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COG Organic Field Crop Handbook


1.4 Manure Management and Composting


Manure is a valuable resource on an organic farm. Livestock are inefficient in extracting nutrients from feedstuffs; typically, 75-90 per cent of major nutrients that are fed to livestock pass directly through the animal into the manure. The extent to which these nutrients can be returned to the soil and made available to subsequent crops will depend on the way the manure is stored and handled.

Organic farmers rarely apply raw manure to their fields; they use composted manure. The composting process imitates the decomposition of organic matter on the surface layer of the soil to turn raw manure into humus. Composted manure slowly releases its nutrients into the soil, enhancing the soil microbiological life, whereas the highly-soluble nutrients in raw manure are quickly leached away and can damage both the soil biology and the crop.

Standards for organic production allow the use of manure that has been stacked and aged for at least six months unless it has been brought in from off the farm, in which case composting is required. Raw manure can also be used but only on perennials or crops not for human consumption. Raw and aged manure should be spread when the soil is warm enough (i.e., when plants are growing) for the micro-organisms to be active.



1. Storage of solid manure

As composted manure is the primary source of fertilizer for an organic farm, care should be taken that nutrients are not lost from the raw manure. Losses of nitrogen can occur as soon as the urine hits the concrete under the animal. Therefore use generous amounts of bedding to soak up liquid wastes and to provide a carbon source for composting the manure. Considerable losses, especially of potassium, can occur as a result of leaching and runoff during storage. This is not only a serious pollution problem, but also a waste of valuable nutrients.



Plans and information regarding manure storage and handling are available from your provincial department of agriculture. The following was extracted from the Ontario Ministry of Agriculture and Food's factsheet #85-052.

Solid manure storage systems should contain three parts:

1. an enclosed area, on a sloped cement pad, preferably under a cover;

2. a perimeter curb to contain and direct the liquids to the low end; and

3. a pit to contain the liquid runoff until it can be pumped and spread on the land.

Locate the manure storage in such a way as to allow for future expansion of the livestock operation. Also, do not block livestock or vehicle flow. Don’t locate the storage within 30 metres (100 feet) of a well or excavate into ground with a high water table. Adjacent existing tile drains should be blocked off. Check your local zoning by-law to ensure that you comply with any municipal requirements. The Agricultural Code of Practice contains information on siting manure storages. Minimum separation distances are provided for distances to neighbors' houses, lot lines and roads.



2. Composting

Composting is the process of decomposing organic matter, whether manure, crop residue or municipal wastes, by a mixed microbial population in a warm, moist aerobic environment. The organic matter is decomposed by the successive action of bacteria, fungi and actinomycetes. In the final stages of decomposition, redworms (or manure worms) assist in the production of stable humus which is the final stage of the composting process.

Young compost that has not reached the stable humus stage, will be high in effective humus and available nutrients but low in stable, colloidal humus. Mature compost, which is close to the final decomposition stage, will have a higher proportion of stable humus, and will be considerably reduced in bulk. Compost at various stages, from young to fully-aged, may be used according to the needs of the soil and the crop.

The nutritive and other benefits of the material will depend very much on the source materials, the conditions under which it was made and the maturity of the compost when it is applied. Young or medium compost will encourage biological activity in the soil. Mature compost will make a greater contribution to soil organic matter levels and soil structure. In general, however, the process results in a net improvement to soil fertility, compared to an application of manure. For example, a field application of 30 tonnes of farmyard manure might supply 3 tonnes of stable humus after a 4-5 year breakdown period. The same material applied as about 22 tonnes of young to medium compost supplies about 4 tonnes, or applied as 15 tonnes of mature compost supplies 5 tonnes of stable humus after the same period.


Advantages of composting

The additional storage and handling requirements involved in the production of compost are offset by the advantages of compost to the organic farmer. These advantages are as follows:

1. Compost supports and encourages the growth of earthworms, bacteria, fungi and other micro-organisms and adds organic matter to the soil. In this way, compost improves the biological, physical and chemical properties of the soil. In comparison, raw manure also adds organic matter but can cause a period of disruption to the soil life by creating an imbalance of nutrients.

2. Manure is acidic; composting increases the pH of the material which can help make the soil a better environment for plant growth.

3. The composting process stabilizes the volatile nitrogen of raw manure into large protein particles and thereby reduces losses.

4. Compost returns nitrogen, phosphorous, potassium, calcium, magnesium and the micronutrients back to the soil. Amounts vary, but a well-prepared mature compost may contain 7.5-15 kg/t (15-30 lbs/ton) N, 2.5-5 kg/t (5-10 lbs/ton) P2O5 and 15kg/t (30 lbs/ton) K2O.

5. The nutrients from mature compost are released to the plants slowly and steadily. The benefits will last for more than one season.

6. The nature of the material and the fungal/actinomycete mycelia contained in the compost and stimulated in the soil by its application help to bind the soil particles into crumbs, greatly increasing the stability of the soil to wind and water erosion.

7. Compost has a lower density, 400-600 kg/m3 compared with typical manure that may be 400-1000 kg/m3. Handling is easier and fewer trips are made to the field.

8. Odor is reduced.

9. Weed seeds are reduced by a combination of factors including the heat of the compost pile, rotting and premature germination. (Any weeds found growing on the pile should be destroyed before they go to seed.)

10. Fly eggs are killed and plant and animal pathogens are reduced if the high heat method of composting is used to raise the temperature of the pile to 60C.

11. Raw manure is one of the primary culprits for pollution of the waterways, and odor from farms is considered an increasing problem in the rural areas. Composting raw manure reduces these problems.


Making good compost depends on having the proper sources of nutrients with a balance of carbon and nitrogen, keeping the pile of compost moist and making sure that there is adequate aeration. The compost pile can heat up to 60-70C due to the microbial activity. However, high temperatures will result in substantial losses of nitrogen in the form of ammonia gas. Farmers with many years experience at compost-making recommend that temperatures are kept below 50C to avoid overheating and nutrient losses.


Materials to compost

The most commonly used materials for the compost pile are manure mixed with livestock bedding. When the bedding (which is predominantly carbon) is mixed with the raw manure (which is an excellent source of nitrogen), you achieve the balance of carbon to nitrogen (25-35:1) needed to begin the composting process.


[Photo 4.2: Compost pile]

Bedding materials vary in their carbon:nitrogen (C:N) ratio from about 80:1 in straw to 200:1 or more in sawdust or shavings. Bedding with a high content of wasted hay, typical for sheep pens, will have a lower C:N ratio. If the bedding:manure ratio is high, and the manure is very dry as with horse operations, it might be beneficial to water the material with a high N additive such as liquid manure imported from a hog operation. In practice, this is difficult to do.

Provided that it contains no hazardous substances and the correct C:N and moisture balance can be maintained, virtually any organic material can be composted. If any of the following can be obtained without transportation expenses, add them to your compost pile -- sawdust, nursery wastes, fruit and vegetable residue from processing plants, feathers, grass and lawn clippings, vegetable market wastes, garden wastes, leaves, wood shavings and even seaweed. But, before using such materials, satisfy yourself that they are uncontaminated by heavy metals or others toxins.

Adding clay soil is also a good idea. The clay will help reduce nitrogen losses by holding any liberated ammonia within the heap until the micro-organisms can stabilize the volatile nitrogen.


[Table 2]

Equipment needed

The unique conditions on each farm means that giving hard and fast recipes for successful composting is not a good idea. Every farmer should be prepared to experiment with materials and techniques. The following methods work successfully for many farmers and are offered here as guidelines.

Use a front end loader to remove the solid manure from where it is stored and to load the manure spreader. The manure spreader should be a "power-take-off" type so that it can discharge its load while parked.


Building a windrow

The site chosen for building the compost piles or windrows should not be near a waterway or tile drains. Ideally, there should be a way to retain the liquids that will leach out of the pile and seep into the soil if the pile becomes too wet when rainfall is high. This can be done if the site selected is on a slight slope, with a receptor pit to catch the run-off. Otherwise, use level land and do not use the same place each year. Heavy clay soil is ideal because it prevents any leachate from reaching the water table.

The tractor pulls the spreader, parks and unloads the manure through the beaters which shred the manure and add air as the pile is being built. The spreader is then pulled ahead about 1 metre (3 feet) and the procedure is repeated. This method is used to form the windrow and for the turning of the pile.


[photo 4.3: Building a windrow]

Windrows created from cattle manure should be made about 1.25 metres (4 feet) high and 2-2.5 metres (6-8 feet) wide. Horse manure can overheat so windrows should only be 0.5 metre (1.5 feet) high for efficient cooling. However, because of the large surface area, shallow windrows can dry out quickly in drought conditions or suffer from leaching in heavy rainfall; both conditions require management correction. It is more practical to layer horse manure as it comes out of the barn and add further layers every few days. Hog manure is very dense and large quantities of straw need to be added; otherwise it will tend to decompose anaerobically.

Any liquid manure that seeps out of the windrow should be pumped back onto the drier materials and allowed to percolate through.

Manure from loose-housing bedding packs may overheat due to the large straw:manure ratio. Limiting the amount of air in the pile will prevent this. This can be done by using a dump trailer to create windrows instead of a manure spreader. Air can also be expelled by tramping down on the pile.



Microbial activity generates heat and the pile can warm to about 60-70C within one week if the hot composting method is used; then decrease over a few weeks. To keep the temperature at 40-50C and reduce the loss of nutrients, manure should be stored so that some decomposition takes place before it is put into windrows. Adding soil will also keep the temperature lower. Overheating stops microbial action and causes excessive nutrient loss, hence temperatures over 60C should be avoided. Temperatures above 55C may be desirable if there are disease problems in the barn. The temperature in the pile can be monitored with a temperature probe 0.5-1 metre (2-3) feet long and corrective action taken if necessary. Overheating may indicate deficient moisture levels, too much N or too much C. In cold weather, warmer conditions can be maintained by covering the pile with black plastic. This will also prevent nutrient loss by leaching.


Turning the pile

Turning the pile is not needed if optimum conditions are met. Some people advocate turning the pile to speed the decomposition process and obtain mature compost in about 10 weeks. This, however, will also likely cause high nutrient losses; turning may be required to improve conditions. The simplest method is to use a front-end loader to push the piles over and reform them. Using the manure spreader will do a better job of remixing the compost. Commercial-brand compost turners are available but are not essential for making good compost.


Moisture and aeration

The moisture content of the pile will often determine if turning is necessary; it should be about 50 per cent. If a moisture meter is not available this can be tested by squeezing the material in your hand -- if it glistens and small moisture droplets appear, the moisture content is sufficient. Beginners at composting tend to have piles that are either too dry or too wet.

If the pile is too moist, water replaces the air in the pile leading to anaerobic conditions. Turning the pile to reintroduce air changes the pile from an anaerobic to an aerobic system. The smell of the compost should be your guide; it should be sweet-smelling. An unpleasant smell indicates that anaerobic decomposition is taking place. If you are in a wet area, either build a roof over the pile or cover the pile with straw or black plastic to avoid leaching of potash and trace elements.

On the other hand, if the pile is too dry, biological activity will cease. In this case, water will have to be added. This is best done when the compost is being turned.


Mineral additions

Mineral additions to the compost, in the form of powdered rock, can be useful. Rock phosphate is often added to the gutter in the barn to reduce immediate nitrogen loss and manure odor. It has the added benefit of increasing phosphorus reserves and encouraging nitrogen fixing, blue-green algae. Clay minerals such as bentonite and montmorillonite are added at any time. They trap liberated ammonia, increase the cation-exchange capacity of the compost and thus make the nutrients more available to the crops and hasten the formation of the clay-humus complex. Small amounts of kelp products or other trace element sources can be added to the compost directly.


Application of compost

Compost piles or windrows take about three months to mature and should be black-brown in appearance with a crumbly texture. Ideally, it should be spread as soon as possible after it is finished. The longer it sits, the more it mineralizes and loses available nutrients. The presence of weeds on the pile indicate that mineralization is occurring and that the compost should have already been applied to the land. Application rates vary depending on the crops, the needs of the soil and the age of the compost but an application of at least 15 t/ha is usually recommended at some point in the rotation.

Applying compost to crop land before spring planting may encourage the growth of weeds. If composting is started just after seeding it should be ready to apply to stubble fields after harvest. Incorporate the compost lightly into the top 10 cm of the soil; if any deeper, much of the nutrient gains and soil conditioning value will be wasted. Cover crops can be seeded immediately after applying the compost. Compost should, however, be applied to growing plants whenever possible; it will not burn them and the nutrients are readily utilized.

As mentioned, young compost is high in soluble nutrients, whereas mature humus has a higher proportion of stable humus. This will determine where you should apply your compost. Crops that are nutrient-demanding, such as winter wheat and corn, should receive applications of young compost. Mature compost applied to these crops will have little immediate benefit. During the transition period some compost should be applied to all the fields to stimulate microbial activity.



3. Liquid manure systems

Many pig, poultry and dairy operations have slurry or liquid manure systems. Raw slurry can lead to serious pollution problems, by fouling waterways and disrupting the flora and fauna in the soil.

A form of composting can be done with liquid slurry by microaerating the slurry in the tanks. The aim of microaeration is to reduce nutrient loss from volatilization which occurs when nitrogen changes into gaseous ammonia. The advantage of this microaeration process is that it cuts down on odors from anaerobic conditions which result in the formation of methane and hydrogen sulphide. This significantly reduces weed seed and pathogens and also reduces nitrogen loss because the nitrogen is converted from ammonia to bacterial protein -- a stable form of nitrogen. Application of liquid manure is most beneficial if applied onto green manure crops in late summer or fall. This is when the ground is dry and the green manure crop can efficiently tie up the nutrients.

The liquid manure systems in use on two organic farms are given here as examples.


Example 1: Liquid runoff from the manure storage area and yard scrapings go into 2 tanks, 15 m and 7.5 m in diameter and 3 m high. An original covering of straw has developed into a living mulch which continually replenishes itself. The cover is necessary to prevent ammonia loss and is a source of carbon. Aeration is achieved with a small submersible diffusion pump, with a 4-hp, 3400-rpm (3 kw) electric motor. The pump is placed at the bottom of the slurry tank where it creates a vacuum, sucks air down a hose and distributes it by agitation throughout the slurry in the form of fine air bubbles. The unit is operated on a timer, running a few minutes every hour depending on the volume and consistency. To begin the process, a water-soluble carbon source such as liquid molasses can be added.

The liquid manure is applied at a rate of 22,000-33,6000L/ha (2000-3000 gal/ac) on winter cereal stubble before seeding oilradish on standing red clover for plowdown, pastures and permanent hay fields.


Example 2: A storage tank, 18.3 m by 3 m deep, is used for six months' storage of liquid manure and yard scrapings mixed with some straw. The microaeration unit is the same submersible diffusion pump used in example 1. A thick crust develops on the top of the tank. The aerator agitator is turned on in March and runs for 6-8 weeks before field application. The liquid manure is applied at 22,000-33,600 L/ha (2000-3000 gal/ac) to the corn fields prior to planting in spring or 11,000-22,000 L/ha (1000-2000 gal/ac) to hay fields or mixed grain crops.



Further reading

Andres, L., "Liquid manure aeration", EFAO newsletter, Summer 1991, pp. 10-12

Lampkin, N., Organic Farming, Farming Press, Ipswich, England, 1990

Gershuny G. & Smillie J., The Soul of Soil, Gaia Services, Erle, Que., 1986

Gray, K.R. & Biddlestone, A.J., "The Composting of Agricultural Wastes", in Biological Husbandry, B. Stonehouse (ed.), 1981


On-Farm Composting, Farming for the Future booklet, Land Stewardship Project, Lewiston, MN, 1991, 8 pp.



Copyright 1992 Canadian Organic Growers. Inc

Reprinted with permission. All rights reserved.


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