Sustainable Subsoil Management

An increasing global population requires great efforts to cover the resulting demand for food in an environmentally friendly and sustainable way. However, in Germany and worldwide, the amount of land available per person for arable farming is decreasing. In addition, the risk of yield losses due to dry summers is increasing and fertilizers are becoming scarcer and more expensive. Arable soils store significant amounts of water and nutrients not only in the plow horizon, but also in deeper soil areas - in the subsoil. The aim of SOIL³ is to improve subsoil access for crops and thus increase water and nutrient uptake from the subsoil.

In field experiments over several years, biological subsoil melioration using deep-rooted alfalfa and technical strip subsoil melioration with compost application were tested. For the second method, a specially developed and patented machine first removed the topsoil, loosened the subsoil to a depth of 60 cm and mixed it with organic fertilizer before returning the topsoil.

The experiments took place on various soils with different climatic conditions (Klein-Altendorf, Thyrow, practice sites) and were supplemented by evaluations of long-term field experiments and the agricultural soil condition survey.

The innovative SOIL³ method increases the volume of soil that can be used by the plants by reducing the resistance to root penetration through subsoil loosening and creating nutrient hotspots and increasing water storage through the application of compost.

Both in the loess soils of the area around Bonn and in the sandy soils of Brandenburg, the roots of the crops grew preferentially into the melioration strips, thus enabling an improved plant growth. Overall, cereal yields were increased by 20 to 25% compared to the non-meliorated control, which indicates improved water and nutrient uptake from the subsoil. Even 7 years after subsoil melioration, an average yield increase of 22% was still achieved. In Thyrow, a yield increase of over 50% was even achieved for maize in the first year. With these yield increases and process costs of 700 to 800 euros per hectare plus the costs for the organic fertilizer introduced, it can be assumed that the SOIL³ technology will pay for itself after 3 to 5 years.

Compared to conventional interventions in the subsoil, the SOIL³ technique is less invasive and delays recompaction of the subsoil, presumably due to the compost and the intensive root penetration in the area of the melioration strips. It supports both carbon storage in the subsoil and soil life. There are no indications of risks from plant pathogens or increased nitrate leaching, but there are indicators of improved water and thus nitrate uptake by the plant, as well as increased microbial immobilization of nitrogen in the subsoil. Restrictions may arise due to the limited availability of melioration materials. The legal situation regarding the introduction of organic materials into the subsoil is currently unclear due to the new German Federal Soil Protection Ordinance (BBodSchV) coming into force in August 2023. It has not yet been possible to clarify whether the BBodSchV, the Fertilizer Ordinance or the Biowaste Ordinance applies.

The main target region for the SOIL³ technology was identified as north-eastern Germany, where sandy soils and dry summers often limit agricultural production. In contrast, subsoil access was improved on loamy and silty sites, primarily through deep-rooted previous crops, i.e. these sites are particularly suitable for biological subsoil melioration or a combination of SOIL³ technology with alfalfa cultivation. The nitrogen-fixing alfalfa creates biopores and also favors yield increases of subsequent cereals in dry years.

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