A reader asked “Am I able to substitute the amonium nitrate in the weekly feed with ammonium sulfate?”
The answer that follows is important for everyone to know:
Ammonium sulfate is only 21-0-0, as opposed to 34-0-0 for ammonium nitrate. In addition, 21-0-0 has substantial sulfur in it, which lowers soil pH. If you WANT to lower your soil’s pH then 21-0-0 will help you do that. However, if your area already has pH lower than 7, because you receive more than 20″ of annual rainfall, then sulfur (and 21-0-0) is probably not the best solution.
34-0-0 is the BEST nitrogen source no matter where you live – if you can get it – but others can be used, including urea (46-0-0). This may be the better replacement if you live in a high rainfall area.
However, urea takes time to become available to plants because it has to undergo multiple chemical changes before becoming available to the plants.
Meanwhile, because nitrogen is volatile, some of the nitrogen can easily be lost to the air before the plants get any. To help reduce the loss of nitrogen through volatilization always mix it into the soil, rather than simply applying on the soil surface.
Use the same quantity of urea as you would ammonium nitrate, again because of the slower availability and losses incurred.