Wednesday, November 15, 2006
283-1

Isotopic N and C kinetics in soil and corn over 25 years with different managements.

Yi Zhang1, C.E. Clapp2, J.A.E Molina3, and D.T. Lee3. (1) 1991 Upper Buford Circle, University of Minnesota, University of Minnesota, 439 Borlaug Hall, St. Paul, MN 55108, (2) USDA-ARS & Univ. of Minnesota, 439 Borlaug Hall, 1991 Upper Buford Cir, St. Paul, MN 55108, (3) Univ. of Minnesota, 439 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108

Soil N and C are two major components supporting plant growth and production. Managements (e.g., fertilization, residue and tillage) heavily influence N and C cycling in agricultural soil systems. Quantitatively documenting N and C dynamics in soil-water-plant system must be included at the long-term continuous field level in order to understand and manage the entire N and C cycles. The paper provides a unique set of continuous data from a 25-year field experiment on a Waukegan silt loam soil, located near Rosemount, MN. Field management involves tillage, residue and N treatments, including two tillage treatments (rototillage and no-till), two residue managements (residue removal and return) and 2 N treatments from 1980 to 2005, with 15N fertilizer added from 1980 until 1995. 15N fertilization provided a tracer to the applied N fertilizer to quantify N uptake by crops and N remaining in the soil. The crops grown were 15 years of corn (1980 to 1994), 4 years of soybean (1995 to 1998), followed by 6 years of corn (1999 to 2005). No fertilizer N was added for the soybean years. Changing crops established an in-situ label of soil organic carbon (SOC) based on the difference in the natural abundance 13C of C4 (corn) and C3 (soybean) plant. Our paper also provides unique field data over a 25-year period for modeling to simulate the dynamics of N, 15N, C, and 13C in the soil-plant system. It offers an advantage of verifying simulation models such as NCSWAP and of gaining insight about the processes that control soil N and C with crop production. Such long-term field information is of strategic significance and necessity in optimizing input and crop yield, decreasing soil N and C losses with reductions in terrestrial greenhouse gases, and improving soil and water quality.

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