Nitrous oxide emissions from an irrigated soil as affected by fertilizer and straw management

Nitrous oxide (N2O) emission from farmland is a concern for both environmen tal quality and agricultural productivity. Field experiments were conducted in 1996-1997 to assess soil N2O emissions as affected by timing of N ferti lizer application and straw/tillage practices for crop production under irr igation in southern Alberta. The crops were soft wheat (Triticum aestivum L .) in 1996 and canola (Brassica napus L.) in 1997. Nitrous oxide flux from soil was measured using a vented chamber technique and calculated from the increase in concentration with time. Nitrous oxide fluxes for all treatment s varied greatly during the year, with the greatest fluxes occurring in ass ociation with freeze-thaw events during March and April. Emissions were gre ater when N fertilizer (100 kg N ha(-1)) was applied in the fall compared t o spring application. Straw removal at harvest in the fall increased N2O em issions when N fertilizer was applied in the fall, but decreased emissions when no fertilizer was applied. Fall plowing also increased N2O emissions c ompared to spring plowing or direct seeding. The study showed that N2O emis sions may be minimized by applying N fertilizer in spring, retaining straw, and incorporating it in spring. The estimates of regional N2O emissions ba sed on a fixed proportion of applied N may be tenuous since N2O emission va ried widely depending on straw and fertilizer management practices.