I conclude that organic matter is somewhat dangerous stuff whose use should be limited to the amount needed to maintain basic soil tilth and a healthy, complex soil ecology.

Fertilizing Gardens Organically

Scientists analyzing the connections between soil fertility and the nutritional value of crops have repeatedly remarked that the best crops are grown with compost and fertilizer.  Not fertilizer alone and not compost alone.  The best place for gardeners to see these data is Werner Schupan’s book (listed in the bibliography).

But say the word “fertilizer” to an organic gardener and you’ll usually raise their hackles.  Actually there is no direct linkage of the words “fertilizer” and “chemical.”  A fertilizer is any concentrated plant nutrient source that rapidly becomes available in the soil.  In my opinion, chemicals are the poorest fertilizers; organic fertilizers are far superior.

The very first fertilizer sold widely in the industrial world was guano.  It is the naturally sun-dried droppings of nesting sea birds that accumulates in thick layers on rocky islands off the coast of South America.  Guano is a potent nutrient source similar to dried chicken manure, containing large quantities of nitrogen, fair amounts of phosphorus, and smaller quantities of potassium.  Guano is more potent than any other manure because sea birds eat ocean fish, a very high protein and highly mineralized food.  Other potent organic fertilizers include seed meals; pure, dried chicken manure; slaughterhouse wastes; dried kelp and other seaweeds; and fish meal.

Composition of Organic Fertilizers

Material % Nitrogen % Phos. % Potassium
Alfalfa meal 2.5 0.5 2.1
Bone meal (raw) 3.5 21.0 0.2
Bone meal (steamed) 2.0 21.0 0.2
Chicken manure (pure, fresh) 2.6 1.25 0.75
Cottonseed meal 7.0 3.0 2.0
Blood meal 12.0 3.0 —­
Fish meal 8.0 7.0 —­
Greensand —­ 1.5 7.0
Hoof and Horn 12.5 2.0 —­
Kelp meal 1.5 0.75 4.9
Peanut meal 3.6 0.7 0.5
Tankage 11.0 5.0 —­

Growing most types of vegetables requires building a level of soil fertility that is much higher than required by field crops like cereals, soybeans, cotton and sunflowers.  Field crops can be acceptably productive on ordinary soils without fertilization.  However, because we have managed our farm soils as depreciating industrial assets rather than as relatively immortal living bodies, their ability to deliver plant nutrients has declined and the average farmer usually must add additional nutrients in the form of concentrated, rapidly-releasing fertilizers if they are going to grow a profitable crop.