Archive for the ‘sorghum sudangrass’ Category

Cost of Cereal Rye and Vetch Cover Crop

Even though our winter cover crop of rye and vetch did not germinate well, I figured I’d go ahead and lay out its cost so we could compare it with the cost of our summer cover crop of sorghum sudan and cowpeas.  Below is the cost for drilling rye and vetch seed into about 22 acres of our neighbor’s fields (where we grew sorghum sudan and cowpeas) plus about 3 acres of our own former grass pasture.  We bought enough seed for 27 acres just in case we ran out.  We planted on Labor Day weekend 2011.    

Seeding rate:  Rye at 40 lbs per acre; Vetch at 20 lbs per acre. 

Seed Cost = $1,284.  (20 – 55 lb. bags of rye at $17.30 per bag, 11 – 50 lb. bags of vetch at $83 per bag, vetch inoculant = $25)

Mycorrhizal Inoculant = $388 (11 lbs)

Drill Rental = $200

Diesel = $22 (~ 5 gallons)

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

Total = $2,054 or about $82 per acre (25 acres total) Sorghum sudan & cowpeas cost $70 per acre, but did not have mycorrhizal inoculant.

New Seed Supplier

Myco inoculant (top), vetch inoculant (right), cereal rye seed (bottom), vetch seed (left)

We bought the seed from Sam Swarey, a seed rep for Pennsylvania-based King’s Agri Seeds.  Mr. Swarey is Amish and lives close to us.  We’re glad we found a knowledgeable seed salesman that can supply us with just about any seed we’d like.  King’s Agri Seeds is focused on grazing and cover crops, which fits us well.  Even though we can’t pick up the phone and call Mr. Swarey, we’re glad we found him and his fantastic customer service.   

Vetch’s Low Price

The vetch seed cost would have been much more expensive, closer to $200 per bag, but Mr. Swarey had bags of last year’s vetch left over and sold them to us at cost.  Yay!

Vetch Inoculant

This inoculant is bacteria that forms nodules on vetch roots and fixes nitrogen from the air.  When the vetch dies (we’ll kill it next spring), the nitrogen will be released into the soil and made available for the next crop.  Very healthy soil might already have the bacteria, but since our soil is so lacking in organic matter and soil life, we thought it was wise to spend $25 and coat the seeds with it.

Mycorrhizal Fungi Inoculant

We bought this from AgVerra and mixed it with the seeds with a little milk before filling the seed drill.  Mycorrhizal fungi are amazing creatures.  They colonize plant roots and make the area around the roots acidic so nutrients like phosphorus, calcium, magnesium, zinc, etc will be attracted to the roots and will enter the plant for nourishment.  Cool, huh?  The fungi have a mutually beneficial relationship with plants because they help feed plants minerals, and the plants feed the fungi goodies made during photosysthesis.  These fungi are also responsible for making a soil component called glomalin.  As the fungi die, the glomalin is sloughed off into the soil.  We want more glomalin in our soil because it’s 40% carbon, and it gives the soil nice fluff and keeps stored soil carbon from escaping.  It’s tough stuff, and it’s exactly what our soil needs.  We decided to spend the money to repopulate our fields with these very beneficial fungi.  This should be a one-time cost.

Cost Comparison with Sorghum Sudan & Cowpeas

The Rye and Vetch cost was over $80 per acre, and the sorghum sudan and cowpeas cost was around $70 per acre.  The sorghum & cowpeas did not include the mycorrhizal inoculant, but we got a very good deal on the vetch price. With our poor rye and vetch germination, we estimate that half the seed did not germinate.  So, about $1,000 of this cover crop price was spent in vain.  We believe the cause of poor germination was the combination of planting into very fluffy soil right before a tropical storm dumped 10 inches of rain.  We learned our “grand” lesson and  for sure won’t make these mistakes again!


More Lessons Learned with Rotovating Sorghum Sudangrass (and a Bright Side)

Our rotovator fought the cover crop, and the cover crop won!  We grew sorghum sudan this summer on our neighbor’s fields as a green manure crop.  We rotovated it in early August to incorporate most of the crop into the topsoil.  We wanted the crop to feed the soil life and turn into organic matter.  Our goal is to move this dusty, sandy soil toward crumbly, black, “chocolate cake” soil that makes plants and animals thrive.

Rotovator Failed to Kill Sorghum Sudan

We also wanted the rotovator to kill the crop so we could plant the next cover crop of cereal rye and vetch for the winter.  We had very limited success here and still can’t tell what we did wrong with the rotovator!

Frosted sorghum sudangrass, 3 feet tall after failed rotovating

You can see the sorghum sudan in this picture taken in mid-November, about two weeks after a killing frost.  The sorghum sudan completely re-grew from the roots after rotovating and is finally starting to die from a cold snap.  Finally!

Rotovating is supposed to easily kill a crop, so we obviously did something wrong.  Perhaps the blades were not set deeply enough.  Perhaps we went too fast.  These scenarios are both perplexing though, because on the last field we set the blades to the deepest possible level, and the crop still grew back just as thick.  And the speed – we were going so slowly, I’m embarrassed to admit how long it took us to cover 20 acres.  Let’s just say days, and I won’t say how many!

I have heard that sorghum sudan easily grows back from the roots, such as after animals eat it down to the ground.  So maybe we just have to take extra steps when rotovating this crop and disturb the roots more?  We rotovated two acres of old grass pasture, and the grass died completely, no problems there.

Fluffy Soil Not Good for Planting

Another problem we need to figure out is extra fluffy soil.  The soil that the rotovator left behind was fluffed up, so much so that our boots would sink down about an inch when we stepped on it.  Turns out this does

our 7-foot rotovator

not bode well for the next crop.  We rented our county’s seed drill to plant the winter cover crop of rye and vetch about three weeks after rotovating, and it germinated very poorly.  I asked our Extension Agent for his opinion, and he said seed with poor soil contact has trouble germinating, and the 10 inches of rain from Tropical Storm Lee that we got right after planting likely made things worse.

So how do we make a good strong seedbed after rotovating?  We had the rotovator’s backboard down most of the way; maybe it should be down all the way.  Also, we can use time.  All the extra air eventually leaves the soil.  The soil needs at least 4 weeks to fully digest plowed down vegetation anyway (especially with no spraying of microbes), so we’ll just wait longer.  Our Extension Agent said our boots shouldn’t sink more than ¼ inch.  Any more than that, and the soil is probably too fluffy for drilling seed.

So far, I’m far from in love with rotovating!  It takes forever, and its performance feels like false advertising, far from the praise rotovators receive for their ability to kill plants, incorporate them, and make a nice seedbed all in one pass.  Surely it’s not too good to be true!  Hopefully it’s something we’re just missing.

Bright Side

Okay, enough of the whining!  There is a bright side.  Sorghum sudan is unrivaled among cover crops it its ability to produce biomass.  It gave us three good growths on zero added nitrogen fertilizer, and the root system below ground probably came close to mirroring the plant above ground.  We mowed twice and rotovated once, so that’s a good sloughing off of roots times three.  As the roots die and break down and form organic matter, the empty spaces will make great tunnels for earthworms.

Sorghum sudan’s other significant contribution is its amazing allelopathic (natural weed killer) effect!  During the 2010 summer season, these soybean fields were inundated with roundup resistant weeds like marestail and water hemp.  I can’t find nary a one now!  When we converted our own fields from GMO soybeans to grass pastures, we had to beat back marestail for 2 years by mowing.  Sorghum sudan is extremely helpful in this area!

Moving On…

We mowed the sorghum sudan for the last time in mid-November, as it was dying from frost.  The clippings made a good mulch for the soil.  The rye and vetch cover crop is growing well here and there, and cool-season weeds, Italian ryegrass volunteers (from previous winter cover crops) and the mulch do a good enough job of covering the soil in the other spots.  For this reason, we’re not going to replant the rye and vetch.  We plan to mow-kill the winter covers in the spring and then plant another summer cover crop like buckwheat.

Learning How to Rotovate a Green Manure Cover Crop

In mid-August we rotovated (shallow-tilled) our sorghum sudangrass and cowpea cover crop.  This post will describe the learning curve we encountered with our first time rotovating and how we got it to work.

Good mix of brown and green plant material

We planted this cover crop at the end of April, let it grow to about 5 feet tall, and mowed it in July.  Our bush hog made a lot of nice mulch.  After a week or so, the sorghum sudan and cowpeas came charging back mean and green and grew about 18 inches.  This is exactly what we wanted.  We wanted to rotovate green plant material “green manure” to feed and jumpstart soil life, and brown mulch material to breakdown and transform into organic matter.  These fields (our neighbor’s) were previously planted in no-till roundup-ready soybeans for at least a decade.  Organic matter is very low, below 2%.  Our goal is to stimulate all the soil critters to grow and multiply and bring life back to the fields.

our 7-foot rotovator

Rotovators are tillage tools, like a very wide garden tiller.  Our rotovator is 7 feet wide.  It has no wheels.  Instead, it skids along the ground like a sleigh, and the tractor’s 3-point hitch keeps it level.  We rotovated 25 acres of sorghum sudan and cowpeas (our neighbor’s fields) and two acres of our own grass fields.  In addition to the rotovator, our tractor was carrying a homemade spray tank on the front.  The spray tank is described here, and the spray mix (beneficial soil microbes and other goodies) is described here.

Why Rotovate?

We want to decrease the time it takes for the fields to get healthy.  Our own fields, which were previously under the same soybean farmer, have been in pasture grass for the past 3 years.  We’ve been mowing 2 or 3 times per year, fertilizing, and applying compost.  Unfortunately, we’ve seen very little improvement in the grass.   After studying biological farming techniques, we’re convinced the soil needs some disturbance to break up the sandy, crusty topsoil and to get a good dose of plant material and biology into the root zone.

Incorporating a green manure crop is essentially chopping plants and feeding them to the soil.  Five percent of a plant’s makeup comes from the soil (ash/minerals), and the remaining 95% comes “free” from photosynthesis of sunlight, water and air.  Incorporating the minerals (now in plant form) and all the free stuff like carbon, vitamins, and plant metabolites, provides a huge benefit to the soil in terms of improved soil structure and energized soil life.  We’re aiming for “chocolate cake” soil:  very dark, loose, and crumbly with high organic matter and a very healthy soil ecology.

Starting Out

Our goal was to rotovate as fast as possible (to decrease time in the tractor) and still be satisfied with the results.  In terms of results, we wanted to see most of the mulch incorporated into the top 4 inches of soil with a good mulch cover left on the surface for protection.  We also wanted to see a relatively smooth seedbed, but not so smooth that our sandy soil was pulverized.

We quickly discovered that getting our desired results would take a lot of trial and error!  On top of taking a large amount of time, rotovating includes many variables:  tractor speed, rpm, soil moisture, rotovator blade depth, vegetation content, row coverage (overlapping), and the position of the rotovator’s back gate.

Rotovating too slowly- powdery soil with little surface mulch

Lesson #1:  Don’t go too slowly.  On the first day, we started rotovating in our tractor’s 2nd lowest gear at about 1900 rpm.  (The rotovator manual said 1900 was the max).  This is moving VERY slowly, about 2 mph.  2nd gear cut the plants off at ground level but left them all on the soil surface.  The blades seemed to be bouncing a little instead of digging down.  Then we tried 1st gear at 1900 rpm.  Going slower allowed the blades to get into the soil, but the rotovator now chopped the soil way too much and turned it into powder.  All of the vegetation was incorporated with hardly any protective mulch on top.  It was getting dark, and we hadn’t even finished two acres.  We decided to sleep on it and try again tomorrow.  That night, it started raining heavily.  I had nightmares recalling the old 1930s TVA movie clips showing drastic soil erosion!  I didn’t feel good about the soil turning to powder.  It felt like a giant step back, and I was worried.

Pile made by rotovator catching mulch from previous row and dragging it.

The next morning, we walked out to look at the fields.  No erosion at all, everything was fine.  Except now in the morning light, we could see all the big piles of soil and mulch the rotovator created.  One side of the rotovator kept catching on the mulch in the previous row and dragging it until it balled up big enough to discharge out the side.  It was discouraging because we didn’t want to bring our tractor back over those nice and fluffy rows to smooth out the piles.  The tractor is heavy and would compact the soil and remove all the air that microbes need when they’re working.  Looked like we’d be pitch forking them by hand!  (We did.)

Lesson #2:  Don’t rotovate bone-dry soil.  We waited a few days for the rains to stop and the soil to dry out.  We knew 1st gear was bad, so we tried 2nd gear again at a little lower rpm, 1800, and we also set the blade depth deeper.  Voila!  It worked!  Most of the mulch was getting incorporated with some left on top.  But the major lesson here was soil moisture.  After the rain, the moisture level was now just right.  The soil’s aggregates stayed together in nice, small clumps.  It was too dry on the first day, and that’s why it got pulverized so easily.

Uneven seedbed from rotovating in 3rd gear with gate up

Lesson #3:  Leave the back gate down if you need a smooth seedbed.  We were still making the big piles though, and we couldn’t figure it out.  We decided to go faster, in 3rd gear, and lift the rotovator’s back gate up so all the mulch could leave without balling up.  This just helped make the piles a little smaller.  Also, keeping the back gate up left the soil surface very uneven.  That was another concern because we didn’t know how the drill (planter) would perform in a seedbed that bumpy.  We put the gate back down.

Lesson #4:  Don’t overlap rows.  It wasn’t too much longer when we discovered what was making the big piles.  I was bringing an iced tea out to my hubby in the tractor.  When he saw me to his far left, he turned his head and waved.  I saw the tractor and rotovator steer to the left far into the previously rotovated row, and a giant pile came out the side!  From then on, we concentrated hard on keeping the rotovator squarely on unrotovated ground.  This was hard to do continuously, but it worked!  We ended up leaving very narrow strips of the cover crop standing just so we’d avoid the piles.  This didn’t look very good, but we’re fine with it because the sorghum sudangrass and cowpeas will both die at frost.

Just right - moist soil, most of plant incorporated with plenty of protective mulch left on top

Lesson #5:  Do lots of test runs on the day you’re rotovating.  We ended up going back down to 2nd gear at 1800 rpm for most of the job.  The cover crop was very lush and thick in some places, and we needed a slower speed for most of it to get incorporated.  However, when we rotovated our 2 acres of pasture grass, we could go back up to 3rd gear.  The density of the vegetation makes a difference.

With all the variables involved, it’s key to test before you start to find the happy medium for that day.  Make sure your soil has some moisture (but not anywhere near wet) and start testing to see what speed and rpm gets most of the plant material below the surface and still leaves a protective mulch cover on top.   And if you start creating big piles, stop overlapping the rows!

Hurricane Irene Side Note:  Irene came two weeks later with 85 mph winds and 10 inches of rain.  The next morning, there was surprisingly little water standing and no sign of erosion.  The large quantity of mulch, both below and above the surface, protected the soil well.

Adding Biology to Our Soil with AgVerra and Tainio Products

Tractor with 3-point hitch rotovator and front-mounted spray tank on forklift attachment

We sprayed biology (beneficial microbes), enzymes, microbe stimulants, and molasses onto our sorghum sudangrass and cowpeas cover crop just before we rotovated it into the soil.  Our rotovating is described here, and our home made spray tank and molasses adventure is described here.  Our soil has very low organic matter and is lacking in earthworms and other signs of soil life.  Because we were already going to the trouble of rotovating, we applied beneficial biology while we were at it.  Our goals are to help the cover crop residue break down quickly so we could plant our winter cover crop soon and also to get good microbes into the soil so the soil can start coming back to life and creating organic matter.

Good residue breakdown with Tainio products in topsoil. 3 weeks after rotovating. Neighbor's east field - 1.9% organic matter, 6.6 pH, 5.6 CEC

We attended a fantastic farm meeting at Keystone Bio Ag near Lancaster, PA this summer.  They were selling many Tainio products, and we purchased Spectrum, a mix of beneficial microbes and Pepzyme Clear, an enzyme product that stimulates microbe reproduction.  The cost for enough to cover 10 acres was $240.   We were also in contact with AgVerra, a company I found through Acres USA.  They offered to include us as one of their project farms.  In return for feedback on their products, we got 50% off.  Whatta deal!  They sent us 20 acres worth of their Stubble Digester product, a mix of microbes that are especially good at breaking down plant residue quickly, and PTM,  a mix of beneficial soil microbes plus goodies like kelp extract, fulvic acid, and plant growth regulators.  The cost for 20 acres worth was $280 (half off) or $14 per acre.

Besides having a hard time keeping our farm cat away from the Spectrum because it smelled like fishy cat food and also curbing my hunger because the Stubble Digester reminded me of crushed oreos, all products were very easy to work with and get into the spray tank.  All products dissolved really well in the tank.

The AgVerra products offered better visibility coming out of the spray tank.  Their Stubble Digester and PTM are jet-black in color and ended up giving the spray mix a slight oily (not greasy) consistency.  This allowed us to see the spray mix cling to the leaves.  It reminded us of vinaigrette dressing!   This is not a huge benefit, but as newbie farmers, it felt good to actually see the product landing where we wanted it, and it helped us verify that our spray tank was working.

We did not speak directly to the Tainio company, but Keystone Bio Ag had good customer service and pointers in using the products.  AgVerra also had excellent customer service – they have nice product information online, and Alfred went above and beyond to help with product selection, suggestions on our home made spray tank, etc.

Good breakdown with AgVerra products, 2.5 weeks after rotovating. Neighbor's west field - 1.5% organic matter, 5.9 pH, 5.0 CEC

We started first with the Tainio products on our neighbor’s east field, which is their best field in terms of soil tilth, organic matter and mineral content.  The soil in this field is much easier to shovel than their other fields.  AgVerra’s products went on our neighbor’s remaining lower-quality fields and on the 2-acre slice of our pasture.  We took these pictures this morning, 2.5 to 3 weeks after rotovating and 6 days after Hurricane Irene’s 10 inches of rain.  Both products seem to be working really well.  The residue has broken down so nicely that we could plant our winter cover crop now, except the soil is too wet for heavy equipment.

I’m excited to see what our winter cover crop looks like this fall and next spring.  Maybe I’ll discern a difference in the two lines of products at that time, although the soil quality difference between the fields might explain any distinction.  We’ll see!

Mowing Sorghum Sudan & Cowpea Cover Crop – Wow That’s Alotta Mulch!

I’ve spent this whole weekend mowing our cover crop on our neighbor’s 25 acres, and I’m still not done!  Wow, the sorghum sudan got away from us big time!  The average height was around four feet, but in some areas, it was starting to form seed heads, and the tops reached up to 10 feet.  It was kinda terrifying mowing stuff this tall, especially on a slope, but fun at the same time.

When sorghum sudan gets this tall, its stems can get close to an inch in diameter.  This isn’t good for our plan to rotovate (shallow-till) all the plant matter into the soil so it can decompose and eventually transform into organic matter.  Stems this thick are very fibrous and will take a long time to break down, and we need good decomposition so rough plant matter won’t foul the planter when we plant our winter cover crop in late August. We’ll see what happens!

Thankfully, our bush hog is a good shredder.  Alfred at AgVerra advised us to bush hog the crop twice.  The first time we set the bush hog at the tallest setting, going very slowly in our tractor’s second-lowest gear.  The second time we drove faster with the bush hog at the lowest setting to get a good shred on the thick standing stems.  This worked really well.  It takes forever, of course, but the huge amount of plant matter will hopefully be worth it!

Going so slowly on the tractor gave me plenty of time to observe the crop.  The cowpeas looked really good in most places.  Even though they were getting shaded by the soghum sudan, the cowpeas were dark green, healthy, and just about to flower.  I’d definitely plant this combination again, using more cowpeas and not letting the sorghum sudan get so tall!

It’s nice to think about how much good this cover crop is doing for the soil!  The size of plants above ground are mirrored in the size of their roots below ground.  With a crop this tall and thick, that is A LOT of root mass below ground!  When the crop dies, the roots will decompose, transform into some organic matter, and create lots of channels in the soil.  These channels are nice airways, allowing for better water infiltration and making good tunnels for earthworms.  Also, since plants are photosynthesis factories, shredding all of this plant matter and giving it to the soil means we’re feeding the soil all the carbon, hydrogen and oxygen that the plant has assimilated from air and water, not to mention all the plant goodies – carbohydrates, vitamins, plant hormones, etc.  Since we’re not removing anything from the fields, the net benefit to the soil is huge!

We’ve heard that after a good cutting, sorghum sudan will send down even deeper roots and put on more leafy growth.  This will be great for rotovating some green matter into the soil to mix with all the brown mulch material.  We plan to rotovate in early August.  We’re working on making a front-mounted boom sprayer for our tractor.  We aim to spray the mulch with microbes, enzymes and sugars to speed the decomp process and to rotovate all in one trip across the field.  We’ll let you know what happens!

Update on Sorghum Sudangrass & Cowpeas Cover Crop, and Groundhogs Show How Bad our Soil Is

Unfertilized sorghum sudan cover crop 30" tall seven weeks after planting

In this earlier post, I laid out all our hopes and dreams for our very first cover crop attempt.  This cover crop begins our restoration effort to help our neighbor’s fields recover from abuse and years of no-till roundup ready soybeans.  We want the cowpeas and sorghum sudangrass to fight weeds and to provide a lot of biomass that will eventually turn into organic matter.


The sorghum sudan and cowpeas emerged and established nicely.  We’ve had nice amounts of moisture this season.  The sorghum sudan is about 30 inches tall and the cowpeas are about 6 inches shorter.   We planted both on April 30th; this is slow growth for sorghum sudan.  Its color is a kinda sickly yellow-green, and its leaves are narrow, signs we interpret as nitrogen deficiency.  With organic matter around 1.5 to 2%, the soil has very little capability to supply nitrogen to growing plants.  The cowpeas, which look better than the sorghum, are probably supplying some nitrogen, but the demand likely far outpaces the supply.

Weed Fighter and Biomass Provider

Cowpeas well-established, but getting shaded by sorghum sudan

Plenty of weeds are growing too, especially common ragweed and roundup resistant marestail.  But so far, the sorghum sudan is outpacing them.  Regarding biomass, we decided not to fertilize even though we know the sorghum sudan loves nitrogen because fertilizer is so expensive and because the rate of growth is meeting our low expectations for our first cover crop attempt.   We want lots of biomass to till in later this summer, but not so much that we feel completely overwhelmed in our first go at rotovating.  We also want the biomass to break down quickly so we can plant the winter cover crop by the end of August.    

Groundhog Phenomenon

Around groundhog holes, sorghum sudan is twice as tall, thicker, and a deeper green

The groundhog dens have a story to tell!  Around each entrance, the sorghum sudan is twice as tall, a darker green, and has much thicker stems and leaves.  It feels like the groundhogs are mocking us!  What’s going on?  Obviously the soil around the entrances is much better than the “topsoil” in the fields.  Louis Bromfield in Pleasant Valley wrote about how groundhogs drag subsoil up to the surface, and if your crops look better around groundhog holes, that’s proof that your subsoil is better than your topsoil.  Sad, sad, sad!  I’ve also heard that groundhogs poop around their den entrances to fertilize what’s growing there so it provides better cover.  Based on my limited knowledge, I’m going with the poop.  Mr. Bromfield could be right, especially since some nutrients like calcium, sulfur, and boron leach down into the subsoil so easily, but I’ve soil tested the groundhog soil, and it’s worse than the surrounding field’s soil test.  I believe that the fields’ limiting factor is microbes – bacteria and fungi living in the soil.  Groundhog poop can supply that, and microbes help the soil come alive and help deliver nutrients to plants.  We see the same amazingly better plant growth around compost piles on our fields.  Even though it’s a bummer, it’s helpful to see this difference.  It’s a reminder of where we’re headed and how much better our grass and crops will grow… eventually.

Our Plan

Man, I wish we had hoardes of animals to provide these microbes!  We don’t have the time to take care of animals right now, so we’re investigating soil inoculants.  They’re pretty cheap (around $5 per acre), and they can help jumpstart soil life.  We plan to inoculate the sorghum sudan and cowpea cover crop just before we rotovate it in.  Also, when we plant the next cover crop, we plan to mix the seeds with mycorrhizal fungi.  This is probably the most important inoculant, one that is tied closely with organic matter creation in the soil, and one that early evidence shows is easily destroyed by lots of roundup.  I’ll talk more about this in a later post.

What’s Next

As described in the earlier post, we want the sorghum sudan to grow to about 3 to 4 feet tall, then mow it so it will set down deeper roots.  We’re hopeful it will grow that tall by the time the ragweed and the marestail start to set seed.  No matter how tall the sorghum is, we’ll mow for weed control.  We’ll wait one to two weeks for a green regrowth, spray the crop with inoculants, then rotovate it in.  I’ll let you know how it all turns out.  Thanks for reading!

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.