Five soils from the South of England were incubated with additions of magnesium fertilizers; two also received magnesian limestone. After two years, the recovery of the added magnesium by 0.5 h extraction with 1 M ammonium nitrate was 75-89%0 for kieserite granules, 6444% for calcined magnesite powder ( < 1 mm), but only 20-41% for calcined magnesite granules (1-3 mm) and 26-32% for ground magnesian limestone. These were all much greater than the Mg dissolved by extracting the fertilizers directly in 1 M ammonium nitrate.In calcareous soils, recovery of Mg was less from the calcined magnesite but most of this reduction was due to its particle size rather than to soil pH.The four magnesium sources are evaluated as fertilizers for agriculture. Kieserite is the most reliable means of raising low soil Mg status.