Nutrient dynamics in tropical acid soils amended with wood ash

Sustained growth and yield can be achieved when adequate quantities of nutr ients are regularly returned to the soil. The effects of wood ash and lime on the dynamics of soil nutrients were studied in the laboratory using colu mns of mixed samples of topsoils from three tropical acid soils (Kandiudult ). Amendments were applied to attain 80% base saturation and at amount corr esponding to I and 2 times the content of exchangeable Al. The soil columns were leached for a period of 90 days with an amount of deionised water equ ivalent to the annual rainfall. Available nutrients in the soil was measure d with NH(4)OAcEDTA pH 4.65 extract. In general, wood ash affected leachate composition more than lime. Application of wood ash led to increases in co ncentrations of DOG, NO3, SO4, Ca, Mg and K in the leachates and losses inc reased with wood ash application rates. Available Ca in the soil subsequent to leaching increased with both wood ash and lime, while available Mg and K increased with wood ash but was not affected with lime. Increases in the leached and available Ca, Mg and K were significant with wood ash applicati on compared to liming. In this particular experimental conditions, an annua l maintenance dressing with wood ash of 4.6 t.ha(-1) in soil Mb, 5.7 t.ha(- 1) in soil Me and 4.3 t.ha(-1) in soil Nk would provide enough Ca to compen sate losses. However, when taking into account simultaneous additions of Mg and K with wood ash, only their leaching losses can be recovered. Therefor e, adequate supplementation with ME and K fertilisers is still needed to ob tain maximum crop yield for the next growth cycle.