How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

Published Sep 5, 2019  

When it comes to creating a cover crop mix, the options are endless. You need to determine what kind of species you’ll use, how many you’ll use, and at what seeding rates. For anyone new to cover crop blends, these decisions can be overwhelming.

Fortunately, there are several free tools available today that can guide both new and experienced cover crop users through the process of developing their own mix. One of those is Green Cover Seed’s SmartMix Calculator. In this article, we’ll walk you through how to use SmartMix to create a multispecies blend that gives you the results you want.

Start with the Basics

The calculator starts by requesting some basic information about your location and your plans for the mix. This includes how many acres of the mix you plan on seeding, how you will seed it, and what the following cash crop will be.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

SmartMix will also ask for the zip code of the acres where you’ll be seeding this mix to pull up the average annual rainfall, the approximate dates of the first and last frosts, and the Plant Hardiness Zone — all of which will help it recommend species.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

You’ll also need to decide your seeding and termination dates, which will tell you the length of your selected growing period, as well as the number of base 50 growing degree days and base 40 growing degree days, which indicate warm- and cool-season crop growth, respectively.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

Another important field on the first page is irrigated inches. While this field allows any farmers with irrigation systems to indicate whether they plan on irrigating their cover crops, it can also be used to let the calculator know if you’re going into a wetter or drier season than usual. If you think the time your cover crops will be growing will be drier, you can input a negative number, while if you expect it to be wetter than usual, you can input a positive number.

Decide On Your Goals

Before you start selecting species for your mix, you need to decide what you want to achieve with your cover crops.

In fact, Keith Berns, co-owner of Green Cover Seed and developer of SmartMix, says you should never buy cover crop seed without knowing what your goals are. The reason for this is because it’s hard to determine what species to select if you don’t know what you’re trying to do.

“Cover crops can do so many different things — everything from erosion control to suppressing weeds to breaking compaction to fixing nitrogen to supplemental grazing,” he says. “We need to know what you want to do so we can know whether to use wheat or rye or triticale or oats, because each one may have strengths and weaknesses when it comes to those different goals.”

Having goals also lets you know whether your cover crops succeeded or failed. “How do you know if it has been a success if you didn’t know what you were trying to accomplish?” Berns asks.

If you’re not sure what your goals are, Green Cover Seed can help. Berns says they will take growers through a series of questions, such as “Do you think you have compaction issues? Have you seen erosion? Are you trying to suppress weeds? Do you have livestock?” to help pinpoint what they want their cover crops to do.

SmartMix lets you rank up to three goals, and the goal with the highest priority gets the most weight as the calculator scores each species.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

Selecting Species

The next step is to add species to your mix. When you click on the “Add Species” button you’ll see cover crops separated into four categories: excellent, good, marginal and risky.

Berns says these ratings aren’t always perfect — sometimes a species is listed as marginal that maybe shouldn’t be — but in general you should stick to the excellent and good categories.

There will likely be several species to choose from. In the example shown below, there are 32 species listed as excellent and 43 in the good category. For new cover crop users, it may be overwhelming trying to decide which species to choose.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

Green Cover Seed is trying to solve that by providing educational content on each cover crop. Berns says they’re currently working to add short videos on the species selection page where growers can learn more about the cover crop and see how it performs out in the field. Clicking on the play button under a species will bring up the video. 

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

You can also learn more about a species after you’ve added it to the mix. Next to every species is an information icon (see image below) where it will take you to a page that provides information on how that species can be used, its advantages and disadvantages, tolerances and more.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

Evaluating Your Mix

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

Once you’ve selected your species and added them to your mix, you’ll see several meters update. The first to pay attention to is the progress for each goal.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

“Your No.1 goal should always be at 80% or higher or you probably aren’t going to be happy with what you’re trying to accomplish out there,” Berns says.

How compatible your goals are to each other will increase the likelihood of how high those percentages can be. If your goals aren’t compatible, then you’ll probably struggle to achieve all of them.

For example, nitrogen fixation and long-lasting residue are two goals that are not complementary to each other. To fix nitrogen you need a lot of legumes, Berns says, which are typically pretty poor for having long-lasting residue.

“The more you run that goal up, you’re probably going to run the other one down,” he says.

On the other hand, long-lasting residue and weed suppression are complementary goals because they both need species that will provide a lot of soil coverage and take longer to break down. Berns says if you pick goals that complement each other, you may be able to get them all over 90% on their goal progress.

If you find your goals are not complementary to each other, you’ll either need to decide to let go of one of the goals or choose different ones.

The next meter is your mix’s carbon-to-nitrogen (C-N) ratio. The ideal ratio will depend on what your goals are.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

“It’s going to be the best indication of how long your residue will last or how fast your nutrients will cycle,” Berns says.

He adds that C-N ratio is not only dependent on the species you choose, but how long your growing period is.

“Even the high-carbon crops are going to have a low C-N ratio when they’re in the vegetative stage,” he explains. “It’s going to be very difficult to get a C-N ratio above 30 if it’s only growing for 60 days.”

Berns recommends playing “what if?” scenarios in the calculator to see how changes in your seeding and termination dates affect your goal scores and C-N ratio.

At the bottom of the screen, you’ll also see Mix Effect Potential Ratings for nitrogen fixation, grazing, drought tolerance, frost tolerance, winter hardiness, diversity and salinity tolerance. Berns notes that it’s hard to get a good nitrogen score unless you have all legumes seeded at high rates.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

Ideal Seeding Rate

Another important meter to pay attention to is the full rate. While some prefer to look at creating mixes by seeds or pounds per acre for each species, Berns says Green Cover Seed didn’t feel it was a strong way to determine how much seed you need. Instead, they prefer to look at the percentage of a full rate (what the rate would be if you were seeding a species by itself).

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

The SmartMix calculator recommends achieving a full rate of 125%, and if the AutoAdjust is turned on (see top right of calculator), it will automatically set your mix to achieve that rate. So if you have five species in a mix, each would be seeded at 25% of its full rate.

How to Use the SmartMix Calculator to Create the Perfect Cover Crop Mix

The reason for 125% is based on trials Green Cover Seed has done. Berns explains that it’s been a good benchmark to shoot for when you have four to six different species in a mix. The greater the diversity in your mix, the higher you can push the full rate percent.

The reason for this is due to less competition between species, Berns explains. For instance, in a field of corn, the most competition to corn is another corn plant because they need the same nutrients and water, and they’re rooted at the same depth and have the same canopy height.

“Everything is the same, so that’s a very highly competitive environment,” he says. “If you’re doing just one thing, you wouldn’t necessarily want to do more than 100% or you start the law of diminishing returns.”

But when you start mixing things together that have different rooting depths, canopy heights and nutrient needs, it’s not as competitive of an environment. If you’re mixing a lot of warm- and cool-season species, Berns says you can get up to 150% full rate or higher because the cool-season crops won’t be growing aggressively when it’s hot, and once you have a frost the warm-season crops will die.

Another situation where the seeding rate can be pushed higher is when you’re grazing the mix, because those species are not likely to reach full maturity. On the other hand, if a grower is in a really dry environment or is interseeding into another crop, they may only seed at a rate of 75%.

To determine the ideal seeding rate for your farm, Berns recommends drilling your mix at different seeding rates in a field so you can see if there are any differences later. Seed one strip 25-30% higher, the next strip 25-30% lower, and the rest of the field at the recommended rate.

“The next year you may want to push your seeding rate a little higher, or if you didn’t see much of a difference, cheat back a little to save a little bit of money,” he says. “That’s how you learn, by just taking a little extra time to do those types of things.”

While AutoAdjust divides the full rate percentage evenly among each species to reach 125%, you can turn it off to adjust the rates manually.

If you’re a new cover crop user, Berns recommends leaving AutoAdjust on before you select your species, then making any changes after you see what the calculator recommends.

“Once you start having some experience and seeing what you’ve done on your own farm in the past, you can just leave that off and plug your own numbers in,” Berns says.

Start Early, Get Feedback

Berns says the most common mistake he sees farmers make with SmartMix is not asking for help. If you’re using the calculator and you’re not sure about your mix, you can leave some notes for Green Cover Seed (in Step 4) and then submit it.

“We’ll get back to them and make a recommendation, we can follow up with more questions or provide a shipping quote,” Berns says, adding that hitting the submit button is not a commitment to ordering seed. “We always follow up with everybody and we always review everything.”

He notes that with new SmartMix users, they may recommend substitutions or some changes to better achieve their goals while keeping the seed costs the same or lower.

Berns also recommends farmers start playing around with the calculator ahead of time to educate themselves on the different options and plan for what they’d like to do in the future.

Green Cover Seed is always trying to improve the tool, Berns says, and they plan to come out with some new features and updates periodically. He adds they always appreciate getting feedback from users and you can contact them with any suggestions or ideas you have.

For more information on using the cover crop calculator, Green Cover Seed has video tutorials to help guide you into creating the perfect mix for your operation.

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