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The Transi琀椀on to
Organic Partnership
Program (TOPP)
Prepared for USDA Organic by AcresUSA., The Voice of Eco-Agriculture
www.ACRESUSA.com | 1
Soil & Plant Testing Basics
for Organic Farming
THE BASICS OF MODERN SOIL AND PLANT TESTING FOR THE
ORGANIC FARMER EXTEND BEYOND SIMPLE NPK ANALYSES TO EXAMINATIONS
OF MICRONUTRIENTS, WATER, SOIL BIOLOGY AND LEAF SAP
“DON’T JUST GUESS — TEST.”
This sen琀椀ment is becoming the
mantra of modern agriculture. The
promise of be琀琀er plant, water and
soil data is that it enables growers of
all sizes to farm in ways that reject excess use of synthe琀椀c chemistry and to
produce healthier food in a more eco2 | Copyright AcresUSA
logically sound way.
In this ar琀椀cle we’ll discuss various
types of tests that are being used by
organic growers, star琀椀ng with plant
sap analysis — a new test that is becoming vital for growers of all di昀昀erent crop types due to its ability to
pinpoint which nutrients plants need.
We’ll then touch on the importance
of water quality — an o昀琀-neglected
aspect of organic farming — and will
cover several di昀昀erent methods of
soil biological tes琀椀ng that o昀昀er powerful insights into soil health. We’ll
conclude with a look at new and old
methods of soil chemical tes琀椀ng.
PHOTO COURTESY OF BIOME MAKERS
SAP TESTING
Plant sap tes琀椀ng is increasingly becoming one of the most important
tools for organic growers. It o昀昀ers
incredibly precise snapshots into the
true health of the plant and allows
farmers to ascertain the e昀昀ec琀椀veness of their soil and foliar amendments, as well as cultural management prac琀椀ces.
Sap is the plant equivalent of blood
in humans. A sap analysis isn’t the
same as plant 琀椀ssue analysis, in which
a leaf is turned into ash and then analyzed for its compounds. In sap testing, labs use proprietary processes to
extract sap and then analyze it using
di昀昀erent laboratory equipment. The
An example of data from a sap analysis; young leaves are light green bars and older leaves are dark green.
PHOTO COURTESY OF ADVANCING ECO AGRICULTURE
www.ACRESUSA.com | 3
best prac琀椀ce is usually to take samples every couple of weeks throughout the growing season in order to be
able to respond with targeted applica琀椀ons — usually with foliar feedings.
As mentioned above, a sap test
tells the grower exactly what is in
the plant. It can be used to ascertain
in-season plant health — for example, what nutrients are in excess or
in short supply (excesses are usually
more problematic, and more difficult to resolve)? What diseases and
pests are the crops susceptible to?
Did the previous application have its
desired result?
Tests range from $70 to $100 per
test from several U.S.-based labs.
While this can add up, and may not
make 昀椀nancial sense for smaller-scale
growers of a number of di昀昀erent
crops (i.e., market vegetable farmers),
sap tes琀椀ng has become an incredibly
powerful tool not just for specialty
crops but also for corn, soy and co琀琀on
growers, as well as for pasture.
WATER TESTING
The mineral content of water that is
used for irriga琀椀on, and especially for
foliar applica琀椀ons, is being recognized
as of immense concern to farmers of
all kinds. Organic growers in par琀椀cular are realizing that water isn’t just
water — its quality can have a huge
e昀昀ect on plants, par琀椀cularly in how
they take up applied nutrients.
Water tests themselves are not new,
and many labs o昀昀er them; it’s just
their signi昀椀cance that is increasingly
being realized. They are inexpensive
— less than $50 — and only need to
be performed once every few years.
Bicarbonate levels are par琀椀cularly important for farmers to be aware
of. Anything over 120ppm should be
addressed — ideally through reverse
osmosis, although some new sulfur
burners and carbonic acid systems do
work well. High bicarbonates — hard
water — can dras琀椀cally reduce the effec琀椀veness of the nutrients that are
applied. Given the rela琀椀vely high cost
of nutrient inputs, 昀椀xing your water
so that what’s applied goes to work
should be a no-brainer. Water tests
are perhaps most important in greenhouses and for foliar sprays.
Agricultural water tests usually also
report pounds per acre-inch of water
applied for salts like calcium, magnesium, potassium, etc. Growers can
count this as part of their fer琀椀lizer
budget if they irrigate.
Labs that offer sap testing:
Nova Crop Control
h琀琀p://www.novacropcontrol.nl/en
Apical Labs
h琀琀ps://apical-ag-home.com
New Age Labs
h琀琀ps://newagelaboratories.com
SOIL BIOLOGY TESTING
Microbial tes琀椀ng is the newest type
of lab analysis for farmers. Just as we’ve
come to realize the importance of our
gut microbiome, so organic farmers
are increasingly understanding how
vital soil microbial life is to the health
of plant — and thus the desire to test
that soil to know what’s happening in
it. Several new tests are on the market
that provide farmers a glimpse into the
bacteria, fungi and other organisms
in their soil and that o昀昀er recommenda琀椀ons on how to grow and/or alter
those microbial communi琀椀es.
One note of cau琀椀on with biological
tes琀椀ng, besides the fact that there’s
rela琀椀vely li琀琀le baseline data, is that
microbial popula琀椀ons change quickly
based on weather, season, the plants
in the ground, the distance of the soil
Water that has high levels of bicarbonates — which can adversely a昀昀ect the absorp琀椀on of nutrient inputs — can be
treated with reverse osmosis (RO) systems (le昀琀) or sulfur burners (right).
4 | Copyright AcresUSA
PHOTO COURTESY OF BIOME MAKERS
Labs that offer soil microbial
testing:
Microscopy tes琀椀ng — Soil Food Web
h琀琀ps://www.soilfoodweb.com
PLFA and Haney tes琀椀ng — Regen Ag Lab
h琀琀ps://regenaglab.com
DNA tes琀椀ng — Biome Makers
h琀琀ps://biomemakers.com
The same equipment that analyzes the DNA of humans and any other living thing
can be used to determine the microbial makeup of the soil, providing organic
farmers a glimpse into the bacteria, fungi and other organisms in their soil and
giving them an opportunity to try to grow and/or alter those communi琀椀es.
sample from the plants, and many
other factors. Keep in mind that this is
a developing 昀椀eld of study.
One of the earliest, and simplest,
forms of biological tes琀椀ng is microscopy. Take a sample, put it on a slide,
and take a look at it under a microscope. This method provides undeniable results — you can see the bacteria and fungi with your own eyes
— but it su昀昀ers from how long it takes
(and how expensive it is) to learn how
to iden琀椀fy the di昀昀erent microbes, and
the fact that the vast majority of microbial species are uniden琀椀昀椀ed.
A di昀昀erent method is a PLFA
(phospholipid fa琀琀y acid) test. This
test measures chemical signals that
arise from di昀昀erent groups of microbes — fungi (arbuscular vs. saprophy琀椀c), bacteria (gram-posi琀椀ve vs.
gram-nega琀椀ve) and protozoa. It also
provides the fungal:bacterial ra琀椀o,
which can help a grower discern the
state of their soil (perennial crops
and grasslands perform be琀琀er with
fungal-dominated soils; annual crops
prefer bacterial soils).
Another new test on the market
is the Haney test, which, along with
providing other metrics like amount
PHOTO COURTESY OF BIOME MAKERS
of available nitrogen, measures microbial respira琀椀on. In other words, it
doesn’t measure microbes directly,
but it does give the farmer a general
benchmark on how much microbial
ac琀椀vity is going on underground.
Finally, the newest type of microbial
measurement is the DNA test. It provides a comprehensive analysis of all
the DNA of the biology that’s in the
soil, iden琀椀fying the millions of di昀昀erent
species — both pathogens and bene昀椀cials (although all living organisms can
be either good or bad, depending on
the context) — and categorizing them
into func琀椀onal groups. It has the power to tell growers things like “your nitrogen-昀椀xing bacteria are low” or “you
have plenty of phosphorus-solubilizing
bacteria.” This method of tes琀椀ng holds
enormous promise, although since it’s
new, the benchmarks are only now being established. It’s also expensive —
about $200 per test.
SOIL CHEMISTRY TESTING
Finally, despite all the excitement
(and, at 琀椀mes, hype) over sap, water
and biological tes琀椀ng, tradi琀椀onal soil
chemistry tests are s琀椀ll vital for the
organic farmer. But these days there’s
more available than the tradi琀椀onal
NPK & pH tests, and educated growers can bene昀椀t from a number of different types of soil chemistry tests.
The Haney test, men琀椀oned above
because it includes a biological component, also provides advanced soil
chemistry metrics. In addi琀椀on to the
tradi琀椀onal data (NPK, pH, etc.), it gives
an es琀椀mate of nitrogen credit — i.e.,
pounds per acre of available N in the
soil bank. The test can prove its value
by this metric alone — growers who
know they have X pounds of N available know that they don’t need to apply increasingly expensive inputs. The
test also o昀昀ers several carbon tracking measurements.
A soil mineral assay, also known as
a mining assay or “total nutrient diges琀椀on” test, is an inexpensive test
that’s been available for a long 琀椀me
but that is only now being recognized
for its value. Modern organic farmers understand that the bacteria and
fungi in the soil are able to receive
signals from plants and can transform
molecules from forms the plant can’t
use into bio-available forms, feeding
those new molecules back to the plant
in exchange for root-exudate sugars.
Given this knowledge, a soil mineral
assay tells the grower the total mineral content of their soil, allowing them
to know whether the nutrients their
plants need — whether in available or
unavailable form — are present. Microbes can’t make unavailable nutrients
www.ACRESUSA.com | 5
available if the nutrients aren’t there in
the 昀椀rst place. A soil mineral assay tells
the grower the total elemental composi琀椀on of the macro- and micronutrients
in the soil. This is an inexpensive test
that only needs to be run once.
Finally, there are the tradi琀椀onal acid-extract tests, which are s琀椀ll incredibly useful. Growers should consider
excesses 昀椀rst and seek to address
those. Balancing the soil, par琀椀cularly
for calcium and magnesium, provides
the proper founda琀椀on for healthy
soil. These tests can also iden琀椀fy micronutrient excesses and shor琀昀alls.
An exci琀椀ng development is that in昀椀eld versions of many of the tests discussed above are either available or are
coming soon. On-site tests of course
o昀昀er less precision than in the lab, but
they deliver quicker results. Examples
include meters that can provide leaf
nutrient data (Crop琀椀x) and soil biology insights (MicroBiometer). Simple
refractometers are also insigh琀昀ul for
measuring plant sugar levels (Brix).
Is there any reason organic farmers
should be skep琀椀cal of modern soil and
plant tes琀椀ng methods? Cost can certainly be an issue — not every test described above needs to be performed
on every acre every year. But when
considering cost, growers should remember what they stand to save in
terms of unnecessary input costs —
or gain via improved yields and quality. Educa琀椀on, as well as consul琀椀ng
with a good organic agronomist, is a
wise way to navigate the various testing op琀椀ons available today.
This ar琀椀cle was wri琀琀en by AcresUSA, in coordina琀椀on with the Organic Crop Improvement Associa琀椀on
(OCIA) Interna琀椀onal. OCIA is the TOPP administrator for the Plains Region. This ar琀椀cle is supported
through the United States Department of Agriculture
(USDA) Transi琀椀on to Organic Partnership Program
(TOPP). TOPP is a program of the USDA Organic Transi琀椀on Ini琀椀a琀椀ve and is administered by the USDA Agricultural Marke琀椀ng Service (AMS) Na琀椀onal Organic
Program (NOP).
6 | Copyright AcresUSA
In-昀椀eld tests are beginning to o昀昀er real-琀椀me analysis of plant and soil health.
Crop琀椀x (le昀琀) uses broadband near-IR signals to detect plant nutri琀椀on and
disease condi琀椀ons, and MicroBiometer (right) interacts with a smartphone to
es琀椀mate microbial biomass and fungal:bacterial ra琀椀o.