Also remember that there is likely no single cover crop that is right for your farm see Cocktails or Mixtures , below. Finally, think through exactly how and when you will seed , terminate and plant into your cover crop. Do you know a reliable source for cover crop seeds, what will the weather be like, can you get into the field, do you want it to winterkill, and what labor and equipment will you need?
Find information to help you answer these questions in Selection and Management , but above all, consult local expertise, including other farmers. Legume cover crops red clover , crimson clover, vetch , peas , beans can fix a lot of nitrogen N for subsequent crops, generally ranging from pounds per acre, depending on growing conditions.
You can usually reduce your nitrogen fertilizer inputs following a legume, but they are not very good at scavenging nitrogen that is left over after your cash crops. Legumes also help prevent erosion, support beneficial insects and pollinators, and they can increase the amount of organic matter in soil, although not as much as grasses. Legumes differ in their productivity and adaptability to soil and climatic conditions.
If a legume fits your cover crop objectives, seek additional information in the Overview of Legume Cover Crops section of Managing Cover Crops Profitably or with local expertise to identify the best ones for your conditions. Non-legume cover crops include the cereals rye , wheat , barley , oats , triticale , forage grasses annual ryegrass and broadleaf species buckwheat , mustards and brassicas , including the forage radish.
Non-legumes are most useful for scavenging nutrients, providing erosion control, suppressing weeds and producing large amounts of residue that adds soil organic matter. Plant a non-legume whenever a field has excess nutrients, particularly nitrogen. When planted as a fall cover crop, non-legumes consistently take up pounds of nitrogen per acre. If large amounts of nitrogen are left in the soil from the summer crop or due to a history of manure applications, non-legumes can scavenge upwards of pounds per acre.
Depending on your conditions—including soil residual nitrogen status—you may not be able to reduce your nitrogen fertilizer inputs for the subsequent crop, particularly in the first few years of cover cropping.
Cover crop mixtures offer the best of both worlds by combining the benefits of grasses and legumes, or using the different growth characteristics of several species to fit your needs.
Compared to pure stands of legumes or non-legumes, cocktails usually produce more overall biomass and nitrogen, tolerate adverse conditions, increase winter survival, provide ground cover, improve weed control, attract a wider range of beneficial insects and pollinators, and provide more options for use as forage. However, cocktails often cost more, can create too much residue, may be difficult to seed and generally require more complex management.
One of the biggest challenges of cover cropping is to fit cover crops into your current rotations, or to develop new rotations that take full advantage of their benefits. There may be a role for cover crops in almost all rotations, but the diversity of cropping systems precludes addressing them here. Find more information by reading Crop Rotation on Organic Farms and Managing Cover Crops Profitably , reviewing the Crop Rotations page of this topic room, and consulting local expertise.
Whether you add cover crops to your existing rotations or totally revamp your farming system, you should devote as much planning and attention to your cover crops as you do to your cash crops. Failure to do so can lead to failure of the cover crop and cause problems in other parts of your system. No-till farming or other conservation agriculture systems are good opportunities to plant cover crops.
The cover crop mulch can increase water infiltration and also improve moisture availability by preventing evaporation. Cover crop residue helps control weeds, which is especially important in organic no-till agriculture.
Plant cover crops in organic farming to provide nitrogen, manage weeds and improve soil health. In organic no-till farming , use a roller-crimper to kill the cover crop and leave the mulch on the soil surface to conserve water. Or, incorporate the cover crop into the soil sometimes called a green manure before planting your main crop.
The table below gives dry matter levels above ground residues only for some common cover crops established in late summer and early fall. The numbers were collected from cover crop plots in Southwestern Ontario.
These may not show as great an organic matter return as some of the cover crop work from the United States, however it is important to consider climatic differences and how the cover crop is incorporated into the crop rotation. But don't despair! It may be a slow process, but it's possible to improve over time. Cover crops and manure certainly help. Work to either improve or at least maintain organic matter.
If you do nothing and continue cropping, your organic matter levels will continue to drop. Building organic matter is a slow process, maintaining it is probably more realistic. For example : Soil organic matter is measured in the top 15 centimeters or to plow depth. Assuming an average residue return of 5, kilograms from the above table:. The addition of fresh organic material is important in stimulating soil biological activity.
Cover crops also help to maintain soil life by shading the soil and moderating soil conditions. Some cover crops fix nitrogen but many more require nitrogen to grow. Grass cover crops like rye and Brassicas like oilseed radish are excellent scavengers of nitrogen left behind by the main crop or from manure applications. Cover crops that take up nitrogen can help to reduce nitrogen losses due to leaching.
This reduces the potential for the contamination of shallow aquifers by nitrates. Nitrogen " catch crops " are used to prevent winter injury to perennial crops such as grapes and fruit trees. Cover crops such as rye seeded in late summer and early fall take up the excess nitrogen — preventing the perennial crop from continuing vegetative growth and encouraging hardening off for the winter. When the cover crop is killed the nutrients held in the plant tissues are returned to the soil and can be used by the following crop.
Work done by in Ontario Dr. Eric Beauchamp on cover crops and nitrogen release suggests that growers should be aware of the nitrogen release potential from their cover crop species. Oilseed radish is an excellent nitrogen scavenger but as it winterkills the tissues start to break down before the spring crop is in place and needing nitrogen. Some nitrogen losses can occur.
In contrast, ryegrass tends to hold onto the nitrogen more tightly, with the main release occurring in early to mid summer. Clovers tend to release nitrogen in early summer also. Timing of the nitrogen release may be important if growing crops like small grains, tomatoes and other fruiting vegetables. Legume cover crops can fix nitrogen for a subsequent crop.
Organic growers often include this type of cover crop in order to produce nitrogen for the rest of the crop rotation. Some cover crop species are credited with making more phosphorous available to other crops through the action of the roots.
Deep-rooted cover crops can bring nutrients up from deep in the soil profile. Some cover crop species maybe a non-host for a pest or may release materials that are toxic to the targeted pest. For example many common cover crops have been rated for their ability to support root lesion and other nematode populations see Chart Cover crops like marigolds and pearl millet do not support or do not allow the nematode to reproduce. Other cover crops like some mustards , particularly those with high glucosinilate and euricic acid levels in the plant tissue can create a "natural fumigant" through the chemical breakdown of the these materials.
That episode focused on traditional cover cropping, but there are many variations you can use in your garden. Some cover crops can require time and a little brute force to work in. Winter rye is a common option, in part because it will grow through even harsh winters.
Austrian winter peas can be much easier to work in, but they provide many of the same nutrient and soil protection benefits you may need from a cover crop.
Red clover is so resilient, you can broadcast the seed onto frozen ground. The seed will survive ongoing cold temperatures and will sprout as temperatures warm and the soil softens. This is known as frost seeding. As long as you broadcast the seeds before the first sign of weeds sprouting, the red clover will have time to germinate, grow and be ready to work into the soil before you plant your edibles after the last risk of frost has passed.
So, when is a cover crop ready to work into the soil? Jack explains that the plant is storing up nutrients right through the point at which it sets flower. The sugars produced by the plant are focused in the flower. While in that form, everything you want transferred from the flower into the soil food web is at the perfect stage.
When a flower transforms to seed, the sugars in the flower turn to starch. As a starch, the energy and nutrient benefit are no longer available to the soil. So, the ideal time to cut down a cover crop is after flowering and before the seeds set. There are nutrients stored in the foliage, flowers and roots of the weed. Option one feeds the most nutrients and organic matter directly into your soil, but it can also take more effort to mix that much material into your garden bed.
Option two can provide plenty of benefit with less physical effort. The nutrients within the foliage will still find their way into your soil once the composted material is added to your bed later.
Once you turn the plant materials into the soil, there are certain microorganisms which are triggered to go into digestion mode. They go to work to break down all that fresh organic material. If you sow seeds during this period, the seeds may actually be digested right along with the cover crop.
By the time these edamame have set seed, they are no longer as valuable as a nutrient-rich cover crop. You can still enjoy the delicious seeds, and the remaining foliage and roots would provide some benefits to your soil if you cut them back and turn them in.
Jack recommends that you allow weeks for the cover crop to be broken down by the soil food web before you sow any edible crops. Roots break down more quickly than foliage, so if you are short on time, turning in just the roots will reduce that digestion period. You will likely still see some dry plant material in the soil at that point. So how does all of this impact soil structure?
After all, most gardeners now know that it can be detrimental to break up existing soil structure, which is why a no-till approach is becoming commonly-accepted as most beneficial for a healthy soil food web and, therefore healthy soil. Vegetable crops prefer soil which has been disturbed and aerated, but tilling tends to go deeper than is beneficial.
The complex soil structure further down is left intact. Tillers tend to reach further into the soil surface, breaking up more of the structure without the benefit of all the organic material and nutrient benefit provided by the cover crop. Jack and his Stone Barns team have developed a complex cover crop system to work in tandem with crop rotation for optimal soil health. Perhaps you have limitations that prevent you from working with cover crops at all?
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