133-2 The Quantity and Mineralization Rate Constant of the Active Pool of Soil Organic Nitrogen Under Corn-Soybean-Wheat Rotation in Southern Ontario.

See more from this Division: SSSA Division: Nutrient Management & Soil & Plant Analysis
See more from this Session: Macronutrients: I
Monday, November 3, 2014: 1:15 PM
Long Beach Convention Center, Room 104C
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Jessica Stoeckli1, Mehdi Sharifi2, Raul ponce-hernandez1, Catherine Eimers1, David Hooker3, Craig F. Drury4, Craig F. Drury4, Greg A. Stewart5, Ian McDonald6, Bernie Zebarth7, Tarlok Singh Sahota8 and D. Keith Reid9, (1)Trent University, Peterborough, ON, Canada
(2)1600 West Bank Drive, Trent University, Peterborough, ON, CANADA
(3)University of Guelph, Ridgetown, ON, CANADA
(4)Agriculture & Agri-Food Canada, Harrow, ON, Canada
(5)Ontario Ministry of Agriculture, Food & Rural Affairs, Guelph, ON, Canada
(6)OMAF, Guelph, ON, Canada
(7)Potato Research Centre, Agriculture & Agri-Food Canada, Fredericton, NB, Canada
(8)Thunder Bay Agricultural Research Association, Thunder Bay, Thunder Bay, ON, Canada
(9)Agriculture & Agri-Food Canada, Guelph, ON, CANADA
The soil organic nitrogen (N) greatly contributes to the soil N supplying of agricultural soils in humid environment.  However, soil organic N is not a homogenized pool. Sharifi et al. (2007) defined three distinct soil mineralizable N pools using a long-term aerobic incubation study:  labile (Pool I), intermediate (Pool II) and stable (Pool III). Pool I is composed of the labile organic N pool and is the amount of N released within the first two weeks of the aerobic incubation. The objectives of this study were to (i) determine the quantity and mineralization rate constant (k) for Pool I, and (ii) to explore the relationship of Pool I parameters with field-based indices of soil N supply (yield, relative yield and plant N uptake) in a selection of grain corn (Zea mays) sites in Southern Ontario. Soil samples from 13 experimental corn trials that were under a corn-soybean-wheat rotation were incubated at 25oC and 55% water filled pore space for 24 weeks and leached at days 0, 2, 4,7, 14, 28, 42, 56, 70, 84, 112, 140 and 168.  The quantity of N mineralized and k of Pool I was then related to field-based indices of soil N supply. The labile organic N values ranged from 11-103 mg N kg-1 with a mean of 42 mg N kg-1 and contributed up to 50% of the total N mineralized over the course of incubation.  The mineralization rate varied from 0.09-0.81 mg N wk-1 with a mean of 0.35 mg N wk-1 and was approximately 50 times larger than the mineralization rate of Pool II.   The mineralization rate was significantly correlated with yield, relative yield and plant N uptake (r=0.27, 0.31 and 0.42) but the N mineralized during this time period was not (r=0.28, 0.13 and 0.20). These findings suggest that Pool I contributes a significant portion to the N supplying capacity of agricultural soils, however, the quality of this pool may be a better indicator of N availability under field conditions.
See more from this Division: SSSA Division: Nutrient Management & Soil & Plant Analysis
See more from this Session: Macronutrients: I