Biochar application method affects soil moisture and seedling establishment

Authors: Phillips, Claire; Meyer, Kylie; Trippe, Kristin

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2020
Publication Date: 6/3/2020
Publication URL: https://handle.nal.usda.gov/10113/6973884
Citation: Phillips, C.L., Meyer, K.M., Trippe, K.M. 2020. Biochar application method affects soil moisture and seedling establishment. Geoderma. 375. https://doi.org/10.1016/j.geoderma.2020.114457.
DOI: https://doi.org/10.1016/j.geoderma.2020.114457

Interpretive Summary: The rapid expansion of juniper woodlands over the last century has degraded millions of acres of rangeland by severely limiting soil and surface water. Biochar is produced from low value feedstocks and generally is used to improve soil deficiencies. Converting juniper to biochar is one option for using the low-value biomass that results when from juniper is logged. We evaluated the utility of juniper biochar as a soil amendment for improving restoration of native grasses. We hypothesized that biochar could expand the window of favorable soil climate conditions for seed establishment by slowing soil drying. In a greenhouse experiment we showed that the method used for amending biochar influenced germination and survival of native bunchgrass seedlings. Applying biochar on top of the soil was not effective at keeping water in the soil, and inhibited germination. In contrast, mixing biochar into soil significantly slowed soil drying and increased seedling biomass by 70%. However, computer simulations indicated that biochar could increase, have no impact, or decrease soil moisture content, depending on application method and moisture conditions. These results suggest a possible role for biochar in altering soil microclimate and enhancing seed establishment, but also show that outcomes are dependent on application method and precipitation conditions.

Technical Abstract: Juniper biochar was evaluated for its utility in improving restoration of native bunchgrasses. We hypothesized that biochar could expand the window of favorable conditions for seedling establishment by slowing soil drying. In a greenhouse study, applications of biochar on the soil surface were compared to incorporation of biochar, and improvements in water content, germination, and seedling survival were evaluated. We then expanded on these findings by simulating soil water content under weather and drainage conditions that might be encountered in the field, using the Hydrus-1D model parameterized with moisture-retention curves for the biochar and soil. The greenhouse study showed that applying any depth of biochar on top of soil was not effective at improving soil water content, and furthermore inhibited germination of bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve). In contrast, mixing biochar into soil significantly slowed initial drying and increased seedling biomass by 70% compared to unamended soil. However, moisture benefits of biochar incorporation were temporary, and as the soil dried, the treatment with incorporated biochar lost more water than soil that was unamended or that had biochar as a top layer. Model simulations suggested that a surface application of biochar had no benefit under wet conditions, but once the biochar was dry tended to reduce evaporation of the underlying soil and improve water content at seeding depth. This study suggested that biochar can improve, have no effect, or worsen soil water content, depending on the application method and the timing and quantity of moisture additions.