How to increase utility of nitrogen in manure – the Danish case

Blicher-Mathiesen, G., Andersen, H.E., Rasmussen, A., Rolighed, J. & Carstensen, M.

 

Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark.

 

In Denmark, the first Action Plan for the Aquatic Environment was adopted in 1987 with target of a 50 pct. reduction in the nitrogen load to the aquatic environment. The measures in the plan were directed towards the individual farmer and included a.o. an obligation to establish slurry tanks with nine months storage capacity and a ban on slurry spreading from harvest to November 1. on fields destined for spring crops. At that time, farmers  applied chemical fertilizers in amounts  that almost solely covered the crops demand for fertilizer.  The farmers did not fully acknowledge the fertilizer value of manure. Therefore, the manure nitrogen was applied in excess and caused a significant nitrogen leaching to the aquatic environment.

The rationale of the first Action Plan was that increased manure storage capacity would allow farmers to apply manure at the most favorable time from a nitrogen utilization point of view and thus reduce the application of chemical fertilizer.

However, this voluntary reduction in the application of chemical fertilizers did not materialize to the degree anticipated. Therefore, the governments implemented restrictions on the actual consumption of chemical fertilizer and manure from 1994 onwards.

In order to transfer the Danish experience to other countries it is necessary to have knowledge on the interplay between manure storage capacity, timing of manure application, application technology and the effects on nitrogen utilization and on nitrogen leaching.. In this study, we present how the Danish farmers in the Agricultural Monitoring Program step-wise increased spring application of manure and adjusted the applied amount of chemical fertilizers to increase utilization of nitrogen in manure. How some farmers did not use excess nitrogen and some did. Using data on nitrogen leaching obtained by suction cups below the root zone we analyze the effects of application of both chemical fertilizer and manure and of the timing of manure application.