Cover Crop Mixtures: Calculating Seeding Rates
In order to maximize the functionality of each species in a cover crop mixture, it is necessary to minimize competition among individual crops and optimize each one’s ability to perform. Seeding rate is important for achieving the best representation of all species in a mix. This video will walk through several examples on how to calculate seeding rates to optimize cover crop performance.
- [Kristy] Incorporating a cover crop mixture into your crop rotation requires you to balance several aspects associated with growing different plant species at the same time, and it can raise many practical questions.
One important piece is figuring out the appropriate amount of seed to include for each species when planting a mix.
After watching this video, you will have a better understanding about how to calculate seeding rates when planting diverse mixtures of cover crops.
In a separate video, I went over tips for making a cover crop mixture.
To review, they can included: identify the desired cover crop services that you wish to achieve, known what time of year you need the cover crop to fit into your rotation and choose species that will be productive during that time, pick a set of cover crops that provide the desired services and the adapted growth period that you identified in steps one and two, select species that work well together in a mix, and identify any drawbacks or missing services and replace any species as necessary.
This Making the Most of Mixtures publication can help you wade through the details of making these decisions.
Once you have determined the appropriate seeding mix and planting method, you can calculate the seeding rate.
First, it is important to know the monoculture seeding rates for the crop species you wish to include in your mix.
This table provides a selection of monoculture seeding rates for many popular winter cover crops, but a more comprehensive table of species that also includes many of their associated features can be found in the Penn State Agronomy Guide.
Certain species of cover crops are highly competitive with other crops, and it is suggested that their rates be reduced to ensure that all species are well-represented in the mix.
These include forage radish which should only be seeded at two to three pounds per acre, canola is recommended at three to four pounds per acre, oats, which should be seeded from 20 to 40 pounds per acre, and sorghum-sudan grass, which is recommended to be seeded at 15 to 20 pounds per acre in a mix.
Additional considerations for all grass species that are often competitive is to reduce their monoculture seeding rates by 1/4 or even 1/2.
On the other hand, because legume crops are weak competitors, it is best to keep these seeding rates close to those used for stands of monocultures.
Here's an example of a simple mix that includes three species that don't have any feature overlap.
For example, annual ryegrass is a winter-hardy grass, crimson clover a legume, and forage radish is a brassica species that winterkills.
Here are the species with the respective monoculture seeding rates.
Now let's consider the mixture.
As a grass, annual ryegrass will be seeded at 1/4 of its monoculture seeding rate.
I chose 1/4 instead of 1/2 because this crop will dominate in the spring.
And because we also want crimson clover well-represented in the spring, I went with a lower rate of annual ryegrass.
As a weakly competitive legume, crimson clover stays at its monoculture rate.
And forage radish, which is highly competitive, gets reduced to three pounds per acre.
Because it will be the only cover crop really growing in the fall, I went with the larger seeding rate of three compared to two pounds per acre.
This sums up to a total of 20 pounds of seed per acre.
Seeding rates of similar species should be reduced even further when planted in a mix.
For example, here's a sample mixture that includes five species, three of which have overlapping functions.
Annual ryegrass, cereal rye, and triticale are all winter-hardy grasses and will be considered as a group.
Crimson clover is unique as the only legume.
And although oats are technically a grass, this fall's planted variety will winterkill and therefore occupies a different functional space than other grasses considered in this mix and will be considered separately.
As always, start with the monoculture rate for each species.
The winter-hardy grass species rates are then cut in half.
The noncompetitive legume remains at its monoculture rate.
And as a highly competitive species, the seeding rate of oats is recommended at 40 pounds per acre.
Here I choose to seed oats at the higher end of its range because it will be the only cover crop really represented in the fall.
In consideration of the overlapping functions for several species in the mix, the mixture seeding rates for each species is divided by the number of species in that group.
In this case it's three.
The final seeding rate for each species is then carried over and sum up for a total of 95 pounds of cover crop seed per acre.
You'll notice that I rounded up some values for practicality.
It is important to note that cover crop mixtures express themselves very differently based on season and location.
This chart represents data that were collected in a single year from four farm sites across Pennsylvania that use the same exact cover crop mix planted at the same time at each location.
Overall, fall biomass varied substantially based on location, ranging from 2,000 pounds per acre in Centre County to 5,700 pounds per acre in Montour County.
Species expression within the mix was also very different.
While rye dominated in Centre and Berks County, canola was very dominant in Lancaster and Montour Counties, which also had the best representation of peas in the mix.
Determining appropriate seeding rates and combinations of species in a mixture can be difficult.
Start with suggestions provided in this video.
Talk to other farmers nearby who might have their own experiences.
Start on a small acreage.
Observe the results and then make adjustments as necessary.
Consider this as a process and keep trying new things to find what works best for your farm.
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