It’s tough to think about prevented planting, but coming up with a plan for those fields now is critical for following through with effective management. Bottom line is that something needs to be growing on those fields in 2020 to use water and prepare them for 2021. You may be thinking about a field that still has a 2019 crop on it that won’t get a 2020 crop or a field that is wet now and you’re fairly confident you won’t get it planted.
Here are things to think about as you develop a plan:
Be sure to prepare the field for a cover crop just like you would for planting a cash crop. Take care of any ruts or uneven residue, manage the weeds prior to planting and get the cover crop seed in the ground. If you can’t seed the cover crop, think about broadcasting with some light incorporation (if that’s the only way to get into the field).
To determine a mix to use — first, think about what cash crop you may plant or have the option to plant on that field in 2021. This will help you decide if you want the cover crop to over winter (cereal rye, winter wheat, winter camelina) or if you want the cover crop to winter kill. Cereal winter annuals could be used on prevented planting acres if you plan to go to a broadleaf crop in 2021. Choose a cover crop that will winter kill if going to a grass cash crop in 2021. Knowing what you will plant in 2021 will also help you avoid disease transfer from the cover crop to the next year's cash crop. For example, don’t plant barley on this field in 2020 for prevented planting if you want the option to plant barley on the field as a cash crop in 2021. Also, don’t use radish in 2020 if going to canola in 2021.
Next, think about your goal for the cover crop mix. Grazing, haylage, high moisture use, nitrogen builder, mycorrhizal are all options, and it is likely a combination of goals that you’re after. If grazing or using for haylage, check out Kevin Sedivec’s circular (R-1759) on full season grazing mixes for guidance. If high moisture use, consider a mix of warm and cool season grasses that will consistently use a lot of moisture throughout the summer/fall. Nitrogen builders will include a mix of legumes — I like forage peas but in a full season, you may get enough out of a clover for the cost of the seed. I do not use vetches, and especially steer clear of hairy vetch. Don’t forget to inoculate. If going to corn in 2021, make sure a grass that will winter kill or some mycorrhizal cover crop species is included. A mix of turnips and radish (non-mycorrhizal) on prevented planting prior to corn can cause issues with P uptake in corn the next year.
Also, think about weed pressures on a field when choosing a cover crop mix. If there is a lot of weed pressure, consider a monoculture of just grasses on the field to leave an option of a herbicide pass mid-summer. Cereal rye or another winter annual grass can be a really nice option for a monoculture — it won’t head out in 2020 and will grow in spring 2021 to continue to use more moisture. If weed pressures are low, consider a diverse mix to really see what cover crops can do. But remember to always manage weeds prior to planting a cover crop.
Lastly, I have a 2 pounds per acre or less rule of thumb. It doesn’t work for every cover crop, but when it comes to radish, turnip, sorghum sudan grass or clovers, generally 2 pounds or less is enough. This will help keep the cost down for the mix and also allow multiple species to grow in the mix.
Take the opportunity to learn what cover crops can do for soil health as you gain experience on prevented planting fields.