Macronutrients
N-P-K
Most commercial fertilizers in the United States contain
macronutrients that are necessary for plant growth. The three main macronutrients are nitrogen
(N), phosphorus (P), and potassium (K).
These micronutrients are listed as concentrations in fertilizers
relative to one another such as 10-20-10.
The concentrations are listed on all bags of fertilizers sold with the
first number relating to the concentration of nitrogen, the second for
phosphorus, and the third for potassium.
Any ratio of these concentrations of elements is sufficient to provide
the needed amounts for plant metabolism, however, be careful in using high
nitrogen fertilizers so as not to damage the tissue of the plants.
These three macronutrients are necessary for plant growth,
development, and cell metabolism.
Nitrogen is important because it is used in producing proteins, enzymes,
nucleic acids, and found in chlorophyll.
Without nitrogen present plants have stunted growth and will often die
if nitrogen is unavailable. Phosphorus
is found in nucleic acids, phospholipids, and in production of ATP (cellular metabolism
and energy). A lack of phosphorus also
causes stunted growth and often leaves that are deep green. There is no supporting evidence that phosphorus
promotes blooms in most plants (see plant physiology perspective),
so you may not want to push high phosphorus fertilizers on your plants or spend
extra money on them. You will note that
the fertilizer I use has a higher concentration of phosphorus than either
nitrogen or potassium. This concentration is so that I
can avoid high levels of nitrogen, and that I do not burn the roots or growth of
the plants. Potassium is responsible
for osmosis and ionic balance in cells, opening and closing of stomata on
leaves (allowing gas exchange), and as an enzyme activator. In short, your Stanhopea would not grow and bloom well if they lacked any of these
macronutrients.
Other Macronutrients
Other macronutrients that are essential for plant metabolism
include carbon, calcium, hydrogen, oxygen, sulfur, and magnesium. Carbon, hydrogen, and oygen are obtained
from the air and water and are essential elements during photosynthesis. Calcium is used in the formation of cell walls
and in the mitotic spindle during cell division. In my poor quality water, there is an
abundance of calcium and salts in the water, so I usually do not have to worry
about a lack of calcium. Only those
individuals who use deionized water or filtered water would have to worry about
calcium levels. Calcium is also present
in small amounts in many organic fertilizers.
Magnesium is essential in photosynthesis, respiration, DNA and RNA
synthesis, and assists in forming bonds with nitrogen. Magnesium is also involved with enzyme
activity. Sulfur is an essential component
in synthesis of coenzymes and vitamins essential to plant metabolism.
Micronutrients
Several Stanhopea
species are semi-terrestrial or lithophytes and I therefore treat them similar to other terrestrial orchids such as Sobralia,
and Zygopetalum by providing them
fertilizer with micronutrients. These
are elements that are essential for plant metabolism and growth. The fertilizer that I use has trace
concentrations of boron, copper, iron, manganese, molybdenum, and zinc. These are all metal/mineral elements that are
necessary for plant metabolism. Boron
may have a role in cell elongation, nucleic acid synthesis, hormone response,
and membrane function. Copper and iron
are required by enzymes in redox reactions and in photosynthesis. Manganese is an activator of eznymes in plant
cells for both respiration (citric acid cycle) and photosynthesis. Molybdenum is associated with nitrate
assimilation and nitrogen fixation. Zinc
has a role to play in enzyme activity and chlorophyll biosynthesis. Plants that lack available iron and manganese
can have yellow leaves and appear stressed.
Berg, L. 2008.
Introductory Botany: Plants People and the Environment, Second
Edition. Thompson Higher Education,
Belmont, California.
Taiz, L. and E. Zeiger 2010.
Plant Physiology, Fifth
Edition. Sinauer Associates, Inc.,
Publishers, Sunderland, Massachusetts.
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