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**Z. Liu, B. Dugan, C.A. Masiello, and H. Gonnermann, Rice University**

Hydraulic Conductivity and Soil Water Retention of Soil-Biochar Mixtures Z. Liu, B. Dugan, C.A. Masiello, and H. Gonnermann, Rice University Good afternoon, everyone. It is my great pleasure to be here to present our work: Let me Acknowledge my coauthors, my phd advisors: B and C. and our collaborator, H. Our work is funded by NSF and Shell center

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Motivation CO2-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. Our motivation of this work are: the CO Hydraulic conductivity describes how fast water drains through soil.

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**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. Explain what is FC, PWP, and AWC; Fc increase Also pwp increase Result in Plant available increase less than fc and pwp

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**K and Soil Water Retention Methods**

Column Water Sand+biochar Leachate 4 cm h 25 cm Mesh L r1 r Water Sand+biochar Nylon Filter ω Reservoir tube Filter tube Explain More detailed, more practice Use ‘sand+biochar’ instead of ‘soil sample’ in the figure Let me show how did we measure K and soil water retention. We measured K by falling head experiment. We put sand+biochar mixture into a column and pour water in the column to monitor how hydraulic head changed with time. The K is calculated by this equation. K is equal to sample length dived by time differences between t and t, times ln hydraulic head at t diveded by hydraulic head at t. We measure soil water retention by centrifuge method, we pour sand biochar into a centrifuge tube and saturated the sample. Then we put these sample into centrifuge spin then at certain centrifuge speed, the water will come out from the end of sample during centrifugation. When centrifuge force is equal to soil suction. Which means the sample get equalibrium. We measure and water content of sample and calculate soil suction by this equaltion, ψ=ρω2 (r2-r12)/2g

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**Adding up to 6 wt% Biochar, K↓ by 78%**

2mins, remind what is K, x axis Separate into 2 slides, start with average K vs amendment rate, then next K vs flushes Explain what is K, what is x axis, y axis, legend, define NB, BC, An order of K drop, with adding more Spend more time to describe figure, increase of flush, we see change of K, the key point here is the K drease from 0-6% Color figure, avoid yellow, blue-red, bigger figure Delete b), explain axis, K is in log scale, BC (linear scale), significant decrease (78%)

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K↓ with Flushes 2mins, Separate into 2 slides, start with average K vs amendment rate, then next K vs flushes Explain what is K, what is x axis, y axis, legend, define NB, BC, An order of K drop, with adding more Put pics to show BC moved after conclusion slide Color

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

Explain each dots, point out what’s size of sand Why choose 6wt%

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**Potential Mechanisms + +**

Grain size effect: pore throat size and tortuosity r L r + L r + Model to explain grain size figure Add 1 more pic to show when BC is the same to sand, it doesn’t change pores K is mainly controlled by pore space between biochar and sand. L

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**More Biochar, Higher Water Content**

Soil Water Retention Curves Bigger legend, explain FC, FWP and AWC More practice, More clear, Existing results FC increase by BC, our results also show PWP, color figure 1, Say how did we get FC, PWP,(BY EX-VG) and AWC=FC-PWP, 1 more slide backup for ex-VG More Biochar, Higher Water Content

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**More Biochar, Higher Plant Available Water**

11.8 ± 0.9% 8.1 ± 0.9% 2.9 ± 0.4% 4 ± 1% Delete a, write out field capacity….. in the figure Make it more clear that fc increase, pwp, increase, but awc doex not increase as much as fc Point out importance of plant available, We see improvement of plant available water, but not as much as fc, the increase of field capacity is not all plant available, show number of FC, PWP, AWC in the figure 1.7 ± 0.4% 1.2 ± 0.5% Field capacity, permanent wilting point and plant available water content increase with biochar amendment rate.

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**Pyrolysis T and Biochar Grain Size Have NO effect on Available Water Content at 6 wt%**

Animation (blue and green line disappear) Break into 2 figures Most of water in biochar-amended sand is not available to plants.

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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. Practice, don’t just read the slide

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**Extended Van Genuchten Model**

Where ψc is solved by: Zhang, Z. F., 2011

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**Biochar Skeletal Density**

Biochar Migration Particle Size (mm) Biochar Skeletal Density (g/cc) <0.251 1.59 ± 0.01 1.497 ± 0.009 1.47 ± 0.01

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