The story

Together with farmer Joost Samsom from Wilnis, a subsurface iirrigation pilot is starting this autumn. This pilot aims to develop a way to counter soil subsidence at lower costs and with less material than conventional methods.

Soil subsidence

Soil subsidence is a persistent problem in the Western peat meadows. The ground sinks right under houses; since taking over the farm in 1991, Joost has had to add an extra step to get his front door! Soil subsidence occurs in summer when the groundwater drops. Water from ditches does not penetrate far enough into a parcel of land to replenish the supply. The dry part of the peat then comes into contact with oxygen. As a result, peat oxidises, CO2 is released and the land loses carry capacity. Every year, soil in this area subsides by about one centimetre.

Keeping it wet underground

A possible solution is to retain moisture underground during dry periods. This can be done by pipe systems, such as underwater drainage or a peat meadow infiltration system. But these are expensive in both material and installation, and a farmer is left with drain hoses underground. However, it can be done differently.

By creating trenches below the water level of ditches, water spreads out properly with just one pipe for the first four metres at the edges of the plot. An additional advantage is that, in contrast to conventional drainpipe applications, these tubes can be installed using an ordinary tractor. This avoids a large part of material and installation costs.

Subsurface irrigation

The innovation we are testing is called subsurface irrigation, or subirrigation. The aim of the pilot is to gain knowledge about the functioning of a subsurface irrigation system on peatland. It is somewhat similar to mole drainage, which is used to drain a wet plot of land. In subsurface irrigation, however, the corridor is constructed below the ditch water level in order to supply the plot with water from below, thus reducing dehydration.

In order to carry out research with different water levels and soil types, we want to carry out this pilot with several farmers. Starting as an initiative at Joost’s farm, this is part of a larger project “subirrigation against subsidence”.

Wageningen University & Research calls subsurface irrigation “a promising application”, according to the autumn edition of Wageningen World based on the Lumbricus project on sandy soils in the East and South of the Netherlands. Research on peat soil is still very limited, so the practical and theoretical lessons learnt during this pilot will be invaluable. Both Waterboard Amstel Gooi and Vecht and Water Board De Stichtse Rijnlanden (HDSR) have pledged to co-support this project.

Pilot fund

The innovation is an idea of organic farmer Joost from Wilnis. With the help of the pilot fund of Wij.land he is able to further develop his innovation. With the pilot fund Wij.land wants to enable farmers to experiment on the farm with solutions that have a positive impact on soil, water and/or biodiversity, linked to a good earnings model. If you have an idea, test it here.

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