Steps to building your soil organically

 

1.  Start with compost.

A ½ inch layer of compost per year is enough to sustain your soil’s fertility after the soil has been built to an ideal level.  You may apply more initially to build your soil.  Compost composition varies widely depending on what materials were used to make it and how long it has been aged.  A typical municipal compost will have an analysis close to 1-1-1, of which only about 50% of the N may be expected to be available in the first year.  Composts made from animal manures will have more N; if they haven’t been composted for long, this N may be in the form of “hot” ammonia, which can burn crops if used in excess.

2.  Use organic mulches.

A 1 to 2 inch layer of grass clippings applied as a surface mulch year is enough to sustain your soil’s fertility after the soil has been built to an ideal level.  Other mulches are relatively low in N, so should be used in combination with other sources of N, or with leguminous cover crops.

3.  Use cover crops.

Leguminous green manures like hairy vetch, field peas, and white clover “fix” nitrogen from the air.  Other green manures, like oats, rye, and buckwheat, help soak up surplus nutrients like a sponge, keeping it from being lost, as well as building organic matter.

Cover crop seed sources: 

Peaceful Valley Farm Supply, PO Box  2209, Grass Valley, CA  95945 (888) 784-1722.  www.groworganic.com

Johnny’s Select Seeds, 184 Foss Hill Road, RR 1 Box 2580, Albion, ME  04910-9731.  (207) 437-4301.

Fedco Seeds, PO Box 520, Waterville, ME 04903-0520.  Call (207) 873-7333 for catalogue; they do not accept telephone orders.  Excellent prices for larger quantities

4.  Apply other organic fertilizers only if needed as indicated by a soil test.

If a specific nutrient isn’t in the soil to start with, nothing short of importing it as a fertilizer will get it there:  composts and mulches from plants grown there will lack it, and cover crops will struggle to grow.  Your soil might also need a little boost of nitrogen in the spring when soils are cold and wet and nutrient release from organic matter is slow.

Remember N-P-K:  Nitrogen-Phosphorus-Potassium (K).  Choose a fertilizer that has a nutrient ratio closest to the ratio recommended on your soil sample report.  If you can’t take a sample, choose the fertilizer that has the ratio closest to 3-1-2.  That is the approximate ratio of nutrient uptake by most plants.  A product with a 6-2-4 ratio would work too; you would just use half as much.  A fertilizer that is 5-5-5 or 10-10-10 is not balanced!

5.  Fertilize ornamentals only very lightly.

Since you are not harvesting them and removing nutrients from them, they should be cycling the same nutrients back to the soil if you leave their residues to decompose in place.  If you do remove dead parts, a little compost and regular mulching should be sufficient.

The most sustainable and least expensive organic fertilizers are products made from whatever organic waste materials are available in your region.

Nitrogen Sources

Nitrogen is the nutrient most likely to be in short supply.  There is no such thing as an organic nitrogen fertilizer that does not contain any other nutrients.  Those which are plant-derived tend to have ratios that are closest to the ideal of 3-1-2.  Excess N can leach and become a groundwater contaminant.

 

Alfalfa Meal

 

 

3 - 0.5 - 3

 

Alfalfa is a leguminous plant with a fairly balanced NPK ratio and many other essential plant nutrients.  It is an excellent all-purpose fertilizer and is most often sold in farm or pet stores as pelleted animal feed or hay.  If locally grown it is a “best buy”.

 

Soybean Meal

 

6 - 1.5 - 2

 

Soybean meal is a fairly balanced, nitrogen-rich fertilizer.   If locally grown it is a “best buy”.

 

Fish Products

 

variable

check label

 

Many different fish-based products are available in both powdered and liquid forms.  They are usually rich in readily-available nitrogen and have fair amounts of other nutrients, but they may be expensive.  The soluble forms are convenient for mixing with irrigation water in organic greenhouses.

 

Blood Meal

 

12 – 2 - 0

 

A slaughterhouse by-product, blood meal is a relatively expensive source of highly soluble nitrogen.  Use it only as a quick boost for valuable crops, never more than ½ pound per 100 square feet.

 

Bat or Bird Guano

 

variable

check

label

 

Guano is dried manure deposits from bat caves or seabird colonies.  It is usually highly soluble and therefore not a top choice.  Also, harvesting may not be regulated to prevent harm to active bat or bird colonies.  May be expensive.

 

Kelp Meal

 

1.5- 0.5- 2.5

 

Kelp meal is made from ground, dried seaweed and is a good source of potassium and many trace elements.  Liquid kelp products are convenient for watering into greenhouse seedlings.  They are often blended with fish products for a more balanced nutrient content.

Phosphorus Sources

P is the primary fertilizer responsible for pollution of rivers and lakes, so use P fertilizers only if a soil test indicates that P levels are low.  Since P does not leach down into the soil readily, P fertilizers should be mixed thoroughly into the soil.

 

Bone Meal

 

1- 11- 0

 

An animal slaughterhouse by-product.

 

Rock Phosphate

 

0 - 3 - 0

 

Phosphate rock is a mined material with a total P content of up to 30%, although fertilizer labels usually list only the available P content, which is around 3%.

Potassium Sources

There are no known environmental problems caused by excessive potassium.

 

Greensand

 

0 – 0 - 7

 

Also called glauconite, greensand is a natural mined mineral with a potassium content of up to 7 %.  It is a good slow-release source of K, although K deficiency is rare when soils receive regular applications of compost or grass clippings.

 

Potassium Sulfate

 

0 – 0 - 45

(+ 18%S)

 

A mined product.  The potassium is fairly quickly available.  Potassium sulfate also contributes sulfer, an essential plant nutrient which may be deficient from sandy soils.

 

Sul-Po-Mag

(also called Langbenite)

 

0 – 0 - 26

(+ 22%S + 8% Mg)

 

A mined produce.  The potassium is fairly quickly available.  Sul-Po-Mag also contributes sulfer and magnesium.

Other Soil Amendments

 

Limestone

 

Lime (calcium carbonate) is used to correct an acid soil (low pH).  It should never be applied without a soil test to determine the correct application rate or it may make the soil too alkaline (high pH).  Thus it is not recommended merely as a source of calcium.  If magnesium is needed in addition to liming to adjust pH, use dolomitic limestone.

 

Gypsum

 

Gypsum (calcium sulfate) is used to supply calcium if the there is no need to adjust pH.  Calcium is rarely deficient in Minnesota. Sometime gypsum is recommended to improve the tilth of the soil, but its effectiveness is controversial.

 

Borax

(Mule Team)

 

To address a boron deficiency.  The line between boron deficiency and boron toxicity is very thin, so be very careful not to over apply.  Use only according to soil test recommendations.  Typical recommendations are 1/5 to 1/10 ounce per 100 square feet!   It is very difficult to apply that lightly!

 

(adapted by Lois Braun from “How to Fertilizer Your Garden”, Organic Gardening Magazine, July/August 2000, pp 46-51.)