This was one of the worst years in the history of US agriculture for honeybee declines. Depressing as that sounds, it was difficult to believe as I stepped out into a summer cover crop field in our Lancaster County research plots. Even a quick glance registered more species of insect, butterflies, and bees than I could identify, drawn by the buckwheat component of the mix in full flower. Even more will be drawn as the sunflowers burst into bloom.
This field was planted in a 4-species mix, composed of buckwheat, the summer legumes cowpeas and sunn hemp, and sunflower in mostly even proportions (the seeds are all similar sizes and were easily mixed in the drill). The mix was established as a quick-growing cover crop after spring-planted oats plots came off and before a fall planting of winter annuals.
Several notable things were happening in that field. There were almost no weeds. Although the mix is purely broadleaves, there was minimal Japanese beetle damage. Most of the growth was in a high-quality vegetative stage, with no lodging. Lodging can be great for groundcover and weed suppression, forming a dense, moisture-trapping mat, but is not ideal if you are looking to be able to harvest the crop as an alternative forage, since it makes harvest difficult and contributes to rot. Lodging is usually a result of high populations, advanced maturity (the plant gets tall and the seedhead makes it top-heavy), heavy rain and winds, or some combination of these.
There was some interference from the previous oats plots, and this may not be completely bad news. Decaying plant residue often secretes chemicals that make it difficult for other crops to germinate, and this is known as allelopathy. If you are no-till planting another crop into the residue as we did, this may delay germination, as well as block proper seed placement without a deep-cutting no-till drill and a high seeding rate. However, allelopathy does not often discriminate – it also inhibits weed growth. And once the cover crop begins to grow, it still shoots up more quickly than most of the weeds, maintaining the advantage. The high residue from the oats also helps suppress weeds.
The mix was slow to establish and take off – most likely from allelopathic effects – but at this stage has proven to be quite competitive with weeds. Looking out over the field, though, the legacy of the oats’ allelopathy was still visually striking. Spots where the plots had been were much shorter than buffer areas.
We want to analyze these samples for nutrient content, similarly to having a forage sample analyzed. This tells us what the crop pulls up from the soil or contributes through its own biomass, and we can get a sense of what nutrients would have leached were it not for that cover crop, and what fertility it will contribute to the following crop.
I noticed that the different species grow well in combination with each other, providing a diversity of heights and benefits – buckwheat attracts beneficial insects and pollinators; cowpeas fill in with lower; twining growth, nitrogen fixation and a deep taproot; sunn hemp and sunflowers grow tall and rigid, providing structure for the mix as a whole, as well as organic matter. Plus, as Eli Weaver, our farmer-collaborator says, the sunflowers draw the bees THEN the birds. Many kinds of bees swarm the giant flowers, but as the seeds mature later on, it will also draw a variety of birds. In this way, you can create mix that feeds the soil and the resident wildlife.
We like to encourage creative uses of our cover crops in mixes, and what species you choose to combine depends on your needs and location. Mixes need not be complicated and often do well with only a few different species, but we often recommend combining various types like legumes, grasses, and broadleaves. With more diversity, each species in the mix will have a unique benefit to contribute. For us, the beneficial insect life was only the most visible of these.