Coordinated nitrogen and sulfur management in S-deficient soils

Background
Although there is approximately 4 million ha S-deficient soils in the cultivated areas of the Canadian prairie Provinces, an additional 8 million ha is estimated to be potentially deficient (Solberg et al., 2007). Much of the research to date has focused on the effect of N fertilization on N20 emission and /or carbon sequestration. To our knowledge, although there are a few studies have been conducted on the combined effect of Sand N -fertilization on carbon sequestration (Nyborg et al. 1999; Malhi et al. 2010; Malhi 2012; Giweta et al. 2014) there is currently very little information on N and S fertilization in S-deficient soils in terms of nutrient supply (N and S) and GHG (N20) emissions. Preliminary observations from the University of Alberta Breton Plots suggest that soils having a long-term history of Nand S fertilization (Dyck 2014) may have lower fertilizer N-induced N20 fluxes because S oxidizing bacteria can use N02 as an electron receptor to produce N2 (Sun et al. 2012), effectively short-circuiting the nitrifier N20 production process. This research investigates the interaction of both S and N fertilization with respect to fertilization history on an S-deficient soil on N20 emissions.

Proposed Research
The long-term fertilizer and rotation treatments of the Breton Classical Plots will be used to assess the effects of long-term Nand S fertilization, liming and crop rotation on soil properties and GHG emissions in response to contemporary fertilizer applications. Observations from previous CFI-funded research at the Breton Plots show that soils having a long-term history of N and S fertilization may have lower fertilizer N-induced N20 fluxes and we request funding to further investigate the soil process responsible for these observations. This will be achieved through laboratory soil incubations and field gas flux measurements.

The Breton Classical Plots consist of 8 fertility treatments superimposed on 2 rotations: a 5-year wheat-oats-barley-hay-hay (WOBHH) rotation and a 2-year wheat-fallow (WF) rotation. The WF plots and the east half of the WOBHH plots are limed every 5 years to maintain soil pH above 6.0 while the west half of the WOBHH plots does not receive lime.

We will investigate the effects of long-term Nand S fertilization on soil GHG emissions by comparing weekly growing season GHG fluxes from the control (no fertilizer added), NPKS, NPK, PKS, and Manure treatments of the limed and unlimed halves of the wheat phase of the WOBHH and both phases of the wheat-fallow rotation. Field gas flux measurements are in progress for the 2014 growing season. These measurements will be supplemented with Plant Root Simulator (Western Ag Innovations) measurements of soil nutrient supply.

Deliverables
A written report summarizing the 2014 N20 fluxes, comparing them with fluxes measured in the 2013 field season will be submitted. The cumulative N20 emissions over these two growing seasons will also be compared to soil properties (pH, SOC, TN) measured on soil samples and nutrient supply rates measured with PRS probes.