Soil Microbial Responses to Potassium-Based Black Liquor from Straw Pulping

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 - 1 soil, corresponding to 1200 kg K ha - 1 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 - 1 , 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, β-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, β-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.