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Raising boron levels in soil using borax  RSS feed

 
James Freyr
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Location: Middle Tennessee
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Here's a calculation I came up with this morning so I could raise the boron levels in my raised beds 1ppm per square foot using regular borax. 10 pounds of borax contain approximately 10% boron by weight, or 1lb. 1lb of any element spread over 1 acre = 1ppm in a furrow slice.

So 1 acre = 43560 sq ft.
My 19 raised beds total 768 sq ft.
768 = 0.017% of 43560

10lbs = 4530 grams (approximately. close enough for what I'm doing)
1lb = 453 grams

453 grams of boron will cover an acre at 1ppm, so I need 0.017% of 453 grams, which is 7.7 grams of boron for my 768 sq ft of raised beds, or 77 grams of borax. 77 grams of granular borax spread over 768 sq ft = approx. 0.1 gram per square foot, close enough for what I'm doing.

0.1 gram of borax will add approximately 1ppm of boron to 1sq ft of soil 6 inches deep.
one my my 4x8 raised beds has 32 sq ft and needs approx. 3.2 grams of borax per bed. 3.5 grams, for all intensive purposes, is 1/8 oz.

I have digital scales with accurate readability to the tenth of a gram, so I was able to easily weigh out 3.2 grams of borax. 3.2 grams of borax hardly fills a tablespoon, so broadcasting the granules by hand was out of the question. I added the borax to a full watering can and watered it in with even distribution to the best of my ability. I discovered borax dissolves in cold water about the same speed as a snail crossing a desert, so I pitched it and started over with a couple cups of piping hot water, and with a little stirring it quickly dissolved and I added that to my watering can and topped it off with water.

I hope this will help anyone who wants to boost boron levels in their small garden   If anyone sees an error in my math, please let me know.
 
r ranson
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That math is making my head spin.  But I bet it's useful.  Thanks for doing the calculations.



Some thoughts about adding boron to the soil.  I know my soil is low in boron because of where I am for a few reasons, mostly because that's the soil makeup in my area.  I add boron to the soil in the animal pastures in the fall about once every 3 or 5 years (as it needs it).  This changes the dominant plants in the fodder and I believe it has a positive effect on the mariner's ability to feed plants. 

I use 1 kilo of borax per 1/4 to 1/2 acre. 

I remember somewhere that one can have too much boron in the soil, so maybe it's good to know a bit about what your soil contains before giving it any additives - I'm frugal and hate buying stuff that I don't really need.  What are your thoughts on this?
 
Larisa Walk
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Location: South of Winona, Minnesota
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When we do soil consults we first get a complete soil test including micro-nutrients, then bring the boron level up to the point where it's about 1/1000th the level of available calcium in the test.  An acre of soil roughly 6 inches deep is 2 million dry pounds of soil so figuring out your bed's soil volume and dividing by 21780 (43560 cubic feet divided by 2 for supplementing the top 6 inches of soil) is pretty straightforward. You need about 1 pound of available boron to match 1000 pounds of available calcium, and anywhere from 7.7 to 9 pounds of borax to yield a pound of boron depending on whether your source is 13% or 11% boron. So if a soil test tells you that, for instance, you have 1.6 pounds of available boron and 3200 pounds of available calcium per acre (or 0.8 ppm boron and 1600 ppm calcium (ppm X 2 = pounds/acre)) your target would be an additional 1.6 pounds per acre (or per 2 million dry pounds of soil), which is anywhere from 12.3 to 14.5 pounds of borax . Boron isn't terribly soluble in cold water but it is still quite soluble over the length of a growing season and it leaches out of a soil pretty easily, so adding it once every 5 years is a boom or bust strategy for your crops if it's needed. Better to test yearly, at the same time every year, and supplement boron accordingly. Once you determine your typical boron loss per year in cropping and due to rainfall, a few years of testing will tell you what a yearly application should be without further testing. It doesn't take much boron to make a healthy crop but it does require a bit and definitely not too much.
 
James Freyr
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Having inadequate levels of boron can really hold things back in plant and crop growth. It is commonly recommended that soils have 2ppm of boron. It is also generally agreed that amounts over 4ppm is when symptoms of boron toxicity arise. Plants can be very sensitive to excessive boron and the last thing anyone wants is too much. Like Larisa mentioned, getting a soil test from a lab is really the best way to know what amounts are in the soil and how much to add. If boron has never been added to a soil, it's generally safe to add 1ppm. Soils in America used to contain adequate amounts, but no so much anymore. It's been written that the fertile plains from texas north into canada used to have naturally occurring levels as high as 3-4ppm, but a 100+ years of poor farming practices and lousy soil management depleted those amounts long ago.

I think your kilo of borax to 1/4 acre is safe and over a 1/2 acre certainly is, especially spread out over years. Boron is an anion, and humus is what holds onto it, whereas calcium for example is a cation and clay soil particles is what holds onto them. Humus is organic matter, but not all organic matter is humus. Just one of the many benefits of sufficient organic matter in soil is the formation of humus, which will in turn hold onto more anions and have them available for plants and microbes. And on a side note, excessive potassium ties up boron.

I recently did a soil test on some land my wife and I are buying, and the boron levels came back ranging from 0.2-0.3ppm, so I definitely have some work to do starting this fall, and boron isn't the only mineral deficiency I'll be addressing.
 
r ranson
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I suspect crops need more than pasture.  With pasture, good mineral balance is important too.  But with pasture, the animals are returning the 'harvest' to the soil immediately, whereas some of the crop harvest is usually taken off site.  I imagine this has some relation to how often we add amendments to the land.

 
Kerry Rodgers
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r ranson wrote:I add boron to the soil in the animal pastures in the fall about once every 3 or 5 years (as it needs it).  This changes the dominant plants in the fodder and I believe it has a positive effect on the mariner's ability to feed plants.

Your comment made me wonder whether there are any *specific* indicator plants for too little or too much boron?  What are your dominant plants changing from/to when you add, R?
 
r ranson
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Kerry Rodgers wrote:
r ranson wrote:I add boron to the soil in the animal pastures in the fall about once every 3 or 5 years (as it needs it).  This changes the dominant plants in the fodder and I believe it has a positive effect on the mariner's ability to feed plants.

Your comment made me wonder whether there are any *specific* indicator plants for too little or too much boron?  What are your dominant plants changing from/to when you add, R?


Just from personal experience, I noticed this property has a really difficult time growing clover.  After we applied borax for the first time, the clover started growing just fine.  I don't know if there's an actual causal relationship there, but it's a correlation I've seen on the farm. 
 
James Freyr
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While laying in bed last night I realized my decimal point was in the wrong spot and 768 = 1.7% of 43560, not 0.017%.

R ranson, yes I do believe crop needs are different than pasture needs, however I think the 2ppm target for boron still remains the same. I've read in books and also been told by my neighbor to raises cows on pasture that ruminants effectively capture about 30% of the minerals in the grasses and other plants they consume from pasture and 70% passes thru them and gets returned to the soil surface. And like you mentioned about crop harvest taken off site, like cutting hay and selling it to neighbors for example that is 100% mineral removal. Yes you are right about how both of those do indeed have a relation as to how often mineral amendments need to be done.
 
Bryant RedHawk
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Other than the one error you found James, I have to ask the question. Is 6" depth really all you intend to treat with the boron?
Don't forget that roots of vegetables generally reach down to a depth of 18 to 24 inches and some go much deeper than that.
I think that you might need to consider the root depth when calculating how much borax to use to treat for low boron.

Redhawk
 
James Freyr
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Hey Redhawk, I did the calculation for 6 inch depth to have a base value to work with, but my raised beds are 12 inches deep, so I can double the amount to treat the raised beds. I haven't gotten as far as applying more to treat the native soil beneath. A question for you, I have some concern with applying too much at once, right now the boron I did apply is still mostly near the surface and I haven't had enough rain to "wash" what I've applied deeper into the beds. That's at least how I think it works, maybe I'm wrong?
 
Bryant RedHawk
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Yes sir, that is how it works, it will leach down and if you can test the surface, when the level drops just reapply because what was in the top six inches is now in the next 6 inches.
Borax is great because you can see where you have applied it and if you were to do a spring application then a fall application, in two years you would have good levels of boron down to 24 inches, which would be outstanding for your plants.

Along with the boron you need to know the magnesium level and the zinc level, the three interact and a defect in one can lead to less available for uptake of the others.
I like to shoot for a 2ppm of each, as long as you are close it will workout nicely.

Interestingly enough one of the things most soils have a defect in is silicon so a little DE sprinkle does good things too.

Redhawk
 
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