In the Belgian marsh-area many soils have a bad surface-structure. Their top soil is non-calcareous, while the subsoil presents a considerable amount of lime. In many cases an impermeable claylayer is found at a depth of 30-40 cm. After heavy rainfalls these soils show a strong degradation of the structure. The topsoil is muddy, with a typical shiny appearance and the seeds do not run out or only partially. These soils can be improved by deep- ploughing to 50-100 cm, given that the calcareous subsoil is brought to the surface. After this process had been successfully applied in 1952 as a field experiment, there was no decrease of yield. In 1955 the yield had increased with 8 %. The soil had become more productive and the new topsoil needed no more liming
