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Some soil pH questions

 
pioneer
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Location: Sydney, Australia. Subtropics
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Traditionally I have just relied on compost to balance pH, but some plants in my small gardens aren't doing so well, so I'd like to investigate further. Here are a few questions that come to mind...

1) Whats the difference between adding lime or ash to bring up pH?
2) How does soil compaction (areas with low oxygen) affect pH?
3) How accurate are home pH test kits?
4) Does soil temperature affect pH?
 
pollinator
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1) Ash acts as a fertilizer as well.
2) I don't know
3) Accurate enough for most uses. My favorite is just to pour vinegar over the soil and watch it foam.
4) Soil temperature prevents some plants from taking up certain nutrients. So does alkalinity. Sometimes it's both. It depends on the plant. Soil temperature doesn't affect alkalinity as such.

Hopefully someone will chime in who has more information for you.
 
gardener
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Location: Vilonia, Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
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Good questions Ben.  

When we are trying to change the pH of soil, we have to think about Ionic exchange since that is why we are so interested in pH as growers.

Soil pH affects many aspects of plant growth, this is primarily because of the effect pH has on the microbiome organisms.
If the plant is primarily desiring bacteria as their helpers, then highly acidic soil (like for Blueberries) is not desired, high acidity shuts down or kills most of the beneficial bacteria species.
If we need fungi for primary helpers then we don't have to be as concerned with the pH, we can't ignore it but there is a larger error allowed.

Lime or Agricultural lime particularly acts as a buffer as well as an ion source, Ash also acts as a buffer but it will need replenishment more often than lime would need. (lime about every 4-6 years, Ash about every 2-3 years)
Ash can be free since most of us can create it from our own resources, lime is almost always a purchase item. (If you pour vinegar on some soil and it fizzes, that is pretty alkaline soil and needs to be tested and adjusted usually)

Soil Compaction brings with it a plethora of problems including water rejection, you aren't going to see much rain soak into a soil that is compacted.
Compaction also retards or stops root growth away from the plant, roots need to be able to push through the soil.
O2 is the same as water infiltration, no crevasses to seep into, no water or O2 can get in to provide the requirements of the plant roots, fungi mycelium or the many bacteria species we desire.
Compaction can have an affect on pH but the other issues are far more important to address.

The accuracy of "home pH test kits" is totally dependent upon the type of meter is used to detect the ionic exchange rate.
Good (accurate) pH meters can be had for 60 dollars, these are hand held, pen type meters and they come with good directions and calibration solution.
The first thing to look for when shopping for a pH meter is 'Does this meter have the ability to be calibrated and is the solution to do that calibration included with the meter?'
When shopping for pH meters, the rule of thumb for researchers is if it costs less than 250 US dollars, it will not meet the accuracy needs of a researcher. (Note that I am being specific here, farmers and other growers do not need accuracy to within 0.01%)
For most of us, if the pH meter will read within 0.05% we are in the super accurate (for our needs) range, we can get by nicely with an accuracy of 0.2%.

Soil temperature is rather low on the affect list when it comes to pH. While it will have an effect on pH, it really doesn't cause a move that is significant enough to be a concern to the grower.

Hope that helps you out.

Redhawk
 
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Bryant RedHawk wrote:
For most of us, if the pH meter will read within 0.05% we are in the super accurate (for our needs) range, we can get by nicely with an accuracy of 0.2%.



+1. Remember that the pH scale is logarithmic (not linear), so between pH 5.0 and 5.5 is a huge difference, making sub-% errors insignificant.
 
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Get a soil test before you start adding chemicals to the soil.

Contact your local Cooperative Extension Office about where to get it done, and to find out how much a general test costs.  Most run $10-20.  Their websites usually tell or show you how to take a sample -- you don't just scrape some dirt  off the ground.

If you soil has a low pH, you can add a moderate amount of ash.  But if it has a nearly-neutral (6.5) or higher pH, adding ash may increase the pH to the point where some of the other nutrients will not be available to the plants.
 
Ben Schiavi
pioneer
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Thanks guys, awesome info
 
master pollinator
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If you are having problems with "some plants in your garden", then I doubt it is your soil PH doing so.

You always get your PH right before adding fertilizers because that unlocks the plants ability to glean nutrients.

If your whole garden was suffering, I would say that PH problems was the case, but since you only have a few suffering, i am betting that your micronutrients are lacking. The major nutrients like NPK would affect a higher amount of plants. For instance if you lacked nitrogen, almost all of your garden would be suffering, not just a few plants. So I would do a soil test and figure out what you are lacking.

I am just guessing, but I bet it is iron, copper or zinc...something along those lines; the specific plants that are struggling, particularly liking a micronutrient that is just not there in your soil.

You got to test though because as I always say! It is just a guess, unless you test!
 
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