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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.


Figure from Kautz et al. 2013, Soil Biology & Biochemistry

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.

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