By boiling a I : 2 suspension of soil in water under reflux for 15 minutes, a quantity of boron was extracted which gave a good index of the amount available to plants. If this ‘available’ boron fell below 0.7‐1.0 p.p.m. of air‐dried soil, raan (brown heart) was liable to occur in swedes grown in the area. Dressings to the soil of up to 30 lb. of borax per acre increased the available boron by substantial amounts. The boron content of the swedes cropped was also raised considerably and the incidence of raan lowered, and no toxic effects of borax treatment were noted. There was no effect on yield of roots and only a little on dry‐matter content. An application of limestone to a heavy soil, bringing the pH up to 8‐1, caused only negligible symptoms of raan in a swede crop and did not appear to fix any of the applied boron.