Building a Healthy Soil
The key to success in building a healthy soil is effective management of the soil organic matter. As discussed earlier, the organic matter is made up of three parts: active, moderately stable and very stable. The active portion is the part that management can have the most influence on. The organic matter pool continually experiences gains and losses. If the addition of organic material to the soil exceeds the losses, organic matter levels increase; if the losses exceed the gains, organic matter levels will decrease. Table 8-5, Effects of Different Management Practices on Gains and Losses of Organic Matter, lists a number of practices and their effect on soil organic matter.
It is important to keep in mind that soil and its management are part of the overall crop production system. Soil is also a central part of the agricultural ecosystem. Changes made in the crop production system over the years have far-reaching effects on all other systems. When taking steps to improve soil quality, think about the changes being made and how they may affect other components of the crop production system.
The addition of organic residues is the only sure way to increase soil organic matter levels. Soils that are well aerated, such as sands, break down residues quickly, making it more difficult to build soil organic matter (SOM) levels. Soils with higher clay contents break down residues more slowly, requiring less organic residues to maintain or increase the SOM level.
Providing a variety of residue types, such as manure, crop residues, composts, cover crops, biosolids, etc, will support a diverse group of soil life. Determining the right organic matter level for a soil depends on the soil texture and the aggregate stability target. Table 8-6, Soil Organic Matter Percentage Levels for Different Soil Textures,shows organic matter targets for various soil textures. The targets indicate soil organic matter percentages to aim for to improve soil productivity. The levels for maximum aggregate stability were derived from research (Health of Our Soils Report, AAFC Ottawa) to determine what levels of SOM would give aggregates the most resistance to the erosive forces of water.
Livestock manure is an excellent source of organic matter for the soil. Applying manure to the soil will provide other benefits, such as a greater diversity and activity of organisms and better soil structure. See Table 8-7, Effects of 11 Years of Manure Additions on Organic Matter Levels.
Consider the following when using manure as an organic matter source:
- Manure will add organic matter but also adds nutrients. Use the information in Table 9-8, Typical Amounts of Available Nitrogen, Phosphate and Potash From Different Types of Organic Nutrient Sources, to help avoid over-application of nutrients that could lead to loss into the environment.
- 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. See Table 9-9 for a listing of typical manure types and their dry matter levels.
- 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.
|Application Rate (tons/acre/year)|
|None||10 Tons||20 Tons||30 Tons|
|Organic Matter (%)||
|Source: Building Soils for Better Crops, (Magdoff) SARE Outreach, www.sare.org|
Note: The original organic matter level was 5.2%. The study was conducted on continuous corn silage on a clay soil adding dairy manure. The manure application also improved soil aggregation and the amount of pore space.
Applying compost to the soil is another way of adding organic matter. Compost will supply relatively low amounts of readily available nutrients but will release nutrients 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 residues as well. Fresh residues will likely stimulate more production of the sticky material that holds 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
Sewage biosolids, like manure, are another source of organic matter and nutrients for the farm. As a regulated material, sewage biosolids are monitored to address environmental quality, food safety and human health issues. Sewage biosolids are available for application on agricultural land in many parts of the province. The application rate for a field is based on the soil test results for the field and crop nutrient requirements. The amount of organic matter applied will depend on the rate and type of biosolid.
When applying sewage biosolids, similar to any land operation, ensure the soil is fit, to avoid soil compaction. Work with the applicator to ensure the timing fits with your crop production system.
Visit the OMAFRA website at www.ontario.ca/crops to learn more about biosolids.
Other Agricultural and Non-Agricultural Source Materials
There are a variety of other organic materials that can be applied to soil to add organic matter. Knowing the dry matter content and nutrient content of the material will help calculate application rates and provide an indication of how much organic matter is being added. It is also important to know the carbon-to-nitrogen ratio of the material to assess any potential impacts on nitrogen availability. When calculating the rate of application, consider the physical amount applied and the implications for the rest of the cropping system.
Applying Organic Materials to the Land
The application of organic materials to the land is done to increase organic matter levels and also to add nutrients to the soil. To achieve the maximum benefit and protect the environment, consider how they are applied.
Do I have to incorporate the material?
- Incorporate materials with an odour immediately or as soon as possible.
- Incorporate materials containing ammonium nitrogen as soon as possible to reduce nitrogen losses.
- A certificate of approval or regulation may require incorporation.
- 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 tillage/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 will be sufficient to incorporate most materials. Incorporating some of the material and leaving the rest on the surface is generally best.
- Full inversion mouldboard plowing will leave a layer of material at plow depth that will not readily decompose and may affect water movement through the soil.
Growing cover crops is a common soil management practice for many Ontario farmers. There are a lot of good reasons to grow cover crops but it is often hard to put a dollar value on the return from growing them. Cover crops are an important part of a system of soil maintenance - particularly important on the lighter soils with lower organic-matter or on fields with short rotations and little return of crop residue or manure. It is important to know the goal when planting a cover crop and to select the best one for that job. Table 8-8, Matching Cover Crop Choices to Function, looks at the various reasons for including cover crops in a rotation and the potential cover crops that best meet those goals.
Choosing a Cover Crop
There are often several cover crop options for any one goal or function. Consider specific farm needs and management style to select the best cover crop for a farming system. Table 8-9, Choosing a Cover Crop, gives examples of the questions that should be posed when considering a particular cover crop.
Characteristics of Cover Crops
Information on the most commonly used cover crops is provided in Table 8-10, Characteristics of Cover Crops Grown in Ontario.
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 accu-mulate 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 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; do not attempt to establish them late in the fall, as the growth will be disappointing.
Winter cereals are highly versatile cover crops. They can be planted in summer and will tiller and thicken due to their need for vernalization or a cold treatment 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 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 pro-tect 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 con-trol measures are not normally required. They should not be allowed to go to seed, as the volunteer seed can become a significant weed problem.
New and Emerging Cover Crops
Every year new crops are tried as cover crops. Often these species are from different parts of the globe and may not be well adapted to Ontario growing conditions. For more information on new and well-known cover crop species, see the OMAFRA website at www.ontario.ca/crops or the Midwest Cover Crop Council at www.mccc.msu.edu.
Crop rotation is an integral part of the crop production system. The greatest benefit to a good crop rotation is increased yields. A well-planned crop rotation will help with insect and disease control and aid in maintaining or improving soil structure and organic matter levels. Using a variety of crops can reduce weed pressures, spread the workload, protect against soil erosion and reduce risk. Legume crops in the rotation have become more valuable with the increased cost of nitrogen. Research and experience have proven that a good crop rotation will provide more consistent yields, build soil structure and increase profit potential.
|Species||Building Soil Structure||Weed Suppression||Grazing Potential||Quick Growth||Root Type|
|Spring cereals||Good||Good||Very good||Very fast||Fibrous|
|Winter wheat||Good||Good||Very good||Fast||Fibrous|
|Winter rye||Very good||Very good||Very good||Very fast||Fibrous|
|Sorghum sudan||Good||Good/Fair||Very good||Very fast||Coarse fibrous|
|Ryegrass||Very good||Fair/poor||Good||Slow to establish||Fibrous|
Broadleaves - Legumes
|Hairy vetch||Good||Fair/poor||C2||Slow to establish||Tap with secondary fibrous|
|Red clover||Good||Fair||C2||Slow to establish||Weak tap/ fibrous|
|Sweet clover||Good||Fair||C2||Slow to establish||Strong tap|
|Field peas||Poor||Good/fair||C2||Fast||Weak tap/fibrous|
Broadleaves - Non-Legume
|Buckwheat||Poor||Very good||Poor||Fast||Weak tap/fibrous|
|Oilseed radish||Fair||Very good||Good||Fast||Moderate tap|
|Other brassicas, i.e., forage radish||Fair||Very good||Good||Fast||Moderate tap|
|100 kg/ha = 90 lb/acre|
|1 Oilseed radish, buckwheat and the grasses do not fix nitrogen from the air but are scavengers of nitrogen from soil and manure applications.
2 Clover legumes make good feed or grazing, however feeding pure legumes can cause bloat.
The basic rule of crop rotation is that a crop should never follow itself. Continuous cropping of any crop will result in the build-up of diseases and insects specific to that crop, and cause a reduction in crop yields. The more often the same crop has been grown in the field in the past, the greater this impact will be. For example, the practice of growing two or more years of soybeans is becoming increasingly common. Perhaps the greatest impact of back-to-back years of soybeans has been the accelerated spread of soybean cyst nematode (SCN). The increased number of years of soybeans in the rotation is also increasing the susceptibility of Ontario's soils to erosion.
In fact, the structure of soils in corn-soybean rotations can actually be poorer than that of soils that are in continuous corn production. For example, a recent study found that erosion following an intense June rainstorm in first-year corn following 2 years of soybeans was twice as high as following corn, wheat underseeded with red clover or alfalfa. Relatively poor soil structure after 2 years of soybeans not only increased erosion susceptibility but also reduced soil porosity, which resulted in less rainwater infiltration. Reduced rainwater infiltration increases the likelihood of erosion, yield-reducing water ponding and/or soil moisture deficits; all of these effects can reduce crop productivity, particularly in years with weather-related stress.
The greatest benefit from crop rotation comes when crops grown in sequence are in totally different families. The two families are grasses (monocots) and broad-leaves (dicots). The grasses include forages grasses, cereals and corn. Soybeans, white beans, alfalfa and canola are examples of broadleaf crops. Table 8-11, Corn Yield Response to Rotation, provides an example of the type of response to crop rotation that is possible.
The fibrous root systems of cereal and forage crops (including red clover) are excellent for building soil structure. Studies have shown that the benefits of including wheat, and especially wheat plus red clover, may persist beyond just the following year. Underseeding red clover into wheat resulted in yield increases every year for 3 consecutive years compared to when red clover was not included in 4-year rotation systems.
In choosing which crop to grow, consider the economics of the entire rotation instead of a single crop in isolation.
Also, be aware of any potential insect or disease problems that could affect crops later in the rotation. Cover crops in the rotation may also have an impact on diseases and pests, either positive or negative.
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