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Sodium-based black liquor from fiber pulping for papermaking creates challenging waste disposal issues. By substituting NaOH with KOH in the pulping process, the resulting black liquors may be land applied as an environmentally beneficial disposal alternative. Incubation studies examined the effect of KOH-based black liquor on soil pH, electrical conductivity (EC), microbial biomass, CO 2 evolution, and soil enzyme activities in a silt loam soil. Amended soils with black liquor at rates up to 67.2 mL kg 21 soil, corresponding to 1200 kg K ha 21 were incubated at 24°C for 60 d. Increasing application rates increased soil pH, indicating that black liquor has potential as a fluid liming material. Soil EC increased with black liquor application rates, but only up to 1.04 dS m 21 , suggesting that black liquor application at these rates would not cause a salinity problem. Carbon dioxide evolution rate peaked at 2 d of incubation, and then gradually declined until the end of incubation. Metabolic quotient significantly increased with increasing application rates. Soil microbial biomass, CO 2 evolution, dehydrogenase, b-glucosidase, and arylsulfatase activities generally increased with increasing application rates throughout the incubation period. In contrast, increasing soil pH with KOH alone generally decreased CO 2 evolution and soil dehydrogenase, b-glucosidase, and arylsulfatase activities, indicating that this liquor effects in increasing soil microbial activity were possibly attributable to organic constituents contained in this liquor rather than its high pH.

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.

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