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

Abstract

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 financially prohibitive. The effects of paper pulp sludge and lime on the dynamics of soil nutrients was studied in the laboratory using columns of mixed samples of top soil from three tropical acid soils (Kandiudult). The soil columns were leached over a period of 90 days with de‐ionized water in amounts equivalent to the annual rainfall of the sampling site. To assess the amount of nutrient that may become available to plants, NH4OAc‐EDTA pH 4.65 soil extractant was used. For all soils, application of paper pulp sludge or lime to tropical acid soils generally resulted in an initial flush and increased concentrations of Ca, Mg, SO4, dissolved organic carbon (DOC) and inorganic carbon in soil leachates. Compared with liming, application of paper pulp sludge reduced NO3 leaching. The amount of leached Ca, DOC and inorganic carbon (mainly HCO3‐) increased substantially with the addition of paper pulp sludge or lime. In relation to nutrients, the most meaningful amendment effect that persisted after leaching was a substantially increased available Ca in the treated soil. In addition to increasing Ca levels, the addition of paper pulp sludge increased the concentrations of leached and available Ca. To sustain yield increase with paper pulp sludge, calculation of the optimum quantity to be returned to the soil should be based on losses of Ca by leaching and by plant uptake.

Chemical and leaching properties of paper mill sludge

“…cellulose fibres, lignin), composting and land applications are also attractive alternatives to disposal (Voundi Nkana et al, 1999). According to the criteria of the Ministry of Agriculture and Forestry in Finland, the organic matter content of compost (expressed as LOI), has to be at least 20% (dry weight) for it to be classified as a soil improver.…”

“…The main organic components in the paper mill sludge are wood and cellulose fibres of different lengths, lignin and to some extent also organic binders. The main inorganic components in the paper mill sludge are kaolinite (clay) and calcium carbonate, which are paper additives, as well as heavy metals present as impurities, which mainly originate from the wood raw material (Voundi Nkana et al, 1999;Zhang et al, 2004).…”

Pulp and paper effluent management

“…Voundi Nkana et al (1999) studied the dynamics of nutrients in tropical acid soils amended with paper mill residuals or lime in the laboratory using columns of mixed samples of top soil from three tropical acid soils. Application of the paper mill residuals or lime to all the tropical acid soils generally resulted in an increased concentration of Ca, Mg, sulfate, dissolved organic carbon (DOC), and inorganic carbon in soil leachates.…”