Cover Crop Mixtures: Calculating Seeding Rates

This video provides step-by-step instructions for calculating seeding rates when including multiple species in a cover crop mixture.
Cover Crop Mixtures: Calculating Seeding Rates - Videos


Cover crops protect soil, air, and water when incorporated into crop rotations and including a mixture of multiple species can enhance the benefits they provide. Individual crop species often have different functions and growth periods making it necessary to balance the seeding rates and optimize individual attributes each species provides in a mixture. This video provides step-by-step instructions for calculating seeding rates when including multiple species in a cover crop mixture.


Agroecology Alternative Crops Conservation Cropping Systems Soil Organic Matter, Health, and Fertility Organic Agronomy

More by Kristy Borrelli 

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- [Kristy] Cover crop mixtures are increasing in popularity across the farming landscape, but incorporating a mix into your crop rotation requires you to balance several aspects associated with growing different plant species at the same time.

These beneficial crop mixtures can present unique challenges and bring up many practical questions, such as what is the appropriate amount of seed to include for each species in the mix?

After watching this video you will have a better understanding about the importance of including cover crop mixtures and more specifically how to calculate seeding rates when planting diverse mixtures of cover crops.

The numerous benefits of cover crops are well understood and farmers across the country are observing improvements in air, water, and soil quality on their farm when including cover crops in their rotations.

They're also finding that these benefits positively benefit crop yields and their overall bottom line, which likely explains the increase in the popularity of cover crops.

With all of these benefits accounted for, it is important to note that certain species of cover crops are more adept at certain functions than others.

Therefore it it is important to identify goals associated with the specific needs on your farm to match cover crop species that are appropriate for meeting these goals.

Similar to most agronomic crops, cover crops species typically fall into three general categories, each of which have different features and functions.

Grasses, like annual rye grass, acquire great amount of biomass and are known for scavenging nitrogen, preventing erosion, and controlling weeds.

Brassicas and mustards, like radish, are known to prevent erosion, but also reduce soil compaction and suppress weeds.

Finally legume crops like crimson clover are known for their ability to fix their own nitrogen.

Individually cover crop species can excel at providing separate functions.

However, they also have their won drawbacks.

For example, forage radish suppresses weeds in the fall and breaks up soil compaction, but because it is a winter field species, it contributes to nitrogen leaching in the spring.

Clover fixes nitrogen, but the minimal amount of biomass it produces is not very effective in suppressing weeds.

Cereal rye prevents nitrogen leaching, but immobilizes nitrogen for the following cash crop.

Incorporating these individual species into a mixture, therefore allows the farmer to maximize the multiple benefits that cover crops provide.

More comprehensive information about this topic can be found in the bulletin, make the most of cover crop mixtures, that is available on the Penn State Extension website.

Here are few tips for making a cover crop mixture.

First, identify the desired cover crop species that you wish to achieve in a certain area on your farm.

These could include things like reducing erosion or building nitrogen or suppressing weeds.

Two to three top priorities is a good place to start.

Second, it is very important to know what time of year you need the cover crop to fit into your rotation, and choose species that will be productive in that growth window.

Third, pick a set of cover crops that provide the desired services and the adapted growth period that you identified in steps one and two.

It isn't necessary to go overboard with species in a mix.

It is okay to only have two species if that's what works for your farm.

Typically two to three species is a good starting point.

Fourth, select species that are complementary with each other and work together well in a mix.

Finally, identify any drawbacks and missing services and replace species as necessary to amend any missing features.

Many print and online publications are available to help you wade through this information and make the right choices, include the making most of cover crop mixtures bulletin that I mentioned earlier.

Once you have determined the appropriate seeding mix and planting method, calculate the seeding rate as follows.

It is important to know the monoculture seeding rates for the crop species you selected.

This table provides a selection of monoculture seeding rates for many popular cover crop species, but a more comprehensible table of species, including many other associated features can be found in the Penn State Agronomy Guide.

Certain species of cover crops are highly competitive with other crops and it's suggested that their rates be reduced as follows to ensure that all species are well represented in the mix.

These include forage radish, which should be only seeded at two to three pounds per acre, canola recommended at three to four pounds per acre, oats which should be seed 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 is to reduce their monoculture seeding rates by a quarter or even by a half.

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 sample mixture 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 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 quarter of it's monoculture seeding rate.

I chose a quarter instead of a half, because this crop will dominate in the spring and because we want crimson clover to be represented as well in the spring, I went the 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.

And because it's the only cover crop really growing in the fall, I went the larger seeding rate, the three compared to a two pound per acre seeding.

And this sums up for a total of 20 pounds of seed per acre.

Seeding rates of similar species should also be reduced even further when planted in a mix.

For example, here's an example of a 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 variety will winterkill and therefore occupies a different functional space than the 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 cut in half.

The non-competitive legume remains at it's monoculture rate and as a highly competitive species, the seeding rate of oats is recommended at 40 pounds per acre.

And here I chose to seed oats at the higher end of it's range because it will be the only cover crop represented in the fall.

In consideration of the overlapping functions for several species in the mix, the mixture of seeding rates for each of these species is divided by the number of species in that group, in this case three.

The final seeding rates for each species are the carried over and sum up for a total of 95 pounds of seed per acre.

You will 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 from four farm sites across Pennsylvania that use the exact same cover crop mix planted at the same time at each location.

Well rye dominated in Centre and Berks Counties, canola was very dominate in Lancaster County and Mountour County, which also had the best representations of peas in a mix.

Across locations, the mixes are not very uniform.

Determining appropriate seeding rates for each species in a mixture can be difficult.

Start with the suggestions provided in this video, plant a small acreage, observe the results, and then make adjustments as necessary.

Consider this as a process and keep trying new things to find out what works for your farm.


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