Why Irrigate?

• Necessary for container production

• Increase growth rate

• Consistent production schedule

• Ease of digging.

• Fertilizer Solvent.

• Winter Protection – frost protection

• Seals in and activates fumigants and herbicides.

Water Sources

• Well

– Often (not always) best quality, less disease

– Expense (installation), quantity, regulations

• Municipal water

– Low soluble salts

– Unreliable, expensive, possibly unavailable

• Surface Water

– Disease, contamination, algae, soluble salts, land

– Recycling, regulations

Water Use Reporting Regulation

• If you are capable of pumping > 70 gallons/min or 100,000 gallons/day you must keep track of monthly water use and report it to MDA annually.

Terms

• Field Capacity (FC)- Amount of water a field will hold after drainage and runoff.

• Infiltration rate- rate water moves into the soil.

• Irrigation should not be supplied at a rate higher than the infiltration rate.

Determining Pump Requirements

• Irrigation- inches per acre

• Pumping capacity- gallons/minute

• To convert acre-inches to gals: 1 acre-inch of water equals 27,154 gallons.

Determining Water Delivery Needs

• Given FC = 30%, infiltration rate = 0.75 in / hr and want to maintain upper 9 in. of soil between 75-100% of FC, system 60% efficient

• Max water can apply/acre = 0.75 acre-inch/hr / 0.6

= 1.25 acre-inch/hr x 27,154 gal/acre-inch

= 33,943 gal/hr/acre

• Amount needed = (30% x 9 in) - (30% x 9 in x 75%) = 0.7 inches

Water for 56 minutes (0.7/0.75 x 60 minutes) or

31,680 gal (0.7/0/75 x 33943)

• 300 acre nursery, 12 irrigation hours/day, need to irrigate 25 acres at a time:

= 25 x 31,680 gal/hr/acre

= 792,000 gal/hr or 13,200 gal/min.

Pump Selection

• Maximum volume of water delivery required

• 1 PSI = 2.31 feet of head

• Total dynamic pumping head in feet.

– Rise from pumping level to highest delivery point

– Friction loss for main and longest lateral line

– Sprinkler operating pressure in feet.

– Other friction losses in feet, estimated at 10% of total head

Pump Horse Power

• BHP = brake horsepower, the operating horsepower

• 1 HP = 33,000 ft-lb min^-1 = 0.746 kw

• BHP = (GPM x 8.35 (lb/gal) x total head (ft)) / (33,000 (ft lb/min x pump efficiency)

• To deliver 13,200 GPM with 500 ft of head and a pump with a 75% efficiency need BHP of:

• (13,200 GPM x 8.35 lb x 500 ft) / (33,000 ft-lb min-1 x 0.75) = 2227 BHP

• BHP should be increased 25-30% when using gas or diesel engines to supply power

Determining Irrigation Duration

• Given FC = 30%, infiltration rate = 0.75 in / hr and want to maintain upper 9 in. of soil at 50% of FC, system 60% efficient

• 30% of the 9 in. of soil is water at field capacity, or 2.7 in

• To replace 50% of 2.7 in. need to apply 1.35 in water to soil.

• 1.35 / 0.60 = 2.25 inches water

or 2.25 in x 27,154 gal/acre-in = 61,097 gal/acre.

• Irrigation duration = 2.25 in / 0.75 in/hr = 3 hours

Irrigation Distribution Uniformity (DU)

• Uniform irrigation distribution ensures that all plants in an irrigation area receive approximately the same amount of water.

• Important for maximizing efficient use of water.

• Desire a distribution uniformity greater than 80%.

Causes of Low Uniformity

• Improper irrigation pipe selection

• Improper operating pressure

• Inadequate selection of irrigation sprinklers or emitters

• Inadequate sprinkler overlap

• Wind effects

• Time- affects pump efficiency, pressure regulation, nozzles

• Blocking or damage of emitters

• 90° patterns will result in 4 times the water applied versus 360 ° patterns

• 180 ° patterns result in 2 x

Calculating Distribution Uniformity for Overhead Irrigation

• Place collection cans (straight sided) in a grid in irrigation block to be tested.

• Run irrigation system for at least 15 minutes.

• Measure depth of water in each can.

• Determine average of depths in each can.

• Determine average of lowest 25% of cans.

• Divide average of the lowest by the overall average to get DU.

Calculating Distribution Uniformity for Micro-Irrigation

• Measure time to fill identical bottles from at least 18 emitters per irrigation zone.

• Sum the lowest 1/6 of the measurements.

• Sum the highest 1/6 of the measurements.

• Plot the point on the following nomograph.

• Nomograph will show DU range, want greater than 80%.

Daily Irrigation Checks

• Amount applied is appropriate for container size and plant type

• Operation of nozzles (rotation, pattern, fogging)

• Moisture content of substrate before watering

• Drainage from containers

• Rain gauge to check if system ran

Weekly Irrigation Checks

• Flow rate and pressure at pump outlet and inlets to each zone

• Plants grouped in zones according to water requirement

• Plants spaced so canopies just touch

• Read all flow meters

• Additional for low volume systems:

• Emitter placement and clogging

• Filters cleaned and checked

• Lateral lines flushed

• Cleaning agent injected

Six Month Irrigation Checks

• Nozzle pressure with pitot tube

• Wear of nozzles with drill bit or other item

• Risers are vertical

• DU in several locations

• Water penetrating canopies of representative plants

• Sprinkler heads and nozzles are uniform in each zone

• Rain shut-off

• Water holding capacity of substrate for container sizes

• Pump performance- flow, pressure

• Check if zones are running according to controller

Sprinkler Systems

• Sprinkler heads perform properly over specific operating pressures

– Too high = fogging

– Too low = doughnut-shaped spray pattern

– Both = poor DU

• Pitot tube with pressure gauge used to monitor pressure at nozzles. Measure several nozzles within a zone at various distances from inlet.

Microirrigation Systems

• In-line pressure or flow regulators at manifold

• In-line pressure or flow regulators at laterals

• Pressure-compensating emitters

• Measure pressure at inlet and end of laterals to determine pressure drop

• Modified pressure gauge to measure pressure at emitters

Determining Application Rate of Sprinklers

• Depth of water applied over an irrigated area during an irrigation event in inches/hr

• Three methods:

– Calculated from flow rate into zone

– Average flow rate and area covered by each sprinkler

– With catch cans or rain gauges

Flow Rate Calculation

• Application rate (AR) = flow rate / area

• Example- flow rate of 200 gpm, 2 acre zone

– AR = 200/2 = 100 gpm/a

• Convert to inches/hr

– 1 acre inch of water = 27,154 gallons

– (100 gpm/a * 60 min) / 27,154 = 0.22 inches/hr

Sprinkler Calculation

• AR = 96.3 q / (Sl * Sm)

– q = Sprinkler discharge rate in gpm

– Sl = Sprinkler spacing along lateral in ft

– Sm = Sprinkler spacing between laterals in ft

• Example:

– q = 3 gpm, with 30 x 30 ft sprinkler spacing

– AR = 96.3 * 3 / (30 * 30) = 0.32 inches/hr

Direct Measurement

• Attach hose or otherwise catch water as it leaves a nozzle, measure amount captured over time period divide by area covered by sprinkler. Do for several nozzles per zone.

• Catch cans or rain gauges- measure application rate at or near target- use at least 16 cans or gauges evenly distributed over area. Calculate the average to determine AR

Emitter AR

• Measure application into zone with flow meter, divide by number of emitters in zone

– Ex: Flow rate = 200 gpm, 200 emitter/zone = 1 gpm per emitter

• Collect a known volume of water from randomly selected emitters throughout the system and divide by time each was collected. Measure at least 16 emitters.

Irrigation Efficiency

• Effectiveness of an irrigation system in delivering water to plants.

• Effectiveness of irrigation in increasing plant production, including time, compared to non-irrigated crops.

Efficiency Definitions

• Irrigation efficiency- volume of water delivered to the target (pot) divided by volume of water input into the system

• Crop water use efficiency- crop yield divided by volume of water to produce the crop

• Irrigation water use efficiency

– a. Volume of water beneficially used divided by the volume of water input to the irrigation system

– b. Increase in crop yield over non-irrigated yield divided by water applied through irrigation

• Reservoir storage efficiency (E_s)- the volume of irrigation water available from an irrigation reservoir divided by the water delivered to the reservoir, usually < 1

– Losses in E_s due to seepage, evaporation, transpiration

– Reduce losses by using deeper reservoirs with smaller surface area

– Use less permeable lining material

– Cover reservoir / tanks- usually not practical

– Reduce vegetation in and around reservoir

• Water conveyance efficiency (E_c)- volume of water delivered for irrigation divided by volume of water placed in the conveyance system

– Open channel conveyance, usually < 1

– Pipeline conveyance, close to 1

• Irrigation application efficiency (E_a)- volume of irrigation water available and stored in the root zone divided by volume delivered by irrigation system, < 1

• Overall irrigation system efficiency (E_o)- multiply all efficiency components together:

E_o = E_s x E_c x E_a

Losses in Efficiency

• Non-uniform application

• Poor system design

• Improper installation

• Poor management

• Equipment failures

• Excessive or inadequate application

• Evaporation/drift

• Runoff (surface or subsurface)

• Leaks in pipes

Sprinkler Irrigation and Efficiency

• Weather & Time of Day - hot, low humidity, wind = greater evap. loss

• Angle of throw

• Droplet size

• Interception

• Non-uniform application

• Insufficient overlap, want 50-100%

Microirrigation and Efficiency

• Much lower losses to evaporation, drift

• Sprayers and microsprinklers prone to evap and drift loss

• Primary loss of efficiency due to non-uniform application

• Drip systems lose only a little to evap from the soil

• Sprayers and microsprinklers lose to both wind and soil evap/drift

Example 1

• Open reservoir with E_s = 0.6

• Open channel conveyance with E_c = 0.8

• Sprinkler system with E_c = 0.25

• E_o = 0.6 x 0.8 x 0.25 = 0.12 or 12%

• This means the reservoir for this system needs to be over 8 times the plant irrigation requirement.

Example 2

• Aquifer reservoir with E_s = 1

• Pipe conveyance with E_c = 1

• Drip system with E_c = 0.85

• E_o = 1 x 1 x 0.85 = 0.85 or 85%

• This means that the system only needs to pump 18% (1.0 / 0.85 = 1.18 or 118%) more water than the plant irrigation requirement.

Effective Irrigation Efficiency E_e

• E_o corrected for water which is reused or is restored to the water source without a reduction in water quality.

• E_e = E_o + (FR) x (1.0 - E_o)

• FR is the fraction of runoff, seepage or deep percolation that is recovered.

Example of E_e Calculation

• Pump from aquifer, E_s = 1

• Conveyed in pipe, E_c = 1

• Sprinkler irrigate, E_a = 0.25

• E_o = 1 x 1 x 0.25 = 0.25 or 25%

• Recycle runoff, recapturing 50% of water, FR = 0.5

• E_e = 0.25 + 0.5 x (1 - 0.25) = 0.63 or 63%

Irrigation Water Use Efficiency E_u

• 2 Definitions:

• The ratio of the volume of water beneficially used to the volume delivered by the irrigation system. Ratio without units.

• The ratio of the increase in production of the marketable plants to the volume of water applied by irrigation for irrigated as compared to non-irrigated crops. Ratio expressed as plants per volume water.

Calculation of E_u for Definition 2

• E_u = (Y_i - Y_o) / V

• Y_i = marketable plants produced with irrigation

• Y_o = marketable plants produced without irrigation

• V = volume of irrigation water applied

• Can incorporate time of production also

• This calculation allows evaluation of the economic benefit of irrigating.