This might be helpful.

http://www.gardenfundamentals.com/fertilizer-selecting-the-right-npk-ratio/

Thanks! Still hoping Al can post a link to the article.

Is this post what you are looking for? -click me-

Or -this one- same post but much more discussion/questions/answers...

Thanks, Rina.

Al

I'm actually looking for the scholarly (I assume) article that shows that plant nutrient uptake ratios are approximately 3:1:2. Thank you for the other links, though!

Not necessarily scholorly, but there's this:

"That
one single fertilizer will suit all plants sounds much like wishful
thinking for many gardening enthusiasts. But – in spite of what
often is said and written on the topic, it is quite logical.

“All
plants need the same nutrients in the same proportions,” says
Professor Tom Ericsson, researcher in plant nutrients at the Swedish
Agricultural College in Ultuna. “Therefore, specialty fertilizer
products aren’t necessary”.

Specialty
fertilizer products are becoming more and more common in garden
centers. There are special fertilizers for roses, rhododendron,
orchids, pelargoniums, citrus, cacti, tomatoes, bedding plants,
potatoes and more. There are also specialty fertilizers for plants
growing under similar conditions, such as vines or bonsai. To provide
your plants with the nutrients they require seems both complicated
and expensive judging by the assortment offered.

But
– do all these plants really have such specific nutrient
requirements that these fertilizers are necessary? And how can it be
that one fertilizer can cover the needs of all bonsai, or all vines?
They belong to a wide range of genus and species, and should,
logically, have totally different needs regarding one or the other
nutrient. It becomes even more confusing when you see how the
ingredients vary between different products aimed at the same type of
plant.

Tom
Ericsson has showed in his research that different plants’ need for
nutrients isn’t all that specific as the fertilizer producer will
have us believe. The truth is that specialty fertilizers are
unnecessary and that fertilizing correctly is pretty simple.

If
you choose a well-balanced fertilizer it will fit all vines and all
bonsai. The same fertilizer will work equally well for pelargoniums,
citrus, beddingplants, rhododendron, roses and all other plants –
even orchids and cacti. They all want the same nutrients served in
the same proportions at an even rate. The only difference is the
amount they want, or rather how fast the rate of delivery should be.
Fast growing plants need more nutrients than slow growing ones, but
still at the same proportions.

All
you need to think of is the dosage and the regularity. For container
grown plants Tom Ericsson has a recipe that will solve the problems
all at once.

Choose
a liquid, well balanced fertilizer containing all the nutrients the
plants need. Add 1 ml to 1 quart of water (4ml/gallon), and use it
for all your plants. It makes a weak nutrient solution that you will
use year round, each time you water.

That
different plants have different needs for nutrients doesn’t matter
using this method. It suits them all. Because the nutrients are added
with the water it is a self regulating system. Fast growing plants
that need more fertilizer will also need more water. When more water
is supplied, so is more fertilizer.

“The
method works equally well for plants with low nutrient needs”, says
Tom Ericsson, who himself is an enthusiastic grower of many slow
growing species, such as cacti, orchids and tillandsia. They all need
very little water, getting small amounts of fertilizer. Cacti and
orchids are grown in fast draining substrates, and some of the water
and fertilizer will drain out right away.

If
you grow plants completely without substrate, in the case of
tillandsia and some species of orchids, you can submerge them in a
bucket of water with the same nutrient solution a couple of times per
week. 1ml/quart of water is so weak that all roots will tolerate it.
One argument for using specialty orchid food is that regular plant
food is too concentrated. This is a peculiar argument to Tom
Ericsson.

“The
concentration depends on the dosage. The dose I recommend is not too
strong for any plant”

Tom
Ericsson recommends applying the same dosage both summer and winter
because plants need nutrients not only for growth, but also for
maintaining already existing plant parts. As plants need less water
during the winter months – due to less light, lower temperatures
and the resulting reduced growth – the fertilizer applied will be
diminishing. Even in winter the method is self regulating.

We
grow plants indoors during the winter during sometimes extreme
conditions. When plants are placed above heating ducts the
evaporation rate from both soil and plants becomes very high. The
need for water increases, but not because the plant is in active
growth. In such conditions, it’s better to reduce the fertilizer
dose by half.

“One
ml of fertilizer per quart of water will work for most situations,
but it is not a holy grail”, says Tom Ericsson. Each person needs
to experiment a little to find the right dosage for his or her
specific conditions.

Using
1 ml of concentrated fertilizer per quart of water will deliver about
50mg of nitrogen in the nutrient solution, assuming the ratio of N is
5g/100ml. However, liquid fertilizer ingredients vary quite a bit,
and the dosage may need to be adjusted for this reason.

Growing
plants that require high doses of fertilizer in order to mature,
flower and set fruit within one growing season may also require
adjustment of the fertilizer dose.

“According
to research done with Brugmansia, tomatoes and sunflowers by my
students, they require 4ml concentrated fertilizer per quart of water
for maximum growth.”

Fertilizing
the garden follows the same principles as fertilizing containers. All
nutrients that plants require should be applied at the same
proportions as they are found in plant tissue. (See table below.)
Nutrients should reach the soil at an even rate. Sudden, large
applications of nutrients cannot be absorbed by plants and the
surplus is leached out to groundwater and waterways.

Tom
Ericsson’s fertilizer method works just as well in the garden.
However, it is rarely practical to administer fertilizer by watering
the entire garden. The space is too large, and during rainfall no
watering will be done and therefore no fertilizer applied. Also, many
of us like to use organic fertilizers in the form of manure and
compost, since they add beneficial microorganisms and improve soil
structure. In areas where it might be difficult to work in solid
fertilizer materials, is the watering method an excellent solution,
according to Tom Ericsson.

–
In
the garden, where fertilizing isn’t done as often as in containers,
can the fertilizer dose be increased. If you apply fertilizer twice
during the growing season, 50ml concentrated fertilizer per 10l (2 ½
gallons) of water should be applied per 1m2
(9 sq.ft.) each time. It is a very moderate dose, completely harmless
to all plants. This dose will add 5gr of N per 1m2
each
season, corresponding to 50kg (100lb) of N per hectare (2 ½ acre),
which is about half of what is applied on agricultural soils.

Watering
in the fertilizer makes nutrients immediately available to roots.
It’s a good method to induce growth in plants that have slowed down
or stopped growing.

Other
than that, Tom Ericsson encourages people to mimic nature when we
apply fertilizer. Not removing dead plant material, allowing it to
naturally deteriorate, is one example.

–
The
purpose of fertilizing is to increase the fertility of the soil. It
can be achieved by fertilizing more frequently and in smaller doses.
It reduces the risk of unnecessary leakage of nutrients. The gardener
also needs to recognize whether plants really need extra fertilizer.

–
Increasing
fertility in the garden should primarily be done with organic
material produced in the garden. This production can initially be
stimulated with the aid of chemical fertilizers.

Plants
absorb nutrients from soil moisture in the form of ions. Tom Ericsson
underscores that it doesn’t matter to plants whether nutrients come
from organic or chemical sources. Correctly used, both types can
provide the even flow of nutrients at plant roots that we want.

In
part, this is what Tom Ericsson intends by telling us to mimic
nature. In nature nutrients do not suddenly appear in large amounts,
nor do nutrient levels change quickly. Organic material is constantly
being decomposed, adding a continuous supply of nutrients to soil
moisture.

–
The
concept that organic fertilizers always are better out of an
environmental point of view is not correct, says Tom Ericsson.
Unfortunately, the truth is that leakage of, among other things,
nitrogen (ammonia gas) can be quite substantial. This is especially
true when organic material is applied on top of the soil, such as
grass clippings.

One
of Dr Ericsson’s students has shown that up to 25% of the nitrogen
content in grass clippings disappears in gases when it is applied on
top of the soil. Therefore it should be worked into the top layer of
the soil and the loss of nitrogen will be significantly reduced.

Grass
clippings do have an almost perfect ratio of nutrients. However, in
fertilizer trials with tomatoes, it has been shown that the sulphur
in grass clippings is very tightly bound, resulting in poorer growth
compared to commercial fertilizers. Increasing the amounts of grass
clippings can offset this deficit, although leakage of other
nutrients will increase. A better solution is to complement the grass
clippings with extra sulphur in the form of potassium sulfate.

Manure
and compost should also be worked into the soil, to minimize nitrogen
leakage. Manure from cows, horses, pigs, sheep and goats is pretty
much well-balanced. Bird manure may need complementing with
potassium, depending on the garden soil. Clay soils rarely need such
additions.

–
One
aspect of using manure is moving fertility from farm fields to
gardens. How does the farmer compensate loss of fertility from his
fields? It isn’t easy to use fertilizers in an ecologically sound
way when you consider the entire chain of effects.

Regular
applications of fertilizer is of paramount importance. In the cases
of nitrogen, phosphorus and sulphur; plants can function well
regardless of plentiful or sparser availability, as long as supply is
continuous. This is the reason that plants growing in lean soils in
nature do not show any deficiencies, in spite of poor access to
nitrogen. Slow growth will be the only indicator. When access to
nutrients change, as in the case of fertilizing seldom but with high
rates of fertilizer, deficiency symptoms will occur when nutrient
levels diminish. Deficiency symptoms will also occur at low levels of
other nutrients than nitrogen, phosphorus and sulphur.

If
nutrient access is unbalanced, i.e. plants are getting more than they
need of certain elements, but less than they need of others, the
substance they need the most is the one that is going to limit
growth. Whatever nutrients are available in excess, will be absorbed
by the plant to a certain point. In come cases, this may lead to
toxicity. Too much nitrogen will lead to excessive foliage production
and less flowering. Too much potassium or phosphorus will not lead to
ill effects. There will be no toxic symptoms and the gardener may not
realize that the soil contains five times more phosphorus and twice
as much potassium as needed.

The
fact that different species of plants grow on different types of soil
does not mean that the one needs more of a certain nutrient than the
other. It just means that the plants have developed strategies to
adapt to certain conditions.

Acid-loving
plants have adapted to acid soils. Their need of calcium is still the
same as any other plant. Nutrient requirements do not differ from
plants that thrive in alkaline soils. The problem for acid-loving
plants is that they have not developed a method to limit their
calcium uptake, and will absorb too much of it when available,
resulting in too high pH-values in cells. Some acid-loving plants
also have difficulties absorbing iron, which is tightly bound in
alkaline soils, another reason why they thrive in low pH soils. This
all pertains to the plants ability to handle nutrients, not to the
actual nutrient needs of the plant.

Continued below