Manipulating rangeland soil microclimate with juniper biochar for improved native seedling establishment

Authors: Phillips, Claire; MEYER, KYLIE - Oregon State University; HANSON, CHAD - Oregon State University; BIRAUD, SEBASTIEN - Lawrence Berkeley National Laboratory; Trippe, Kristin

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2020
Publication Date: 12/4/2020
Citation: Phillips, C.L., Meyer, K.M., Hanson, C.V., Biraud, S., Trippe, K.M. 2020. Manipulating rangeland soil microclimate with juniper biochar for improved native seedling establishment. Soil Science Society of America Journal. 85(3):847-861. https://doi.org/10.1002/saj2.20207.
DOI: https://doi.org/10.1002/saj2.20207

Interpretive Summary: Encroachment of western juniper and invasive grasses have substantially degraded sagebrush-steppe ecosystems of the Western U.S. To control the invasion of western juniper, land managers typically harvest and burn trees, as juniper biomass has few uses and limited economic value. This study evaluated whether converting juniper to biochar and applying the biochar to rangelands could enhance seedling establishment of planted native bunchgrasses. In a field trial, biochar was found to have minimal impacts on establishment of bluebunch wheatgrass seedlings. Biochar also had no impact on soil moisture, temperature, or soil fertility. However, soil in locations where cut juniper had been piled and burned had increased nitrate availability, which subsequently enhanced seedling establishment. The trial showed juniper biochar caused no harm, but provided no clear benefits for native seedling establishment.

Technical Abstract: Encroachment of western juniper (Juniperus occidentalis Hook.) and invasive grasses have substantially degraded sagebrush-steppe ecosystems of the Western U.S. Here we evaluated whether juniper that is converted to biochar could be used in restoration seeding to improve establishment of native bunchgrasses. We hypothesized that juniper biochar could expand the window of favorable soil climate conditions for seedling establishment, either by darkening the soil surface and hastening warming in the early spring, or by enhancing soil water retention and slowing drying in the late spring. The influence of biochar application on soil albedo, temperature, and moisture were evaluated over two years, along with impacts to soil fertility and establishment of bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] Á. Löve). Plots amended with biochar were compared to plots with burn scars, where cut juniper had been piled and burned, and control plots, which were areas located between burn scars where no biochar was applied. Biochar caused a small decrease in surface albedo, but no change in soil temperature, or in situ soil moisture. Biochar had no impact on seedling establishment or growth over two years compared to control plots. Seedling establishment was highest in burn scars, possibly due to higher nitrogen availability. Biochar had minimal effects on soil physical and chemical characteristics, even when applied at a higher amendment rate than could be provisioned by the abundance of juniper biomass on the landscape. This trial showed juniper biochar caused no harm, but provided no clear benefits for native seedling establishment.