Science Forums 2

[Philip Small]

I am still working this through. I've sent a sample to the lab and also contacted a bunch of other soil scientists (CS, HL, regional ag extension types, etc). Here's what I told them:

I am dealing with a difficult to understand garden soil situation.

I added 50 lbs of crushed and screened charcoal to 132 SF of garden and increased my soil pH higher than anticipated, especially considering the 50 lbs of peat that went in with it.

Today I collected soil samples and sent them to a lab for testing: do you have any "must see" soil analysis that you would be interested in?

I'll be getting OM, NO3, NH4, avail P, exch cations (Ca, Mg, Na, and K), pH, texture, (coarse sandy loam, I anticipate), Zn, B, plus some trace minerals. I have also asked the lab for a titration-based recommendation as to how much acidification (as elemental sulfur) is needed to drop the pH to various target levels. That should give us a decent handle on buffer capacity.

Store-bought hardwood charcoal dominated my char addition. Earlier I had it (Cowboy brand charcoal) tested for calcium carbonate equivalent. It came back at 2.6%. If representative, 50 lbs over 132 SF is equivalent to only 434 lbs/A of lime. Clearly that is not the whole story here. Soil was pH 6.5, is now pH 8.0 to 8.5 down to 18 inches (rock below that), thus the effect I am seeing seems at least an order of magnitude higher. If the charcoal had been 100% CCE (it wasn't), the addition would have been 16500 lbs/A lime equivalent, but that seems about what it would take to account for the magnitude of the increase.

A combination of possible explanations presents themselves:

• The soil/peat mixture I am working with has an extremely low buffering capacity.
• My pH kit reagent is unreliable.
• I added more wood ash to the compost than I am accounting for.
• The observed effect is highly transitory.
• My math is seriously off.