Organic farming is by definition based on and dependent on biological systems. Philosophically as well as practically these systems support the expression rather than the suppression of biological and micro-biological processes. The prohibition against using synthetic pesticides, herbicides, and fungicides as well as synthetic fertilizers both guarantees and magnifies this expression. Ultimately this means that organic practices are at the same time incredibly simple and incomprehensibly complex. In fact, the more biologically complex, both temporally & spatially, the farming system becomes, the less the human intervention is required to keep it operating.
Talking about weed management in organic production systems is a huge challenge. It is a challenge because weeds are often a significant challenge for organic farmers--this is confirmed and pointed out by non-organic neighbors heading into the coffee shop in town! But more importantly, talking about weed management is a challenge because it is so complex from the biological perspective. Additionally, by necessity, specific weed management practices vary because they are usually quite specific to geography, climate, soil type, rotation sequence, the presence or absence of livestock, and the goals of a particular operation.
If there is one adage to which all organic farmers subscribe to it would be: You can't do just one thing. On the one hand this is an operational edict--you can't just grow wheat (or lentils, or flax, or any other single crop), you can't just cultivate, you can't just green manure. Organic certification guidelines specify it, practical experience verifies it. On the other hand the adage is a universal biological truth--even the simplest practice will have a myriad of consequences. Organic farming is a complex and inter-related living system. Green manuring a cover crop affects more than just fertility; adding a crop to the rotation affects more than just disease cycles; cultivation affects more than above ground vegetation, and on and on. Thus the weed management strategies outlined below are not just weed management strategies. They are likely to be disease management strategies, insect pest management strategies, yield enhancement strategies, soil building strategies, and much more. Each must be considered within the entire matrix of decisions and the whole system of the farm. Seldom are they applied in cookbook fashion on an organic farm. All organic farms probably employ many of them in any given year, but seldom in exactly the same sequence or for exactly the same reasons year after year.
STRATEGY: CULTIVATION-- mechanical disturbance of soil weed root zone.
Tools:
A. Pre-seeding cultivation
B. Night cultivation
C. Seeding cultivation
D. Pre crop emergence cultivation
E. Post crop emergence cultivation
STRATEGY: CROP ROTATION -- disruption of weed life-cycles.
Tools:
A. Four-year annual crop rotation
Year 1: Green manured legume
Year 2: Cereal grain
Year 3: Pulse crop (for grain, hay, or green manure)
Year 4: Buckwheat or Oil seed (often with biennial legume companion crop)
B. Annual/Perennial
Year 1: Cereal grain or other cash crop (with alfalfa companion crop)
Year 2: Alfalfa for hay
Year 3: Alfalfa for green manure
C. Montana Medic Farming
Year 1: Flax or Cereal grain cash crop (with annual medic companion crop)
Year 2: Regenerating medic (cover crop, green manure, and/or pasture crop)
Year 3: Annual cash crop
Year 4: Regenerating medic (cover crop, green manure, and/or pasture crop)
STRATEGY: COMPETITION -- physical and biochemical suppression.
Tools:
A. Seeding of Cash Crop
1. Seed selection (high quality seed of competitive species & varieties)
2. Relatively high seeding rates
3. Timely seeding relative to soil conditions & weed emergence
4. Narrow seed spacing/cross seeding
B. Empty space competition
1. Companion cropping with small seeded legume (especially sweet clover, medics, alfalfa)
2. Timely seeding of companion crop relative to cash crop & weeds
C. Competition based on relative plant architecture
1. Short weed suppression with understory of prostrate or semi-prostrate cash or companion crop
2. Tall weed suppression by clipping, grazing, electrocution
D. Biochemical/micro-biological competition
1. Alleleopathic effects (rye, clover, mustard, green manured lentils)
2. Micro biological destruction of soil weed seed bank
3. Changed soil environment
STRATEGY: COMMON SENSE/COMPASSION
Tools:
A. Weed elimination is not the goal--it is impossible and unwise.
B. Weeds are teachers (our challenge is to address the causes & not the symptoms)
It has only been in the past half decade that organic farming has gained the credibility to attract widespread scientific investigation. Over the next 20 years, we will see an exponential growth in research of the above and additional strategies. In the meantime, the following contacts are listed as selected sources of information and/or practitioners of the above weed management strategies for prairie agriculture:
Non-chemical weed research:
AG CANADA, Lethbridge, Alberta (403) 327-4591
Dr. Robert Blackshaw
Dr. Jill Clapperton
Dr. James Moyer
Montana State University, Bozeman, Montana (406)-994-5717
Dr. Bruce Maxwell
Organic Cropping Systems:
Eric Leicht, Marysburg Organic Growers, Spalding, Saskatchewan (306) 287-3954
Neil Strayer, Growers International, Inc. Belle Plaine, Saskatchewan (306) 693-3767
Dwayne Smith, Grainworks Inc., Vulcan, Alberta (403) 485-2808
Robert Quinn, Montana Flour & Grain, Big Sandy, MT (406) 378-3105
David Oien, Timeless Seeds, Inc. Conrad, MT (406) 278-5770
Dr. James Sims, Timeless Seeds, Inc. Bozeman, MT (406) 582-1576
Organic Certification : Organic Crop Improvement Assn. International, Bellefontaine, OH (973) 592-4983