- D. Cressman et al., Ecologistics Ltd., Waterloo, Ontario
Evaluation Summary (Tech. Transfer Report Summaries)
View Download Final Report [1619 KB pdf]
Associated SWEEP/LSP Research
Completed: October, 1990
soil quality, nitrogen, anhydrous ammonia, soil erosion, soil pH
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 25°C 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.
(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank,
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
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.
Thursday, May 19, 2011 01:57:26 PM