There's a difference between plant food,
fertilizers


April 01, 2011

by  Roy Cook, Victoria County Master Gardener

edited by Charla Borchers Leon,
Victoria County Master Gardener
Gardeners' Dirt
PHOTOS BY ROY COOK/VICTORIA COUNTY MASTER GARDENER
Fertilizer types and mixtures are numerous and can contain one, several or numerous plant nutrients in one bag.  Sometimes, they can be specifically formulated for a special plant or crop based on that plant's needs, i.e. fruits, vegetables, flowers, etc.  They usually perform quite well, especially if that plant is grown and harvested/removed continuously in, and from the same site, as these nutrients are removed and need to be replenished.  A soil test is recommended to accurately address what is lacking and can prevent over applications problems.
Many people confuse plant nutrition with plant fertilization. Although it is common for many fertilizers to be called plant food, it is a misnomer. Fertilizers are not plant food.

NUTRITION VS. FERTILIZATION

Plant nutrition refers to the plant needs and uses of the basic chemical elements. Fertilization is the term used when these elements are supplied to the environment around the plant.

Plants produce their own food using water, carbon dioxide and energy from the sun. This food (sugars and carbohydrates) is combined with the plant nutrients to produce protein, enzymes, vitamins and other elements essential to plant growth.

Fertilizers are materials containing plant elements or nutrients. Generally, they are added to water or soil, but some can be added to water and sprayed on leaves.

MACRONUTRIENTS

There are at least 16 essential nutrients for plant growth. Carbon, hydrogen, and oxygen are found in air and water. The major soil nutrients are nitrogen, phosphorus and potassium with calcium, magnesium and sulfur being the secondary soil nutrients.

Nitrogen - Nitrogen is a part of all living cells and a necessary part of all proteins, enzymes and metabolic processes involved in the synthesis and transfer of energy. Nitrogen is part of chlorophyll, the green pigment of the plant that is responsible for photosynthesis. Nitrogen often comes from a fertilizer or manure application and from the air (legumes get their nitrogen from the atmosphere).

Phosphorus - Like nitrogen, phosphorus is an essential part of the process of photosynthesis. Phosphorus is involved in the formation of all oils, sugars and starches and helps with the transformation of solar energy into chemical energy, proper plant maturation and withstanding stress. It also encourages blooming and root growth. Phosphorus often comes from fertilizer, bone meal and superphosphate.

Potassium - Potassium is absorbed by plants in larger amounts than any other mineral element except nitrogen and in some cases, calcium. It is essential for reducing plant stress caused by drought, temperature extremes, pest problems, etc.

Calcium - Calcium, an essential part of plant cell wall structure, provides for normal transport and retention of other elements as well as strength in the plant. Although rarely deficient, sources of calcium are dolomitic lime, gypsum and superphosphate.

Magnesium - Magnesium is part of the chlorophyll in all green plants and essential for photosynthesis. It also helps activate many plant enzymes needed for growth. Soil minerals, organic materials, fertilizers and dolomitic limestone, as well as Epsom salt are sources for plants.

Sulfur - Sulfur is an essential plant nutrient for production of protein, and promotes activity and development of enzymes and vitamins. Sulfur also helps in chlorophyll formation, improves root growth and seed production, and helps with vigorous plant growth and resistance to cold. Sulfur may be supplied to the soil from rainwater. It is also added to some fertilizers as an impurity, especially the lower grade fertilizers. The use of gypsum also increases soil sulfur levels.

MICRONUTRIENTS

There are a number of micronutrients that also aid in plant growth.

Boron - Boron helps in the use of nutrients and regulates other nutrients. It aids production of sugar and carbohydrates and is essential for seed and fruit development. Sources of boron are organic matter and borax.

Copper - Copper is important for reproductive growth, aids in root metabolism and helps in the utilization of proteins.

Chlorine - Chlorine aids plant metabolism, and is essential for photosynthesis

Iron - Iron is essential for the formation of chlorophyll. Sources of iron are iron sulfate and iron chelate.

Manganese - Manganese functions with enzyme systems involved in breakdown of carbohydrates and nitrogen metabolism.

Molybdenum - Molybdenum helps in the use of nitrogen.

Zinc - Zinc is essential for the transformation of carbohydrates and regulates consumption of sugars. Zinc is also part of the enzyme systems which regulate plant growth. Sources of zinc are zinc oxide, zinc sulfate and zinc chelate.

Cobalt - Cobalt is needed by plants recently established and needed for nitrogen fixation.

Most all the micronutrients are found in ample supply in the average soil and very rarely do they need to be applied as a fertilizer unless in extremely high management and production of a plant or in hand-mixed soil media or potting soils.

SUMMARY

A soil test will help determine the content and amount of fertilizer needed. Nutrient intake of plants is a fine-tuned system. Too little or too much of one nutrient can upset the system.

If either organic or inorganic fertilizers are applied too heavily, they may cause the plant tissue to burn, be chlorotic or result in plant death.

Read product labels carefully and follow directions to avoid toxicity problems.

Without a soil test it is difficult to determine the exact amount of fertilizer a plant needs.

To get a soil test bag and form, contact the Victoria County Extension office at 361-575-4581.
FERTILIZING TIPS

*Soil test before fertilizing to better understand which nutrients are needed.
*Select fertilizers based on soil deficiencies and plant needs.
*Fertilizer bag numbers represent the percent of nitrogen, phosphorous and potassium.
*Allow compost or manure to fully decompose before applying to lawn or garden.
*Organic fertilizers come from plant or animal sources.
*Inorganic fertilizers are made from petroleum products and chemicals.
*Never over fertilize. Too much hurts more than it helps. Follow package or bag instructions.

Fertilizer Macronutrients

Nitrogen
Phosphorus
Potassium
Magnesium
Calcium
Sulfur

Fertilizer Micronutrients
Iron
Boron
Zinc
Copper
Manganese
Molybdenum
Chlorine
Cobalt
The Gardeners' Dirt is written by members of the Victoria County Master Gardener Association, an educational outreach of Texas AgriLife Extension - Victoria County. Mail your questions in care of the Advocate, P.O. Box 1518, Victoria, TX 77901; or vcmga@vicad.com, or comment on this column at www.VictoriaAdvocate.com.