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27 April 2017 Nitrogen balance in century-old wheat experiments
Rezvan Karimi, H.H. Janzen, E.G. Smith, B.H. Ellert, R. Kröbel
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Managing nitrogen (N) inputs to sustain high yields while minimizing losses to adjacent environments remains among the foremost aims in agroecosystems. We studied the N balance in a study established in 1911 at Lethbridge, AB, Canada. The experiment includes three cropping systems — continuous wheat (W), fallow–wheat–wheat (FWW), and fallow–wheat (FW) — with a factorial of two N rates (0 and 45 kg N ha-1) and two phosphorus (P) rates (0 and 20 kg P ha-1) superimposed beginning in 1967. In unfertilized subplots, grain yields generally increased for the first eight decades, but then declined, perhaps partly because of growing N deficiency. Yield response to N increased over time, especially under continuous cropping and when co-applied with P. Soil N concentration in the surface 15 cm declined in the first few decades, and then approached an apparent steady state. Application of N increased soil N, roughly in proportion to the amount of residue returned. For the first half-century (1911–1967), N removal was approximately equivalent to the loss of soil N in the surface 15 cm. Since then, however, when the soil organic N was near steady state, removals of N in grain exceeded N inputs by approximately 20–30 kg N ha-1 yr-1, suggesting an input from outside sources, perhaps partly from atmospheric NH3. This study demonstrated the importance of long-term experiments in evaluating the N balance of cropping systems, and indicated the potential significance of non-fertilizer N inputs from outside sources in such ecosystems.

© Her Majesty the Queen in right of Canada 2017. Permission for reuse (free in most cases) can be obtained from RightsLink.
Rezvan Karimi, H.H. Janzen, E.G. Smith, B.H. Ellert, and R. Kröbel "Nitrogen balance in century-old wheat experiments," Canadian Journal of Soil Science 97(4), 580-591, (27 April 2017).
Received: 20 September 2016; Accepted: 1 February 2017; Published: 27 April 2017

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long term
long terme
Nitrogen balance
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