Banding of Phosphorus Fertilizer in the Spring
In order for crops to grow and develop, soil nutrients (chemical elements)
need to be absorbed by roots and distributed throughout the plant. These
nutrients, coming from soil parent material or from added fertilizers, function
in structural and metabolic systems, enabling the plant to carry on living
processes. To obtain full yield potential and to produce high-quality crops,
the soil must contain enough nutrients to support vigorous plant growth
throughout the life cycle. Since the weathering of soil parent material
is a slow, long-term process, assuring proper nutrition for crop plants
generally requires the addition of fertilizers to the soil.
When a gardener decides to fertilize, he is faced with the choice of which
fertilizer to use and the task of determining how much fertilizer to apply.
No universal guidelines are available for answering these questions as soils
differ in fertility and crops differ in their nutritional requirements.
The gardener must apply what seems to be correct amounts of fertilizer based
on soil tests, plant analysis, previous experience and advice from others.
Modifications can be made during the season or in the following year based
on how the crop is growing and on the amount of time remaining in the current
season.
In the fertilization of crops, growers must first be concerned with supplying
the primary macro-nutrients - nitrogen, phosphorus and potassium. Since
organic or natural fertilizers have variable chemical composition, a balanced
or adequate supply of all of the primary macronutrients from a single organic
fertilizer is unlikely. Therefore, more than one kind of organic fertilizer
is usually needed to provide sufficient crop nutrition in any system of
organic gardening. This situation differs from that of synthetic fertilizers
which are manufactured to contain one, two or all three of the macronutrients
and can be purchased in practically any formulation.
The organic grower has a limited number of phosphorus fertilizers to choose
from. Plant residue, farm manure and compost are, practically, too low in
phosphorus to be considered for any purpose other than maintaining soil
fertility following a build-up of this element in the soil. Residues from
the bodies of animals are excellent sources of phosphorus, with bone meal
being the most significant among available animal residues.
Rock phosphate, mined from deposits, has a high phosphorus content, but
must break down into a clay form before it can be utilized by plants. This
process may require from 2 to 3 years or longer depending upon the pH of
the soil.
Colloidal rock phosphate, taken from a lower grade ore than regular rock
phosphate, is more readily available to plants because of its infinite fineness
and a process whereby nutrients in the soil are carried to the plant roots
through the exchange of tiny electrical charges between the roots and the
soil.
Superphosphates are manufactured by treating rock phosphate with sulfuric
or phosphoric acid, thus simulating the action of acid soil and the rock.
If soil pH is too high or alkaline, essential elements such as phosphorus
and iron become unavailable for plant use even though they may be present
in the soil. Unavailability of mineral elements is caused by temperature,
physical encapsulation by soil calcium or chemical changes associated with
added nutrients.
The unavailability of phosphorus and iron can cause serious plant problems.
Phosphorus is represented by the middle number on every fertilizer analysis
and is responsible for flowering and root development. A phosphorus deficiency
resulting in lack of flowering and poor root development clearly causes
problems.
The obvious answer to rectify a mineral deficiency would seem to be to add
additional quantities of the needed mineral. However, minerals must be added
in such a manner that they are available for plant uptake over a period
of time rather than immediately. If released too quickly, the minerals may
be unavailable or inaccessible because of cold soil temperature, physical
encapsulation or chemical change.
One successful approach is to concentrate the deficient or unavailable minerals
in a mass or bank which cannot be acted upon as rapidly as if the minerals
were evenly distributed throughout the growing area. The mineral band offers
seedling plants or transplants a continuous, reliable source of needed nutrition
in a concentrated zone. This approach can increase the availability of phosphorus
and iron in the area of the band.
When banding superphosphate (0-20-0) to insure phosphorus availability,
make a furrow 3 inches deep (for seed) or 6 inches deep (for transplants)
in the planting area. Into this furrow, evenly distribute 1/2 pound (1/2
cup) of superphosphate (0-20-0) per 10 linear feet of bed. This band of
phosphorus will provide a concentrated source of available phosphorus (for
use as a "starter" solution) for young and growing plants. Cover
the band of super phosphate with 2 inches of soil. When planting in an iron
deficient, plant chlorosis-prone soil, add 1/2 pound (1/2 cup) of iron sulfate
(copperas) to the 1/2 pound (1/2 cup) of superphosphate (0-20-0) per 10
linear feet of bed. If seeds or transplant roots are planted directly into
this concentrated mix, growth could be stunted. The 2 inches of covering
soil serves as a buffer zone. If colloidal rock phosphate (0-2-0) is used,
seeds and transplants can be planted at the standard planting depth directly
into colloidal rock phosphate banded into the planting furrow at the rate
of 5 pounds per 10 linear feet.¶