- D. J. McKenney, Department of Chemistry and Biochemistry, University
of Windsor, Ont., and C. F. Drury, Research Station, Agriculture
Canada, Harrow, Ont.
(Tech. Transfer Report Summaries)
View/Download Report [1064 KB pdf]
Associated SWEEP/LSP Research
Completed: May, 1992
ridge tillage, no-till, moldboard plow, surface run-off,
tile run-off, nitrate, nitrite, nitric oxide, nitrous oxide, nitrogen,
corn, yield, Kentucky bluegrass
Concerns over contamination of natural water systems and rising
costs of production in the agriculture industry have led to increasing
use of conservation tillage methods as a means of reducing these
effects. Reduced tillage, however, also affects water movement,
aeration and N-transformations in soils. A simplified N cycle diagram
for soils is shown in Figure 1. The research described in this report
was focused on several of these aspects as summarized below.
Nitrate Loss in Surface and Tile Runoff with Conservation and
Nitrate concentrations and total volume of surface and tile runoff
from conventional (moldboard plow) tillage (CT), no-tillage (NT),
ridge tillage (RT) all planted in continuous corn, and Kentucky
bluegrass (BG) treatments, were measured over three years, 1989
to 1991. All corn tillage treatments received a total of 178.6 kg/ha
N annually over the growing season. The volume of water drained
through the tiles in the corn tillage systems always exceeded the
volume in surface runoff, typically by factors of 2 to 4. Tile outflow
was greatest from the CT treatments, least from BG and approximately
equal from RT and NT treatments in 1989 and 1990. Concentrations
of NO3- in tile water from CT, RT and NT treatments
exceeded the maximum recommended safe limit of 10 mg/l N in 79%
of runoff events with flow-weighted concentrations between 12 and
17 mg/l N in 1989 and 1990. Flow-weighted NO3-
concentrations were only 1.2 and 2.6 mg/l N from BG in 1989 and
1990 respectively. The total NO3- lost in
tile water in 1989 was 18, 14, 14 and 1 kg/ha N from the CT, RT,
NT and BG treatments, respectively, whereas in 1990 there was 29,
20, 20 and 3 kg/ha N lost from the CT, RT, NT and BG treatments.
Nitrate losses in surface runoff were lower than tile runoff with
maximums of 2.6 kg/ha N for the RT and NT treatments in 1989 and
5.5 kg/ha N for the RT treatment in 1990. In 1989 and 1990, both
RT and NT treatments had greater yields and N-uptake than the CT
treatment. A serious drought in 1991 limited corn yield, N uptake
and NO3- loss.
Background and Potential Denitrification Variation with Depth
Under Conservation and Conventional Tillage
Background and potential denitrification was measured in Brookston
clay soil at depths to 0.9 m under several conservation tillage
plots and a conventional moldboard plow tillage plot. The objective
was to identify possible effects of the various tillage treatments
on denitrification and on NO3- loss. Background
denitrification (NO + N2O) was estimated in intact cores
in 1989 and 1990 using a gas flow-through system which permitted
net NO and N2O production rates to be measured. Rates
decreased with increasing depth under all tillage treatments but
no correlation was evident between background denitrification and
tillage, perhaps due to the large spatial variability observed.
Potential denitrification estimates were made using excess added
NO3- and the C2H2 blockage
method (Yoshinara et al., 1977). Estimates were obtained in 5 cm
increments to a depth of 0.9 m. In all cases the top 5 cm increment
showed highest potential for denitrification. Among the tillage
treatments the highest potential was with the no-till Kentucky bluegrass
plot and intermediate potentials in ridge till and no-till corn
plots and lowest in the conventional till plot. Carbon dioxide production,
NO3- and NH4+ levels
followed the same pattern with depth. The relatively low denitrification
potential below the uppermost soil layer suggests that in these
plots denitrification would not be expected to greatly ameliorate
NO3- loss by leaching.
Nitric Oxide and Nitrous Oxide Production: Water and Oxygen
This study was designed to determine the effects of water and
O2 on the speciation of denitrification gases (NO and
N2O). Nitric oxide was found to be the principal end
product from soil incubated under low moisture conditions, whereas
the relative amount of N2O increased under wetter moisture
regimes. The total amount of NO plus N2O produced increased
with increasing water content for the Brookston clay loam whereas
it peaked at 15% water content with the Fox sandy loam. The decrease
in NO plus N2O at higher water contents was probably
the result of the subsequent reduction of N2O to N2
in the Fox sandy loam soil. The residence time of the denitrification
gases in the soil increased with increasing water content, hence
facilitating the subsequent conversions of NO to N2O
and N2. The thickness of the water film surrounding the
microbes affected both the diffusion of O2 through the
water and into the microbes as well as the diffusion of denitrification
gases (NO, N2O, and N2) from the microbes
into the atmosphere. In the sandy loam soil, O2 content
and soil water affected both the amount and species of evolved denitrification
gases. Oxygen was more effective in decreasing NO production at
lower than at higher water contents.
Although conservation tillage (RT and NT) decreased the concentration
and total loss of NO3- the concentrations
generally exceeded the 10 mg/l N recommended limit. Further reduction
could perhaps be achieved through use of cover crops, intercrops
or controlled drainage systems. In conservation tillage systems,
particularly RT, losses of N by denitrification would likely be
reduced if nitrogen fertilizer was added below the surface 5 cm
zone. Since tillage influences water infiltration and storage and
the aeration status of the soil the overall denitrification rate
is affected as well as the ratio of NO:N2O. Thus tillage
indirectly affects the environmental impacts of these important
atmospheric trace gases, and also contributes to the observed large
spatial variability in flux of these gases from soils. Greater levels
of NO evolve from drier soils and relatively greater levels of N2O
from wetter soils. Under all tillage systems both background and
potential denitrification decreased markedly with depth reflecting
low populations below the surface layer. Hence in the plots used
in this study, denitrification would not be expected to greatly
ameliorate loss of NO3- by leaching.
(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank,
The report covered three separate experiments all related to
the occurrence of nitrogen losses from soil under a variety of tillage
The first experiment compared the affected volume, concentration,
and total amount of NO3- lost from surface
and tile run-off, under ridge till, no-till, and moldboard plow
systems planted to corn, compared to a Kentucky bluegrass treatment.
As the amount of nitrogen utilized by plants will reduce the nitrogen
available to be leached, grain corn yields and nitrogen uptake of
the three tillage plots were compared.
The plots were centred above tile placed at a depth of 0.6 m.
Both surface and tile water were collected from natural rainfall
events. Rainfall for 1989 was below average, for 1990 above average
and in 1991 there were drought conditions. The results of the study
showed that the greatest movement of water for all of the corn tillage
systems was through the tile rather than surface run-off. The corn
tillage system that had the greatest volume of tile flow was the
moldboard plow system.
Grain corn yield and tissue nitrogen under the ridge till and
the no-till plots was higher than the moldboard plow system. The
higher nitrogen uptake in the conservation plots over the moldboard
plow plots was similar to the reduction in the amount of NO3-
lost by leaching. While the concentration of NO3-
from the tile was less under the conservation tillage it was still
above drinking water standards. Bluegrass sod was the only treatment
that consistently had both surface and tile run-off waters within
drinking water standards.
The objective of the second experiment was to identify the effects
of various tillage methods on the denitrification process with depth.
The treatments consisted of bluegrass, and continuous corn under
ridge tillage, no-till and moldboard plow as in the first experiment.
Soil cores were taken in October 1989 and July 1990 and background
levels of nitric oxide and nitrous oxide were determined by using
the continuous flow technique. Potential denitrification estimates
were determined by using the acetylene inhibition technique.
Background denitrification rates were about the same level in
1989 and 1990 and decreased with depth under all tillage systems.
No relationship between tillage systems and production rates was
demonstrated between the two years. Large variations in rates persisted
within and among sampling sites. Both background levels and potential
denitrification decreased with depth.
The objective of the third experiment was to study the physical
effects of water on NO and N2O production under conditions
favouring denitrification. The combined effect of O2
and soil water content on NO production was also studied.
At times it was difficult to determine if the information provided
in the report was the results of the study or part of a literature
review. The differences in weather conditions that occurred between
the three years provides some interesting information. However,
further trials should be conducted to determine if the results obtained
for each of the three years is an accurate indication of surface
and tile run-off as well as corn yield for each system. No explanation
was given as to why in 1989 there was a greater loss of NO3-
per event than 1990.
Study 2 only looked at potential denitrification rates under
laboratory conditions rather than actual rates under field conditions.
This was a lab study not a field study and further examination is
needed to determine if the results are transferable to field conditions.
The length of the study should have been longer than 2 years before
making estimates on the potential for denitrification.
Continuous corn is known to degrade both surface and subsurface
soil structure over time, which could affect the results. Monoculture
corn is not used as extensively as it once was on Ontario farms.
Mulch tillage, the most popular conservation tillage system for
lowland clayey soils was not included in this study. The no-till
system used in the study, the planter shoe tillage, is not common
in Ontario. With this in mind another system of no-till, one more
representative of what is used in Ontario, should have been studied.
Nail-like spikes extending above each statistical box are not
explained. It could be assumed that these refer to the Standard
Deviation of Error, however it would be preferable if this were
Carbon levels affect denitrification, however the organic matter
levels in the various zones within the profile are not reported.
SWEEP Report #17 - Effect of Ammonia
on Soil Properties and Relevance to Soil and Water Quality
SWEEP Report #28 - The Effect of Split
Applications of Nitrogen on Corn Yield Under Ridge and No-Till Conditions
SWEEP Report #35 - Nutrient Distribution
and Stratification Resulting from Conservation Farming
SWEEP Report #37 - Effects of Tillage
on the Quality and Quantity of Surface and Subsurface Drainage Water:
LSP7017 - Cropping and Soil
Management Effects on the Dynamics of Crop Residue Derived-N on
the Coarse Textured Soils in Southern Ontario
LSP7018 - Nitrogen Research
with Corn Using Conservation Tillage
LSP7020 - Nitrogen Conserving
Future Research: ( ) indicates reviewers suggestion
for priority, A - high, C - low.
(A) Research on the nitrogen cycle is needed but not in field
Thursday, May 19, 2011 03:56:20 PM