Ammonium Nitrate vs. Ammonium Sulfate for Lawns

Ammonium Nitrate

• Ammonium nitrate is a granular fertilizer that provides plants with a heavy dose of nitrogen over a short period of time. Supplying your lawn with nitrogen encourages the growth of stems and leaves. This fertilizer supplies roughly equal amounts of nitrogen in the ammonium and nitrate forms that plants can draw from the soil immediately. The combination of these chemicals limits the affect of ammonium nitrate on the pH of lawns compared to ammonium sulfate. Ammonium nitrate is a concentrated source of nitrogen that contains 34 percent nitrogen by weight.

Ammonium Sulfate

• Lawns that are deficient in sulfur and nitrogen are the best candidates for ammonium sulfate. Adding ammonium sulfate to a lawn that is deficient in sulfur produces a deeper green color and thicker growth. Ammonium sulfate is made from anhydrous ammonia and sulfuric acid, and it contains 21 percent nitrogen and 24 percent sulfur by weight. The nitrogen in ammonium sulfate is all in the form of ammonium, which contributes to its tendency to lower soil pH.

Spread It on, Wash It In

• Ammonium nitrate and sulfate are applied over the surface of existing lawns and then watered into the soil. The best time to use these fertilizers on your lawn is during the spring or fall in the morning just after the lawn has dried. Both types of fertilizer can burn your lawn if it comes into contact with wet foliage. After you have applied these fertilizers, you need to water your lawn to wash the fertilizer off the blades of grass and into the soil.

Salt, pH Dangers

• Applying ammonium nitrate or sulfate to your lawn increases the amount of salt in the soil and lowers its pH. Ammonium sulfate lowers the pH of soils more than ammonium nitrate and has a slightly higher salt content. Applying a heavy dose of these fertilizers during hot weather can limit the ability of your grass to take up water, causing it to turn brown.

Conditions for Application

• You can use an application of ammonium nitrate to encourage grass to regrow on lawns that develop bare patches after severe heat damage during the summer. The best time to use ammonium nitrate is during relatively cool weather in the spring or fall when your lawn is not being stressed by drought or high temperatures. Ammonium sulfate can also provide a quick boost in nitrogen, but it is not suitable for lawns with a low pH or high salinity level. The best use for ammonium sulfate is fertilizing sandy lawns that are lacking in both nitrogen and sulfur.