I'm wanting to determine soil ph, so I got the Luster Leaf Rapitest Soil ph test kit (#1612).

I'm trying to read the ph, but not sure exactly what the number indicates...
*Is the color-coded ph the measurmenet for the ph of the soil,... or the ph of the soil+water (the water used to mix the test sample and powder)?*

I used water of 3 different ph's, and got 3 readings for the same soil (fresh soil used for each test taken from same batch of soil.

using ph:
5.5 water gave a reading of about 6.3
6.8 water gave a reading of about 6.5
7.5 water gave a reading of about 6.8

If you're trying to determine the pH of the water, just use the test kit and the water.

If you're trying to determine the pH of the soil, use distilled water for the solution.

Tap water can alter the results of a soil test, and well water can, too. Ground water more or less follows the pH of the soil, unless there is something strong that is altering the pH.

The color is determined by the pH of the solution, no matter what it is made of.

Sue

Testing 6.8 water alone, gave a color result of about 6.8

Also, I'm now unsure about the previous reading from the 5.5 water -that water came from a fresh unopened steam distilled spring water bottle, but the ph strips show it as about 5-5.5, and the test strips have been validated already. So I can't trust the results using that water, which seem to be off the color chart scale so I'll disregard that result.

So the results that I'm certain of are these:

6.8 water + soil gave a reading of about 6.5
6.8 water alone gave a reading of about 6.8
7.5 water + soil gave a reading of about 6.8

(all are +/- .2)

So how to calculate the soil's ph from these... considering that the solution is 1 part soil and 7 parts water, and allowing that every whole value below 7 is 10 times more acidic than the next higher value?

Or, with a +/- .2 margin of error you could conceivably be looking at water alone with a pH of 6.6 and soil+water with a pH of 6.7. In other words, the water and the soil solution trade places within the margin of error as far as which is more acidic. In other...other words, for all practical purposes, they're pretty much the same. I would just say the soil is 6.7 and call it a day. That is, of course, assuming that the test kit is accurate. I don't have any experience with it so can't say one way or the other.

Tap water is not going to respond the same as distilled when mixed with the soil due to its mineral content. I would tend to trust the result with distilled.

Your 6.8 water gave a reading of 6.5, so likely the soil is lower than 6.5 and was brought up. Even 7.5 water only got it to 6.8, consistent with soil pH below 6.8. The 5.5 water, presumably not buffered at all, gave 6.3 so the soil can't be lower than 6.3. I'd call it 6.4.