The document summarizes the results of heating the soil in a high tunnel using an underground heating system. Key points:
1) Heating the soil allowed the high tunnel to remain 10-20 degrees warmer than an unheated tunnel, allowing crops to be grown 8 weeks earlier.
2) Tomatoes and cucumbers grown in the heated tunnel were of higher quality and yielded more than those grown outside or in an unheated tunnel.
3) A potassium deficiency caused hard centers in tomatoes late in the season, but was addressed with foliar potassium applications.
This PowerPoint helps students to consider the concept of infinity.
Solar Heating of High Tunnels
1. Dallas Flynn
Mary Flynn
Thaddeus McCamant
Frazee, Minnesota
2. Ground is slow to
warm
Cold soils inhibit
plant growth and
can cause nutrient
deficiencies
Require
supplemental heat
during cold spells
3. Traditional Outside
100
90
80
70
60
50
40
30
20
10
0
3/31 4/1 4/2 4/3 4/4 4/5 4/6 4/7 4/8 4/9 4/10 4/11 4/12 4/13 4/14 4/15 4/16 4/17 4/18
The high tunnel warmed the air to 80F by 11:00 AM, but the
air temperature dropped quickly at night. Nighttime lows in
tunnel equaled outside (empty tunnel).
4. Heat the soil
beneath the high
tunnel
Air is heated in
solar panels,
pumped through
tile two lines three
feet below the soil
surface.
5.
6.
7. Fans push air from
the soil through the
solar panels back to
tile lines
Fans are controlled
by thermostats:
Fan starts when air in
solar panel reaches
125F, stops when
temperature in soil
panel drops to 85F
8. Two lines of T-tape
per bed
“Dick’s Super Soil”
◦ Decomposed peat,
◦ pH 7.4, high CEC,
low potassium
9. Cold soil can cause nutrient deficiencies, root
diseases, reduced germination, poor growth
Heating the soil could cause the air
temperature to be warmer at night
10. Sun warms soil, Soil continues to
emit IR
Soil emits infrared Infrared transparent
radiation, which Infrared trapping
heats air plastic
11. Warm soil would
emit a large
amount of infrared
radiation, altering
the nighttime
temperature of the
high tunnel
13. Solar panels could not keep tunnel above freezing
during coldest part of the winter
◦ Cold winter -40 two times in January
Soil-heated tunnel was warmer than unheated tunnel
◦ 10 degrees warmer (mean temperature)
◦ 20 degrees warmer (overnight lows)
Soil temperature: 31.4
Overwintered spinach, kale in heated tunnel
*F
F ly n n H T I
8 0.0
7 0.0
6 0.0
Temperature in 5 0.0
heated tunnel
4 0.0
3 0.0
Blue line = air 2 0.0
Brown line = soil 1 0.0
0 .0
-1 0 . 0
Fe b 0 5 Fe b 1 2 Fe b 1 9 Fe b 2 6
TM P TM PA TM PB
14. Soil rose above freezing on March 4 in heated tunnel
Soil rose above 45 on March 15
Nighttime lows stayed above 45 on March 15
10-15 degrees warmer than unheated tunnel between
March 7 and April 15
Soil temperature in raised bed: March-April
Heated Tunnel Traditional Tunnel
90
80
70
60
50
40
30
20
10
0
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1-Mar
2-Mar
4-Mar
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8-Mar
1-Apr
3-Apr
5-Apr
7-Apr
9-Apr
16. Planted tomatoes
and cucumbers on
March 15
Tomatoes grew
well, but cukes
were stunted
Started cutting
spinach and kale
first week of March
Radishes in early
May
17. • Started picking
tomatoes on June 8
• Started selling
tomatoes and
cucumbers at local
farmer’s markets on
June 16
18. High yields both in
tomatoes and
cucumbers
Quality was
excellent at first
19. Roll sides manually
Put shade cloth on
first week of July
Thermostatically
controlled exhaust
fan at the peak of
tunnel
20. Core of tomatoes was hard
Yellow shoulders
Okay for processing, but not for fresh market
Gave extra tomatoes at the market
Assumed problem was weather related
21. Gray color right
inside the skin
Difficult to see
without cutting
tomato
Hard center core
Not in heirloom
varieties
Most likely due to
potassium
deficiency
22.
23. Began in late July
Applied weekly foliar
potassium (KDL) and
continued to early
fall
Problem disappeared
three weeks after
starting the KDL
sprays
Amended soil with
greensand
24. Green beans
Radishes
Kale
Carrots
Lettuce
Everything was
good except onions
25. Aphids in peppers,
eggplants in August
Controlled with
ladybugs
Poor fruit set in
eggplants and
peppers in spite of
enormous plants
Will buy
bumblebees early
next year
30. Sales increased 35%
in 09
Tomatoes and
cucumbers were 8
weeks earlier in
heated tunnel than
in unheated tunnel
31. Good year to have a
heated high tunnel
All crops were better
in the heated tunnel
than in unheated
tunnel or outside
garden
Good quality
Few diseases
Picked tomatoes
from June 8 to
November 15