1. Carbon sequesTRAtion in a tilled and untilled field in lesotho, southern africa
N.S. Eash1, W. Bruns1, F.R. Walker1, D. Lambert1, M. Wilcox1, M. Marake2.
1University of Tennessee, Knoxville; and 2The National University of Lesotho, Roma

3. Residue

4. OM & Erosion
80% reduction w/ 30% cover!!
From Brady and Weil, 2002

6. Lesotho “Kingdom in the Sky”
Over 80% of the country lies above 5,900 ft
Population 2,3 million (81% rural)
11,720 square miles
Economy: water & electricity, agriculture, livestock, & labor

10. Maize Yields

11. C Sequestration 5-year USAID project on conservation agriculture
Determine CA impact on gender, economics, networks…
And C sequestration
Problem is that losing C is a fast process, gaining C is a slower process
Evaluated eddy flux and Bowen’s Ratio Energy Balance (BREB)—I chose BREB

12. Carbon Cycle Energy + CO2 Winter=cold
More C is lost than is added under
many of our “conventional” practices
Plants and roots
CO2
harvest C
lost
Microbial
decay
tillage
CO2
CO2
CO2
CO2
CO2

13. BR Ira Sprague Bowen published:
I.S. Bowen The ratio of heat losses by conduction and by evaporation from any water surface. Phys. Rev. 25:
Calculated the energy balance of any body of water that is thermally insulated on three sides (most lakes)
BR= H/LH where
H = sensible heat; and
LH = latent heat
He really wanted to know why it was cooler on the lake when he was fishing –if there was a wind blowing– than on land.

14. I think he could not catch fish
Bowen’s friends
Bowen
Bowen bad at fishing so started thinking…

15. BR + Energy Balance Today we add in some other components:
Rn = Net radiation
G = Conductive soil heat flux
H = sensible heat (heat by convection)
LE = latent heat
Which gives us the following energy balance for terrestrial systems:
Rn –G = H + LE
And the actual Bowen Ratio (BR) is:
B = H/LE
A positive BR indicates energy into the system (and that CO2 is also being sequestered if we add that into the measurements…)
We can add in CO2 flux because of commonality in transfer coefficients for water vapor and CO2

16. Instrumentation
Measure the following at two heights (0.1-m and 1.1-m above the canopy):
CO2
Relative humidity via psychrometers (fans move air over wet and dry bulbs at 5-m sec-1
Net radiation
Soil heat flux
Wind speed (anemometer)
Soil temperature
Soil water content
Soil CO2 flux for comparison

19. Carbon Dioxide
[CO2] No-Till
[CO2] Tilled

20. Delta-CO2 No-Till
Delta-CO2 Tilled

21. Energy Balance
No-Till
plow

22. Bowen Ratio

23. Bowen Ratio - (No-Till) Cloudy Day Energy Balance - No-Till Cloudy Day
You can see that sun comes out around 0700 on day of year 345, and soil heat flux (G) begins to decrease as the net radiation (Rn) increases, increasing sensible heat (H). Clouds com in around 1700 hours and as the sunsets, the soil heat flux (G) increases. Day of year 346 has much lower Rn values and higher soil heat flux (due in part to energy released by microbial respiration?) because it was overcast.

24. Finally…
A negative CO2 flux means that CO2 is being sequestered; a positive value means that it CO2 is being lost from the system
Units are kg CO2-C sec -1
Perhaps something like kg ha-1 year-1 based upon Julian Day 55 which is pretty much after grain fill.

25. Conclusions
BREB is providing data suggesting that at our paired site in Lesotho the CA site is sequestering C at a rate fairly close to published values.
BREB is a finicky setup that provides good data if diligence prevails.
It is not easy…
We are grateful to Tom Sauer (USDA-ARS NSTL) for his assistance.

27. References
Bowen, I.S The ratio of heat losses by conduction and by evaporation from any water surface. Phys. Rev. 27:
Held, A.A., P. Steduto, F.Orgaz, A. Matista, and T.C. Hsiao Bowen Ratio/Energy balance technique for estimating crop net CO2 assimilation, ad comparison with a canopy chamber. Theor. Appl. Climatol. 42:
Johnson, J., D. Reicosky, R. Allmaras, T. Sauer, R. Venterea, and C. Dell Greenhouse gas contributions and mitigation potential of agriculture in the central USA. Soil Till Res. 83:73-94.