Irrigation Requirements Based upon the book Rain Bird Irrigation Design Manual From Chapter 3

This is where the questions begin… When we’re trying to figure out what we do with all of that information we have... We can start to ask those burning questions...

Those burning questions… How often do I water? It depends... How long do I water? It depends... How much water do I apply? It depends... ON WHAT?

Well... On a bunch of stuff of course! Water requirements are partly determined by: Plant species Soil types Local climate Slope

Water Loss Mostly occurs in two ways from the landscape... What are they? Transpiration – water used by the plant and lost through the leaf surfaces... Evaporation – water lost from the surface of the soil...

Combined Water Losses The combined losses of transpiration and evaporation is called Evapotranspiration (ET)

The maximum water use for plants of any given species in a given climate is called... Reference Evapotranspiration (ET O )

Crop Coefficients An ET O multiplied by a predetermined crop coefficient can determine an ET rate for a specific plant or turf Reference: sp

ET Rates Provide information like: Just how much irrigation water actually needs to be applied to specific plant materials for successful growth

More Water Losses Other factors affect daily ET losses – such as... Daily temperatures Humidity Rainfall Wind speed Full sun Cloud cover or fog

Climate PET Table PET is the Potential Evapotranspiration It is the maximum average water requirement for plants in a given climate It’s measured in inches per day

Climate PET Table According to the Climate Pet table ( Rain Bird Design Manual pg.19 ) – we live in a warm dry climate

Climate PET Table South Bay PET Midsummer highs of 70°F to 90°F Less than 50% humidity With a.20 to.25 inches per day evaporation loss This info will help us match irrigation with plant needs

Soil Provides a medium for root growth Also creates a reservoir for water

Soil Texture Through the use of a soil texture analysis (settling test) we can determine the amounts present of: Sand... Silt... And clay A percentage of the three seperates determine the texture of a given soil

Soil Texture Triangle

Soil Texture and Who Needs It? Soil absorbs water and holds it like a sponge And Soil of a given texture... And at a given volume... Can only hold a given amount of water Makes sense doesn’t it?

Heavy or Light Soils Sandy soils are often referred to as “light” soils Water infiltrates into sandy soils quickly Sandy soils drain rapidly and do not hold water well

Heavy or Light Soils Clay soils are often referred to as “heavy” soils Water infiltrates into clay soils very slowly Clay soils hold water and do not drain well

So... Soil texture determines the amount of water that can be applied at any one time!

Soil Texture Texture WILL affect the choice of heads and nozzles we choose Why?

Soil Texture Texture WILL affect the rate at which water can be applied to soils Why? Texture WILL affect the duration of watering cycles

Soil Texture Texture WILL affect the duration of watering cycles How?

Maximum Wetting Patterns Traditional wetted profiles form in: Sandy soils – “carrot” pattern Loamy soils – “radish” pattern Clay soils – “onion” pattern

Soil Wetting Patterns In coarse soils – or sandy soils Water tends to spread vertically before horizontal movement occurs

Soil Wetting Patterns In fine soils – or clay soils Water tends to spread horizontally before much vertical movement occurs

Maximum Wetted Diameter The greatest diameter water will spread from an emitter

Maximum Wetting Patterns Relationship of vertical and horizontal movement of water in soil up to a maximum wetted diameter In other words – water only spreads so far horizontally before downward movement begins Once maximum wetted diameter is reached water movement is downward

Soil Characteristics Chart Rain Bird Irrigation Design Manual pg. 20

Water Application It’s important we don’t apply water faster than it can infiltrate into the soil Excessive application can lead to: Puddling Runoff Erosion Waste

Puddling

Runoff

Erosion

Slopes Slopes cause their own set of problems Infiltration rates will vary Infiltration rates decrease because of high potential for runoff

Don’t Forget about Slopes… Slopes guide selection of sprinkler heads and nozzles Slopes guide head placement Slopes determine the rates at which water can be applied They determine the length of irrigation cycles

Texture vs. Precipitation Rain Bird Design Manual pg. 21

An Inappropriate Use… Drip emitters are often inappropriate for use in coarse soils Why?

A More Appropriate Use… Micro-sprays or conventional irrigation may be a better choice for coarse soils Why?

Soil Wetting Patterns Rain Bird Design Manual pg. 21

Some Soil Terms Soil moisture is held by soils three ways Determined by the porosity or variation of pore sizes in soils This affects the availability of soil moisture to plants

Soil Porosity Soil is not completely solid So what else is in it? Organic matter – plant bits & fungi (live, dead and decomposing) Critters – bacteria & animals And? Air

Soil Porosity Soil porosity measures pore space in any soil Determines rate of water infiltration – movement of water into soils, and Water percolation – water movement down through soils

Soil Porosity “Coarse” soils or sandy soils consist of larger pore spaces called Macropores Water infiltrates quickly Water percolates quickly Coarse soils DO NOT hold water well

Soil Porosity “Coarse” soils or sandy soils: Can be irrigated for longer periods Resist runoff Typically require more frequent irrigation Runtimes can be longer

Infiltration Percolation

Soil Porosity “Fine” soils or clay soils consist of small pore spaces called Micropores Water infiltrates slowly Water percolates slowly Fine soils DO hold water well

Soil Porosity “Fine” soils or clay soils: Must be irrigated for shorter periods Prone puddling and runoff Typically require more frequent irrigation Runtimes must be shorter

Infiltration Percolation

Soil-Water-Plant Relationship From the Rain Bird Irrigation Design Manual pg. 20

Available Water Amount of water in soil readily available for plant use

Soil Moisture Gravitational water Occurs after irrigation or heavy rainfall Drains rapidly from soil Not readily available to plants

Soil Moisture Capillary water Moisture held loosely within the soil pore spaces Available to plants

Soil Moisture Hygroscopic water – moisture held tightly against soil particles – unavailable to plants

When It Dries Out…. Permanent Wilting Point (PWP) The boundary between capillary water and hygroscopic water Fine line between availability and unavailability of water to plants Continued soil moisture conditions beneath PWP result in plant death

The Right Amount Field capacity – The boundary between gravitational water and capillary water The upper limits of soil moisture Water available to plants