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Frequently Asked Questions: Field Crops Section
Forages:
- Why are forages important in organic systems?
- Is a nurse crop required for perennial forage establishment?
- Should organic producers use legume inoculants?
- How are weeds managed in organic forage production?
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Perennial forages, legumes in particular, are incorporated into crop rotations for nutrient cycling. Nitrogen provided in a form available for subsequent plant growth is a valuable contribution in organic systems. Other rotational benefits of forages include breaking disease and pest cycles, weed suppression, and also providing a "break" for the land and soil. Arable crop production usually translates to annual cultivation. In contrast, perennial forages withhold land from cultivation, mimicking nature in the short-term. The brief interlude that perennial forage stands offer organic rotations is extremely important with respect to soil health. Withholding land from cultivation reduces the aerobic decomposition of existing soil organic matter, and the perennial forages also contribute fresh organic matter. Increased soil organic matter enhances soil structure, water holding capacity, and biological activity (e.g., earthworm populations). The increased organic matter content of soil under perennial forages helps bind soil particles into aggregates, creating pores within the soil profile. These pores are vital in promoting root growth as well as for water infiltration.
Is a nurse crop required for perennial forage establishment?
The establishment of a perennial forage stand can be accomplished in a number of ways. However, under organic management, it is almost always done with the aid of a nurse crop. Because the seeds of perennial plants tend to be small and the seedlings non-competitive, the protected environment offered by a young stand of grain provides sufficient shelter to allow for the germination and early growth of perennial grasses and legumes. However, while the aggressive early growth of the grain also assists with the control of weeds in the stand, it can also compete against the newly establishing forage stand. For this reason, the nurse crop is sown at a rate significantly lower than would normally be used if full grain production were the goal.
Should organic producers use legume inoculants?
Inoculation refers to the introduction of Rhizobium bacteria into the soil so that root hairs of seedlings will become infected and form nodules that enable the legume to fix atmospheric N. However, many soils lack sufficient numbers of specific Rhizobia needed for adequate N fixation, optimum growth and high yields. Inoculation is needed to correct those deficiencies by sticking thousands of highly effective N2 fixing Rhizobia to each seed just prior to planting. It is important to note that organic producers must consider the source of their legume inoculant. Many inoculants are being produced through the use of genetic engineering (or modification) and are therefore not permitted in organic agriculture. The inoculant carrier (material containing the Rhizobia, usually peat or liquid) must also not contain prohibited materials.
How are weeds managed in organic forage production?
Weed management strategies can be classified into two categories: cultural and biological control.
Cultural control strategies include:
- Seed into a clean field.
- Use seed that is weed-free (i.e., certified) or free of problem weeds (i.e., quackgrass, perennial sow thistle, Canada thistle, knapweed, scentless chamomile, leafy spurge, etc).
- Use forage crops and varieties recommended for your area.
- Seed into a firm, well-prepared seedbed at the recommended rate and depth.
- Plant early to reduce the presence of annual weeds, as most annual weeds are heat loving and don't germinate until May.
- Use a companion or nurse crop during establishment.
- Mow (preferably with a flail mower) above the height of the forage. This is often beneficial in preventing annual weeds from smothering forage seedlings.
- Harvest forage crops before weeds go to seed. Most seeds remain viable after passing through livestock.
- DON'T OVERGRAZE PASTURES.
- Fertilize, rejuvenate, or renovate older pastures to keep them productive, thereby preventing the establishment of invading weeds. Organic producers using compost have the benefit of a slow releasing N source, which can help prevent a flush of N-loving weeds.
- Remove weeds from adjoining fence lines and road ways.
Biological control strategies include:
-
The use of living organisms, such as insects, fungi, and bacteria, is a viable alternative in the control of problem weeds in forage crops. For example, a flea beetle imported from Hungary effectively feeds on the roots and leaves of leafy spurge, a common weed in western Canada.