Any discussion about fertilizers should begin with at least a brief overview of plant nutrition. There are 16 elements required by plants for healthy growth. Of these, three are supplied by air and water-carbon, hydrogen and oxygen.
The other 13 are divided into three subgroups: primary nutrients, nitrogen, phosphorous and potassium; secondary nutrients, calcium, magnesium and sulfur; and micro-nutrients, zinc, iron, manganese, copper, boron, molybdenum and chlorine. All of these elements are essential regardless of the amounts required.
These nutrients work together in a delicate balance to promote plant growth. An excess of one nutrient can reduce a plant's ability to absorb another. The role of any fertilizer is to improve the fertility of the soil. The soil supports plant life and is the vehicle that supplies the necessary nutrients to the plant. The more fertile, that is rich in organic matter, a soil is, the more likely it is to yield a healthy and abundant garden.
Fertilizers commonly are divided into two different categories: synthetic, or chemical, fertilizers and natural, or organic, ones.
Plants cannot tell the difference between the two. The difference between the two types is evident in their impact on the soil. Organic fertilizers feed the soil not the plant and help maintain overall soil fertility by contributing vital organic matter and enhancing the soil structure in addition to supply ing plant nutrients. The organic varieties usually are derived from the byproducts of once-living organisms or from rock powders.
Organic fertilizers are released gradually. They form a storehouse in the soil, and the plant takes up the nutrients as it needs them.
Soil fertility is maintained and enhanced for the long-term benefit of the garden. Synthetic/chemical fertilizers are formulated to be fast-acting. Most synthetic fertilizers are salt- or acid-based. They typically have a higher nutrient grade level than do natural, organic fertilizers and often are intended to be immediately available to the plant - except for the timed, slow-release types.
In many cases the plant can use only 10 percent to 15 percent of the available nutrients in synthetic/chemical fertilizers. The rest is essentially wasted, possibly creating side effects and suppressing many beneficial soil organisms.
With excessive use, they can even reduce soil fertility with excessive use.
