IN THE FIELD
MIXING
COVER CROPS AND MANURE Cover crops can capture leachable nitrate — but do they take up too much nitrogen in the process? by Matt Ruark
C
orn silage production offers a great opportunity to plant cover crops for erosion control and water quality benefits. In Northern climates, cover crops can be hard to establish following grain harvest, but if corn is harvested for silage by late September, grass cover crops can grow quickly and provide valuable ground coverage. Winter rye is the most popular cover crop in this scenario, as it will survive the winters in the northern U.S. and provide benefits up until termination in the spring. Other popular grass cover
crops include oat and spring barley, which can grow quickly during the fall but will die off during the winter. This has the advantage of reducing an extra trip across the field to terminate the cover crop, but the dead biomass may not provide adequate erosion protection in the spring.
Concerns about fall application Many questions still remain when using cover crops, especially when manure is applied in the fall. While fall applications are essential to overall manure management, application at this
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time does create risk of nitrate leaching into groundwater or to surface waters via tile drainage. Cover crops can help trap leachable nitrate during the fall and early spring months before planting. We do not expect, though, that this “trapped” nitrogen will be returned to the next corn crop. The question at hand is how much nitrogen from the manure is left for that next corn crop? In a perfect world, the cover crop would just trap the nitrogen that would be leached, but recent studies in Wisconsin have revealed they also tap into the nitrogen that would be available jofnm.com
10/22/20 9:18 AM
