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COG Organic Field Crop Handbook
2.2 Choosing Crops for a Crop Rotation
There are five major considerations when selecting crops for your crop rotation:
1. Value as cash crop or livestock feed.
2. Soil building
3. Conserving nutrients
4. Weed and pest control
5. Labour and equipment demands
1. Crop value
Although certified organic crops can sometimes command a 20 percent premium over conventionally grown crops this does not mean that any one crop will receive a premium. Because the organic marketplace is still very small, the supply and demand balance is still very tenuous and can widely fluctuate from month to month. Many organic farmers recommend contacting distributors and retailers to learn from them which crops are in high demand. In this way field crops can be contracted for in advance which means that the farmer shares the risk with the distributor on what tonnage is eventually taken off the field.
On a mixed farm feed requirments will to a large extent determine which crops are grown in the rotation. However it is worth considering changes to feed rations to allow more flexibility.
2. Soil building
Green manures play a valuable role in the crop rotation for their ability to rebuild the soilÕs structure, conserve moisture, control erosion, and reduce the leaching of nutrients off the farm (see Section 1.6.).
Techniques that help to build up the soil:
¥ Ensure a balance of cash crops ( corn and soybeans) and soil- conserving cover crops (clovers).
¥ Deep rooted crops (sweet clover, alfalfa) should alternate with shallow-rooting crops (cereals) to help keep the soil structure open and assist in drainage.
¥ Alternate between crops with high-root biomass (rye) and low-root biomass (oats). Pasture grasses with their high root biomass provide soil organisms, particularly earthworms, with food.
¥ Alternate crops that are high moisture users (corn) with plants that require lesser amounts of moisture (barley).
¥ Allelopathic crops (rye and sunflowers) should be alternated to prevent a build up of their natural chemical toxins.
¥ Alternate nitrogen fixers (legumes) with high nitrogen consumers (corn and winter wheat)
3. Conserving nutrients
Nitrogen is a major nutrient and the key regulator of ecological processes. A considerable percentage of nitrogen fertilizer never reaches the crop; it is lost to the atmosphere as nitrogen gas, nitrous oxide, or ammonia, or to the groundwater as nitrate. Most of this loss occurs where and when there is no crop on the field. The soil is most exposed during two periods. First, from the time of seeding until the plant has grown big enough to create a canopy over the soil, and secondly, after the crop is harvested.
An organic farmerÕs priority is to prevent loss of nutrients from the farm, and to improve the native soil fertility.
Techniques that help conserve nutrients:
¥ Avoid leaving the soil bare by planting cover crops and undersowing.
¥ Plant green manure crops
¥ In order to meet all of the farmÕs requirements from within the system nitrogen-fixing crops, should alternate with high nitrogen demanding crops .
¥ Legumes should feature often in the crop rotation. They are an essential part of the crop rotation because of their ability to fix nitrogen.
¥ Heavy feeding crops should be followed by medium or light feeders.
¥ Also include pasture in the crop rotation for its valuable role in recycling nutrients and in soil conservation. To be nutritious and palatable to livestock, a pasture should contain a wide variety of grasses and legume.
¥ Store manure to prevent nutrient runoff and use composted manure.
Division of Crops into Nutrient Demand Categories for Rotation Purposes.
Heavy feeders: corn, sunflowers, canola, oil radish, winter wheat, spelt.
Medium feeders: Spring wheat, oats, rye, winter barley
Light feeders: Spring barley, flax, buckwheat, soybeans
4. Weed and pest control
Organic farmers do not usually have major problems with insects and plant diseases in field crops. The plant and insect diversity on organic farms creates a balance in the agro-ecosystem. Certain weed and pest problems that do arise are usually traceable to inappropriate crop rotations. (See Sections1.8 and 1.9)
Techniques that help control weeds:
¥ Slow-growing crops which are more susceptible to weed invasions, should follow weed suppressing crops.
¥ Alternate between warm-season and cool season crops, so that you alternate your seedingdates, and your tillage dates. This means that one year you can eradicate early germinating weeds, and the next year late germinating weeds.
¥ Include plants that have natural weed germination inhibitors (like rye and sunflowers) in the rotation.
¥ Include forage legumes in the rotation. They compete well with weeds and choke them out.
¥ Include row crops that give the opportunity for mechanical weed control.
¥ Avoid too many years of perennial forage in the rotation as this may encourage the growth of perennial weds.
¥ If you have a particular problem, like Canada thistle, adjust the rotation to include a control measure. For example, Canada thistle can be destroyed by clipping it at the bud stage, and then every 21 days after that. A rodweeder works well for this operation, and clover in the rotation provides an excellent opportunity for such control. Research on organic farms in Ontario has also found that three to four years of alfalfa hay works as a control by starving thistle and nutsedge reserves.
¥ Grow pure stands of alfalfa, rye and buckwheat to choke out persistent annual weeds.
Specific techniques for pest control:
¥ Where risks of disease or soil-borne pest problems exist, potential host crops should only occur in the rotation at appropriate time intervals. Have a four year gap between growing brassicas or cruciferae or potatoes in the same field, and grow a break crop in the intervening years.
¥ Avoid excessive use of cruciferous green manures, (e.g. rape), that encourage certain insect pests.
4. Labour and equipment demands
of the system
One of the advantages to the farmer of growing different crops, is that when there is diversity of activity, the work load is distributed over the year. When large acreages are planted to one crop, pressure at harvest time is intense. A diversity of crops on the farm will help spread the work load during the cropping season.
When going through the transition years, a farmer should consider the labour and equipment requirements for the different crops in the crop rotation, and ensure that there will not be a Òtime crunch.Ó Composting for the first time, also needs to be incorporated in the farmerÕs schedule, and the needed equipment may have to be adapted from existing equipment.
Some farm machinery gets used for so few hours a year that great savings can be made if farmers come to an agreement to share equipment. oire lesser amounts of moisture.Cmixed stands of forageoroil radishTfive1. Economics
2T that help build up the soilcash s(corn and soybeans)cover (red clover, oats) (soybeans) (buckwheat). (rye) (oats) (barley)
¥ Balance allelopathic crops (rye and sunflowers) to prevent a build up of the natural chemical toxins which inhibit the growth of weed species.
¥ Alternate nitrogen fixers (legumes) with high nitrogen consumers (corn and winter wheat.)3NitrogenA large percentage include crops that are both high nutrient consumers, and crops that contribute nitrogen and other nutrients to the soil. Avoiding the soil bare, 1.6, and compost manure,Section 1.5T that help conserve nutrients4O in field crops1.8for wmanagement1.9 for pTthat help controlsred clover, Tthat help pestscontinual5W there is diversity of crops and activityA general guideline is that if crops are planted two days apart, there will be one days difference in harvesting dates.
savings can be made if farmers come 1.6apted from existing equipment.
Techniques that help control pestsonce every four years and should be grown iferous green manures, (e.g. oil radish
Table 5 outlines some disease considerations that should be taken into account when designing your rotation. 5
When there is aand farming activitiesis more evenly distributed entire If you are cthis be incorporated in the farm le. Time may be needed to adapt existing equipment. Major equipment adjustments may not be necessary however, because ssavings can be made if farmers greement to share equipment.
Finally it is important to remember that a crop rotation is not "cast in stone" . Conditions on the farm are continually changing as are the markets for organic crops. You may want to reconsider the possibilities at regular intervals. Do not sell straw off the farm, incorporate residues or use for livestock bedding.
Crop nutrient removal figures are given in Appendix E
1alfa, rye or and diseaseSimilar crops (e.g. small grains) should be seperated by a crop of a different type - a legume or broadleaf crop such as oil radish or buckwheat.nic crops. You alternate your seeding and Demands on labour, equipment and knowledge
ic crops can sometimes command which crops are in high demand. Identify the markets before planting so that price and quality required are known and risk is minimized.
eorn and soybeans) and soil-Diversify the rotation in terms of moisture use - some crops are high moisture users (corn) others require lesser amounts (barley).
.om the time of tillagesfigures are given in Section III.oblems that do arise are oftenmixed hay stands,once every four years;sdisease and Demands on l,and knowledge.omposting
If you are introducing to the rotation crops with which you are unfamiliar, determine whether you have the knowledge on how to grow the crop. Guidelines for some crops are provided in Section III. .emember that a crop rotation can be flexible loss of nutrients from the farmhe system, nitrogen-fixing crops; be sepa
" Our rotation generally tries to alternate spring and fall seeded crops and we start the rotation with the heavy feeders after the sod. They would be corn, wheat and to some extent spelt, and then the end of the rotation would be more rye, barley and then underseeded back to the hay. We try to throw in once in an 8 year rotation at least one winter cover crop of red clover and one cover crop of oil radish."Gerry Poechman, Ger-Mar Farms
Copyright © 1992 Canadian Organic Growers. Inc
Reprinted with permission. All rights reserved.
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