Organic gardening Ammonium nitrate - Ammonium Sulfate – Or Urea?

Small things can sometimes make a big difference in gardening results. For example, AMMONIUM NITRATE (34-0-0) is much different than AMMONIUM SULFATE (21-0-0) or UREA (46-0-0) - even more than the % of nitrogen.

AMMONIUM SULFATE ((NH4)2 - SO4 - - 21-0-0-24S)
1. Supplies two vital nutrients for crop growth – nitrogen and sulfur. This can be good or bad, depending on whether or not you need the extra sulfur. Sulfur lowers pH, and if you live in a high-rainfall area you do not want that. If you receive less than 20" of rain per year however, the sulfur may help improve your high-pH soil conditions. And the sulfur is in the sulfate (with oxygen) form, which is the only form in which it is available to plants.

2. Its low-cost and ready availability in most places means you can get nitrogen wherever you are.

3. It is only 21% nitrogen, and not immediately available to plants because it must go through a chemical change. This can be good in some situations and bad in others. If your plants need an immediate shot of N you may be disappointed - especially in cold weather - because the change happens very slowly in cold weather. Conversely, in hot weather you may be happy with NH4 because the nitrogen is more stable and does not volatilize so quickly, thus providing nutrition for a longer time.

AMMONIUM NITRATE (NH4 NO3 - - 34-0-0)
1. Combines the stability of the ammonium form with the immediate availability of the nitrate form to provide immediate nitrogen - even in cold weather - with a much higher % of nitrogen than the sulfate form.

2. Usually costs more than either sulfate or urea, and is not available in many places, because of the potential use in making a powerful explosive.

3. Only provides one nutrient - nitrogen. Again, depending on your situation, this can be positive or negative. In places receiving more than 20" of annual rainfall more sulfur is often not desirable, and therefore ammonium nitrate is the better solution.

UREA ((NH2)2CO - - 46-0-0)
1. Not available to plants until several chemical changes take place - therefore the least favorable choice, especially if an immediate "fix" is needed.

2. Losses from volatilization during the chemical changes make it very important not to apply on the surface of the ground.

3. Often the least cost to purchase, and with the highest % of nitrogen it appears to be the best value, but it is usually the least desirable of the three nitrogen sources.