[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Zinc deficiency in E. Horemani

In the past I've encountered the various nutrient deficiencies
in my tanks: nitrogen, calcium, potassium, iron, and even
phosphorus. The tapwater is very soft, I only test for nitrate,
and nutrient additions are imprecise, i.e. a teaspoon of this,
half a teaspoon of that. Generally things seem to work out.

During the last six months the thirty or so oldest leaves of
a rapidly growing red E. horemani have been showing signs of
some deficiency. It displays as patches of transparency, a
loss of pigmentation or chlorosis beginning at the edges of
the leaves and working inward. The ten newest leaves are
invariably fine. It has been a year since it was first potted.
Nothing is added to the soil and the plant has to compete for
the circulating PMDD. It produces at least ten leaves monthly.

Nitrogen, magnesium and potassium are in abundance. Phosphorus
seems fine as there is lots of other plant growth. So what's
left? The symptoms might be due to a shortage of zinc or
maybe molybdenum, so I decided to review the makeup of the
micronutrient mix in the original PMDD formula and the probable
requirements of the plants.

According to my hydroponic source (Resh, Howard M., Hydroponic
Food Production), the ratio by weight of iron to zinc in dry
plant tissue is 5:1; of iron to molybdenum, 1000:1. These are
surely averages; however, when one compares them with the
ratios of the same elements in the Chelated Micronutrient Mix
made by Plant Products Limited one gets 17.5:1 and 117:1
respectively. The mix contains about 8 times the amount of
molybdenum that one might expect to be required, but only about
30% of the zinc. This might be a problem for some fast growing
species if iron is maintained at a marginal level which barely
supports the rate of uptake.

I went out and bought a small amount of Zn:EDTA and adjusted
the PMDD to obtain a Fe:Zn ratio of about 5:1. Then I trimmed
off all but the youngest leaves. That was three weeks ago and
so far the older leaves remain solid. Another month and I will
know for sure.

My questions are, "Has anyone entertained the notion that zinc
deficiencies may be occurring? Am I incorrect about the iron
to zinc ratio? Has anyone had similar problems with potted
swords? Am I jumping to conclusions?"

There are a few people who make their fertilizer from scratch.
How much chelated zinc do you add? What is recommended in the
academic texts? 

Dave Whittaker
ac554 at FreeNet_Carleton.ca