by Karl Foord, Extension Educator, University of Minnesota. Presented at the 2015 Minnesota Statewide High Tunnel Conference, Beginning Grower Workshop.

1. Using Drip Irrigation in
High Tunnels
State Wide High Tunnel Conference
Wednesday, February 17, 2015
Baxter, Minnesota
Karl Foord

2. Outline
• Advantages of drip irrigation
• Plant water use
• Soil characteristics
–Water holding capacity
–Water movement
• Drip systems
–Equipment & assembly

3. Outline cont.
• Monitor
–Water quality
–Application timing
• Fertigation
–Regulations

4. Drip irrigation advantages
• Efficient & uniform application of
water
• Establish transplants
• Maintain optimum growing
conditions
• Maximize yield & quality
• Effective application of some
nutrients

5. PLANT WATER USE

6. Soil moisture
• Generally the most limiting
element in maintaining uniform
plant growth & high quality
produce
• This deficiency can occur even
before visible wilting occurs

7. 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

8. 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

9. 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

10. 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

11. 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

12. SOIL CHARACTERISTICS

13. Soil characteristics
• Drainage
• Compaction layer limiting root
growth
• Soil texture
–Water holding capacity
–Water movement

15. inches of water per foot
of soil
Range
Coarse sand 0.24 - 0.48
Fine sand 0.60 - 0.96
Loamy sand 0.84 -1.44
Sandy loam 0.96 - 1.80
Loam-clay 1.68 - 2.40
Ranges in available water capacity
for soil textures
Soil texture

16. Water
movement in
soil

17. Wetting patterns with drip
irrigation
Distance between emitters

18. DRIP SYSTEMS

19. DRIP TAPE
CHARACTERISTICS &
PLACEMENT

20. Drip irrigation systems
• Low pressure & small water
supply
• Moderate labor
–Easily automated
• Works well with plastic mulches

21. 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

22. 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

24. 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

25. Drip tube placement
Single-row crops:
tomatoes, cucumbers,
muskmelons
Place tube in
center off-set from
plant 4 – 5 in.

26. Drip tube placement
Plants off-set down the
row
Double-row crops: eggplant ,
peppers, strawberries
Place tube
in center of
bed

27. 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

28. Drip tube installation prior to
plastic mulch
To keep tape
from shifting:
bury 1 – 2 in.

29. Apply mulch after drip tube
installation
Hand application
of plastic mulch

30. Apply mulch after drip tube
installation
Mechanic
al
applicatio
n of
plastic
mulch

31. MONITORING THE
SYSTEM

32. Water Quality
• Groundwater (Chemical clogging)
–Iron
–Calcium
• Surface water (Biological & Physical
clogging)
–Algae
–Sand & silt
–Bacterial slime

33. 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

34. IRRIGATION TIMING

35. Irrigation Water Applied in 2005
Average Inches per Day
High Tunnel Tomatoes at Staples, MN
m @
m ï
m ž
m M
m ü
m ª
m Y
m
m ·
Inchesofwaterperday

36. Critical nature of irrigation
timing
• Significant fluctuation from day
to day based on weather
conditions

37. 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)

39. Soil water monitoring
SensorsTensiometers

40. Sensors

41. 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

42. Soil water
assessment

43. Good Range
for High
Tunnels - 25
to 40
centibars

46. 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

47. CHEMIGATION /
FERTIGATION

48. 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

49. Fertigation system safety
• Install injection unit as bypass
upstream from filter and
pressure regulator and
downstream of anti-pollution
equipment

50. 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

51. Fertigation systems

52. Fertigation
tank
Fertigation
bypass
Control
timer Pressure
regulator
Filters
Backflo
w device
Pressure
gauge

53. REGULATIONS

54. 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

55. Resources
• http://hightunnels.cfans.umn.edu/
• http://hightunnels.cfans.umn.edu/resourc
es/irrigation-resources/

56. Extension Materials

57. Author
• Karl Foord Ph.D. MBA
• Regional Educator, Horticulture
• foord001@umn.edu

58. Handouts
• PowerPoint handout
• Extension Materials
• Drip irrigation and extension information for
high tunnels

59. 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/cr
opsystems/DC5886.html

60. • 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