Soil fertility

In organic farming, production is very dependant on the fertility of the soil. In this context soil structure plays a big role because it has significance for the movement of water, nutrients and heat, and thereby for the growth of the microflora, the fauna, and the plants.

This project examines how the physical and biological aspects of soil fertility are influenced by organic farming (long-term effects) and different soil tillage strategies (short-term effects). At Rugballegaard investigations are also in hand to examine the effects of alternative tillage systems in different rotations. The objective in the latter case is to develop soil tillage strategies that are pertinent to organic farmers.

Causal relationships between, for example, the microbial status of the soil and its structural characteristics (aggregate stability etc.) is a major area of research interest. This is being investigated using alternative de-scriptive methods in the field, as well as traditional laboratory methods. The latter are being applied to both undisturbed, and remoulded and aggregate soils.

The project combines physical and biological measurements. The former includes the structural strength of the soil, measured as the shear annulus strength of undisturbed soils, the indirect tensile strength of simple aggregates, and the wet stability of aggregates. Furthermore, measurements of oxygen diffusion and air permeability will provide an evaluation of the entire porosity system's characteristics. The biological measurements include respiration, microbial biomass, extracellular polysaccharides, levels of ergosterol, hyphal lengths of the fungi, as well as investigations of VA mycorrhiza. Most emphasis will be placed on a description of those biological parameters which are thought to have significance for structure formation and stabilisation.

Summary
Publications

Project title
I.3 The fertility of soils in relation to organic farming and tillage practices

Project leaders
Per Schjønning and Susanne Elmholt,
Danish Institute of Agricultural Science,
Research Centre Foulum, P.O. Box 50, DK 8830 Tjele
Tel: +45 8999 1900, Fax: +45 8999 1619,
E-mail: Per.Schjønning@agrscidk

Project participants
Kasia Debosz, Gunner Mikkelsen, R. Labouriau, Karl J. Rasmussen, Lars Munkholm, Danish Institute of Agricultural Science
Iver Jacobsen and Peter Schweiger, Risø National Laboratory