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Feedlot waste management
7. Manure removal and stockpiling

Environmental Engineers and Extension Officers, Delivery

Introduction

The removal and storage of manure prior to disposal is an important part of the waste management program of a feedlot. Between yard cleaning and manure removal, manure may be temporarily mounded within yards. Longer term, manure storage is often in stockpiles outside the yards.

Removal of manure

Cattle in feedlots produce 1 to 2 tonnes of manure per head per year. Given that the removal of manure is a real cost to the feedlot operator, efficient removal of this product is important.

Manure can be removed directly from the pad if the manure pack is 100 mm deep or deeper. Usually a front-end loader, scraper or grader would be used for primary yard cleaning. A bob-cat may be useful for cleaning around troughs and under fences. However, if the manure pack is shallow or hard, a light ripping may be necessary to break up the manure prior to removal. It may also be necessary to scrape the manure into a mound prior to loading. During the removal of manure, the pad should be graded to ensure that the surface is uniform and any pot-holes are filled in.

Between the base soil and the manure layer is an interface layer. It consists of mixed compacted soil and manure and is about 50 mm deep. The interface layer forms an impermeable barrier, which prevents contamination of ground water by nitrates and salts in the manure. The interface layer must not be removed during yard cleaning.

Mounding of manure

Some managers use short term mounding of manure as a waste management tool. During yard cleaning, manure is formed into a mound in the yard. This allows flexibility in manure management programs. It permits all yards to be quickly cleaned out while equipment is available or when other conditions are suitable. It also allows an increased interval between full-yard clean outs. The volume of manure to be disposed of may also be reduced by up to 50%. However storage of the manure in this way will reduce its nitrogen content and subsequent value as a fertiliser.

Stockpiling manure

Although some managers like to spread manure removed from the yards immediately onto land utilisation areas, this is not always possible. Manure that has been removed from yards, but cannot be used productively straight away, must be stored in an appropriate manner, usually by stockpiling.

By maintaining a stockpile, yards can be cleaned out as frequently as required, even when spreading machinery is not available or when agricultural land is not ready for the application of manure. Stockpiling of manure also allows decomposition of the manure, which reduces the amount of manure that must be applied to land, but also reduces the nitrogen content of manure, making it less valuable as an organic fertiliser. The amount of stockpiled manure should, therefore, be kept minimal and manure utilised as soon as possible.

Manure containing rocks is unsuitable for immediate use since these objects can damage manure spreading and crop harvesting equipment. Manure may, therefore, need to be stored in stockpiles prior to screening.

Construction of stockpiles

Stockpiles that have been properly constructed and maintained have little potential to pollute the local environment.

Manure should be added to the stockpile in thin even layers. The layers should be dry (25% moisture content) otherwise spontaneous combustion may occur. Manure usually has a moisture content of 45% or less when it is removed from yards and is usually at least partly stabilised.

Following the addition of each layer, the stockpile should be compacted. This is particularly important if manure is to be stacked deeper than about 1.8 m. Stockpiles should also be shaped so that they shed rain. An even surface should be maintained by periodic grading. This helps to avoid ponding of water on the pile.

Stockpiles must be built within a controlled drainage area. This means that they should be protected from external runoff by drains and/or diversion banks. Runoff from stockpiles must also be controlled to prevent runoff from contaminating watercourses.

Composting manure

An alternative to stockpiling of manure is composting. This process uses microorganisms to stabilise organic material such as manure. It occurs under moist, aerobic conditions, usually at warm temperatures (due to the generation of metabolic heat by microorganisms). Composted manure does not produce an offensive odour and can, therefore, be stored without causing nuisance.

Composting involves the addition of air and/or straw to the manure. Air is usually added by turning the pile from time to time. Straw is added to increase the carbon to nitrogen ratio and to add air to the centre of the pile. This improves the quality of the manure by converting nitrogen into a form useable by plants and breaking down cellulose and lignin. Composting concentrates plant nutrients. It also improves the structure of the manure, allowing it to be handled and applied more easily than fresh manure. Composted manure is also more appealing as a saleable item.

Fresh manure may contain compounds that inhibit seed germination and plant growth. However, composting destroys these compounds. Any weed seeds in the manure are usually killed due to heating.
Windrow composting is the usual method of composting. The manure is broken up to eliminate any large lumps. It is then placed in windrows approximately 1 m to 2 m high and 4 m wide. Front-end loaders (or similar equipment) are used to turn the manure about once a week over a two month period. Frequent turning of the windrows speeds up the composting process by aerating the manure, increasing the temperature, releasing excess heat and evaporating excess moisture.

Conclusion

Efficient removal and handling of manure not only minimises waste management costs, but also optimises the value of the manure in terms of nutrient content and physical structure. In the past, feedlot manure was regarded as difficult and costly to dispose of. Consequently, there was little incentive for managers to clean yards. However, it is now regarded as a valuable, saleable commodity and more attention should be given to maintaining its value as a fertiliser. Traditionally, manure has been stockpiled, sometimes for years without being used. Manure is perishable and this seriously depletes the nutrients in the manure. Short term stockpiling or composting of manure are storage methods that help to maintain the high nutrient content of the manure while allowing flexibility in timing the application of the manure onto agricultural land.

Further information

Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.

Last updated 24 January 2006


 

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