Brian Marsh

UCCE Farm Advisor, Kern County

Achieving Uniform Anhydrous Ammonia Application

     Anhydrous ammonia (NH3) is the least expensive form of nitrogen fertilizer, containing 82% nitrogen and is applied on thousands of acres each year. With a boiling point of -28F, NH3 is a gas at atmospheric pressure thus requiring pressurized tanks to keep it in a liquid form. The tank pressure is also utilized to propel the material from the tank, through the regulator and distribution system into the soil. Typically, a variable diameter orifice is used to meter the NH3. The flow rate is based on a calculation of desired application rate, equipment width and speed, with adjustments made for changes in tank pressure or ambient temperature. At the point of regulation the pressure drops, the NH3 begins to vaporize, and both liquid and vapor are transported through the delivery system. The assumption that this liquid and vapor combination will flow uniformity through the system can be greatly over estimated. Differences in uniformity of application from two different systems are shown in Figure 1. Fertilizer application from each delivery shank was measured. One system (light gray) has been properly setup and calibrated. The average output was very close to the calculated application rate and the variation between the shanks was very low and not significantly different. The target application rate is shown as the horizontal line. The other system (black) has not been well cared for, but is still in use. The result is a gross misapplication of NH3. Not only did the application rate not equal the calculated rate the variation between the shanks was very large. These two systems were compared for uniformity of application and the effects on crop growth in a field study. While the same amount of fertilizer nitrogen was applied by both systems in the field, the degree of variability was calculated to be about 15% compared to more than 50% for the poorly maintained system. The result was excessive nitrogen applied to some areas while other areas did not receive enough. Plants growing in areas of under application will not have sufficient nutrients for optimal crop production while the areas of over application have the potential to negatively impact nitrate movement to ground water. The lack of uniformity of fertilizer nutrients in the field has been shown to cause greater variability in yield.
     Most anhydrous ammonia application equipment is rarely checked for proper calibration and uniformity of application. The physical characteristics of anhydrous ammonia cause difficulty in measuring output along with the potential for physical harm to the operator if proper safety procedures are not followed. Anhydrous ammonia is a great affinity for water, including moisture in the body. Areas of the body that are especially sensitive are the eyes, nose, and throat. With the proper equipment, a tune-up of application equipment can safely be done. Safety equipment includes: rubber gloves, ammonia type goggles or face shield, respirator, long sleeve shirt and pants, and plenty of water. An equipment tune-up includes an application rate that should be between 10% and 90% of the meter's rated output. The filter screen should be cleaned regularly. Metal flakes from the tank can easily partially or completely block openings. The distribution manifold should be mounted horizontally with the same number of openings as distribution shanks and evenly spaced around the manifold. The hoses should be of uniform length with no crimped or bent hoses and the excess mounted in horizontal loops. The outlet holes on the knives should be clean and of the same size. To test the output the following are needed: 5 gallon bucket for each knife, 100 pound scale, tape measure, and stop watch. To conduct the test 1) place a bucket under each knife. 2) lower the knives into the bucket. 3) measure the distance from the knife opening to the water surface, adjust to a uniform depth. 4) raise knives and weigh the buckets. 5) open control valve, system to operating pressure. 6) lower knives, start timer. 7) add NH3 for set period. 8) raise knives, stop timer, shut off valve. 9) allow NH3 gas to move away. 10) reweigh buckets. 11) repeat 3 times. If the results are within 10% of each other the system is ready to go. If not, recheck the tune-up items. With proper calibration, uniform application is possible with positive results for crop growth.