Alfalfa Meal Heating Up Soil

mprevost(7)September 26, 2006

Here's a question for all you organic experts....

I use alfalfa meal (along with dehydrated chicken manure) as fertilizer in my garden. The alfalfa meal, when added to soil, heats up for a while (haven't measured how much but it gets warm like a compost pile if you use enough). Of course, this shows that the soil microbes are going crazy, but I wonder if this thermophillic activity may have other effects. I already know from experience that you can roast plants by adding alfalfa meal to the planting hole. But when worked into soil, could it also

* kill off other beneficial microbes (bad thing)?

* kill pest larvae or grubs in the soil (good thing)?

* kill earthworms (bad thing)?

What effects might the high temperatures have on the soil?

[BTW, blood meal does not seem to heat up like this. Haven't figured out why except that alfalfa has both nitrogen and carbon at the same time.]


--- Mike R. Prevost

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oldmainer(z5 Maine)

Hi Mike...ya gotta be puttin' us on just a mite...:-)anyway I would keep a water hose handy just in case ya set yer yard on fire...:-) Have you been in the sauce by any chance?...:-) Franklin

    Bookmark   September 26, 2006 at 3:27PM
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chesnok(z6 AR)

i've read an article about this in a booklet. the idea was that the heat allowed planting to begin 6 weeks earlier. it said it is wise to plant seedlings in peat pots to protect young roots.
it says that the ideal soil temp range for cool-weather veges is 75-80, and 90-100 for warm-weather ones.

    Bookmark   September 27, 2006 at 11:37AM
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chesnok wrote: "i've read an article about this in a booklet. the idea was that the heat allowed planting to begin 6 weeks earlier."

Yes. That's a cool idea. A good mulch can help hold the heat in also. It can stay noticable warmer under heavy mulch for a couple of weeks. You also might could germinate seeds in the ground in cooler temps if you heated the soil somehow. Sort of like a temporary hotbed.

Also, it seems that "alfalfa heat" could be an alternative to soil solarization if the temps could get high enough to kill pathogens (~120 def F?) and you'd be adding organic matter, NPK, and trace nutrients at the same time. This might only be a good idea when preparing a new bed however, because it seems like it could harm earthworms. And it might only be useful on a small scale given the cost of alfalfa meal.

Just thinking...

--- Mike R. Prevost

    Bookmark   September 27, 2006 at 12:41PM
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mprevost, I use dehydrated alfalfa pellets (50 pounds/ $10) and my 4 year old grandson has the job of adding a cupfull per planting hole. You know about QC and 4 year olds -- some holes are over-filled and some famished.
Regardless, all of the 90 (broccoli, cauliflower, brussels sprouts, cabbage) plants we put in two weeks ago look very perky. These are all cool season plants and if they were getting bottom heat I would expect wilting.
I would be suspicious that the chicken manure was your cause of heat.

    Bookmark   October 1, 2006 at 3:33PM
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I've never used chicken manure, but what steve is saying kinda makes sense. Generally, alfalfa meal is really good.

I recently came across this pretty cool sight loaded with information on gardening:

Make sure to check out their organic gardening section.

Here is a link that might be useful:

    Bookmark   October 2, 2006 at 1:00AM
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Steve, I haven't had trouble with alfalfa pellets heating up, just meal. I'm not sure why. I have heard that alfalfa meal is just ground up alfalfa pellets. Perhaps, since the meal is ground up, it has much more surface area for the microbes to attach to so it decomposes faster. I dunno.

I put down some alfalfa meal and chicken manure on the surface of the soil before applying a thick mulch layer. It heated up quite a bit. After things cooled down some, I planted my broccolli (about 2 weeks ago) and they appear to be doing very well. The soil was still a little warm but the plants seemed to like it. I have read that warmth can stimulate the roots to grow. Of course, too much heat will cook them as I have found out through experience.

Perhaps it's the checken manure AND the alfalfa, but alfalfa meal itself is often reccommended as an ingredient to get your compost pile cooking quickly. I've seen it do just that. Added some to my pile this weekend.

--- Mike R. Prevost

    Bookmark   October 2, 2006 at 10:49AM
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peggy_g(Melbourne,Fl Z9)

Think the problem is with the chicken manure, hot nitrogen, not the alfalfa meal...didn't respond earlier as I thought this was a know that if you over use anything, even wonderful alfalfa, with all its beneficial growth properties, you "might" screw the plant enviroment up. Hey, I've done just that with other items; so I won't cast blame...Just don't want good ole alfalfa meal to take the rap for hot chichen manuer...or what ever happened...even organics can be harmful...think arsenic.

    Bookmark   October 13, 2006 at 11:09PM
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junkmanme(z5 N. NM, USA)

Some years ago, I tilled in a pickup load of chicken manure into my garden area in the Fall. Garden was approx. 16' x 30'. That Winter the snow immediately melted in the garden area, although we often had 6 to 10 inches of snow in the rest of the yard. You could lay your hand on the soil in the garden in January and feel the heat!

I also suspect that the heat is from the chicken manure. It is much "hotter" than other manures.

just my 2 pesos worth,
Best Regards,

    Bookmark   October 16, 2006 at 1:41PM
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Junkmanme wrote: You could lay your hand on the soil in the garden in January and feel the heat!

Wow. That's interesting. I used the bagged, dehydrated chicken manure with the alfalfa meal. Perhaps that is the culprit and not the alfalfa meal.

Do you think the heat hurt your soil in any way? Did you notice a reduction in earthworms or an increase in disease the following year?

It's amazing that the heat lasted so long. Thanks for the story.

    Bookmark   October 16, 2006 at 1:52PM
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dchall_san_antonio(8 San Antonio)

I hope someone will read this and actually take some temperatures with a digital, stem-type thermometer. Here's how:

1. First test your thermometer by stirring it in a coffee mug full of ice cubes and just enough water to cover the ice cubes. Stir it long enough to get a reading of 32 degrees F plus or minus 1/2 degree. If it takes longer than 5 minutes you may as well get a new thermometer. Try it again with distilled water ice and distilled water before you throw the thermometer away.

2. Test the soil temp at a depth of one inch below the soil. Mark an inch mark on the stem of the thermometer and plunge it into the soil in several places.

Then you can report your freezing water temp and soil temps back here. Test somewhere where you did not use the alfalfa meal, too.

    Bookmark   October 21, 2006 at 9:35PM
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joepyeweed(5b IL)

Here is what I think.... I think if you applied enough of any green material that you could get some heat... however I doubt it would be enough to kill earthworms... more likely the worms would start to feel the temperature increase and they would move (go deeper or head east) until such times at the conditions were more to their liking.

as far as microbes go, the heat is microrobes and the heat indicates an increase in microbial activity... and we aren't truly selective in good and bad microbes - ...

    Bookmark   October 22, 2006 at 11:00AM
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oldmainer(z5 Maine)

Hi folks...this hot soil myth could rank right up there with the back yard compost piles catching on fire...and the dew ponds...:-) Ya gotta love this site at times...:-) If it isn't folklore...BS...myth''s Voodoo/Witchcraft...:-) Franklin

    Bookmark   October 25, 2006 at 6:43PM
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People-I agree with those of you that have specified the majority of the heat is likely caused by the chicken manure decomposing. The Alfalfa has an excellent Nitrogen/Carbon ratio & helps to further stimualte this process. I think the earthworms are smart enough to know where to go. They secrete substances & also digest bacteria, much of it anaerobic; thus removing many pathogens. One of the the vendors for Alfalfa Meal promotes an increase in earthworm activity. I don't know yet if this has been thoroughly studied & confirmed, but it might have some minimal merit since we know what attracts earthworms.

    Bookmark   January 13, 2008 at 2:57AM
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Hi topgunja,

Thanks for the response. My gardening experience is limited to only a few years. Throughout that time I've used only bagged composted chicken manure, alfalfa meal, soybean meal, and various mulches (leaves, grass clippings) to fertilize my soil.

I have not seen this heating up occur without significant concentrations of alfalfa meal. Without a lot of alfalfa meal, it does not heat up. But if you put a lot of alfalfa meal under mulch or in a hole, it gets REAL hot in a couple of days. Like as hot as a very hot compost pile. 150 deg F or so.

Another strange thing happens. The soil becomes gray over time -- almost like fluffy gray snow. It smells like compost -- very earthy. Not foul. Well... the hot soil smells very foul when it's hot (like decomposing alfalfa, whew!), but it is not foul when I dig up the plants and fine the gray snow soil. I think that the gray is from some kind of cellulose eater. From my research, I think it is the hyphae of actinomycetes.

The plants grow fine, but it's kind of a pain because this heat can go one for a couple of weeks before it settles down (especially if there is also soybean meal). I'm still not sure if it's a good thing, but I tend to think that the heat may be good to kill off some soil diseases and soil pests. It also warms the soil in the spring (like a hot bed). With practice it may be useful. One thing is for sure -- it increases the microbial life in the soil.

Alfalfa meal and soybean meal have become so expensive here that I use very little of it compared to what I used to. I mostly rely on bagged composted chicken manure and lots of leaf mulch.

--- Mike R. Prevost
Mad Scientist Gardeneer

    Bookmark   January 13, 2008 at 8:20AM
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Franklin wrote:
Hi folks...this hot soil myth could rank right up there with the back yard compost piles catching on fire...and the dew ponds...:-) Ya gotta love this site at times...:-) If it isn't folklore...BS...myth''s Voodoo/Witchcraft...:-) Franklin

Hi Franklin!
May be the dew ponds is a myth... it is more like it is not well researched. But what was really well researched is soil and ground waters. The results are published in a book "Soil waters, ground waters" A.F.Lebedev.
These book is not a theory or fairy tale, but is a summary of a lots of scientific measurements. A conclision of the book is: ground waters (in the wells) are formed not by rains, but by the vapour codensed in the soil from atmosphere (underground dew).

A.F.Lebedev is a founder of Soil phisics (not Voodoo) in USSR.

    Bookmark   January 17, 2008 at 9:37AM
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Help! I'm relatively new to gardening. Last year after a bad garden try, I had it plowed. I applied light applications of lime in Oct. and again in Jan. with light applications of bone meal and blood meal. Now the nurseryman says to use alfalfa meal before rototilling in March. I plan on using mulch over landscape cloth to control weeds (old bone have a hard time with weeding). Should I use the alfalfa meal? When? How much? My garden is 15x32.

Here is a link that might be useful: Garden Web

    Bookmark   February 1, 2008 at 9:17AM
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You don't have to worry about alfalfa heating up your soil unless you use lots of it concentrated in one place. If you use a whole 50lb bag worked into a 4x14 area and covered with mulch, it WILL heat up.

I don't know what the optimal application rate is for you but I would think you could put as many as 3 or 4 50 lb bags on you 15x32' area and work it into the soil without it heating up.

But again, I don't see any detrimental effects to it heating up. It definitely gets the soil microbes going good. I think it heats up because it's a very good combination of carbon and nitrogen that is ground into small bits which give it much more surface area for the microbes to chew on. I think all that contributes to its rapid composting.

Soybean meal (about 6% N) is another thing to consider along with bagged composted chicken manure (3-4% N + lots of other good stuff). The bagged chicken manure may very well be much cheaper. I've not been using much alfalfa or SBM lately because of the cost. $10-12 per 50lb bag in my area vs $4-5 per 40lb bag for chicken manure.

Hope that helps.

--- Mike R. Prevost

    Bookmark   February 1, 2008 at 11:16AM
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marshallz10(z9-10 CA)

Sounds like you are sheet composting, a variation of trench composting. From my experience as a long-time professional horticulturist/gardener/landscaper/organic farmer, you folks are using way too much high-N organic material. Most of the N will go off as gas or wash out as nitrate -- plants don't have that great of need for N. Moreover, if the organic material is concentrated at depth, lack of oxygen will cause the material to go sour (anaerobic fermentation) and give off toxic gases and liquids.

I grow a lot of cool/cold-season crops. Optimum germination temperatures are less than 75F, most less than 70F. You can't get lettuce to germinate at higher soil temperatures.

    Bookmark   February 1, 2008 at 12:07PM
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I have used bottled fertz with alfalfa meal and it did not heat up the soil more than usual. I think if it was used in a compost tea for feeding time that there would be no excess heat. The heat would come from the direct exposure of the meal in rapid decomposition or chemical reaction to the soil. I don't know about the chicken manure but I think they eat alfalfa and so do cows so it might be in their fertilizer too. That could cause a reaction too.

    Bookmark   September 15, 2008 at 5:47AM
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