Research on composts with different origins

17 December 2021 - Published by Hanne Lakkenborg Kristensen
Last year ILVO, James Hutton Institute and Arhus University examined the different composts, coming from different production locations in the North Sea Region. The research and the results are the starting point of the Soilcom project.

Next years the advice towards the composting companies and the resulting adjustments in the composting process, will lead to optimized quality composts.  The results are also used to define the right quality indicators of the compost. These quality indicators are important for both the production process and for growers to know which compost can be of added value for their cultivation.


Physical characteristics

James Hutton institute (JHI) is specialized in research on the physical characteristics of the compost. At the start, examined the fundamental properties of the composts, such as particle size distribution (PSD), bulk density and dry matter content.  Dry matter contents of the composts ranged with values between 50% and 79%. Also the density of the composts differed considerably from each other with values between 200 and 400 grams/ litre. Some of the composts had about 20% particles larger than 15mm, were other composts didn’t contain any of these particles larger than 15mm. Also the hydraulic conductivity was measured. This gives an insight in how easy water infiltrates through the compost. Also the infiltration of water in a combination of soil with compost was measured. This year the infiltration of water in soils with compost addition will be measured for different soil types: sandy soils, clay and silty clay.

In the SOILCOM project we are especially interested in the effects of compost addition to the soils. In 2021 the JHI will look for the impacts of the compost addition on the water holding capacity of the soils, saturated conductivity and field capacity. This is done both under laboratory conditions and in the fields.


Biological characteristics of the compost

In the project ILVO is investigating the biological characteristics of the composts. In both production and application of the composts it is important to know which microbiome is present in the compost. And what to expect of soil health after adding compost to the soils. ILVO uses two methods: the Hot Water extractable Carbon and phosphate (HWC method). And potential N mineralisation as means to know the soil microbial activity.

By using the PLFA method (phosfoLipid fatty acid method) ILVO is giving an overview of the presence of bacteria, fungi and nematodes. Specific groups of organisms are defined by this method: Gram+ bacteria, Gram- bacteria, non specific bacteria, actinomycetes and AM fungi (arbuscular mycorrhiza) and fungi.

The last group of soil organisms are the nematodes. Often a group of organisms were growers are afraid for. Of the different composts, ILVO made a nematode index to show the diversity of nematodes in the composts.


Chemical characteristics of compost

Of course there is also a large interest in the chemical characteristics of the compost. What can we expect of the fertilizing value of the composts? The composts were analysed for different aspects:

  • Electro conductivity
  • NO3  and NH4, the direct available N instead of the total N. The higher the NO3 the more mature in general the compost is.
  • Cation Exchange Capacity, or the amount of electrostatic binding places for cations to be exchanged to plant roots. An important indicator of quality.
  • Total macro elements and heavy metal content.
  • And pH and organic matter content


Quality and interesting relationships

All the characteristics together give a good overview of the quality of the composts and what to expect when applied to soils. This extensive amount of information collected in SOILCOM will be used in the different work packages as input for development of advising compost producers, growers and farmers and policy makers about specific quality composts for specific soils and conditions.