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Hydraulic Conductivity and Soil Water Retention of Soil-Biochar Mixtures Z. Liu, B. Dugan, C.A. Masiello, and H. Gonnermann, Rice University.

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Presentation on theme: "Hydraulic Conductivity and Soil Water Retention of Soil-Biochar Mixtures Z. Liu, B. Dugan, C.A. Masiello, and H. Gonnermann, Rice University."— Presentation transcript:

1 Hydraulic Conductivity and Soil Water Retention of Soil-Biochar Mixtures Z. Liu, B. Dugan, C.A. Masiello, and H. Gonnermann, Rice University

2 Motivation CO 2 -driven acceleration of hydrologic cycle will result in both increasing drought and more intense precipitation events; Biochar may improve crop productivity by: Reducing speed of infiltration, holding water on the landscape longer; Increasing plant available water. GOAL: test the effect of biochar on these properties and determine controlling mechanisms in sandy soils.

3 Key Points: Adding Biochar to Sand Adding up to 6 wt% biochar can decrease hydraulic conductivity (K) by up to 78%; Adding up to 10 wt% biochar can increase field capacity (from 3-12%), permanent wilting point (from 2-8%) and plant available water (from 1-4%); Biochar grain size alters K; however, neither biochar grain size nor pyrolysis temperature have a large effect on plant available water.

4 K and Soil Water Retention Methods ψ=ρω 2 (r 2 -r 1 2 )/2g Column Water Sand+biochar Leachate 4 cm h 25 cm Mesh L r1r1 r Water Sand+biochar Nylon Filter ω Reservoir tube Filter tube

5 Adding up to 6 wt% Biochar, K by 78%

6 K with Flushes

7 Biochar Particles Smaller than Sand Decrease K at 6 wt% amendment

8 Potential Mechanisms Grain size effect: pore throat size and tortuosity K is mainly controlled by pore space between biochar and sand. + + r L r L r L

9 Soil Water Retention Curves More Biochar, Higher Water Content

10 More Biochar, Higher Plant Available Water Field capacity, permanent wilting point and plant available water content increase with biochar amendment rate. 2.9 ± 0.4% 11.8 ± 0.9% 1.7 ± 0.4% 8.1 ± 0.9% 4 ± 1% 1.2 ± 0.5%

11 Pyrolysis T and Biochar Grain Size Have NO effect on Available Water Content at 6 wt% Most of water in biochar-amended sand is not available to plants.

12 Conclusions Adding up to 6 wt% biochar can decrease hydraulic conductivity by up to 78%; Biochar particles smaller than sand decrease K; Adding up to 10 wt% biochar can increase field capacity (from 2.9 ± 0.4% to 11.8 ± 0.9%), permanent wilting point (from 1.7 ± 0.4% to 8.1 ± 0.9%) and plant available water (1.2 ± 0.5% to 4 ± 1%); Biochar grain size and pyrolysis temperature do not have large effect on plant available water content; Most of water in biochar-amended sand is not available to plants.

13 Extended Van Genuchten Model Where Zhang, Z. F., 2011 ψ c is solved by:

14 Biochar Migration Particle Size (mm) Biochar Skeletal Density (g/cc) < ± ± ± 0.01


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