Background and aims of Soil3

Below the plow horizon...

In arable soils, the subsoil starts below the plow horizon, usually at a depth of about 30 cm, which corresponds to the average tillage depth in conventional agriculture. There is no uniform definition for the lower boundary of subsoil, as this also depends on how deep the soil has developed, i.e. at what depth the parent material of soil formation (rock or sediment) is located. In contrast to the topsoil, the subsoil is usually less rooted, low in humus, and, depending on the soil type, can have depletion and accumulation zones of various substances.

 ... hidden resources

Although compaction often occurs at the bottom of the plow horizon, making it difficult for crops to grow deeper roots, the subsoil is nevertheless not 'dead'. It can contain enormous resources of nutrients and water, but these are often inaccessible to roots and microorganisms, firstly because they are not evenly distributed but are localized, and secondly because they often exist under layers that limit root growth due to their penetration resistance. In addition, due to the low humus content, there is the possibility of sustainable storage of CO2 from the atmosphere in the subsoil, which contributes to the mitigation of climate change.

It is therefore important to know the subsoil and to understand the processes taking place in it.

© O. Schmittmann, Univ. Bonn

Which method of subsoil melioration was developed and why?

To ensure the yield potential of arable soils and increase their productivity in the long-term, there is an urgent need to incorporate subsoils, with their considerable stocks of nutrients and water, into sustainable agricultural strategies. Various methods of mechanically modifying the soil profile to increase root growth and the accessibility of subsoil resources have existed for a long time.

Soil3 aims to optimize the use of the total soil volume for plant growth by reducing the physical penetration resistance of the subsoil, creating nutrient hotspots and storing water in the subsoil. This is achieved through the one-time incorporation of organic material into the subsoil. For this purpose, trenches 60 cm deep and 20 cm wide are made with a trencher at defined distances, which are filled with compost, greenwaste, straw or sawdust. The material is mixed in by feeding it into the decending soil material directly behind the injection coulter.

Evaluation of the Soil3 technique

The mechanical subsoil melioration developed in Soil3 will be compared, in terms of its benefits for soil quality and yield increase, with biological subsoil melioration, i.e., the use of deep-rooted precrops such as alfalfa, as this also increases the accessibility of subsoil resources. In addition, the benefits of combining both melioration techniques will also be investigated.
Regional characteristics such as soil type and climate are incorporated into the evaluation of the different techniques.
Socio-economic factors of the Soil3 technique are elicited by calculating the process parameters based on the Central Field Trials and demo trials, and the acceptance of the method among users is determined in surveys.

Most important results from the first 5 years

  • yield potential: 23-55% yield increase
  • sustainability: at minimum 5 years

With the Soil3 technique, yield gains were consistently achieved in the first four years (23% for cereals). For maize, under the dry conditions in Thyrow, even a yield increase of over 50% was observed in the first year using the Soil3 technique. The combination of mechanical and biological subsoil melioration also resulted in a yield increase of about 20%.

  • expense costs: approx. 800 €/ha, plus costs for organic material (e.g. compost, greenwaste, straw)
  • social acceptance: high with regard to the importance of the subsoil, variable with regard to new techniques
Wuchshöhe CF3 en
© K. Schweitzer, HU Berlin
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