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SWEEP Report #17

Effect of Ammonia on Soil Properties and Relevance to
Soil and Water Quality

D. Cressman et al., Ecologistics Ltd., Waterloo, Ontario

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

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Associated SWEEP/LSP Research



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Completed: October, 1990

Key Words:

soil quality, nitrogen, anhydrous ammonia, soil erosion, soil pH

Executive Summary

Injection of anhydrous ammonia (AA) into soil causes high pH and high ammonia concentrations in an ammonia retention zone around the point of injection. These conditions might decrease soil productivity and increase erosion because they can cause hydrolysis of organic C, loss of soil structural stability, and inhibition of microbial activity. Two laboratory experiments (Experiment 1 and Experiment 2) were conducted to determine effects of AA on these soil properties and nutrient availability. In Experiment 1, three soils that ranged from 12 to 42% clay and 2.6 to 4.6% organic matter were packed moist into 15-cm long and 5.0-cm diameter columns. Soil columns were injected with reagent grade ammonium hydroxide solution (1931 mg N) at a depth of 0.5-cm below the soil surface at the top end of each column. Columns were incubated at 25C and some were sampled at each of 1, 7, 28, and 112 days after injection. Sampling involved removing four 1-cm segments from the top of a column (depths 1 to 4) and a 1-cm segment from the bottom of the column (depth 15) for analysis. Experiment 2 was similar to Experiment 1 except that it involved only one soil, 129 mg N injected, and samplings at 1, 7, and 28 days.

Concentrations of exchangeable NH4-N in Experiment 1 were uniform throughout the columns by day 7 and changed little to day 112. On day 7 they ranged from 1007 to 1660 mg/kg-1, which is similar to maximum expected concentrations in the NH3 retention zone at usual field rates of application of AA. Maximum pH values were 8.8 to 9.2 and pH remained above 8.0 by day 112. Concentrations of water-soluble organic C increased to day 28, and then decreased to day 112 apparently because of microbial assimilation and dissimilation. Production of carbon dioxide from the soils was not detected until day 28 or later. Wet aggregate stability was initially decreased by ammonium hydroxide and then largely regained when microbial activity resumed. Ammonium hydroxide seemed to cause an increase in available P of 21% in one soil, and a decrease in available K of 3 to 14%.

On day 1 in Experiment 2, NH4-N ranged from 760 mg/kg-1 in depth 1 to 5.9 mg/kg-1 in depth 15., while pH ranged from 8.6 to 6.9. Nitrification caused a continual decrease in NH4-N to day 28, when pH was about 5.2 for all depths. Concentrations of water-soluble organic C did not significantly vary with depth and decreased from 627 mg/kg-1 on day 1 to 380 mg/kg-1 on day 28. Between days 7 and 28, wet aggregate stability increased while water-dispersible clay decreased for all depths.

It was concluded that AA could cause an initial loss of wet aggregate stability in the NH3 retention zone, but this loss is likely to be regained when microbial activity resumes. Possibility of leaching of water-soluble organic C from the NH3 retention zone by rainfall or irrigation, and long-term changes in microbial populations, might prevent regaining of structural stability under field conditions.


Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)

Two laboratory experiments were designed to verify possible harmful side-effects of anhydrous ammonia (AA) application. According to past research, there is evidence that AA will raise soil pH, increase ammonia to toxic levels in the soil, destroy soil fauna and reduce structural stability. To test this, measurements of soil pH, ammonium and nitrate nitrogen, other nutrient levels, microbial activity, clay dispersion and soil structural stability were taken at several depth intervals over time.

The findings suggest that microbial activity is reduced initially by toxic levels of ammonia gas and/or nitrite levels but resumes after nitrogen is converted to more available forms or is lost from the system. Soil structural formation is temporarily decreased but resumes at normal development rates after microbial activity resumes. Other nutrient levels are not likely to be affected in the ammonia-N band.


Under laboratory conditions, AA has little net negative effect upon soil quality. Rainfall simulation in similar conditions may have verified these conclusions.

However, field conditions are far more complex. The long-term effects of continued use on soil fauna needs to be examined. The effect of ammonia on soil biology could be difficult to isolate from that of tillage, pesticides and other factors. Further, it would be difficult to contrast changes in soil quality in the field. Tillage and cropping practices may overshadow AA 's contribution to soil degradation.

The only practical tip from this work might be: continual use of AA may be harmful to your soil, so try other forms and timing of N application. [The Ontario Ministry of Agriculture and Food already strongly advocates crop rotation for many reasons - particularly in grain-based cropping systems. This practical tip is not new.]

Future Research: ( ) indicates reviewers suggestion for priority, A - high, C - low.

(A) Field research would be useful to understand the N-cycle but marginally useful to improve our understanding of soil quality.




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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 01:57:26 PM