Seeding cover crops into perennial sod

It can be done without chemicals

By Gabe Brown

First I want to thank everyone for your phone calls and e-mails with comments and questions. I have tried to respond to each of you individually, but I am going to use this article to respond to by far the most frequently asked question:

“How do I seed a cover crop into an existing pasture?”

I don’t want to kid you. This is not easy, as it is highly dependent on good seed placement and adequate moisture.

Let us consider a scenario for seeding into a cool season, tame-grass pasture with some legume diversity, as this is the most common situation. The reason for seeding the cover crop would be to improve nutrient cycling in order to improve the perennial species that are already in the paddock. Nutrient cycling is enhanced by diversity and by the breakdown of dying and decaying roots. A diverse mix of annuals will do this.

Think of it this way: If you leave a cropland field go unattended, what happens? You normally get a flush of weeds, and the weeds will not be just one species. This is nature’s way of jumpstarting nutrient cycling.

Many of you will be interested in seeding a cover crop to spring pastures. I know of successes with this when herbicides are used to set back the perennials prior to seeding the cover crop. But this is extremely difficult to do without chemicals in a northern climate with cool-season perennials as the dominant pasture species because you are seeding when the perennials are most actively growing. That is why we wait until the cool seasons are slowing down to do our cover crop seeding.

Let’s look at a scenario for seeding a cover crop after the spring growth flush for perennial cool season forages. First we need to set back growth of the existing stand. Obviously we could use a herbicide, but many of us do not want to do that, so the next best way is to use livestock. It is best to graze the paddock hard the previous fall to weaken root reserves, and then graze it early and often the following spring before your intended cover crop planting. In other words, let the livestock go back on the pasture much sooner than you normally would. This will force the plants to use much of their stored carbohydrates, so they will be less vigorous and thus not as competitive with the cover crop.

By this time you should be past the peak growing season for the cool season species. It is now time to interseed a predominantly warm season cover crop mix.

If at all possible, do this without mechanical tillage, as tillage destroys soil aggregates and structure and harms soil biology. Most no-till drills on the market today are able to seed directly into this type of a sod.

Good seed-to-soil contact is critical. It is important that enough force is available to cut through the residue, get the seed to the desired depth, and hold it in place while the seed trench is covered with just the right amount of soil to ensure germination. The majority of failures I see in seeding cover crops into existing perennial paddocks are caused by failing to achieve all of the above.

Next, have the correct species in the mix. Since we are seeding this as the temperatures are rising, we want to have predominantly warm season species. Which species will vary depending on your environment, rainfall and what time of year you want to graze the crop. Work with a knowledgeable seed supplier who knows your area and has your best interests in mind.

In my environment I prefer to use sorghum-sudangrass, hybrid pearl millet, cowpeas and forage soybeans for a base that will make up the majority of the mix. To that base I will add brassicas such as a grazing-type kale, along with a deep-rooted daikon radish. I also like to add a pound or two of sunflowers to the mix, as they have a deep root that helps cycle nutrients from deep in the soil profile.

If you are going to graze this mix during the late fall and winter, adding hairy vetch and/or turnips would be wise, as they provide excellent winter forage. Buckwheat is added to help make phosphorus available and to attract pollinators. I prefer to add species such as safflower and phacelia to the mix, as both will attract beneficial insects and they have very good root structure. Livestock do not readily eat them but that is OK, as we need to leave residue (armor) on the soil surface. Be aware that safflower has sharp spines and is not pleasant to walk through.

Wait to graze
I prefer to not graze this mix until it is either close to maturity or after a killing frost, as we want to give it as much time as possible to grow and develop a root system. When we do graze it, we use high stocking densities and make sure to leave at least 50% of the aboveground biomass. This will give us that all-important residue on the soil surface that will not only protect the soil, but also feed soil biology such as earthworms. Realize that some of your perennial species will be growing along with the cover crop species, so they will provide additional forage.

The next year I would use the same protocol by grazing early and often again and following with a cover crop mix. I would add some diversity to the mix and use some species that I had not used the previous year. I like to use annual vetches and clovers along with other broadleaf species. I also add chicory and plantain to the mix, as these will become established and be a permanent part of my pasture mix. Again, graze this late and leave plenty of residue.

The third year I would graze it once early on, and then I would go in and seed any additional perennial species I wanted to add to the pasture mix. What these species are depends on how you are going to use that particular paddock. I subscribe to the belief that more diversity is better, as it provides the livestock with a more complete ration. By this time you should notice that the existing species will appear healthier, as they will be receiving the benefit of the increased nutrient cycling.

I have also gone into existing paddocks with a fall-seeded biennial mix. On my operation, a mix of winter triticale, hairy vetch, winter pea, sweetclover and daikon radish works well. We usually get a fall rain that provides good germination. This mix will overwinter well with adequate snow cover. Daikon radish is the exception, but its job is to capture excess nitrogen from the legumes and release it as the radish decomposes in the spring. We graze this mix in the spring. We have found it makes for an excellent calving pasture in May and June.

Try to avoid haying
One could hay this mix, but realize that you are depleting nutrients from that paddock anytime you remove the aboveground biomass and haul it away. If you feel you have to hay it, it is best to feed the hay back on that paddock. The decaying roots from this fall-seeded biennial mix will provide nutrients for the perennials in the paddock.

Gabe Brown finishes beef on his family’s ranch near Bismarck, ND.