This results in a total of 86 bales per stack. The plastic is placed over the stack, and the edges placed into the trench and covered with soil to seal the stack air-tight. After the plastic is placed over the hay stack and sealed into the trench, it should be checked for holes usually caused by hay stems puncturing the plastic during covering. The hose from the ammonia tank is placed under the plastic. Anhydrous ammonia tanks have a capacity gauge to meter the proper quantity of ammonia into the stack.
Ammonia leaves the tank as a liquid and then turns into a gas and fills the area under the plastic.
Depending upon how fast the ammonia is allowed to flow into the stack, the plastic can balloon out and become very tight. It usually takes three to five hours to apply the proper amount of ammonia to the stack. When ammonia is being applied, the stack should be checked about every hour to make sure the process is proceeding normally. After 1 to 2 days, the ammonia will be absorbed into the hay. As a general rule, hay should remain sealed under the plastic for about 30 days before feeding.