Residual value of ferrous sulfate for clover production on humic sandy podsols

The residual value of ferrous sulfate, as an iron fertiliser, was measured in 3 field experiments using yield of dry herbage of clover (Trifolium subt erraneanum L.). The clover was grown on limed acid peaty sandy soils and th e iron fertiliser was spread over the soil surface. In 1995, the effectiven ess of freshly applied iron was compared with that of iron applied 1-5 year s previously. Additions of iron increased clover herbage (DM) yield by abou t 0.80 t/ha in October. The longer the period since iron was applied, the l ess effective was the fertiliser. Iron applied 1 year previously was about 60% as effective as current iron while iron applied 5 years previously was about one-third as effective as current iron for herbage production. About 15-20 kg of freshly applied iron/ha was required for maximum DM yield of cl over. The critical concentration of iron in the whole shoot of clover plant s for 90% of maximum DM yield was about 70 mg/kg.