AbstractThe size of the root system was measured by means of electrical capacitance in relation to the soil in field experiments with three varieties of tetraploid red clover over a period of 3 years. The root system was greatest in the first year, smaller in the second year and least in the third year. The plants that gave an above‐average yield in any cut always had above average‐sized root systems in the preceding period, but usually after cutting, the size of their root systems decreased, an effect which was accentuated by plants drying out. The plants that dried out during the experimental period always had below average‐sized root systems in preceding periods. It was found in four cuts that the herbage dry matter of the plants with larger roots contained a smaller proportion of nitrogenous materials and ash, and more fibre, but the yield of all measured nutrients and elements increased. The ash of the herbage DM of these plants contained more potassium, calcium and magnesium. The quantity of mineral materials absorbed per unit of size of root systems was higher in the plants with larger root sy