Essential Plant Nutrient Elements
Vegetable plants, like all other green plants, require several
nutrient elements for growth, development and productivity. Among the
necessary plant nutrients are carbon, hydrogen and oxygen, available
from the atmosphere and from water; and nitrogen, phosphorus,
potassium, calcium, magnesium and sulfur supplied from the mineral
portion of the soil. These elements are used by plants in relatively
large amounts and are referred to as macronutrients. Micronutrients,
or trace elements, used in small quantities, include boron, chlorine,
copper, iron, manganese, molybdenum and zinc. These 16 plant
nutrients, whether used in large or small quantities, are absolutely
essential for plant vigor and productivity. A deficiency of any of
these nutrient elements canlimit plant growth and development, and
ultimately yield. Fortunately, most Ohio soils contain sufficient
amounts of the micronutrients to support plant growth. However, soils
may be lacking in some of the macronutrients, particularly nitrogen,
phosphorus, and potassium. It is the job of the gardener, therefore,
to ensure the presence of all the essential elements supplied by the
soil in the right quantities and the right chemical forms for plant
use. This is done by supplying organic matter and by the judicious
use
of fertilizers to maintain or increase soil fertility.
pH and Soil Fertility
Soil pH is the level of acidity or alkalinity of the soil that has an
affect on fertility. Most vegetable crops prefer a slightly acid pH
of 6.0 to 6.8. Nutrient elements in the soil may be chemically tied
up or bound to soil particles and unavailable to plants if the pH is
outside of this range. Soil pH can be raised by applying ground
agricultural limestone which contains calcium and some magnesium.
Lowering soil pH is achieved by adding sulfur, either in its
elemental
form or as a component of some fertilizers.
Regular Fertilizer Applications
The gardener cannot assume fertile soils will not require a periodic
fertilizer application. Plant nutrients are lost from the soil over
time through use by plants and by leaching with water. It is
important
that these lost nutrients be replaced. Low-fertility soils will
require not only maintenance fertilizer applications to replace lost
nutrients, but also applications that will improve the overall soil
fertility and support plants at a productive level. It is impossible
to determine the fertility level and pH of garden soil by looking at
it. Fertilizer and lime applications are best made based on the
results of a soil test. This service is available through your local
Cooperative Extension office. Test results are accompanied by
recommendations as to the kinds and amounts of fertilizers and lime
needed to improve the fertility of the soil.
Commercial Fertilizers
Nitrogen is the plant nutrient most often in short supply in the soil.
It is usually necessary to supply this element each season.
Phosphorus and potassium are also required in large amounts. Nitrogen
is essential for vigorous vegetative growth and development.
Phosphorus is necessary for good root development and for fruit and
seed production. The role of potassium is not as well understood, but
is important for overall plant development. For this reason, these
are the three nutrients that we almost always find present in
commercial fertilizers. Commercial fertilizers, whether organic or
inorganic, always have three numbers printed on the bag or container.
These numbers or analysis represent the percentage of nitrogen (N),
phosphorus (P2O5) and potassium (K2O) in the product. For example an
8-16-16 analysis fertilizer contains 8 percent nitrogen, 16 percent
phosphorus and 16 percent potassium. The rest of the product is an
inert carrier material. A complete fertilizer will have a number for
all three nutrients. Some fertilizers are incomplete, that is, they
contain only one or two of the nutrients. Urea, for example, has an
analysis of 45-0-0, and contains 45 percent nitrogen with no
phosphorus or potassium. Inorganic or chemical fertilizers usually
have a higher analysis than most organic fertilizers and are less
expensive. The nutrients in chemical fertilizers are in a form that
is readily available to plants. Organic fertilizers contain nutrients
in forms that must be chemically changed in the soil before the
plants can use them. These nutrients, although not immediately
available, are usable to the plants over a longer period of time.
Some chemical fertilizers will contain nutrients in both readily
available and slow-release forms. Organic fertilizers are less likely
to burn plants and often contain several micronutrients in addition
to nitrogen, phosphorus and potassium.
Application Methods
Fertilizers are often applied over the garden area before planting and
then are tilled or spaded into the soil. Calibrated spreaders used
for lawn fertilizer application can be effectively used for applying
garden fertilizer. Do not use fertilizers containing herbicides in
the vegetable garden. Row or band applications make the most
efficient use of small amounts of fertilizer. This method allows for
fertilizer placement near the plants where it will be of the most
use. Make small furrows about three inches to each side of the row
and two to three inches deep. Use caution, however, so that seeds or
roots do not come into direct contact with the fertilizer. In lieu of
a soil test recommendation, apply two to three pounds of fertilizer
per 100 feet of row. Select the fertilizer analysis according to the
type of vegetable grown. For leafy vegetables, high nitrogen
fertilizers, such as 12-12-12 or 15-15-15 analyses are appropriate.
For vegetables grown for their fruits, seeds, roots, or bulbs, such
fertilizers as 6-24-24, 6-12-18, and 8-16-16 or equivalent are
satisfactory. Growing healthy, productive plants in the vegetable
garden involves attention to many cultural details. Since
fertilization is just one of these details, fertilizers should not be
considered a cure-all for all gardening problems. When properly used,
fertilizers are extremely valuable in obtaining good gardening
results. However, fertilizers cannot correct or improve poor soil
structure that requires additions of organic matter. Nor can it
compensate for an incorrect pH or unfavorable weather conditions.
Choosing inappropriate vegetable cultivars, and not practicing weed
or pest control cannot be corrected by applying fertilizers. The use
of fertilizers is just one of a number of integrated gardening
practices that lead to gardening success.
The author gratefully acknowledges the work of James D. Utzinger and William M.
Brooks, on whose original fact sheet this is based.
-----------------
All educational programs conducted by Ohio State University Extension
are available to clientele on a nondiscriminatory basis without regard
to race, color, creed, religion, sexual orientation, national origin,
gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and
Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868
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