Performing Department
Plant & Soil Science
Non Technical Summary
Soil carbon credits, which can be accrued through the use of conservation-tillage and grassland restoration practices, can be bought and sold in a stock-exchange-like market (Schneider and McCarl, 2003) to off-set carbon dioxide (CO2) emissions to the atmosphere from large companies and utilities. The agricultural community has a competitive advantage in the carbon economy because soils, if properly managed, can sequester atmospheric carbon as soil organic carbon (SOC). Conversion from conventional- to conservation-tillage practices provides a management mechanism for increasing soil carbon stocks. Marketing carbon credits can represent an added economic incentive to producers to continue using or convert to more environmentally friendly and sustainable agricultural management practices. Additionally, perennial biomass energy crops, many of which are grasses and may be a future focus of US producers, also have the potential to sequester SOC, adding an economic dimension to dedicated energy crops (Lemus and Lal, 2005; Liebig et al., 2005; Omonode and Vyn, 2006; Tillman and Lehman 2006). For the carbon economy to be politically-, legislatively-, and economically-viable, science-based methods for monitoring and verifying SOC changes must be accurate, sensitive, and practical. However, soil carbon sequestration rates have been developed for carbon credit accrual in upper-mid-western states, but not for southern states. Since potential carbon sequestration is generally greater for soils with low SOC (VandenBygaart et al., 2003), southern soils (i.e., Alfisols and Ultisols), particularly those of the Mississippi River Delta region and other areas throughout the southern US, may have a greater potential for carbon sequestration than upper-mid-western soils (i.e., Alfisols and Mollisols) due to the generally lower SOC contents. If carbon credits for the southern US are set based on the soil carbon sequestration potential of upper-mid-western soils, producers will likely not be fully compensated for their conservation practices if soil carbon sequestration potentials are indeed greater in the southern US than in the upper mid-west.In addition to initial SOC level, soil carbon sequestration depends on soil texture (Ihori et al., 1995; Percival et al., 2000; Brye and Kucharik, 2003), land use or management system (West and Post, 2002) and time (i.e., consistent duration of current land use or agricultural management system; Potter et al., 1999; Brye and Kucharik, 2003; Tolbert et al., 2002; Post et al., 2004). Therefore, it is essential to develop appropriate soil carbon sequestration potentials for Mississippi soils, across varying soil textures and cropping systems, so that producers can maximize economic benefits for employing more-sustainable, conservation-tillage practices and contribute to decreasing the rising atmospheric CO2 concentrations.The build-up or accrual of carbon from the atmosphere can occur in soil, biomass (e.g.., forests), and oceans and is known in general as carbon sequestration. Since soil is estimated to contain nearly double the amount of organic carbon contained in the atmosphere, it is believed that soil can act as a significant carbon sink because of soil's known responsiveness to modification (i.e., various residue and general soil management strategies; Baker et al., 2007). Lal et al. (2003) projected soil carbon sequestration rates of 24 to 40 Mt C yr-1 if widespread adoption of conservation-tillage practices, generally defined as any tillage practice that leaves enough crop residue to cover 30 % of the soil surface, occurred throughout the US. In a global analysis based on 67 long-term experiments, West and Post (2002) reported that 57 (± 14) g C m-2 yr-1 could be sequestered in the soil by conversion from CT to NT. Similarly, Post and Kwon (2000) reported a mean global carbon sequestration rate of 33.2 g C m-2 yr-1 upon conversion from agriculture to grasslands. However, soil carbon sequestration is not a continuously increasing ecosystem function. By documenting SOC accumulation under different climates, land uses, and soils, it is expected that the results of this project will provide producers, and policy makers credible and comprehensive information on the environmental merit of adopting different land uses such as bio-energy crops and conservation-tillage practices in the southern US. It is also expected that the project will facilitate the establishment of a carbon-trading farm economy in the southern US by providing credible and realistic data on soil carbon sequestration potentials.
Animal Health Component
10%
Research Effort Categories
Basic
90%
Applied
10%
Developmental
0%
Goals / Objectives
The soil C sequestration potential of common cropping systems and land uses, including bio-fuel crops, on benchmark soils throughout the southern US are largely unknown. Similarly, the impact of climate regime, which can have a varying effect across the southern states, on soil C sequestration potential is largely unknown. Therefore, to address these present knowledge gaps and unify present research activities in the southern and south-eastern US into a common goal, the overall objective of this regional research project is to assess the soil carbon sequestration potential of common agricultural and natural ecosystems of varying ages on benchmark soils across the southern region climate gradient. Though the main study objective will be on direct assessment of soil carbon sequestration potential, several related sub-objectives will also be explored, namely i) evaluate the effects of land use, crop rotation, tillage practice, soil texture, and ecosystem age/rotation duration on soil carbon concentration, content, and sequestration and related soil physical and chemical properties, ii) quantify and understand the physical and chemical processes that relate to and control soil carbon sequestration, and iii) investigate spatial variability issues associated with soil carbon content and sequestration.
Project Methods
In each of several different land use areas, soil samples 0- to 5-cm and from 5- to 15-cm deep will be collected annually from a grid system with the grid spacing appropriate for the size of the management area. Samples will be air-dried, and sieved to < 2-mm particle size. Basic soil characterization will include: 1) total carbon and nitrogen by combustion analysis; 2) 1:1 soil:water pH; 3) cation exchange capacity via sum of salt-exchangeable cations via inductively-couple plasma spectroscopy; 4) MS soil test extractable potassium, phosphorus, calcium, magnesium, and sodium via inductively-couple plasma spectroscopy. Standard soil characterization (texture, mineralogy, pH, cation exchange capacity, organic matter content, etc) will also be determined. Topography (slope and aspect) will be determined using the continuous elevation measurements and GIS software. Data will be analyzed determine the effects of soil physical and chemical properties and land use/cropping system on soil C and N sequestration. Soil carbon sequestration rates will be expressed within upper and lower limits of their associated variability. Soil physical and chemical data will be correlated with soil carbon to determine their relationships. Correlations will be assessed using statistical models for spatial data. The spatial analysis will begin with a linear regression model, or possibly a principal components regression model if the independent variables are extremely correlated. If spatial correlation is present, an appropriate variogram structure will be selected to adjust for the spatial correlation.