Fertilizer injector systems are standard equipment in
today's greenhouses. There are many types of injectors on the market.
Basically, they work the same. A concentrate of water-soluble fertilizer is
mixed in a tank. Water-soluble fertilizers dissolve completely in water and
stay in solution. The concentrations of the water-soluble fertilizers are also
easily adjusted. The fertilizer concentrate is then mixed with the water in
exact proportions before irrigating plants. With fertilizer injectors growers
can provide exact levels of nutrients.
There are a number of advantages to using fertilizer
injectors. The greenhouse plants are provided with constant liquid feeding.
This is especially important with soilless media that have a low cation
exchange capacity. The plants are fertilized when they are watered thus
reducing labor. All the plants of a particular crop receive the same levels of
nutrients. This assists in producing a uniform crop. In addition, adjustments
to the level of nutrients in solution can be made easily.
Calculating ppm
Nutrients in solution are measured in pans per million or
ppm. Growers can refer to tables in reference books or to instructions with
their injector system to determine the amount of fertilizer needed to reach a
desired ppm. However, growers must also understand how to calculate parts per
million (ppm) of fertilizer nutrients.
Slow Release
Fertilizers
Slow release fertilizers are self- defined by their name.
These products continually discharge a small amount of nutrients over a period
of time They are available in two forms. One form consists of a water-soluble
fertilizer held within a plastic resin or sulfur coating. The coating is
designed to allow a small
amount of fertilizer to be slowly released. They have the
appearance of little round beads and are sometimes mistaken as insect eggs by
the uninformed. The other type of slow release fertilizer comes in a granular
form. This type releases no more than I percent of the fertilizer in a 24-hour
period.
The use of slow release fertilizers has declined with the
increased use of water-soluble fertilizers through injector systems. Growers
have a much greater control with the fertilizer injector systems. However,
there are some advantages to the slow release fertilizers. Slow release
fertilizers can be safely mixed with the growing medium prior to planting. Slow
release fertilizers provide a more constant supply of nutrients than
water-soluble fertilizers. This is particularly true when watering is less
frequent. Slow release fertilizers work well when capillary mats are used to
water plants. Also, slow release fertilizers can be used to extend the shelf
life of plants once they leave the greenhouse.
NUTRIENT DEFIENCY
Plant quality and thus, profits, are lost if the plants
cannot obtain the essential nutrients from the medium. Even if only one
necessary nutrient is missing, the plant can develop deficiency symptoms. For
example, nitrogen promotes the growth of green, leafy tissue. If the available nitrogen
is low, the plant may take on a yellow appearance. The growth rate slows and
the plant often is stunted. This happens even when all the other essential
nutrients are available.
If a plant fails to receive the needed nutrients, it will
show signs of nutrient deficiency. Nutrient deficiencies most often surface as
an unhealthy plant appearance. Symptoms vary with the nutrient that is in short
supply. Common symptoms of deficiencies include discoloration of the leaves,
death of leaf tissue, and stunted growth. Because of the complex interactions
of nutrients in plant processes, deficiency symptoms for different nutrients
are often very similar. Laboratory tests, including the analysis of plant
tissues, can be used to determine which nutrient is lacking.
SOLUBLE SALTS
The damage caused by soluble salts is through a process
known as reverse osmosis. As the salt concentration builds up in the growing
medium, it prevents water molecules from being absorbed by the roots. In severe
cases, water is drawn from the root cells into the growing medium. The
resulting damage caused by soluble salts is the burning of the roots. Wilting or
the death of leaf tissues follows the injury or death of the roots.
Damage from soluble salts can be avoided by preventing a
buildup of soluble salts in the growing medium. A good practice is to water the
plants until water drains from the container. As the water flows through the
growing medium, it carries soluble salts with it. This is known as leaching.
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