Black Liquors from Bluegrass Straw Pulping: Effects on Corn Growth and Soil Properties.
Canming Xiao, Department of Crop and Soil Sciences, Washington State University, Pullman, WA 99164-6420, William McKean, University of Washington, Seattle, WA 98195-6613, and William L. Pan, Dept. of Crop & Soil Sciences, Washington State University, Pullman, WA 99164-6420.
Crop straw residues represent an alternative fiber source for papermaking. However, black liquors generated from straw pulping can be used as soil amendments that can either improve or degrade soil quality. Substitution of KOH for NaOH pulping chemistry should generate a black liquor that can be used a beneficial amendment. A growth chamber experiment was conducted to determine (i) whether K-based black liquor had potential as a K source, and (ii) evaluate the effects of black liquors from bluegrass straw with KOH, NaOH or substitution of 50% NaOH with 50% KOH on corn growth and soil properties. Three black liquors applied at a lower rate (100 mg C kg-1 soil) increased corn dry biomass compared to non-amended control. K-based black liquor increased corn dry biomass compared to KCl at the same K rate, therefore the corn response to the lower rate of black liquors was not related to K supply. All black liquors applied at higher rates (from 200 to 500 mg C kg-1 soil) decreased corn biomass, but not lower than non-amended control . These negative responses did not appear to be related to salinity issues, since increases in EC were marginal. The negative responses were most severe with the Na-based black liquor, despite the fact that the sodium exchange percentage was much lower than 15%. The results of this study suggest that while pulping black liquor can be beneficial to plant growth, optimal ranges of application need to be defined.