Impact of N Fertilizer Source and Drainage on Spatial Variation in Nitrous Oxide Flux.

Use of artificial drainage and irrigation may affect environmental N losses by changing soil moisture conditions around drainage tile lines.  Previous research in claypan soils in Missouri has indicated that application of polymer-coated urea (PCU) resulted in lower soil nitrous oxide (N₂O) flux compared to that of urea in relatively high rainfall years.  However, little information is available on the possible spatial variation that may exist in soil N₂O flux between drainage tile and subirrigation lines depending on seasonal differences in rainfall.  The objective of this research was to determine differences in soil N₂O flux after application of different N fertilizer sources under a range of soil moisture conditions imposed by drainage and irrigation. A field trial planted to corn was conducted in 2006 and 2007 at the University of Missouri Greenley Experiment Station.  Treatments were arranged in a split plot design with 3 replications consisting of main plots of: i) no drainage or subirrigation,  ii) drainage with tile drains spaced 6.1 m apart and no subirrigation, and iii) drainage with tile drains spaced 6.1 m apart and subirrigation.  The main plots were split into a control and N fertilizer treatments of either spring-applied pre-plant injected anhydrous ammonia, or broadcast-applied urea, or PCU (ESN, Agrium) applied at a rate of 168 kg N ha^-1.  Soil surface N₂O flux, soil temperature, soil water content and soil inorganic N (NH₄⁺-N and NO₃^--N) were measured periodically throughout the growing season at a distance of 0 or 3.0 m from the drainage or subirrigation lines. The results of this study suggest that subirrigation in claypan soils causes spatial variation in soil water content that affects the fate of applied fertilizer N.  Use of PCU assists in reducing nitrous oxide flux under conditions that promote high soil water content.