|METHODS OF HERBICIDE SOIL INCORPORATION
The soil herbicides are incorporated by three methods: rainfall, irrigation or mechanical incorporation.
Rainfall as a means of herbicide soil incorporations
The amount of rainfall needed to put soil herbicides into solution in order for them to become active for weed
control is 0.5 inches. The amount varies when the soil moisture content is taken into account. The higher the
moisture content of the soil, the lower the amount of rainfall needed to move the herbicide into the soil. Once the
herbicide is in the soil solution it dissolves according to its solubility in water. Lower amounts of rainfall will
dissolve some herbicides but the amount of control is not commercially acceptable with amounts of rainfall
below 0.5 inches.
The label of the particular soil herbicide will give label rates for the different soil types and amount of organic
matter that the herbicide is applied to. The amount of rainfall recommended on the Gowan Triflurin 10G label is
0.5 inches or more.
Slow gentle rains are most effective in moving herbicides into the soil. High intensity rains with runoff can move
the herbicide to unwanted areas of concern.
Herbicide Incorporation by Irrigation
Flood irrigation is used successfully for soil herbicide incorporation. The use of sprinklers to incorporate
herbicides is one of the best methods of incorporating many of the herbicides.
One of the drawbacks to sprinkler incorporation is when the sprinkler water is also used to germinate the crop
seed. In the case of lettuce in the desert areas high amounts of water may be needed over a long period of time
for crop seed germination and this results in the herbicide being leached to a depth lower than the weed killing
Surface drip irrigation is used for incorporation and is on the label of several herbicides. The area treated can be
identified with formulas that are given on the herbicide label. The number of emitters or the linear feet of the
buried line of the system is used in the calculations.
Granule forms of herbicides are often broadcast over the growing crop or bare ground and then incorporated by
irrigation. This method can be done by flood or sprinkler irrigation. EPTC one of the very volatile herbicides is
applied and incorporated by flood irrigation. Metam Sodium, a fumigant soil herbicide, is applied and
incorporated effectively through sprinkler irrigation. Caution is required when applying herbicides through
sprinkler systems due to the potential for drift to non-target crops.
Incorporating Herbicides Mechanically
Reduction of volatility and photodecomposition are two of the main reasons for mechanical incorporation.
Because herbicides adsorb to soil colloids, mechanical incorporation of the soil will mix herbicides in the soil
more accurately than irrigation or rainfall.
Soil Conditions for mechanical incorporation
Herbicides should be incorporated when the soil is moderately dry. The herbicide will adsorb on the soil colloids
at a greater extent in dry soils. When a herbicide is adsorbed on the soil colloids, less degradation of the
herbicide will occur. Good incorporation happens when the soil flows during incorporation. Dry soils flow during
incorporation. Wet soils have a tendency to form clods, lumps or slabs. If the soil can be tilled properly, it can
be incorporated with a herbicide.
For ideal soil incorporation of herbicides, the soil should be cool, dry, free of crop residue and if the soil is
cloddy, the clods should break up easily with the incorporation.
Depth of incorporation
The equipment operating depth is not the same as the mixing depth. The mixing depth will vary with the
equipment and the condition of the soil.
To measure the mixing depth, lime or other colored powder can be incorporated in the soil. Mixing the rate of
herbicide to a depth that is below the label recommendation will dilute the chemical resulting in poor weed
The herbicide labels specify the depth to which the herbicide should be mixed in the soil. A soil herbicide is a
product, that is applied to a volume of soil by incorporation. The volume of soil is made up of the area (acreage)
times the mixing depth of incorporation. If the herbicide is incorporated to a depth of more than the label
recommends, the volume of soil increases. This increase in volume dilutes and reduces the amount of herbicide
needed for weed control.
The herbicide must be able to contact and enter the germinating seed or weed seedling in order to kill it. Most of
the weed seeds are located in the top 1 1/2 inches from the soil surface. Soil incorporation of herbicides should
mix the herbicide in the top three inches. The label states the depth of the herbicide for the weed to be
controlled. Perennials like nut grass require a depth of 5 to 6 inches for control.
The label for trifluralin, a dinitroaniline, states that the herbicide should be incorporated to mixing depth of 2 to 3
inches. This label states that for pre-plant incorporations of trifluralin for winter wheat in some of the states a
depth cut at 1 to 2 inches is sufficient.
Volatile herbicides move as a gas within the soil. Trifluralin moves as much as 1 inch in the soil and EPTC moves
as much as 4 inches in the soil. This movement is based on the conditions of the soil.
In general a speed of more than 5 miles an hour is required for proper incorporation. Some equipment has to be
operated at slower speeds . These include the P.T.O. Driven Equipment (tillers, cultivators and hoes). Other
equipment should be operated at higher speeds. These include the rolling cultivators used in lay-by applications.
As the optimum speed of operation is approached, mixing and horizontal distribution increase. Above the
optimum speed of operation horizontal distribution decreases because depth is difficult to maintain at higher
speeds. Horizontal mixing is desired in soil incorporation of herbicides.
The implements that result in horizontal and vertical mixing of herbicides to the recommended depth are what is
needed for good soil incorporation. Good soil flow for the required soil mixing is produced when the speed of
the implement is traveling at a fast enough rate. Inadequate mixing of the soil can result in both crop injury and
poor weed control throughout the field. Some areas will have excessive amounts of herbicide and other areas
will have too little herbicide.
Because incorporation equipment is larger and heavier than normal cultivation equipment, tractors designed for
the normal cultivators cannot pull the heavier incorporation equipment at speeds necessary for good
incorporation. Use an incorporating tillage device smaller than typically matched with your tractor. This will
make up for the needed horsepower to pull the tanks and spray material and still operate the sprayer equipment.
Number of Passes Needed for Soil Incorporation
When the soil is relatively dry without heavy crop residue, single pass incorporation can be very successful with
the right incorporating equipment. Unfavorable conditions like wet soil or heavy residue will require two passes
through the field with the incorporation implement. If the crop residue is very heavy a disk or plow operation
may be needed before attempting to incorporate the herbicide.
When mechanically incorporating dry herbicide granules the label will specify two incorporations. The first
incorporation pass covers the herbicide granules and places them in the area of weed contact and the second
pass of incorporation is done a few days after the first to allow the herbicide to be released from the granule.
The delayed incorporation allows the herbicide to be mixed with the proper volume of soil.
The C-Shank Field Cultivator
The C-shank cultivator is an implement used to incorporate herbicides. The mixing depth of the C-shank
cultivator is 1/2 of its operating depth. Each shank is equipped with a sweep that is at least as wide as the
effective shank spacing to till the soil evenly across the width of the implement. Sweeps too wide will
concentrate the chemical where they overlap and sweeps too narrow will leave untreated streaks with weeds.
The implement has to be level otherwise the shanks will go too deep or too shallow resulting in streaks of
weeds. Slow or excessive speeds can be the cause of weed streaks .
C-shank field cultivators work well in heavy crop residue and rough soils. Because the C-shank gives less
complete mixing of the herbicide in the soil; a harrow used behind this implement will improve the
The S- Shank Field Cultivator
The S- Shank field cultivator is a very good implement for surface mixing or for the second pass of a two-pass
incorporation. The vibrating motion of the flexible S-tine field cultivator shatters the soil. The mixing depth of the
S-Shank field cultivator is about 2/3 to 3/4 the operating depth. This is because of the shattering affect of the
When there is restriction of the vibration action of the S-Shank field cultivator the incorporation of the herbicide
is reduced. This is why the S-Shank field cultivator works more efficiently on tilled soil. For second pass
incorporation if the tines of the S-shank cultivator are set too deep, it will dig up untreated soil. The maximum
recommended operating depth of the S-shank cultivator is 3.5 to 4 inches.
Equipment specifications for the S-Shank field cultivator is for 2.5-inch sweeps on 4-inch shank spacing or 4-
inch sweeps on 6 inch shank spacing. Because of the vibrating motion of the tines sweeps do not have to
overlap. S-Shanks cannot accommodate larger sweeps.
Depth control is one of the strong points of S-Shank field cultivators, but because they don’t go deep enough
they are not recommended for single pass incorporation unless the label states the need for shallow mixing
depths. When compared to the tandem disk or the C-Shank field cultivators the horizontal mixing of S-Shank
field cultivators is one to one and a half times better.
The Use Of Discs For Soil Incorporation
In agriculture discs are used in many cultural practices. Discs can be used as an implement of incorporation.
Because of the high amount of incorporation of herbicides, the manufacturers of tandem disks have altered their
disks to be used in the incorporation of herbicides. To increase the mixing of herbicides in the soil disc company
manufactures make a lighter disk with smaller blades that are spaced closer
The manufacturer’s efforts to adapt the tandem disk for herbicide incorporation have made the tandem disk an
excellent tool for single and double pass incorporation. It will handle rough fields with large amounts of crop
The heavier discs with large disc blades, over 22 inches or spaced 9 inches apart can be used with some of the
volatile herbicides. The volatility of some of these herbicides can make up for an inadequate job of
incorporation. With non-volatile herbicides the mixing, especially horizontal, with the large offset discs is
inadequate for incorporation.
Of the two types of disk blades available, the spherical (flat angled) blades cut, invert and mix the herbicides in
the soil, while the conical (curve angled) disk blade cuts and inverts the herbicide with no mixing. The spherical
should be used for herbicide incorporation. Tandem discs will mix the herbicide at half the operating depth.
The angle of the tandem disk gangs determines the distance soil is moved. When the front gang of disk blades
throws out more soil than the rear gang of disk blades returns, adjustment of the angle of the disc gangs must be
made. This is done so that the amount of soil thrown by both gangs are equal. Otherwise a poor result of
Disc Depth Setting
The front gang of disk blades will tend to go deeper and bury the herbicide therefore the disk must be leveled
front to rear for even distribution of the herbicide.
During the second pass the disk will mix the herbicide deeper (3/4’s of the operating depth) than the first pass. If
the operating depth for the first pass was 6 inches the second pass should be set at 4 inches. This is because the
herbicide incorporation mixing depth with a tandem disk is half the operating depth on the first pass. When using
the disk for a double pass incorporation of a herbicide, the second pass setting of the operating depth should be
reduced by a 1/3. The first and second pass herbicide mixing will both be in the 0 to 3 inch depth of the soil.
PTO Powered Units
The PTO powered harrow with the tines moving horizontally is one of the powered units used for herbicide
incorporation. For increased mixing the spray should be directed into the tines instead of spraying the soil in front
of the incorporation. PTO powered harrows should not be used at speeds over 5 miles per hour. The
incorporation with this powered unit mixes the chemical in the top three inches.
Rotary tillers are powered units used for herbicide incorporation. They have a mixing depth of 2/3 of the
operating depth. The L-shaped blades mix the herbicide better than the units with knife blades. At speeds over 4
miles per hour loss of good mixing can occur.
The PTO units mix the herbicide in the soil and for volatile herbicides they seal the soil over the herbicide. This
activity prevents losses and allows the gas of the volatile herbicide to spread throughout the soil in the soil‘s air
Harrows are used to knock down the ridges and mix the herbicide in the top 1/2 to 2 inches of soil.
Rolling baskets, coil-tine and flexible spike harrows are used for this purpose. The coil-tine and flexible spike
harrows are the most common.
Coil Tine Harrows
Coil tine harrows used behind disks, C-shank field cultivators and combination implements provide residue
shedding and leveling of the soil. A three bar harrow is recommended with 3-inch spacing between the tines. To
maintain uniform mixing the coil tine harrow should be attached by two arms per harrow 6-7 inches behind the
last row of tillage gangs.
Down pressure and tine angle are the two adjustments for coil tine harrows. With a coil tine harrow aggressive
mixing increases, as the tines are perpendicular to the soil surface. This aggressive mixing decreases as the tines
are angled toward the rear. In high residue situations the tines will plug up when in the perpendicular position. As
residues decrease the tines should be set perpendicular with as much down pressure as possible without
interfering with the tine lateral movement or increasing the vibration.
Flexible Spike Harrows
Flexible spike harrows are suspended from the rear of the implement penetrating the soil with their own weight.
Flexible spike harrows have five bars with spike harrow teeth separated by 1.5 inches between spikes. This
narrow spacing gives effective lateral soil movement for herbicide mixing. This harrow levels the soil and sheds
Adjustments of Herbicide Incorporation Equipment
With all incorporation implements adjustment in the field is necessary to get good incorporation. Specific field
conditions call for different adjustments. The recommended instructions on the equipment should be followed.
The equipment used for incorporation should be adjusted in the field under the conditions where it will operate.
The type of incorporation equipment and adjustments of that equipment are very important factors in obtaining
successful herbicide incorporation.
Incorporating equipment adjustments include the following:
1. The equipment must be level, both front to back and side to side.
2. Adjust to the desired operating depth. This depth should be adjusted during the day as the soil and moisture
3. The implement wings have to be adjusted for operation at the same depth as the main equipment. Adjusting
the eyebolts or adding weights will level the wings.
4. Different sized tires will require more adjustment or the changing of the tire size to match the rest of the tires
on the rig.
5. Adjust the rig so that all soil is worked across the width of the equipment.
6. Missing shanks or worn tillage components can result in uneven incorporation.
7. Tire tracks will require an extra shank behind the tire to even out the incorporation.
Manufacturers have done a great deal of incorporation research with the herbicides they produce. The use of
trade names in this course is solely for the purpose of providing specific information. It is not a guarantee or
warranty of the products named, and does not signify that they are approved to the exclusion of others of
suitable composition. Use pesticides safely. Read and follow directions on the manufacturer's label.
References & Work Cited
Gowan Trifluralin 4 Label
Grisso, Robert, Dickey, Elbert, Martin, Alex, Equipment Adjustments for Herbicide Incorporation
G90-983, Cooperative Extension Institue of Agriculture and Natural Resources, University of
Nebraska Lincoln 9/7/00
Zollinger, R. K., 2000 North Dakota Weed Control Guide
North Dakota State University Extension Service W-253, 1/2000
Moomaw, R. S., Klein, R. N., Martin, A. R., Roeth, F. W., Shea, P. J., Wicks, G. A., Wilson, R. G.:
Factors That Affect Soil-Applied Herbicides
Published by Cooperative Extension Service Institute of Agriculture and Natural Resources University of
Donald R. Daum, Professor of Agricultural Engineering In consultation with: Nathan L. Hartwig, Professor of
Weed Science, William S. Curran, Assistant Professor of Weed Science. Herbicide Incorporation Equipment
Pennsylvania State University