ARS | Publication request: Standardizing Aerobic Incubation Methods: Is It Possible?

Submitted to: American Society of Agronomy Abstracts
Publication Type: Abstract
Publication Acceptance Date: November 7, 2005
Publication Date: November 7, 2005
Citation: Griffin, T.S., Honeycutt, C.W., Albrecht, S.L., Hubbard, R.K., Powell, J.M., Sistani, K.R., Torbert III, H.A., Wienhold, B.J., Woodbury, B.L. 2005. Standardizing aerobic incubation methods: is it possible?. American Society of Agronomy Abstracts. ON CD

Technical Abstract: Aerobic incubation methods have been widely used to assess soil nitrogen (N) mineralization, but standardized protocols are lacking. A single silt loam soil (Catlin silt loam; fine-silty, mixed, superactive, mesic, Oxyaquic Arguidoll) was subjected to aerobic incubation at seven USDA-ARS locations using a standardized protocol. The incubations were conducted at multiple temperatures, which were combined based on degree days (DD). Soil water was maintained at 60% water-filled pore space (WFPS; Constant) or allowed to fluctuate between 60 and 30% WFPS (Cycle). Soil subsamples were removed periodically, and extracted in 2 M KCl; nitrate (NO3) and ammonium (NH4) concentrations in extracts were determined colorimetrically. For each location, the rate of soil organic matter N (SOMN) mineralization was estimated by regressing soil inorganic N (Ni) concentration on DD, using a linear model. When all data were included, the mineralization rates estimated from five of the datasets were not statistically different, with a rate equivalent to 0.5 mg N kg-1 soil day-1. Two locations exhibited significantly higher SOMN mineralization rates. To assess whether this may have been due to pre-incubation conditions, time zero data were excluded and regression analysis was conducted again. Using this data subset, SOMN mineralization rates from six (of seven) datasets were not significantly different, but the seventh dataset still resulted in a higher rate estimate. Fluctuating soil water did not greatly affect estimates of SOMN mineralization rate, but increased variability approximately ten-fold. This composite dataset demonstrates that standardization of aerobic incubation methodology is possible.