Soil Replenishment in drought and high heat and high humidity

[Meadowlark]

Like a lot of places, its 100 deg and 100% humidity every day here in East Texas with no rain in sight. Not much, other than okra will grow in these conditions which really started at the end of May here.

My approach is to use this time and these conditions to rebuild soils.

At the end of May I harvested well over 500 pounds of onions and new potatoes from these two rows.

After discing/tilling these two rows, I broadcast Sunn Hemp as an experimental cover crop. It supposedly thrives in high heat and high humidity.

Two weeks later the cover was well established and on its way to spectacular growth.

Two more weeks elapsed continuing the 100 and 100 conditions and the Sun Hemp provided a growth rate of about two inches per day with dense coverage. Photo June 18.

Now here we are today July 20 about 8 weeks after the original rows were harvested of onions and potatoes, tilled, and planted in Sun Hemp. Vegetation is well over 10 feet and very dense. 100% weed prevention achieved in the soil seeded w/Sun Hemp.

Time to shred it and add tons of fresh, green organic matter to the now replenished soils. With shredding complete, I will turn all this under and then take a soil sample to compare to the depleted harvested soil. Stay tuned for results. I'm particularly interested in Nitrogen addition amounts, if any.

Previously in a different set of rows, I had experienced over 200% Nitrogen addition from the use of alfalfa in a similar manner.... except the conditions were far more favorable.

Looking forward to seeing the results from soil tests...probably in a couple of more weeks or so. Follow this thread if you are interested in the results.

 

[MoreRootsMoreFruits]

Intrigued to see the results of this

 

[Mr_Yan]

@Meadowlark is that shredding just with a machette and pruning shears or did you use heavier equipment?

I don't till, how do you think that would work as a mulch rather than tilling in?

Complete aside - I listen to a podcast host based in the DallasFortWorth area (think he said around 30 min west of Fort Worth) who says the Asian type yard long pole beans continue to live and produce through the summer when "only okra" will live. Have you tried those or heard similar?

 

[Meadowlark]

Thank you for your response.

Actually, a shredding lawn mower works really well but in this case I used the tractor/4 ft pto mower which provided needed power to shred that stuff. It really is a lot of material. Very thick. It certainly could be done w/machete, but it would require a younger person that me, LOL, especially in this heat! I suspect it is common to use a machete in the tropics where this plant is widely used for nitrogen fixation.

I'm using some of it as a mulch in my Hügelkultur containers...looks like a great mulch. I'm thinking it will work just fine as a mulch. In fact, I'll probably gather up a pile of it to use later. There is ample material.

Yes, I have done the "asparagus" beans or so-called yard long beans several times. It is true that they will produce in hot weather, but they get kind of tough and pithy, so I gave up on them preferring instead to using my canned green beans from earlier this year.

 

[skinyea]

You are living the dream!!! one day I will be there

 

[YumYum]

Interesting. So it is a legume. Do you have to innoculate the seeds or something? I use crimson clover over the winter but I've never actually tested before and after or innoculated them. Actually the soil test from the CO-OP here doesn't test for nitrogen with the "full test" so I wouldn't know anyways. Maybe it has to be requested separately or something?

One thought comes to my mind is that if sunn hemp does not have a taproot then wouldn't it use up the other elements (P, K, calcium, mangesium, etc) in the surface of the soil only to put them back in when tilled under. Nitrogen and carbon is gained and possibly good microbes?

 

[Meadowlark]

Thanks for your interest, YumYum.

Yes, it is a legume. " 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. It has been reported to add over 100 lbs of nitrogen per acre."

The seed I buy is already inoculated. I can't imagine a soil test that does not measure nitrogen. That's pretty much the key for me

One of the unique things about Sunn Hemp is its ability to thrive in very hot and humid conditions...making it a perfect soil conditioner to use during that time of year here when almost nothing grows in the garden and even if it did the garden isn't very pleasant at 100 deg and 100% humidity. I've used field peas successfully in this role in the past as well as soybeans but neither can add near the nitrogen that Sunn Hemp is rumored to add. Alfalfa here does the job on nitrogen but suffers mightily under the high heat (100 deg) and high humidity (100%) conditions of summer. Hence, I prefer to use alfalfa for my fall/winter/spring covers. In fact, that bed of shredded Sunn Hemp will be followed up with alfalfa soon and it will remain there until next spring when the soil will be ready for production again.

Over the years, I've improved my soil to have abundant P, K, calcium, etc. and only needs nitrogen and organic matter. Sunn Hemp is perfect for that, seemingly. It also serves as an excellent rotation facilitator.

The soil test will tell me a lot. So far, I'm very impressed with Sunn Hemp as a summer soil conditioner. I have not seen anything that can add organic matter in the volumes of Sunn Hemp in a short time.

You could grow it in 6b providing you can get about 10 consecutive weeks of warm (hot) weather. Nighttime temps need to be above about 60 deg. It is intolerant of cooler temps.

 

[Meadowlark]

The results are in from the before and after soil tests.

Reminder, the soil from recently harvested rows of onions and potatoes (see first post in this thread) were planted in Sunn Hemp for 8 weeks and soil tests were compared in the "before and after".

The 8-week Sunn Hemp growth/shred increased Nitrogen in the depleted onion-potato rows by 285%. The increase in Nitrogen was from 11.7 ppm in the onion/potato rows to 34.3 ppm after growing/shredding Sunn Hemp for 8 weeks (optimal is considered anything above 32 ppm by my lab).

All micro/macro nutrients showed improvement especially Iron content.

This is the first soil test result I have ever seen in which I have received this recommendation from a lab:

"No N-P-K Fertilizer Required for the next 4-6 weeks!"

 

[Mr_Yan]

Nice work @Meadowlark

 

[Meadowlark]

Thank you, Mr. Yan.

I'm trying to compute how much synthetic nitrogen (in pounds or whatever) would be required to raise an 800 sq ft garden area from 11.7 ppm to 34.3 ppm of N.

As I am a retired "rocket scientist", please don't tell me it isn't rocket science, lol .

Been there and done that.

Soil science is far less exacting, but I'm just looking for approximations.

 

[Mr_Yan]

I'm an electronics engineer by training and automation controls engineer by profession and I don't mess with the soil chemistry calcs. My go-to crutch is "add more organic matter" and assume it will be fine. I don't care how you get it there but it will remedy a whole lot. That's how I stumbled on the hugelkulture / wood core beds.

I'm looking for a northern analog for the sunn hemp you used. But with how I run my garden I think it will be stick with fall leafs as mulch and daikon radish. Though red clover does look promising.

 

[Meadowlark]

Can you get 8 consecutive weeks of temps well above about 60 deg. including nighttime temps?

If so, Sunn Hemp may work for you. I deliberately chose 8 weeks for my study hoping that would provide useful info to gardeners north of me. Of course, I get well over 20 weeks above that threshold making Sunn Hemp ideal for summer heat/humidity soil replenishment and cover cropping.

By the way, I've been doing this "hands-on" nitrogen fixing experimentation for over three decades now in garden soil....and I can categorically say I have never, ever seen anything that even approximates what Sunn Hemp does to soil in short times (8 weeks) ...alfalfa is the only thing I've seen even close and it's not really close especially considering the time frame for Sunn Hemep of 8 weeks and the time frame for alfalfa measured in several months, even years. I'm definitely going to expand my use of Sunn Hemp to larger garden spaces and longer periods of time.

I can add that red clover you mentioned is good, but not nearly as good as alfalfa and not even close to Sunn Hemp in my experiments to date. ... but as they say results may vary.

 

[YumYum]

As I am a retired "rocket scientist", please don't tell me it isn't rocket science.

Well I'm sure you would appreciate how to figure it up as to just telling you the answer then.

11.7 ppm N * 2 = 23.4 lb/acre of N.
34.3 pmm N * 2 = 68.6 lb/acre of N.

68.6 - 23.4 = 45.2 lb/acre of N increase. So you added the equivalent of 45.2 lbs of N per acre.

But you want to know how much per 800 ft2.
1 acre = 43560.04 ft2 so:
800 / 43560.04 = 0.0183654560464132.

0.0183654560464132 * 45.2 = 0.8301186132978766
so you added 0.83 lbs of N in 800 ft2.

 

[YumYum]

This is the first soil test result I have ever seen in which I have received this recommendation from a lab:

"No N-P-K Fertilizer Required for the next 4-6 weeks!"

To further extend your thinking, to the best of my memory from the vegetable crop handbook (link in my sig), most crops recommend that you till in about 50 lbs/acre of N before planting, then at some point in the future add more N. Since you added 45 lb/acre of N , that basically matches what they said.

 

[Meadowlark]

Well I'm sure you would appreciate how to figure it up as to just telling you the answer then.

11.7 ppm N * 2 = 23.4 lb/acre of N.
34.3 pmm N * 2 = 68.6 lb/acre of N.

68.6 - 23.4 = 45.2 lb/acre of N increase. So you added the equivalent of 45.2 lbs of N per acre.

But you want to know how much per 800 ft2.
1 acre = 43560.04 ft2 so:
800 / 43560.04 = 0.0183654560464132.

0.0183654560464132 * 45.2 = 0.8301186132978766
so you added 0.83 lbs of N in 800 ft2.

Yes, that is the way I figured it also using that x2 multiplier for lbs/acre. Thanks for the confirmation.

Some have claimed 120 pounds per acre added with Sunn Hemp. I'm guessing that 45 lbs/acre is probably due to only 8 weeks and complete drought and possibly even every day 100 deg or higher. I'll take 45 pounds per as spectacular.