NPK ratios?

most phosphorus is supplied in nature as animal wastes (guano is high in
PO4) and will typically not be readable as a major component of most
soils. It simply is removed very quickly and does not easily combine
with other soil elements. Nitrogen can combine with calcium rather well
and remain stored. Not that I think that it is overly important in the
ratio, just that its very nature is quite different than nitrogen or
potassium.

As to its importance, it is further down the line of nutrients, but is
very neccessary for all plant developement.

Jim mentioned that ammonias are not taken up directly by plants, which
is quite true. Ammonia (NH4, that is nitrogen with 4 hydrogen atoms
attached) is first converted to NO2 via bacteria. This is the first
step of nitrification. Plants are still incapable of using this
compound. It is further brocken down to NO3 via other bacteria and then
is available to plants as their main energy source.

The total equation runs something like this:

2NH4 + 2OH + 3O2 > 2H+ + 2NO2- from which the H (hydrogen)
evaporates/recombines leaving 2NO2- + O2 > 2NO3 , with nitrate as the
end product. The process is understood, but the actual bacteria are
still not 100% confirmed. It may be various types in various
environments, as this is a fundimental process found in all organic systems.

As to ratios in general, I believe one must consider what they wish to
achieve and how they plan on doing that. A plant in a container is not
really a very natural thing. The potting mixes, other than providing
nutrients and a specific type of substrate for the plant, also provide a
specific type of environment for other life forms. A classic case is
with potted orchids. When they are planted in pine bark they require 3
times the nitrogen as when they are planted in a non reactive medium.
The bacteria found in pine bark take up nitrogen to degrade the bark at
an enourmous rate! The catch is, when the bark is finally digested by
the bacteria, the nitrogen is once again available, often burning the
roots of the plant! A reason why repotting is an important issue in
general. It is not just a case of providing new material for the plant,
rather a complete exchange to remove dangerous wastes, as well.

As bulbs are largely resting plants, with only a handful being quasi
evergreen, they are storage oriented. This would indicate a larger
requirement of PO4, which, assumedly in nature, is provided by animal
droppings diluted and transported via the seasonal rains. Although I am
not certain, it is possible that these same rains dissolve potassium
(K+) from the soil. I take it this reaction will largely hang from the
soil type.

Something that lit a little light in my head was Jim's mention that
bacteria are a general enemy of bulbs. Of course, this is generalized,
as there are beneficial bacteria involved, it's just dependant on the
view point! Could feeding ammonia based fertilizers exacerbate the
bacterial problems? Clearly, the plants cannot profit directly from
ammonias, rather require a converted form (nitrates) to process. This
would tend to say that, especially for potted plants in a closed
environment, that urea is a poor nutrient! It is ammonia and must first
be assimilated by bacteria before the plants can profit from it. In the
open garden this may not be a problem, but in a pot, it could simply
feed the bacterias and damage the plant.

Just a few thoughts,

by the way, I always choose a lower nitrogen fertilizer, such as a
14-9-15 (+2Mg +Tr) time release (8 month), but that is only low in
relation to the potassium! I use this with all my potted plants.

--
Jamie V.

_______________________

Köln (Cologne)
Germany
Zone 8

jamievande@freenet.de