Cover Crop-Based
Conservation-AG
Systems for Organic
Vegetable Production
Dr. Ron Morse
Department of
Horticulture
Virginia Tech
What is Conservation
Agriculture (CA)?
• CA is a bio-diverse paradigm—an holistic
attempt to mimic natural agroecosystems.
• CA strives to simultaneously obtain high
crop yields and conserve or ideally
enhance soil quality on an annual or
biannual basis.
CA Emphasizes Use of:
minimal soil disturbance
(reduced tillage)
permanent soil cover
(living or dead mulch)
intensive crop rotations
or perennial sods
Question: Why integrate organic and CA?
Answer: Integrating organic and CA makes
an ideal system (system ideotype) because
their combined philosophies and practices
best mimic native agroecosystems and are
thus highly sustainable.
Current status of Organic CA Systems:
Organic CA is not widely practiced
throughout the world.
Why? It’s hard to break out of old traditions!
Organic growers have traditionally used
mechanical cultivation to manage weeds.
CA farmers have traditionally used chemical
herbicides to manage weeds.
Question: Is organic CA an oxymoron?
Answer: Although difficult, organic CA crops
can be successfully produced using highbiomass cover crop-based techniques.
Situations in which
organic CA is least
likely to succeed:
1. Compacted, poorly
drained soils
Possible solution—use
permanent raised
beds.
Situations least likely to
succeed:
2. Cold, wet spring soils
Possible use winter-kill
cover crops and
shallow zone-till in
early-mid spring.
Situations least likely to
succeed:
3. Weedy fields—
especially perennials
Possible solution—use
aggressive IWM practices
for 12-36 months to lower
weed seedbank.
Situations least likely to
succeed:
4. Imbalanced, infertile soils
Possible solution—use
aggressive INM practices
to achieve nutrientbalanced fertile soils.
Situations in which
organic CA is
most likely to succeed:
1. Sloping, highly erodible
soils
Situations most likely to
succeed:
2. Late summer planted
crops
Situations most likely to
succeed:
3. Crops that form a rapid,
dense leaf canopy
Situations most likely to
succeed:
4. Staked or erect-growing
crops in which
alleyways can be
mowed
Uses of cover crop residues:
A. No-till (NT)—cover crops are killed and
retained as a dense, uniform mulch over the
entire field.
NT is difficult because:
Cover crops must be mechanically killed before
planting.
NT systems require specialized equipment for
plant establishment and weed management.
Uses of cover crop residues:
B. No-till, living mulch (NT-LM)—cover crops are killed
only in the areas (zones) where cash crops are grown
(grow zones); cover crops are keep alive (living mulch)
in the alleyways during the growing season.
NT-LM is difficult because:
Cover crops must be mechanically killed in grow zone
areas.
Specialized NT equipment is required to establish cash
crops.
Living mulch in alleyways must not encroach or shade
cash crops.
Uses of cover crop residues:
C. Green manure, zone-till (GM-ZT)—cover
crops are shallow incorporated in grow
zones; cover crops are either killed or
keep alive in alleyways.
GM-ZT is relatively easy because:
No specialized equipment is required for zone
tillage and plant establishment.
Weeds in grow zones can be managed using
conventional methods.
Uses of cover crops:
D. Green manure, conventional tillage (GMCT)—cover crop residues are shallow
incorporated over the entire field.
GM-CT is easy:
Conventional equipment is readily
available.
Weed management can be achieved
using mechanical cultivators.
Conclusions:
Although there are many associated challenges, organic-CA
systems can produce the best of both worlds—high crop yields,
improved soil quality, and many emergent or synergistic
properties such as pest suppressiveness and crop quality.
Success with organic CA can be achieved when selecting wellsuited environments and following recommended practices;
examples include:
Fertile soils with low weed populations (many crops)
Fall crops (broccoli); staked or erect growing crops (tomato)
Crops forming rapid, dense leaf canopies (squash- and
cabbage-family species)
GM-ZT systems, using simple conventional equipment (many
crops)