A short-term assessment of carbon dioxide fluxes under contrasting agricultural and soil management practices in Zimbabwe

Authors: O'DELL, DEB - University Of Tennessee; Sauer, Thomas; HICKS, BRUCE - Metcorps; THIERFELDER, CHRISTIAN - International Maize & Wheat Improvement Center (CIMMYT); LAMBERT, DAYTON - University Of Tennessee; LOGAN, JOANNE - University Of Tennessee; EASH, NEAL - University Of Tennessee

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2015
Publication Date: 2/15/2015
Publication URL: http://handle.nal.usda.gov/10113/60352
Citation: O'Dell, D., Sauer, T.J., Hicks, B.B., Thierfelder, C., Lambert, D.M., Logan, J., Eash, N.S. 2015. A short-term assessment of carbon dioxide fluxes under contrasting agricultural and soil management practices in Zimbabwe. Journal of Soil and Water Conservation. 7(3)32-48.

Interpretive Summary: Determining how much the greenhouse gas CO2 is released or consumed by agricultural systems is of interest with regard to global climate change. Measuring CO2 production is one way to determine whether the crop and soil is acting either as a source or sink of CO2. If it is a sink, CO2 is being removed from the atmosphere and stored in biomass and soil. This is good for global climate change, crop production, and soil quality. Although there are a lot of CO2 measurements for many different cropping systems, there is very little data for cropping systems in developing countries in Africa. In this study, CO2 transport was measured for fallow, tilled fallow, wheat cover crop, and lupin cover crop in Zimbabwe. Several weather and soil properties were also measured in each of the four small fields. A CO2 transport monitoring system was designed to work under conditions of limited technological support and training. The results indicate that the wheat cover crop was a CO2 sink, the fallow treatments were sources, and the lupin cover crop was a small source. These results are likely due to the uptake of CO2 by the strong wheat growth. The fallow systems lost CO2 through decomposition of plant residue and had no growing plants to take up CO2. The lupin cover crop was very sparse indicating that the plant growth nearly offset CO2 loss from residue decompostion. These results are of interest to researchers and policymakers interested in cover crops in conservation agriculture (CA) systems as potential climate change mitigation and soil quality improvement practices for southern Aftrica.

Technical Abstract: Two of the biggest problems facing humankind are feeding an exponentially growing human population and preventing the negative effects of climate change from record concentrations of atmospheric greenhouse gases (GHGs). Agriculture could address both of these problems. For example, tillage and cover crops increase yields by improving soil fertility and sequestering carbon (C). If one considers agriculture to be one of the biggest drivers of deforestation and land degradation, then directly and indirectly it could be responsible for as much as one third of global GHG emissions. Research can demonstrate which agricultural practices sequester C in concert with other co-benefits of increased soil fertility and yields, i.e., sustainability. This is especially important where there is a lack of detailed data on farming conditions (e.g., climates and soil types) and on small farmholder practices such as in developing countries. The study presented here was conducted at an agricultural research station in Zimbabwe, with the intent to (a) demonstrate the utility of micrometeorological methods for measuring CO2 exchange rates between the surface and the atmosphere, and (b) to quantify differences in such exchange rates for a variety of agricultural surfaces. Four Bowen ratio energy balance systems were established in June 2013 on 0.64 ha sites at the International Maize and Wheat Improvement Center (CIMMYT) in Harare, Zimbabwe, comparing the following practices: conventional plowing followed by fallow, untilled followed by fallow, no-till followed by planting of winter wheat (Triticum aestivum), and minimum till followed by planting of blue lupin (Lupinus angustifolios L.). Continuous micrometeorological and other environmental properties were collected through October for the estimation of CO2 flux density of the contrasting tillage and cover crop practices. Calculations showed that the winter wheat cover crop produced a net sequestration of 953 g CO2 m-2, while a bare-fallow till plot emitted 556 g CO2 m-2 and a bare-fallow untilled plot emitted the most at 804 g CO2 m-2. The blue lupin cover crop emitted less than both fallow plots at 288 g CO2 m-2. Our micrometeorological methods reported here can discern differences in exchange rates between cover crop types and can even distinguish small differences between land that is tilled and that which is not.