What should I do with used woodchip bedding?
Nutrients in used bedding are a valuable resource that, when applied to land, can reduce fertiliser costs and increase pasture production.
The Pastoral 21 research programme measured the nutrient values and rates of nitrogen (N) released from freshly-collected and composted bedding material. The material was recovered from a covered wintering shelter with a woodchip floor.
"Woodchip" covers a number of products including post peelings, log chips and bark. It varies in size and source (green or recycled wood from various types of trees). Used woodchip bedding is a mixture of woodchip and effluent.
The Pastoral 21 research found that each wet tonne of material contained:
- 4.8 kg of nitrogen (N) or 0.48% N
- 1.2 kg of phosphorus (P) or 0.12 % P
- 6.8 kg of potassium (K) or 0.68% K
Carbon: Nitrogen (C:N) ratio
Used bedding is high in carbon (due to the wood component). A high C:N ratio indicates that most of the N is locked up and not readily available to plants.
Used bedding material usually has a high C:N ratio (greater than 20:1). Soil incubation studies showed that the N in this material was not immediately available to plants. Used bedding that had been stored and slightly composted for 12 months had a lower C:N ratio of 17:1 and N was immediately available for plant uptake.
Spreading on pasture
The trial recovered 287 tonnes of used bedding which was applied to pasture at low rates of 20m3/ha, once a year. This did not choke grass or interfere with subsequent silage harvesting. However, 20m3/ha did not use much of the total volume of used bedding e.g. a 200 hectare milking platform would only use 4 tonnes of used bedding.
Spreading on cultivated land
Incorporating woodchip into land before sowing crops or grass allows higher application rates. You can use bedding straight from the shelter or pad (without composting), but the N will not be available until the bedding rots.
Most farmers are choosing to compost woodchip for 12 months on a sealed pad before incorporating it into the soil. Woodchip composting can be done in a number of ways but simply leaving it on a sealed surface works well for some farmers.
Tipper trucks can dump large volumes onto soil - it can be spread around with a blade and then power harrowed in. Successful composting makes something very similar to soil, which can be dispersed by a spreader before being power harrowed in.
Tips for success
Get it tested. Woodchip products are highly variable, so request a C: N ratio test and compost analysis on used woodchip. A C:N ratio of less than 15:1 is best for N availability.
Woodchip N is more readily available if you can store and compost the bedding for 12 months or more prior to use. During composting, some N will be lost to air so get a C: N ratio test before using it.
Storage and spreading
Ensure storage and composting of used barn bedding follows regional council requirements. This will require a hard surface and capture of any run-off liquid.
Avoid spreading on calving paddocks because excess K increases the risk of metabolic disease around calving.
Dairy effluent is high in K. Growing plants can take up more K than they need, leading to high levels of K in the leaves. When eaten, excess K interacts with other nutrients in the cow’s diet and can lead to metabolic diseases caused by magnesium or calcium deficiencies.
Correct timing and rate of manure application is essential for reducing animal health risks. To protect cow health, application decisions should be made based on soil and woodchip test data.
Home chipped logs can have very large chunks that take longer to break down. A matchbox-sized chunk is good for cow comfort and for composting.
If you plan to compost waste woodchip, check your regional council requirements for capturing run-off.