1. 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

2. 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.

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

4. 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

5. 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%)

6. 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

7. Biochar Particles Smaller than Sand Decrease K at 6 wt% amendment
Explain each dots, point out what’s size of sand
Why choose 6wt%

8. 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

9. 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

10. 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.

11. 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.

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.
Practice, don’t just read the slide

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

14. 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