Organic Amendment User’s Guide

The organic amendments described here are available as OMRI certified.  Note that in some cases, especially with the micronutrients, OMRI certification requires that a deficiency be measured on a soil test before application of the amendment is allowed.

Nitrogen
Phosphorus
Potassium
Calcium
Magnesium
Sulfur
Boron
The sulfates and chelates
Silicon

Nitrogen Amendments

Soybean Meal

A good source of nitrogen, and may be obtained from organically grown soybeans.  The trouble is that until it is digested by microbes it tends to set plants back and keep them from growing.  It is best used in a situation where it may be applied at least 2-3 weeks before planting.  For more information see this study from North Carolina State University.

Feather Meal

A good, slow release source of nitrogen.  One application at planting is often enough for the entire crop.  Although it is acceptable for use as an OMRI amendment, recognize that the bag you buy at the feed store is likely a product of industrial chicken farming.  

Bat Guano

A potent source of nitrogen – a little goes a long way and it’s easy to overdo it.  This is product that is mined from natural deposits in caves.

Amino Acids

This is a fairly new product on the amendment scene.  Amino acids come as a soluble powder and therefore are suitable for soil drench or foliar feeding rather than as a one-time soil amendment at planting.  They have the advantage of being very available and are suitable for fine tuning your nitrogen application.

Fish Fertilizer (liquid concentrate)

Not to be confused with fish hydrolysate (which can be a good source of phosphorus).  Some of these fertilizers are high in nitrogen without much added phosphorus or potassium.  As a liquid it must be applied fairly frequently.  Despite it being “deodorized” the stuff really doesn’t smell good.

More about nitrogen


Phosphorus Amendments

A word about fertilizer labels…  Many fertilizers are labeled with three numbers, N, P and K.  For example, Alaska fish fertilizer is 5-1-1.  The “P” number reported is actually phosphate, P2O5, which is about 44% phosphorus.  The “K” number is actually potash, K2O, which is about 82% potassium.

Soft Rock Phosphate

A mined product that is good for bringing up the overall phosphorus level in the soil.  Although it averages 20% P2O5, only 2 – 3 % is available, and then only in acid soils.  Under neutral to alkaline soil environments its effect is almost non-existant.  A biologically active soil increases phosphorus availability, perhaps because organic acids around biological systems decrease soil pH.  Unlike MAP or DAP, the presence of soft rock phosphate in the soil does not discourage plants from forming micorrhizal associations, according to Dr. Christine Jones.  In our experience it takes several years for the effect of a soil application to be fully realized.  

Bone Meal

A product of industrial agriculture, bone meal is a source of phosphorus.  It also contains sodium in relatively high quantities.  We have used bone meal as an amendment under fruit trees, only to find that voles were attracted to it (perhaps to the sodium) and undermined the tree to get at it! 

High P Fish Hydrolysate 

This is a liquid fish concentrate that has been cold processed using phosphoric acid (e.g. Neptune’s Harvest Fish Fertilizer).  As with all liquid products it would be applied through the growing season rather than as a bulk application before planting.


Potassium Amendments

A word about fertilizer labels…  Many fertilizers are labeled with three numbers, N, P and K.  For example, Alaska fish fertilizer is 5-1-1.  The “P” number reported is actually phosphate, P2O5, which is about 44% phosphorus.  The “K” number is actually potash, K2O, which is about 82% potassium.

Compost

Compost usually has a large amount of plant available potassium, and repeated applications of compost can result in a buildup of excess potassium in the soil.  That said, compost is the best source of potassium for a soil, due to all of its other benefits.  Our potassium targets are on the low side so that compost may be continued to be applied.

Potassium Sulfate  

This is a good source of potassium for soils where compost applications or SulPoMag are not appropriate.  Much of the North American production comes from the Great Salt Lake in Utah.

K-Mag, Langbienite or SulPoMag

This is a mined product that has a high amount of potassium, magnesium and sulfur in a form that is readily available to plants.  It is our understanding that if your soil needs these three elements, this is a good choice.

Greensand

Greensand is a mined product that contains a high percentage of the green mineral glauconite.  Although it has a fairly high potassium content, the potassium solubility is extremely low, <0.1% of the total potassium present, and thus is not a good source of potassium.

Kelp

Kelp is a good source of potassium along with balanced micro-nutrients, and is a bio-stimulant.  It may be found in liquid concentrate form for application throughout the growing season.  It is a good product to add to other foliar nutrient sprays, since it helps increase biological activity.  Bagged powdered kelp, although expensive, is also available.  

Wood ashes

Ashes are the white powder left by complete combustion, and are not to be confused with biochar or charcoal. The nutrients in wood ash vary according to their source, and have a fertilizer value of perhaps 0-1-7, and are 25% to 45% calcium compounds. They are extremely alkaline, impact soil biology, and will raise pH. Our ashes go into the greenwaste container, never into our neutral/alkaline soil. It is better to raise soil pH and increase calcium with lime and increase potassium with compost or potassium sulfate (if potassium is deficient) than it is to use wood ashes as a soil amendment.


Calcium Amendments

Ag Lime (Calcium Carbonate)

Agricultural (ag) limestone (lime) is a mined material primarily made up of calcium carbonate. While it supplies plenty of calcium, it also raises the pH of the soil due to the carbonate component.  Some soils need this liming agency plus the calcium. In those cases it is a very appropriate amendment.  

You may be offered a choice of grades – the grade is the fineness of grind of the limestone.  In general finer grades will be faster acting.  

Ag lime takes up to three years to become fully available in the soil, with relatively equal amounts of calcium available each year.  During this time the standard soil test, Mehlich 3, will give erroneous results for CEC and the amount of available calcium.  Instead of using the M3 test, if ag lime has been applied in the last three years the AA8.2 test should be used.

Dolomite

The existence of dolomite is a good reason to get a soil test before applying any mineral.  Dolomitic limestone contains calcium along with a healthy dose of magnesium.  If your soil does not need magnesium, dolomite is not an appropriate amendment.  Magnesium, while an essential plant nutrient, is rather hard to remove from soil when in excess and tends to tighten soils.  Many sticky clay soils have excess magnesium.  

OrganiCalc carefully calculates the amount of dolomite a soil needs to balance magnesium with the other cations.  Additional ag lime may also be recommended and it is important to include it as ag lime rather than substituting dolomite.  

Gypsum

Gypsum is calcium sulfate and so it is a source of both calcium and sulfur.  Unlike ag lime, it does not change the pH of the soil.  It is a very appropriate amendment for supplying calcium in cases where the pH is already over 6.6, even if there is adequate sulfur in the soil.

Gypsum is relatively soluble in the soil and is used in cases where there is an excess of sodium or potassium or magnesium, along with enough water to move the excesses down through the soil profile.  The sulfur in the gypsum will solubilize the excesses and allow them to move out with the water.  

Gypsum takes about 6 months to become fully available in the soil.  If gypsum has been applied in the last 6 months the AA 8.2 soil test should be used instead of the Mehlich 3.

Oyster Shell Flour

This product is also available as a fast acting source of calcium.  It has about the same amount of calcium as ag lime and may be substituted for ag lime.  Like ag lime it will raise pH.


Magnesium Amendments

Magnesium Sulfate (Epsom Salts)

A very soluble source of magnesium.  This is the same powder you may have dissolved in water to soak a sprained ankle.  Because of its solubility this product is best applied in small doses over time or as a drench or foliar spray.  

Dolomite

See the discussion above under calcium amendments

SulPoMag

See the discussion above under potassium amendments


Sulfur Amendments

Gypsum

Gypsum is a good source of sulfur as well as calcium (see discussion under calcium amendments).  In cases where a soil is in need of sulfur does not have excess calcium, gypsum is a good amendment.  The sulfur in it is readily available but is not toxic to soil biology.

Ag Sulfur

This is elemental sulfur and should be used in a limited manner to supply sulfur when gypsum is not appropriate but sulfur is needed.  In large doses sulfur can be toxic to soil biology and because of this OrganiCalc limits the amount that can be applied at any one time to 100 pounds per acre or less. Sulfur is a necessary element for plant growth and some soils tend to be very low in it.  Sulfur also reduces the pH of the soil and it can be used to remove excesses of cations such as calcium, magnesium.  

Ag sulfur is also useful in cases where the soil pH is too high. For example, if soil PH is high due to the use of high pH irrigation water, sulfur may be used to lower the pH.  However, in some cases high soil pH is due to the high pH of the soil parent material and it is futile to attempt to lower the pH with sulfur.  

More about sulfur


Boron amendments

Borax

This is a mined product that may be found in the laundry detergent section the grocery store.  The white granular powder is somewhat soluble.  Boron is a necessary nutrient but it is toxic in excess, so it is worth considering how it will be applied.  One method of application is to dissolve borax in water and spray it evenly on the soil.  Another method is to mix the powder evenly with bulkier amendments and spread the result evenly.  Borax lends itself to the latter method.

Solubor

Solubor is a more soluble form of boron with twice the elemental boron as borax.  If using it as a replacement for borax, use 1/2 as much.  It is best used dissolved in water and either sprayed evenly on the soil, or as a foliar.

Iron (Fe), Manganese (Mn), Copper (Cu), Zinc (Zn), Cobalt (Co) amendments


The sulfates and the chelates

All the elements listed above are available as sulfates (e.g. iron sulfate).  The sulfates may be applied to the soil but they are not generally plant available form.  They must be metabolized by the soil biology before being transformed into a form that plants can take up.  

Manganese in particular is difficult to get into the plant by broadcasting manganese sulfate due to manganese forming tight bonds with other elements in the soil that cannot be broken by soil biology.  The manganese becomes unavailable.  

More about copper


Silicon amendments

The silicon in sand is fairly tightly bound up and despite silica, SiO2, being the main component of sandy soil, it is not very soluble in the soil solution.

Wollastonite is a mined source of silicon in the form of  calcium inosilicate, CaSiO3.  Silicon uptake in the plant has been found to correlate to low susceptibility to powdery mildew and rusts and wollastonite has been found to be a good source of silicon for the plant.  This link reports a field trial of various silicon and liming sources on powdery mildew in pumpkins.

Basalt rock dust has been found to release silicon in low pH, weathered soils.  Basalt rock dust has other advantages of increasing nutrient availability in these soils and in areas where basalt is found, such as the northeast US, it may be obtained relatively inexpensively.