A common illusion about fertilizers is that they are direct nutrients which must be promptly absorbed or they will be lost (either leached out of the soil by rain, or locked up in some insoluble, unusable form). The fact is that instead of being used directly to any extent, most of the nutrients in fertilizer compounds are quickly blotted up by soil organisms such as bacteria, fungi, protozoa and actinomyces. Gardener's Loam contains billions upon billions of such organisms which occupy the soil mass so completely that very little in the way of soluble plant food can escape them. They act as reservoirs of fertility, releasing it when they die. Since their life span is short, such food is not tied up for long periods, but merely saved for later use by plants. The role of microorganisms in conserving fertility cannot be overestimated.
The ideal fertilizer would be one that supplied every needed element of nutrition for the crop being grown, at a rate that would take advantage of all available light, heat, moisture and oxygen needed by plants. This ideal material would supply some nutrients in quickly-available form for immediate growth, yet would contain other nutrient fractions that would be released so slowly that a single application in spring would continue to feed until cold stopped plant growth in fall. All through this cycle of combined slow and fast release, enough surplus nutrients would be given off to provide food needed by soil organisms to carry on their functions.
Claims for various materials are endless and often self-contradictory. In general it may be said that chemical and mineral fertilizers are more readily available for immediate use by plants, while organic materials (which must undergo more involved decomposition before
they can be absorbed) are slower in action and last longer in the soil. These distinctions are being gradually eliminated by the development of long-lasting chemicals that release fertility even more slowly than some organic manures.
The claim most often made for organic fertilizers is that they "do not burn." By burning is meant injury (dehydration) of the roots or crown of the plant, and a browning of part or all of the foliage, sometimes resulting in the death of the entire plant. The tissues are not "burned" as in a bonfire; the burn is a drying-out caused by the withdrawal of water from tissues by the hygroscopic action of "thirsty" chemical materials. Since some manufacturers make a big issue of this "non-burning" quality, many home gardeners have come to regard it as an important factor in selecting a fertilizer product for use.