December 2020 - 21

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It's a nitrogen thing
If you're an apple grower, then pandemic
aside, did you have an 'on' year or an
'off' year in 2020? Mike Williams, CEO of
California-based OMEX®
Agrifluids, takes a
closer look at the problem of alternate yield
bearing, explaining why it's an agricultural
issue to resolve, rather than a natural
occurrence to overcome.
This phenomenon, where small yields of large
fruit (off years) are followed by large yields of
small fruit (on years), is a recurring problem
for apple growers. But why does it happen,
and how can we reduce the problem?
It's a common question that customers put
to our team of agronomists; with orchards
dormant for the winter, now's a good time to
discuss it and think about taking appropriate
steps to banish it for 2021.
We usually concern ourselves only with the
current crop as it swells and ripens on the
branch, but in fact the apple tree grows three
crops at once. Of course, there's the crop we
see on the branch. But in development are
not just the flowers for the next crop, but the
budwood for the crop after that too. Thus our
2021 agronomy year will also influence our
2022 and 2023 harvests.
Herein lies the problem. With these three
crops developing simultaneously, albeit at
different stages, branches in different parts of
the growth cycle compete against each other
for resources. To ensure even production
across seasons - eliminating the alternate
yield bearing - the plant needs to allocate
equal emphasis to vegetative growth (shoots)
and reproductive growth (flowers for next
harvest, as well as fruit development for
current harvest).
Under non-agricultural conditions, the tree
would manage this process itself; we rarely see
alternate yield bearing occur in nature. In fact,
it's largely an agricultural phenomenon, created
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by the way we farm crops and influenced by
prevailing weather conditions. And what's the
single most important influence on where the
plant allocates its growth? The level and form of
nitrogen available.
Not all nitrogen is created equal
You see, not all forms of nitrogen have
the same effect. Take nitrates, which are
transported to the leaves for processing. As
nitrate levels accumulate, the plant responds
by increasing production of the plant hormone
auxin - a stimulant of vegetative growth
and apical dominance. When nitrates are the
dominant form of nitrogen, we see increased
internode length (the space between leaves on
the stem), faster shoot growth and increased
height. Together, these create the classic
'leggy' appearance, characterized as a 'nitrate
effect'.
Amine nitrogen, conversely, behaves quite
differently. It's processed in roots and favors
production of the cytokinin hormone. In cases
of amine dominance, the plant emphasizes
fruit and flower development. Internodes are
shorter and there's slower, more even shoot
growth: the 'bushy' effect.
That's the laboratory view. But how does this
pan out in the field?
Well, when we apply conventional fertilizers
to a crop, no matter what kind of nitrogen we
apply - nitrate, amine, ammonium - that
nitrogen is quickly transformed into the nitrate
form, which the plant takes up. The more
nitrogen we feed, the more unbalanced the
crop becomes: it allocates a disproportionate
resource to vegetation at the expense of
flowers and fruit.
Played through successive seasons, this
creates the cyclic 'boom and bust' that
leads to alternate yield bearing. Then we're
compounding the effect: every year when
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The secret lies with a stabilized form of
amine. After application, its nitrogen remains
available in the amine form, without degrading
to nitrate. OMEX®
Cell Power®
SizeN®
,
developed by scientists at the British firm
Levity Crop Science, does precisely this: it
holds nitrogen in the amine form.
Taken up by the tree, this stabilized amine can
influence growth partitioning - the way in
which the tree allocates growth. It's a nitrogen
supplement rather than a solo source; growers
should use it in conjunction with conventional
inputs, rather than as a substitute. Used on
perennial tree crops, it helps the tree distribute
growth more evenly between vegetative and
reproductive development - delivering the more
even fruit and flower development we want.
Shortening the internodes allows more fruit
per unit length of branch. It also reduces
the need for pruning (keeping that valuable
nitrogen in the plant, rather than on the
clippings pile) and makes for a better canopy
shape. This 'growth in the right places' strategy
will bring yield benefits to all three parts of
the growing cycle - and make alternate yield
bearing a thing of the past.
Cell Power® SizeN®
should be applied regularly
through the season, using drip or foliar
application at 2qts/acre per month.
For more information on products please
contact OMEX®
Agrifluids at OmexUSA@Omex.
com, www.omexusa.com or call 559-661-6138.
The product names and brands referenced
here are registered and trademarks of OMEX®
Agrifluids, Inc. © OMEX®
we prune, we prune back the yield potential,
because much of our applied nitrogen has
gone into the very stems and branches we're
meticulously removing.
How do we break the cycle?
Agrifluids, Inc. 2020.
Email omexusa@omex.com
FGN | DECEMBER 2020 | 21
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December 2020

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