Garden Soil

[Philip Small]

This year we made 132 square feet of raised beds 6 inches deep. It was about 1/2 top soil (pH 6.5) and 1/2 other stuff: 50 lbs charcoal (80% Cowboy Brand, 20% I made from maple branches and woodworking scraps), 50 lbs peat (pH 5.0), 50 lbs chicken manure, and 250 lbs well composted maple leaves and kitchen scraps. I am not double counting the 1/3 of the charcoal that went through the compost and the compost was up at pH 8.0 as a result. The not-composted portion of the charcoal itself was soaked in fish emulsion and was up at pH 8.5, the maximum my Hellige Soil Reaction kit will read to, so it could have been higher, and probably was considering my results.

added 10/24/08: See "lab results are in", below, for correct soil pH.

It was cold this year and everything started out very slow and looked a little chlorotic. My wife and I didn't coordinate very well and we doubled up on our response resulting in over-fertilizing 2X with MiracleGro (TM): We got HUGE squash and melon vine production as a result.

The soil pH starting out indecipherable with the kit, with bits of peat at 5.5 and bits of charcoal at 8.5. Five months later it has evened out, but it is surprisingly high considering the amount of peat that went in. It is up at 8.0, and I want it back down at 6.5 like I had it before I started. I'll back off on the charcoal for next year until I can coax the soil down below 7.0 using elemental sulfer. Plus maybe the rain and snow melt this winter will wash some of the reactive compounds a little deeper.

I have had pH 8.0 garden soil before and the garden never looked this good. I am quite pleased and expect increasingly good production from this 132 SF.

[freeztar]

Great post Philip.

Although I've passed through Spokane, I've never 'experienced' it. From what I saw, it seems that there are patches of conifers strewn about, especially north of there. I seem to recall Richard Black saying that his pine needle droppings were providing acid to the soil. Perhaps you can do without the sulfur?

In any case, it's always good to hear of char experiments. I must admit that I'm a bit jealous. Hopefully I'll have some garden space for next year. Perfect time for newlyweds to buy their first house right?

Living vicariously,
freezy

[Michaelangelica]

Great Phillip
Some pickies at harvest time please?

[maikeru]

Sounds like a successful experiment!

I have one comment on the 8.0 pH. Even though it's somewhat high, from what I remember reading and discussing, some of the carbon and inherent char residues should oxidize with time, forming organic acids which will lower the pH a bit and also provide for more nutrient-holding capacity and exchange. Don't sweat it. Like Freeztar mentioned, you could skip the sulfur and try pine needles instead. I think it's better to keep adding complex organic mixes, so you can add important macro- and micronutrients to the biochar to keep the plants and microbes happy.

[Philip Small]

I now believe my abnormal increase in soil pH is due to a combination of low soil buffering capacity and the apparently high ash content of the biochar I manufacture. I use a modified open barrel approach and was estimating that I could achieve about 20% efficiency. i.e. about a pound of charcoal for every 5 pounds of dry wood. I anticipated getting about 10% ash at that rate. If my efficiency is instead lower, say 10%, it could have doubled my ash content, and thus the liming effect. It may not be the only reason for my quite surprising jump in soil pH, but certainly the first to consider.

I have updated Gardening with Biochar FAQ per my experience:

5.0 What happens after biochar is in the soil?
5.01 Does biochar affect soil pH?
Raising soil pH is biochar's most important contribution to influencing soil quality. (Source) Soil pH mostly influences the relative availability of nutrients. At low pH, aluminum toxicity is particularly harmful to plant growth. Aluminum toxicity is an extensive and severe soil problem and biochar is the most available and obvious solution that we have to combat it. Soil phosphorus availability is highly dependent on soil pH range, and thus biochar can be used to substantially increase phosphorus availability for soils that are below the ideal soil pH range of 6.5 to 7.0. (More on biochar and soil pH >> biochar.pbwiki.com/Soil-pH)

Soil pH
Continued from 5.01

The ideal garden soil pH is 6.0 to 7.0. Phosphorus becomes available through biological transformation. Available phosphorus that is not taken up by plants and soil microbes is subject to geochemical fixation. The degree of fixation is regulated to a large extent by soil pH. Phosphorus is least available at high and low soil pH. At soil pH above 7.2 to 8.5, phosphorus fixes as insoluble calcium phosphates. At soil pH below about 5.5, iron and aluminum phosphates form, reducing phosphorus availability. Phosphorus availability is greatest between 6.0 and 7.0. For this reason, more than any other, pH 6.0 to 7.0 is considered the ideal soil pH range for most garden plants.

Liming Effect of Biochar. The ash content of most biochars has a slight liming effect: it tends to increase a neutral or acidic soil pH to a more alkaline pH. Ash tends to have a pH of 12 - 13, and charcoal tends to have a minimum ash content of 2-10%. At 10% ash, the effect a tonne of charcoal might be equivalent to as much as 1/10 tonne of lime. At the high end of the target biochar application range (50 MG/ha) (see 4.01), soil pH would increase equivalent to lime applied at 5 tonnes/ha, enough in some cases to increase soil pH by 1.0 unit. In my garden I applied a high rate of high ash content biochar and observed soil pH rise from 6.5 to over 8.0. If you are applying substantial amounts of biochar you should test your soil pH and compare it to the ideal for your plants.

If your soil pH is below 6.0, and you are not trying to grow plants that need sub-6 pH (examples: Aechmea, Aspidistra, Camelia, Hydrangea (Blue), Orchid) you can rest assured that your soil's acidity level will improve quite significantly from the addition of biochar. At higher pH levels, the addition of thoroughly matured compost to the soil can enable so-called acid-loving plants to thrive in a soil of pH 7. This is because the natural chelating effect of the organic matter allows it to maintain the availability of trace elements to plant roots. (Hendreck, 2002, Growing Media..)

Accordingly, adding so much biochar that you take your soil pH above the ideal range may not be a problem if 1) soil nutrients are both abundant and balanced and 2) the soil contains a substantial amount of thoroughly mature compost.

Plant Symptoms of Excessive Soil Alkalinity. Visible symptoms of nutrient deficiencies can be most informative in establishing that soil pH has become a problem worth dealing with. Because of a cool, moist spring 2008 season, iron chlorosis was the first clue that I had induced elevated soil pH.: Unlike the more common nitrogen chlorosis, iron chlorosis affects new growth first, turning it pale green, then yellow-green, and in extreme cases, to almost white. Leaves showing iron chlorosis often retain green veins. Even in mild cases where yellowing is slight, growth is noticibly reduced. Iron chlorosis usually clears up when soil warms up.

Another visible symptom of elevated soil pH is phosphorus deficiency. This is a more persistent effect than iron chlorosis. Plant development is slow, growth is stunted with very limited root growth. Many plants develop dark green leaves with purplish or reddish hues in the leaves and petioles.

Hypography note: Although the garden looked magnificently overgrown by the end, _all_ my plants were slow to develop and were reluctant to flower. Poor flower and fruit yield is a symptom of P deficiency. It is also a symptom of excessive N fertilization, which may have been a contributing factor. And while tomato and squash plants had great root masses by the end, not so with the beans, peas, strawberries, peppers, beets, and radishes which had very little below ground, indicative of limited phosphorus availability. Parsnips are still waiting to get pulled. The squash and tomato plants broke out of the doldrums and then never stopped growing when it got hot (positive biochar effect!) and eventually making for a very impressive looking garden. However the other (non-tomato, non-squash) plants never really kicked in like they should have. We felt that the peas and beans should have yielded at least twice as much, especially considering the ideal weather they had.

Other nutrient deficiency symptoms associated with high soil pH are yellow mottling on young leaves (manganese deficiency) and rosetted new growth. Both boron and zinc deficiency can cause rosetted new growth. Boron deficiency can also cause the plant to become a dark green. Copper can be deficient in high pH soils: new shoots won't open, the whole plant is pale colored and young leaves are thin and yellow.

Responding to Biochar-induced Excessive Soil Alkalinity. If it looks as if biochar-induced high soil pH is a concern in your garden, you might consider simply waiting it out: the caustic (ie alkaline) contituents in ash are reactive, that is, they are not persistent. If your soil has a high buffering capacity, associated with high clay, high calcium, and/or high organic matter content then you should see soil pH moderate with time. Otherwise, there are several steps you can take to mitigate biochar's lime effect:

• Use a reduced alkalinity feedstock for your biochar. Little has been published in this area, however, biochar derived from pine-needles is purported to have an acidifying effect on alkaline soil.
• Use a high bio-oil condensate content biochar. This implies a lower temperature biochar as well as an effort to recover bio-oil condensates (example: wood vinegar) from the producer gas and returning it to the charcoal.
• Water processing can eliminate liming characteristic of charcoal: the alkaline constuents of charcoal are soluble. The downside is that ash-based nutrients (especially Ca, K, and S) are also removed.
• Increase applied organic matter. Peat can be especially effective in this regard. Peat applied at 2.5 lbs per square yard is capable of reducing pH by 1.0 unit in some soils.
• Apply an acid-effect fertilizer, an approach which is more effective in combination with applied organic matter. Examples of acid-effect fertilizer are ammonium sulphate, urea, or an ammonium phosphate.
• Apply sulfur, an approach that requires time and microbial activity. To reduce pH by 1.0 unit, apply 1.2 oz per square yard on sandy soils, or 3.6 oz per square yard on other soil types. Elevated soil sulfur is known to raise the hotness of peppers and onions. If you like your onions, leeks, shallots and garlic to be mild, you might want to shy away from this one.

[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.

[Michaelangelica]

I tested the pH of the Ozzie char I used this time.
It was 6.
So I'll see.
Certainly my gardenias are not looking happy although I just tested the soil around them and it too is six.
Carnations in pots are looking great they love char.

[Philip Small]

I got the results back from the lab (top 12 inches = pH 6.8) and they don't support my field kit (pH 8.0). This makes total sense. Considering how long I've been nursing my bottle of indicator solution (stuff goes bad), I truly should have seen this coming. I hope my humble apologies for a premature and boneheaded call are acceptable.

Soil pH did come up from pH 6.5, but certainly not enough to cause any of the nutrient problems I was speculating on. In fact, the lab has available P at 53 mg/kg (10 is adequate), so even if I was to induce pH 8.0, I am unlikely to see P deficiency symptoms.

Other highlights, Organic matter is up at 8.6%, clay is 0.6%. CEC is up at 39.6 and must be largely accounted for by the compost and charcoal. Nitrate-N is high at 24.4. I see higher in my work, but am very glad I have the charcoal to help hold it. Email me at psmall2008 AT landprofile DOT com if you want to receive a copy of the soils data as an xls file.

I learned valuable new stuff in the process of digging into the books, and in discussing my problem with other soil scientists. Researcher Christoph Steiner kindly wrote me to tell me that he observed that the chicken manure he used raised soil pH more than the charcoal he used. I also stumbled across the handy fact that charcoal above pH 8.2 (buffered to that point by CaCO3) indicates CaCO3 has been replaced with CaO b/c it was made at closer to 1000oC than 600oC. Higher temp is common for boiler ash, thus the proliferation of published data that indicates wood ash in the pH 12-13 range.

[Michaelangelica]

Phillip what lab did you use and was it expensive?

I have to do something about my confusingly silly soil.

My indicator solution is about two years old
How long it sat on the shelves before that who knows?

[Philip Small]

My analysis was done by USAg Analytical at 1320 E Spokane St, Pasco, WA 99301. 509-547-3838. I don't know if they have the USDA-APHIS certification to receive soil samples from oversees, but you should certainly be able to find similar labs in OZ.

USAg's "complete" package: NO3-N, NH4-N, P, K, S, Ca, Mg, Na, B, Zn, Mn, Fe, Cu, OM%, pH, soluble salts (ECe) (USD$45) and added texture (USD$15) plus CEC (USD$20). Lime requirement (USD$15) can also be added.

Control Labs in California has their soil prices posted. (much appreciated) Their complete is more complete (includes CEC, lime requirement) (USD$75) and can add texture (USD$36).

If you are not doing a test package (just pH for example) I have found that walking in the sample and asking for a non-rush price break, is often well received.