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
Residue
OM & Erosion 80% reduction w/ 30% cover!! From Brady and Weil, 2002
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
Maize Yields
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
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
BR Ira Sprague Bowen published: I.S. Bowen. 1926. The ratio of heat losses by conduction and by evaporation from any water surface. Phys. Rev. 25:779-787. 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.
I think he could not catch fish Bowen’s friends Bowen Bowen bad at fishing so started thinking…
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
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
Carbon Dioxide [CO2] No-Till [CO2] Tilled
Delta-CO2 No-Till Delta-CO2 Tilled
Energy Balance No-Till plow
Bowen Ratio
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.
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 30-50 kg ha-1 year-1 based upon Julian Day 55 which is pretty much after grain fill.
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.
References Bowen, I.S. 1926. The ratio of heat losses by conduction and by evaporation from any water surface. Phys. Rev. 27:779-787. Held, A.A., P. Steduto, F.Orgaz, A. Matista, and T.C. Hsiao. 1990. Bowen Ratio/Energy balance technique for estimating crop net CO2 assimilation, ad comparison with a canopy chamber. Theor. Appl. Climatol. 42:203-213. Johnson, J., D. Reicosky, R. Allmaras, T. Sauer, R. Venterea, and C. Dell. 2005. Greenhouse gas contributions and mitigation potential of agriculture in the central USA. Soil Till Res. 83:73-94.