by Julie Grossman, Assistant Professor | Department of Horticultural Science, University of Minnesota Presented at the 2015 Minnesota Statewide High Tunnel Conference.

1. Optimizing soil health in season
extension environments through
innovative cover crop management
Julie Grossman
Department of Horticultural Science
University of Minnesota, Twin Cities
Co-PI’s:
Mary Rogers, Steve Poppe

2. Soil and nutrient management
differs in high tunnel situations!
Nutrientneedscanbegreater
Moisturelimitedàorganicmatter
canspreadmoisturefarther

3. High tunnels are more
intensively managed
• Increased soil nutrient removal
• Increased traffic
• Extended season promotes back-to-back
cash crops
What is the impact of this increased
management on soil quality after many
years?

4. Solid
fraction
Pore
space
Organic matter: All
living or formerly living
material in a soil

5. Organic matter influences
soil structure, nutrient
storage, biological activity,
water and air infiltration,
erosion! Wow!
From http://kearney.ucdavis.edu/OLD%20MISSION/Old%20MAIN.htm
Soil organic matter (SOM)
is the organic (C-containing)
soil component.
“Particul
ate
organic
matter”
(POM)

6. Plant
residue
Readily
decomposable
(ie,
“POM”)
decomposi;on
Plant
available
N
Microbial
Biomass
Stable
humus
Decomposi;on
of
organic
materials,
like
plant
residues,
promotes
soil
organic
maEer
development
• Decomposition rate is controlled by:
• Residue biochemistry
• Association with decomposer microorganisms
• Climatic conditions; temperature and moisture

7. Par;culate
Organic
MaEer
(POM)

8. Particulate organic matter (POM) includes leaf
fragments (lf) and root fragments (rf).
Leaf Fragment

9. Jones et al.,
C = Mucilage
halo, stained
with analine
blue

10. How does soil quality differ after
8 years of HT production?
Conventional
management
Organic
Management
Measure of soil
quality
HT Field HT Field
pH 7.8 7.0 7.7 7.6
Salinity: EC (dS
m-1)
0.16 0.065 0.30 0.059
Total C (g kg soil-1) 17.5 19.3 22.4 22.4
POM C (g kg
soil-1)
1.65 1.51 4.2 3.02
Knewtson et al, 2012

11. 0
1000
2000
3000
4000
5000
6000
7000
Total soil N Readily
Mineralizable
Carbon
Basal
respiration
Microbial
biomass
Organic
Conventional
(µg C02-C) (µg C02-C)
mg per kg-1
Reeve and Drost, 2012
Organic Management Increases Soil Biological
Properties in High Tunnels
(µg C02-C)

12. How does organic management
differ?
• Synthetic water-soluble
fertilizer used
• Delivered through
fertigation
• Delivered directly to root
zone
• Various pre-plant
incorporated composts
and plant residues
• Ideally coupled with
fertigation using OMRI
approved sources
– More expensive
– Can clog drip lines
Conventional Nutrient
Management
Organic Nutrient
Management

13. Hairy Vetch: AU Early
Cover (Auburn Univ),
winter hardy Early Cover
(NY), AU Merit
Austrian Winter Pea,
Whistler and Variety
unstated
http://aggie-horticulture.tamu.edu/extension/Texascrops/foragelegumes/index.html, NCAT
White Lupin, TifBlue78
Crimson Clover:AU Robin, AU
Sunrise,Tibbee, Dixie
Subterranian clover, Denmark
Berseem clover, Bigbee
Hairy Vetch, Purple
Prosperity, USDA
Cover Crops

14. Crop residue
Available Nitrogen
Decomposition
Legume based cropping system
N2
Biological
Nitrogen
Fixation

20. Four cover crop single
species and mixtures
Sown in two locations:
• North Central Research
and Outreach Center
(Grand Rapids, MN)
• West Central Research
and Outreach Center
(Morris, MN)
Austrian
winter pea
with rye
(50-75 lbs/acre)
Red
Clover
(10-12 lbs/acre)
Winter rye,
hairy vetch,
fall radish
(50-75 lbs/acre)
No cover
crop control

21. Mow
Early
Plant
greens ($$)
Mow
Late
More biomass
and N
Spring 2015 each plot
split by:
• Early mowing to
additional cash crop
(More $$?)
• Late mowing for
increased cover crop
growth (More N??)
• Cost benefit analysis
Should you take advantage of
the spring to grow more N, or
grow more crop?

22. Data we will collect
• Cover crop biomass
• Harvestable yield
• Soil quality
measures:
– POM
– Permanganate
oxidizable C (“POX”)
– EC
– Available N
• Outreach activities:
– Field days
– On-farm trials in
2016

23. Shoveling snow into open tunnel in
Grand Rapids for improved plant
protection… (Dec, 2014)
…however, snow was melted by mid
January (Jan, 2015)
Initial challenges…

24. Evidence of winter kill of vetch/rye
mix in Morris (Jan, 2015)