Timing is important for cover crops
Timing is important when it comes to using and managing cover crops — for example, termination timing, timing for interseeding and timing for seeding date post-harvest. This means cover crops should have a level of management similar to cash crops to get the most out of the investment and avoid any potential issues.
Fall or spring termination should be considered depending on moisture conditions and next crop in rotation. Cover crops use water, and if conditions are dry and the soil profile is not being recharged with rains, then fall termination should be considered.
Using a winter annual cover crop like cereal rye may require termination in the spring depending on moisture conditions. Cereal rye can use a lot of moisture, so it is important to terminate even if the plan was to plant soybean into a living cereal rye. It is also important to terminate cereal rye 10 to 14 days in advance of planting corn.
Cover crops should be interseeded into corn after five- to eight-leaf to avoid competition. If the cover crop is seeded too early or grown as a companion crop with corn, it can hurt yields. For flying cover crops into soybean, we are still working on timing but typically this is done right before leaf drop.
Farmers are also playing with the idea of broadcasting cover crops into wheat after the final spray pass — again, we don't know a lot about this, so be cautious. There is a risk of cover crops growing too much under soybean or wheat and interfering with harvest.
Try to follow the combine with the drill for seeding cover crops after small grain harvest. This will get cover crops growing along with volunteer small grain and hopefully lead to a good representation of species seeded while using volunteer small grain as part of the mix. If the drill is not able to follow the combine, then consider spraying out the volunteer small grain (and weeds), then seed the cover crop mix. There can be differences in biomass production of cover crops seeded within three weeks of each other (as seen in our on-campus plots) or even within six days (in fields I recently visited).
As a rule of thumb, try to get a cover crop in the ground by Aug. 15 and consider adding 20 pounds of nitrogen to start it growing. By September, drop the radish and other species from the mix and consider using a winter annual like cereal rye (only if it fits with your rotation and goals).
Timing matters when it comes to cover crops. Consider these tips to have a good experience and help reduce risk in using this soil health building practice. Much of this information is posted on the NDSU Soil Health webpage or follow me on Twitter (@NDSUsoilhealth) to get timely tips.