Technical Yearbook 2023

are more proliferated in the micro pores than in the macropores. The effect of compaction on microfauna in the subsoil will therefore be small. Bouwman and Arts (2000) 8 found in their research that the total numbers of nematodes were not affected by compaction. They have found that their distribution under soil compaction over the various feeding types has shifted increasingly towards a population with more herbivores and fewer bacterivores. 8 Conclusion The main benefit of conservation tillage of reduced soil disturbance and the build-up of organic material with all its benefits, cannot be denied. This does not apply to all soil types and under all climatic conditions. Due to an increase in conservation tillage equipment size and weight, like 350 kW tractors and combine harvesters that can weigh up to 60 tons, subsoil compaction tends to increase and build up over time. A reduction in soil pore spaces due to compaction will also influence water infiltration, water redistribution to the deeper profile, aeration, root growth rate and rooting depth. A temporary water table can also develop on a compacted soil layer which will cause anaerobic conditions and roots to die. This will reduce yields and the profitability of farming. Soil compaction also negatively impacts macro soil fauna. Earthworms and springtail numbers decline due to soil compaction. It seems from the literature that micro-fauna and -flora are not that sensitive to soil compaction. If this subsoil compaction is not alleviated annually, or at least every two years, the farmers will experience yield losses of up to 20% in the first year after compaction. Only in soils that freeze annually, can the compaction be alleviated naturally through the freezing and thawing action. 

FIGURE 4. Change in weight of (a) front wheel loads of combine harvesters as quoted by Keller and other authors (2019) 17 from data of Schjønning and other authors (2015) and (b) rear wheel loads of tractors (data source: Deere & Company, Moine, IL, USA).

of macropores, 5 the habitable pore spaces for macrofauna are reduced, and therefore also the numbers of macrofauna like earthworms, 16 springtails and arthropods. The numbers of Mesaphorura macrochaeta and Protaphorura armata were impacted by an increase in bulk densities. Their numbers decreased when the bulk density (compaction) increased from 1.02 to 1.56 g cm -3 . 19

Soil compaction lowers the species richness of surface-active arthropods, while it does not have a big influence on the numbers present in the soil. 22 In a study done on the black soil of Northeast China, it was found that the abundance and richness of bacteria and arbuscular mycorrhizal fungi were greater in conservation tillage than in conventional tillage practices. 30 The microfauna and flora

FIGURE 5. Change in wheat yields between 1961 - 2016 in Scandinavia. Conservation tillage started in the late 1980s. Note the declining trend since 1990. 17

References https://www.wineland.co.za/soil-compaction-the-silent-killer-of-conservation-agriculture/

For more information, contact Eduard Hoffman at ehoffman@sun.ac.za.

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TECHNICAL YEARBOOK 2023