Soil compaction in agriculture poses a threat to soil functions on the land used for agriculture. Especially in subsoils of  30-60 cm depth, there is a tendency of compaction accumulation and impact on soil functions.

The consequences of damaged soil structure can vary widely: compacted soils tend more strongly to become waterlogged since precipitation water cannot run off quickly enough and filling of the pore system can quickly displace soil air. The resulting reduced oxygen supply can impact root growth and harvest yield.

Decimated water absorption and groundwater recharge contribute to surface runoff and soil erosion. In heavy rains soil compaction can also promote flooding. Waterlogged soils have higher rates of emissions of nitrous oxide, methane, and hydrocarbons and can thus play a role in global warming.

The Federal Soil Protection Act requires that soil compaction be avoided to the greatest extent possible. The Federal Soil Protection and Contaminated Sites Ordinance does not as yet contain regulations to avoid risks as test and trigger values have not yet been established.

It is therefore very important that soil compaction be prevented effectively. Up to now there have been no concepts on how to derive precautionary recommendations for action that take into account both the site-specific risk and the stress factors related to agricultural processes and machinery. The formulation of best practice recommendations is therefore very general and often limited to requiring that tyre pressure be adjusted to match the manufacturer’s recommendation.

Such recommendations neither take account of local differences nor of the effects of machinery stress exerted on subsoils. As a result, compliance with the demands of the Federal Soil Protection Act is not always achieved at present.

The project objective was to develop a test concept based on soil physical conditions and with which to assess the soil’s actual, locale-specific vulnerability to compaction.

The following areas were focal points:

• Derivation and representation of potential mechanical susceptibility of subsoils to compaction from soil maps
• Evaluation of the influence of soil moisture on mechanical susceptibility to compaction
• Evaluation of present soil structural properties based on indicators
• Derivation of vulnerability facing soil functions from soil maps
• Derivation of process-related soil pressure in subsoils.

In wet or very damp soil conditions, all of Germany’s agricultural crop land is vulnerable to interference of capacity (two-thirds ranking either ‘very high’ or ‘high’), or is at risk of exceeding the threshold values above which long-term damage occurs.

At 80% field capacity, vulnerability is divided in equal parts of three into the classes ‘high’, ‘medium’, and ‘low’. Since ‘medium’ class is considered in need of consulting services, it must be assumed—given actual moisture conditions- there is a need for such services for at least one half of all agricultural crop land.

The present project has produced an inventory of Germany’s agricultural crop land subsoils that indicates the need for widespread action while providing a method for the derivation of action measures.

Consulting services lack up-to-date information on soil moisture that accounts for local weather conditions as well as information on the pressures exerted on subsoils by machinery.

More information

• Map of vulnerability of subsoils to compaction under real moisture conditions PDF / 238 KB, in German
• Final report in German