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  • From: Steve Diver <steved AT ipa.net>
  • To: Market Farming <market-farming AT lists.ibiblio.org>
  • Subject: Re: [Market-farming] mint compost, potting up tomatoes
  • Date: Tue, 5 May 2009 11:20:08 -0500 (GMT-05:00)

Rachel -

In your original post it sounded like you made your own
mint compost.

But in retrospect it sounds like bought the compost
from these suppliers, but they didn't know you were
aiming for a potting mix.

The salts are measured by an EC meter, Electrical Conductivity,
which are available in pocket meter sizes for $150 or less.

Hanna makes a Combo meter with pH/EC/Temp, which is very handy.
Many other brands available from Hach, etc.

When elements go into solution as ions, they become salts.
So the EC meter measures all these salts that come from
Sodium, Potassium, Chloride, etc.

When EC is too high, it burns roots and/or roots don't
like to go down into the mix.

Bottomline is that dilution is the solution. Mix
the compost with peat moss, perlite, and other stuff.
The EC of final mix is what matters to plants.

Or, get a higher grade compost with low salts that is
suitable for potting mixes. EC is one of the top criteria
for potting-mix grade composts. These are usually the
best, premium composts that you can find.

Large-scale composting results in various grades materials
from low-grade to high-grade. The low grade stuff is partially
digested organic matter where you can still see bark and
shreds of parent material; it's OK for mulching around trees.

Here's a couple of charts that show ranges for EC in compost
and good-to-bad levels.

Sorry to hear that, but it sounds like you're back on track
and better yet it wasn't herbicide contamination.

Steve Diver
http://www.sustainablegrowthtexas.com

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Compost analysis
University of Missouri Soil and Plant Testing Laboratory
http://soilplantlab.missouri.edu/soil/compost.htm

Table 1. Compost analysis interpretation


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Woods End_Interpreting Waste and Compost Tests
http://www.woodsend.org/pdf-files/compost.pdf

SALINITY, ELECTRICAL CONDUCTIVITY: Soluble salt level (salinity) in
a sample is estimated based on measurement of the electrical
conductivity of a saturated paste.

Components contributing most to salinity are sodium, potassium,
chloride, nitrate, sulfate, ammonia, and VOA.

Table. Evaluation of SALINTY in Compost Tests, mmhos/ cm


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USDA Soil Quality Test Kit
SECTION II: Background & Interpretive Guide
for Individual Tests
http://soils.usda.gov/sqi/assessment/files/section2.pdf

The electrical conductivity (EC) of soil-water mixtures
indicates the amount of salts present in the soil. All
soils contain some salts, which are essential for plant
growth. However, excess salts will hinder plant growth by
affecting the soil-water balance. Soils containing excess
salts occur both naturally and as a result of soil use
and management.

The electrical conductivity measurement detects the amount
of cations or anions (salts) in solution; the greater the
amount of anions or cations, the greater the electrical
conductivity reading. The ions generally associated with
salinity are Ca2+, Mg2+, K+, Na+, H+ (cations), or
NO3-, SO4-, Cl-, HCO3-, OH- (anions).

Table 5. Electrical conductivity measurement and salinity
classes for a 1:1 soil:water suspension

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