What Is Plant Fertilizer Made Of?

Fertilizers in the hands of skilled gardeners are like spices in the hands of Cordon Bleu chefs. They are the final ingredient in the process producing the healthiest and most abundant plants.
The major ingredients in both organic and chemical fertilizers are nitrogen, phosphorus, and potassium. The amounts in which they are present, and the sources from which they come, are what distinguish the two types of fertilizer.

Types

Fertilizers are either organic or chemical. Organic fertilizers feed not only plants but the soils in which they grow. Chemical fertilizers, produced from non-renewable substances including natural gas, coal, and rock minerals, nourish plants without providing lasting benefits to the soil.
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Identification

Every commercial fertilizer has a series of three numbers separated by hyphens, known as the N-P-K ratio. Those letters stand for Nitrogen-Phosphorus-Potassium. These three nutrients are essential for plant growth.
If the sum of the numbers for the three ingredients is larger than 15, 5-10-5, for example the fertilizer contains 5 percent nitrogen, 10 percent phosphorus, and 5 percent potassium.
Any fertilizer whose N-P-K numbers total more than 15 percent, or which has a single number greater than 8 percent, is a chemical fertilizer.

Organic fertilizer ingredients

Organic fertilizers have only natural animal, plant, or mined mineral materials produced without chemical fertilizers, pesticides, herbicides, or hormones.
Organic fertilizer ingredients which provide nitrogen, phosphorus, and potassium are seed meals, specifically alfalfa, cotton, and canola seed.
Blood meal has similar nutrients, but feeds plants and improves soil more quickly than seed meal.
Because both seed and blood meals are acidic, some organic fertilizer contains acid-neutralizing lime of calcite, dolomite, or a 2:1 mix of both.
Bone meal boosts the organic fertilizer's phosphorous content. Fish meal and fish emulsion are good sources of nitrogen.
According to Rodale's All-New Encyclopedia of Organic Gardening,"kelp meal is a source of potash, vitamins, dozens of trace minerals, and growth-promoting hormones."
Other organic fertilizer ingredients include compost, granite meal, gypsum, peat moss, soybean meal, wood ash, and worm castings.

Chemical fertilizer ingredients

Ammonia and ammonium derivatives; potassium sulphate and calcium phosphate; nitrates and nitrites; and urea--almost every compound found in chemical fertilizers occurs in Nature.
They rarely, however, occur as pure forms. They're mineral salts found either in rocks or as a mix of organic elements requiring extraction by chemical synthesis, like the Haber process isolating ammonia from natural gas.
Chemical fertilizers also have inert fillers or other chemicals which play no role either in plant growth or soil improvement. In his book Gardening in Hard Times: Growing Food When It Counts," Steve Solomon says that fertilizers with high N-P-K counts labeled as "complete," frequently lack calcium, magnesium, and other trace minerals which help plants resist insects and diseases.

Warning

According to the Garden Counselor Lawn care Site, chemical fertilizers with high N-P-K concentrations can bind with the soil's other nutrients, making them unavailable to plants. Most chemical fertilizers are water soluble. Heavy rain may leach them deeply into the soil, beyond the reach of the plants' roots.
The cottonseed meal in some organic fertilizers may contain pesticide residues.

Resources

• International Fertilizer Industry Association