The Askov Long-term Experiments on Animal Manure and Mineral Fertilizers have been a continuing source of information on the relationship between fertilization, plant nutrition, soil fertility and the environment since 1894. For more than 110 years the effects of varying applications of N in artificial fertilizer and animal manure have been compared.

-  Internationally the experiments are also unique and few other sites can boast field experiments supported by well-documented fertilization plans dating back more than a century, points out professor Bent Tolstrup Christensen from the Danish Institute of Agricultural Sciences (DIAS). He continues:

-  The long-term experiments are important for our understanding of crop nutrient requirements in agricultural systems. For many years the experiments were mainly of national interest, but during the last decades there has been an ever-increasing level of interest from researchers abroad. We regularly receive requests for data from the long-term experiments and also for soil samples for special investigations, usually as part of project collaborations with our research group.

Bent Tolstrup Christensen hopes that in the long term the experiments will form part of a European research platform that will give scientists in the EU access to a network of long-term experiments in farming and forestry. The initiative for this activity has been taken by a colleague from INRA, a French sister organisation to DIAS.

A wide range of projects

Originally, the objective of the experiments was to compare the effects of varying N, P and K fertilization levels on crop production and the development of soil fertility when animal manure was replaced by mineral fertilizers. The plots have now become a unique experimental site for specific projects within soil quality, soil fertility, crop nutrient supply and similar topics.

Bent Tolstrup Christensen summarises some current projects exploiting the resources embedded in the Askov long-term experiments:

• An analysis of the long-term effects on yield of the 10% reduction in nitrogen applications - a result of the restrictions imposed by the Second Action Plan for the Aquatic Environment.
• The recalibration of the turnover parameters incorporated into the DAISY simulation model using measurements of soil carbon content dating back to 1923. The DAISY model is increasingly used for analyses of the relationship between crop production and the environment.
• A number of soil samples have recently been sent to Belgium where a team of Belgian, Australian and Chinese researchers will analyse the change over time in the mobility and availability of copper in animal manure applications.
• A project that includes colleagues from the UK has determined the abundance of carbon-14 and the stable isotopes of carbon, nitrogen and sulphur in soil and plant samples taken from the archive associated with the long-term experiments. The archive contains samples dating back to 1923.

Anniversary report

A report in celebration of the 110th anniversary of the long-term experiments will be published by DIAS in the autumn of 2005. The report will present the changes that have taken place in soil and plant parameters from 1894 to 2004 with particular focus on the later years.

With the present level of interest in the Askov long-term experiments, Bent Tolstrup Christensen is confident that this unique facility will remain a gold mine for innovative projects within many research areas.

For further information please contact:
Research professor Bent Tolstrup Christensen
Department of Agroecology, Research Centre Foulum
Tel.: +45 8999 1709