Delmar Holmstrom, AAFC
Agricultural Resources Team
Residue management is used around the world as an effective soil conservation
practice on a wide range of agricultural crops. However, the concept of
residue managed potato production is relatively new. Potato producers
on Prince Edward Island have been experimenting with residue management
since 1993 and some farmers have adopted the practice on their entire
Considerable on farm evaluation of the practice has been cooperatively
performed between producers; the Prince Edward Island Department of Agriculture
and Forestry; and Agriculture and Agri Food Canada. A number of commercial
potato fields were selected and subjected to split tillage treatments
in 1994 and 1995 to evaluate the impact of residue management on potato
yields and quality, potato disease levels, soil moisture levels, soil
erosion levels, plant tissue nitrogen levels, tillage costs and potato
equipment modification requirements.
This fact sheet will explain where residue managed potato production
can be practiced and how it should be performed as well as provide a summary
of the research findings.
What Is Residue Managed Potato Production?
In a system of residue managed potato production, farmers perform conservation
tillage that will result in considerable residue from the previous crop
being left on the soil surface, after the potato crop has been planted.
Residue level is typically expressed in % surface cover and is measured
after potato planting but prior to the first cultivation. The final residue
level is dependent upon a number of factors including the original amount
of residue available, the tillage implements used, the number of tillage
passes as well as the depth and speed at which tillage was performed.
By following recommended conservation tillage practices, producers can
easily obtain 30% surface residue cover after potato planting. Conventional
tillage, which includes Fall moldboard plowing along with Spring discing
and harrowing, will result in less than 3% of the soil surface being covered
with residue from the previous crop, even with good crop rotations.
Crop residue, lying on the soil surface, will reduce runoff velocity
and allow increased infiltration of water into the soil profile. Surface
residue will also control erosion by reducing the impact of raindrops
hitting the soil surface. The energy associated with raindrop impact can
break up soil aggregates into smaller and more erodable soil particles.
In addition to reducing water erosion, surface residue will have the added
benefit of reducing wind erosion.
The residue level can be determined by placing a measuring tape or string
with 100 equally spaced markings diagonally across potato drills, after
planting but prior to cultivation, and counting the number of markings
that have a piece of residue greater than 3mm (1/8 inch) in diameter directly
beneath it. When using this procedure, consistently use either the upper
or lower side of the tape. Each mark with a piece of residue beneath it
will represent 1% residue cover. The residue level for the field can be
determined by totalling the number of marks with residue. The process
should be repeated several times and averaged in order to obtain a representative
residue level for the entire field.
Where Can Residue Managed Potato Production Be Practiced?
Residue managed potato production can be practiced on any field in which
potatoes are grown in rotation with forages and or cereals. Proper crop
rotation, which is the cornerstone of all soil conservation technology,
is the key requirement in order to perform residue management. The previous
crop must be a high residue producer in order to achieve surface residue
levels in excess of 30% after potatoes have been planted. Cereal crops
have the potential to produce a wide range of residue levels depending
on the species and variety grown. Forage land must receive a fall application
of glyphosate, in order to be able to perform residue managed potato production
the following year.
Residue Managed Potato Production Following a Non-Underseeded Cereal
Residue managed potato production on land where the previous crop was
a cereal that was not underseeded begins with the harvest of the cereal
crop.To maximize the surface residue level, the straw must remain on the
field. However, the straw should be chopped and uniformly spread by the
combine so that it does not pose problems during either tillage, potato
planting or harvesting.
A single tillage pass should be performed, immediately after cereal harvest,
with either a set of tandem discs or a chisel plow equipped with sweep
points and a rear mounted leveller. Unharvested grain that is laying on
the ground will receive good soil contact, germinate, and produce an excellent
cover crop before winter. Most potato fields in Atlantic Canada have complex
topography making it difficult to avoid tillage at steeper grades over
the entire field. Therefore, this late summer tillage operation should
not be performed with an implement that leaves furrows in the field. Farmers
commonly till cereal land with a conventional chisel plow equipped with
twisted shovel points. If tillage is performed at too steep an angle up
and down the slope, the furrows created with these points can transport
large volumes of runoff during rainfall or snowmelt events, causing excessive
soil erosion rates. Ideally, this late summer tillage should leave large
amounts of residue on the soil surface from the previous cereal crop,
it should leave a rough soil surface with no preferential flow paths for
runoff, and it should provide a good environment for unharvested grain
to germinate. Fields that are left in this state will be highly resistant
to both wind and water erosion the following winter.
In the spring, perform a single pass with a tillage implement that is
capable of cutting trash, tilling the entire soil profile to an acceptable
working depth and producing a level seedbed. There are a number of commercial
tillage implements on the market that can perform these multiple tasks
in a single pass. If purchasing a new tillage implement be careful to
select a working width that matches available tractor horsepower. The
tractor should be capable of hauling this type of implement at a ground
speed of 8-10 kph (5-6 mph) at the desired working depth, in order to
break up clods and produce a level seedbed. The rear leveller must be
heavy duty and can be either rolling baskets or spike tooth harrows. The
rolling baskets will do a better job levelling and will bring more residue
back to the soil surface but they will not perform well in stoney conditions.
Some farmers are modifying chisel plows which they currently own, in order
to perform residue management. The chisel plow should be equipped with
a gang of coulters, followed by 45cm (18in) sweep points at a overall
35cm (15in) shank spacing followed by a leveller that has been mounted
on the rear toolbar.
Soils with high surface residue levels do not dry out or warm up as early
in the spring as those that have been moldboard plowed. Under normal spring
conditions, expect that tillage on residue managed fields will be delayed
by several days early in the planting season. Remember that if fields
are worked when soil moisture levels are too high, clods will develop
and soils will become compacted. Fields with drainage problems may not
be good candidates for residue management.
Some farmers who practice residue management on cereal land, perform
two tillage passes in the spring with conventional equipment which they
currently own. They make one pass with a set of tandem discs followed
by a second pass, several hours later and just prior to potato planting,
with an S-tine harrow equipped with a rear mounted leveller. The time
interval between equipment passes allows the soil to dry out and after
harrowing can result in a less cloddy, smoother seedbed. However, surface
residue levels will be reduced by approximately 10 percentage points,
to between 18-22%, by performing the second tillage pass.
Residue Managed Potato Production Following a Forage Crop:
Residue managed potato production on land where the previous crop was
a forage involves the use of the herbicide glyphosate and considerably
reduced tillage. Many Atlantic potato producers have been applying glyphosate
on forage land to control quackgrass in the following potato crop. Traditionally,
the use of glyphosate has been followed by conventional fall moldboard
plowing and spring discing and harrowing. This combination of herbicide
use and tillage results in surface residue levels of less than 1% after
potatoes are planted. Visual field observations indicate degraded soil
structure and erosion rates that appear to be much higher than those on
fields that were conventionally tilled with no herbicide use.
Potato producers using glyphosate on forage fields in the fall, must
obtain an excellent kill with the herbicide, if they wish to satisfactorily
perform residue management. Glyphosate is most effective when it is applied
to active growing plant foliage. It is recommended that forage fields
be clipped approximately 5 weeks prior to the glyphosate application date
to ensure that foliage is actively growing and at the most desirable growth
stage. Quackgrass should be at the 3-4 leaf stage to be effectively killed.
Glyphosate should be applied at least 3 days before the first killing
frost (cooler than -3 C). If glyphosate is being applied to forage stands
that contain considerable legumes, it is advisable that the application
date be delayed as late as possible but still prior to the first killing
frost. Soil microbes are less active under cooler soil conditions in converting
organic nitrogen, which was fixed by the legumes, into the leachable nitrate
form. This would ensure maximum nitrogen availability for the following
years potato crop. If the forage stand contains predominantly grasses,
the late glyphosate application date is less critical. If timothy is the
predominate grass species and it is actively growing, it would be advantageous
to apply glyphosate earlier in the season, to retard corm development.
Fully matured timothy corms can create harvesting problems under wet digging
conditions in a residue management system if they are the predominate
forage species. Glyphosate should not be applied if the weather forecast
predicts either rain or temperatures below 0 C within 6 hours after application.
Glyphosate application rates of 2.5 litres/ha (1 litre/acre) will give
a good kill under ideal conditions. However, with residue management,
application rates of 3.75-5.0 litres/ha (1.5-2.0 litres/acre) are recommended
to ensure a complete kill, especially on fields with a heavy stand of
forage or a high incidence of quackgrass. A surfactant should be used
if glyphosate is applied with a rate greater than 150 litres of water
per hectare or if there is a heavy dew and/or free water on the surface
of the foliage.
It is recommended that no fall tillage be performed on forage land that
has received an application of glyphosate. The herbicide replaces the
need for fall tillage and when spring arrives the forage residue is practically
laying loose on the soil surface. Some farmers perform a tillage pass
in the fall with either a set of tandem discs or a chisel plow, to enable
the soil to dry out and warm up earlier in the spring. However, this fall
tillage operation will reduce the surface residue level to between 30-45%
cover depending on the tillage implement used and the operating depth
and speed. This reduced surface residue can make the field more susceptible
to both wind and water erosion the following winter. Under no conditions
should a forage field, that has received an application of glyphosate,
be tilled in the fall with a moldboard plow or with an implement that
leaves furrows in the field (i.e. a chisel plow equipped with twisted
shovel points). If a chisel plow is used in the fall, it would be desirable
to use either straight points or sweep points followed by a rear mounted
spike tooth leveller.
In the spring, producers have experimented with a number of tillage scenarios.
An acceptable seedbed for potatoes can be achieved by performing a single
tillage pass with the same combination tillage implement that was described
in the cereal section. However, most farmers feel that they can prepare
a more desirable seedbed if they perform a tillage pass several days before
potato planting with the combination implement that is capable of cutting
trash, tilling to the desired depth and levelling, followed by a second
tillage pass just prior to planting. The second tillage pass is typically
performed with either a S-tine harrow equipped with the rear mounted leveller
or with the same combination implement used on the first pass. Residue
levels are not substantially reduced if the second pass is performed with
an implement that has a rolling basket leveller. Most producers prefer
the two tillage passes because the soil can dry out and warm up prior
to planting and there is a reduction in the number of clods. It will require
approximately 10 hp/foot of implement width to perform satisfactory tillage
with the prescribed combination tillage implement when used as a primary
tillage tool on glyphosate killed forage land in the spring.
Residue Managed Potato Production Following a Underseeded Cereal Crop:
Residue managed potato production techniques on land where the previous
crop was a underseeded cereal will depend on the underseeding mix used.
During the combine operation, the cereal crop should be cut at less than
15cm (6 in.) above ground level and the straw should be chopped and uniformly
spread over the field.
If the underseeding mix contained grasses, the field would require a
fall application of glyphosate in order to perform residue management.
Tillage requirements would be similar to those for residue managed potato
production following a forage crop.
If the underseeding mix only contained perennial legumes such as red
clover, crimson clover or alfalfa, the field should be tilled in mid to
late October with a chisel plow equipped with straight points and a rear
mounted spike tooth leveller. Spring tillage requirements prior to planting
potatoes would be similar to those used with non-underseeded cereals.
The perennial legume will be actively growing when spring tillage is performed
but can be easily controlled with herbicides after the potatoes have been
Experimental research work is being undertaken on Berseem Clover which
is an annual clover that produces considerable biomass but will winterkill
if surface soil temperatures drop below -8C (18F). The research will determine
whether residue management can be performed with no fall tillage and with
spring tillage similar to that required for residue managed potato production
following a forage crop.
Potato Equipment Modifications Required For Residue Management:
All producers who are planting potatoes in a system of residue management
are using conventional planters. However, some adjustment of the double
disc openers and covering discs are required to ensure that seed pieces
are planted at the proper depth with adequate soil cover. Some farmers
have installed trash cutting devices in front of the double disc openers
to deal with excess surface residue and ensure better seed piece spacing.
Serrated coulters can be installed on a tool bar which runs the width
of the planter and is welded or bolted to the planter hitch. The coulters
are mounted in front of and mid way between each double disc opener to
cut a path through the residue directly in front of the planter shoe.
Producers have not made any modifications to cultivating and hilling
equipment when converting to residue management. Producers have used both
the single pass hill forming equipment or the disc and
shovel type hillers.
Modern harvesters equipped with either blowers or pinch rollers appear
to do a good job removing trash on fields where residue levels were in
the 30% range after potato planting. Residue on most potato fields that
were either in cereal production or forage on a 3 year potato/grain/hay
rotation the previous year posed no problem at harvest time. However,
tractors had to gear down under wet digging conditions when harvesting
fields that were in forage the previous year where either the fall glyphosate
kill was inadequate or the forage stand was predominantly timothy with
well developed corms. Harvesters with independently powered blowers, which
direct a jet of air across the rear cross conveyor, have higher air capacities
than typical PTO driven units and are superior at removing residue.
The potential savings on tillage costs in a residue management system
will depend entirely on the types of implements used and the number of
equipment passes when compared to an individuals conventional tillage
system. Currently it is estimated that moldboard plowing costs approximately
$85/ha ($35/acre) and a discing or harrowing pass costs $50/ha ($20/acre).
Under conventional tillage on forage land, producers are moldboard plowing
in the fall followed by 2 discing and/or harrowing passes in the spring.
When compared to 2 spring tillage passes in a residue management system,
costs could be reduced by $85/ha ($35/acre). Glyphosate, applied
at a rate of 3.75 litres/ha (1.5 litres/acre), would cost producers $42/ha
($17/acre). This amount could be deducted from the cost of the conventional
tillage system if glyphosate is not used in the conventional alternative.
Producers may find that if they get an excellent kill with the glyphosate,
their herbicide requirements could be reduced the following spring. Producers
may also find that if they practiced residue management on their entire
potato acreage they could get by with a reduced compliment of tillage
equipment on their farm.
A rainfall simulator was used on a number of potato fields with split
tillage/herbicide treatments, following both cereal and forage crops,
to determine the relative effectiveness of residue management in reducing
erosion rates. Forage fields were split into 3 tillage treatments including
a conventional treatment with fall moldboard plowing followed by spring
discing and harrowing; a second conventional treatment with similar tillage
but including a fall application of glyphosate; and a third treatment
that was residue managed. The rainfall simulator tests were performed
in the spring after potato planting but prior to cultivation on each treatment.
Results from the forage sites are presented in Figure 1
and represent the stabilized erosion rate that occurs after the runoff
rate has become constant. The conventionally tilled sites with surface
residue levels of less than 3%, had erosion rates that were 18 times higher
than the residue managed sites with 30-35% surface residue. Erosion rates
were 27 times higher on the conventionally tilled sites that included
the fall application of glyphosate when compared to the residue managed
sites. The rainfall simulator tests confirm visual observations that erosion
rates are most severe on fields where glyphosate and conventional tillage
are used in combination with each other.
Figure 1. Relative Erosion Rates
Grain fields were split into 2 tillage treatments including a treatment
that was fall plowed followed by spring discing and harrowing and a second
treatment that was residue managed. Because of the wide range in residue
levels on the residue managed grain sites we have not run a sufficient
number of rainfall simulator tests at the various residue levels to confirm
statistical significance of the results. Visual field observations indicate
almost no wind or water erosion on residue managed sites during the winter
prior to potato planting and tremendously reduced erosion rates following
planting and prior to cultivation as evidenced by the rainfall simulator
tests. During hilling, most of the residue is shoved into the potato hill
making the field susceptible to rill erosion between the drills during
intense summer rainfall events. After harvest, much of the residue that
has not broken down ends up on the soil surface, where it can assist in
reducing erosion rates in the winter after potato production. Do not depend
on this remaining surface residue to provide complete erosion protection.
Potato fields should be cover cropped or mulched after harvest to provide
the required erosion control. If money saved from the reduced tillage
in a residue management system is spent on cover cropping or mulching,
potato farmers could produce a crop of potatoes for traditional out of
pocket costs, while substantially reducing erosion rates and the detrimental
effects of siltation on the environment. The level of erosion control
can be further enhanced by strip cropping and or terracing if required.
Soil Moisture Levels and Potato Yields:
Potato producers in Maine, who have practiced residue management on potato/grain
rotations for a number of years, indicate that their main reason for adopting
the practice was for improved soil moisture levels. On PEI, soil moisture
levels were monitored on the split tillage treatments during 1994 and
1995. Although we were not able to measure significant differences, it
should be noted that the in field variability in soil moisture is so great
that the sampling location can drastically alter the results. Higher residue
levels on the soil surface can conserve moisture by significantly reducing
surface runoff during natural rainfall events or while irrigating. Surface
residue also acts as a mulch, cutting down on evaporation. Growing potatoes
under a system of residue management should not be considered as an alternative
to irrigation. However, by growing potatoes on fields that have higher
organic matter and or surface residue levels, the need for irrigation
can be reduced and if required the benefits will be maximized.
Fields with the split tillage treatments were located at various sites
across PEI during 1994 and 1995. July and August precipitation amounts
were well below normal during both years at the sites East of Summerside.
No significant differences were recorded in yields between the residue
managed and the conventionally tilled treatments in either year at these
sites. Fields with split tillage treatments near Souris experienced ideal
soil moisture levels as a result of adequate precipitation throughout
the growing season in 1995 resulting in no significant differences in
yield. However, in 1994 precipitation in the Souris area was marginal
with an effective rainfall event occurring approximately every 2 weeks.
Yields near Souris in 1994 on the residue managed treatments ranged between
13-25% higher than those that were fall moldboard plowed and spring disced
and harrowed. In addition, the residue managed treatments had on average
8% more tubers in the greater than 55 mm size range. In terms of yield,
it appears that increased surface residue levels have little impact when
precipitation amounts are either ideal or when conditions are extremely
dry. However, yields do respond positively when rainfall amounts are marginal.
The most common producer concern regarding residue management in potato
production is its conceived impact on disease levels, especially Common
Scab and Rhizoctonia. Samples were taken from each treatment on PEI fields
with split tillage trials in 1994 and 1995. Tubers from the various samples
were observed by qualified potato pathologists. Varieties grown included
Russett Burbank, Frontier Russett, Butte, Shepody and Superior. Although
Common Scab and Rhizoctonia were present in some fields, there was no
significant difference in the level of incidence between tillage treatments.
Tubers were also inspected for a host of other bacterial and fungal diseases
with no significant differences in the level of incidence between tillage
Plant Tissue Nitrogen Levels:
Potato leaf samples were collected throughout the growing season from
the various treatments in the split tillage trials on PEI and analyzed
for tissue nitrogen levels. All treatments on each field received the
same level of nitrogen input although fertilization rates varied between
farms. On the forage sites, plant tissue nitrogen levels were lowest on
the residue managed treatments but were well above stress levels at all
sites. Nitrogen stress was more evident in plant tissue from the 2 year
potato/grain rotation. Stress was most severe on the residue managed sites
and in some cases approached critical levels. It appears that residues
with high carbon:nitrogen ratios can tie up nitrogen
that was intended for the potato crop. Although measured yields were not
less on the residue managed treatments when compared to the conventionally
tilled treatments, lack of nitrogen may have been a limiting production
factor especially on the residue managed grain sites. Forage fields with
high populations of legumes are less likely to experience nitrogen stress
than those that were predominantly grass the year previous to potato production.
Based on producer experiences and research conducted on PEI, it appears
that residue managed potato production is a highly viable production alternative.
Producers will benefit from reduced tillage costs, improved moisture conservation,
and reduced erosion rates with no observed negative impacts in terms of
potato quality or disease level.
One of the more positive aspects of residue managed potato production
is that any producer with modern equipment can adopt the practice with
minimal out of pocket costs in terms of machinery modifications and he
can implement the practice with little ongoing technical support.
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welcome your questions or comments.