NPK ratios?

Wed, 30 Jan 2008 20:57:31 PST
I agree with Jim about phosphorus often seeming excessive in many
formulations. I can't think of many soils in nature that would be especially
high in P and arid climate soils especially are often very low in it.
Perhaps something like 5-3-15 or 5-5-10 would be suitable for many bulbs.
But it is often difficult to locate sources for unorthodox ratios once one
moves away from 20-20-20 and the like.

On Jan 30, 2008 2:53 PM, J.E. Shields <> wrote:

> Diana and all,
> I agree with Diana --- my understanding from 30 years ago is that ammonium
> nitrogen is absorbed under all conditions relatively poorly by plant
> roots,
> compared to nitrate.  On the other hand, ammonium is the preferred form of
> nitrogen for all fungi and many bacteria.  Len Doran drove this point home
> to those of us whom he undertook to coach:  Ammonium feeds the pathogens
> trying to kill your bulb, nitrate feeds the plant!
> In Narcissus poeticus (Vickery et al, 1946, cited in Rees) they found that
> the plant tissue analyzed as follows:
> Bulbs grown on nitrate as source of nitrogen, 15.9 g N per 50 bulbs
> Bulbs grown on ammonium as source of nitrogen, 14.0 g per 50 bulbs.
> My bibles, (post Doran), have been
> "The Growth of Bulbs" by A. R. Rees, pub. by Academic Press, New York &
> London, 1972
> and
> "The Physiology of Flower Bubls" by A. de Hertogh and M. Le Nard, pub. by
> Elsevier, Amsterdam & New York, 1993
> The point made by Doran was the same as that made by Rees:  Bulbs need
> nutrients in the approximate ratio the nutrients occur in the healthy bulb
> tissue.  Plants are also limited by any nutrient that is present in
> significantly less than needed levels.  Unfortunately, only Gladiolus,
> Lilium, and Tulipa have been studied in detail.  As a general thing, the
> ratio of N, P, and K in plant tissue is about 4 N to 0.3 P to 2 K.  The
> precise ratios can vary not only from genus to genus but from cultivar to
> cultivar.
> The question of the effects of nutrient ratios on efficiency of absorption
> is not resolved so far as I can recall -- or my knowledge may be decades
> out of date.  I am not aware the N, P, and K affect each others absorption
> rates.
> Mg (magnesium), Ca (calcium) and K (potassium) are similar in ionic charge
> (Mg and Ca) and in size (Ca and K) and are said to be able to interfere
> with each other's absorption.  This alone might indicate that applying
> calcium at a different time than magnesium would increase the
> effectiveness
> of the applied nutrients.
> Loading the fertilizer up with phosphate is relatively harmless in
> soilless
> growth medium.  In soil, excess phosphate can tie up iron, calcium, and
> probably a couple of the trace elements, depending on the ambient soil
> pH.  Phosphate is of course essential for plant growth, but in
> significantly smaller amounts that N and K.  I've never understood where
> people are coming from when they recommend high phosphate fertilizers;
> this
> just does not make physiological sense to me.
> Jim Shields
> in cold central Indiana (USA)
> At 01:12 PM 1/30/2008 -0800, you wrote:
> >It is also my understanding that nitrate nitrogen, in the form of
> potassium
> >nitrate or calcium nitrate, is better absorbed at lower temperatures, so
> >this is important for those bulbs that grow during the winter.  The
> >formulation I use has both ammonium nitrite and potassium nitrate, but
> the
> >main ingredient is potassium nitrate.
> >
> >Diana
> >Telos Rare Bulbs
> *************************************************
> Jim Shields             USDA Zone 5             Shields Gardens, Ltd.
> P.O. Box 92              WWW:
> Westfield, Indiana 46074, USA
> Tel. ++1-317-867-3344     or      toll-free 1-866-449-3344 in USA
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