Like so many other nutrients, sulfur has
a plethora of roles in proper plant func-
tion. It is a component of chlorophyll and
necessary for protein synthesis, which
help plants to regulate the photosynthe-
sis processes. Sulfur is also needed for
nitrogen fixation in plants that can pull
nitrogen from the environment, meaning
legumes and other nitrogen-fixing
plants are particularly susceptible to
sulfur deficiencies. Sulfur and nitrogen
are further linked in plant physiology;
sulfur is responsible for the activation of
key nitrogen enzymes. It is therefore not
surprising that sulfur deficiencies are
usually always addressed concurrently
with nitrogen deficiencies.
Symptoms of Sulfur Deficiency
Sulfur is highly abundant in the
soil. It falls to the earth from a wide
range of both natural and man-made
processes, such as volcanic activity
and pollution. It is not, however,
widely available to plants until it
is mineralized. Sulfur is also easily
leached out of soil during heavy rains
or when exposed to irrigation. For
this reason, it is not unusual for sulfur
deficiencies to occur in plants.
Correctly identifying a sulfur deficiency
can be difficult, as it can look like other
nutrient deficiencies and symptoms may
not appear until the deficiency is quite
severe. Sulfur is not highly mobile in a
plant’s vascular system. If a deficiency
occurs, it will first present itself in the
new growth. If the deficiency continues,
it will then continue to the older growth.
Plants affected by insufficient sulfur are
hard to distinguish from plants defi-
cient in nitrogen. Both cause yellowing
of the leaves, but nitrogen deficiencies
begin with the older leaves first. To
further complicate proper diagnosis, a
plant may well suffer from both nitro-
gen and sulfur deficiencies concurrently.
However, if caught before they spread
through the plant, the tell-tale sign of
dual problems will be a healthy-looking
mid-section with chlorotic growth above
and below. If not caught in time, it would
be nearly impossible to distinguish the
two without a lab-performed tissue anal-
ysis or by conducting a fertilizer test.
For a lab analysis, it is important to
collect proper samples. In the absence
of specific instructions from the lab,
select up to 10 new-growth leaf samples
and wash them off with distilled or
deionized water before sending them.
Sulfur is easily leached out of soil during heavy rains or when exposed to irrigation.
This way, the analysis won’t be tainted
by any sulfur residue that may have
fallen on the leaves from rain or other
atmospheric conditions. To perform a
fertilizer test on a crop to determine if
the deficiency is due to a lack of nitro-
gen or a lack of sulfur, multiple plants
are needed. Obtain a fertilizer contain-
ing both nitrogen and sulfur, such as
ammonium sulfate, and one that is just
nitrogen, such as urea. Apply an appro-
priate amount of the nitrogen-only
fertilizer on one section of plants and
an appropriate amount of the nitro-
gen-plus-sulfur fertilizer on the other.
If both sections of plant respond favor-
ably to the treatment, it was a nitrogen
deficiency. If only the section treated
with the nitrogen plus sulfur fertilizer
responds, it was a sulfur deficiency.
grow cycle
89