Presentation by University of Minnesota professor Carl Rosen for the 2009 Minnesota Statewide High Tunnel Conference, held in Alexandria, MN on Dec. 2-3, 2009.

1. Managing and
Amending Soils for
Productive Yields
in High Tunnels
Carl Rosen
Department of Soil, Water, & Climate
University of Minnesota
© 2009 Regents of the University of Minnesota

2. Topics
 Considerations before planting
 Site selection
 Yield potential in a high tunnel
 Satisfying nutrient needs
 Preplant amendments
 Importance of soil testing
 Nutrient management
 Without fertigation
 Nutrient sources – organic and controlled release
 With fertigation
 Nutrient sources & timing of application
© 2009 Regents of the University of Minnesota

3. Site Selection
 Ideal soil is a well-drained sandy loam to silt
loam
 Medium to high organic matter levels (3.5 to
6%)
 Consider growing green manure crops before
planting/establishing the tunnel
 Sorgum-sudan
 Rye or oats
 Legumes such as field peas, clover
© 2009 Regents of the University of Minnesota

4. Improving Soil Physical Properties
 Compost addition
 1-2 lbs compost per
sq. ft.
 Use good quality
compost
 Beware of herbicide
residuals
© 2009 Regents of the University of Minnesota

5. Yield Potential & Nutrient Needs
 Yields in a high tunnel can be 2
to 4 times the yield obtained in
the field
 Higher yields will require more
nutrients, but knowing how much
to apply is a challenge
 Lack of nutrients – deficiencies
 Excessive nutrients – salt build up
 Both situations affect yield and
quality © 2009 Regents of the University of Minnesota

6. “Book Values” for Tomatoes
N P K
Plant Part -------- lb per ton F.W. ------------
Fruit 3.4 0.4 6.0
Vines 2.6 0.4 3.4
Total 6.0 0.8 9.4
A 50 ton yield/A would require:
300 lbs N/A
40 lbs P/A (92 lbs P2O5)
470 lbs K/A (564 lbs K2O)
© 2009 Regents of the University of Minnesota

7. Satisfying Nutrient Demand in a
High Tunnel System
 Release of nutrients from the soil
 Importance of good preparation
 Addition of fertilizer
 Preplant
 During the growing season
 fertigation
© 2009 Regents of the University of Minnesota

8. Amendments Before Planting
 Have soil tested before
applying amendments
 pH, OM, nitrate-N, P, K,
Ca, Mg, micronutrients,
soluble salts
 Retest yearly, especially if
problems are occurring
© 2009 Regents of the University of Minnesota

9. Soluble Salts (EC)
 Based on saturated paste:
 < 2 mmhos/cm (dS/m) - no
problems
 3-4 some plants affected
 5-7 many plants affected
 >8 only salt tolerant plants
survive
 Most soils in Minnesota have
low salts, but salts may
accumulate with excessive
fertigation
© 2009 Regents of the University of Minnesota

10. Soil pH
 Acceptable range: 5.5-7.5
 Adjust before planting
 Acid soils – use calcitic or dolomitic
limestone
 Alkaline soils – use compost, sphagnum
peat, elemental sulfur
© 2009 Regents of the University of Minnesota

11. Phosphorus and Micronutrients
 Base P application on soil test level
 Greater than 41 ppm is considered very high for most
vegetables/fruit
 Incorporate before planting if soil test indicates a need
 Potassium phosphate, DAP, MAP
 Numerous micronutrient sources
 Composted manure
 Use starter solutions high in P for transplants
© 2009 Regents of the University of Minnesota

12. Nitrogen and Potassium
 A portion should be applied before planting
 Base K fertilizer application on soil test – most can be applied preplant
 Greater than160 ppm is considered very high for most vegetables/fruit
 potassium chloride (0-0-60)
 potassium sulfate (0-0-50)
 potassium magnesium sulfate (0-0-22); acceptable organic source
 For soluble N sources, apply about 1/3 – 1/2 of the required N before
planting
 urea (46-0-0)
 ammonium nitrate (34-0-0)
 calcium nitrate (15.5-0-0)
 potassium nitrate (13-0-44)
 composted manure (variable)
© 2009 Regents of the University of Minnesota

13. Nutrient Management
Without Fertigation
 Organic systems
 Composted manure
 Type of compost
 Moisture content
 Crops grown
 To supply equivalent of 100 lbs available N/A:
 Dairy manure compost: 2700 lbs/1000 sq. ft.
 Poultry manure compost: 900 lbs/1000 sq. ft.
 Incorporate 6 to 8 inches into soil
© 2009 Regents of the University of Minnesota

14. Nutrient Management
Without Fertigation
 Use legume cover
crops
 Warm season cover
crops can be planted
later in the season
© 2009 Regents of the University of Minnesota

15. Nutrient Management
Without Fertigation
 Conventional system
 Composted manure
 Soluble fertilizers
 Controlled release N fertilizers
 Coated urea
 Osmocote
 Be sure that release rate is fast enough for the crop
being grown
 For most vegetables – 50 to 70 day release is needed
 Temperatures are warmer in a high tunnel – faster release
© 2009 Regents of the University of Minnesota

16. Nutrient Management
With Fertigation
 Injection of one or more nutrients into the
irrigation water
 Review the Minnesota Chemigation/Fertigation
Permit Application and Safety Requirements
 www.mda.state.mn.us
 Submit the Minnesota Chemigation/Fertigation
Permit Application to MDA
 Main requirement is to have recommended anti-pollution
and safety devices
© 2009 Regents of the University of Minnesota

17. Nutrient Management
With Fertigation
 Primarily used for nitrogen and
potassium
 Urea-ammonium nitrate (28%N) (liquid)
 Calcium nitrate (15.5% N)
 Potassium nitrate (13% N; 44% K2O)
 Potassium chloride (60%; K2O)
 Blends eg. 20-20-20
 Soluble sources of organic fertilizers
are available, but are expensive and
may cause clogging
 Some fish emulsions have been successfully
used
© 2009 Regents of the University of Minnesota

18. Solubility of Common Fertilizers
Material Composition Salt index Solubility
%N %P2O5 %K2O lbs/gal H20
Calcium nitrate1 15.5 0 0 53 8.5
Potassium nitrate 13.0 0 44 73 1.1
Ammonium nitrate 33.5 0 0 105 9.8
Urea 46.0 0 0 75 6.5
Ammonium sulfate2 21.0 0 0 69 5.9
Potassium chloride 0.0 0 60 116 2.3
Potassium sulfate2 0.0 0 50 46 0.6
Diammonium phosphate2 18.0 46 0 30 3.6
1May cause clogging if irrigation water is high in bicarbonates
2Not recommended for use with calcium nitrate or if irrigation water is high in calcium
© 2009 Regents of the University of Minnesota

19. Mixes to Avoid
 Phosphorus compounds with calcium or iron
 Calcium with sulfate and bicarbonate
 To avoid precipitation problems two stock tanks
should be used, one for calcium nitrate and iron
chelate and the other for the remaining fertilizers
 Alternatively apply P fertilizer preplant
© 2009 Regents of the University of Minnesota

20. Rate and Timing of Application
 Preparing soils and applying preplant nutrients is
still important - compost or fertilizer
 About 2/3 of N and K needs can be applied
through fertigation
 Timing is not as critical as rate
 Once per month
 Once per week
 Every time there is an irrigation event
© 2009 Regents of the University of Minnesota

21. Fertigation
 Use a batch loading fertigation approach
 Inject total volume of nutrient during an irrigation event
 Total volume of fertilizer for batch loading depends on the
area of the irrigated zone and the desired nutrient rate
 The injection rate does not need to be precisely controlled
 The injector should apply the chemical solution in a time
period that does not result in over-irrigation, otherwise
leaching will occur
© 2009 Regents of the University of Minnesota

22. Meeting the Demands for Crops
with Different Requirements
 Fertigate crops at different
times
 Allows for varying rates to be
applied
 Fertigate to meet the
demands of the crop
needing the lowest amount
of nutrients
 Make up difference with
preplant fertilizer
© 2009 Regents of the University of Minnesota

23. Determining the Rate of N and K
to Apply
 Most conventional
recommendations are
based on lbs N or K2O/A
 Ounces per linear feet of
row is more practical for
high tunnels
 Based on 4ft spacing
between rows
 100 linear ft = 400 sq. ft.
© 2009 Regents of the University of Minnesota

24. N and K Fertigation Schedule for
Tomatoes - lb/A basis
Days after Planting Daily N Weekly N Seasonal N Daily K2O Weekly K2O Seasonal K2O
----------------------------------------- lb/A--- ----------------------------------------------
Preplant ---- ---- 50.0 ---- ----- 100.0
0- 21 0.5 3.5 61.5 1.0 7.0 121.0
22- 49 0.7 4.9 81.1 1.4 9.8 160.2
50- 70 1.0 7.0 102.1 2.0 14.0 202.2
71- 91 1.1 7.7 125.2 2.2 15.4 248.4
92-112 1.0 7.0 146.2 2.0 14.0 290.4
© 2009 Regents of the University of Minnesota

25. N and K Fertigation Schedule for
Tomatoes – oz per 100 ft basis
Days after Planting Daily N Weekly N Seasonal N Daily K2O Weekly K2O Seasonal K2O
--------------------------------- oz/100 linear row ft --------------------------------------
Preplant ---- ---- 7.3 ---- ----- 14.7
0- 21 0.07 0.50 9.0 0.15 1.1 17.8
22- 49 0.10 0.70 11.9 0.21 1.5 23.5
50- 70 0.15 1.05 15.0 0.29 2.0 29.7
71- 91 0.16 1.12 18.4 0.32 2.2 36.5
92-112 0.15 1.05 21.5 0.29 2.0 42.6
1
assumes 4 ft spacing between rows; lb/A X 0.147 = oz/100 linear ft of row.
lbs/A x 0.147 = oz/100 linear ft of row
© 2009 Regents of the University of Minnesota

26. Calculating the Rate of Fertilizer
to Inject
 Example for urea-ammonium nitrate (28%)
 Area to fertilize – 200 linear feet (800 sq. ft.)
 Liquid (28% N) – 3 lbs N/gallon
 Recommendation is 10 lbs N/A
 10/3 = 3.33 gallons/A
 3.33 gal * 800/43560 * 128 oz/gal = 7.8 fl oz
 Use similar approach for granular except
conversion to lbs product rather than fl. oz. is
made
© 2009 Regents of the University of Minnesota

27. Amount of UAN Solution for
Various N Rates per Acre
N Rates lbs/ac 1 2 3 4 6 8 10
28% 0.33 0.67 1.00 1.33 2.00 2.67 3.33
Gallons/ac
28% fl. 0.39 0.78 1.16 1.55 2.32 3.10 3.88
oz/100 linear
ft of row1
1Assumes a between row spacing of 4 ft.
© 2009 Regents of the University of Minnesota

28. Summary
 Soil test before planting
 Incorporate compost if needed to improve soil physical
and chemical properties
 If needed adjust acid soil pH with lime
 Incorporate P and micronutrients before planting based
on a soil test
 For organic production use composted manure before
planting © 2009 Regents of the University of Minnesota

29. Summary
 For conventional systems, use fertigation
with soluble N and K sources or use
controlled release fertilizers
 A portion of the N and K can be applied
before planting
 Total rate applied is more important than
timing
 Use the tables provided to estimate
amounts of nutrient required on a linear
foot basis
© 2009 Regents of the University of Minnesota