Propagation: Soil chemistry problem

Discussion in 'HortForum' started by sgbotsford, Oct 5, 2019.

  1. sgbotsford

    sgbotsford Active Member

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    I just got a new load of compost from City of Edmonton.

    I performed the following test:

    Packed a pot solidly with compost to a density similar to what I use transplanting.

    Applied 1 inch of water, waited for it to drain, and added about another inch. (1 liter of water total for a 3 liter pot.)

    Let it sit over night.

    Applied half a liter of water.

    Collected the first leachate out of the bottom of the pot.

    Measured the electrical conductivity. 10.8 mS/cm . My water is moderately high, at about .7 mS/cm

    Made up a batch of my standard soil mix which is compost, field soil, peat moss in roughly even proportions. 5.8 mS/cm

    Tested the soil in an old potted plant. 1.2 mS/cm

    I'm using an Oakton PCS tester. New batteries. Temperatures have been about 7 C, but I'm assuming that the meter corrects for this. (If it doesn't then the readings are going to be even higher.

    My understanding is that 1.5 mS/cm will start showing problems with a lot of plants, and anything over 4 is a death sentence for anything but a halophyte.

    Can I wash this compost? Spread it out in a 2 foot thick pile, and set a sprinkler to put several feet of water through it?
     
  2. Sulev

    Sulev Active Member

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    You may test this compost with some containers and fast sprouting vegetable seeds, that have low tolerance to saline soils, like beans, peas or onions. If the soil is problematic, then sprouts should show it soon. You may add some containers of your older soil to the test as a control sample.

    According to the https://open.alberta.ca/dataset/8ab...4e-86e9-60031d253aa6/download/2001-518-17.pdf there are forage crops that tolerate as high as 20 mS/cm (=dS/m) and sugar beets tolerate as high as 16 mS/cm.
     
    Last edited: Oct 5, 2019
  3. sgbotsford

    sgbotsford Active Member

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    Good idea. Any source of tolerance for common ornamentals?
     
  4. Sulev

    Sulev Active Member

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    Sorry, can't answer that. High salinity is normally not an issue in my country.
    Quick web search gives, that the Canadian Columbine or Eastern Red Columbine (Aquilegia canadensis ) should be one of the most sensitive ornamentals. As I have no experiences with growing Aquilegia, I have no idea how fast it sprouts and what is it's availability in seed stores/gardening centres. Butterfly Blue aka Pincushion Flower (Scabiosa columbaria), Mexican False Heather (Cuphea hyssopifolia) and Cardinal Flower (Lobelia cardinalis) can also be indicative to saline soils, because of their sensitivity.
     
  5. Sulev

    Sulev Active Member

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  6. sgbotsford

    sgbotsford Active Member

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    Not as useful as I'd like. I'm not growing food crops. I'm growing spruce, pine, larch, fir, poplar, willow, birch, most native boreal eco-system woody plants, some eastern hardwoods, oaks, maples, hawthorn,

    However, I'm interested that sensitivity isn't nearly as great as I thought -- the area on the graph labeled sensitive goes up to 8 mS/cm, so my 'death sentence' comment is hyperbolic.
     
  7. sgbotsford

    sgbotsford Active Member

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    Hmm. My understanding isn't correct. There are a few plants sensitive at 1.5, but the Sensitive category goes all the way up to 8 mS/cm So I was a bit hyperbolic.

    Anyone know where I can find the sensitivity of Spruces, Pines, Birches, poplars, larches....
     
  8. Sulev

    Sulev Active Member

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    Your tree species would take way too much time for a quick test. It is much easier to buy a package of pea seeds just for testing, because the pea will sprout in days. If the pea will grow well, as I suspect, you will get answer to your question within weeks. With tree seeds it would take months at least.

    My first link gives information about saliness tolerance of some trees also. You may try Larix or some other sensitive species listed there, if you still like more time consuming tests.
     
    Last edited: Oct 6, 2019
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  9. sgbotsford

    sgbotsford Active Member

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    Trying to avoid making live tests. I have 20,000 trees to transplant in the coming year. At this time of year there isn't sufficient time before frost for live tests even with annuals.

    A test using peas, or indeed any single species isn't as helpful as you'd think. One source I found did hydroponic tests with dogwood seedlings (Cornus sericea) at mixes up to a pH of 8.2 and EC of 7.9 mS/cm with no problems. One species of wild rose is ok with ECs in the low 30's

    A summary of the research for many boreal species is here:

    https://open.alberta.ca/dataset/23ca14d3-f3fc-4be3-9e18-ccba6ca157d5/resource/20b5b1a4-e661-4e3b-92a9-19980d7215d7/download/salinitysodicityphborealreport-jun2000.pdf


    As is common with this sort of thing, the answers are variable, and thresholds are vague. Initial intolerance just shows as slower growth -- the plant is devoting more energy to pumping ions back into the soil. Other effects are ion dependent. Actual salt (sodium and chlorine) have effects at lower levels for many plants, and may affect particular tissues (necrotic leaf margins, cambium)

    My idea is two fold:

    A: Find a replacement soil ingredient to replace all/part of the compost.
    B: Find figures for as many of my species as possible

    From this I can tailor a new soil mix, or set of soil mixes that is tolerable to my species.
     
  10. Sulev

    Sulev Active Member

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    I suggest to give your soil samples to analyse in some accredeted lab, before you trash this rather huge amount.
    I personally believe, that they will get lower score, and even if not, then the compost is still not lethally salty for your plants.
    You may even repeat your own test, it is possible to do some mistake there, a simple thing like using contaminated test tube may lead to biased results.
     
  11. sgbotsford

    sgbotsford Active Member

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    This is slop shop chemistry. I'm using my tap water, as that's what the plants will get. I've got an analysis of the tap water, done by the province, and the numbers I get for it are comparable.

    Sure, my technique may be wrong, but if so it's consistently wrong.

    I have read that EC in compost tends to increase with time and saturated water conditions: Stuff that is bound to organics break free. I have had poor results with certain classes of plants, which make me think that I have had a borderline problem for some time. This batch of compost has almost twice the EC of the previous batch.

    Soil EC tests.
    Test is made by adding 1/2 liter water to a 3 liter pot of soil, capturing the initial leachate, and measureing the EC.

    W = water
    OC = Old compost
    NC = New compost
    HP = Houle Country Peat moss
    FS = Field soil
    MX = standard mix using new compost, peat moss, field soil.

    Day 1
    OC 4.9
    NC 7.6
    HP 1.0
    FS 0.8
    MX 5.6

    Day 2
    OC 4.8
    NC 10.8
    HP 1.1
    MX 4.0
    FS not measured.

    Day 3 All measurements at 5 C
    W 0.78 ds 7.62 pH
    OC 3.65 6.3
    NC 9.1 5.3
    FS 0.34 7.4
    MX 2.5 6.4

    Appears that the field soil is acting as an ion sink. Note that it cuts the dissolved material in my tap water by about half. Given the silt/clay content this isn't a surprise.

    While the instrument is nominally capable of 3 sig fig readouts, I'm taking that with a grain of salt. (pun intended) pH takes a long time to stabilize, getting to within 1 pH unit almost instantly, then slowing going down for over a minute. Tomorrow I will make my measurements twice, with a recalibration between.
     
  12. sgbotsford

    sgbotsford Active Member

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    Interesting idea. if it was marginal, this would be the way to go. But these readings are over the top. Conductivity is linear -- twice as much crud (of the same kind) = twice the conductivity. If I was worried about a 10-20% error, I would agree -- my technique could be at fault. But we're talking about numbers that are 6 to 10 times commonly accepted target EC values. I already have to make sure that I have a 20-30% leaching fraction to prevent salts buildup form my irrigation water. (EC = 770 ┬ÁS/cm)

    This is slop shop chemistry. I'm using my tap water, as that's what the plants will get. I've got an analysis of the tap water, done by the province, and the numbers I get for it are comparable.

    Sure, my technique may be wrong, but if so it's consistently wrong. Dirty test tube (baby food jar...) isn't going to make a difference with high EC soils with low solubility salts. The soil will act as a buffer.

    I have read that EC in compost tends to increase with time and saturated water conditions: Stuff that is bound to organics break free. I have had poor results with certain classes of plants, which make me think that I have had a borderline problem for some time. This batch of compost has almost twice the EC of the previous batch.

    Soil EC tests.
    Test series started by packing a 3 liter pot with the material, and watering with 1 liter of my tap water. Pots were allowed to sit for a day.

    Test is made by adding 1/2 liter water to a 3 liter pot of soil, capturing the initial leachate, and measuring the EC.

    OC = Old compost
    NC = New compost
    HP = Houle Country Peat moss
    FS = Field soil
    MX = standard mix using new compost, peat moss, field soil.
    W= tap water

    All measures are mS/cm

    Day 1
    OC 4.9
    NC 7.6
    HP 1.0
    FS 0.8

    Day 2
    OC 4.8
    NC 10.8
    HP 1.1
    MX 4.0
    FS not measured.

    Day 3 Adding pH measure -- 2nd number
    W 0.78 7.62
    OC 3.65 6.3
    NC 9.1 5.3
    HP 1.0 5.2
    FS 0.34 7.4
    MX 2.5 6.4

    Day 4
    W 0.53 fresh from hose. No setting time. (CO2 uptake?)
    OC 3.28 6.2
    NC 8.7 6.3
    HP 0.7 6.1
    FS 0.4 7.3
    MX 1.45 6.5

    This amount of water is roughly what plants would get in two weeks.
     
  13. Tom Hulse

    Tom Hulse Active Member 10 Years

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    I suspect your new compost having twice the EC of your previous batch reflects a younger, hotter batch from city, less composted. Every old garden book warns about using fresh compost like this, they knew it from experience without EC meters! :) Your info about compost EC increasing with time & saturation I believe is only for a limited time and including a change from dry to saturated; more generally nutrients/salts in compost will always reduce over time. The conventional wisdom has always been to let it bake longer and it is safer.

    One thing I do in small batches that I don't know if it would be practical on your scale: when mixing a new batch of soil (about once a year), I always buy my compost & manures for next year, at least a full year ahead of time, and let it cook longer. I get a much more stable mix with a higher percentage of structural carbon and lower, less risky nutrient levels. That nutrient stability is so important I think for any crop that will be in the pot longer than a season. I think your conifers would really appreciate allowing the compost to age longer. I get the feeling you have a square peg / round hole situation when trying to use super-green, fresh compost on crop that doesn't like high organics. The other thing you might consider if you have to use this batch is just reducing the percentage of compost in your mix. So I wonder if you might consider altering your mix to half the compost, then replace it with something roughly in the range of 1/4 peat, 3/4 bark fines (or whatever combo gives you the right water retention you want).

    Last thing I'll throw out there, I'm sure not an expert at EC testing, but are you sure about allowing your pots to sit for a day between normal watering and testing? That would seem to yield much higher EC results than other published methods, like this one, that prescribe only a 30-60 minute window. Why not just grab a few jugs of distilled water at the grocery store. You're comparing "proper" levels that were measured by others using distilled, even when they of course are not using distilled water to normally water their crops. So your 'this is the water my plants will get' argument doesn't hold water. ;)
     
  14. sgbotsford

    sgbotsford Active Member

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    My info seems to say that it takes a while for soil to reach equilibrium with water. Once it is close to equilibrium, additional time doesn't change much. I've also done the 1 part soil 2 parts water (W:W) method with a 4 hour wait and get basically the same numbers. Most of the tests also are made at room temperature. I'm working at near freezing temps (0 to 5 C) My meter auto corrects for this, but common sense suggests that equilibrium times are going to be longer.

    I suppose a reasonable test would be to use the 1:2 method and measure repeatedly and see how it changes with time.

    ***

    I split the pile in half, and spread it out 18" thick, then ran a sprinkler on it for 6 days, putting about 24 inches of water total on it. My hope is that this will rinse the bulk of the crud out. We've got cold weather right now, so I'm waiting for it to warm up. I will treat it like an archeology dig, and make a step trench and test at various levels. I expect to find low salts in the top N inches, and very high salts in the bottom M inches, and some sort of gradient between. It may mean I use my pile by taking it off in 6 inch layers.

    The old compost has had a year of precip through it -- about 20 inches, but was covered for part of that time.
     
  15. Tom Hulse

    Tom Hulse Active Member 10 Years

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    I'm not sure if rinsing will solve much of your problem, and I would be cautious about trusting any temporarily lower readings after rinsing, since that "crud" you mentioned is not a part of it, it's ALL of it. Green compost (it's green/young/early/immature by evidence of your double-high EC readings vs. your last batch) is still in the process of turning organics through the nitrogen cycle. At the early stages, that ammonium and other early non-usable forms of nitrogen are still being heavily generated by the gradual breakdown of the organics. So rinsing today does almost nothing for the ongoing breakdown of organics that is going to happen tomorrow and the next day and in the pot.
     
  16. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Also one thing to factor in to your planning is that spreading it out thinly instead of a compact pile reduces the heat generated and can almost shut off the aging process for the winter, since the denitrification process that breaks down and ages compost happens mostly in that 60 to 86 degrees F range, and the pile needs height to generate those temps in the winter.
     
  17. sgbotsford

    sgbotsford Active Member

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    You may be right.

    This is nominally material composted at 120- 140F degrees for 150 days. It's certainly not green. The load as it came off the truck was warm, but far from hot. (I doubt that the bulk mass could cool much in a semi-trailer during the 2 hour trip.)

    Remember too that the year old stuff while lower, was not hugely lower.
     
  18. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Hmm. That's only 5 months. Maybe a different perspective on "green": Our local compost for all the yardwaste in the Seattle area is composted for a minimum of 6 months, and usually much longer, especially the bagged stuff I get. They guarantee it has been brought to at least 150F for 3 continuous weeks of that time. When I drive by their mountain-high piles there is white steam rolling off the top of the pile. And still, I think this is too immature for my potting soils (unless the soil will be for the real nutrient pigs like some annuals, bananas, Brugmansia, etc.) and so I let it go an extra year. So from that perspective I would say yours is definitely green. Also, as I mentioned before, the measured differences in your EC readings of old vs new compost, if correct, demonstrate as fact that the compost is immature.
     
  19. sgbotsford

    sgbotsford Active Member

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    Good point.

    So, pile it back togehter, and put a tarp on it? We're in winter now. I suspect it won't warm up.
     
  20. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Yeah, I'm sure you're right. Well you need your soil, and you're a business, so you'll have to make use of this compost at some point. I imagine this whole next year will be a cost/risk balance you'll have to find between using part of it now and saving most of it for later. So a few things you might partially combine into a plan:
    - I would pile high & tarp the new stuff; separate out and start using the old stuff now.
    - Depending on labor costs, you might work with slightly smaller batches than normal for this coming year, to allow a little more time for the new compost to mature; and to allow for a separate, lower-EC mix for your conifers or whichever you think is more sensitive.
    - Start researching bark as an ingredient, especially for the conifers, and comparing which bark products you can find in bulk locally. I like fir bark fines as an ingredient for conifers. Stay away from "forest products" or landscape chips or anything with lots of wood that is not bark.
    - Continue to use the new, high-EC compost but in much lower percentages and mix as late as possible to give it more time in the pile. At double-EC, the nutrients will still be there even when diluting with bark, just in a more concentrated, volatile form; so mix well and use it sparingly!
     

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