The composition of poultry litter can vary greatly between chicken farms, and even within farms between growth cycles, in response to management decisions (stocking density and number of growth cycles), bedding material type and feed wastage. This makes predicting the average nutrient content of poultry litter difficult and the most accurate way is to analyse the batch supplied. Craddock and Hollitt (2010) provided the most comprehensive dataset on the characteristics of poultry litter in Australia. They collected and analysed 123 spent litter samples from a variety of bedding materials for their chemical properties (Table 5). Ranges in this data have a two-to-three-fold difference for some constituents, so end users are encouraged to understand the make-up of the product they use.
Table 5. Chemical properties (dry weight basis) of spent litter from different bedding materials (average and range) (adapted from Craddock & Hollitt, 2010)
| Element | Straw (n = 28) | Sawdust (n = 28) | Wood shavings (n = 65) | Multi-batched (n = 4) |
|---|---|---|---|---|
| Moisture (%) | 20 (15 – 25) | 25 (20–29) | 26 (21–31) | 21 (21–22) |
| Total N (% db) | 4.0 (2.0–5.3) | 3.8 (2.8–5.9) | 3.9 (2.8–5.5) | 4.0 (3.6–4.3) |
| Total P (% db) | 1.1 (0.7–1.8) | 1.2 (0.8–1.5) | 1.3 (0.7–1.7) | 1.7 (1.3–2.0) |
| Potassium (% db) | 2.2 (1.6–2.8) | 1.8 (1.3–2.5) | 1.9 (1.1–2.8) | 2.4 (1.9–2.7) |
| Sulphur (% db) | 0.63 (0.5–1.1) | 0.54 (0.4–0.7) | 0.51 (0.3–0.7) | 0.58 (0.5–0.8) |
| Zinc (% db) | 0.04 (0.02–0.05) | 0.04 (0.03–0.05) | 0.04 (0.03–0.04) | 0.05 (0.04–0.07) |
| Copper (% db) | 0.02 (0.01–0.02) | 0.02 (0.01–0.02) | 0.01 (0.01–0.03) | 0.01 (0.01–0.02) |
| Manganese (% db) | 0.05 (0.04–0.08) | 0.04 (0.03–0.06) | 0.05 (0.04–0.08) | 0.07 (0.06–0.07) |
Nitrogen loss via ammonia volatilisation will also change the nitrogen levels of spent litter. The amount lost will depend on a variety of interactive factors, however the litter will lose nitrogen if it is stockpiled, composted or reused for multiple growth cycles. The storage conditions and management will influence the amount of nitrogen lost as ammonia. For example, wetter litter or litter that is turned will lose more ammonia via volatilisation. Barker (1990) reported total nitrogen losses of 17–30% from various litter treatments (stacking, covered and uncovered piles).
A survey of growers (Watson & Wiedemann, 2018) found that the nutrient concentration of spent litter has declined over time. This has been due to lower meat chicken density and minimum litter depth requirements in accreditation schemes, essentially a dilution effect. This has reduced the nutrient value and sale price of spent litter as a fertiliser. The price of synthetic fertiliser will also impact the price of spent litter.
Further nitrogen losses will occur during land application of spent litter. How and when it is applied, and storage conditions prior to application, will affect the amount lost as ammonia. If spent litter is spread on the surface of a soil and not incorporated or washed into the soil, significant quantities of nitrogen will be lost via volatilisation (Griffiths, 2007). Losses are typically 15–50% of the ammonium fraction (5–20% of total nitrogen) when poultry litter is surface applied (Mitchell & Donald, 1995).
