Learned something about soil PH today

[Droptine1844]

Took a soil sample of field that I rotate corn and beans in last week, took my results to the co op expecting to need a bit of lime after my test said my PH 5.9. After showing the agronomist the results he said he would add any lime because my buffer PH is 7.74. Never had seen it heard this talked about. Apparently Iowa uses the buffer number because it is what will be available, my understanding. He even warned if I added 1 ton of lime per acre as the rest said I’d be too basic and need to offset it.

 

[Bassattackr]

He would or would not add lime?

Buffer pH is high compared to your tested pH, which tells me you have lower buffering capacity - IE: Adding lime will move the needle. Conversely, if your buffer pH is close to your tested pH (high buffering capacity), it would take a lot more lime to adjust your soil pH.

Combine a low buffering capacity with your lower CEC, and a lime application would have a quicker effect than you may think.

In more plain terms: Your soil pH tells you IF you need lime. Your buffer pH tells you how much lime is needed.

Like this:

 

[Droptine1844]

He would or would not add lime?

Buffer pH is high compared to your tested pH, which tells me you have lower buffering capacity - IE: Adding lime will move the needle. Conversely, if your buffer pH is close to your tested pH (high buffering capacity), it would take a lot more lime to adjust your soil pH.

Combine a low buffering capacity with your lower CEC, and a lime application would have a quicker effect than you may think.

In more plain terms: Your soil pH tells you IF you need lime. Your buffer pH tells you how much lime is needed.

Like this:

View attachment 131189

According to the agronomist he said no lime test again next year and see where I stand

 

[Thinkin Rut]

Just another set of numbers...My soil test said my PH was 5.7 with a buffer of 6.6. I told him I planned on planting alfalfa and he said add 2 ton ag lime and disc in then another soil test in the fall.

 

[Bassattackr]

According to the agronomist he said no lime test again next year and see where I stand

Something to ask him..

What would change in the soil chemistry or profile a year later that would test different? Unless you recently put ag lime on previously?

I’m curious myself. Maybe @Muddyrem knows?

 

[Muddyrem]

Something to ask him..

What would change in the soil chemistry or profile a year later that would test different? Unless you recently put ag lime on previously?

I’m curious myself. Maybe @Muddyrem

My guess is he’s dealing with a retail agronomist? I would agree there may not be a need for lime with a PH at 5.9 and buffer at 7.74. Lime is relatively inexpensive however still added cost that may not move the needle in profitability in a corn/bean rotation in 2026 growing season. Plus, majority of your liming crews have moved over to spring gas/getting stuff ready to plant so terrible timing trying to get any lime applied currently if that was the OP’s intentions.

I agree, with a buffer that high, adding even just 1ton/acre is going to help raise that PH, 5.9 is ok for grain production but most guys def would like to see that up around 6.3-6.5. Cheap insurance to plug one of the biggest limiting factors in majority of guys operation (out of wack Soil PH).