Each year I come into contact with local growers that are led to believe that water run applications of anhydrous ammonia hardens the soil. They are concerned that applying this form will lead to losses in soil quality and crop yields. These beliefs are based upon opinions from those who do not understand local soil and water conditions.
I believe that water run anhydrous ammonia applications make good sense in the area irrigated by the Lower Colorado River and here are my reasons. 1. Economic Sense: The cost of ammonia historically has been 1/2 (on per unit N basis) that of other nitrogen fertilizers such as UN-32 and Urea. At my last check, the cost for NH3 was $0.35/lb N compared with $0.57/lb N for UN-32. This means a typical water run of 30 lbs N/ac of NH3 would save the farm $6.60 per acre. 2. Agronomic Sense: NH3 is a good “maintenance” fertilizer. It must convert to Nitrate before becoming completely available to root uptake. It has been said, it is the “next irrigation” fertilizer and moves into the plant over time. In this sense, it could be considered “slow release”. If plant analysis shows adequate levels of Nitrogen and if the crop is entering a time of high Nitrogen demand, NH3 is a good form to apply to maintain those levels. 3. Soil Sense: NH3 does not cause hard soil where the source of the water is the Colorado River. Yes, precipitation of Calcium Carbonate occurs with applications, but the sodium hazard of the River Water (SAR) does not increase to severe or even moderate levels. Water analysis of samples taken during these water run applications show the precipitation of ~100 lbs Calcium per acre foot of water, but the sodium hazard increase(2) SAR unit 2.1-3.3 and R-Na from 1.7-2.2. Both are considered in the no restriction on infiltration category(1) with Colorado River Salinity (ECw 0.85). Therefore: Water run Anhydrous ammonia does not harden the soil in our area. NH3 is an acid-forming fertilizer, It converts over-time to nitric acid and actually reduces soil pH. 3. Environmental Sense: Yes, NH3 can burn the lower leaves where it contacts plants and roots on very sandy soils with over-application. And, NH3 is a gas and can be lost during water run applications. Therefore, I recommend neutralizing the water pH with sulfuric acid during the water run, this keeps the NH3 in solution and reduces plant burn and Nitrogen loss. NH3 is immobile in the soil and does not contribute directly to Nitrate pollution of groundwater (see agronomic sense above). Also, NH3 stimulates micro-organism growth as it is converted to Nitrate.
Safety/liability Concerns: While NH3 applications are lauded above, it must be stated that NH3 is a noxious gas and must be handled and monitored only by trained professionals. Some commercial fertilizer companies no longer supply this fertilizer because of high insurance liability costs and these safety concerns.
All considerations taken in stride, NH3 can be a good tool to have in the growers tool box to maximize production and minimize costs.
1. Soil Improvement Committee. Western Fertilizer Handbook. 9th Edition. Danville, Il; CPHA, 2002.
2. Ayers, R. S., and Westcot, D. W. Water Quality For Agriculture. Rome Italy; FAO of the United Nations. 1985