Researcher draws attention to legumes

Sowing grass/clover mixtures makes better use of phosphate in the soil, says researcher Wiepie Haagsma of Praktijkonderzoek Plant & Omgeving (Applied Plant Research, PPO) in Lelystad. In this interview, she gives her views on organic matter, monocultures and active soil life.

Why is organic matter so important in the soil?

"Organic matter is the food of soil life and gives structure to the soil. It sits between the soil particles and makes the soil stable. This creates stable pores in the soil in which roots can grow and in which air can penetrate deep into the soil. The pores also have an important function for water drainage and collection. Finally, organic matter ensures good water buffering. As a result, the soil is better protected against drought. Organic matter also improves nutrient buffering".


What is a good percentage of organic matter in the soil?

"It's difficult to say, really. It is very dependent on the type of soil and its use. Organic matter should also be active, soil life should be able to benefit from organic matter in other words".

How is active organic matter made?

"The addition of fresh organic matter brings the soil to life. A combination of different types of organic matter works best in this respect. Legumes provide more nitrogen, while straw delivers carbon. A lot of nitrogen is needed to digest straw. By bringing straw and legumes together on the field, the result is often better than the average of both individually. This goes to show that organic matter in the soil has to be managed continuously. Which crop residues are left behind, what is the next crop, which green manure has been sown and how can you best stimulate soil life?"


Does an active soil life affect the absorption of nutrients, such as phosphate?

"Certainly. Soil life plays an important part in the release of bound phosphate. Soils with little soluble phosphate (low PAL values) regularly appear to nonetheless have no phosphate deficiency. Legumes play an important part in this respect. Their roots form mycorrhiza association, more so than other plants. These are fungal threads that stimulate roots to make minerals available. If legumes are sown in grassy fields, more phosphate becomes available".

Wiepie Haagsma

Livestock farmers who want to improve soil phosphate utilisation are therefore advised to sow a grass mixture containing clover.

"Yes, you could improve phosphate availability by sowing, for example, clover in a field. But in any case it is best not to strive for monocultures. Soil life is much more active when there is a variety of plants. Compare it with people: our gastrointestinal system works better when we eat a variety of foods. You could compare the soil to our stomachs. You could even develop grass mixtures with varieties that actively stimulate soil life. Little research has been done into this".


Learn more about how clover benefits grassland.


So stimulating soil life is always about looking for the right balance?

"Correct. Mixtures have a more positive effect on soil life than monocultures. If sowing crop 1 and crop 2 is combined, the yield can turn out higher than the average for individual sowing. Sowing a combination of grass and clover is a step that every livestock farmer can easily take".


What else is important in maintaining a rich soil life?

"One thing that many farmers forget is soil compaction. Machines are getting heavier. Although tyres are also getting broader, they do not sufficiently compensate the weight gain. As a result, the soil is pressed too tightly and dense layers are formed in the ground. In addition, the tyre pressure is often incorrect. Although contract workers do have pressure cycling systems on the wheels, I have noticed that they do not always use them. Livestock farmers should be more critical of their contractors in this respect. It benefits soil life and grass production".

Collaboration with Wageningen University & Research

Applied Plant Research in Lelystad (PPO) is part of Wageningen University & Research. Barenbrug collaborates with the research institute on the Roughage and Soil project. The aim is to develop measures that will enable livestock farmers to reduce the difference between current and potential forage yields in a sustainable manner. In this context, sustainable is understood to mean increasing the current yield of roughage through improved and more efficient crop management with improved soil quality and without higher losses of fertilisers and additives.