Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2003
Publication Date: 11/1/2003
Citation: Clapp, C.E., Allmaras, R.R., Molina, J., Hayes, M., Chen, Y., Layese, M.F. 2003. Use of stable isotopes to study dynamics of soil and water carbon and nitrogen. Agronomy Abstracts. S03-clapp571277-oral.
Technical Abstract: The isotopic composition of C in plants is governed by the process of photosynthesis. C4 plants such as corn have average d13C values of about -12 per mil; C3 plants such as soybean have average values of about -26 per mil. Analyses of 13C can provide information as to type of plant material that contributes to soil organic carbon (SOC) or humics in soil and water. Differences in 13C of C3 and C4 plants have been used for labeling of SOC for organic C turnover studies. This paper presents C and d13C analyses of soils and humics (humic acid and fulvic acid) from a variety of soils, peats, coals and different sources of water. We found a wide spread of d13C values for mineral soil humics indicative of plant type. Water humics from different sources had d13C values of about -27 to -29 per mil. Separating SOC storage into relic and current crop sources has significantly improved our understanding of the main and interacting effects of tillage, crop residue, and N fertilization for managing SOC accumulation in soils. Analyses of organic N, 15N, and d15N were also carried out on soils from long-term field experiments to compare the dynamics of C and N. Simulation modeling of the long-term field data has allowed some insight about rates of C and N rhizodeposition and the processes that control the incorporation of below-ground residues into the SOC.