Part A - Soil Erosion, Phosphorus Losses and Corn Yield
Deterioration of agricultural land by soil erosion and compaction has encouraged
the use of conservation tillage with residue management in southwestern
Ontario. Many types of conservation tillage systems have been developed
but all are characterized by reduced tillage with over 30% crop residue
on the soil surface. Zero and ridge tillage are examples of two conservation
tillage practices which leave sufficient crop residue to reduce water flow
velocities, increase water infiltration and produce less soil compaction.
Conservation tillage has been shown to be effective in reducing soil loss
by fluvial transport and in some cases increasing crop yield.
Phosphorus (P) in subsurface, surface and lake waters has been linked
with algal blooms which impairs water use and can lead to shifts in aquatic
species and populations. Phosphorus in subsurface and surface runoff from
agricultural activities has been associated with sediment-phase transport.
Thus, common belief held that a reduction in sediment transport would result
in reduced phosphorus transport.
Southwestern Ontario is characterized as ideally suited for agricultural
production because of its proximity to large U.S. and Canadian markets,
adequate and well distributed rainfall, fertile soils and favorable climate
for crop production. Because of its proximity to large populations and the
largest freshwater resource in North America, past and current agricultural
practices have been intensively investigated with respect to yield and to
a lesser extent on impairment of water quality. A study was begun in 1984
to identify sediment and phosphorus transport from a poorly drained, Brookston
clay loam soil, cropped to corn under three tillage practices. Water quality
and yield from a conventional (fall plow, spring disk and midseason cultivation)
tillage treatment, was compared with that from a zero tillage (no tillage
other than that associated with seeding and fertilizer application) and
ridge tillage (ridges reformed in mid-season) treatment. Research results
for the contract period January, 1988 to September 30, 1990 are reported
herein.
Rainfall was measured with a rain gauge at the site to determine input.
Surface and subsurface runoff for each runoff event was quantified from
depth of water over a weir. Water samples were collected manually from each
treatment throughout the hydrograph for sediment and orthophosphate analysis.
Total soluble and sediment P were also determined over the three year period
but an error in analysis invalidated the results for the 1988 and 1989 samples.
These phosphorus forms were determined for the 1990 season. The sediment
and orthophosphate concentrations were averaged within an event and event
transport or loss was calculated from the product of average concentration
of the component of interest and runoff volume. Annual losses were computed
as the sum of event losses for the year. Surface and subsurface amounts
were expressed as percent of total loss. The year was divided into three
seasons, before planting (or fertilizer application, January 1 to planting),
growing season (planting to September 30) and after harvest (October 1 to
December 31). The seasonal losses were reported as a percent of total loss.
A wide range in climatic conditions from dry to wet growing season occurred
over the duration of the study which affected grain yield, erosion and nutrient
transport. Grain yield was similar within years from each of the tillage
treatments. In 1988 (a dry year) and 1989 (a wet year) yields were low averaging
6 t/ha. In 1990 (a normal year) grain yield averaged 9 t/ha with slightly
greater yield from the conservation tillage treatments than from conventional
tillage. Conservation tillage has been reported to increase yield on well
drained soil because of moisture conservation from crop residue but yield
effects on poorly drained soils have been inconsistent and may be decreased.
Excessive soil moisture during crop development as occurred in 1989, has
been reported to reduce grain yield on Brookston soil.
Conservation tillage had a variable effect on sediment transport. In
two of the three years, sediment transport was reduced by the conservation
tillage treatments compared to that from conventional tillage. No tillage
effects on sediment transport were observed in one year (1990) probably
because no major runoff producing events occurred in the spring when soil
erosion was most susceptible and sampling was terminated in September, 1990.
Soil loss averaged over three years was 530±11 kg/ha from ridge tillage,
391±14 kg/ha from zero tillage and 897±14 kg/ha from conventional tillage.
Zero tillage was more effective at reducing erosion than ridge tillage over
the three years. A greater proportion of sediment transport occurred in
surface runoff from the conservation tillage treatments whereas subsurface
transport accounted for a greater proportion of sediment loss from conventional
tillage. It is possible that much of the sediment transported through subsurface
drainage from conventional tillage originated from preferential surface
flow through cracks developed when soil moisture content was low.
Generally, dissolved (ortho) phosphorus transport was higher from zero
tillage than from ridge or conventional tillage. Dissolved phosphorus transport
was lowest from conventional tillage. Annual dissolved phosphorus transport
ranged from 2.7 to 10.4% of that applied from 1988 to 1990. Subsurface drainage
accounted for greater than half of the orthophosphate loss from the conservation
tillage treatments in two (1988 and 1990) of the three years. In 1989, surface
runoff loss exceeded subsurface runoff loss of orthophosphate from zero
tillage. Over 74% of orthophosphate transport from conventional tillage
was from subsurface drainage in two of the three years. The seasonal loss
pattern for dissolved phosphorus and water runoff were similar. The cumulative,
three year sum of dissolved phosphorus transport was 74 to 174% higher from
the conservation tillage treatments than from conventional tillage (1665±45
g/ha). Orthophosphate transport was 57% higher from zero than ridge tillage
(2895±751 g/ha).
Preliminary studies indicated that total soluble P and total phosphorus
(sum of sediment P and soluble P) transport was higher from the conservation
tillage treatments than from conventional tillage. The proportion of soluble
P transported as orthophosphate was less from ridge (47%) and conventional
tillage (56%) than zero tillage (80%). Sediment phosphorus loss was similar
between ridge and conventional tillage (199±14 and 197±43 g/ha, respectively)
but higher from zero tillage (266±33 g/ha). Thus, much (84 to 93%) of the
phosphorus transported from the conservation tillage treatments and conventional
tillage occurred in the dissolved form. Other studies have shown that up
to 98% of phosphorus transport may be associated with the sediment phase
but that leachate from crop residue can account for considerable soluble
phosphorus transported from conservation tillage treatments. Ridge reforming
in ridge tillage may incorporate some of the crop residue with soil allowing
for greater residue decomposition which could account for the greater release
of soluble P from ridge compared to zero tillage. Sediment P and orthophosphate
transport was higher from zero tillage than from ridge tillage because of
P enrichment of runoff, but total P (the sum of all P forms) loss was higher
from ridge tillage because of the greater proportion of other soluble P
forms. Total phosphorus transport, assuming all P originated from fertilizer
ranged from 7±0.3% from conventional to 15±7% from ridge tillage. Since
total P forms were only determined from January to September, 1990, further
research is required to substantiate these results. Tillage effects in this
year were not statistically significant because of the high variability.
Phosphorus and sediment transport was also measured from a sod treatment
in 1990. Results are not directly comparable to the corn treatments because
sod received twice the amount of phosphorus as corn. However, several interesting
inferences with the corn treatment can be made. Water runoff from the sod
treatment was less than that from the corn treatment and ranged from 14
to 28% of the rainfall. Sediment transport was reduced to 129 kg/ha which
was 30 to 37% of that from the conservation tillage treatments. Over 90%
of the sediment loss occurred through subsurface discharge compared to 42
to 68% from corn culture. Dissolved orthophosphorus transport from the sod
(6.5% of applied) was similar to that from ridge tillage (6.4%). The percentage
of total phosphorus loss (14±1%) from the sod treatment was also similar
to that from ridge (15±7%) tillage. As noted for ridge tillage, much of
the total phosphorus transported from sod was in the soluble form.
This work indicates that for a poorly drained, Brookston clay loam soil,
conservation tillage effectively reduced soil erosion but not phosphorus
transport. Transport of soluble forms of phosphorus were higher from both
conservation tillage treatments than from the conventional tillage treatment
indicating that these tillage practices may result in increased phosphorus
bioavailability and reduced water quality. Further research will be needed
to confirm the result that total phosphorus transport is also increased
with conservation tillage. Thus, if the Great Lakes water quality objective
with respect to phosphorus is to be met, alternative or modified conservation
tillage systems will have to be developed. The introduction of crops which
have a low fertility requirement may result in lower recommended rates of
fertilizers and hence improved water quality. Research at Agriculture Canada,
Harrow is continuing to study alternative crop and soil management practices
that affect water quality (herbicides and nitrate) but resources are not
available to include phosphorus. The approach is to develop a management
system, whereby through water table control, a favorable environment for
efficient use of nutrients applied for crop growth will occur.
Part B - Herbicides
Conservation tillage with residue management has been proposed as the most
effective means to reduce soil deterioration in southwestern Ontario. Residue
management with conservation tillage has reduced soil erosion, increased
organic matter content and reduced soil compaction. In some situations,
impairment of water quality by pesticide contamination has been reduced
by conservation tillage treatments. However, increased impairment of water
quality has also been observed. A three year study was conducted on a poorly
drained, low slope Brookston clay loam soil to investigate the effect of
conventional tillage (fall plow, spring disk and mid season cultivation),
zero tillage (direct planting in previous crop residue) and ridge tillage
(planting in 15 to 20 cm high ridges, reformed in midseason) on surface
and subsurface transport of atrazine and metolachlor applied preemergence
to corn. Each runoff producing event was monitored to calculate the proportion
of rainfall originating as runoff and water samples from the runoff events
were collected for determination of herbicide concentration. Herbicide transport
in the runoff was then computed for each event from the concentration profiles
and runoff volumes. Residues of atrazine and its major dissipation product,
des-ethyl atrazine, and metolachlor were determined in soil from the three
tillage practices throughout the growing season and related to herbicide
transport in the aqueous phase.
The proportion of rainfall originating as runoff was independent of tillage
but dependent upon rainfall intensity, duration and antecedent soil moisture
content. Less runoff (23% of rainfall) occurred in 1988 which was a dry
year, compared to 28% in 1989, a normal year, and 36% in 1990, a wet year.
Subsurface runoff exceeded surface runoff in all treatments. A greater proportion
of the runoff occurred from the surface of the conservation tillage treatments
compared to conventional tillage. The greater proportion of runoff from
the surface of the conservation tillage treatments could impact on water
quality since herbicide concentrations are higher in surface than subsurface
runoff water.
Runoff producing events which occurred soon after herbicide application,
transported the largest amount of herbicide. Where surface and subsurface
runoff events occurred, herbicide concentration was highest in the surface
runoff water and the mean concentrations were higher from the conservation
tillage treatments than from conventional tillage. Herbicide concentrations
of the runoff water were higher for metolachlor than for atrazine. However,
because of the longer soil persistence of atrazine and inclusion of the
primary metabolite, des-ethyl atrazine, in the amounts, less metolachlor
was lost in the runoff water than atrazine. Tillage had no effect on transport
quantities of atrazine and its metabolite or metolachlor. Average three
year transport quantities for triazine (sum of atrazine and des-ethyl atrazine)
were 58±1 g/ha from ridge, 36±3 g/ha from zero and 62±13 g/ha from conventional
tillage representing 3 to 4% of total atrazine applied from 1988 to 1990.
Up to 25% of the total triazine transported from the tillage treatments
was the dealkylated (des-ethyl atrazine) product. Corresponding average
transport quantities for metolachlor were 46±3 g/ha from ridge, 48±1 g/ha
from zero and 53±6 g/ha from conventional tillage representing 2% of that
applied. Atrazine and metolachlor on crop residue were readily leached into
soil by rainfall received soon after application.
Minor changes in soil persistence of atrazine and metolachlor were related
to tillage. Atrazine and its dissipation product persisted longer than metolachlor
in two of three years and in some years both herbicides showed greater persistence
on ridge tops than in the valley of ridge tillage. Soil persistence of the
herbicides was longer in conventional than zero tillage.
In conclusion, tillage and crop residue did not influence herbicide transport
in surface and subsurface runoff from a level plane, poorly drained soil.
The proportion of rainfall appearing as runoff was similar among tillage
practices therefore the lack of a herbicide response to tillage was not
unexpected. The quantity of herbicide transported from the three tillage
treatments was less than 8% of that applied in the worst year while the
three year cumulative loss amounted to less than 4% of that applied. Transport
quantities of herbicide were more related to incidence of runoff producing
events to herbicide application, rainfall intensity and duration, and antecedent
soil moisture content. Tillage practices which alter the hydrologic response
of watersheds will impact more on herbicide transport losses than tillage
alone. Thus, tillage combined with other cultural practices such as band
application of herbicide over the seed row, intercropping with a grass or
legume forage, or adopting post emergence weed control strategies with low
persistence herbicides should be investigated to determine their effect
on impairment of runoff.
Part A: A three year study was conducted to identify sediment
and phosphorus transport from a poorly drained, Brookston clay loam soil,
cropped to corn under three tillage practices: conventional, no-till and
ridge tillage. Water quality and corn yields were measured for all plots
and compared. Rainfall was measured and surface and subsurface runoff was
quantified for each rainfall event. Water samples were taken and analyzed
for sediment and orthophosphate.
The results indicated that conservation tillage had a variable effect
on sediment transport. In 2 of the 3 years, sediment transport was reduced
by the conservation tillage treatments compared to that from conventional
tillage. Zero-tillage was more effective at reducing erosion than ridge
tillage over the three years. A greater proportion of sediment transport
occurred in surface runoff from the conservation tillage treatments whereas
subsurface transport accounted for a greater proportion of sediment loss
from conventional tillage.
Dissolved phosphorus transport was higher from zero tillage than from
ridge or conventional tillage. In 2 out of 3 years, subsurface drainage
accounted for greater than half and 74% of the orthophosphate loss from
conservation tillage and conventional tillage treatments respectively. Sediment
phosphorus loss was similar between ridge and conventional tillage but higher
from zero till. Ridge reforming in ridge tillage may incorporate some of
the crop residue with soil allowing for greater residue decomposition which
could account for the greater release of soluble P from ridge compared to
zero tillage.
Transport of soluble P was higher in no-till and ridge till than conventional
tillage. This work concludes that for a poorly drained, Brookston clay loam
soil, conservation tillage effectively reduced soil erosion but not phosphorus
transport.
Part B: A three year study conducted on a poorly drained,
low slope Brookston clay loam soil to investigate the effect of conventional
tillage, zero tillage and ridge tillage on surface and subsurface transport
of atrazine and metolachlor applied preemergence to corn. Each runoff producing
event was monitored to calculate the proportion of rainfall that left as
runoff (which was collected to determine herbicide concentration).
The proportion of rainfall that ran off the plots was independent of
tillage but dependent upon rainfall intensity, duration and soil moisture
content. Subsurface runoff exceeded surface runoff in all treatments. A
greater proportion of the runoff occurred from the surface of the conservation
tillage treatments compared to conventional tillage. The greater proportion
of runoff from the surface of the conservation tillage treatments could
impact on water quality since herbicide concentrations are higher in surface
than subsurface runoff water.
Runoff producing events which occurred soon after herbicide application,
transported the largest amount of herbicide. Herbicide concentration was
higher in the surface runoff water compared to subsurface runoff and mean
concentrations were higher from conservation tillage than from conventional
tillage treatments. Tillage had no effect on transport quantities of atrazine
or metolachlor. Atrazine and metolachlor on crop residue were readily leached
into soil by rainfall received soon after application. Herbicides showed
greater persistence on ridge tops than in the valleys in ridge tillage.
Soil persistence of the herbicides was longer in conventional than zero
tillage.
Tillage and crop residue did not influence herbicide transport in surface
and subsurface runoff on poorly drained soil.
