Influence of soil texture and organic matter content on bulk density, air content, compression index and crop yield in field and laboratory compression experiments

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In the years 1971–1980, the effects of compaction during spring sowing was investigated in more than 100 field experiments in Sweden. The experiments had similar field plans, with four levels of compaction created by tractor traffic, and were usually sown with barley ( Hordeum vulgare, L.). Soil from 70 of the sites were ground and passed through a 2 mm sieve, and then compressed in a uniaxial compression test. The data were used to study the influence of soil texture and organic matter content on soil physical properties and crop yield in the field and after uniaxial compression. In the field, bulk density decreased while air content increased with increasing organic matter content. On soils with >50 g kg −1 organic matter all traffic treatments on average increased yield compared to untrafficked soil, while yield in the most compacted treatment was 11% lower on soils with <30 g kg −1 organic matter. The compression index in the field was virtually unaffected by soil texture and organic matter content, while the compression index obtained in the uniaxial test was positively correlated to the clay content. Contrary to the field results, a high organic matter content was not correlated to a decrease in the degree of compactness or an increase in air content in the uniaxial compression test. Compression was greater in the laboratory than in the field, especially at high stress levels and for soils with high clay and organic matter content. The experiments demonstrate the importance of organic matter to reduce negative effects of compaction. They also demonstrate the difficulty in assessing soil susceptibility to compaction from a traditional uniaxial compression test.