Agriculture Reference
In-Depth Information
Calcium sources:Agricultural sweet lime (Calcium carbonate) and gypsum
(Calcium sulfate) are the preferred sources of calcium. Gypsum supplies readily
available Calcium, and is also a good source of Sulfur, an element that is seriously
lacking in most agricultural soils.Agricultural lime supplies Carbon as well as
Calcium. Carbon helps make a soil less sticky. If you already have plenty of
Carbon in your soil as organic matter, but are low on Sulfur, gypsum is a better bet.
The various rock phosphates and regular superphosphate also contain
significant Calcium, but their Calcium content is chemically bound to Phosphorus
and is not available in exchangeable form, so should not be considered as part of
the Calcium being added to balance the CEC ratios.
As a rule, don't use
Dolomite
lime, regardless of what you may have read in
various gardening topics, unless you are sure that you need Magnesium. Dolomite
is a high Magnesium limestone. Using dolomite will tighten the soil, reducing air in
the soil and inducing anaerobic alcohol fermentation or even formaldehyde
preservation of organic matter rather than aerobic decomposition. If the soil test
calls for more Magnesium, Magnesium sulfate (Epsom salts) or K-Mag (also
known as Sul-Po-Mag, sulfate of potash magnesia, or Langbeinite), are generally
safer and quicker acting sources of Magnesium than dolomite. Magnesium oxide is
the purest and quickest acting Magnesium additive, but is not presently allowed
under USDANOP organic rules, for some reason.About the only time dolomite
lime might be called for would be if the soil already had too high a level of Sulfur to
use Magnesium sulfate (Epsom salts) or K-Mag, or if other sources of Magnesium
were not available. If one is not concerned with being “certified” organic under
USDArules, Magnesium oxide is the best bet. MgO (Magnesium Oxide) is around
50% Mg, a much higher percentage than dolomite lime (13% Mg) or Epsom salts
(10% Mg) so it is also a much cheaper source of Mg. If you are not concerned
about being certified by the government, I would recommend using MgO.
Agricola's chart says that Phosphorus and Potassium should be equal, but that's
not as simple as it looks. On a bag of fertilizer sold in the USAor Canada, such as
10-10-10, the numbers stand for NPK, in that order. The N number is for Nitrogen,
but the P number actually stands for
phosphate,
P2O5, and the K number stands
for
potash,
K2O (K is from the German word Kalium, meaning Potassium).
Phosphate is 44% Phosphorus, while potash is 83% Potassium. So, one needs
about twice as much phosphate as potash for the P and K to be equal.A10-20-10
or a 2-4-2 fertilizer would have that correct ratio.
It is also important to know what form of P and K the soil test is listing. Some labs
give the P number as phosphate, P2O5, so you can take that times .44 and find the
actual amount of Phosphorus in your soil. Some give the K number as K2O, some
as actual K. It is best to request that the lab results be listed in parts per million of
the pure element being measured.
.
Although this chart emphasizes
minerals,
you would not have much luck trying to
grow food in a soil that wasn't bio-active even if it contained the perfect mineral
