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

Soil and nutrient management differs in high tunnel situations!

Nut

rient

nee

ds c

an b

e gr

eate

r

Moisture lim

ited à organic m

atter

can spread moisture farther

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?

Solid fraction

Pore space

Organic matter: All living or formerly living material in a soil

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.

“Particulate organic matter” (POM)

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

Par;culate  Organic  MaEer  (POM)

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

Leaf Fragment

Jones et al., 2009

C = Mucilage halo, stained with analine blue

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

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)

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

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

Crop residue

Available Nitrogen

Decomposition

Legume based cropping system

N2

Biological Nitrogen Fixation

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

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?

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

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…

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