Soil Aggregation and Microbial Responses to Straw Pulping Byproducts

Wastes from straw pulping in paper manufacturing can be used as soil amendments depending on their chemical composition. Polysaccharides and lignin, the major organic components of these products, are potentially important in soil aggregation. Incubation studies were conducted to determine (i) the extent of soil water-stable macroaggregate (WSM) formation following application of black liquor (BL) and fine fiber (FF) from KOH-based bluegrass pulping as soil amendments, and (ii) the relative importance of fungi and bacteria in the enhanced WSM formation. Soil respiration rates peaked 2 d after the addition of BL or FF, while maximum WSM formation occurred at 20 d of incubation. Compared with BL- or FF-amended soils receiving no biocides, BL- and FF-amended soils receiving fungicide had decreased WSM, while BL- and FF-amended soils receiving bactericide had increased WSM, suggesting that fungal activity was more responsible than bacteria for the BL- and FF-enhanced WSM. Dehydrogenase and β-glucosidase activities did not correlate with soil respiration in BL- or FF-amended soils receiving biocides, suggesting that these enzymes may not be useful as indicators of soil microbial activity under these conditions. Additions of BL and FF at a rate of 1.5 g C kg -1 increased soil respiration dehydrogenase and β-glucosidase activities, and WSM, suggesting that both byproducts have potential as beneficial soil amendments.