Immediate and long-term effects of fire and ash-fertilization on a Zambian miombo woodland soil

Abstract

The effects of burning and ash-fertilization were studied by regular time-serial sampling for 9 years after burning of piled vegetation in miombo woodland. Substantial immediate increases of available phosphorus were observed down to 40 cm soil depth; as the increase was not parelleled by an increase in pH, this may have been caused by heat rather than increased solubility of phosphorus complexes with iron and aluminum as ash is leached down into the soil. Increased levels phosphorus were also found in plots burned 16 years previously. Topsoil showed an increase in organic carbon as well as total nitrogen. The increase in total nitrogen was short-lived and the soil content of nitrogen declined rapidly to that seen prior to burning. The carbon: nitrogen ratio increased according throughout the period. The immediate increase and later depletion of exchangeable, non-acid cations, during fallow and regrowth, were paralleled by a slight increase in cation-exchange capacity with soil depth over the period.