Agriculture Reference
In-Depth Information
Monoammonium Phosphate (MAP) 11-52-0
Monoammonium phosphate (MAP) contains a lot of phosphate and a fair amount of am-
monium, too. I've used this one in regions where I couldn't find any soft rock phosphate, or
to “loosen” existing phosphate, when I seemed to have plenty on a conventional soil test,
but not much available on a Reams test. I've also used it for this purpose at the same time
as applying soft rock. Diammonium phosphate (DAP) has a very high pH and ties up
tightly with calcium, so it isn't recommended.
I would only use MAP if nitrogen and phosphorus are both low, at 1 to 4 pounds per
1,000 square feet, combined with molasses, while focusing on soft rock phosphate in the
long term. Phosphoric acid prices have skyrocketed around the world, so MAP is quite ex-
pensive right now for farmers, but it's not so bad on a garden scale. I've purchased 50
pounds for less than $30. Of all the chemicals, this is probably the first one I would recom-
mend if you can't find soft rock phosphate because it's just so important to get some avail-
able phosphate in there, but it's also one of the most difficult to find.
