower application rates gives best horizontal water distributionWet soil gives the narrowest water distributionManagement can provide only minor improvement in water distributionSoil texture is the primary determinate factorCrop ET/System flow rateWater requirementMAD/stress Root zone Salt Tolerance leaching requirementFrequency28Water useETc = ETo x Kc

Where:ETc = Crop Evapotranspiration rate, in/day, (mm/day) ETo = Reference evapotranspiration, ETo or ETr, in/day, (mm/day) Kc = Crop coefficient for specific crop

References (NEH Chapter 2 Irrigation water requirements, irrigation Guide)29

30Instructor Note: Make the point that a crop water needs change during the season and to avoid deep percolation the water application may need to be changed also.ET for TreesBig tress need more water than small trees

Mature tress on close spacing need same amount of water per acre as large trees on wider spacing

So if there is several blocks of the same type of tree using the same flow rate per tree, but on different spacing. Each block needs to be design for a different number of hours per week.Pruning if the same percent canopy cover exists on two blocks of the same type of plant use the same ETPercent canopy cover is defined as % of ground surface shaded at noon.Cover crop come in all sizes shapes and types and may have an additional ET component upwards 15 - 20%For cover crop grown all season long, the micro/drip system needs to be a microspray that wets a large percentage of the surface area

To crop or not to cover crop?33Drip systems the ground surface is moist almost all the time which increase evaporationThe small frequent irrigations contribute to little or no plant stress

These two factors may increase the ET by as much 15% above published rates.

Designing for less than Peak ETRegulated Deficit Irrigation (RDI)Wine grapes (increase sugars)Almonds (start of hull split)Tomatoes (increase solids)Regulate early growth of trees and vines ( trying to avoid spindly mature trees)FrequencyMaximum Frequency

Example: AWC(MAD)=1.2, ETc=0.30

Is MAD still applicable with a drip system?

Net ApplicationNIR = ETc * f - Pe

e. g. If f = 2 days, ETc =.3/day, and Pe=0.0 Then NIR =.6

37Considerations on Published ETLoam or heavier textured soil with at least 60% wetted volumeDesign for the peak month of a normal year Situations of low soil water capacityDesign flow rates may need to be 10 -15% higherLow water holding capacities are caused by:Small percentage wetted areaSand or rocky soilsShallow soilsShallow root systems (e.g. avocadoes or some produce crops)Transpiration ratios - Unavoidable lossesTable 7-15. Seasonal transpiration ratios for arid and humid regions with various soil textures and rooting depths.

Climate zone and root depthTR1 for indicated soil textureVery courseCoarseMediumFineArid 5.0 ft (1.5 m)1.151.101.051.101.101.051.051.051.001.051.001.00Humid 5.0 ft (1.5 m)1.351.251.201.251.201.101.151.101.051.101.051.001Seasonal transpiration ratios (TR) are for drip emitters. For spray emitters add 0.05 to TR in humid climates and 0.10 in arid climates39Emission Uniformity Distribution Uniformity is a mathematical expression used to quantify differences in the amount of water received by the plants throughout the field

Emission UniformityPoor EU

Good EU41Instructors note: Explain DU using visual examplesEmission/Distribution UniformityWhats the highest EU that you can have?

42Actual vs. Potential EUActual EUs are lower than the Potential and are dependent on the following System DesignSuitabilityManagement43EU Deteriorate with timeAllowable pressure difference determined by brand new design EU

Required system capacity by estimated EU after several years44What can cause Poor EU?Pressure DifferencesUneven spacing Unequal drainageOtherPlugging etc.Wear45Emitter typeSpacingft, TopographySlope%EU range%Point source on perennial crops>13uniform ,285 to 90Point source on perennial orSemi permanentcrops