SUBSOIL STRENGTH AND YIELD OF VEGETABLE CROPS

In a field experiment over two years, broad beans (Vicia faba), cabbage (Brassica oleracea var. capitata), leeks (Allium porrum) and red beet (Beta vulgaris var. esculenta) were grown on a sandy clay loam soil in which a range of bulk densities and penetration resistances had been established by (1) thorough loosening to 0.9 m by trenching, (2) artificially compacting with tractor wheelings or (3) leaving unloosened. Loosening the soil substantially increased, and compacting it decreased, yields of all four crops. The mean penetration resistance of the subsoil at field capacity correlated negatively with dry matter production. The relationship was broadly similar for all crops and years, showing a decrease in dry matter production of about 1 t ha-1 per 0.5 MPa increase in resistance over the range examined.