Carbon cycling under dryland wheat as influenced by crop residues and nitrogen fertilizer

Dr Benjamin Ellert1, Dr. Henry Janzen1

1Agriculture & Agri-food Canada, Lethbridge, Canada

Agroecosystem carbon stocks are dictated by the balance between inputs from net photosynthesis and outputs from harvested commodities and decomposition.  In dryland grain and oilseed cropping systems of western Canada, typically the grain is harvested and exported from the system, and the residues or non-grain portions of the plants are returned to the land where they decompose, for the most part, back to CO2.  Increasingly, we are asking more of our cropping systems by increasing harvest intensity and exporting the above-ground residues for other uses.  We established an experiment in 1999 with three levels of of crop residues (returned, removed, or supplemented) and two levels of nitrogen fertilization (with and without).  The supplemented residue treatment was imposed to assess the extent to which agroecosystem C stocks might be enhanced by increasing C inputs.  The cumulative influence of these treatments on C and N cycling will be discussed.  The residue and especially N fertilizer treatments influenced crop yields and the amounts of residue returned to the land each year.  Yields were also influenced by interannual variability in precipitation and crop water use efficiency.  Soil and residue samples were collected to assess the amounts and locations of organic C and total N accumulated in the system.  Inorganic soil C also was measured, but stocks were too variable to discern temporal changes.  Temporal changes in soil C and N stocks will be compared with long-term cumulative residue inputs.  The implications of the results for managing soil organic matter in annual cropland will be discussed.

Biography: Benjamin Ellert is a Research Scientist in biogeochemistry with Agriculture & Agri-Food Canada at Lethbridge, Alberta.  He studies the biogeochemistry of agroecosystems and gleans insights insights from assorted long-term field experiments.

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