Submitted to: International Humic Substances Society Conference
Publication Type: Proceedings
Publication Acceptance Date: 7/21/2002
Publication Date: 7/21/2002
Citation: Layese, M.F., Clapp, C.E., Allmaras, R.R., Copeland, S.M., Molina, J., Linden, D.R., Baker, J.M. 2002. Nitrogen-15 and natural abundance c-13 changes under different tillage, residue and fertilizer management. International Humic Substances Society Conference. p.330-331. Interpretive Summary: Maintaining soil organic matter is vital to sustaining soil quality and crop production and is strongly influenced by management such as cultivation, residue management, fertilization and crop rotation. Soil carbon and soil nitrogen are two major components of soil organic matter which are important in maintaining soil organic matter. For evaluating the dynamics of soil carbon, the natural abundance carbon isotope (C-13) has been used as the in situ marker of soil organic matter while enriched labeled nitrogen has been used as the tracer for soil nitrogen. Data for this study came from a long-term experiment involving tillage, residue and nitrogen management at the University of Minnesota Research and Outreach Center in Rosemount, MN. Our objective was to determine the effects of tillage, residue and nitrogen fertilizer treatments on nitrogen and carbon measurements. Findings on soil organic carbon and nitrogen storage under corn and soybean crops with different tillage and residue management can provide valuable information to environmental scientists, agriculturalists and consultants concerning global carbon and nitrogen budgets.
Technical Abstract: Soil samples were taken in Spring from micro-plots of enriched N superimposed on a 2x2x2 factorial combination of tillage, residue and fertilizer treatments. The experiment was started in 1980 with 2 tillage treatments [till (T); no-till (NT)], 2 residue options [residue returned (r); residue harvested (h)] and 2 N rates [2; 20 g N m-2 as (NH4)2SO4]. The 2 and 20 g N m-2 rate corresponded to 40 atom% and 4 atom% N-15, respectively. Corn was grown for 15 years (1980 to 1994) and subsequently cropped to soybean for 4 years (1995 to 1998). Fertilizer N was not added when soybean became the crop. Analyses were run on soil samples in years 1980, 1985, 1992, 1994 (end of corn year) and 1999 (end of soybean year) using elemental analyzer (Carlo-Erba) and a stable isotope ratio mass spectrometer (Fisons Optima) continuous flow system. Effects of tillage, residue, and N fertilizer treatments on N and C measurements were most evident at the surface (0-15 cm for T and 0-7.5 cm for NT). Soil N content decreased progressively with time under T tillage, and h residue treatments. Soil N, labeled N and percentage fertilizer N recovery were significantly higher in r residue than h residue treatments. No-till resulted in significantly higher soil N content, higher labeled N and higher % N recovery than T treatments. N fertilization affected soil N, labeled N and percentage fertilizer N recovery: higher N rate resulted in higher soil N content; however, the reverse is true with labeled N and percentage fertilizer N recovery. Soil C content decreased with time under low N fertilization, under T tillage and under h residue treatments. Soil C content, delta 13C values and proportion of corn-derived C were significantly affected by residue treatments: r residue resulted in higher soil C than h residue treatments; and in the corn years, higher delta 13C values and higher proportion of corn-derived C. Soil C and delta 13C were significantly higher under NT than T and higher at high N than low N rate. Soil delta 13C, as expected, increased during the corn years and decreased during soybean years.