NUTRIENT DENSE CROPS COURSE — REAL FOOD CAMPAIGN
January 23RD 2011 Taught by Dan Kittredge at The Mountain School, Vershire.
Notes, observations and thoughts from Li Shen and Diana Wright.
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Philosophy
Soil Tests and Mineral Balancing
Seeds & Seed Inoculation
Potting Soils
Monitoring Plant Health
Real Foods Campaign
Other information
STARTING OBSERVATION, CORE ASSUMPTIONS & PHILOSOPHY
The activities and recommendations of Dan Kittredge / Real Food Campaign and the work to
promote nutrient dense crop production start from the observation that food crops in the US have
been declining in nutritional value for many years. An apple bought and eaten today does not
deliver as much nutrition as an apple eaten 50 years ago. The drop in nutritional value seems to
be a decline in the variety and concentration of both minerals and complex molecules (such as
complete proteins and antioxidants).
The goal of the work is to maximize the vitality and health of all aspects of agriculture —
human, animal, crop, and soil life.
The core assumptions about how to reverse the trends in declining nutritional value are:
1) Make sure the necessary building blocks are available to the plants through soil
testing and mineral balancing. The crops will then both grow better and produce a
harvest with higher mineral content. Apparently the replication of human DNA
requires 84 different minerals, so eating food with many different minerals is
important to us.
2) Create the conditions for the plant to grow well so it can mature (reach important
physiological mileposts) before setting fruit or being harvested. The harvested crops
will then contain more complex molecules. The activities under this heading include
monitoring the health of individual plants (Brix tests), building soil ecosystem health
(balance of fungi and bacteria), etc.
3) Select for plant varieties that have the genetic potential to deliver good nutrition and
are well adapted to local conditions through seed saving, seed sorting, and selection.
4) Shift your mindset from “successful farming requires waging war against pests and
diseases” to “successful farming requires healthy plants and soil ecosystems to reduce
the crop’s attractiveness to pests and deliver more nutrition to humans and livestock.”
The motivating philosophy behind this work is that, by attending to the nutritional quality of
crops we can improve human health and
• reach higher individual potential and function better ourselves,
• create better functioning farms (while perhaps reducing total acreage needed as each
plant delivers more nutrition),
• reduce pesticide use and create healthier and more resilient agro-ecosystems.
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Our own genetic potential and that of our crop plants is far greater than we are achieving today.
SOILS TESTS AND MINERAL BALANCING
The principle at play in mineral balancing is Liebig’s Law of the Minimum. This says that, while
plants require several dozen macro- and micronutrients to grow well and produce all of the
molecules and compounds they have the genetic potential to produce, the actual growth and
development will be limited by whichever one nutrient is most deficient. For example, cobalt (a
trace element) is the central element in the vitamin B-12. If cobalt is not available in sufficient
concentration, adding more nitrogen fertilizer will not help the plant produce B-12. On the other
hand, if the ratio of one of the trace elements is excessively high, it can cause the plant to suffer
from other deficiencies.
Mineral balancing addresses a field’s mineral deficiencies and excesses in such a way that the
nutrients are available in proper proportion to each other for the crops being grown. The key here
is to pay attention to the micronutrients. Just because only small amounts are needed does not
mean they are unimportant!
Fall is the best time to do soils testing and to add soil supplements. Both should be done every
year. Annual fall soil tests will show what has been used up over the growing season and will
allow you time to add more minerals well before spring planting.
Soil Tests
Soil acidity (pH)
This often gets too much attention. On most fields (even in New England), getting the mineral
balance right and increasing soil organic matter will tend to bring pH into a good range for most
crops. So, attend to minerals and soil organic matter first.
Test for minerals
There are 3 kinds of soil tests for minerals: strong acid, weak acid, and water.
Strong acid test (the kind used by most ag extension services) is good at helping understand the
underlying mineralogy, but does not show what is actually available to plants in the field under
normal growing conditions. This test may overestimate what is available and so not indicate a
deficiency when there really is one.
Weak acid test better mimics the growing conditions and so shows what is actually available to
the plants in the field.
Water test (ex: home test kits) can to easily underestimate what is actually available to plants,
and so lead you to apply too much of some minerals.
Dan Kittredge uses Logan Labs soil test (see Real Food Campaign website for soil test form).
• Base Plus or Agridyne II Test for non-metals sulfur (S) and phosphorous (P)
• Exchangeable Cations for nutrients available to plants
• Base Saturation/ Strong Acid test, for total levels of non-trace metals: calcium (Ca),
magnesium (Mg), potassium (K), sodium (Na).
• Micronutrients – trace minerals
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Farm Test
Soil sampling
For each field, take 6 cores, 6” deep. Combine these to create a representative soil sample for the
test.
Interpreting the soil test results
Total Exchange Capacity (TEC) or Cation Exchange Capacity (CEC): the capacity of the soil to
hold positively charged ions (cations). A value of 8-12 milliequivalents (ME) is average. Sandy
soils have low CEC due to coarse particle size and lack of negative surface charges to hold
minerals. Clay soils have high CEC because the particles have a huge surface area with many
charged groups on these surfaces, to bind lots of minerals. Humus increases the soil’s holding
capacity, so CEC can be increased by spreading compost, cover cropping, or adding clay
(practical in smaller gardens). The difference between TEC and CEC is that TEC takes into
account the effect of hydrogen, to supposedly give a better reflection of the full potential cation
storage capacity of soil.
Base Saturation: the fraction (%) of CEC that is taken up by each cation In addition to the
desirable macronutrients, cation exchange sites can also be occupied by hydrogen ions.
Recommended Mineral Levels in Soil
The ‘desired value’ of a mineral changes according to the Cation Exchange Capacity (CEC) of
the soil. The soil test will give you your actual value and the desired value for each mineral.
Recommended
levels
Mineral
(as ppm or %
base saturation as
given in soil test
results)
Comments
Macronutrient Anions (negatively charged acid-forming elements)
Sulfur (S)
75 ppm
Water-soluble, leachs out, tend to be low & be
a limiting factor.
Most soils contain 15 ppm S and only achieve
20% of potential yield.
S can get too high in greenhouses. Leave them
open to weather for 3-4 months.
Important in forming essential amino acids &
therefore proteins. N:S ratio of 10:1 in forage test
is an indicator of protein in forage.
Phosphorus (P)
75 ppm
Easily leached from soil. Animal manure leads
to high phosphate levels. Excessive phosphate
inhibits symbiotic fungi.
Macronutrient Cations (positively charged elements)
Calcium (Ca)
70-75%
Ca is treated as a nutrient, not as an agent to
raise pH. Do nothing if soil pH is between 4.5
and 8.5; microbes can adjust local pH.
Ca is important for strong cell walls & internal
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cell signaling. If soils were limed in the past,
probably don’t need more Ca.
Magnesium (Mg)
Potassium (K)
15-18%
The ratio of Ca:Mg:K is important. Mg is
essential to chlorophyll production.
3-5%
Important for fruit size. K deficiency is a
limiting factor, contributes to lower leaves dying
off early.
Trace Elements/ Micronutrients (essential but often toxic in excess)
Boron (B)
3 ppm
Iron (Fe)
60-80 ppm
B (and S) are important for resisting pests &
diseases. B ‘facilitates’ S that ‘facilitates’ Ca. B
enables plants to get Ca from soil. Ca helps cells
resist fungal penetration into cells.
Important for flowering, fruiting & seed
formation. 80-90 ppm is considered toxic by
university extension services, but it is not toxic
when soils have adequate organic matter plus a
healthy biota.
Manganese (Mn)
80-90 ppm
Copper (Cu)
4 ppm
Zinc (Zn)
8 ppm
Aluminum (Al)
<200 ppm
Typically high in acidic New England soils.
Cobalt (Co)
2 ppm
A component of Vit B12 / cyanocobalamine.
Molybdenum (Mo)
1 ppm
Essential for bacterial nitrogen fixation.
Selenium (Se)
0.5 ppm
Silicon (Si)
50 ppm
General Recommendations for Addressing Mineral Deficiencies
Soil Amendments should be added along with organic material (compost, humates, biochar) and
allowed to sit through the winter. Soil microbes will work on powdered minerals, which are not
especially available to plants, to make them into a more available form. Even better would be to
grow cover crops for a year, to incorporate the supplements, or to add the minerals to your
compost pile at first turn.
The exception is soluble mineral salts, - Epsom salts, SulPoMag and wood ash should be applied
to in spring. Borax should be split into three doses and applied at intervals through the season.
In the garden, apply minerals to the entire garden, not just the beds. The roots of plants and soil
fungal filaments penetrate the entire area, well beyond the beds!
Mineral sufficiency increases disease resistance, yield and flavor and the crops are more
nutritious to us. (And to livestock too – if minerals are adequate the grain consumption by
livestock decreases.)
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You will need to calculate how deficient your soil is for each nutrient.
Then look at the amendments available to you. These will often have more than one nutrient in
them, so you may be able to “kill two birds with one stone.” But, you may also need to hold back
on applying an amendment because you don’t want to go over the target on one mineral while
bringing up the concentration of another. This is the balancing act!
Several applications over a growing season are better than one big dump, unless you do it in the
fall. If the field needs more than the recommended maximum application rate, spread the
applications over several years. (Remember, it took centuries of farming to deplete these soils.
Don’t try to adjust everything in one year.)
Deficiency
What to add
Maximum Application Rate
(ppa = pounds per acre)
Sulfur (S) + Ca
Gypsum (Ca sulphate)
up to 500 ppa
S + Mg + K)
SulPoMag
300-500 ppa
S+K
K-mag, K sulphate
200-300 ppa
S + trace minerals
Sulphate salts of trace minerals
Phosphorus (P) + Ca
Colloidal soft rock phosphate
Tenn. brown rock phosphate
black hard rock phosphate
P+K
Compost
Calcium (Ca)
Calcium carbonate (Calcite or
Hi-cal lime)
Also aragonite, eggshells
Ca + Mg
Dolomite (2 Ca : 1 Mg),
calcium magnesium carbonate
500-2,000 ppa
Ca + S
Gypsum
500 ppa
Ca + P
Soft rock phosphate
500-2,000 ppa
Ca + P + trace minerals
Carbonatite
500-2,000 ppa
500-2,000 ppa
500-2,000 ppa
(Note: calcium is a ‘lazy’ mineral and moves slowly into soils and plants)
Magnesium (Mg) +Ca
Dolomite
500-2,000 ppa
Mg + S + K
SulPoMag/K-mag
300-500 ppa
Mg +S
Mg sulphate/Epsom salts
200 ppa
Potassium (K)
Clean wood ash, not from
industry (10% K and 3% Ca in
soluble form) spread in spring
after snowmelt thinly &
evenly.
Application rate not given.
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K +Mg + S
SulPoMag, K-mag
300-500 ppa
K +S
Potassium sulphate
200-300 ppa
K +P
Compost
Trace Minerals
Boron (B)
Borax (11% boron),
up to 30 ppa per year,
Solubor (20 % boron)
up to 15 ppa
split into 3 applications;
excessive
boron is toxic to plants
Manganese (Mn)
Manganese sulphate
5-20 ppa
Copper (Cu)
Copper sulphate
5 ppa (10 if very low)
Zinc (Zn)
Zinc sulphate
5-10 ppa
Example — What Amendment and How Much
Handy rule of thumb
2 lb per acre (2 ppa) = 1 ppm in top 6” of soil.
OR 2 ppa / 1 ppm
A)
Desired/target value for boron (B):
3 ppm
Soil test result for B:
1.41 ppm
Need to raise the B level by:
1.5 ppm (approx)
Recommended total application:
1.5 ppm x 2 ppa / 1 ppm = 3 ppa of B
CHOICES
Borax (11% boron):
3 ppa B / 0.11 lb B per lb borax =
27.3 lb per acre borax
(Note : this under the max application rate of up to 30 ppa per year borax, so it’s OK)
OR
Solubor (20 % boron):
3 ppa B / 0.20 lb B per lb Solubor =
15 lb per acre Solubor
(Note : this just at the max rate of up to 15 ppa per year Solubor, so it’s OK)
In either case, split the total into thirds and apply 3 times over the growing season.
B)
Soil Test
Sulfur (S)
Calcium (Ca)
Magnesium (Mg)
Potassium (K)
Desired
75 ppm
2070 ppm
219 ppm
237 ppm
Measured
64 ppm
2332 ppm
155 ppm
401 ppm
Deficient or Excess?
Deficient by 11 ppm
Excess
Deficient by 64 ppm
Excess
Try to address the deficiencies in S and Mg, without increasing Ca and K.
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CHOICES
Gypsum (Ca sulphate) — Don’t use because there is already excess Ca.
SulPoMag (S, K, Mg) — Don’t use because there is already excess K.
K sulphate — Don’t use because there is already excess K.
Mg sulphate/Epsom salts (Mg + S) — Yes. Apply at up to 200 ppa.
HOW MUCH TO APPLY?
...using the rule of thumb (2 ppa gets you 1 ppm increase)
If you apply 22 ppa epsom salts, you will get 11ppm increase in S and 11 ppm increase in
Mg. This is a good amount of S, but still low Mg.
OR
If you apply 128 ppa epsom salts, you will get 64 ppm S (excess) and 64 ppm Mg.
Conclusion: S is a soluble and mobile nutrient (an anion), so excess is likely to move quickly out
of the field. It is probably OK to put on excess S in order to raise the Mg level sufficiently. So
apply 128 ppa epsom salts. This is under the maximum application rate of 200 ppa per year.
Other Micronutrients (like cobalt, molybdenum, selenium, aluminum, silicon, etc.)
Use glacial gravel till, granite dust, basalt dust, volcanic rock (contains 60 elements) alluvial
outwash clays (e.g. azomite) that can contain 50-60 elements, humates, high energy clays,
biochar, sea minerals (e.g. Sea Crop from Advanced Eco Agriculture.)
Humus
There is a very large debate going on in soils science about what humus and humates really are.
Scientists have recently identified the ‘humus molecule.’
Compost contains in the order of 20% humus.
Humates consist of ancient organic matter in a state between peat moss and coal, and contain 7090% humus.
With high soil humus and healthy microbe populations, plants can withstand some overdoses of
trace elements.
SEEDS & SEED INOCULATION
Newly germinated seedlings must have optimum amounts of nutrients and the proper soil
microbes (inoculants), water, air and temperature available to them immediately. Achieving
robust growth right from the beginning is most important. If seedlings get off to a slow start they
are unlikely to achieve their full genetic potential.
The biggest, heaviest seeds provide the best start. They come from plants that have attained most
of their genetic potential and contain more stored nutrients and minerals.
If you have the opportunity, buy seeds with the fewest number per ounce.
Some suppliers offer seeds graded by size – number 10 seeds are bigger than number 4 seeds.
Others sell ‘unsized’ seed.
None of our regular seed suppliers sells top-quality seed. The growers sieve off the best seeds
before passing the rest on to corporate distributors who then sieve them some more. Places like
Johnny’s and FEDCO have no control over the quality of seed they get. They get seed from
Washington State and even from overseas. High Mowing sells seed they grew themselves.
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(Look up the Organic Seed Alliance on the Real Food Campaign website for efforts to improve
things in the future.)
Once your seeds have sprouted, be ruthless in culling by the length of germination time (keeping
only those seedlings that were quick to sprout). And then cull again in a few weeks by rate of
growth and seedling vitality. Remember, each plant is going to produce more than you are used
to.
Seed inoculation with spores of mycorrhizal fungi and beneficial bacteria is the most important
factor in giving plants a head start. Many beneficial microbe species are now absent from our
soils due to past cultural practices. In general, crop species (except for brassicas) have primary
symbiotic relationships with fungi, while most weed species have symbiotic relationships with
bacteria. The bacteria are there in the soil, but the fungi populations have often been set way
back by over tilling and other soil disturbances.
We can obtain seed inoculants from many sources e.g. BioGenesis. Use one with both fungi and
bacteria. Most of our crops rely more on fungi, except brassicas that rely more on bacteria.
Dan suggests we inoculate our seeds when they are new: Take a fraction of a teaspoon of
inoculant, tip it into the seed packet, shake, tip all into a sieve, collect the unabsorbed inoculant
and use it for more seed packets. Re-close the seed packets and store. The inoculant will stay
viable for years under perfectly dry conditions.
(The next newsletter from Real Food Campaign will carry an article about inoculants.)
POTTING SOILS
Consider adding mineral supplements to potting soil. (See article in Dec RFC newsletter on
constituents of potting soil from different sources.)
Most potting soils are deficient in calcium and trace minerals. In such soil the plant may have
lost 40-60% of its yield potential by the time it is transplanted to the field.
Potting soils may contain excessive nitrogen, which is not beneficial.
(One of the course participants recommended Elliott Coleman’s blocking mix as a potting soil.
Dan refused to give any recommendations.)
MONITORING PLANT HEALTH
More on this over the growing season.
The Brix Refractometer is a handy way to monitor some less visible aspects of plant vitality
through the growing season. (The Johnny’s Seed catalog also says that they use it in their squash
breeding program.)
Brix is a measure of the bending of light by a liquid (such as plant sap or fruit juice). The Brix
units are calibrated on the density (or specific gravity) of sugar solution. Calibration: one Brix
unit = how much light is refracted (bent) by passing through a 1% sucrose solution.
Juice is squeezed from the plant sample with a garlic press or modified vice grips. A drop is
placed on the glass of the refractometer, covered with a second glass and read through the
eyepiece. (Dan uses a maple sap refractometer, 0-32 Brix units.)
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In practice, refraction is not only caused by dissolved sugar, but by the sum of all the dissolved
compounds in sap or juice, including sugars, amino acids, minerals and oils.
The higher the concentration of sugars, minerals, etc. in the sap, the greater the bend in the light
and the higher the Brix number. The target Brix reading for leaves is 12.0. (See Brix chart on
RFC website.)
Brix is generally a measure of quality, but it can be subverted. Thus if plants are not watered for
two weeks their Brix values will increase because they are dehydrated which has the effect of
concentrating their soluble constituents.
REAL FOOD CAMPAIGN
Food Quality Metering Project
How can food quality be measured objectively?
RFC has developed a ‘point and shoot’ ‘tricorder’ that measures crop and produce quality using
near infra-red spectrum analysis. The tricorder measures 25 different parameters related to
mineral content, vitamins, anti-oxidants, flavor etc.
The next goal is to test the tricorder on half a million pieces of produce from growers across the
USA. The spectrum analysis will be correlated with lab analysis of minerals and nutrients in
samples of the same produce. From each batch of produce, 500 tricorder readings will be taken,
along with 5 lab analyses. The soil type, soil history, seed varieties, planting date , farming
practice etc will also be noted.
The Anecdotal Documentation Project
Dan said that if we use the soils tests and amendments as specified by RFC they will give us
foliar sprays and drenches. In return we are asked to document the growth of our crops, take
pictures, measurements etc and put our profiles and results on the website.
OTHER INFORMATION
Essential oil spray for late blight: Myco-Stat
Good potting soil (Liana Hebb): Vermont Compost Fort V
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