Temporal Variability In Water and Nitrogen Flux From Tile-Drained Fields Fertilized with Dairy Slurry.

Source and transport challenges associated with application of dairy slurry to tile-drained crop lands in northern climates are multiplied by seasonal time constraints and potentially large flushes of subsurface drainage effluent and nitrate-nitrogen occurring during the spring snowmelt.  This study was conducted to measure subsurface drainage flow and nitrogen losses from silage corn fertilized by two methods.  Anaerobically digested dairy slurry was either injected in autumn or fertigated during the growing season by mixing slurry and water and applying through center pivot irrigation.  The experiment was conducted on large fields where drainage areas were 42 ha (104 ac) and 27 ha (67 ac) for the injected and fertigated areas, respectively.  Above normal snow fall and below normal temperatures during the two seasons of study, 2009-10 and 2010-11, resulted in season-long snow coverage, above-normal snow depth, and large snow melt runoff events both years.  Through the spring snow melt periods of the two years, nitrate-nitrogen losses were less for the fertigated treatment by 38 kgN/ha (65% decrease) for spring 2010 and 1 kg N/ha (7% decrease) for spring 2011.  However, the difference in nitrogen losses for the two treatments increased throughout the growing season, suggesting that the effects of the fertigation persisted beyond the initial spring losses.  In 2010, total corn plant biomass yields averaged 6% lower (p=0.09) for the fertigated treatment; however, total nitrogen uptake for the two treatments was virtually identical.  Compared to fall injection of dairy slurry, fertigation of the slurry to silage corn during the growing season appears to reduce subsurface nitrate-nitrogen drainage losses in climates subjected to spring snow melt events.  The effect of fertigation on yield is inconclusive after two years.  Study of atmospheric losses of manure-derived nitrogen during fertigation is needed.