Laying-hens for soil fertilization

Summary in the original language of the document

The Norwegian population of laying-hens comprises about 3.5 million, out of which about 240 000 are certified
organic. Breeding for high egg production and low body weight, combined with larger body weight in chicken
hampering the utilization of the same slaughter lines, has reduced the interest for utilizing laying-hens for food
purpose. Most hens are currently disposed of by gassing with CO2; either in the house or in a container being
brought to the farm. Dead hens are then transported to Hamar in South-East Norway, to become incinerated in
the only Norwegian plant for category 1-organic materials. Mobile slaughtering systems are relevant for poultry.
After slaughtering, the animals could be used for food, or processed by milling and enzymatic hydrolysis into
valuable oil and soluble proteins. Residual sediments contain valuable nutrients such as nitrogen, phosphorus and
calcium. When utilization for feed is not an option, it would be beneficial to utilize the spent laying hens as a
fertilizer on farm. This may decrease the costs of the farmer, and be a much better utilization of organic matter
and plant nutrients.
The project “Complete and Bio-economical Exploitation of Laying-Hens” (2015-27), funded by the Regional
Research Council of Mid-Norway, studied the effect of sediments as fertilizers for ryegrass, and observed the
decomposition of chopped, dead laying hens mixed with soil. The idea was to reveal about how much soil would
be needed to decompose a hen, to assess whether e.g. a former storage room for solid manure could be utilized
for decomposing spent laying hens.
Sediments were an efficient fertilizer for ryegrass, especially when finely milled. The growth was then larger with sediments than with calcium nitrate for the initial two cuts. Finely milled sediment also had a more significant
effect to increase the phosphorus concentration in the soil.
Pots of chopped hens mixed with soil were stored for 4 months at 10-15 °C. With 1 part of hen to 3 parts of soil
(by weight), the chopped hens were quite well decomposed and the odor was not too unpleasant. Mechanical
treatment of the mixture during storage would contribute to increase the decomposition. Around the particles of
chopped hen, solid aggregates were formed, where fungal hyphae were observed. Solid particles such as feathers
and bones were not completely decomposed over 4 months, but for the softer particles, a large proportion was
decomposed.