Soil microbial activity, aggregation and nutrient responses to straw pulping liquor in corn cropping

The cereal and grass seed cropping systems of the Pacific northwestern USA generate a valuable fiber source for papermaking. Pulping straw with KOH produces black liquor, an organic waste effluent with potential as a K source and soil amendment. The objectives of this study were to determine if black liquor from wheat straw pulping with KOH improves soil quality including soil aggregation, microbial biomass and microbial activity, and corn yield. A 2-year field trial with a randomized complete block design was conducted with black liquor or KCl applied at 168 and 336 kg K ha−1 at two sites, respectively, planted to corn in Central Washington. Black liquor applied at rates of 168 and 336 kg K ha−1 slightly increased soil pH by 0.2 to 1.4 units and electrical conductivity by 0.0 to 0.8 dS m−1 at both sites, and significantly increased soil test K compared to the nonamended control by 199 to 368 mg K kg−1 soil in the top 5 cm at Paterson and by 44 to 200 mg K kg−1 soil in the top 5 cm at Prosser. Corn had no yield response to the application of either K sources, black liquor, or KCl applied at both rates at both sites. Generally, black liquor applied at these rates increased soil dehydrogenase, β-glucosidase, and arylsulfatase activities, microbial biomass C, and soil wet stable macroaggregates in the top 5-cm soil at both sites. The results of this study suggest that the organic-rich waste liquor from wheat straw pulping with KOH may improve soil quality and soil test K without reducing crop productivity.