Enlivening
Soil using Organic Fertilizers
by Carl Rosato
Soil Fertility
Fertile soil is a mixture of
well-balanced minerals, high organic matter, good aeration and bountiful soil life. The
biology or life in the soil is at its healthiest when the nutrients are plentiful and balanced, and there is sufficient oxygen. The
top few inches of soil is the most vital, holding about 70% of the life and 70% of the organic matter. Below
6 inches the roots are feeding on mostly soluble nutrients since the micro-organisms are not able to thrive without sufficient
oxygen.
It is crucial to leave the soil as undisturbed as possible.
Increasing the quantity of earthworms and planting deep-rooted plants will let air into lower levels
of the soil. Micro-organisms like bacteria, fungi, actinomycetes, algae, nematodes and
protozoa, need oxygen to contribute directly to the release of nutrients to the plant. There
are many symbiotic relationships going on between roots, organic matter, clay and micro-organisms to support the plant. Soil
that is worked too wet annihilates air and water space, destroying the environment that microbes need. Tending soil for optimum
production means adding minerals and compost every year. Balanced, fertile soil makes
for higher yields, better flavor, less disease and insect pressure and more nutritious food.
Compost
The best
and cheapest organic fertilizer is compost. It contains organic matter, calcium, phosphorus,
potassium, nitrogen and many micro-nutrients and is a great food source for the biology in the soil. Compost
made from plant residues and animal manures that have been fully decomposed can be applied every year at 1 to 8 tons per acre. Compost
made from branches, leaves and plant residues without manures are best for orchards since this best supports fungal growth. Forests
have soils that are inhabited predominantly by fungal growth. Orchard soil biology closely
resembles forest soil biology. Compost made with manure supports bacterial growth
which is good for annual plants. Compost containing woody residues mixed into the soil robs plants of soil
nutrients. Too much compost in the soil is hard for the soil to break down quickly and
will temporarily tie up nutrients.
(Note: 1/10
inch of compost per acre = 40 tons)
Taking a Soil Sample
The aerobic zone is usually only 6-7” deep and should be all you need to sample. Using
a tube type soil probe or a shovel, take a minimum of five probes in different zones of the area being tested. Mix
the soils together for each sample. It should be about 1½ cups.
The highest rates of soil fertility are seen in the testing done in May and June, the lowest in the winter.
Reading the Soil Test
There are many labs around the country that give soil results. The
following recommendations are based on lab results from A&L Ag Labs inModesto, California. Every lab uses different testing methods so the numbers
will not be the same. It is best to use one lab consistently to track annual results.
(Note: To covert pounds per acre to pounds per 100 square feet divide by 440.)
Organic Matter (O.M.)
Increasing organic matter levels
will help with the soils texture, structure, drainage, aeration, water holding capacity and dramatically improve soil biology. Working
soil wet destroys organic matter. Organic matter (humus) holds three times more nutrients
than clay.
2% Organic matter is poor. Over
4% O.M. is ideal.
Phosphorus
Phosphorus is most important in the
storage and transfer of energy in the plant. It is essential in every metabolic process,
protein synthesis, and nitrogen fixation. It is crucial for root development. Optimum
phosphorus levels are needed for rapid seedling growth, winter hardiness, disease resistance, efficient water use, early maturity,
and maximum yield. Phosphorus needs to be placed where it will be used, as it is less
mobile in the soil than any other nutrient.
Phosphorus becomes immobilized at
low pH by large concentrations of aluminum, zinc and iron, and at high pH by too much calcium.
Soft rock phosphate is the fastest working phosphate. 300#/acre is the minimum
application. 2000#/acre of soft rock phosphate should supply enough phosphorus for decades.
P1 tests immediately availability. 25 ppm is the minimum and
above 40 ppm is ideal.
P2 tests for future availability. 40
ppm is the minimum and above 60 ppm is ideal.
Potassium
Potassium is a regulator of metabolic
activities. It is essential for photosynthesis and protein synthesis as well as carbohydrate
transport and storage. It promotes root reserves, winter hardiness, cell development,
strong walls, and reduces stalk lodging. Potassium improves water use efficiency, increases
yield, improves crop quality, and reduces incidence of disease.
Most soils
have less than 1% of the potassium available. There are about 30,000 to 50,000 lbs. per
acre of potassium in an average soil. It is possible to release small amounts of potassium
over time by increasing microbial activity with compost.
Apply sulfate of potash in April
for orchard crops. Avoid winter and autumn applications as the potassium will be tied
up in the soil before it can be used.
Too much potassium ties up boron and manganese.
2% cation saturation potassium is the minimum and 5% is much better.
Magnesium
Magnesium is an essential component
in the chlorophyll of green plants. It is also necessary for metabolic processes and
in every operation involving phosphorus. Magnesium levels have important interactions
with calcium, sulfur, and nitrogen. The ratio of magnesium to calcium should be around
one to six.
Having a soil with too much magnesium will take more
nitrogen because the excess magnesium makes the soil too tight.
The higher levels
of magnesium in a sandy soil will help to tighten the sand. For sandy soil the optimum
would be 16% to 20% and for clay soils closer to 12%. It will always be necessary
to add more nutrients to a clay soil than to a sandy soil.
(Note: Two pounds of sulfur
will take out one pound of magnesium when there is at least 60% calcium.)
Calcium
Calcium is part of cell walls and membranes; it controls movement in and out of cells, reacts with
waste products and neutralizes toxic materials. Calcium activates many enzyme systems,
it improves microbial activity and it enhances uptake of other nutrients. Having the
correct amount of calcium in the soil will require less nitrogen. The calcium will loosen
the soil and make more nitrogen available. Too much calcium can tie up all other nutrients
especially magnesium, potassium, boron, zinc and copper.
Calcium cation saturation needs
to be over 60% before you add gypsum (calcium sulfate) to lower excess magnesium otherwise the sulfur in the gypsum will take
out the calcium first. Add limestone first to raise calcium to 60%, and then add enough
gypsum to raise calcium levels to 68%. One third of applied calcium will become available
the first year and it takes 3 years to be completely utilized.
Limestone applied to the surface of the soil will work its way into the soil at the rate of 1” per year.
(Note: Applying more than 1 ton per acre of gypsum will put too much sulfur in the soil. Don’t
add over 4 tons per acre of limestone in any one year.)
Sodium
Widespread in nature, sodium is found in all plant material in amounts large enough to be analyzed. Yet
although it does not seem to be necessary to the growth and development of plants, it is used advantageously, particularly
when potassium is low. Sodium seems to be able to partly substitute for potassium.
Excess sodium is a problem in many dry areas. Sodium toxicity
to plants is often observed in saline and alkali lands and unfavorable soil structures can be present due to high sodium as
well. Any time your sodium and potassium together are over 10% then the manganese won’t
be able to get into the plant.
With sodium levels below .1 % add 200 lbs. rock salt to raise levels to over .5%. Apples
get their best color with sodium levels over .5%. .5 - 3% is ideal.
pH
The acidity and alkalinity of soil is measured as pH . For
the most fertile soil,
the cation saturation is balanced and the pH will fall into
a range of 6.3 – 6.8.
C.
E. C.
C. E.C. is the Cation Exchange Capacity and is a number which represents the
soils ability to hold onto nutrients. A sandy soil has a C.E.C. of between 4 and 9 and
cannot hold onto very many nutrients. A heavier clay soil would have a C.E.C. of over
16 and hold more nutrients than a sandy soil
Cation Saturation
Cation saturation is the percentage of calcium, magnesium, potassium, sodium and hydrogen on a
soil test. The ideal calcium would be 68% to 72%. The
ideal magnesium depends on how much sand or clay the soil contains. For sandy soil the
optimum would be 16% to 20% and for clay soils closer to 12%. The ideal potassium
would be at least 2% and 4% to 6% is better. The ideal sodium is at least .5% and not
over 3%.
Nitrogen
Nitrogen is an essential constituent of proteins such as chlorophyll, enzymes, and hormones. It
has a predominant role among the soil nutrients and is needed in substantial amounts, but is also the most likely to be deficient. It
is rapidly used by crops, can be volatilized into ammonia, and is easily leached. However,
an excess of nitrogen can produce an imbalance in plant metabolism resulting in poor plant quality and susceptibility to pests
and disease.
Dangers of nitrogen overuse include: zinc deficiency,
copper deficiency, burns out humus, drives out calcium but leaves magnesium and depletes sulfur. The more excess nitrogen
that you use the more you will have to replace nutrients that were carried away by the leached nitrogen.
Nitrogen and sulfur can leach out calcium. Nitrogen never
leaches out magnesium, only sulfur does.
Sulfur
Sulfur is a component of several amino acids which
are essential for forming plant protein. It helps develop enzymes and vitamins, promotes
nodule formation on legumes, aids in seed production, is necessary for good root development, improves taste, increases protein
and reduces nitrates.
Sulfur is often deficient in organically managed
soils. Without sufficient sulfur the rate of organic matter decomposition is decreased. Humus
helps hold sulfur in the soil. Sulfur feeds microbes and builds organic matter levels. Sulfur
is very soluble and needs to be added in some form every spring.
Two pounds of
sulfur can leach out one pound of either calcium or magnesium.
Sulfur can also
leach out sodium and boron.
Sulfur at 10 ppm. is the minimum and over 15 ppm. is
ideal.
(Note: Don’t apply more than 400#/acre sulfur or seed will have trouble
germinating and soil biology will be damaged.)
Zinc
Zinc is essential for the transformation of carbohydrates
and formation of protein.
Zinc should always be at a higher level than copper.
36% Zinc sulfate is the best form to apply.
10 lbs.
of zinc sulfate will raise zinc levels 1.8 ppm.
Don’t add more than 40#/acre
of zinc sulfate to raise levels 7.6 ppm.
Zinc is needed at a minimum of 4 ppm; 6 to 8 ppm
is ideal and above 10 ppm is excessive.
Manganese
Manganese holds and sets fruits, vital in many plant functions.
Manganese sulfate is 23-27% manganese and it is the best form for raising soil levels.
25#/acre of manganese sulfate will raise levels by 3.5ppm.
Add a maximum of 200#s/acre of manganese sulfate to raise levels 28ppm.
Manganese is needed at a minimum of 20 ppm, 40 ppm is ideal.
Iron
Iron is essential for the formation of chlorophyll and for photosynthesis.
Iron always has to be higher than manganese; when manganese is higher than iron it will tie up the iron. Over
75% cation saturation calcium will start tying up iron.
Ferrous
sulfate is the best form to apply. (Note: Don’t get it on the leaves or it will
burn them. Ferrous sulfate will stain concrete.)
100#/acre ferrous sulfate will raise iron levels 10.5 ppm.
Don’t
apply more than 400#/acre ferrous sulfate per year to raise levels 44 ppm.
Iron is
needed at a minimum of 20 ppm, over 50 ppm. is ideal.
Copper
Copper is a enzyme activator and is a catalyst for respiration.
Copper and boron are disease fighters. High organic matter soils tie up copper,
most severe copper deficiencies are on high organic matter soils. Excessive copper can
effect phosphate, zinc and iron uptake.
Above 10 ppm, plenty of phosphates are needed
because copper can tie up phosphorus the same way phosphorus can tie up copper.
Too much
nitrogen stops the uptake of copper.
Add no more than 10#/acre of 23% copper sulfate
every six months to the soil, this will raise soil levels .6ppm.
Copper is needed
in the soil at 1.5 ppm minimum and over 4 ppm is excessive.
Boron
Boron promotes maturity with increased set of flowers, fruit, yield and quality.
Boron is necessary for nitrogen conversion. Good boron levels
make for good disease resistance
Boron is the only micro-nutrient
that once corrected will still need to be applied every few years.
For excessive
boron levels, make sure you have good calcium levels and then emphasize potassium. High
calcium soils can cause a tie up of boron.
Add no more than 10# Solubor per
acre once a year to raise levels .2 ppm.
For fungus control keep boron
levels above 1.5 ppm.
Boron levels of .8 ppm is the minimum, 1.5 ppm is ideal and
2 ppm is the maximum.
Formula to determine the optimum nutrient levels.
To figure desired calcium: CEC X optimum % (68%) X400 minus existing calcium.
To figure desired magnesium: CEC X optimum % (12% to 18%)
X 240 minus existing magnesium.
To figure desired potassium: CEC
X optimum % (5% to 7%) X 390 minus existing potassium
An example for calcium would
be a soil with a CEC of 10.0, and a desired calcium percent of 68%. Change from PPM to
#/acre on soil test by multiplying by 2.
10 X .68 X 400 = 2720 lbs. of
calcium. If the soil already has 2120 lbs. of calcium, 2720-2120
= 600 lbs. of calcium needed. With 600 lbs. of calcium in a ton of limestone this soil
would require a ton to raise calcium levels to 68%.
Organic Fertilizers
· Kelp is a good source of micronutrients. Add
400 lbs. per acre to give the soil a balanced dose of micronutrients.
· Magnesium sulfate (Epsom salts) has 10% magnesium and 6% sulfur.
· Dolomite has 11% magnesium and 25% calcium.
· Potassium-magnesium-sulfate (sul-po-mag) has 11% magnesium,
22% sulfur and 22% potassium.
· Limestone is about 33% calcium. Don’t
apply more than 4 tons of limestone in any one year.
· Gypsum contains about 22% calcium and 16% sulfur. Gypsum
will not change the pH because the sulfur and the calcium balance each other out. Don’t
apply more than 1 ton /acre of gypsum or else there will be too much sulfur in the soil.
· Soil Sulfur is 92% sulfur
· Sulfate of potash has 50% potassium and 18% sulfur.
· Azomite is a ancient seabed deposit. Apply
at 400 to 1,000#/acre.
· Activate is a humate. Apply
at 50 to 400#/acre.
· Nutra-min is a ancient seabed deposit. Apply
at 400 to 2,000#/acre.
Tricks of the trade!
· Sweetness? Keep high levels of potassium, copper, sulfur and
phosphorus.
· For disease resistance keep high levels of copper, boron and
phosphorus.
Recommended Reading:
· The Soul of Soil, Grace Gershuny & Joseph Smillie
· Hands on Agronomy, Neil Kinsey
· Fertile Soils, Robert Parnes
· www.omri.org for information about organically approved fertilizers.
Carl Rosato
Soil Consultant
6176 Old Olive Hwy.
Oroville Ca. 95966
(530) 589-1696
