Re: Protea and Iron

At 10:34 AM 5/13/99, John Atkinson wrote:
>At 07:38 12/05/99 -0400, Xavier wrote:
>
>>I have no references readily at hand, but I have rarely read anything on
>>Australian Proteaceae without the author mentioning the toxicity of
>>phosphorus.

        I couldn't resist doing a little library research on this topic
today at UC Berkeley.  I looked into Hawaiian soils and into soil and
nutritional requirements of Protea's.  I found:

a)  Hawaiian rainfall is *very* variable, from as low as 30"/year to 70" in
higher elevations of the big island and Oahu and, of course, over 200" on
Kauai.  The texture is also diverse with clays, clay-loams, silts and
sands.  Under these circumstances I'd expect to find wide differences in pH
even within one island.  Unfortunately the Hawaiian soil surveys that I
read said nothing of pH.

b)  deficiencies of zinc are reportedly widespread in Hawaii.

c)  the leading US soil text, by Brady, makes a passing reference to
'elements that can--in excess--lead to deficiencies of minor nutrients'.
Under iron Brady lists molybdenum, sulfur, manganese, zinc and.....ta
da....phosphorus.

d)  most of the Univ. of Hawaii literature concerns the big money crops,
sugarcane, beef, bananas, et.al.  No mention is made in connection with any
of these crops of P toxicities.  Hawaiian farmers apparently routinely add
P.

e)  the idea that Protea's are P sensitive apparently is a hot topic among
fanciers.  The last big Protea scientific meeting (Proceedings of the 4th
International Protea Working Group Symposium) had a paper on just this
subject by two Israeli researchers.  They admittedly studied only one
cultivar but I got the impression that the whole tenor of the article was
meant to dispel the notion that P toxicity was a problem with Proteaceae.
These researchers found no evidence of P toxicity and that growth was
increased with P fertilization!
        And, perhaps more significantly, these folks reported that *root
hair initiation completely ceased on Protea's at pH's over 6.0*.  They
listed an 'ideal' pH for protea of 4.7 to 5.7.  If that is correct I'd
expect to see interveinal chlorosis at pH's in the mid 6's.

Jerry Heverly, Oakland, CA
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index