INFLUENCE OF SOIL TEXTURE AND ORGANIC-MATTER CONTENT ON BULK-DENSITY,AIR CONTENT, COMPRESSION INDEX AND CROP YIELD IN-FIELD AND LABORATORYCOMPRESSION EXPERIMENTS

In the years 1971-1980, the effects of compaction during spring sowing was investigated in more than 100 field experiments in Sweden. The ex periments had similar field plans, with four levels of compaction crea ted by tractor traffic, and were usually sown with barley (Hordeum vul gare, 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 da ta were used to study the influence of soil texture and organic matter content on soil physical properties and crop yield in the field and a fter 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 in creased yield compared to untrafficked soil, while yield in the most c ompacted treatment was 11% lower on soils with <30 g kg(-1) organic ma tter. The compression index in the held was virtually unaffected by so il texture and organic matter content, while the compression index obt ained in the uniaxial test was positively correlated to the clay conte nt. Contrary to the field results, a high organic matter content was n ot correlated to a decrease in the degree of compactness or an increas e in air content in the uniaxial compression test. Compression was gre ater in the laboratory than in the field, especially at high stress le vels and for soils with high clay and organic matter content. The expe riments demonstrate the importance of organic matter to reduce negativ e effects of compaction. They also demonstrate the difficulty in asses sing soil susceptibility to compaction from a traditional uniaxial com pression test. (C) 1998 Published by Elsevier Science B.V. All rights reserved.