September 2022 - 20

PLANT HEALTH
Hydroponics
Systems
Of Plant Nutrition
&PRINCIPLES
Essential nutrients, function, deficiency and excess of growing plants without soil.
BY ELSA SÁNCHEZ, ROBERT BERGHAGE, THOMAS FORD, FRANCESCO DI GIOIA AND NICK FLAX
H
ydroponic can be defined as growing
plants in water containing nutrients.
Examples of this type of hydroponic
systems include NFT (nutrient film technique)
systems and deep-water float systems where
plant roots are set in nutrient solutions. Another
definition of hydroponic is growing plants
without soil. With this definition, growing plants
in soilless media (potting soil) or other types
of aggregate media such as sand, gravel, and
coconut coir are considered hydroponic systems.
Here, we are using hydroponics to mean growing
plants without soil.
ESSENTIAL NUTRIENTS
Plants cannot properly function without
17 essential nutrients. These nutrients are
needed so that processes critical to plant
growth and development can occur. For
example, magnesium is a critical component
of chlorophyll. Chlorophyll is a pigment used
to capture energy from light that is needed
in photosynthesis. It also reflects green
wavelengths and is the reason most plants
are green. Magnesium is the center of the
chlorophyll molecule. Table 1 (page 22) lists the
plant roles of essential nutrients.
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Essential nutrients can be broadly categorized
as macronutrients and micronutrients.
Macronutrients and micronutrients are both
essential for plant growth and development.
Macronutrients include carbon, hydrogen,
oxygen, nitrogen, phosphorus, potassium, sulfur,
calcium, and magnesium. Micronutrients include
iron, manganese, zinc, boron, molybdenum,
chlorine, copper and nickel. The difference
between macro- and micronutrients is the
amount required by plants. Macronutrients are
required in higher amounts than micronutrients.
Table 1 shows the approximate plant content of
essential nutrients.
Plants get carbon, hydrogen and oxygen from
air and water. The rest of the nutrients are from
soil or, in the case of hydroponics, from nutrient
solutions or aggregate media. Sources of
nutrients available to plants are listed in Table 1.
pH
It is impossible to discuss plant nutrition
without considering pH. In hydroponics, we are
primarily concerned with the pH of the water
used to make up nutrient solutions and irrigate
plants. pH is a measure of the relative acidity
or hydrogen ion concentration, and it plays an
important role in plant nutrient availability. It
is measured using a 0- to 14-point scale where
0 is the most acidic, 7 is neutral, and 14 is the
most alkaline. The scale is logarithmic, and each
unit represents a 10-fold change. This means
that small changes in values are large changes
in pH. For example, a value of 7 is 10 times
higher than 6 and 100 times higher than 5.
In general, the optimal pH range for growing
vegetables hydroponically is 5.0 to 7.0.
Figure 1 (page 23) shows the relationship
between nutrient availability and pH.
Along the bottom of the chart are different pH
values between 4.0 and 10.0. At the top of the
chart, the relative acidity or alkalinity is shown.
Within the chart, relative nutrient availability
is represented by a bar. The wider the bar is,
the more the nutrient is relatively available. For
example, the nitrogen bar is widest between a
pH of 6.0 to 7.5. This is the pH where it is most
available to plants. It is very narrow between
4.0 and 4.5 and not as readily plant available.
It is also important to consider the alkalinity of
the water. Alkalinity is a capacity measure - it
measures the capacity of the water to neutralize
the acid. This is due primarily to the combined
amount of carbonate (CO3
) and bicarbonate (HCO3
),
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September 2022

Table of Contents for the Digital Edition of September 2022
