Anhydrous ammonia applicators are farm machines that place nitrogen fertilizer below the soil surface so crops can use it during growth. The system usually includes a tractor, a pressurized nurse tank, hoses, a metering system, a toolbar, knives or injectors, and sealing wheels. This machinery matters because nitrogen strongly affects plant growth, crop yield, and farm economics.
It also matters for safety because anhydrous ammonia is stored under pressure and can injure skin, eyes, and lungs if released.
Inside the applicator, liquid ammonia flows from the nurse tank through valves, filters, hoses, and a rate controller before reaching the injection knives. When pressure drops near the outlet, some ammonia can vaporize, so the system must control both flow rate and placement depth. The knives open narrow slots in the soil, the ammonia is injected below the surface, and closing wheels or covering disks seal the slot to reduce gas loss.
Good application depends on correct pressure, temperature, travel speed, soil moisture, and calibration of the metering system.
Key Facts
- Anhydrous ammonia has chemical formula NH3 and contains about 82% nitrogen by mass.
- Application rate relation: fertilizer delivered per area = mass flow rate ÷ field area rate.
- Field area rate = implement width × travel speed, with unit conversions applied.
- Tank pressure depends strongly on temperature because NH3 exists as a pressurized liquid and vapor mixture.
- Injection depth is commonly about 10 to 20 cm to help seal ammonia in moist soil.
- Mass of nitrogen applied = mass of NH3 applied × 0.82.
Vocabulary
- Anhydrous ammonia
- Anhydrous ammonia is a nitrogen fertilizer made of NH3 with no water mixed in, stored as a pressurized liquid.
- Nurse tank
- A nurse tank is the pressurized tank that carries anhydrous ammonia to the applicator in the field.
- Toolbar
- A toolbar is the frame behind the tractor that holds the injection knives, hoses, valves, and sealing devices.
- Rate controller
- A rate controller is a device that adjusts ammonia flow so the target fertilizer rate is maintained as speed or conditions change.
- Injection knife
- An injection knife is a soil-opening shank that places ammonia below the surface and helps direct it into the furrow.
Common Mistakes to Avoid
- Confusing NH3 with liquid nitrogen is wrong because anhydrous ammonia is a chemical compound containing nitrogen, while liquid nitrogen is elemental N2 used mainly for cooling.
- Ignoring unit conversions in application rate calculations is wrong because acres, hectares, meters, feet, hours, and seconds must match before using formulas.
- Assuming the tank is empty when liquid flow stops is wrong because vapor pressure and trapped ammonia can remain in hoses, valves, and fittings.
- Placing ammonia too shallow is wrong because the gas can escape from the soil before converting to plant-available forms, reducing efficiency and increasing hazard.
Practice Questions
- 1 A toolbar is 12 m wide and the tractor travels at 8 km/h. What field area rate does the applicator cover in hectares per hour?
- 2 A farmer applies 120 kg of NH3 per hectare. How many kilograms of nitrogen per hectare are applied if NH3 is 82% nitrogen by mass?
- 3 Explain why an anhydrous ammonia applicator uses injection knives and sealing wheels instead of simply spraying ammonia on the soil surface.