Sorghum Sudangrass and Cowpeas Cover Crop

Planting sorghum sudangrass and cowpeas using St. Mary's County's drill

We’re trying out our first cover crop on our neighbor’s fields.  Like our fields, our neighbor’s land was farmed in roundup-ready soybeans for a good while (we think 10 years).  Organic matter is very low, around 1.5%, and the soil seems lifeless.  Instead of immediately planting perennial grasses like we did with our fields, we’re going to give our neighbor’s soil some extra TLC and a good dose of tough love (disturbance) to try to jump-start this soil into healing itself and becoming hospitable to soil life.

Because summer is approaching, we decided to plant sorghum sudangrass and cowpeas as a cover crop.  Both of these love the heat!  Sorghum sudangrass is a cross between sorghum (relative of corn) and an African grass.  Cowpeas are good ole’ black eyed peas.  We’re hoping the sorghum sudangrass will grow thick and tall and provide support for the climbing cowpeas.  Like corn, sorghum sudangrass loves nitrogen, and the cowpeas are a legume, so we want the cowpeas to fix nitrogen and provide it to the sorghum sudangrass.

Our Goals

sorghum sudangrass

Organic Matter:  Our primary goal for this cover crop is to provide tons of biomass to the soil.  According to this very useful handbook on covercrops, sorghum sudan is “unrivaled for adding organic matter to worn-out soils”.  It quickly grows 5 to 12 feet tall and usually results in at least 2 tons of biomass per acre.  We plan to kill and incorporate this biomass into the soil by rotovating.  With the help of soil life, this biomass will decompose and start to become organic matter in the soil.    Cowpeas grow quickly too and should provide another ton or so of biomass per acre.  Compared to the stiff, crunchy sorghum sudan biomass, cowpea biomass (vines and leaves) is softer and will break down quickly.  After going from year after year of soybeans, we think the soil life will like snacking on these two crops for a change. 

Weed Choker:  After many years of roundup-ready soybeans, the weed pressure in these fields, especially with round-up resistant weeds, is immense.  Both of these cover crops have been shown to out-compete weeds, but sorghum sudan is especially great at it.  This crop actually kills weeds by secreting allelopathic compounds from its seedlings, shoots, leaves, and roots.  The same handbook cited above, page 107, says this compound is strongly active at extremely low concentrations, comparable to synthetic herbicides.  Amazing! 

Iron and Clay cowpeas

Healthy Disturbance:  The tough love I mentioned above is all about disturbance.  This soil has been in no-till soybeans and sprayed with roundup for many years now.  It has gotten very little food in terms of plant matter.  By growing very strong and dense covers and incorporating all that plant matter in the soil by shallow tilling, we intend to shock the soil in a good way and jump start it into heading in the right direction.  Nature uses disturbance quite a bit to initiate renewal (think of forest fires or huge buffalo herds).  We’re convinced that our own fields would be better off if we planted successions of cover crops instead of perennial grasses.  This is the 3rd season we’ve had grass, and the grass gets a little better every year, but the soil seems stuck in a bad place in terms of soil life (crusty, dusty soil, very few earthworms, etc.). 

Method and Cost

We rented St. Marys County’s no-till drill (planter) and drilled about 30 lbs per acre of sorghum sudan and 15 lbs per acre of cowpeas (Iron and Clay variety) on April 30th.  We inoculated the cowpeas with the bacteria that help cowpea roots fix nitrogen.

Seed Cost = $1,175.  (15 bags of sorghum sudan at $30 per bag bought locally, 7 bags of cowpeas at $60 per bag + shipping, inoculant = $35)

Drill Rental = $200

Diesel = $30 (~ 7 gallons)

Labor = $160 (8 hours at $20 per hour)

Total = $1,565 or about $70 per acre (22 acres total)

This being our first cover crop, we have no basis on which to judge the cost, but the cost seems high to us.  In the future, we intend to lower the seed costs by only buying seed that’s available locally (no shipping costs).  We can also lower the diesel and labor costs by getting more experienced with planting different seeds and learning to use the drill.  We had a hard time adjusting the drill to spit out the seeds at the right rate – this took about an hour.  We were also moving the tractor very slowly in order to notice groundhog holes and dodge them in time. 

Our Plan for the Growing Season

Grow & Mow:  As long as the cover crops are out-competing all the weeds, we’ll let the sorghum sudan and cowpeas grow until they’re 3 or 4 feet tall and then mow them.  The cover crop handbook says this encourages the sorghum sudan to tiller and put down even deeper roots for regrowth.  Deeper roots are fantastic – they go into the subsoil, break up compaction, and bring up long-lost minerals and put them in the plant.  When we incorporate the plants into the soil, the minerals will be placed in the top soil and the roots will eventually turn into organic matter. 

Fertilize?:  We haven’t decided if we’ll fertilize or not.  We’ll watch the sorghum sudan, and if it’s starting to look wimpy and nitrogen deficient, we might spread some ammonium sulfate.  It’s $12 per 50 pound bag, and each bag has just over 10 pounds of nitrogen in it.  We’d probably spread at least 50 pounds of N per acre, so the cost could add up quickly.  However, ammonium sulfate also supplies nice amounts of sulfur, which this soil needs badly.  We’ll see – we might end up in a situation where it’s beneficial to “buy” more biomass by fertilizing with ammonium sulfate.     

Rotovate & Wait:  After a good re-growth, we’ll kill the cover crops by rotovating them into the soil, probably in early August.  A rotovator is like a very wide garden tiller for a tractor.  If the sorghum sudan does produce a lot of biomass, we will need to give the soil 2 to 3 weeks to start breaking all the biomass down.  By the end of August, we’ll plant the next round of cover crops for the fall/winter season.  We’ll look for crops that this soil hasn’t seen for a long time, probably cereal rye and hairy vetch. 

Updated June 23, 2011 here.


13 responses to this post.

  1. Hi,

    I came across your website while trying to find a local source for cowpeas and I truly like what you’re doing.

    I’m going to use cowpeas and buckwheat this summer and then cowpeas and sorghum sudan in the late summer to winter kill. But, I’m having trouble finding a local source for cowpeas. I see that you had your’s shipped, who did you order from?



  2. Thanks for reading and commenting! Hope your buckwheat goes well, we’re planning to use buckwheat next summer. I got our cowpeas at They were great to work with, but the shipping for 7 50lb bags was around $175. 😦 If you’re closer to the west coast, I recommend Hearne Seed, also online. They are very responsive too, but coming from California, the shipping was higher. Good luck!


  3. Thanks for the post. Someone else commented on my blog and pointed this out to me. I’ve downloaded the cover crop guide, and have already dove into headlong.

    We are really looking forward to experimenting with clover, hairy vetch, pearl millet, op corn, and sudan when we land on our little farm.

    Thanks again for sharing, and keep sharing the dream.


  4. How are you planting your cover?


    • The St. Mary’s County Soil Conservation District’s no-till drill has two seed containers. We put the cowpeas in the smaller container and set the rate to 15 lb per acre, then we dumped the sorghum sudan in the larger container and set that rate. Both are coming up nicely- about 4 inches tall now. We hope as the weather heats up they’ll really take off.


  5. Check out welter seed company in Iowa. They split the shipping cost with you. Really enjoyinh your blog. Great parallels between our farms as I try to create nutrient-dense forages here in NH. Cheers!


    • Hi Jeff, I love your farm website! Your grass looks great in the pictures. Thanks for the Welter Seed recommendation. I have their catalog but haven’t ordered from them yet. Good luck on your farm – looks like you have a great thing going.


  6. Posted by Paddy Reynolds on June 8, 2012 at 2:23 pm

    Hi Jeff I live in Australia and ranch beef cattle and fat lambs. Historically we grow winter feed(Oats and Rape is popular) I Have a 50 acre block that has been extensively cropped and now is leached of nutrients. Rather than pouring on yet more fertilizer, I planted a cocktail cover crop last summer (millet, white clover, rape and sunflower) result was good. Cattle grazed it out in May . I have not been unable to plant a winter cover crop because it is too wet. I plan to grow buckwheat, cowpeas,chicory,maybe sorghum and someoilseed radish this spring (I am lead to believe that biodiversity is the go) This is all new to me. Would appreciate yourcomments


    • Hi Paddy, thanks for commenting! We planted a summer cover crop cocktail a few weeks ago. I plan to get a post on it published this weekend, so check back! We put a huge variety in the seed mix, drilled it into both killed vetch and existing pasture. It’s coming up very well so far. I too believe diversity is the key. Each plant attracts and hosts its unique set of soil biology, brassicas help earthworm populations explode, etc.


  7. Posted by Jake on October 20, 2014 at 9:10 am

    Did the cow peas produce enough nitrogen for the Sudan or did you have to fertilize? We have mostly sand loam soil on our farm and have done Sudan in the past but fertilizer is a must. With increased nitrogen costs I would love to find other alternatives plus build up our soil.


    • We didn’t fertilize. Admittedly, the sudan looked pretty raggedy, but it did the job we hoped it would do. This was the first sudan mix cover crop we planted. We did a couple more plantings in subsequent summers. Each sudan crop looked better and better as the soil started repairing itself.


  8. Posted by michael on July 14, 2016 at 12:44 pm

    I am here on the East coast of the country and I was looking for additional information regarding how this cover crop did over all.


    • It did amazingly well, especially given how sandy and low in organic matter & nitrogen the soil was. If one lets it grow tall and thick, it also provides excellent coarse mulch after mow-down for no-till fields.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: