Hydraulic Reponse of Macropores, Biochar, and Heat on High-Permeability Soils

Overview

Wildfires can alter soil properties, making soils water-repellent and increasing the risk of flooding, erosion and long-term land degradation. This experiment examined how different soil treatments affect water infiltration and moisture retention in cactus and garden soils, including burned soil, soil amendments mix, macropores, and biochar. Infiltration speed varied strongly between treatments. Burned soil showed slower infiltration than unburned soil (5000 mL average compared to 5150 mL), while the addition of macropores produced the fastest water movement (15-20 second first drops and up to 5300mL total drainage). Biochar and mixed treatments showed intermediate infiltration behavior (5100-5250mL). Across all treatments, total drainage was similar (ranging from 5000 to 5300mL), indicating that differences were primarily related to how quickly water moved into the soil rather than how much water drained overall. Soils amended with macropores or biochar showed greater increases in soil moisture after infiltration than untreated soils. These results demonstrate that soil structure plays a stronger role in infiltration speed than soil composition alone. Macropores consistently reduced the time for water to enter the soil by creating preferential flow pathways, making them the most effective treatment tested in both burned and unburned soils. Biochar increased soil moisture retention but did not consistently improve infiltration speed, suggesting it primarily affects water-holding capacity rather than water movement. In fire-prone regions such as California, poor post-fire drainage has contributed to severe erosion and sediment entering waterways like the Sacramento River. Implementing effective soil treatments can help build more resilient soils and landscapes following wildfires.

Competition history

• CSEF 2026 Earth & Environmental Sciences (Track 2) (Junior Division) · Entry J-09-16

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