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Overwinter Transformations of Nitrate Derived from Soil and 15N‐Labeled Potassium Nitrate
Author(s) -
Heaney D. J.,
Nyborg M.
Publication year - 1988
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1988.03615995005200030013x
Subject(s) - denitrification , nitrate , soil water , nitrogen , potassium , zoology , chemistry , agronomy , environmental science , biology , soil science , organic chemistry
Transformations of NO 3 ‐N from fall through spring were examined in a Typic Cryoboralf and a Typic Argialboll in northcentral Alberta. Nitrogen‐15 labeled KNO 3 (96% atom abundance) was applied at the rate of 2.4 kg N ha −1 to fallow and stubble plots in October and incorporated to a depth of 0.13 m. Isotopic analyses of NH 4 ‐N, NO 3 ‐N, and total‐N were performed on soil samples taken to a depth 0.60 m in November, January, March, and May. Analysis of November samples indicated apparent denitrification, immobilization, and release of 15 N as NH 4 ‐N occurred in both soils. Losses of NO 3 ‐N occurred simultaneously with additions between November and January in 3 of 4 fallow‐stubble/soil combinations. Migration of soil water towards ice lenses in the surface 0.30 m suggested upward movement of NO 3 ‐N took place as the soil froze. Between January and March, NO 3 ‐N levels increased an average of 6.4 mg N kg −1 in the Cryoboralf while recovery of 15 N was unchanged. In the Argialboll, NO 3 ‐N levels remained constant from January to March. Lower recovery of 15 N under fallow indicated that the NO 3 ‐N pool remained active and losses were balanced by gains. In may recovery as NO 3 ‐N accounted for only 1 to 24% of labeled N added in October. Immobilization accounted for 4 to 30%. Trace amounts of 15 N were detectable in the 0.13 to 0.30‐m depth, but not in the 0.30 to 0.60‐m depth. Overwinter loss of labeled N from 0 to 0.60 m ranged from 55 to 86%. Processes affecting NO 3 ‐N remained active between October and May, including periods during which soils were frozen throughout the 0 to 0.60‐m depth.