Choosing a green manure mix

Summary

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suitable for your use
nor as advice.
Your situation is different from anyone else's. Make informed decisions and if necessary get advice

For example,

You may have a hard pan you want to break up. That will make deep roots more important.
You may want to get nutrients or moisture from deep in the soil. This will also make deep roots more important.
You may want to overcome a weed problem. That will make a dense canopy more important.
Your soil may be deficient in nitrogen and that will make a legume cover crop more desirable.

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What this means

If your aim is	You might choose this sort of mix
Weed control	Fast-growing, large-leaved plants that shade the soil surface and compete effectively plus produce a lot of organic matter. Sown heavily, they will provide even more competition for weeds and do it sooner
Increased soil nutrients	Fertilizer, legumes and plants that produce a lot of green material You might turn them in when at least 10% of the legumes are in flower
Fewer problems with pests & diseases	Plants that do not host the pest plus plants that attack the problem such as by hosting predators of the pest or by using Allelopathy - producing substances hostile to the pest
Improving soil structure	Plants high in long-chain molecules, such as cereals and other grasses that produce lots of straw. You might also choose a mix of rooting types (fibrous roots and tap roots) and rooting depths (to spread the benefits throughout the soil)
Breaking a hard pan	Plants with tough, deep roots. Again, you might choose a mix of rooting types (fibrous roots and tap roots) and rooting depths (to open up all the levels and spread the benefits throughout the soil)
Reducing susceptibility to drought	Plants that store a lot of moisture in the soil. Plants that improve infiltration and increase water holding capacity such as by increasing pore space and by improving soil structure. Again, you might choose a mix of rooting types (fibrous roots and tap roots) and rooting depths (to open up all the levels and spread the benefits throughout the soil)
Storing moisture for a following crop with high moisture needs or when a dry season is expected	Plants that store a lot of moisture in the soil. Plants that improve infiltration and increase water holding capacity such as by increasing pore space and by improving soil structure. Again, you might choose a mix of rooting types (fibrous roots and tap roots) and rooting depths (to open up all the levels and spread the benefits throughout the soil)
Soil protection in later tillage, harvest or sowing operations	Plants that improve soil structure. Plants with bulky root systems, particularly close to the surface. Plants with a high level of organic matter on the surface. However, be aware that too much organic matter can clog tillage machinery that is not designed for trash working.
Increasing nitrogen	Lots of legumes and few grasses You might turn it in at the optimal time (your local advisor could help here) to maximize the benefits.

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Using this

Some other factors to consider are

Rate of growth: When you undersow, you may prefer a slower-growing plant so that it doesn't compete strongly with the crop it is growing under. If you want the green manure to swamp weeds and it is growing on its own, not under a crop, you will probably choose a fast-growing variety
Height and width: Tall green manures shade out weeds that grow tall, such as wild oats. Wide ones or broad-leaved ones can shade the whole ground surface quickly. A combination of tall and wide may swamp a major weed problem
Season of growth: Sometimes you can time a green manure to self-destruct, to die off just before you sow the next crop. Choose a variety that runs through its cycle in the time you have available or that dies off at a certain time of year or under certain circumstances. For example many plants such as soybeans flower when daylength reaches a certain level. This also triggers them to complete their annual cycle and this includes dying off. Some plants such as buckwheat (very frost sensitive) and sesame will be killed by frost. Look at your conditions and choose to suit
Legume or not:
- If your aim is nitrogen you will swing towards more legumes and particularly to those that fix the most nitrogen. Your adviser should be able to tell you which varieties fix most nitrogen under your conditions
- If your aim is soil structure improvement, you will choose a mix with more cereals and other plants high in long-chain molecules and fewer legumes. Legumes may encourage an increase in microbe numbers and so an increase in demand for the carbohydrates that your soils needs as "glue" for its crumbs
Bulk produced: Corn (maize), some of the hybrid forage plants plus some of the vetches, some cereals and others will give a lot of bulk. Bulk, particularly grassy bulk, is good for soil structure building and for boosting biological activity. Again, your advisor should be able to help
Rooting type and depth: If the rooting type or depth is different from the crops you grow, you will get nutrients and moisture from a greater volume of soil
Nutrient harvesting pattern: If the plant type, the rooting type or depth is different from the crops you grow, you will probably get different nutrients and from a greater volume of soil
Compatibility with your crops and machinery: Often the more different the green manure is to your crops, the better it will be for your soil. But it may be no use if you don't have and can't get access to any specific machinery you need to handle it
Availability and cost of seed: As always, cost is important and if it is not economical to grow it, it is not much use trying to grow it
Suitability to your area and growing conditions: If you can't get it or it is unsuited to your area, it is not much use trying to grow it
Pests and diseases: Will it host any particular type of disease or pest? Will it help to reduce any particular type of disease or pest?
Storing moisture: for a following crop with high moisture needs or when a dry season is expected. Plants that store a lot of moisture in the soil. Plants that improve infiltration and increase water holding capacity such as by increasing pore space and by improving soil structure. Again, you might choose a mix of rooting types (fibrous roots and tap roots) and rooting depths (to open up all the levels and spread the benefits throughout the soil)

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Taking this further

Timing can be a key factor in getting the most out of a green manure. Sometimes the simplest approach to growing a good green manure is to just mix up any seed you have on hand and sow it. This can be better because it allows you to sow the green manure right now, and thus to take advantage of the extra time it spends producing benefits.

A green manure that gets away because it is in the ground and growing is bringing you benefits, even if they are not the absolute perfect ones. So, often it is better to put a green manure in when you can, rather than waiting until you have the ideal mix of plants.

Plus there are ways to get similar benefits with a pasture in Return a third to the soil

A suitable next step might be:
Decide the key benefits you want from a green manure and begin researching and selecting suitable plants for the mix.

If you are looking at a printed version of this page and you would like to visit it on the internet and get a stack of other info that may assist you, the full web address is
http://www.OrganicExchange.com.au/all/fcmmgm01.htm

Related info:

Green manures

Green manures in orchards and vineyards

Green manures under sweet corn or tomatoes

Beat pests by using advantage

Niche

Do weeds come to heal the soil?

Return a third to the soil

Using SWOT to beat a major weed

Understanding the causes of weed problems

Weed control without chemicals

SWOT analysis to boost profit

Ground cover

Allelopathy

Squeezing a green manure in

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