Impact of Broadcasting a Cereal Rye or Oat Cover Crop before Corn and Soybean Harvest on Nitrate Leaching.

The corn and soybean rotation in Iowa has no living plants taking up water and nutrients from crop maturity until planting, a period of over six months in most years. In many fields, this results in losses of nitrate in effluent from artificial drainage systems during this time.  In a long-term field experiment near Ames nitrate concentrations and load in tile drainage effluent has been monitored for over 14 years.  During the last four years treatments with and without an oat cover crop in a fall chisel plow system and with and without a cereal rye cover crop in a no-till system have been compared. Both rye and oat cover crops were broadcast into standing corn and soybean crops in early Sept.  Over the 4 years both rye and oat cover crops reduced flow-weighted nitrate concentrations in drainage effluent, with rye showing a greater reduction than oats.  Cover crops had no effect on cumulative annual drainage, but fall chisel plowing had less drainage than no-till.  Nitrate-N loss in tile drainage was less for no-till with a rye cover crop, but did not differ among the other three treatments.  Over 14 years a cereal rye cover crop reduced nitrate concentrations by 59% and nitrate load by 57%.