Sorghum + legume, anyone?

Hi,
has anyone had any experience growing sorghum x sudagrass together with a summer legume?
A seed provider I enquired with said that it is better not to mix this grain crop with a legume plant because it would smother it because of shade cast.
On the other hand, a US publication I consulted "Managing cover crops profittably" says that there are a few other cover crops that can be seeded together, fagopirum esculentum being one of them (not a legume) and cowpeas. In my situation though I can't (or may be I shouldn't) use  cowpea because the soil I intend to grow these cover crops is alkaline ("Cowpeas grow in a range of well-drained soils from highly acid to neutral, but are less well adapted to alkaline soils.."), same for the former one.
So just wonder if there is any experience out there with this mix (and alkaline soil) that worked (or not) and which legume did you use.
Best regards

You could try pigeon peas.  They grow to 2m+ in one season, so are not going to be smothered out by tall sorghum.

I have grown both, but have not intercropped them, which is what I plan on doing this year.  When I had them as pure stands, they had a lot of pest pressure, so maybe by intercropping them and adding some pest deterrent plants in with them, I can conquer the bugs.

What is the purpose of this seeding? It makes a big difference if this is for forage, hay, cover in between winter crops...

Zone info? Spain is quite varied...

Is your intention to keep the ground covered in between the sorghum plants? This can work very well because the moisture coming out of the soil and air condensing on the leaves at night preventing soil desiccation. What fine low growing legume grows well in your climate? Are youm intending to harvest the sorghum for seed or to juice the stalks? Will the legume interfere with the harvest method?
I harvest my fields with a scythe for hay mulch and over several generations the fields have sorted out which grasses and legumes like to grow together in different soil and water conditions. For example I have a section of well drained sandy loam with vetch and tall grass. the vetch is growing low now but the grass will send its stalks above it then the vetch will fill the space between stalks. During the summer drought it stands as a solid dry mass protecting the soil then I harvest it to mulch where I don't want winter growth but the seeds have already fallen to start the next seasons growth.

Tj Jefferson wrote:What is the purpose of this seeding? It makes a big difference if this is for forage, hay, cover in between winter crops...

Zone info? Spain is quite varied...

Hi TJ
the purpose is to build soil and after that plant fruit trees. Right now the soil is not in very good conditions, very low in organic matter < 2%, pH 8, quite high in lime and calcium, not salinized though, but compacted because, I reckon, of previous conventional cereal agriculture. Also N levels are not very high.
So the cover crop should jump start the soil conditioning process and creating a medium for microorganisms to thrive and help creating the medium where the trees will (hopefully) thrive as well. After the summer crop is cut, I plan on subsoiling and inoculating the soil with useful microorganisms and micorrhizas, plant the tress and continue with other cover crops.
As for the zone, we are in north east Spain, in central Catalonia. I think USDA hardiness zone 8 or 9, around 600 ml/m2 rainfall (some of it even falling in summertime).

The sorghum x sudangrass hibrid seems to be the best option for 1) a quick summer cover crop and 2) leaves huge amounts of organic matter both on top and within the soil

There are a few wild legumes growing in summertime in the area but I have never seen them growing among a stand of tall grass.
Vetch can grow well there but I think it will be too late in the season to seed it there.

As for the pidgeon pea....well as far as I know it grows as a 2m (more or less)  tall bush it's not really a herbaceous plant.....and also I don't think I can find it around here.

Another thing to consider is that ..... there is already some wheat growing in the same field (the field has been bought after it had been seeded with wheat) and from my limited experience, I would say that it might actually "interfere" with the soil building process I have in mind (and also I don't see the wheat as much of a soil builder if one needs to send plant roots deep down through compacted soil), so I am considering slashing it and use its aerial parts as mulch after the seeding of the sorghum, the roots that will remain in the soil will slowly decompose and bring some organic matter in top soil part. Initially I thought that I could mix the sorghum with the wheat that is growing, then I could slash both the wheat and the sorghum by the end of june and the sorghum will grow back. But lately I have been thinking that if I seed the sorghum among the wheat some competition will start and both will do poorly. SO may be it's better to cut it right before seeding the sorghum and may be add a legume that can help with capturing N, since the soil itself doesn't seem to have much, right now.

Alfa-alfa can probably grow in this soil type but it remains low, so I don't know how well it can fare together with the sorghum hybrid. May be it can also be a matter of how dense the planting of the sorghum hybrid should be, so if it is planted at a low density there can be enough light for the legume (whatever that is) to grow well.

As for the pigeon pea, you could find the seeds in any asian/ethnic/african grocery shop...

André Troylilas wrote:As for the pigeon pea, you could find the seeds in any asian/ethnic/african grocery shop...

Well thanks didn't think about it....but not probably in the quantities I may need. But Pidgeon pea is also a perennial legume from tropical and subtropical areas, probably more apt for hedgerows than for what I want to do here..and I am not sure it would stand the winter even as a hedgerow (in a few years may be.....)
Cheers

the purpose is to build soil and after that plant fruit trees. Right now the soil is not in very good conditions, very low in organic matter < 2%, pH 8, quite high in lime and calcium, not salinized though, but compacted because, I reckon, of previous conventional cereal agriculture. Also N levels are not very high.
So the cover crop should jump start the soil conditioning process and creating a medium for microorganisms to thrive and help creating the medium where the trees will (hopefully) thrive as well. After the summer crop is cut, I plan on subsoiling and inoculating the soil with useful microorganisms and micorrhizas, plant the tress and continue with other cover crops.
As for the zone, we are in north east Spain, in central Catalonia. I think USDA hardiness zone 8 or 9, around 600 ml/m2 rainfall (some of it even falling in summertime).

I don't know if you have visited this thread What we Need to Know about Soil  It might give you some different ideas and even save you some time and money.

Sorghum is a heavy feeder with most of the nutrients ending up in the seed heads, that means that in order to not have it coming up again you have to remove the nutrients packed into those seed heads and those are no longer available.

Clovers and Sweet clover (not actually a clover) are very good options for the soil type you have, they will acidify the soil just enough especially if you add some compost tea at the time you seed.

Mycorrhizal fungi are root dwellers, they need to be added as you plant the tree, right around the root ball. Spreading this type of fungi in soil prior to planting trees will only result in the death of the fungi since you don't have their living quarters already in place.

Redhawk

Hi Bryant,
nope, wasn't aware of this thread. I am really looking forward to read it. Many thanks for making your wisdom available!

The idea of using sorghum is that that is the only fast growing summer grass I could find and that is also capable of sending its roots deep down a compacted soil
Also it looks as if it can be cut at least once, and by doing this helps create an even larger and deeper root system
I also reasoned that since sorghúm roots become woody, after it is cut (and dead) the woody roots might be more easily colonized and decomposed by fungi, than the non woody roots of other cover crops, and since I want a fungi dominated soil for growing trees, this could help.
If I manage to either cut (or graze) it at least once before harvest time, part of those nutrients will remain in the field.
But since it also produces a lot of biomass both over and underground the amount of nutrients that accumulates in the seedheads isn't perhaps that big (in comparison)? (just thinking out aloud about this last comment).
At least this is my understanding from what I read/learned around.

When you mention clover and sweet clover, do you mean as a substitute for sorghum or as an intercrop? As about the compost tea, do you mean by spraying the soil (after seeding) or watering the seeds before seeding?

I intended to inoculate tree roots with micorrhiza at planting time, sorry for not specifying any clerarer in my previous post.
Best regards

hau Antonio, Sorghum will work quite well the way you mention using it. You can actually cut it twice, I know farmers that get two seed crops from their plants doing that.
If you cut it as the seed stalk is forming, you can just let those cuttings lay and rot too.

The clovers are used as an intercrop, the ones I find best for this type of use are the yellow flowering sweet clover (will tolerate a lot of shade, then jump once the sorghum is cut, giving you a rotting mulch of sorghum and a N fixing pollinator attractor).
The true clover I most like is scarlet clover it will perform much like the above sweet clover, red clovers are best as the primary planting instead of the secondary planting.

I like to rake, spread seed, rake to cover then water with compost tea. It gives the seeds their sprouting moisture, minerals, and micro biota for the best start possible.
If it is going to rain within two days of my planting, I hold off on the tea until after the rain is done and soaked in. That way I am not allowing instant leaching of the nutrients.

Redhawk

Hi Bryant
thanks for your last reply.
I had been looking for some other legume other than cowpea and had looked into melilotus (but didn't know that it was also known as sweet clover) and lotus corniculatus. Melitlotus seems to be more drought tolerant and adapted to alkali soil than lotus corniculatus. Still the vendor says that it doesn't tolerate shady conditions....hum, but again, "Managing cover crops profitably" also says that interplanting works with tall crops.....Interesting.

If I have to plan the seeding of both the sorghum and the sweet clover, how should I proceed?
Should I use separate lines for each crop? If yes, at what distance should each line stand from the intercrop line (also in order to reduce shade from the taller plant)?
What seeding rate for each plant would you recommend? And what distance between seeds within the line?
Also I reckon that the seeding depth for each type of seed would be different: deeper for the sorghum and much shallower for the sweet clover.
Should I plant the sorghum first and the sweet clover after? (but how long after)

I was considering using a hand seeder since (I am talking about less than 3000 m2) but may be it could be more useful to use rented tractor operated one, since I reckon I will only do it once,
but I am not sure how easy it is to control the seeding distance within the lines with this kind of machines.
Regards

You could simply broadcast both seeds at the same time. The sweet clover will sprout and sit near the ground in the shade of the sorghum until you cut the sorghum, then the sweet clover will grow tall and flower.
This works for any dual crop planting that has sweet clover as the secondary crop. You can use it with barley, cereal rye, wheat, oats, and corn too.

Many people will tell you that sweet clover doesn't tolerate shade, but they are going on the presumption that you want it to grow in the same time frame as your primary crop (sorghum in your case).
This is the exact method that is used by Mark Shepard on his New Forest Farm, there is no reason to think it would not work for you.

A hand seed spreader will work just fine, simply mix the seeds, fill the hopper bag and go have fun spreading seeds. Don't worry about seed depth for the sweet clover, it will come up.

Redhawk

Sorry for the initial question and delayed reply. Bryant has certainly covered the basics. I have been going through field rehab as well with a former Christmas tree farm, so good times...

For alkaline soils you might also consider alfalfa if you can establish it as an n-fixer and some other biomass producer other than sorghum. Alfalfa is both a perennial and unless I am mistaken goes down up to 30 feet, which is better than a subsoiler by far. I wish I could grow it here but it won't tolerate my pH. Unless I am mistaken it is also a mycorrhizal participant. I thought I was going to get a deep subsoiler and a bulldozer to deal with the compaction here, but with a few exceptions (like where the prior owner had a giant burn pile over the septic field) the compaction is resolving after basically two growing seasons. I broke a pickaxe last year and now can drive a shovel in the worst areas, which are now getting a legitimate vegetative cover. There are a few areas like the old burn pit that I am giving one more chance with natural decompaction. There are plants that will do if for you, do a more thorough job, and hold the decompaction gain. I am trying to use them, and if you want to see the various species along with where they performed/didn't I have a thread with the ongoing experiments and one with the fall/winter version. I have used upwards of 20 species and am one zone different, so may be applicable. The sweet clover tends to grow in similar areas in my experience and gets taller, but I don't think the underground portion is nearly as robust as alfalfa. I really miss alfalfa, it is awesome! Some other aggressively tall legumes I looked at were sesbania, Aeschenomony (probably butchered that), Sunn Hemp, and vetch. Vetch is possibly perennial where you are but the others would not be. Most of those can probably tolerate your pH. I decided to do the Sunn Hemp and Alyceclover. Both are very aggressive biomass producers, and if you have earthworms my really help your compaction. I am not doing sorghum, I'm using millet, but it is a similar plant. If you can in your area I would also recommend buckwheat from the preliminary results this summer, and that has a massive taproot! I have a tractor and access to a seeder, but I ended up broadcasting it anyhow, mostly because I want to see if this is repeatable in areas that are not disturbed.

I would recommend highly the Soils series Bryant wrote. I don't think I understood the horizons until I read that, along with the implications of deep soil disturbance. I am very glad I didn't subsoil, because unless you guess just right on planted species and have a bountiful growing season AND smartly convert to perennial cover, you will have the opportunity to do it again, and maybe again, but with totally dead soil. I was VERY skeptical about the ability of the existing and introduced species to really get the job done, but by and large they have done about 80% of the job, and the soil is still alive. I still have grass in the starter forest, but I also have cardboard and wood chips, and the trees are so far thriving. Gradually the trees will either shade the grass out, promote the cool-weather grass that has expansive root systems, or a little of both. The soil is telling me it is on the rebound by worm counts, local perennials my mom tells me are rare here (!) and infiltration capacity. I have not done a repeat OM soil sample but it was <1% and is now visibly darker soil, so I would assume close to 5%.

Hi Tj,
thanks for sharing your experience.

I think I will use sweet clover for now and seed alfa-alfa after the subsoiling so that the work can be continued for a longer time, since alfa-alfa can live for much longer than sweet clover, but I wonder if having deep rooted perennial grasses in the field can create competition with the trees for nutrients at some point, or is it just that fruit trees feed mostly in the top soil portion so there would be actually no issues of such a competition arising?

I read that both you and Bryant suggest broadcasting the seeds, suggesting that even bigger seeds like those of the sorghum can easily germinate on the soil surface. I read that it would be good to give sorghum seeds a depth of a couple of inches so that they can stay in touch with a more moist soil that if they just lay on the soil surface.

Also, Bryant says

"A hand seed spreader will work just fine, simply mix the seeds, fill the hopper bag and go have fun spreading seeds. Don't worry about seed depth for the sweet clover, it will come up.

If I do this I imagine that quite a few of the smaller seeds (the sweet clover I assume) may actually go down together with a bigger seed....which means I will most probably overseed the sweet clover (which is probably what we are after?). How do I calculate how many seed do I need of each plant type then? The vendor I am looking at says that sorghum goes at 35Kg/Ha but don't specify what the rate would be if mixed with other plants, and the sweet clover 3-5 Kg/Ha if mixed with a cereal.

As a last remark, I am deducing from what I read in your posts that it is not so important that the legume and the cereal are seeded in different lines but it might actually be better that the legumes are seeded in the same line and close to the cereal, so the cereal can benefit most from the N-fixation (when seeded using a hand operated seeder).

Sorry if I am asking for so much assistance on this topic, but it is the first time I do this...and feel quite insecure at times on how to proceed

Antonio,

but I wonder if having deep rooted perennial grasses in the field can create competition with the trees for nutrients at some point

I think there are two reasons people say this. One is that grass maintains a different biome that trees. Bacterial versus fungal. The other is the competition over water at the feeder root level. Your climate will dictate whether the shade and infiltration from the grass is worth the competition. In my situation I am letting the cool-weather grass and affiliated species do my hydraulic fracturing and decompaction as per prior post. I mulch widely around the trees, like to the outside of the dripline. A prior discussion with input from Bryant The Soil Whisperer. I do maintain grass in the alleys between the trees, for alleycrop grazers. These are not tender fruit trees though, basically shade producers with some tough fruit/nut species. I have alleys of trees with what I want to become a tree-friendly biome and the grass biome in strips.

I am deducing from what I read in your posts that it is not so important that the legume and the cereal are seeded in different lines but it might actually be better that the legumes are seeded in the same line and close to the cereal, so the cereal can benefit most from the N-fixation

N-fixers don't release any until they are dead/cut. If you are mowing after they grow it will likely mix well as long as they are inside the radius of your mower.

How do I calculate how many seed do I need of each plant type then?

I use basically a partial pressure calculation. If sorghum is listed at the monocrop rate, and will end up being 50% of your planting, you can do the math. Sweetclover is already calculated from what you are saying. I would rather put down too much than too little, I want no sun reaching the soil in the heat of the summer. The idea is that if you reduce the soil temperature you will have better microbial health.

Antonio, The rule for seed depth is "the larger the seed, the deeper it needs to be planted". things like celery, radishes, and all the other tiny seed plants go in at 1/4 inch to 3/8 inch. Corn goes in at 1 inch to 1 1/2 inches.

Sorghum in commercial settings (such as what your supplier is using for his reference) is usually planted with a seed drill that sets depth and spacing automatically.
For our purposes, you can plant much tighter than if you were going for a sorghum seed crop, we are more about the plant matter than a crop of seeds.

I always use a garden rake on the surface of the space I am going to seed (for anything) then If I have time I use the back of the rake after the seeds are spread. I also try to seed just before a rain is supposed to come, or just after a rain.
That way I don't have to water those seeds to get them to sprout (usually).

You can spread your sweet clover and sorghum either at the same time or make a pass with the sorghum then a second pass with the clovers, either works just fine since the clovers are going to wait for sun to really get growing.

For soil building with plants, you can ignore the seeding rates published, they are for cropping that plant instead of being for soil building.
I've broadcast up to seven different plant seeds in one pass, after scratching up the surface, I've done the same without doing any prep work, both germinated about the same.
If you really want to get deeper soils broken up just add a daikon radish seed or rape seed to your blend and spread.  

As you have deduced, we want N fixers close to the other plants, since we are going for the chop and drop of the sorghum, those N fixers will spring up after the first chop and drop (and the second too, since sorghum will bounce back with a second growth).

Redhawk

I know I'm a bit late to this discussion....What about sweet pea? It'll climb right up that sorghum stalk.

Nathanael Szobody wrote:I know I'm a bit late to this discussion....What about sweet pea? It'll climb right up that sorghum stalk.

Hi Nathanael,
thanks for your suggestion...it's never too late, really!
So what you are suggesting is Lathyrus odoratus, right? I did just a little search and the suppliers in my area don't seem to have it, but by looking at its description it sounds quite an interesting one to try for the soil and climate I am in. May be I'll see if I can get a few seeds from some supplier abroad and multiply it.
The info I found doesn't say much about its root system though, nor if it is a good N-fixer.
Also it seems that most suppliers I found sell it as an ornamental plant.
Regards

Hi Tj,

If sorghum is listed at the monocrop rate, and will end up being 50% of your planting, you can do the math. Sweetclover is already calculated from what you are saying. I would rather put down too much than too little, I want no sun reaching the soil in the heat of the summer.

I realize that I do not know whether I need to seed the two plants at 50/50 rate........is this a common practice when interplanting a N-Fixer and a main crop?

The other big doubt that I have is: in case I decide to broadcast the seeds and I do not want to use a rake (as Bryant suggests, because I find that a bit impractical with more than a few 100s square meters of land, but it may just be my lack of experience with the process: in my case I would need to do it in some 4+ acres/little more than 2Ha) how do I incorporate them in the soil or make sure they are in close contact (I don't have animals that can do this by stomping on them).
Regards

Farms use machinery (tractors, plows, and seed drills with rollers) to get good mechanical soil to seed contact.
If you only have hand tools, then you need to use them since without good soil to seed contact, germination is not as likely to occur with the seedling surviving.

As far as seed ratios, the primary plant you want to grow will be the one with the highest number in the ratio.
If you are wanting to have mostly leaves to rot, then go with more sorghum

I would agree with Bryant, broadcast seeding without soil preparation is super wasteful.  Clover does seem to find its way up but millet so far this spring has been dismal. Pea-sized down to maybe half pea I would say you get good germination, maybe 50%. Millet/sorghum I think you would need to seed 3-4x the rate they recommend for standard planting-- like I said, very wasteful.

I ended up raking 2 acres! I use a real rake not a leaf rake and smack it in the ground, making little pockets and then use the back of the rake to move stuff around, and some seeds fall in the pockets. It took all day, but germination for small seeds is basically zero without it in my experience. Granted I could have disked before and then disked after planting but then I would destroy my existing roots and soil life. I decided destruction of the soil web was not a good exchange for the biomass.

If you don't have a soil web, that biomass is quite temporary anyhow! Grow soil and the plants will be fine.

So what you are suggesting is Lathyrus odoratus, right?

That's correct, and since it is native to Europe....

But really, I would think that no legume will do well with sorghum. My inlaws grow fruit on an industrial scale. They plant sorghum real dense as a cover crop for one year. Then when they plant the orchard they interplant clovers for Nitrogen.

I grow cowpeas. They will grow anywhere as long as they have enough moisture, which is to say, very little. I grow it in the spring and in the fall. Also i know a lot of plant nerds are going to read this and be angry, but the nitrogen fixation of legumes is vastly overrated. Fresh manure is the way to grow; it comes complete with bacteria already actively breaking it down.
-Chrissy, lead grower at Eat Your Sand, sunset zone 27, zone 8b, USA.

I believe a good one for sorghum sudan grass would be a plant called sunn hemp.  Its gaining popularity as a warm season n fixer that is fast growing and tall.  Check it out.  I believe greencoverseed carries it, im sure you can find it at other places as well.

I'd vote for ladino clover. It grows in a variety of conditions, some varieties can put on a lot of biomass and height (6ft) in one season
I've been growing sudex for forage, as long as its warm, it sure grows. It does not put energy into seeds, put into foliage (seed energy would be the straight sorghum)

Hi,
I have not been following this thread for a while now, and I see new knowledge sharing. Many thanks.

Now, I am just trying to figuring out the right time for seeding. The info on sorghum x sudan grass says that there need to be a soil temperature of 18 - 21 ºC (65-70 ºF).
How do I get to know the soil temperature (if I do not have a soil thermometer...does it exist?)?
Can I just deduce it from the air temp? or is there any relationship between soil T and air T?
Thanks

Soil temp can be estimated by average daily air temperature. If you have little soil cover, this temp may be taken in the sun. If you have heavy biomass cover it will approximate the temperature in the shade. The depth of planting will determine how long that temperature needs to have been in that range. For broadcast it is a couple days. For deeper planting it can be >1 week.

Thanks TJ!