This last two weeks has been exceptionally educational for me.

One point that I'm still trying wrap my brain around is some variations in measuring pH.

I had a soil test done last August. The "soil pH" was 6.0. The "pH buffer index" was 6.8. At first I was told that I would need to add a huge amount of lime to get to a pH of 6.5 for my pasture. Then I was told that would have to add only about a half ton of lime per acre because of the "pH buffer index" being 6.8. Then I was told that since I took the sample in August (when pH is typically about .4 lower than in April) and because of the "pH buffer index", I was probably right on right now and shouldn't add any lime.

Naturally I like the last position best!

Can anyone tell me what this "pH buffer index" thing is? Who should I beleive? What should I do?

august vs. April

-- Paul Wheaton (paul@javaranch.com), April 03, 2002

Answers

According to the recommendations for Minnesota soils, if your soil pH is 6.0 and your buffer index is 6.8, an application of 3 tons of aglime are required to raise the soil pH to 6.5.

Buffer Index is a special test which determines “total” soil acidity and more accurately predicts liming needs. The standard soil pH test measures only the soil’s “soluble acidity.” It does not measure the “reserve acidity” which is the acidity attached to soil organic matter and clays.

Two soils with exactly the same soil pH may vary widely in the amount of aglime need to raise its pH depending on the amount of organic matter and clay in the soil. The soil with the higher organic matter and clay content would require more lime due to its higher reserve acidity. Again, the buffer index measures both soluble and reserve acidity, whereas, the standard soil pH test measures only soluble acidity.

Soil pH can be a bit lower at the end of the summer due to leaching of basic cations from the soil during precipitation events (eg, calcium, sodium, potash, magnesium). A buffer index of 6.8 is right at the top of the table where aglime addition is recommended. If your buffer index was 6.9, a liming recommendation would not have been made.

--Happy trails, Cabin fever

P.S. I am a licensed soil scientist


-- Cabin Fever (cabinfever_MN@yahoo.com), April 03, 2002.

CB ?? how do you know how much to add,, whe we dont know the square footage of the pasture yet?? Paul,, unless your dealing with some very sensitive plants, that require an exact ph,, your real close to ritgh where you want to be. the ph buffer index, is an estimate of what your ph would be during the peak growing seasons,, soil tests take that into account the time of the year of the test

-- Stan (sopal@net-pert.com), April 03, 2002.

I see want you mean, I'm so use to dealing with people who farm acreage. The recommendation I gave was supposed to be 3 tons per acre. SHeesh! Stanley, my man, I stand by my definition of index buffer. Don't know who told you that it was an estimate of what your soil pH is supposed to be later in the growing season. (Sorry if I chuckle a bit) Whoever told you that should have his or her license revolked! The only purpose of running the index buffer test is to determine liming requirements...end of story. --Happy trails, Cabin Fever

-- Cabin Fever (cabinfever_MN@yahoo.com), April 03, 2002.

A very good explination, cf. I would have have just said 3 ton also, farmer shorthand I guess! :) Where I live the soils tend to be the other direction, don't think anyone fools with lime here. Not sure what the ph is, but some areas sure make my skin itch! :)

--->Paul

-- paul (ramblerplm@hotmail.com), April 03, 2002.

here in Mich, ,they dont give you a ph index on your soil test, they do give you a ph rating, of what it "should" be duuring the peak season,, that where my confusion was.

-- Stan (sopal@net-pert.com), April 04, 2002.

Stan, soil laboratories will only run the buffer index test if your soil pH is 6.0 or below. In other words, the lab does the standard soil pH test first. If the result is 6.1 or above, the buffer index is not run, and consequently a lime recommendation is not made. If the standard soil ph is 6.0 or below, the buffer index test is run. The result of the buffer index is then used to make a liming recommendation.

-- Cabin Fever (cabinfever_MN@yahoo.com), April 04, 2002.