How can we make intelligent use of the living soil system for sustainable agriculture?

Can we tackle the nitrogen problem and climate change with the help of soil life? Every agricultural soil is full of 'free labour': beneficial bacteria, fungi and soil organisms that support farmers and our environment. This project, commissioned by the municipalities of Fryslân, Groningen, Drenthe and Friesland Campina, provides scientific insights into the potential of soil biology and explores concrete applications for practice.

How does fertilisation affect the functioning of soil life?

In our quest to learn more about soil life, we started with the role of manure.

The aim is to gain a better understanding of how different methods of manure application affect worms and microbiology (soil microbiome) in the soil.

Research: What did we look at and how?

For this study, we used modern DNA techniques to map the entire soil microbiome. The microbiome is a manifestation of conditions, history, quality and management. Our research shows that each farmer creates their own unique 'fingerprint' through the way they farm their land, combined with the characteristics of the soil.

Manure applied by injection and surface application, digestate and solid manure are compared.

Results and recommendations Above-ground fertilisation: a promising method

A striking result of our research is that above-ground fertilisation offers an interesting course of action with significant benefits for farmers and the environment. Advantages of above-ground fertilisation include:

• It stimulates micro-organisms that can fix nitrogen for free. This provides an opportunity to save on artificial fertilisers. Saving on artificial fertilisers reduces the risk of nitrogen leaching into the environment while reducing costs.
• It fits well with the Climate Adaptive Netherlands action programme because it also stimulates micro-organisms that make the soil more drought-resistant.
• It can potentially reduce emissions of greenhouse gases such as nitrous oxide and methane. Further studies with emission measurements are needed to confirm this.

Digestate from mono-manure fermentation: opportunities and challenges

The use of digestate as a fertiliser is controversial, mainly because of the fear of pathogens and the idea that it is at the expense of soil biodiversity. However, our research shows that using digestate as a fertiliser does not increase the risk of pathogens. In fact, digestate fertilisation has a number of advantages over slurry fertilisation.

Because of these positive effects on soil health and the environment, digestate appears to be a better fertiliser than slurry in certain circumstances.

There are also challenges to using digestate. Digestate is a quick source of nitrogen, which is beneficial for plant growth, but this also stimulates nitrifiers in the soil, increasing the risk of nitrate leaching. More research is needed to determine the optimal use of digestate.

If you would like to know more about this topic, please contact Eline Keuning or Jidske Knigge.