Sunn Hemp Experiment

[Meadowlark]

I’m looking to soon start an experiment using Sunn Hemp as a summer cover/rotation crop. The demographics on it are superior to everything else I’m familiar with…higher N2 fixing, significantly higher organic matter added to soil, outstanding weed prevention, incredible soil building, etc. It even surpasses alfalfa in many respects, but it is only for summer conditions. It also is a candidate for use in containers and/or raised beds for the previously mentioned properties.

I’m looking for inputs…that is do you have any interest in my results; do you have any suggestions or comments on the experiment; do you have hands-on experience with Sunn Hemp, etc.

My alfalfa experiment is completed now, and I’ll be reporting on it soon when soil tests are complete.

Just wondering what the interest level is…if any. Thanks.

 

[Marck]

Sunn Hemp (Crotalaria juncea), in the Pea Family (Fabaceae), is a robust herb, native to southern and southeastern Asia. It is now widely grown in the tropics ans subtropics as a fiber crop, cover crop, or source of biofuel. Purported non-toxic varieties may also be grown for livestock forage. In warm temperate regions it shows promise in climates with enough summer heat and rainfall to allow for vigorous growth of biomass.

Caveats to consider when growing Sunn Hemp.

1. Sunn Hemp may exhibit allelopathic properties with regard to the germination of other seed. Therefore some time must lapse after the plant is threshed or turned under before crop seeding. Recommendations suggest at least 16 days. That is why over-seeding is not recommended.

2. Sunn Hemp is unlikely to seed in temperate climates. This will prevent it from becoming a weed but it also means seed must be repurchased each year. Imported seed, usually from India, is more expensive than other cover crop seed, but not prohibitively so.
Still, some comparative cost/benefit analysis should be done to determine if Sunn Hemp is a better choice than other less expensive cover crops.

 

[Meadowlark]

Let's look at some facts:

1) Cost $4.50 per pound of seed off Amazon. Compare to $4.80 per pound of alfalfa seed off Amazon. Other cover crop seeds I've used are much higher.

2) Nitrogen fixing: Sunn Hemp 120 pounds per acre in 9 to 12 weeks (Hoss University). Has anyone priced the cost of N2 fertilizer lately? LOL cost/benefit . Compare to field peas at 25 pounds of nitrogen per acre (Purdue University)

3) Will grow anywhere that has 9 to 12 weeks of soil temps at least 65 to 70 deg. Use has been steadily expanding in more northern locations (Hoss University)

4) Can produce 5000 pounds of dry matter acre in 9-12 weeks (Clark, 2007). I can only imagine the benefits of that.

5) suppresses nematode populations. This caught my attention as the only summer cover crop I've ran across that can do this. Of course, Elbon rye remains my mainstay for nematode suppression but is a winter cover crop.

That's the short version. Plenty more available if you just look. I urge folks to do their own research.

More interesting facts below:

Sunn Hemp: nitrogen-fixing green manure to improve soil quality, reduce soil erosion, conserve soil moisture, suppress weeds and nematodes, and recycle plant nutrients. It grows quickly and can produce more than 5,000 lb dry matter/acre and 120 lb nitrogen/acre in 9–12 weeks (Clark, 2007).

Sunn Hemp is one of the only warm-season cover crops that adds significant amounts of nitrogen to soils. Because it is a legume, this cover crop has the ability to fix nitrogen from the atmosphere and transfer it to garden soils, making it available for successive crops. This makes it a great option to use ahead of heavy-feeding crops like corn or onions. It also works great for restoring nutrient levels following heavy-feeding crops that consume lots of soil nutrients.

Sunn Hemp is a summer annual that performs well in sandy soils and other soil types that may be nutrient-poor as a result of intensive farming. When cut and incorporated into the soil as “green manure”, it provides a considerable amount of organic matter that will improve soil fertility and tilth. In addition to improving organic matter content in soils, it also suppresses nematode populations as the mowed biomass breaks down in the soil. It is a cover crop that’s very adapted and performs well in dry, hot, and windy environments.

Sunn Hemp should be planted when the soil temperature is at least 65-70 degrees Fahrenheit. It may be broadcast and covered. It is an extremely fast-growing and fast-maturing cover crop and typically reaches maturity in 8 to 12 weeks. Because it grows so fast, it works great for suppressing and outpacing weed growth during the warmer months when weed pressure is at its highest. As with all cover crops, it should be cut or mowed before going to seed as this will prevent any reseeding issues in the future.(Hoss University)

 

[Marck]

In warm temperate regions it shows promise in climates with enough summer heat and rainfall to allow for vigorous growth of biomass.

Yes, I agree Sunn Hemp is already widely used for the purposes listed, but its good to think critically about all effects rather than just the hype.

One additional caveat is almost too obvious to mention, but of course any large warm-season cover crop that can't be over-planted is only of use in fields that can be allowed to not produce in mid-Summer. Perhaps one should also weigh the cost-benefit of Sunn Hemp versus growing a nitrogen-fixing crop such as Beans (Phaseolus spp.) or Soy Beans (Glycine max).

 

[Meadowlark]

I have compared to soybeans and beans. Thank you very much for the lovely comments. Not even close.

The whole point of my intended use is as a summer soil building rotational crop. I'm not after produce on the soil I'm renovating, rather after soil renovation for the next garden crop that will most surely follow. I thought that was obvious.
..

 

[Marck]

I'm talking about Sunn Hemp in general. Your personal situation, and whatever comparison you made, and conclusions you've come to, before your "experiment", I might add, is just one example. Thanks for sharing.

 

[Meadowlark]

LOL! I'm not trying to solve the World's problems...just trying out what appears to be a significantly valuable resource for improving my little garden...and sharing whatever I learn while I'm at it. Thanks again for the "lovely" comments.

The experiment may or may not improve my "personal" situation, but that is exactly what I want to find out for myself. Either way I will learn from it and maybe some others will also if they have an open mind on the subject.

 

[Marck]

I do have an open mind on the subject.
There are already is a lot of research about Crotalaria juncea and there are a lot of things to consider when growing it. Discussing both pros and cons is the purpose of a forum thread. What is a positive in one setting may becomes a negative in another.

Yet another caveat to consider is what crop will be planted after the Sunn Hemp. The field will be rich in Nitrogen (N) but not all Fall-Winter crops will use that much Nitrogen and what isn't used will begin to immobilize or volatilize. On study showed that 16 weeks after being mowed on 37% of the N from a Sunn Hemp crop was still available for crops. If growing Sunn Hemp for N-rich green manure, it might be less wasteful to harvest some of it for compost or use in another field.

 

[Meadowlark]

Let’s review the bidding thus far:

• Claim: Sunn Hemp seed is more expensive than other cover crops:
• Facts: demonstrated false, factually incorrect.

• Claim: Sunn Hemp unlikely to seed in temperate climate
• Fact: Under proper soil conditions and adequate rainfall, Sunn Hemp can reach 8-12 feet in southern regions and 4-6 feet in the northern regions of the US in 9 to 12 weeks. (Whitetail Institute). Although sunn hemp is of tropical origin, it has been cultivated in temperate zones as far north as Washington state. UF(IFAS Extension)

• Claim: only of use in fields that can be allowed to not produce while Sunn Hemp is growing.
• Fact: soil renovation, soil building, and crop rotation is most effectively and efficiently accomplished where the activity does not involve harvest, i. e. removing material.

• Claim: Beans as a nitrogen fixing crop may be better:
• Fact: Among modern leguminous crops, beans are considered to be poor nitrogen fixers (Hardarson et al., 1993)

• Claim: 16 weeks after being mowed on 37% of the N from a Sunn Hemp crop was still available for crops.
• Question: In what world can you identify any plant that can match or exceed that much nitrogen addition after that long a period of time?
• Fact: I would be deliriously happy if I allowed a field previously planted in Sunn Hemp to sit idle for 16 weeks and it still had 44 pounds of nitrogen added per acre by Sun Hemp for less than $10.

• Claim: If growing Sunn Hemp for N-rich green manure, it might be less wasteful to harvest some of it for compost or use in another field.
• Fact: I can't imagine planting Sunn Hemp for Nitrogen fixing and nitrogen rich green manure among other things, and then not planting immediately something which would utilize that nitrogen. In that highly unlikely event, composting would be an option.

 

[Marck]

Your claim to be we refuting six claims, one of which was never even mentioned above. It would have been nice if you had numbered them, but it seems clear you are not interested in clear communication. Basically you either didn't understand me or are deliberately trying to mislead. Nice.

Unlike you, I will directly quote your statements rather than paraphrasing and making things up.

Also, I already said I was giving general information to all readers of the thread about Sunn Hemp (Crotalaria juncea).
Not just you. If what I wrote doesn't apply to you, or you are not interested inconsidering the point made, so be it.

Claim 1. (my numbering)

• Claim: Sunn Hemp seed is more expensive than other cover crops:
• Facts: demonstrated false, factually incorrect.

This is the best of your claims. The price of imported Sunn Hemp seed has come down, especially since many other cover crop legumes are not imported. Remember, all I said was "Imported seed, usually from India, is more expensive than other cover crop seed, but not prohibitively so". Actually, there are lower priced cover crop options, especially when you consider recommended coverage rates, but I agree the price of the seed is not a major determining factor.

Claim 2.

• Claim: Sunn Hemp unlikely to seed in temperate climate
• Fact: Under proper soil conditions and adequate rainfall, Sunn Hemp can reach 8-12 feet in southern regions and 4-6 feet in the northern regions of the US in 9 to 12 weeks. (Whitetail Institute). Although sunn hemp is of tropical origin, it has been cultivated in temperate zones as far north as Washington state. UF(IFAS Extension)

This is where I begin to think you are deliberately trying to mislead. I am writing about the plant reseeding in temperate climes. I was not discussing its ability to be grown as a summer crop. What I wrote was "Sunn Hemp is unlikely to seed in temperate climates. This will prevent it from becoming a weed but it also means seed must be repurchased each year". How did you miss this that?

Claim 3

• Claim: only of use in fields that can be allowed to not produce while Sunn Hemp is growing.
• Fact: soil renovation, soil building, and crop rotation is most effectively and efficiently accomplished where the activity does not involve harvest, i. e. removing material.

What the...? Don't come back and repeat the same thing I just wrote and act like you're refuting anything. That's right, when you grow a cover crop, the field is not producing, i.e. no harvest.
I didn't say there was no benefit to growing a non-producing cover crop, but both commercial farmers and sustenance farmers don't always have that option. Once again, remember, I'm was writing about issues for anyone to consider when deciding to grow Sunn Hemp. I was not only just speaking about your situation.

Claim 4

• Claim: Beans as a nitrogen fixing crop may be better:
• Fact: Among modern leguminous crops, beans are considered to be poor nitrogen fixers (Hardarson et al., 1993)

I should be angry about this. I never wrote anything about the nitrogen-fixing ability of beans. How did you get this claim?
What I wrote was "Perhaps one should also weigh the cost-benefit of Sunn Hemp versus growing a nitrogen-fixing crop such as Beans (Phaseolus spp.) or Soy Beans (Glycine max)". This is from the same paragraph as the previous claim.
Again some growers (commercial, sustenance, and otherwise) might prefer to get a crop during the summer growing season, even if less nitrogen is fixed. I fully get that you have an "experimental" field where that is not an issue. So what.
Like I said before (and will probably have to say again), I'm writing about general issues concerning Sunn Hemp. That it doesn't matter to you doesn't make it wrong.

Okay, I'm taking a little break, but later, I'll be happy to discuss the next two "claims".
Actually two parts of the same false claim.

 

[Marck]

Okay, I'm back for more of this fun, a man of my word.

The last (thankfully) two "claims" are really parts of the same, but I'll number them separately for clarity.

Claim 5

• Claim: 16 weeks after being mowed on 37% of the N from a Sunn Hemp crop was still available for crops.
• Question: In what world can you identify any plant that can match or exceed that much nitrogen addition after that long a period of time?
• Fact: I would be deliriously happy if I allowed a field previously planted in Sunn Hemp to sit idle for 16 weeks and it still had 44 pounds of nitrogen added per acre by Sun Hemp for less than $10.

Claim 6

• Claim: If growing Sunn Hemp for N-rich green manure, it might be less wasteful to harvest some of it for compost or use in another field.
• Fact: I can't imagine planting Sunn Hemp for Nitrogen fixing and nitrogen rich green manure among other things, and then not planting immediately something which would utilize that nitrogen. In that highly unlikely event, composting would be an option.

I mentioned, to all readers, that exceptionally high levels of available soil nitrogen cannot usually be maintained for very long. Therefore the timing of any fertilizing should be planned and timed with the subsequent crop in mind.
Meadowlark says he can't imagine not planting a crop that would use all the Nitrogen, well, I can imagine that and it happens all the time in horticulture and agriculture. It's not the end of the world if it happens, but it is inefficient and it can promote weed growth.
While some such weed growth will eventually become more bio-matter, it can also compete with a crop and reduce yield, a quite valid concern to both the professional farmer and home vegetable gardener.

I also suggested that since Sunn Hemp fixes an exceptionally large amount of Nitrogen, some of it might be more efficiently used off-site in a compost pile, or other field. That is an excellent suggestion, if I say so myself, however it is extra labor, and some may choose not to it. If Meadowlark doesn't want to it, that is completely fine.

Conclusion
To conclude, nothing I wrote in this thread was intended solely or even primarily for Meadowlark's benefit. Even my response to his overblown rebuttals of largely bogus claims is directed primarily at third-party readers.
My interest here is in critically discussing the use of Sunn Hemp. As far as I'm concerned that is completely on-topic for this thread.

As for Meadowlark's "experiments' what little interest I might have had in them is gone. I never expected them to be peer-reviewed research, and it is basically just reinventing the wheel, but I now I don't even trust that any experiments will be performed or reported with any attempt at impartiality. All along, he has acted like he already knows the answer a priori and gathering evidence was only a formality. Of course, there already are many research papers and data.
Sunn Hemp already has a long history as a crop in southeastern Texas and elsewhere. Whether it is the best choice in every given situation is something each grower will decide for his or her self.