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

Paper mill sludge is characterized by high concentrations of organic matter and lime and very low concentrations of heavy metals and organic chemicals . Interest in the recycling of paper mill residuals in developing countries is vital because the use of lime and fertilisers by small farmers is finan cially prohibitive. The effects of paper pulp sludge and lime on the dynami cs of soil nutrients was studied in the laboratory using columns of mixed s amples of top soil from three tropical acid soils (Kandiudult). The soil co lumns were leached over a period of 90 days with de-ionized water in amount s equivalent to the annual rainfall of the sampling site. To assess the amo unt of nutrient that may become available to plants, NH4OAc-EDTA pH 4.65 so il extractant was used. For all soils, application of paper pulp sludge or lime to tropical acid soils generally resulted in an initial flush and incr eased concentrations of Ca, Mg, SO4, dissolved organic carbon (DOC) and ino rganic carbon in soil leachates. Compared with liming, application of paper pulp sludge reduced NO3 leaching. The amount of leached Ca, DOC and inorga nic carbon (mainly HCO3) increased substantially with the addition of paper pulp sludge or lime. In relation to nutrients, the most meaningful amendme nt effect that persisted after leaching was a substantially increased avail able Ca in the treated soil. In addition to increasing Ca levels, the addit ion of paper pulp sludge increased the concentrations of leached and availa ble Ca. To sustain yield increase with paper pulp sludge, calculation of th e optimum quantity to be returned to the soil should be based on losses of Ca by leaching and by plant uptake.