How To Build Healthy Garlic Soil

The key to building healthy garlic soil is proper management of the soil organic matter. The organic matter is made up of three parts: active, moderately stable and very stable. The active portion is the part that a garlic grower can have the most influence on. Over time, the organic matter found within the soil continually experiences gains and losses. If the amount of organic material you add to the soil exceeds the losses, organic matter levels will increase, however, if the losses exceed the gains, organic matter levels will decrease.
  

Adding Organic Material

The addition of organic amendments is the only guaranteed way to increase soil organic matter levels. Light soils that have a large amount of pore space, such as sands, tend to break down residues very quickly, making it more difficult to build up soil organic matter levels. Alternatively, heavier soils with high clay contents break down residues slowly, requiring less organic residues to maintain or increase the soil organic levels.

Soil Texture
Targets To achieve maximum aggregate stability
Sands and sandy loam
4
3
Loam and silt loam
4 to 5
4
Clay loam
4 to 5
7
Clay
4 to 6
9
Soil Organic Matter % levels for different soil textures. 


When trying to improve garlic soils, it is beneficial to use a variety of residue types, such as manure, crop residues, leaves, composts and cover crops, as these will support a diverse group of soil life.

How much organic matter your soil will need to make it "ideal" for growing garlic will depend on the soil texture and the aggregate stability target (how well your soil resists breaking down). The table above shows the organic matter targets for various soil textures in order to improve the health and productivity of the soil.

Manure

Livestock manure is an excellent source of organic matter for garlic soils. Overall, it increases the diversity and activity of organisms, and greatly improves the soil structure.

When using manure to increase to increase soil organic matter source:

  • Manure will add organic matter but also adds nutrients. Different manure sources have different nutrient amounts and grower should understand these differences to help avoid over-application.
  • The organic matter content of a manure will vary, depending on the type. Generally, more solids will be added to the soil with solid manure than with liquid manure. Solid manure from cattle (ruminants) will contain more forage parts and bedding than liquid manure. 
  • The application rate will also determine the amount of organic matter added to the soil.
  • Solid manures usually contain more lignin (forage and bedding), which will have a longer-term effect on organic matter than poultry manure without bedding.
  • Apply manure without compacting the soil.
      

Compost

Applying compost to the soil is another way of adding organic matter. Compost will supply lower amounts of available nutrients but will release them over time. The composting process partially decomposes organic matter, so the organic matter added to the soil is made up of more resistant compounds than in fresh manure. It should not be the only source of organic matter as soils benefit from fresh organic residues as well. Fresh residues will stimulate more production of the sticky material that holds soil aggregates together than compost will. Similar to manure, it is important to minimize compaction at application and to avoid excessive nutrient additions.

Composting of manure and other materials will:

  • help stabilize nutrients
  • reduce the amount to spread (volume can be reduced by 30%-60%)
  • produce a better-smelling final product

Other Organic Materials

There are a variety of other organic materials that can be applied to soil to add organic matter, such as, peat moss, alfalfa pellets, waste canola or corn meal, etc. Knowing the dry matter content and nutrient content of the material is important so that you can calculate how much to apply and to know how much organic matter is being added.

It is also important to know the carbon-to-nitrogen (C:N) ratio of the material to assess any potential impacts on nitrogen availability. When using materials that have a high C:N ratio (e.g., wood shavings) microorganisms will use soil nitrogen to breakdown the materials. This will lower the soil nitrogen levels and leave your garlic plants nitrogen deficient.

Applying Organic Materials

To achieve the maximum benefit and protect the environment, you should consider how you will apply your organic amendments to the soil. The following are good questions to ask yourself:


Should I incorporate (till-in) the material?

  • Incorporate materials with an odour immediately or as soon as possible.
  • Incorporate materials high in nitrogen as soon as possible to reduce nitrogen losses.
  • Incorporate nutrient-rich materials on sloping land or flood plains to prevent loss.
  • Leave materials that don't meet the above criteria on the soil surface to help protect the soil. Earthworms and other soil life will help break down and incorporate the material.

How much incorporation is needed?

  • Incorporating organic materials with excessive tillage will expose the soil to erosion and reduce or eliminate the benefits of the organic matter addition.
  • Depending on the material, a minimal amount of tillage is usually enough to incorporate most materials. Incorporating some of the material and leaving the rest on the surface is generally best.
  • Full inversion from plowing will leave a layer of material at plow depth that will not readily decompose and may affect water movement through the soil.

 

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Cover Crops

Growing cover crops is a common soil management practice for many garlic growers. Cover crops are an important part of a system of soil maintenance, especially on lighter soils that have lower organic matter. It is important to know the goal when planting a cover crop and to select the best one for that job.
 

Choosing a Cover Crop

There are often several cover crop options for any one goal or function. Consider your specific needs and management style to select the best cover crop for your growing system. 

Cover Crop Function
Best Choices for Cover Crops
Nitrogen production
Legumes - red clover, peas, vetch
Nitrogen scavenging
Fall uptake - oilseed radish and other brassicas, oat
Winter/spring uptake - rye, winter wheat
Weed suppression
Fast growing/shading plants - oilseed radish and other brassicas, winter rye, buckwheat
Soil structure building
Grasses - oat, barley, rye, wheat, triticale, ryegrass or fibrous root systems such as red clover
Compaction reduction
Strong tap roots that grow over time - alfalfa, sweet clover
Biomass return to soil
Fall seeded - oat, oilseed radish
Summer-seeded - millets, sorghum, sudangrass, sorghum sudan
Erosion protection
Winter rye, winter wheat, ryegrass (well-established), spring cereals seeded early
Nematode suppression

Cutlass mustard, sudans/sorghums (Sordan 79, Trudan 8,) pearl millet (CFPM 101), marigold (Crackerjack, Creole), oilseed radish (Adagio, Colonel)
Cover crop activity is variety- and nematode-specific. To get the most activity, cover crops should be weed free and may require specific handling.


Characteristics of Cover Crops

The following is information on the most commonly used cover crops. 

Grass Crops

Grasses have fine, fibrous root systems that are well suited to holding soil in place and improving soil structure. Suitable grass species for cover crops are fast growing and relatively easy to kill, either chemically, mechanically or by winter weather. Grasses do not fix any nitrogen out of the atmosphere but can accumulate large quantities from the soil.

Grasses are often referred to as either bunch grass or a spreading grass. Bunch grasses generally do not have rhizomes or stolons, just a simple root system supporting the plant. The species with rhizomes or stolons have the ability to send up new shoots from nodes on these structures, allowing the grass to spread and form a sod.

Spring Cereals

Spring cereals are well suited for late-summer and early-fall plantings. Under good growing conditions, spring cereals will produce the greatest amount of crop biomass, making them valuable for feed or ground cover. Once well established, spring cereals are relatively tolerant of frost.

Planting spring cereals in fall is not recommended because of establishment end growth. 

Winter Cereals

Winter cereals are highly versatile cover crops. They can be planted in summer and will tiller and thicken due to their need for vernalization (cold exposure) before reproduction, or they can be planted in fall for soil cover. Winter cereals will generally over-winter well, providing winter and spring erosion protection. These grasses can be used to create spring wind barriers, residue mulch or killed early to minimize residue cover at planting.

Warm-Season Grasses

Warm-season grasses such as sorghum and millet are best suited for planting into the warmer soils of late June, July and early August. They are very sensitive to frost. Root growth is extensive and the top growth lush. Be prepared to mow these grasses to keep stalks tender and prevent heading out. Do not mow closer than 15 cm (6 in.) to ensure regrowth. Some nitrogen may have to be applied to achieve optimal growth.

Legume Broadleaf Crops

Legume cover crops can fix nitrogen from the air, supplying nitrogen to the succeeding crop. Legumes will take up residual soil nitrogen or nitrogen from manure applications. They are approximately 80% as effective as non-legumes in nitrogen uptake from soil. Legumes also protect the soil from erosion and add organic matter. The amount of nitrogen fixed varies between species, although generally, more top growth equals more nitrogen fixed. Some legume species such as alfalfa and sweet clover have aggressive tap roots that can break up subsoil compaction, but this requires more than one year's growth.

Non-Legume Broadleaf Crops

These broadleaf crops cannot fix nitrogen out of the air but may absorb large quantities from the soil. Most of these crops are not winter-hardy, so additional control measures are not normally required. They should not be allowed to go to seed, as the volunteer seed can become a significant weed problem.

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