Most spent litter is used in the agricultural sector (e.g. pastures, turf farms, market gardens, broadacre cropping, horticulture and mushroom farms). Some poultry producers have diversified farms and use their litter for soil improvement and/or as fertiliser for crops and pastures. A component of spent litter also goes to compost and organic fertiliser manufacturers for additional processing and resale. Most growers are responsible for acquiring their bedding material and the subsequent spent litter sales/uses. In some instances, the chicken meat processing company will supply clean litter and handle spent litter sales.

As Griffiths (2007) noted, you need observation, a soil test and a nutrient budget to determine what rate of spent litter to apply and to check that you are getting the desired result. For additional guidance on preparing a nutrient management plan to ensure sustainable application rates, refer to the AgriFutures Australia project PRJ-011090 Development of National Environmental Guidelines for the Meat Chicken Industry.

A good rule of thumb when applying spent litter is to treat it as a phosphorus fertiliser, not a nitrogen fertiliser. If you apply spent litter to crops or pastures to meet their nitrogen requirements, you will likely over-apply phosphorus and risk losing phosphorus to the environment.

For pastures

The amount of litter to apply to pastures will depend on a variety of factors. As Griffiths (2007) stated, this will depend on the soil type, existing soil nutrient levels, crop requirements and the amount of nutrient being removed in animal products, silage or hay. This applies to crops, where the nutrient removal will be via grain and potentially straw. Using sawdust-based spent litter from Table 5 as an example, an application rate of 6t/ha (wet weight) is equivalent to 15m³/ha at a bulk density of 400kg/m³. This would represent an application rate in kg/ha of 171 nitrogen, 54 phosphorus, 81 potassium and 24 sulphur.

Griffiths (2007) recommended for pasture production that soil testing be conducted to identify any phosphorus deficiency. Where extra phosphorus is needed, apply spent litter for two or three years if developing highly productive pastures, then soil test again to check that phosphorus has risen to the desired level. To maintain soil fertility, alternate one year of litter with one year of nitrogen or potassium fertiliser if required. On less-productive dry land or grazing paddocks, the same principle applies but less litter or fertiliser may be required to maintain target fertility levels. Similar principles to this can be used for cropping.

Warn (2013) conducted a study to investigate the value of spent litter as an alternative fertiliser source for pastures in Victoria. Some of the key findings were:

1. Broadcasting spent litter onto pastures can give similar pasture growth responses to conventional fertilisers.
2. In soils with adequate phosphorus levels, pasture responses were mainly due to nitrogen. In the short-term, it is more-cost effective to apply nitrogen (urea) alone rather than litter, based on the prices of spent litter and synthetic fertiliser at the time of the experiment.
3. Soil phosphorus levels and plant tissue levels of potassium increased with increasing rates of either product. Plant tissue levels of copper and molybdenum also increased with increased rates of litter. These elements/heavy metals were still at acceptable levels in soils and plant tissue where very high rates of litter were applied.
4. Soil organic carbon increased by 0.4–0.5% in the topsoil where high rates of litter were applied relative to the Control (nil fertiliser).
5. Spent litter had a positive effect on pasture composition, promoting clover and improved perennial grass content.

For crops

Assessing the value of spent litter as an inorganic fertiliser replacement was undertaken in broadacre, dryland wheat production in SA (Craddock & Hollitt, 2010). From their studies, they recommend rates of 2.5–3t/ha (depending on nutrient content) to build soil reserves and rates of 1–2t/ha for maintenance applications. They concluded that poultry litter is a useful source of nutrients for broadacre crop production, with the value to grain growers being dependent on the comparative cost of key nutrients in synthetic fertilisers. The authors recommend poultry farmers provide litter analyses and application advice to assist setting a competitive price for litter, depending on fertiliser values.

From dryland wheat production studies in South Australia, it is recommended that rates of 2.5–3t/ha of spent litter be applied to build soil reserves and rates of 1–2t/ha for maintenance applications. To gain the best value and ensure sustainable application, it is recommended that poultry growers provide litter analyses and application advice. This will assist setting a competitive price for litter depending on fertiliser values.

The application of spent litter can enhance land productivity by not only improving a soil’s nutrient status, but also its structure and organic carbon levels. However, it can also cause a range of soil degradation problems if poorly managed. Most of these concerns, such as elevated levels of environmentally relevant nutrients (e.g. nitrogen and phosphorus) and elevated heavy metals, are only applicable if too much litter is applied. Devereux (2012) conducted a study to determine nitrogen and phosphorus losses from farms applying spent litter to a variety of crops. The study concluded that the best strategies to minimise nutrient losses were to:

1. Use well-designed vegetative filter strips as close to the source as possible to reduce runoff loss once phosphorus has mobilised in runoff.
2. Apply spent litter to match but not exceed the crop phosphorus requirements, as opposed to nitrogen requirements. This reduced phosphorus runoff losses by 37–47% and prevented excess phosphorus accumulation in the top 10cm of the soil.