“0-20-0” phosphate bat guano 3 times better than “0-7-0” bat guano?
Maybe, but not likely. Plants require the proper balance of 16
nutrients for life. The three soil-derived nutrients that are
needed in the greatest quantity are nitrogen (N), phosphorous (P) and
potassium (K). Most States require fertilizers to state the
percentage of these nutrients on the front of the package with three
numbers. They always list them in the order N-P-K, and the values
indicate the weight-percentage of that nutrient present in the
fertilizer. If any other nutrients are present, they are usually
listed elsewhere on the package. State law may require that a
minimum amount of a nutrient must be present before its content can be
claimed. Usually, this minimum is 1% for N-P-K.
Of the three main nutrients, ABG phosphate contains only phosphorous in
significant amounts. Thus, it is a 0-7-0 fertilizer. But what
does the “7” mean? It theoretically means that at least 7% of the
fertilizer is phosphate that is in a form that is immediately available
to your plants. But there is no universal truth here. We
actually get available phosphate numbers from different labs that range
from 1 to 20%. For example, in Florida, where unique methods are
used, lab results dictate that we would have to label our product as
0-1-0. On the other extreme, a different lab consistently finds
that the product has 15-20% available phosphate. Other lab results
run the entire range between the two.
After a lot of testing by private and State labs, we decided on
0-7-0 as a safe number.
As a comprehensive United Nations-sponsored
report addresses this problem in detail.
That report states that part of the problem with the testing for
available phosphate on rock phosphate and similar materials is that the
tests are more qualitative than quantitative. The U.N. provides that the slightest
variation on the method can result in great variability of the
results. The U.N. report also
states that when a natural substance contains a moderate amount of free
calcite (up to 10%), the accepted available phosphate tests will
under-report the phosphate because the relatively soluble calcite will
consume the weak reagent before it has a chance to attack the less
soluble phosphate-bearing minerals.
Given the general findings of the U.N. report, and the independent
laboratory’s finding that ABG Phosphate contains 10% free calcite, it
appears possible that the available phosphate content of ABG Phosphate
may be underestimated.
Because of all of these
problems with available phosphate tests, we believe the more reliable
test is one that actually measures plant uptake of phosphorous. Under such tests, performed by an
independent laboratory, it was found that plants will take up 12%
phosphate from ABG Phosphate over the course of a growing season. But that does not mean it is the same
as a 0-12-0 fertilizer because ABG Phosphate may be releasing 7%
immediately and the remaining 5% over the course of the season. Conversely, a true 0-12-0 fertilizer
would release its whole 12% at once.
Thus, for labeling purposes, ABG Phosphate is a 0-7-0 fertilizer,
but for annual application rate purposes, it should be applied as a
are not trying to be critical of the fertilizer laws. They are
there for your protection and that is a very good thing, if you
understand them. As a company that is conservative in claiming
available phosphate, our self-serving point here is that of
phosphate-only bat guanos that you might see on the market, there may be little
difference between those labeled as 0-1-0 to 0-20-0, other than which lab
analyzes the product, what body of laws governs their labels, and how
gutsy companies are when choosing a guaranteed minimum on their package. For example, just with our own product,
one customer who repackages the material under its own brand name told us
that they sell their product as 0-7-0 in most states, but as 0-0.7-0 in
Florida. On the other hand, in jurisdictions
that only consider total phosphate, ABG Phosphate could safely be sold as
a 0-20-0 fertilizer.
But this only addresses the
bat guano products. What about the
water soluble phosphate (WSP) products with numbers ranging up to at
least 50% phosphate? It is
reported that after application, WSP stays in a form that is available to
plants for only a certain amount of time, and plants can only take up only
so much phosphate at a time (we will add references for this later). Given the widespread problem of
phosphate pollution in the nation’s water ways, it appears that much of
this phosphate just washes away with the soil. Because of this, some communities in
the U.S. now strictly regulate
phosphate use, even for home owners.
Supporting documents and further information can be found at
the following web sites:
of Phosphate Rocks for Sustainable Agriculture, F. Zapta and R.
Roy, Food and Agriculture Organization of The United Nations (2004)
(available phosphate tests on rock phosphate (includes Indonesian
Phosphate Guano as a type of rock phosphate) are more qualitative than
quantitative. Free calcite in a sample will result in under-reporting of
available phosphate under current testing methods used in most countries.)