Using Drip Irrigation in High Tunnels

State Wide High Tunnel ConferenceWednesday, February 17, 2015

Baxter, MinnesotaKarl Foord

Outline

• Advantages of drip irrigation

• Plant water use

• Soil characteristics–Water holding capacity

–Water movement

• Drip systems–Equipment & assembly

Outline cont.

• Monitor–Water quality

–Application timing

• Fertigation–Regulations

Drip irrigation advantages

• Efficient & uniform application of water

• Establish transplants

• Maintain optimum growing conditions• Maximize yield & quality

• Effective application of some nutrients

PLANT WATER USE

Soil moisture• Generally the most limiting

element in maintaining uniform plant growth & high quality produce• This deficiency can occur even

before visible wilting occurs

Impact of water deficiencies

• Even small amounts of water deficiency can be detrimental – causing:–Slowed growth rate–Lighter weight fruit–Blossom end rot in tomato

Soil water availability

• The amount of soil water available to a plant is a function of:• Plant's potential rooting zone • The soil texture and organic

matter content within that rooting zone

Rooting zone

• The majority of the roots of most vegetable crops are generally no deeper than 10 to 12 inches

• For some crops like onions & strawberries, the depth is closer to 6 inches.

• 6 in. is a good level at which to measure water for root use

Goal for top foot of soil moisture

• To achieve optimum growth:

• Maintain water levels the between 60 and 100% of the soil's available water holding capacity

• Especially during pollination and fruit development

System design & needs

• System needs to meet anticipated plant needs under maximum stress• 3 – 10 gallons per minute per

tunnel

• Dependent on drip flow rate & tubing layout

SOIL CHARACTERISTICS

Soil characteristics

• Drainage• Compaction layer limiting root

growth• Soil texture–Water holding capacity–Water movement

inches of water per foot of soil

Range

Coarse sand 0.24 - 0.48Fine sand 0.60 - 0.96Loamy sand 0.84 -1.44Sandy loam 0.96 - 1.80Loam-clay 1.68 - 2.40

Ranges in available water capacity for soil textures

Soil texture

Water movement in soil

Wetting patterns with drip irr igation

Distance between emitters

DRIP SYSTEMS

DRIP TAPE CHARACTERISTICS &

PLACEMENT

Drip irrigation systems

• Low pressure & small water supply• Moderate labor–Easily automated

• Works well with plastic mulches

Drip tape characteristics

• Emitters manufactured in the tape wall

• Common spacings: 8” & 12”

• Wall thickness: 10 & 15 mm• Maximum operating pressures:

–10 mm @ 14 psi

–15 mm @ 25 psi

Drip tape flow rates

• Goal: wetted soil width 16 – 20 in.

• Flow rate of .67 gpm /100 ft.– 40 gph /100 ft.

• @ 12 psi• Low flow pressure regulator

Irrigation system design

• 1 or 2 lateral lines per row

• When to use 2 rows?

–Strawberries with limited root systems – one drip per row on double row

• Install prior to mulch

• Run two drip tape lines

–one for insurance if have had plugging pbms

Drip tube placementSingle-row crops: tomatoes, cucumbers, muskmelons

Place tube in center off-set from plant 4 – 5 in.

Drip tube placement

Plants off-set down the row

Double-row crops: eggplant , peppers, strawberries

Place tube in center of bed

Drip tube placement

• Place tube EMITTER SIDE UP!

• to keep tape from shifting

–Bury 1 – 2 in. –Secure tape at ends

• Avoid puncturing tube during:

–Planting

–Staking

Drip tube installation prior to plastic mulch

To keep tape from shift ing:bury 1 – 2 in.

Apply mulch after drip tube installation

Hand application of plastic mulch

Apply mulch after drip tube installation

Mechanical application of plastic mulch

MONITORING THE SYSTEM

Water Quality• Groundwater (Chemical clogging)– Iron

–Calcium

• Surface water (Biological & Physical clogging)–Algae

–Sand & silt

–Bacterial slime

Constituent Level of Concern Low Moderate High pH <7.0 7.0-8.0 >8.0 Iron (Fe) mg/L <0.2 0.2-1.5 >1.5 Manganese (Mn) mg/L <0.1 0.1-1.5 >1.5 Hydrogen Sulfide (H2S) mg/L <0.2 0.2-2.0 >2.0 Total Dissolved Solids (TDS) mg/L <500 500-2000 >2000 Total Suspended Solids (TSS) mg/L <50 50-100 >100 Bacteria Count (#/ml) <10,000 10,000-50,000 >50,000

http://www.smart-fertilizer.com/articles/emitter-clogging

http://edis.ifas.ufl.edu/ae032

Have your water analyzed by a laboratory that is qualified to evaluate emitter plugging hazards

IRRIGATION TIMING

Irrigation Water Applied in 2005Average Inches per Day

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Critical nature of irrigation timing

• Significant fluctuation from day to day based on weather conditions

Tensiometer descriptor

• A tensiometer is a hollow tube with a porous ceramic cup at one end.

• The tube is filled with water, sealed with a cap and has an attached vacuum gauge.

• Tensiometers read in centibars (cb)

Soil water monitoring

SensorsTensiometers

Sensors

Tensiometer function• As plants use water and the soil dries out, water

is drawn out of the tensiometer through the ceramic cup. Because the tube is sealed, a vacuum is created and is measured on the gauge.

• Low readings (10 cb) - relatively easy for plants to extract water from the soil

• Higher readings (35 cb) drier the soil - harder for plants to extract water

Soil water assessment

Good Range for High Tunnels - 25 to 40 centibars

Summary

• When 6“ root zone tensiometer reads 30 cb begin watering (buffer incase gets to 40 cb)

• When 12” deep or below root zone tensiometer begins to decrease stop watering ~ 20 cb

CHEMIGATION / FERTIGATION

Chemigation / Fertigation

• Application of nutrients via drip system

• Understand safety requirements– Install anti-pollution and safety devices

• Fertilizer requirements of crop grown

• Fertilizer is compatible with water – Calcium and phosphorus fertilizer should not

be mixed with sulfates

Fertigation system safety

• Install injection unit as bypass upstream from filter and pressure regulator and downstream of anti-pollution equipment

Fertigation system operation

• Bring total drip system to operating pressure before beginning injection

• Conduct test runs to observe performance

• Test time for complete irrigation meeting water needs relative to injection time

• Avoid over irrigation & leaching of nutrients

Fertigation systems

Fertigation tank

Fertigation bypass

Control t imer Pressure

regulatorFilters

Backflow device

Pressure gauge

REGULATIONS

Water use & fertigation permits

• Most water and fertigation permits and rules apply to larger field situations

• If you go beyond your traditional homestead hose rate of 7 gpm – take a closer look at irrigation and fertigation regulations

Resources• http://hightunnels.cfans.umn.edu/

• http://hightunnels.cfans.umn.edu/resources/irrigation-resources/

Extension Materials

Author

• Karl Foord Ph.D. MBA

• Regional Educator, Horticulture

• foord001@umn.edu

Handouts

• PowerPoint handout

• Extension Materials

• Drip irrigation and extension information for high tunnels

References

• Irrometer Co - http://www.irrometer.com/

• Spectrum Technologies - http://www.specmeters.com

• Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota

• http://www.extension.umn.edu/distribution/cropsystems/DC5886.html

• Plant tissue analysis performed by a qualified analytical lab can help you determine crop nutrition needs during the season and tailor the N fertilizer applications to actual crop needs.

• Fertilizers containing sulfate, phosphate, calcium, or anhydrous or aqua ammonium can lead to solid chemical precipitation inside the drip lines, which can block emitters