Dynamics of nutrients in tropical acid soils amended with paper pulp sludge

摘要

Paper mill sludge is characterized by highconcentrations of organic matter and lime and very lowconcentrations of heavy metals and organic chemicals. Interestin the recycling of paper mill residuals in developing countriesis vital because the use of lime and fertilisers by small farmers isfinancially prohibitive. The effects of paper pulp sludge andlime on the dynamics of soil nutrients was studied in thelaboratory using columns of mixed samples of top soil fromthree tropical acid soils (Kandiudult). The soil columns wereleached over a period of 90 days with de-ionized water inamounts equivalent to the annual rainfall of the sampling site.To assess the amount of nutrient that may become available toplants, NH4OAc-EDTA pH 4.65 soil extractant was used. For allsoils, application of paper pulp sludge or lime to tropical acidsoils generally resulted in an initial flush and increasedconcentrations of Ca, Mg, S04, dissolved organic carbon (DOC)and inorganic carbon in soil leachates. Compared with liming,application of paper pulp sludge reduced N03 leaching. Theamount of leached Ca, DOC and inorganic carbon (mainlyHCO3-) increased substantially with the addition of paper pulpsludge or lime. In relation to nutrients, the most meaningfulamendment effect that persisted after leaching was asubstantially increased available Ca in the treated soil. Inaddition to increasing Ca levels, the addition of paper pulpsludge increased the concentrations of leached and available Ca.To sustain yield increase with paper pulp sludge, calculation ofthe optimum quantity to be returned to the soil should be basedon losses of Ca by leaching and by plant uptake.