C Substrate Utilization Potential of Different Chernozems after 21 Years Transplanting to Common Management and Climatic Conditions.

The Soil Quality Experiment at Agriculture and Agri-Food Canada, Lethbridge, AB examines the effects of long-term agricultural management practices on different transplanted soils managed under common topographic and climatic conditions. Soils are continuously cropped to wheat (residues removed at harvest) with N fertilizer application either at 0 or 60 kg N ha^-1. Twenty-one years after transplanting, phospholipid fatty acid profiling and enumeration of N cycling functional genes indicates that initial soil conditions have a dominant long-term impact on abundance and community composition of soil microbes. We further investigated active C assimilation potential in selected transplanted soils using ¹³C cellulose as a C source. Soil microcosms were amended with ¹³C cellulose (97 atm. %) at a rate of 0.5 g C kg^-1 soil and incubated for 11 weeks, during which time CO₂ was monitored. Throughout the incubation C mineralization was affected by both soil type and N fertilizer level (P<0.001) reflecting the general fertility of the original soils prior to transplanting. Likewise, cellulose application also increased the net C mineralization (P<0.04) following a short period of delayed response. Soils originating from native pastureland and long-term manure application (30 tons ha^-1) had greatest net mineralization (1038 and 1045 mg C-CO₂ kg^-1 soil, respectively). The C mineralization rate in the manured soil was low early in the incubation, but highest by the end indicating a long term influence of manure application on soil C dynamics. A short term interaction effect of soil type, N fertilizer and cellulose application (P<0.01) was also observed on N₂O emission from the soils, however following an initial event, N₂O emissions were low. ¹³C-CO₂ will be quantified to assess the priming effect among transplanted soils.