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United States Department of Agriculture

Agricultural Research Service

Research Project: NUTRIENT CYCLING AND UTILIZATION ON ORGANIC DAIRY FARMS

Location: New England Plant, Soil and Water Research Laboratory

Title: Nationally Coordinated Evaluation of Soil Nitrogen Mineralization Rate Using a Standardized Aerobic Incubation Protocol

Authors
item Griffin, Timothy
item Honeycutt, Charles
item Albrecht, Stephan
item Sistani, Karamat
item Torbert, Henry
item Wienhold, Brian
item Woodbury, Bryan
item Hubbard, Robert
item Powell, J Mark

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 2006
Publication Date: January 10, 2008
Citation: Griffin, T.S., Honeycutt, C.W., Albrecht, S.L., Sistani, K.R., Torbert Iii, H.A., Wienhold, B.J., Woodbury, B.L., Hubbard, R.K., Powell, J.M. 2008. Nationally coordinated evaluation of soil nitrogen mineralization rate using a standardized aerobic incubation protocol. Communications in Soil Science and Plant Analysis. 39:257-268.

Interpretive Summary: Aerobic incubation methods have been widely used to assess soil nitrogen (N) mineralization (availability), but standardized protocols are lacking. We incubated a silt loam soil (Catlin silt loam, from central Illinois) at six USDA-ARS locations using a standardized protocol. Incubations were conducted at multiple temperatures at each location, ranging from 11 to 32C, which were combined based on degree days (DD). Soil water was either maintained at an optimal level or allowed to dry slowly, followed by rewetting. Soil subsamples were removed periodically, and the concentrations of nitrate and ammonium in the soil were determined. For each location, mineralization rate for soil organic matter N (SOMN) was estimated by regression. When all data were included, the mineralization rate from four datasets was not statistically different, but two locations exhibited higher SOMN mineralization rates. To assess whether this may have been due to pre-incubation conditions, the data from the first day of the incubation was excluded and regression analysis was conducted again. Using this data subset, the SOMN mineralization rate from five (of six) datasets was not significantly different. Fluctuating soil water reduced N mineralization rate at two (of four) locations by an average of 50%, and also substantially increased variability. This composite dataset demonstrates that standardization of aerobic incubation methodology is possible.

Technical Abstract: Aerobic incubation methods have been widely used to assess soil nitrogen (N) mineralization, but standardized protocols are lacking. A silt loam soil (Catlin silt loam; fine-silty, mixed, superactive, mesic, Oxyaquic Arguidoll) was subjected to aerobic incubation at six USDA-ARS locations using a standardized protocol. 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 and ammonium 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 (zero-order) model. When all data were included, the mineralization rate from four datasets was not statistically different, with a rate equivalent to 0.5 mg N/kg soil/ day. Soil incubated at 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 from five (of six) datasets was not significantly different. Fluctuating soil water reduced N mineralization rate at two (of four) locations by an average of 50%; fluctuating soil water content also substantially increased variability. This composite dataset demonstrates that standardization of aerobic incubation methodology is possible.

Last Modified: 8/1/2014