Agroscope, Institute for Sustainability Sciences ISS, Switzerland

Wheel load-carrying capacity – a useful parameter for practice

Compaction in the subsoil caused by high wheel loads is usually long-lasting, adversely affecting soil functions and productivity. Wheel load-carrying capacity is defined as the maximum wheel load for a specific tyre and inflation pressure that does not result in soil stress in excess of soil strength (defined as precompression stress). We calculated the seasonal dynamics in wheel load-carrying capacity for different tyres ( standard and low-pressure tyres) and for soil under different tillage and cropping systems (mouldboard ploughing, no till, and permanent grassland in the Oberacker long-term field experiment on a sandy loam soil). Wheel loadcarrying capacity was estimated based on in situ measurements of soil matric potential, measurements of precompression stress at various matric potentials, and simulations of soil stress. Calculations were made for a reference depth of 35 cm. Our results show wheel load-carrying capacity to be strongly dependent on soil moisture, and to be higher for low-pressure tyres than for standard tyres. The number of trafficable days – estimated by comparing actural wheel loads of agricultural machinery with the wheel load-carrying capacity – varied between years, and decreased with increasing wheel load of the machinery. Wheel load-carrying capacity is a useful and easily interpreted parameter for portraying compaction risk, and is therefore an effective guide for preventing soil compaction.

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