Upper Midwest Tillage Guide
Tillage implements, purpose and ideal use
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- Different tillage implements
Different tillage implements
Tilling the soil has been a practice used for centuries to produce crops. Tillage is defined as the mechanical manipulation of the soil with the purpose of managing crop residue, incorporating amendments, preparing a seedbed, controlling weeds, and removing surface compaction and rutting.
Since the mid-nineteenth century, most farmers used the moldboard plow as their primary tool. This implement over-turned the soil and buried the previous crop’s residue, leaving only fragments covering less than 15 percent of the soil surface. In the last 50 years, farmers across the country began to use less aggressive primary tillage tools such as the chisel plow. This tool allowed farmers to conduct tillage more efficiently at a lower cost and had the added benefit of reducing soil erosion due to wind and water.
Today, numerous additional tillage implements are available on the market that increase tillage efficiency and reduce soil disturbance and erosion even more. These new implements have options of countless configurations of shanks, coulters, disks and harrows with adjustable depths and pitches. Modern implements allow farmers to control the aggressiveness of their primary tillage and to manage the amount of residue left on the soil surface.
This chapter describes some of the more popular implements, common tillage depths, number of passes needed to prepare a seedbed, and expectations of crop residue coverage during the spring months when the soil is most vulnerable to erosion. Included are emerging technological advances, environmental factors, and methods to successfully leave more residue.
Deep tillage (deeper than 10 inches)
Moldboard plowing inverts the soil to a depth of 8-12 inches, which is measured to the moldboard share’s bottom edge (Photo 1a). Typically, moldboard plowing is conducted in the fall, requiring farmers to make one or two secondary tillage passes with a field cultivator or tandem disk before planting to smooth the soil and pulverize any remaining large soil clods.
Moldboard plowing is the most aggressive tillage practice available and leaves less than 15 percent of the soil surface protected with crop residue during the months after planting (Photo 1b). Because it is the most aggressive tillage option, it also has the highest potential for soil erosion by wind and water and has high fuel, time, and labor cost requirements.
Unlike the moldboard plow, a disk ripper does not completely invert the soil. Instead, it tills the soil to a depth of 12-16 inches with a series of shallow disks, shallow leading shanks (optional), and then deeper, larger shanks (Photo 2a). Some models have broad or winged points on the shanks that increase the amount of soil disturbance. Disk ripping often leaves 35-45 percent of the soil surface covered by crop residue, even though it tills deeper than a moldboard plow.
After disk ripping in the fall, one or two secondary tillage passes with a field cultivator or a tandem disk are needed in the spring before planting. Since more crop residue is left on the soil surface, the potential for erosion is less than the moldboard plow (Photo 2b). However, disk ripping has high fuel, time, and labor cost requirements due to the deep depth of tillage.
Zone till (in-line subsoiler, ripper, paraplow)
In-line subsoiling, ripping, or paraplowing are more generally referred to as deep zone tillage. These "in-line" implements create evenly spaced rows (30-inch spacing) of deep slots to a depth of 15-20 inches using a narrow subsoil shank (Photo 3). Shanks may be completely straight or have a bent leg (paraplow). Deep zone tillage is done in the fall and the crop is then planted directly over the tilled rows.
These implements fracture and break up deep compaction zones and incorporate little crop residue. Therefore, crop residue coverage at the soil surface is left nearly intact. Farmers should only consider zone tillage if deep soil compaction is known to exist. If the subsoil is not compacted, then farmers will not see yield benefits from subsoiling. These implements also have a high horsepower requirement of 30-50 hp per shank.
Medium depth tillage (5-10 inches)
Chisel plow tills the soil to a depth of 6-8 inches using rows of staggered shanks that can be configured in several different designs (Photo 4a). The choice of chisel plow point (shovels, straight points, or sweeps) will vary the level of soil disturbance and affects the amount of crop residues remaining on the soil surface. Preceding the shanks are a gang of straight coulters or disks that size the residue to reduce plugging. Chisel plowing is typically conducted in the fall and is followed by secondary tillage with a field cultivator or tandem disk in the spring before planting. The secondary tillage pass in the spring further lowers the residue coverage. It is ideal to leave more than 30 percent residue coverage after planting to reduce erosion. Therefore, fall chisel plowing should leave 40-45 percent residue on the surface after the chisel pass.
Farmers have the choice of numerous designs and adjustments to the shanks, shovels, and sweeps to affect the amount of residue incorporation. For example, a chisel plow equipped with 2-inch straight shovels will leave 11 percent more residue than a 3-inch twisted shovel (Hanna et al, ISU).
Fall chisel plowing that results in 30 percent crop residue cover after planting can reduce the gross amount of soil erosion by 50 to 65 percent as compared to moldboard plowing that leaves less than 15 percent residue (Photo 4b). Additionally, chisel plowing in the fall has a medium fuel, time and labor cost requirement.
Strip till combines the benefits of chisel plowing and no-till simultaneously in row crop fields. The setup of strip-till implements can vary but most have the following tools set in a series: a flat or wavy residue-cutting coulter, followed by adjustable row cleaners, a primary shank (or coulters) for tilling the strip, two disc blades to gather and berm soil into the tilled strip, and then rotary packing wheels or conditioning baskets to firm the tilled strip of soil (Photo 5a). This prepares narrow 7- to 10-inch wide bands of soil for planting, while leaving the soil and residue between the plant rows untouched as in no-till.
Fertilizer is often placed 5-8 inches deep in the soil immediately behind the primary shank (or coulter) during tillage. This combines the best of both tillage worlds. Strip till has a warmer, drier seedbed compared to no-till that makes it possible to match the early planting dates and high yields of conventional tillage, while its higher residue cover provides the erosion control and improved water infiltration that no-till offers.
The spacing of tilled strips corresponds to planter row widths of the next crop so that seeds are planted directly into the tilled strips. As a result, strip till is well suited for controlled traffic management. Most strip-till equipment manufacturers in the northern Great Plains produce strip till implements with 30-inch, 22-inch, or 20-inch row spacing. Strip tilling is normally done in the fall, but it can also be done in the spring before planting (Photo 5b). The cost per acre is similar to chisel plow; however, chisel plow systems need an extra pass for broadcasting fertilizer and an additional tillage pass for fertilizer incorporation and seedbed preparation.
Ridge till implements build 6- to 8-inch high ridges on 30-inch centers leaving chopped crop residues left on the soil surface between ridges. Ridges are typically built in the fall and then the tops removed for seeds to be placed in during spring planting. The ridges provide a dry and warm seedbed at planting. Tillage is then limited to that performed by the planter and one to two in-season row cultivations for controlling weeds and rebuilding ridges (Photo 6). The height of rebuilt ridges within the season should be controlled to not bury the lower pods if fields are planted to soybeans. After planting, crop residues can cover up to 40 to 50 percent of the soil surface. This percentage will decrease after the first cultivation pass, which should be done before the crop canopies.
The disk loosens and lifts the soil to a typical depth of 5-8 inches with rows or gangs of concave disks set at an angle (Photo 7). If the gangs are arranged with two sections adjoined on one side, it is called an offset disc harrow. If the gangs are arranged with four sections in an X or a diamond shape, it is called a tandem disc harrow. The disk is an aggressive tillage option that incorporates a large amount of residue, eliminates soil clumps and clods, and loosens the depth of tilled soil.
Shallow tillage (1-4 inches)
Vertical till cuts or sizes crop residue and lightly tills the top 1-4 inches of soil. For the purpose of this publication, vertical till is any tillage operation that does not cause a horizontal shearing or a smearing plane in the soil profile. This definition will eliminate any use of shanks, points, and disks. Most vertical-till equipment consists of vertical coulters set between 0- and 10-degree angles (Photo 8a). Vertical till typically maintains a crop residue cover of at least 50 percent of the soil surface (Photo 8b). However, a potential downside to vertical till may occur if crop residues are sized too small and become easily blown or washed away reducing soil coverage. Vertical till is not recommended for incorporating nitrogen fertilizers since much of the nitrogen may be left on the soil surface and is susceptible to volatilization loss.
Field cultivation is a common secondary tillage practice done once in the spring before planting to pulverize smaller soil clods remaining after primary tillage and incorporate broadcasted fertilizers (Photo 9a). Field cultivators are also used as a less aggressive primary tillage practice that is used in soybean stubble prior to planting corn. It leaves soybean crop residues covering 20-30 percent of the soil surface and tends to be a good option for medium textured, well-drained soils (Photo 9b). Field cultivation in the spring has a much lower fuel, time and labor cost requirement than deep and medium depth tillage systems.
Photo 10. Tandem disk tillage.
Tandem disk is similar to the disk, but is less aggressive and therefore provides a shallower tillage option for the top 2 to 4 inches of the soil (Photo 10). Tandem disking is a common secondary tillage practice used in the spring to prepare a smooth seedbed and incorporate broadcasted fertilizers. However, if used as a primary tillage tool, tandem disking can have the same potential downside as vertical tillage, as crop residue becomes prone to blowing or washing away.
No-till is the complete absence of any primary or secondary tillage practices with the goal of leaving the soil undisturbed as much as possible during the entire year. Most no-till planters have residue managers, finger coulters and double disk openers that move some residue from the row and improve seed to soil contact. Similarly, grain drills have a wavy coulter ahead of the seed tube to provide optimal seed placement. This is the only soil disturbance in no-tilled fields. The high amount of crop residues remaining on the soil surface helps maintain or increase soil organic matter, improve moisture retention and decrease soil erosion (Photo 11).
No-till requires special fertilizer application techniques for corn, complete chemical weed control, and specially equipped planters. Due to the potential slower soil warm-up in the spring, no-till typically has been successful in regions with lower precipitation or well-drained coarse or medium-textured soils.
Cost and soil structure impact of tillage
Table 1 categorizes tillage implements based on their relative cost per acre to operate and the potential to have negative soil effects. These numbers are based on an estimate created from the Soil Tillage Intensity Rating (STIR) values of the tillage practice and the Iowa State University Custom Rate Survey.
Negative soil effects of tillage include soil crusting, soil erosion, losing soil organic matter, and poor soil structure. Lower numbers from the chart indicate that tillage systems such as no-till, strip till, and vertical tillage have less potential for soil loss by erosion, will maintain soil aggregation, can maintain or build organic matter, and are less expensive to operate.
Aggressive systems such as moldboard or chisel plowing and deep ripping have a much higher potential for destroying soil structure, creating individual soil particles that are prone to wind and water erosion, and cost the most in fuel and wear and tear on machinery. Note that there are a variety of tillage implements that cover the spectrum of cost and soil impacts.
Table 1. Relative comparison of common tillage practices with respect to cost and soil impact. Scale of 1 to 10 where 1=lowest cost and least soil impact.
|Relative cost ($1) and soil impact (E2)
(1= lowest to 10=highest)
|1$ = the associated cost of the tillage equipment.
2E = structural impact on the soil due to depth and aggressiveness of tillage pass.
Sources: USADA-NRCS STIR equation, 2016 ISU Custom Rate Survey
Field activities performed under wet conditions often cause surface compaction. Primary tillage alleviates the problem, provided fields are not re-compacted. However, tillage is not the only way to correct surface compaction. Biological "tillage" from rotating forage crops or planting cover crops can also help (Photo 12). Perennial crops, such as alfalfa, or cover crops, such as annual rye or tillage radish, may help break up compacted layers. Additionally, many Minnesota soils have a high content of expanding smectite clay minerals that experience annual wetting and drying cycles. These properties shrink and swell the soil, creating deep cracks that can repair compaction damage naturally.
Earthworms are another form of bio-tillage (Photo 13). They create large pores, which increase water infiltration and root growth. Their castings improve microbial growth, nutrient availability and soil structure. Earthworms are quite active and feed by bringing organic debris (residue) from the surface down into their burrows. In a well-populated Minnesota soil, earthworms can recycle 8,000 pounds of soil per acre per year. Full-width tillage systems, such as moldboard and chisel plowing, disrupt earthworm channels, resulting in reduced numbers in tilled fields compared to no-till or similar low-disturbance systems.
Tillage equipment manufacturers have recently been developing new technological advances for tillage implements. Companies are investing in research and the development of variable-depth or variable-intensity tillage implements that can be controlled by wireless touchscreen devices or integrated with emerging soil sensor technologies and decision-support tools for a fully automated tillage management system.
Gates Manufacturing, a North Dakota based company, has patented technology to sense or “read” the crop residue levels and automatically adjust the vertical-till gangs to be more or less aggressive based on the sensed reading (Photo 14). Other features include using preset gang adjustments for different fields with differing residue levels and soil texture.
Salford, an Ontario based company, has recently introduced a variable-depth tillage implement that combines a chisel plow and a wavy coulter vertical till (Photo 15). A farmer can engage both the chisel plow and vertical till for high crop residue conditions or for clayey soils and then automatically raise up the chisel plow for use of only the vertical till coulters when on slopes, sandier soils or low residue areas.
Implement aggressiveness and residue cover
Each tillage implement will disturb the soil differently based on the depth of tillage, size and set-up of shanks, coulters, disks and harrows, speed of operation, the number of passes, and whether the implement turns the soil over or slices through the soil.
A Soil Tillage Intensity Rating (or STIR value) of 10 or less is required to qualify for Natural Resources Conservation Service (NRCS) no-till incentive programs. The STIR value is calculated using the RUSLE2 computer model that predicts long-term average annual erosion by water. This model is based on crop management decisions applied in a field. The NRCS assigns a numerical value to each tillage operation. STIR values range from 0 to 200, with lower scores indicating less soil disturbance. Based on the STIR values, most strip till systems can be used to qualify for the NRCS conservation management/no-till incentive programs (Table 2).
Table 2. USDA-MRCS Soil tillage intensity rating (STIR) values for common tillage operations.
|Double-disk opener planter||2.4|
|Strip till - coulter, 5" depth, 8" berm||7.7|
|Strip till - shank, 7" depth, 10" berm||15|
|Tandem disk, light finishing||19|
|Field cultivator, 6- to 12-inch sweeps||23|
|Chisel, twisted shovel or sweeps||42-49|
|1STIR values range from 1 - 200; lower scores indicate less soil disturbance.|
Tillage effect on erosion and loss of organic matter
Soil structure is formed by the aggregation of individual soil particles (clay, silt, sand, pieces of organic matter) into structural units or peds. Soil aggregation is the movement and then sticking of soil particles together (Photo 16a). Microscopic bacteria and fungi in the soil, as well as plant roots, play a vital role for soil particles to stick and stay together as peds. Their sticky exudates and hyphae physically hold the soil together, helping soil structure to form and persist over time. The more diverse and abundant the microbial population, the faster soil aggregation can build. Between aggregates, many large pore spaces allow roots to penetrate the soil more easily and air and water to readily pass through.
Additional benefits of improved soil structure include the following:
- Reduced bulk density
- Increased aggregate stability
- Resistance to soil compaction
- Enhanced soil fertility
- Improved water infiltration and drainage
- Enhanced retention of plant available water
- Less soil erosion
- Enhanced biological activity
- Protection of soil organic matter
Photo 17. Windblown soil has moved from a low residue field to the adjoining ditch.
Photo 18. Compacted soil layer created by annual tillage.
All these benefits are based on building and preserving soil structure. Tillage breaks apart soil aggregates, damaging the existing soil structure, and adds oxygen to the soil that facilitates the breakdown of organic matter by microbes. Over time, tillage reduces soil biological life. The deeper and more aggressive the tillage, the weaker the soil structure. This leads to more fine aggregates and individual soil particles, which can clog pores and crust the soil surface, slowing water infiltration and increasing runoff (Photo 16b). Smaller soil particles are also highly susceptible to being swept away by wind and water. Valuable topsoil moves into the ditch, or the neighbor's field, or the next state, and is lost forever (Photo 17).
The loss of topsoil severely diminishes a field's productivity. The soil that is moving downslope or off the field is the field's most productive soil. It contains carbon, nitrogen, phosphorus, sulfur, and other nutrients, is lower in salts, and has a more favorable pH than the soil remaining after erosion.
As the soil loses structure, it becomes denser and more susceptible to compaction, because of the loss of larger pore spaces (Photo 18). Compaction inhibits root growth and decreases water-holding capacity. Repeated tillage operations at the same depth may cause serious compacted layers, or tillage pans, just below the depth of tillage. Higher horsepower equipment is needed to get through compacted soil, which results in more wear-and-tear on equipment. Reducing tillage helps preserve the soil's natural structure, making the soil more resistant to erosion and the negative effects of heavy field equipment.
Account for individual field conditions
There is not one tillage management system that will work for every field. Factors such as soil moisture and physical characteristics, slope, and crop rotation play a vital role when deciding which implement is best for each field.
In the Midwest, sandy and loamy sand soils warm up faster and have good internal drainage (Photo 19a). However, they have lower organic matter content and do not have soil structure. It is not possible to create soil structure on sands and loamy sand soils, but the addition of organic materials can improve water holding capacity and internal drainage. Reducing tillage or using no tillage on these coarse soils protects soil productivity and cuts yield risk.
Clay and clay loam soils in the upper Midwest are rich in organic matter, which gives them their characteristic dark brown or black color (Photo 19b). If managed properly, they will develop well-defined structure. These fine-textured soils have poor internal drainage, drying more slowly than sands. In addition, light-colored residue reflects the sun's heat, impeding spring warm-up. With high levels of residue, these poorly drained soils may remain cool and wet long into the spring months, resulting in delayed planting. Consequently, more tillage is traditionally performed on clayey soils.
Improving soil structure will boost internal drainage, speeding up spring warming and drying. Furthermore, since systems such as strip till and no-till do not destroy the continuity of large pores, infiltration and aeration can increase. Subsurface drainage (tile drains) also improves soils with poor internal drainage, making it more feasible to reduce tillage.
Wet soil conditions
Photo 20. Field cultivating at 3-inch depth in wet soil restricted corn roots from growing much deeper.
Soil moisture is probably the most important factor to evaluate. If the soil is too wet for proper soil fracturing in the fall, tillage may be creating more damage to the soil than benefits from the residue incorporation (Photo 20). If the soil is dry near the surface but wet below, shallow up the shanks or disks so that they do not smear the wet layer of soil. A smeared soil will need an additional, deeper pass or two in the spring to break up the dense layer.
For example, if a chisel plow is used in a wet soil to a depth of 8-inches, using a 3-inch spring field cultivation will not alleviate the smeared soil layers created by the chisel plow. This situation might need an in-line ripper set at a 9- to 10-inch depth to eliminate the smeared layers created by the chisel operation during wet conditions.
Moderate soil moisture conditions
If the soil has moderate moisture in the fall (moisture levels below field capacity), a chisel plow or a disk ripper will incorporate some residue and break through compaction and cloddy soils. However, disks are extremely destructive to soil structure, creating a fine, pulverized soil that can easily blow or wash away.
Disks can also create a plow layer, since soils with poor structure compact more easily. While dense soil the disks create may be useful in building roadbeds, disks should be used sparingly in the field. In contrast, equipment with points and shanks lift and separate the soil more along its natural fracture lines and is less destructive than a disk.
Dry soil conditions
If the soil is exceptionally dry in the fall, do not use deep tillage equipment. A chisel plow set at an 8-inch depth will heave-up large clods of soil (Photo 21). Experience has shown that the deeper the tillage in these extremely dry soils, the larger the clods lifted to the surface. In 2011, basketball-sized and larger clods were seen across western Minnesota due to tillage during extremely dry soil conditions. Two to three tillage passes were needed in the spring to create an acceptable seedbed.
Natural alleviation of soil compaction is possible in soils that shrink and swell (crack in dry conditions) during dry conditions (Photo 22). Since dry soils naturally "till" deep into the soil, farmers can focus on creating a good seedbed in the top three inches with shallow tillage. In dry conditions, reduced-tillage systems preserve moisture in the seedbed, enhancing uniform germination and plant establishment.
In the Midwest, research results evaluating the effects of subsoiling have shown few positive yield responses. When yield benefits do occur, they are variable and relatively small. Accurately predicting the effects of subsoiling on crop yields is very difficult, due to differences in soil texture, the level of subsoil compaction, the soil water content, subsequent traffic, and differences in the crop grown and in tillage methods.
In a University of Minnesota study near Waseca, MN, a field was uniformly compacted with a grain cart weighing 20 tons an axle. The field was subsoiled to a depth of 16 inches to break up the compacted soil (Photo 23). Subsoiling failed to increase yields on the 20 ton per axle treatments for either corn or soybeans and decreased corn yield 11 bu/ac in one of the two years. Similarly, a two-year study near Elrosa, MN, found that corn and the following soybean yields were not affected by subsoiling down to 20-inch depth.
To increase the probability of obtaining beneficial effects from subsoiling, the following steps should be considered:
- Determine that a compaction problem actually exists. Dig some plants to examine rooting. Are visual crop symptoms consistent with past wheel traffic? Is there standing water after a rain that also shows a pattern consistent with wheel traffic?
- Determine the depth of the compacted layer.
- Set the tillage implement 1-2 inches deeper than the compacted zone depth. Make sure the soil is dry and fractures to the depth of the shank when subsoiling.
- Leave some areas of the field not subsoiled for yield and visual comparison.
- Avoid re-compacting loosened soil by avoiding future operations on wet soils and using the controlled traffic concepts.
Sloping fields are prone to water erosion. Erosion potential depends on the length and steepness of slope and the soil texture (Photo 24). Highly erodible land (HEL) may require large reductions in tillage intensity to limit erosion and maintain soil productivity. Flat fields have less erosion potential, but sediment loss can be a problem on these fields during intense rain or wind events. Reduced tillage leaves more residue on the soil surface. This residue protects the soil from raindrop impact and slows the downhill movement of soil and water. In addition, standing residue will slow the wind's erosive speed and wick rainfall into the soil faster than bare soil.
If fields have more than a 3 percent slope, minimize the depth and intensity of the tillage pass. The steeper the slope and the more aggressive the tillage, the more mid-slope buffers and planting on the contour are needed and have a return on investment. A handful of creative farmers will not till the tops and sides of slopes in the fields leaving the residue to protect the vulnerable soil.
Crop rotation and residue levels
Crops differ in their adaptability to respond to soil temperature and moisture. Corn, a determinant crop, is sensitive to moisture and temperature. High levels of crop residues can cause uneven emergence and may decrease corn yields. On the other hand, soybean and wheat have greater ability to thrive in a large range of crop residue levels.
The amount of residue in a field before tillage depends on the previous crop and yield. Corn, for example, generates much more biomass than edible beans, soybeans, potatoes, or sugarbeets. Therefore, it is easier to maintain higher residue levels following corn using a variety of tillage systems. Residue durability also differs by crop. While corn residue breaks down slowly, soybean residue is fragile and easily destroyed by tillage, so maintaining adequate residue cover following soybeans is more difficult (Photo 25). Consider the entire crop rotation when evaluating residue cover and tillage systems. In general, a corn-soybean rotation offers more tillage flexibility than continuous corn.
Photo 25. Residue cover directly after harvesting corn (top) and soybeans (bottom).
Source: USDA-NRCS https://www.nrcs.usda.gov/
While not a tillage issue, it is very important to spread residue over the width of the combine to prevent strips of higher residue levels directly behind the combine (Photo 26). This area of high residue can create uneven residue incorporation during tillage and uneven seed placement during planting. Chopping heads and chaff spreaders can help spread stalks and chaff evenly across the field.
Many different tillage choices are available. If you have a 2- or 3-year crop rotation (corn-soybeans, corn-soybeans-wheat), a less aggressive tillage pass can be very effective at managing the crop residues. However, there are fewer choices available to handle the high residue levels of three or more years of continuous corn. Each implement has benefits and challenges.
Managed properly, the beneficial aspects of maintaining high levels of crop residue with reduced-tillage systems outweigh the few negative aspects. Look at your specific situation (soil texture, crop rotation, slope, and soil moisture) to decide what is right for you. In the end, reducing your tillage is key to the long-term productivity of your soil.
- When possible, wait until spring to till, especially on fields with soybean residue. Where fall tillage is conducted, use systems that are done on the contour and leave 40-50 percent residue.
- Reduce the number of tillage passes.
- Set chisels and disks to a shallower depth.
- Use straight points or sweeps on chisel plows instead of twisted points.
- Plant a cover crop, especially after low residue or early season crops.
- Spread residue evenly with the combine.
- Minimize tillage operations up and down slopes.
- Avoid working the soil when it is wet.
Upper Midwest Tillage Guide is a collaboration between University of Minnesota and North Dakota State University
Peer review provided by Richard Wolkowski, Extension Soil Scientist, Emeritus, University of Wisconsin-Madison
Photos are provided by Jodi DeJong-Hughes unless otherwise noted.