Nitrogen Recovery from Organic Manures: Improved Slurry Application Techniques and Treatment – the Danish Scenario

Keywords: Manure, slurry, nitrogen, utilisation, trailing hoses, injection.

The attitude of the Danish farmer to manure has changed from seeing it as a smelly waste to it being accepted as a valuable product. Today, the nutrients in manure are highly recognised as fertiliser for most agricultural crops. The changes in practice have reduced the use of nitrogen in mineral fertiliser by 50% since 1990, and a reduction of nitrate leaching from agricultural land of 41%; a reduction of ammonia volatilisation of 42% has happened over the same period. Dramatic changes in fertiliser practice have taken place, partly forced by legislation. The first legislation was introduced in 1987, and new legislation has been introduced several times since. Denmark has probably the highest level of regulation of fertilisation in the world today. To be able to optimise fertiliser plans and to maximise the utilisation of nitrogen in manure, new techniques for application and new technologies for treatment have been introduced. Application of slurry with trailing hoses is recommended in winter cereal and injection is recommended on bare soil and grass. Broadcast spreading of slurries is prohibited. About one third of the total amount of slurry is injected. Biogas production, separation of slurry and acidification of slurry are treatments that are common today. About 10% of all slurry in Denmark is treated with one of these technologies.

Recommendations are highly based on results from field trials, and this paper gives an overview of the most important results of field trials from 1990 to 2009. The paper also gives an overview of the general recommendations on utilisation percentages for nitrogen in slurry, which depending on slurry type, crop, application method, and time of the year, can be used for fertiliser planning.

Torkild S Birkmose, Danish Agricultural Advisory Service, Udkaersvej 15, Skejby, 8200 Aarhus N, Denmark.

24 pages, 16 tables, 27 references.