Soil compaction: causes, effects and control
On this page
- I: Soil compaction – causes and consequences
- II: Surface compaction
Section I: Soil compaction – causes and consequences
As farm tractors and field equipment become larger and heavier, there is a growing concern about soil compaction. Soil compaction can be associated with a majority of field operations that are often performed when soils are wet and more susceptible to compaction. Heavy equipment and tillage implements can cause damage to the soil structure. Soil structure is important because it determines the ability of a soil to hold and conduct water, nutrients, and air necessary for plant root activity. Although much research has been conducted on soil compaction and its effects on yield, it is difficult to estimate an economic impact because fields vary in soil types, crop rotations, and weather conditions.
What is soil compaction?
Figure 1. Effects of compaction on pore space.
Soil compaction occurs when soil particles are pressed together, reducing pore space between them (Figure 1). Heavily compacted soils contain few large pores and have a reduced rate of both water infiltration and drainage from the compacted layer. This occurs because large pores are the most effective in moving water through the soil when it is saturated. In addition, the exchange of gases slows down in compacted soils, causing an increase in the likelihood of aeration-related problems. Finally, while soil compaction increases soil strength-the ability of soil to resist being moved by an applied force-a compacted soil also means that roots must exert greater force to penetrate the compacted layer.
Soil compaction changes pore space size, distribution, and soil strength. One way to quantify the change is by measuring the bulk density. As the pore space is decreased within a soil, the bulk density is increased. Soils with a higher percentage of clay and silt, which naturally have more pore space, have a lower bulk density than sandier soils.
Myths about soil compaction
There are two wide spread myths about compaction: 1) Freeze-thaw cycles will alleviate a majority of soil compaction created by machinery, and 2) What compaction "Mother Nature" does not take care of, deep tillage or subsoiling will alleviate.
Although soils in Minnesota are subject to annual freeze-thaw cycles and freeze to depths of 3 feet or more, only the top 2 to 5 inches will experience more than one freeze-thaw cycle per year. The belief that freeze-thaw cycles will loosen compacted soils may have developed years ago when compaction would have been relatively shallow because machinery weighed less and grass and legumes were grown in the rotation.
Research conducted in 1960 at Lamberton reported that nine years of cropping and annual freezing and thawing did not remove a compacted soil layer at the bottom of the plow furrow in a Nicollet clay loam (Voorhees, 1983). The 2 1/2 ton, 12-inch wide wheel used to compact the plow furrow exerted a pressure of about 110 pounds per square inch (psi) on the bottom of each plow furrow. The compacted soil drained more slowly and remained wetter after a rain. In this study, corn and alfalfa yields were not affected by the compaction. This was likely due to the timeliness and amount of rainfall. In other studies at Lamberton, compaction due to wheel tracks also persisted over winter at depths of 6 to 18 inches.
While deep tillage (greater than 10 inches) is capable of shattering hard pans created by wheel traffic, it has not been proven to increase yield consistently or for long periods of time. In Midwestern studies where plots with established compaction were split with a deep tillage treatment (14-16 inches), corn yields were either unaffected or reduced slightly (10 bushels per acre) compared to the non-subsoiled plot. The one possible exception would be on an irrigated loamy sand. A lack of consistent positive yield response may be due to:
- Insufficient depth of subsoiling
- Ineffective removal of compacted layer due to high soil moisture levels
- Recompaction of loosened soil by subsequent wheel traffic
- Deterioration of some soil properties by the subsoiling operation
- Detrimental effects caused by compaction were no longer limiting crop yield
What are the consequences of soil compaction for plant growth?
Soil compaction can have both desirable and undesirable effects on plant growth.
Slightly compacted soil can speed up the rate of seed germination because it promotes good contact between the seed and soil. In addition, moderate compaction may reduce water loss from the soil due to evaporation and, therefore, prevent the soil around the growing seed from drying out. Corn planters have been designed specifically to provide moderate compaction with planter mounted packer wheels that follow seed placement.
A medium-textured soil, having a bulk density of 1.2 grams per cubic centimeter (74 pounds per cubic foot), is generally favorable for root growth. [Note: a soil bulk density of 1.2 grams per cubic centimeters is comparable to a non-tracked soil after a secondary tillage operation.] However, roots growing through a medium-textured soil with a bulk density near 1.2 grams per cubic centimeter will probably not have a high degree of branching or secondary root formation. In this case, a moderate amount of compaction can increase root branching and secondary root formation, allowing roots to more thoroughly explore the soil for nutrients. This is especially important for plant uptake of non-mobile nutrients such as phosphorus.
Figure 2. Nitrogen deficiency symptoms in corn.
Figure 3. Potassium deficiency symptoms in corn.
Excessive soil compaction impedes root growth and therefore limits the amount of soil explored by roots. This, in turn, can decrease the plant's ability to take up nutrients and water. From the standpoint of crop production, the adverse effect of soil compaction on water flow and storage may be more serious than the direct effect of soil compaction on root growth.
In dry years, soil compaction can lead to stunted, drought stressed plants due to decreased root growth. Without timely rains and well-placed fertilizers, yield reductions will occur. Soil compaction in wet years decreases soil aeration. This results in increased denitrification (loss of nitrate-nitrogen to the atmosphere). There can also be a soil compaction induced nitrogen and potassium deficiency (Figures 2 and 3).
adapted from Soane et al., 1994
Figure 4. Effects of weather on crop yield response to compaction level.
Research from North America and Europe indicates that crops respond to soil compaction as shown in Figure 4. In a dry year, at very low bulk densities, yields gradually increase with an increase in soil compaction. Soon, yields reach a maximum level at which soil compaction is also optimal for the specific soil, crop, and climatic conditions. However, as soil compaction continues to increase beyond optimum, yields begin to decline. With wet weather, yields are decreased with any increase in compaction.
What causes soil compaction?
Figure 5. Soil crust
There are several forces, natural and man-induced, that compact a soil. This force can be great, such as from a tractor, combine or tillage implement, or it can come from something as small as a raindrop (Figure 5). Listed below are several types of soil compaction and their causes.
Raindrop impact – This is certainly a natural cause of compaction, and we see it as a soil crust (usually less than 1/2 inch thick at the soil surface) that may prevent seedling emergence. Rotary hoeing can often alleviate this problem.
Source: Compaction-Soil Management Series 2. University of Minnesota Extension, BU-7400
Figure 6. Reduced root growth due to compaction from raindrop impact, tillage, and wheel tracks.
Tillage operations – Continuous moldboard plowing or disking at the same depth will cause serious tillage pans (compacted layers) just below the depth of tillage in some soils. This tillage pan is generally relatively thin (1-2 inches thick), may not have a significant effect on crop production, and can be alleviated by varying depth of tillage over time or by special tillage operations.
Figure 7. Wheel traffic
Wheel traffic – This is without a doubt the major cause of soil compaction. With increasing farm size, the window of time in which to get these operations done in a timely manner is often limited. The weight of tractors has increased from less than 3 tons in the 1940's to approximately 20 tons today for the big four-wheel-drive units. This is of special concern because spring planting is often done before the soil is dry enough to support the heavy planting equipment.
Minimal Crop Rotation – The trend towards a limited crop rotation has had two effects: 1.) Limiting different rooting systems and their beneficial effects on breaking subsoil compaction, and 2.) Increased potential for compaction early in the cropping season, due to more tillage activity and field traffic.
Effect of soil moisture and axle load on depth of compaction
Greater axle loads and wet soil conditions increases the depth of compaction in the soil profile. Compaction caused by heavy axle loads (greater than 10 tons per axle) on wet soils can extend to depths of two feet or more (Figures 8 and 9). Since this is well below the depth of normal tillage, the compaction is more likely to persist compared to shallow compaction that can be largely removed by tillage.
A research study conducted in Lamberton, Minnesota (Voorhees et al., 1986) illustrates this effect. The Nicollet clay loam soil was compacted with 10 and 20-ton axle weights. When the soil was dry, most of the increase in bulk density was confined to the top foot with no detectable effect on the bulk density at the 18-inch depth. Under wet conditions the 20-ton axle load compacted the soil deeper than 18 inches. Similarly, under wet conditions on a Webster clay loam at Waseca the 20-ton axle load increased the bulk density to at least the 24-inch depth.
Adapted from Soehne, 1958
Figure 8. Depth of compaction as axle load increases. (Tire pressure remained at 12 psi for all tire sizes.)
Adapted from Soehne, 1958
Figure 9. Depth of compaction as soil moisture increases. (Tire size 11x28, load 1,650 lbs., pressure 12 psi.)
Total axle load, as well as contact pressure between the tire and soil, affects subsoil compaction. Historically, as equipment weight increases, tire size also increases. This avoids drastic increases in contact pressure (pounds per square inch (psi) of pressure exerted by the tire on the soil surface). Axle load for various field equipment are listed in Table 1.
Table 1. Approximate axle loads for field equipment.
|Equipment||Axle load (tons/axle)|
|Slurry tanker – 4,200 gal.||10-12|
|Slurry tanker – 7,200 gal.||17-18|
|6-row combine, empty||10|
|12-row combine, empty||18|
|12-row, full with head||24|
|720 bu. grain cart, full, 1 axle||22|
|Beet cart, full||24|
|Grain cart, 1,200 bu., 1 axle||35-40|
|Grain cart, 1,200 bu., 2 axle||17-20|
|4WD tractor, 325 HP, front axle||13|
|4WD tractor, 200 HP, front axle||7.5|
|MFWD tractor, 150 HP, rear axle||6.5|
Section II: Surface compaction
Density effects due to tillage
Compaction resulting from equipment weights of less than 10 tons per axle is generally restricted to the upper foot of the soil. Compaction in this zone can be largely removed by chisel or moldboard plowing the compacted layer. While wheel tracks are often the most obvious cause of surface compaction, they are by no means the only cause. Livestock and tillage equipment can also produce compaction.
Figure 10. Soil resistance to penetration after 10 years of continuous tillage for four tillage system.
Following ten years of a continuous corn tillage study on a clay loam soil at Waseca (Bauder et al., 1981), a dense compacted layer was detected just below the depth of tillage (4 inches) on the disc treatment (Figure 10). A cone penetrometer was used to register soil strength. The greatest force required to penetrate the top 12 inches was measured on the plot that was spring disked and had no other tillage. The light tandem disc penetrated only the top three inches of soil. Below the 4-inch depth, the resistance to penetration on the disc treatment equaled or was greater than that measured on the no-till treatment and both were considerably greater than the moldboard or chisel plow treatments in the 0- to 12-inch depth.
In tillage studies on a loamy sand at the Sand Plain Experimental Farm, at Becker, Minnesota, comparing no-till, chisel, moldboard and ridge till systems, and at a study on a silt loam at Arlington, Wisconsin, comparing chisel, moldboard and ridge till systems, the greatest resistance to penetration in the 0- to 12-inch depth occurred on the no-till treatments.
In both studies a plow pan was detected just below the depth of operation with the moldboard plow. The Wisconsin study found that with wheel traffic there was little difference in penetration resistance among tillage systems. Soil compaction from wheel traffic tends to mask the effects of tillage on penetration resistance.
Plant response to surface compaction
The effect of compaction on plant growth and yield depends on the crop grown and the environmental conditions that crop encounters. In general, under dry conditions some compaction is beneficial, but under wet conditions compaction decreases yields. Response of various crops, including soybeans, corn, wheat, potatoes and sugar beets, to surface compaction has been studied in Minnesota and in surrounding states. The results of these studies will be discussed by crop.
Research results in Minnesota indicate that the effect of surface compaction on soybean yields depends very strongly on weather conditions and on soil nutrient levels. The yield response from compacting the soil was greater during dry years and when the soil phosphorus tested low. During a 13-year (1973-1985) study on a clay loam soil at Lamberton (Voorhees et al., 1986), the effect of surface compaction on yield was related to the rainfall amounts. When May - August rainfall was less than 14 inches, soybean yields were greater in the tracked rows. However, if the rainfall was more than 14 inches, yields from the tracked beans were less than the tracked rows.
Possible reasons for the increased yields on the "wheel-tracked" treatment during the dry seasons include increased uptake of phosphorus, increased root branching, and reduced water evaporation from the plow layer. This provides more favorable water conditions for nutrient uptake.
At Rosemount, Minnesota (Blake, 1958), axle loads of 4 tons in 1957 and 6 tons in 1958 were applied to the entire surface of a Waukegan silt loam soil prior to planting. Corn yields were reduced an average of 7.5% over the two-year period. Increased levels of soil fertility effectively overcame the yield loss due to compaction.
The yield effects of increasing tire contact pressure on a clay soil in Quebec, Canada, were influenced by the May to September precipitation. When the precipitation was 21 inches, yield decreased as the compaction was increased. When the precipitation was 14 inches, corn yield first increased as compaction increased and then decreased as compaction was increased further. Thus, under dry conditions some compaction was beneficial but too much was detrimental to yield. Under wet conditions any amount of compaction decreased yields and the greater the contact pressure the lower the yields.
Figure 11. Wheel traffic on wheat field
The effect of wheel traffic compaction on wheat yields on a clay loam at Morris depended on the April to June precipitation. Under dry conditions, the wheel-tracked area produced higher yields than the non-tracked area. However, as the precipitation increased, the non-compacted area resulted in higher yields than the compacted area.
In 1980 (Voorhees et al., 1985), wheat yields of non-compacted, fall-compacted, spring-compacted, and fall- and spring-compacted treatments were not significantly different. However, percent protein was significantly lower on the spring-compacted (12.9%) and fall- and spring-compacted (12.7%) treatments compared to the non-compacted treatment (13.6%) (Table 2).
Table 2. Timing effect of compaction on percent wheat protien in Grand Forks, ND.
|Fall and spring compacted||12.7|
In contrast, a 1982-1983 North Dakota study reported that neither wheat yield nor percent protein were significantly different between non-compacted and compacted treatments.
European research has shown that compaction generally decreased wheat and barley yields under wet conditions, while moderate compaction had little effect or slightly increased yields during normal precipitation patterns and increased yields under dry conditions. In all cases, severe compaction decreased yields.
Because of the potato tubers growth pattern and its relatively confined root zone, soil compaction frequently has a detrimental effect on potato yields. There has been a good deal of research confirming lower potato yields due to compaction.
Deliberate packing of the soil in the Red River Valley decreased potato yields 54%. In a two-year study at Grand Forks, Minnesota, compaction reduced potato yields an average of 21%. At Morris, Minnesota, potato yields were reduced 35% because wheel traffic restricted tuber development.
The sugarbeet appears to be less sensitive to surface compaction if it does not interfere with plant emergence. The effects of surface compaction on yields in a North Dakota study are shown in Table 3. Although soil compaction increased beet sprangling, which causes problems at harvest, compaction had no effect on recoverable sugar or root yields in 1980. Compaction was created by repeated passes with a loaded, single-axle, dual-wheel truck (GVW 18000 lbs).
Table 3. Effect of soil compaction on sugarbeet and total recoverable sugar yields, Grand Forks, ND (Giles, 1980, 1981).
|Soil properties||Probe resistance (lbs/inch2)||1979* and 1980 average tons/acre|
|*Compaction increased yields because of a higher final stand (108 vs. 79 beets/100 ft. of row for compacted and non-compacted treatments respectively).|
Soil compaction in the surface layer can increase runoff, thus increasing soil and water losses.
Figure 12. Reduced water infiltration in wheel tracks.
However, when the compacted layer is tilled with a moldboard or chisel plow, the resulting rough, cloddy surface can decrease runoff and erosion. While it sounds contradictory, both effects are possible, depending on the soil and soil conditions encountered.
Field studies at Lamberton have shown greater surface roughness and cloddiness following moldboard plowing where the soil was tracked before tillage. Other studies show that greater surface roughness was caused by greater bulk density before tillage. On soils such as these, which have a relatively stable structure, greater surface roughness can increase infiltration, reduce runoff, and reduce erosion up to the point that runoff begins. Studies at Morris have shown that even after tillage, wheel tracks due to spring planting increased runoff and erosion.
Section III: Subsoil compaction
Subsoil compaction is a serious soil conservation issue and a long-term threat to soil productivity. Most subsoil compaction occurs when the soil is wet and field equipment weights exceed 10 tons per axle. Kinds of equipment most likely to have loads in this range are combines, loaded grain carts, and slurry tankers. Plowing with a tractor wheel in the furrow will pack soil below the depth reached by normal tillage operations and can be another source of subsoil compaction.
Plant response to subsoil compaction
The plant response to subsoil compaction, as with surface compaction, depends on the crop, soil conditions, and the climatic conditions in a particular year. If plants are already stressed for water, subsoil compaction may add to the stress by limiting the growth of plant roots to additional water. If plants are growing in soils that have aeration problems due to high water content, subsoil compaction will slow drainage and could result in an anaerobic root environment that limits nutrient uptake.
Simply put, subsoil compaction can affect:
- Water availability
- N and K uptake
- Plant growth and yield
- Delayed planting and other field operations due to colder and wetter soils
Research studies conducted in northern latitudes show that the effect of severe subsoil compaction may affect crop yields for years. Research results from Lamberton and Waseca, Minnesota, Uppsala, Sweden and Quebec, Canada, show a similar trend of initially lower yields following compaction with axle loads of 10 tons or more. The effect decreased over time, and yields on compacted soil approach the yields on non-packed soil after two to seven years, depending on the soil and climate.
From Vorhees et al., 1986.
Figure 13. Relative corn yields over 12 years with a one-time soil compaction of 20 ton/axle
While these studies show a gradual, natural alleviation of subsoil compaction, the data from Waseca suggests that there is sufficient "residual" subsoil compaction to reduce crop yields in years where there are environmental stresses. Figure 13 shows that corn yields were back to normal within 5 years after the compaction was created. However, in 1988, 1990, and 1993 yields were reduced. In 1988, growing season precipitation was the lowest on recorded history while in 1990 and 1993, the region received above average rainfall (167% and 175% of the long-term average).
This study illustrates that a one-time compaction event can lead to reduced crop yields 12 years later. Under normal farming operations, heavy equipment is used every year. Thus, subsoil compaction resulting from farming practices may be permanent.
Section IV: Control
There are four strategies commonly used in dealing with compaction: 1) avoidance, 2) alleviation, 3) controlled traffic, and 4) acceptance.
Avoidance is the most desirable where it is physically and economically possible. The old adage of "stay off the field until it's fit to work" still applies. However, the possible severe economic repercussions of delaying planting, harvesting, or other operations may outweigh compaction damage or loss. The dilemma the farmer faces in a wet spring or fall is not easy to resolve.
While large, heavy machinery is often blamed for soil compaction problems, it also offers opportunity to minimize compaction. Larger capacity machinery means fewer wheel tracks across the field because of wider working width. If wheel track spacing can be standardized among different pieces of equipment, soil compaction problems can be minimized.
Tracks vs. tires
Tracks, as an alternative for tires, are not new in agriculture. Tracks accounted for 6-10% of all tractor sales between the years of 1925-1966. However, in recent years, the change from steel to rubber tracks, improved ride-ability, increased traction, and research citing that tracks create less surface compaction than tires have increased the popularity of tracks.
Figure 14a. Tractor with tracks
Figure 14b. Tractor with tires
Figure 14c. Combines and grain carts can create compaction as deep as 3 ft.
Tractors equipped with either tracks or tires can create surface compaction. The question is "Which one creates the least amount of compaction"? The answer: both radial tires and tracks will result in similar surface compaction if the radial tires are properly inflated.
Tractors weighing less than 10 tons an axle usually keep compaction in the top 6-8 inches, which can be alleviated by tillage. By and large, even the biggest tractors weigh less than 10 tons an axle. However, combines and grain carts weigh much more and whether equipped with tracks or tires, they can create compaction as deep as 3 feet.
In general, contact pressure largely determines the potential for compaction in the plow layer, while total axle load determines the potential for subsoil compaction. This is important when comparing tracks and tires for compaction effects and depth.
Tracks exert a ground pressure of approximately 5-8 psi depending on track width, length, and tractor weight. Radial tires exert a pressure of 1-2 pounds higher than their inflation pressure. For example, if a radial tire is inflated to 6 psi, the tire exerts a pressure of 7-8 psi on the soil. However, bias tires inflated to only 6-8 psi cannot operate efficiently and easily wear-out with such low tire pressures, consequently they have to be inflated to 20-25 psi.
Research has shown that tractors equipped with either tracks or radial tires create compaction in the top 5-8 inches, however, compaction effects were negligible below that depth. But what effect do tracks have on subsurface compaction when used in conjunction with heavy field equipment, such as grain carts or combines? Keep in mind that depth of compaction is a result of total axle weight and the role of ground contact pressure is secondary. Whether the equipment uses tracks or tires, the total axle load is nearly the same. Tracks will improve traction and ride-ability, but a 25-ton per axle grain cart will still create subsurface compaction.
At times, potentially damaging compaction is unavoidable. What can be done about it? There are two ways of alleviating and lessening the damage caused by compaction: 1) Attempt to remove the compaction or 2) Attempt to reduce the adverse effects of the compaction.
Figure 15. Alleviation of wheel traffic compaction by tilage and overwintering.
Moldboard tillage of the compacted depth has been effective in removing surface compaction in studies at Lamberton (Bauder et al., 1981). Wheel traffic during the growing season increased the bulk density to 1.55 g/cm3 in the surface foot of a Nicollet clay loam (Figure 15). Moldboard plowing this compacted soil in the fall (D) reduced the bulk density in the top foot to similar values measured in the soil without wheel traffic (E).
Where no tillage was done, freezing and thawing over winter reduced the bulk density only slightly and only above the 6-inch depth, (B). In this study, chisel plow and disk treatments (C) were less effective than the moldboard plow in removing surface compaction in one over-winter period. These results confirm that freezing and thawing alone may not remove compaction.
One way to reduce the adverse effects of compaction is to apply fertilizer in a way that increases the availability. Such measures may include row/band application of phosphorus or potassium. Split application of nitrogen or other practices that minimize the loss of nitrogen by denitrification may also alleviate compaction problems.
In the Midwest, research results evaluating the effects of subsoiling have shown few positive yield responses to subsoiling. When they do occur, they are variable and relatively small.
There is a real difficulty in accurately predicting the effects on crop yield from subsoiling a given field because of differences in soils, the level of subsoil compaction, the soil water content, subsequent traffic, uncertainties of future weather conditions, and differences in the crop grown and in tillage methods.
Figure 16. Multiple reasons could contribute to the variable responses to subsoiling.
In a Waseca study, subsoiling to a depth of 16 inches failed to increase yields on the 20 ton per axle treatments for either corn or soybeans and decreased corn yield 11 bu/a in one of the two years.
One strong possibility for the lack of response to subsoiling is that the detrimental effects caused by compaction were no longer limiting crop yield. This could occur either because differences in crop or climatic conditions, such as rainfall, that may alleviate the effects of surface compaction.
Another possible explanation is that the subsoiling failed to effectively remove the compaction because of unfavorable soil moisture conditions at the time of subsoiling. If the soil moisture is too high, subsoiling will be ineffective. The subsoiling and associated traffic can reduce the soil macro-porosity, further restricting the drainage of water through the soil.
Another reason cited for the failure of subsoiling to remove a compacted layer is that subsequent wheel traffic may have reintroduced the compacted layer, thus negating the effects of sub-soiling. A loosened subsoil will have very little bearing capacity, meaning it can't support much weight. An ordinary 2-wheel drive tractor may be sufficiently heavy enough to re-compact the subsoil. Controlled traffic becomes even more important.
To increase the probability of obtaining beneficial effects from subsoiling, the following steps should be considered:
- Determine that a compaction problem actually exists. 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 that subsoiling can effectively disrupt the compacted layer.
- Make sure the soil is dry and fractures to the depth of the shank when subsoiling.
- Avoid recompacting loosened soil by using the controlled traffic concepts.
In a normal year, as much as 90% of the field may be tracked by equipment (Figure 17a). The philosophy behind controlled traffic is to restrict the amount of soil traveled on by using the same wheel tracks. Seventy to 90 percent of the total plow layer compaction occurs on the first trip across the field. By controlling traffic, the tracked area will have a slightly deeper compaction but the soil between the tracks will not be compacted (Figure 17b).
Source: Management Strategies to Minimize and Reduce Soil Compaction. 1999. University of Nebraska, G89-896-A.
Figure 17a. Field coverage by normal annual field operations.
Source: Management strategies to Minimize and Reduce Soil Compaction. 1999. University of Nebraska, G89-896-A.
Figure 17b. Field coverage in a controlled traffic situation.
Corn and soybean farmers who use global positioning systems (GPS), ridge till, strip till, or no-till can confine traffic between certain rows and avoid compacting the row area. This requires proper matching of all machines including combines, grain carts, and manure-handling equipment to confine the compaction to the same between-row areas.
There are occasional reports of adverse effects on plant growth where the wheel tracks are on both sides of the row, but even then the damage is confined to certain rows. Benefits to controlled traffic, using permanent compacted lanes, are improved tractor efficiency and floatation, less powerful machinery needed, and improved timeliness of operations.
Acceptance is waiting for the detrimental effects to be removed by natural forces. However, this may not be practical if there is compaction below the plow layer. The deeper the compaction and higher the clay content, the longer it will persist.
- The effects of compaction on plant growth and yield depend on the crop grown, soil type, and weather conditions.
- Under dry conditions, slight compaction is beneficial but too much is detrimental to yield.
- Under wet conditions, any amount of com- paction can decrease yields as a result of N losses, reduced K availability, and inhibited root respiration due to reduced soil aeration.
- A moderate amount of compaction in the seed zone at planting is desirable in order to provide adequate seed-soil contact.
- Excessive compaction decreases water infiltration and storage, decreases root growth, reduces the soil volume explored by roots and can reduce crop yields.
- Depth of compaction increases as both the soil moisture content and axle load increase.
- Compaction in the plow layer is largely related to contact pressure of the tire. Compaction below the plow layer is related to total axle load.
- Surface compaction can usually be alleviated by moldboard or chisel plowing.
- Subsoil compaction takes years to alleviate.
- In our region, research studies have shown few cases of positive yield response to subsoiling and in some cases subsoiling has decreased yields.
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About the Authors
Jodi DeJong-Hughes is an Extension Educator for Northwest Minnesota with the University of Minnesota West Central Research/Outreach Center, Morris, Minnesota.
John Moncrief is an Extension Soil Scientist – Tillage, Department of Water, Soils & Climate, University of Minnesota Extension Service.
W. B. Voorhees is a Soil Scientist with the North Central Soil Conservation Research Laboratory, USDA-Agricultural Research Service, at Morris, Minnesota.
J. B. Swan is a retired Extension Soil Scientist, University of Minnesota Extension Service.
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