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CARBON QUALITY AND QUANTITY AFFECT THE RETENTION AND MICROBIAL PROCESSING OF APPLIED NITROGEN
Citation:
Holub*, S M. AND R. G. Silva. CARBON QUALITY AND QUANTITY AFFECT THE RETENTION AND MICROBIAL PROCESSING OF APPLIED NITROGEN. Presented at Ecological Society of America's Annual Meeting, Portland, OR, August 01 - 06, 2004.
Impact/Purpose:
To inform the public.
Description:
Excess nitrogen (N) from fertilizer or atmospheric deposition can have harmful effects on the environment and human health. Remediative methods of controlling N leaching and limiting other undesirable effects of excess N need to be explored if N inputs can not be reduced or better managed. The objectives of this study were to determine the effects that different concentrations and forms of carbon (C) have on N retention and transformation, soil CO2 respiration, and N transforming microbial populations and to identify the effect of soil texture on these processes. Three levels of N additions (0, 100 and 1000 kg N /ha) as NH4Cl, including 15N as a tracer, and three levels of C additions (0, 100 and 1000 kg C/ha) as either glucose or tannic acid were applied in a factorial design at two old-field grassland sites with contrasting soil texture in the Cross Timbers of southeastern Oklahoma. Soil and plant samples were collected periodically from both sites for one year and analyzed for total N and 15N. Soil was also analyzed for CO2 efflux, NH4+, NO3-, culturable microbe populations, extractable organic C, and pH. Significant interactions between N and C treatments revealed the complex and interconnected nature of C and N cycling. C additions, especially the most labile glucose, increased soil respiration in the short term but had little other long term effects. Additions of N led to lower soil respiration, lower pH, and lower N retention. The largest and most significant differences were between soil textures. The sandy soil generally had faster rates of N and C cycling and higher rates of N loss than the clay soil. This study indicates that single additions of labile C do little to combat N leaching in the long-term and that soil physical properties such as soil texture are critical to consider when attempting to predict or control N leaching.