Submitted to: Italian Chapter of International Humic Substances Society
Publication Type: Abstract Only
Publication Acceptance Date: 5/4/1995
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Management practices in agroecosystems are fundamental to organic matter dynamics for C sequestration in the terrestrial C pool, and for reduced atmospheric CO2. Natural variation in 13C/12C ratios can be used to assess the fate of recent organic inputs into soil organic matter. Our first objective was focused on organic matter dynamics and C sequestration in agroecosystems with corn (C4 plant) and soybean (C3 plant). Soil samples were collected from a long-term study with different corn/soybean sequences at Lamberton, MN. Whole soil samples from various crop sequence combinations, as well as particulate organic matter, sand, silt, and clay fractions were analyzed for total C and 13C. Analysis of delta 13C values was useful for assessing crop sequence effects on C sequestration in corn- soybean agroecosystems. These data suggest fundamental differences in the dynamics of C derived from corn vs. soybean residue. Our second objective was to survey delta 13C and delta 15N in humic substances from a world- wide collection of soils, peats, sediments, and waters. The delta 13C values of the humic fractions isolated from their natural environments indicated the nature of the plant materials contributing to these humic substances. The delta 13C values for humic substances from the soil solution and from drainage waters are numerically greater than those for the humic substances indigenous to the soils, suggesting that humic substances in the soil solution have origins that are not identical to those in the solid or gel states. The delta 15N data are variable but indicate contributions from farm yard manure (FYM) and fertilizers, with the soil solution/drainage water humics having a greater impact from FYM.