Why important: Spent litter can be used in a variety of ways, although most spent litter produced in Australia is used as a fertiliser in broadacre cropping, horticulture and dairy farms production. Some product also goes to commercial composters and organic fertiliser manufacturers for further processing.
When deciding on spent litter use strategies, consider options that extract the most value from the product and ensure any risks posed due to odour, dust, nutrients, chemicals, pesticides, pathogens, biosecurity and restricted uses are minimised.
Outcomes: The nutrient and carbon value of spent litter is optimised in a manner that minimises any potential environmental impacts.
Performance measures: The beneficial properties (i.e. carbon, nutrients) of spent litter have been considered prior to sale or use. This might mean using it on soils that benefit most from its carbon value, or converting the carbon to energy in waste-to-energy systems.
The by-products produced from further processing of spent litter (e.g. digestate, incinerator ash, and compost) are managed in a way that does impact the environment (amenity, soils, water resources etc).
Best management actions:
Composition
• To ensure spent litter is not contaminated, growers should regularly communicate with suppliers about the origin of clean bedding and request a commodity declaration.
• If levels of contaminates are found in spent litter that exceed jurisdictional requirements that are applicable to its end use, it may be useful to have the feed analysed to ensure pesticides and insecticides are not entering the litter via this pathway.
• Supply information to end users on the constituents of spent litter and risks and restrictions associated with its use. This can be in the form of a chemical analysis or fact sheet on typical industry values. Land Application of Chicken Litter: A Guide for Users (Wiedemann, 2015b) contains useful information that can be supplied to end users on the safe and sustainable use of spent litter.
Storage and Composting
• Where spent litter is stored or composted, it should be done on an impermeable base that is concrete or a 300 mm layer of compacted clay (comprised of two 150 mm compacted layers) that has a design permeability of at least 1×10-9 m/s. Detailed information on achieving this are available from DAF Queensland. Ensure state or local government requirements regarding storage and composting are met.
• If treating spent litter and producing a product that is claimed to be “composted”, ensure it meets the minimum requirements of the Australian Standard AS4454-2012 (Australian Standards, 2012).
• When spent litter is composted, it should be maintained in an aerobic condition to avoid excessive odour generation. This will mean maintaining optimum moisture levels and turning regularly (or using aerators to provide oxygen).
Environmental hazard mitigation
• Avoid application of litter close to open waterways and maintain a vegetative filter strip (VFS) between cropping areas and waterways. A well-designed and maintained VFS located as close to the application site as possible will reduce phosphorus losses once phosphorus has been mobilised in runoff. Note that a VFS may become ineffective with high application rates and excessive stormwater runoff. Details on designing and maintaining VFSs can be found in the AgriFutures Australia project PRJ-011090 ‘Development of National Guidelines for the Meat Chicken Industry’.
• Avoid application on steep slopes (>10%) and drainage features in the landscape where the material may be carried with runoff, particularly when these areas are near open waterways, as most runoff is via drainage features/depressions.
• Carefully manage applications on permeable soils, particularly in groundwater recharge areas.
• Ensure spent litter or composts used for spreading are in a moist and friable condition to minimise odour and dust generation and subsequent impacts.
Nutrient management plans
• When raw spent litter or compost product is used on crops and pastures, ensure it is applied at sustainable rates to avoid negatively impacting water resources (ground and surface) and soils. This is best achieved via a well-designed nutrient management plan (NMP) or fertiliser management plan to reduce the risks of nutrient runoff and leaching. Detailed information on how to develop an NMP can be found in material developed for AgriFutures Australia project PRJ-011090 ‘Development of National Guidelines for the Meat Chicken Industry’.
• Use litter to supply pasture or crop phosphorus requirements, rather than as a nitrogen fertiliser/source. Because litter is not a balanced fertiliser, applying it as a nitrogen source will likely result in the over-application of phosphorus. Applying spent litter to match crop phosphorus removal, as opposed to nitrogen removal, can substantially reduce phosphorus runoff and prevent excess phosphorus accumulation in the surface soil. This does not mean that application each year should meet the amount removed. Different soils have different capacities to store/bind phosphorus, and this affects the amount of phosphorus available to plants. Building phosphorus-deficient soils up to sustainable agronomic levels and/or applying three years of phosphorus requirements in three-year rotations are acceptable practices provided excess available phosphorus does not accumulate in the soil surface and is lost in runoff.
• Additional inorganic nitrogen fertiliser, e.g. urea and potash, may need to be applied to meet crop nitrogen requirements in intermediate years.
• In soils with adequate phosphorus levels, it may be more-cost effective to apply inorganic nitrogen fertilisers rather than spent litter. This will also reduce the risk of potential nutrient loss to the environment.
Horticultural crop management
• The period between application of spent litter and crop harvest should be as long as possible.
• Untreated spent litter must not be used on growing sites within an exclusion period of 45 days from harvest for most vegetables. This period should be 90 days for vegetables like rockmelon and lettuce, where the outer layer comes into contact with the ground.
• Alternatively, spent litter may be used within the exclusion limits if subjected to a treatment verified to achieve E. coli <100 cfu/g and Salmonella Not Detected/25g.
• Ensure untreated spent litter is not applied in rainy or windy conditions and is incorporated into the soil after application to prevent dust or runoff if applied adjacent to high-risk crops.
• Spent litter is considered treated if it has been subjected to the times and temperatures proven to kill human pathogens. Before using, obtain evidence from supplier to substantiate treatment process, such as a certificate confirming that compost has been treated in accordance with Australian Standard AS4454-2012 (Australian Standards, 2012).
• Refer to the Guidelines for Fresh Produce Food Safety 2019 (FPSC A-NZ, 2019) for detailed information on applying raw and composted spent litter to horticultural crops.
Restricted uses of spent litter
• Livestock must not be fed or have access to spent litter, whether raw or composted. Ruminants are not allowed access to RAM (i.e. meat meal, that could be in the litter from spilt feed). Botulism toxins from poultry carcasses that may have decomposed anaerobically in the litter also pose a risk to livestock.
• Be aware of state and chicken meat industry biosecurity and manure use guidelines, as the application of spent litter and compost may be limited or require withholding periods in areas used for grazing or crop production.
• Check and adhere to local regulations regarding spent litter storage and land application in WA, as stable fly is a declared pest under the Biosecurity and Agriculture Management Act 2007.
• In WA, spent litter should only be stockpiled for less than three days before covering with plastic to avoid it becoming wet. Alternatively, spent litter should be removed immediately from farm and used as a blend for compost, or sprayed with insecticide to prevent fly development.
• Livestock should be kept off pasture following spent litter application for long enough to ensure that ruminants can no longer access it via grazing.
Testing, recordkeeping and ‘warning and informing’
• Keep records of any spent litter sales, including dates, recipient details and destinations.
• Inform contractors and end users of the risks and restrictions associated with the use of litter. An example form can be found in Appendix D – Example agreement for the removal and utilisation of spent litter from a meat chicken farm.
• When spent litter is to be used in crop production with higher risks (e.g. horticulture industry), have spent litter tested annually for nutrients, pathogens and heavy metals and check levels of metals against state and industry guidance. More frequent testing is required if changes are made to the production system or litter material.
• Limitations exist in WA regarding the storage and use of raw spent litter, due to problems with stable fly breeding. Refer to regulations in that state for information about restrictions.
Alternative uses and additional best practice information
• Operate anaerobic digester in accordance with the parameters specified by the manufacturer to ensure efficient operation and adhere to relevant workplace health and safety requirements.
• Additional guidance on land application of spent litter, including sustainable application rates, and typical nutrient and heavy metal contents of spent litter, can be found in the Land Application of Chicken Litter: A Guide for Users (Wiedemann, 2015b).
