Organic matter
Is best used as an amendment rather than a source of fertilizer. In addition to coarse sand, inorganic amendments include calcine clay products, pulverized volcanic rock, perlite and diatomaceous earth. Liquid products break the surface tension of water around the soil particle and allow deeper earth penetration. They do not increase the pore space of a soil. They therefore cannot be considered soil amendments and are properly called adjuvants. Liquid products are not substitutes for amendments.
Interest in organic gardening
Has been successful largely because the practice encourages the use of organic matter as an amendment, thereby improving soil texture. This practice improves the environment for good root growth and the development of soil microorganisms that make nutrients more readily available.
Organic matter
Also supplies some nutrients, but most forms of organic matter are rather low in amounts when compared with the commercial inorganic sources. From the standpoint of plant use, it makes no difference whether the nutrients are supplied from organic or inorganic sources since the plants can only use the nutrients in the basic inorganic form. The difference is primarily in the availability. For instance, nitrogen from organic sources is released more slowly than from most commercial fertilizers.
Slow release of nutrients
Would be desirable in a soil already adequate in nutritional levels. Though if the soil is deficient in one or more nutrients, it’s usually desirable to add commercial, more quickly available fertilizers to correct the deficiency.
Before adding fertilizers to a soil
First determine whether a problem in growing healthy plants is due to nutrition or a physical property of the soil, such as poor texture. A plant in a “tight”, poorly aerated soil may not do well because the root system is unable to utilize the present nutrients. Amendment with organic matter to “open up” the soil first is more appropriate in this case than adding a commercial fertilizer.