Differing pH results

[Tompkins]

Due to forgetting it had already been done, I have a field that been tested twice in 18 months. Once in March 2017 and again a few weeks ago.
Unfortunately the samples have not been taken from the same points but the pH is wildly different. The March 17 result is 7.1 whilst the result from a few weeks ago was 6.2! P, K, and Mg are all about where I would expect, just the pH has dropped very quickly.
Could this be due to the conditions at the time of testing? Obviously the land was very dry when tested recently compared to a saturated soil coming out of winter in 2017.
I must admit such a low pH reading has taken me by surprise and I'm more inclined to go with the previous result.

 

[cricketandcrops]

I would say it’s due to how dry soils are, best thing to do is get out in field with pH kit and double check

 

[MNBVCXZ]

If you’ve sampled an acid patch that wasn’t sampled the year before, the result you have would be expected.

 

[Wheatland]

I’m finding the ph results back this autumn are unexpectedly low generally. I’m having some retested but in the meantime applying a reduced lime application and will top up at a later date

 

[An Gof]

Due to forgetting it had already been done, I have a field that been tested twice in 18 months. Once in March 2017 and again a few weeks ago.
Unfortunately the samples have not been taken from the same points but the pH is wildly different. The March 17 result is 7.1 whilst the result from a few weeks ago was 6.2! P, K, and Mg are all about where I would expect, just the pH has dropped very quickly.
Could this be due to the conditions at the time of testing? Obviously the land was very dry when tested recently compared to a saturated soil coming out of winter in 2017.
I must admit such a low pH reading has taken me by surprise and I'm more inclined to go with the previous result.

Rain, Rain, Rain it just washes lime away

 

[Brisel]

If you’ve sampled an acid patch that wasn’t sampled the year before, the result you have would be expected.

This.

@Tompkins - what's the soil type? Try and sample different soil zones - you'll get very different readings. Whole samples sent away to a lab will be ground up, including any stones which can throw a high pH reading despite being in acid soils.

 

[Bogweevil]

Due to forgetting it had already been done, I have a field that been tested twice in 18 months. Once in March 2017 and again a few weeks ago.
Unfortunately the samples have not been taken from the same points but the pH is wildly different. The March 17 result is 7.1 whilst the result from a few weeks ago was 6.2! P, K, and Mg are all about where I would expect, just the pH has dropped very quickly.
Could this be due to the conditions at the time of testing? Obviously the land was very dry when tested recently compared to a saturated soil coming out of winter in 2017.
I must admit such a low pH reading has taken me by surprise and I'm more inclined to go with the previous result.

This is normal - pH testing is very approximate. For it to be otherwise would require an impractical number of samples.

 

[chipchap]

My agronomist does all comprehensive soil testing for us, however I get an Old School agricultural merchant to do pH testing as well. The two sets of results broadly tally, but the old chap does several discrete tests across the field and highlights any hot spots. Better job imho.

 

[Tompkins]

This.

@Tompkins - what's the soil type? Try and sample different soil zones - you'll get very different readings. Whole samples sent away to a lab will be ground up, including any stones which can throw a high pH reading despite being in acid soils.

Light sandy loam, free draining, underlying sandstone. I'm going to perhaps apply half rate now and re-test again in more normal conditions?

 

[solo]

If the harvested crop has not used all the nitrogen then you may have acidifying effect from residual N in the autumn which is not present in the spring after a wet winter. Results here on sandy loam have always varied similar to yours between autumn and spring testing.

 

[Two Tone]

pH isn't actually testing acidity. What it is actually testing are Hydrogen ions. As a rule of thumb, the greater the concentration of hydrogen, the more acidic the soil is, but not always so. Different soils will alter a pH test result, without there actually being any difference in acidity. Time of year and soil condition will also vary results using a pH test.

Then you get the anomaly of being recommended to use a form a Calcium to rectify an alleged acidity problem on soils that are already rich in Calcium. You might as well set fire to £50 notes as fast as you can and save yourself the time and worry of using these types of lime in such cases on such soils. Especially so if the at soil also contains Iron and even worse if you are also using Tripple Super Phosphate on them.

 

[Iben]

pH isn't actually testing acidity. What it is actually testing are Hydrogen ions. As a rule of thumb, the greater the concentration of hydrogen, the more acidic the soil is, but not always so. Different soils will alter a pH test result, without there actually being any difference in acidity. Time of year and soil condition will also vary results using a pH test.

Then you get the anomaly of being recommended to use a form a Calcium to rectify an alleged acidity problem on soils that are already rich in Calcium. You might as well set fire to £50 notes as fast as you can and save yourself the time and worry of using these types of lime in such cases on such soils. Especially so if the at soil also contains Iron and even worse if you are also using Tripple Super Phosphate on them.

What would you use then?

 

[Two Tone]

Farming in the Cotswolds is a classic example of where we have high Calcium, high Iron soils that still show as being acidic using a pH test.

If we use triple super phosphate it locks up very quickly with the calcium to make a strong cation bond and form calcium phosphate, which is what our teeth are made of and is very insoluble.

We can break that bond by using Sulphur to form calcium sulphate, gypsum. This then releases the locked up phosphate.

If we have been applying TSP and lime to our high iron and calcium soils, you probably don’t need to apply any more phosphate for decades. But your standard tests will still show that you do. The only way to prove that you don’t is to do a full Albrecht test which will show not only what is available, but what is locked up and can be made available again.

If you do still need to apply phosphate, use MOP or DAP, as these forms won’t lock up.

In our own situation, we haven’t applied any phosphate or lime for 12 years now. We use Sulphur and our yields have gone up dramatically. The financial savings alone have been enormous! A win win situation.

 

[Andy Howard]

Why do you think lime companies like testing after harvest? They sell more lime! I do testing in the early spring. 6.2 isn't low really. 6.4 is ideal.

 

[DRC]

My agronomist does all comprehensive soil testing for us, however I get an Old School agricultural merchant to do pH testing as well. The two sets of results broadly tally, but the old chap does several discrete tests across the field and highlights any hot spots. Better job imho.

I've bought my own kit, as the old boy I usually buy lime off, walks around with his wooden box of test tubes, and nearly always comes back with the stock answer, it could do with a ton to the acre!.
Get agronomist to do more comprehensive tests on a few fields every year.