Cover crop soil nitrate-N conservation after seed corn
click image to zoomFigure 1. High clearance male row destroyer with cover crop seeder. In 2010, University of Nebraska began evaluating the planting of a cover crop to manage nitrate-nitrogen in the soil following seed corn production. The goal was to use cover crops to utilize the nitrogen during the offseason to minimize potential leaching.
In 2010, 2011, and 2012 we set up a replicated study where we planted different cover crop mixtures in a seed corn field in Merrick County. One goal was to select cover crop species which would winter kill, in order to eliminate the cost of herbicide or tillage in the spring to destroy the cover crop. Cover crop species also were selected with fall cattle grazing in mind. Cover crop seed was broadcast over plots at the time of male row destruction in late July, using a Herd orbital spreader (Figure 1).
- No cover crop
- Turnips, radishes, rapeseed, spring barley, oats
- Turnips, radishes, rapeseed, spring barley, rye.
Cost for cover crop seed ranged from $5.25 per acre for the turnips to $24.11 per acre for the blends. With input costs in mind an additional treatment of turnip/radish was added in 2011 at a cost of $7.65 per acre. Male row destruction and seeding took place August 9, 2010 and Aug. 11, 2011.
click image to zoomFigure 3. Turnip cover crop, November 2010. Figures 2-4, taken November 10 before the first frost, show 1) no cover crop, 2) turnips only, and 3) a cover crop blend, respectively. We observed every year that rye and oats had reduced emergence within their respective blends. Broadcast seeding resulted in better stands of turnips, radishes, rapeseed, and spring barley.
click image to zoomFigure 4. Cover crop blend of turnips, radishes, rapeseed, spring barley, and rye, November 2010. Cover crop species or blends varied somewhat in 2011 and 2012, but treatments with and without a cover crop were standard in all years. Fields were grazed by cattle beginning in the fall and through the winter. By mid-spring each year, cover crop biomass had disappeared, either from grazing or winterkill. Consequently, soil residual nitrate-N conserved by cover crop uptake in the fall was returned to the soil in manure or urine, or in decomposing cover crop biomass, through the winter and into the spring.