Salam, D. E. 2011. Nitrogen fertilization effects on litter decomposition dynamics and soil carbon in agricultural system. Thesis, Michigan State University, East Lansing, Michigan, USA.

I examined the effects of three N applications (0,134,291 Kg N /ha) on corn (Zea mays) and wheat (Triticum aestivum) litter decomposition rates, soil and litter enzymes, soil C pools, and litter chemistry at the W.K. Kellogg Biological Station Long-Term Ecological Research (LTER) site. There were no changes in litter chemistry after decomposition under N fertilization and the litter decomposition rates did not respond to N fertilization but there was significantly (P = <0.001) greater mass loss in corn (73% mass loss) than wheat (63% mass loss). Laboratory incubations indicated that soil C-mineralization significantly declined (P=0.0001) under 291Kg N/ha in comparison to 0N. There were no significant differences in light fraction (LF) C and N between treatments receiving 0 and 291 Kg N/ha. The C concentration (mg/g of LF) of the LF organic matter increased by 8% in June and 1.6% in Aug in the high N treatment in comparison to 0N, and the N concentration (mg/g of LF) increased by 16 % in June and by 8% in Aug under 291 Kg N/ha treatment in comparison to 0N. The fertilizer N had no effect on total soil C or chemically labile organic matter while the activity of hydrolase and oxidase enzymes in soil and in both types of litter showed temporally variable response to N. The results of this study indicate that N fertilization does not increase litter decomposition rates under no-till management systems, had variable effects on soil enzymatic activity, and substantially reduced soil CO2 flux in the lab.

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