A nurse tank is a portable, pressurized tank mounted on a trailer that stores and transports anhydrous ammonia, a nitrogen-based fertilizer, from a central storage facility to farm fields. It acts as a mobile supply station, feeding the chemical into an applicator or toolbar that injects it directly into the soil. The name “nurse” comes from its role: it nurses, or replenishes, the smaller application equipment so farmers can keep working without returning to a fixed storage site.
How Nurse Tanks Work in the Field
During planting and fertilizing season, farmers need to apply nitrogen across hundreds or thousands of acres. A fixed storage tank at a fertilizer dealership holds the bulk supply, but that tank isn’t going anywhere. The nurse tank bridges that gap. A farmer fills the nurse tank at the dealership, tows it to the field behind a truck, and connects it to an applicator, which is the implement that actually knifes the ammonia into the ground.
The connection process is straightforward but requires care. You couple the nurse tank’s hose to the applicator, keeping the hose end pointed away from you and making sure the connectors are clean. Valve handles get hand-tightened. Before towing, the hitch pins must be secure and safety chains attached. Once connected in the field, the pressurized ammonia flows from the nurse tank through the hose and into the applicator’s distribution system, which feeds it into knife-like injectors spaced along a toolbar pulled behind a tractor.
Standard Sizes and Construction
Nurse tanks come in two common sizes: 1,000-gallon and 1,450-gallon capacities. They sit on purpose-built trailer frames called running gears, which are heavy-duty enough to handle the weight of pressurized ammonia. A typical running gear uses a 6-by-4-inch rectangular steel tube frame with reinforced heavy channel tank mounting brackets. Larger models feature tandem walking rear axles (two axles that shift together over uneven ground) and a helper lift on the tongue to make hitching easier.
Track width varies by size. A 1,000-gallon dual-tank setup has a rear track width of about 93 inches, while a 1,450-gallon version widens to around 102 inches. Both typically have a 60-inch front track. The tanks themselves are steel pressure vessels built to hold a minimum design pressure of 250 psi, as required by OSHA regulations.
What’s Inside: Anhydrous Ammonia
The primary substance carried in nurse tanks is anhydrous ammonia (NH3), a nitrogen fertilizer that exists as a clear liquid under pressure. At atmospheric pressure, it boils and becomes a gas at just minus 28 degrees Fahrenheit. That phase change is what makes it both useful and dangerous. When injected into soil, the ammonia rapidly expands into gas and bonds with soil moisture, delivering a concentrated dose of nitrogen right where plant roots can reach it. It’s one of the most efficient ways to fertilize large-scale row crops like corn.
The term “nurse tank” can also refer to portable tanks used for other liquid fertilizers or agricultural chemicals, but in common usage, it almost always means anhydrous ammonia. The pressurized nature of NH3 is what drives the specialized design and safety requirements that set these tanks apart from ordinary chemical storage.
Built-In Safety Features
Because anhydrous ammonia is stored under significant pressure, nurse tanks carry multiple layers of safety protection. Every tank is equipped with a pressure relief valve that accesses the vapor space above the liquid. If internal pressure exceeds 250 psi, this valve opens automatically and vents vapor to prevent a catastrophic failure. OSHA requires these relief valves to start discharging at or below the tank’s design pressure and to have enough capacity to keep the tank from ever exceeding 120 percent of that rating.
Excess flow valves are built into both the liquid withdrawal valve and the fill valves. These internal valves snap shut automatically if liquid flows out too fast, as would happen if a hose ruptured or a valve sheared off during transport. Hydrostatic relief valves are placed anywhere in the plumbing where ammonia could become trapped, allowing it to vent safely rather than building pressure in a closed section of pipe. Every tank must also have its fittings protected from physical damage by an approved roll cage, which keeps valves and gauges intact even if the tank tips over.
Health and Environmental Hazards
Anhydrous ammonia’s ability to evaporate instantly is what makes it so hazardous to handle. Contact with skin causes severe chemical burns because the ammonia pulls moisture from tissue as it vaporizes. Inhaling the gas can cause asphyxiation. Eye exposure can cause blindness. These aren’t theoretical risks. They happen every year during fertilizer season, particularly when equipment is old, poorly maintained, or operated without proper protective gear.
Tanks must be labeled on both sides, front, and rear with the words “ANHYDROUS AMMONIA” and “INHALATION HAZARD” in letters at least 4 inches tall. Before transferring ammonia, operators should position equipment so the wind carries any escaping vapors away from homes, buildings, livestock, and growing crops.
Transport and Regulatory Requirements
Towing a nurse tank on public roads falls under U.S. Department of Transportation hazardous materials regulations. Every tank must be marked with the proper shipping name or common name on each side and each end. It must also display the correct hazmat placard. The only exception: if one end of the tank is crowded with valves, fittings, regulators, or gauges that physically prevent a placard from being properly placed and visible, that single end is exempt from marking. All other surfaces must comply.
Lighting, reflectors, and standard trailer safety equipment (chains, brakes where required, proper hitch) all apply. State regulations may add additional requirements on top of federal rules, so what’s legal in one state may not be in another.
Inspection and Maintenance Schedules
Federal regulations require nurse tanks to undergo an external visual inspection every year. A full pressure test, either hydrostatic (using water) or pneumatic (using air or gas), is required every five years. These inspections must be performed by a qualified inspector. Any pressure-bearing components of a heating system on the tank, if one is present, also get a hydrostatic test every five years at the maximum system design operating pressure, held for five minutes.
Between formal inspections, operators should check hoses for cracking or wear, verify that all valves open and close properly, confirm the pressure gauge reads accurately, and ensure the roll cage is intact. A nurse tank that passes its pressure test but has a corroded hose or a stuck excess flow valve is still a serious hazard. Seasonal maintenance before spring application is standard practice at most farm operations and fertilizer dealerships.