1a. Objectives (from AD-416)
Continue investigation of the manipulation of terrestrial ecosystems which can offset human induced carbon emissions to the atmosphere for the next 40 years by sequestering additional amounts of carbon in soils and vegetation.
1b. Approach (from AD-416)
Develop field experimental protocol to evaluate the spatial variability of C storage in soils under different regimes. Develop protocol for chemical fractionation of soil carbon pools that will delineate the effects of climate on carbon storage. Develop predictive interpretation methodology for describing carbon compartmentalization as a function of changing climate. Develop N-15 pool dilution technique to quantify nitrogen pools and processes in soils under different climatic regimes and the effect on C storage.
3. Progress Report
Soil carbon storage is important for maintaining healthy soil and has recently been recognized as a means to reduce carbon dioxide (CO2) emissions from the burning of fossil fuels. Our research is considering the soil C inputs from switchgrass and the effect on the nitrogen cycle of soils. Switchgrass (a biofuel crop) has a dramatic effect on soil C stocks with an estimated 15 to 20% increase in soil C compared to corn in just 3 years. The cultivars Kanlow and Cave in Rock input the most C into the soil and have the greatest effect on soil nitrogen. Fertilizer nitrogen retention in the soil increased with the planting of switchgrass over conventional corn rotations. Fertilizer use efficiency ranged from 40 to 55% compared to 30 to 40% in corn rotations. Switchgrass grown as a biofuel appears to increase soil quality and nitrogen use efficiency. In another C storage study we found that the addition of radio-labeled simple to complex C compounds to each soil produced a rapid initial burst of 14CO2 with a traditional decline over time. We found a good correlation between the 1 day C utilization and the % of substrate remaining after 125 d. We also found a good positive correlation between the % sand content of the soil and the % substrate remaining after 125 d. These findings indicate that substrates that can be used readily by soil microorganisms are processed rapidly into more recalcitrant forms of C and persist in the environment longer as stored C. This information may be used in agricultural systems to manage crop residues for maximum C storage. In addition, traditionally sandy soils have been neglected in terms of potential C storage, however, our results clearly indicate there is a positive relationship between % sand and long-term C storage, possibly due to aeration and faster initial decomposition.