Organic Nutrients 101

by Andres Dean  •   More and more growers and gardeners are becoming interested in organic cultivation as a clean and safe alternative to conventional agriculture and synthetic fertilizers. But the world of organic nutrients can be overwhelming to the uninitiated.

Here, we provide a brief overview of many of the most common organic fertilizer commodities. These organic nutrients are derived from three sources; mineral products mined from the earth, plant products, and animal products.

It should be noted, however, that because these organic inputs come from the natural world, a level of variability in terms of physical and chemical properties, as well as quality, is expected among different sources of these products. It’s recommended to source your organic nutrient products only from trusted, reputable suppliers.

 

 

The Most Common Organic Nutrients

Alfalfa Meal

Typical N-P-K: 3-0-3

Alfalfa Meal provides nitrogen and potassium as well as calcium, magnesium, and other micronutrients and trace elements. It helps to stimulate the growth of beneficial microbes and earthworms as well as contributing organic matter to the soil and improving soil structure. Alfalfa Meal contains the naturally occurring plant growth hormone Triacontanol, as well as the naturally-occurring wetting agent Saponin. Finally, Alfalfa is a biologically active product and can serve as a microbial inoculant for compost teas and extracts.

Agricultural Lime

Agricultural Lime is calcium carbonate mined from limestone or chalk deposits and pulverized into a fine powder. Lime is an effective and inexpensive way to add calcium and raise the pH of agricultural soils.

Basalt Rock Dust

Basalt Rock Dust is mined volcanic rock, finely milled to increase the surface area. The broad spectrum of minerals and trace elements in Basalt Rock Dust provide the nutrients needed by the essential bacteria, fungi, and other microorganisms that make up the soil food web, as well as providing a wide range of essential plant micronutrients.

Blackstrap Molasses

Typical N-P-K: 0-0-3

Blackstrap Molasses contains a wide variety of nutrients and trace elements as well as carbohydrates which act as an immediately available energy source for soil bacteria, boosting the bacterial life in the soil and enhancing the soil food web.

Blood Meal

Typical N-P-K: 14-0-0

Blood Meal is derived from dried and sterilized blood from the animal agriculture industry. It is the highest percentage source of natural organic nitrogen, essential for vegetative growth in plants. Blood Meal is highly soluble and is quickly made available for plant uptake. Blood Meal is also a good source of iron.

 

Bone Meal

Typical N-P-K: 2-14-0

Bone Meal is ground and sterilized bones from the animal agriculture industry. It is an excellent source of phosphorus, and provides calcium and nitrogen as well. Research shows that phosphorus availability from bone meal may be diminished when soil pH exceeds 7.

Cottonseed Meal

Typical N-P-K: 5-2-1

Cottonseed Meal is a byproduct of cotton production. It is the leftover husks after the cotton has been processed and the oil has been extracted. Cottonseed Meal is a great source of organic nitrogen as well as phosphorus and potassium. It is also somewhat acidic, which makes it an excellent choice for plants that thrive in lower pH soils such as roses and blueberries. Most cotton production today is genetically engineered, and only non-GE Cottonseed Meal is acceptable for use in certified organic crop production.

Crustacean Meal

Typical N-P-K: 4-1-0

Crustacean Meal is made from the ground exoskeletons of crustaceans such as lobsters, crab, shrimp, and prawns. Some products may contain a mixture of different animal shells while others may be derived from a single species such as Crab Meal or Shrimp Meal. All are good sources of nitrogen, phosphorus, calcium and magnesium. Crustacean Meal also contains chitin, which has been demonstrated to activate systemic defenses in many plants. 

Dolomite Lime

Dolomite Lime is composed of calcium magnesium carbonate and is mined from dolomite deposits and ground into a powder. It can be applied to raise soil pH, and may be a good substitute for Agricultural Lime in soils where increased magnesium levels are desired.

Epsom Salts

Epsom Salts are the common name of Magnesium Sulfate which is commonly used in gardening as a source of magnesium, an important plant nutrient.

Feather Meal

Typical N-P-K: 12-0-0

A high percentage source of natural organic nitrogen, Feather Meal is derived from sterilized and ground feathers from the poultry processing industry. It is less soluble than Blood Meal, and as a result the nitrogen is released more slowly for uptake by plants.

Fish Meal

Typical N-P-K: 9-6-1

Fish meal is a commercial fishing byproduct made from the bones and offal left after processing. It is an excellent source of nitrogen, phosphorus, potassium, calcium, and micronutrients. 

 

Fishbone Meal

Typical N-P-K: 4-16-0

Fishbone Meal is a byproduct from commercial fisheries. One of the highest natural sources of available phosphorus, it also contains nitrogen, calcium, and magnesium.

 

Glacial Rock Dust

Glacial Rock Dust is mined from glacial moraines deposited in the last Ice Age. These glaciers scoured through multiple mountain ranges with different geologic histories, resulting in a highly diverse mineral composition. The broad spectrum of minerals and trace elements remineralizes soil, providing the nutrients needed by the essential bacteria, fungi, and other microorganisms that make up the soil food web, as well as providing a wide range of essential plant micronutrients.

Greensand

Greensand is mined Glauconite, an iron potassium silicate mineral that also contains a broad spectrum of other trace elements that feed the soil food web. It provides a natural slow release of these nutrients, and is also useful in breaking up hard clay soils and improving soil structure.

 

Gypsum

Gypsum is mined calcium sulfate which adds calcium and sulfur to the soil. It is particularly useful as a way to add calcium without raising pH levels like agricultural lime and dolomite do.

High Nitrogen Bat Guano

Typical N-P-K: 7-3-1

Bat Guano is essentially a bat manure product, rich in nitrogen, phosphorus, potassium, and micronutrients. It is an excellent option for vegetative growth, but it can be a vector for the fungus that causes White-nose Syndrome in wild bat populations. For this reason, sale has been discontinued in Canada.

Insect Frass

Typical N-P-K: 3-1-3

Insect Frass is a rich fertilizer containing nitrogen, phosphorus, potassium, and essential plant micronutrients. It is derived from the droppings and exoskeletons of insect larvae. Frass also contains chitin as well as chitinase, an enzyme that helps to break down chitin. For this reason, Insect Frass may be of interest to growers looking to trigger certain responses related to plant defense. If it has not be sterilized as part of the production process, it can be an excellent biological inoculant for compost teas and extracts.

 

Kelp Meal

Typical N-P-K: 1-0-3

The most popular Kelp Meal is ground Ascophllyum Nodosum North Atlantic Kelp which contains a broad spectrum of plant nutrients and trace elements, as well as numerous natural compounds beneficial to plants and soil microorganisms. (Read next: How to Build a Super Soil)

 

Langbeinite (K-Mag)

Typical N-P-K: 0-0-22

Langbeinite is a potassium magnesium sulfate mineral naturally occurring as pretty pink crystals. Containing 22% Potassium, 11% Magnesium, and 22% Sulfur, Langbeinite is neutral so it will not affect soil pH when added to provide these nutrients. It is often used on plants with a low salt tolerance.

 

Leonardite

Leonardite is a mineral formed from fossilized soil humus and is used as a source of naturally occurring humic and fulvic acids.

 

Mineralized Phosphate

Typical N-P-K: 0-13-1

Mineralized Phosphate, also referred to as High Phosphorus Bat Guano or Fossilized Bat Guano, is an excellent source of phosphorus and also contains calcium. It is mined from biogenic deposits in caves in Pacific Island countries. 

Neem/Karanja Cake

Typical N-P-K: 4-1-2

Neem cake and Karanja Cake are made from the residue left over after the oil has been extracted from the kernels. Although Neem and Karanja are different plant species, Neem and Karanja Cake have very similar horticultural uses and are therefore often mixed together or used interchangeably.

Neem and Karanja are excellent sources of non-animal derived nitrogen. Neem/Karanja Cake enhances soil structure, increases water-holding capacity, and has been known to increase earthworm populations. 

Oyster Shell Flour

Oyster Shell Flour is derived from ground oyster shells. It adds calcium to the soil while also balancing acidic soils. Oyster Shell Flour can be used as an alternative to agricultural lime, but the pH buffering effects will typically occur more gradually. It is also a source of micronutrients and trace elements.

 

Potassium Sulfate

Typical N-P-K: 0-0-50

Potassium Sulfate is the primary source of potassium, one of the three most important fertilizer plant macronutrients and is used throughout agriculture and horticulture. The world’s largest potash reserves are located in Saskatchewan, and depending on the manufacturing process, many are acceptable for use in certified organic crop production. (Read next: 8 Tips for a Successful Side-by-Side Grow Trial)

 

Rock Phosphate

Typical N-P-K: 0-3-0

Rock Phosphate is a mined mineral and is a cost-effective source of phosphorus and calcium. Most Soft Rock Phosphates have a lower amount of available phosphorus (P2O5) typically ranging from 3-8%, but have a much higher total phosphorus often around 27%, which is gradually released to plants over 3-5 years.

Soluble Seaweed Extract

Typical N-P-K: 0-0-17

Soluble Seaweed Extract is a concentrated extract of Ascophyllum Nodosum North Atlantic Kelp and is used as a water-soluble application of the plant micronutrients, trace elements, and natural compounds beneficial to plants found in North Atlantic Kelp.

Most commonly used as a foliar spray, Seaweed Extract may be sold in either liquid or dry powder form. Some products may contain elevated potassium levels due to the use of potassium hydroxide in the extraction process.

Soybean Meal

Typical N-P-K: 7-1-2

Soybean Meal is made from ground soybeans. Soybean Meal is the highest percentage source of non-animal derived nitrogen available. Most soy production today is genetically-engineered and only non-GE soy is acceptable for use in certified organic crop production.

Micronutrient Supplements

There are also a variety of supplements designed to correct specific micronutrient deficiencies. Many of these require a soil analysis demonstrating a deficiency in order for their use to be permitted in certified organic crop production. These micronutrients are only required in trace amounts, so low application rates are typical and it is recommended to consult an agronomist for application recommendations based on soil test results.

Examples of these micronutrient supplements include: Ferrous Sulfate (Iron), Copper Sulfate, Zinc Sulfate, Manganese Sulfate, Granubor (Boron), and Sodium Chloride.

Note: Many animal-derived organic nutrient products have odors that may attract wildlife. Take precautions when storing them and to incorporate them thoroughly into your soil if there is a possibility of animals entering your garden.