Animal manures have long been an important input into organic and biodynamic growing systems. They still have a major role to play, as a compost ingredient and accelerator, a relatively plentiful and cheap source of organic matter, and for their nutrient content. Organic growers can demonstrate local sustainability by recycling the resource of animal manures in their area. It is much more difficult to design sustainable agricultural systems without animals, and they play a vital role in establishing the farm as an ‘organism’. The ‘organism’ concept was the origin of the term ‘organic’, and the first people to use it envisaged an essential role for animals as converters of otherwise unused harvests, weed controllers and soil improvers.

Certified organic farmers are however severely restricted by organic standards, with respect to total quantities per hectare over time and manure management. Though the press was quick to make assumptions when a well-known juice manufacturer had a contamination issue, this was proven to originate from conventional sources, not organic growers. Organic growers believe that the restriction that standards place upon feeding of any manure or animal waste back to other animals that has ensured that, even to this time, no animal born and bred on an organic farm has contracted BSE.

Standards issues and animal manure

Whereas conventional growers can use raw manure willy-nilly, organic growers are subject to surveillance and monitoring from their certifier, especially with regard to the following:

• The source of the manure and the potential for contamination (monitored by analysis if necessary)
• The total quantity applied over time (tonnes per hectare)
• Composting systems (ingredients, temperature, moisture, aeration, runoff, quality of the final product – also subject to monitoring if necessary)

The quantities of nutrients applied in manures over time and the justification for this (soil analysis, harvest losses, stage of soil development etc)

The international standards (IFOAM and CODEX), national standards (AQIS-administered National Standard for Organic and Bio-Dynamic Agriculture, NOP, JAS etc) and certifier standards (BFA, NASAA) all place limitations upon how animal manure is utilized.

Design of the nutrition program

Animal manures should be used in association with organic management practices such as green manure, crop rotation, careful cultivation and irrigation, use of mulches and soil cover. The status of soil nutrition and changes over time is ideally monitored by soil analysis [link to soil analysis pages?] Other nutrient sources should also be used to augment manures. These may include rock dust fertilizers, seaweed and fish products, humic acid, animal byproducts (whey, blood, bone, etc), and vegetable sources of organic matter. Manure is rarely adequate on its own, because it is seldom possible to select manures that provide a balanced fertility over along time frame. Although, as a generalization, it could be claimed that manure is a reasonably well-balanced fertiliser, the selective removal of nutrients by the crop or by leaching may eventually lead to soil imbalance.

Composting prior to use

All animal manures, from both certified and uncertified sources, must be composted prior to use on certified land. An exception to this is provided where manure comes from normal stocking practices.

Quantity limitations

Additions of around 15-20T/Ha per annum are generally considered acceptable for composted manure. This may vary depending upon the level of production obtained. For instance higher quantities may be justified in intensive greenhouse production.

The ideal is for the volume of manure added over the longer term (10+ years) to be not more than the quantity supplied had the same area been stocked with animals.

Mulch

Materials applied to the soil surface as mulch do not require composting prior to use, except where they come into direct contact with the edible plant parts, in which case only organically certified mulches are allowed. Growers should consult their certifiers standard to identify time restrictions between applying un-composted slurries or manures and planting of organic crops.

Animal manure slurry and manure teas

Slurry imported from outside the farm requires permission from the certifier. Slurry, imported or produced on farm, should be aerobically digested prior to application, unless followed by two consecutive green manure crops. The use of liquid preparations should be part of a longer-term soil building strategy, and not purely a source of soluble nutrients.

Environmental management

Organic farms must contain or restrict off farm contamination and the quality of run off water is a major feature of this obligation. Concentrated animal manure has the potential to damage stream ecology.

Food safety requirements

All organic standards include the general obligation that application of manures, animal products and slurries be carefully managed to prevent food safety risks for edible crops.

Stocking practices for livestock

Standards prevent high stocking rates being used to concentrate manures over long periods, but do not prohibit a short period of high stocking immediately prior to cultivation. In fact this practice is a vital weed control strategy for many croppers, with fertility from manure as a side benefit. Stocking rates should be linked to local climatic, fodder production on farm, stock health, nutrient condition of pastures (and stock), and impact on the environment.

Feeding animal manure

The feeding of animal manures to livestock is completely prohibited, regardless of any treatments such as drying.

Commercial products

Many organic growers collect (or have delivered) manures from local sources and compost them on-farm. For growers unable to do this themselves, there are many commercial products available.

Concentrated animal manure products

Pelletised or granulated composted chicken manure is widely available under various different brand names. These products are generally permitted as part of overall fertility program. Such products are concentrated because they have been composted, but also because they are generally heated and compressed into the pellet. Many of these products have added urea or other nutrients that are not acceptable in certified organic production. Even certified products may also be available in similar formulations that are not permitted, so always look for the certification label. Uncertified products may be used at the growers risk.

Composted manures

Composted manure is available from many sources. Because of the bulkiness of these products they are generally available locally, rather than via national distribution. Pig manure is particularly suited to this use, as it comes as slurry suitable for mixing with bulky waste products. Cattle manure from feedlots and chicken manure is also available. These products vary considerable with respect to organic matter content, nutrition, homogeneity (indicates degree of composting) and consistency between loads. Certified product is preferable because growers must take the full risk when using uncertified product. An example of certified nationally distributed pig manure compost is the ‘Gro-Mor’ (ACO).

The nutrient value of animal manures

Animal manure contains some N, P and K, and trace elements. The actual nutrient value of manure varies considerably depending upon species, age of the animal, type and quantity of bedding material, nutrient content of the feed and how the manure has been handled.

Older animals have less nutrient demand than younger animals, so their manure is more valuable. Animals that are recovering from drought and lactating animals, may also convert more of their food to their own needs, so their manure has lower nutrient content. The type of bedding material influences the quantity of urine captured and the speed of breakdown. Straw breaks down rapidly when compared to lignin and cellulose material such as wood shavings or rice hulls.

Cow manure is rich in beneficial microorganisms. When fresh it is less concentrated than other manures, with higher moisture content.

Horse manure is ‘hot’ because it has high N content and low moisture. Value will vary if bedding is included and depending upon the quantity and urine content of the bedding. If fresh it heats up quickly when composted.

Poultry manure should always be composted prior to use, because it is high in soluble nitrates. Nitrogen from poultry manure is rapidly available to plants due to its high uric acid content. The uric acid gives rise to ammonia concentrates that are easily lost by volatilization. Always use a respirator when cleaning chicken houses, as manure dust may contain pathogens and irritants. Broiler litter is usually based upon rice hulls, wood shavings or sawdust, although some growers use shredded paper or seaweed. Egg layer manure has no bedding, and is much more concentrated. Beware of boron content in sensitive soils (boron may be used for pest control in bedding).

Sheep manure is high in nitrogen but comes in a tightly packed pellet. With less air than horse manure, it does not heat up compost as well.

Pig manure is concentrated when fresh but is generally only available as slurry or dried slurry. Slurry can be mixed with dry materials for composting or applied to bulky green manure crops.

In calcareous soils, the phosphorus fertiliser value of manures is equal to superphosphate, because inorganic P undergoes rapid precipitation reactions in high pH conditions. Phosphorus from manure is also available at cooler soil temperatures. Potassium from manure is in a readily available form.

Regular laboratory analysis is notoriously inaccurate at measuring the N content of compost. Under normal conditions, the recorded N content rarely rises above 1.5% (dry weight), although the actual levels may be higher.

Nitrogen losses

Fresh manures initially loose nitrogen as ammonia, which is readily volatized and lost to the atmosphere. This produces the characteristic sharp smell of wet manure. Losses are higher if the pH of the manure is high, because nitrification bacteria work best at lower pH. Eventually nitrate is formed, and this is subject to loss by leaching.

Age of the manure is the single most important factor influencing N content. Generally speaking nutrition (especially nitrogen) reduces with age. Storage conditions dramatically affect nutrient loss. Wetting, drying, microbial activity and temperature affect nitrogen loss. The best ways to preserve nutrition are:

• Spread manure out to dry rapidly and store in a dry condition
• Compost the manure. There will also be nitrogen losses during composting, but the finished product is more stable.
• Incorporate into soil when very fresh. This is rarely possible due to collection and handling problems, and according to organic standards must be followed by two green manure crops.

Nitrogen is lost most rapidly when moist manure is exposed to air, especially in warm, windy conditions with a high evaporative potential. Covering compost heaps with soil will limit movement of ammonia into the atmosphere. Soil may be added to compost that has a very high N content, to limit losses or the compost heap may be covered with an outer layer of soil.

It is normal that 50% of the total N in manure is lost during the composting and application process.

About 30 – 90% of organic N will be converted to ammonia and then to nitrate, during the first year after incorporation. During the next few years, about 5 – 6% of organic N is converted. After that a small quantity of residual N remains, however if manures are added every year, this residual level becomes critical for the operation of organic principles, and many organic growers rely upon it for their productivity.

Why raw manures are not permitted

Fresh manure may contain a large dose of soluble nitrates and phosphates, which may have the same negative effects as synthetic fertiliser. Raw manures also have the potential to carry infection to the harvested parts and to pollute water resources. Un-composted manures may also contain weed seeds, animal parasites and residues of antibiotics, hormones and other animal health products. These are generally unstable with heat and are rapidly converted to harmless substances during composting.

Contamination in manure

Apart from veterinary medicines mentioned above, it is possible that pesticides and heavy metals are found in manure. Pig manure has long been associated with high copper levels. Pesticides may be partially broken down during composting, but heavy metals will be concentrated. If any single source of organic matter is used as a major input over time, it is wise to have it analyzed.

Salt levels in manure can be high if the source animals were fed on irrigated pasture. Dairy manure, for instance is often up to 2-4% potassium and 1% sodium. Animals that have unrestricted access to salt licks may have twice the salt concentration in their manure.

Weed seeds are best removed by composting processes that reach temperatures of 55 – 65 degrees, and remain there for several days.

Conclusion

Manure is a valuable resource that should be utilized on organic farms. Raw manure, except where dropped naturally by grazing animals, should be composted prior to application, and all imported sources of manure should be composted before incorporation into certified organic land.

Horticultural growers who have used manure over many years should check their soils with an Albrecht-style laboratory report, to ensure that selective crop removal of nutrients has not left them with high levels of residual potassium. Whereas most soils need organic matter, oversupply of nutrients is a problem in established horticulture districts. Otherwise the use of composted manure remains a vital component of sustainable agriculture systems.

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