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SWEEP Report #4

Assessment of Soil Compaction and Structural Degradation
in the Lowland Clay Soils

L. Leskiw, Can-Ag Enterprises, Guelph, Ontario

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

View / Download Final Report [1240 KB pdf] (no appendices)

Associated SWEEP/LSP Research



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Completed: May, 1988

Key Words:

compaction, yield reduction, compaction measurement, visual symptoms, causes of compaction, extent of compaction, lowland soils, clay soils, clay loam soils

Executive Summary

Highlights of the major subject areas on subsoil compaction and structural degradation covered by this study in five counties in Southwestern Ontario are included in this summary. Recommendations and conclusions are based on results of field investigations, farmer interviews, laboratory analysis and review of scientific literature dealing with the problem of subsoil compaction on agricultural lands.

The Problem

This study focuses on the soil layer below the plow layer (i.e. about 15 to 30 cm below ground surface). Soil compaction may include one or more of these conditions: degraded soil structure; reduced size, abundance and continuity of vertical cracks and pores; smearing; increased soil bulk density; layering; and, altered rooting pattern and depth. These conditions tend to reduce the soils' ability to produce abundant crops due to deterioration of root zone quality. Soil permeability is also reduced and this results in increased runoff and erosion.

The main goal of this study was to determine the magnitude and extent of subsoil compaction and to evaluate its agricultural and environmental impacts.

Agro-Environmental Setting

Southwestern Ontario is intensively farmed, the main crops grown being corn, cereals, beans (soy and white), hay and fresh vegetables.

Soils studied include predominantly clays, clay loams, silty clay loams, and silty clays on level to very gently undulating topography. Parent materials are either till, lacustrine deposits or lacustrine veneers over till. Soil drainage commonly ranges from imperfectly to poorly drained and many sites examined are tile drained. To manage these fine textured, level soils for some of the crops grown, especially corn, many farmers try to get on their fields as early as possible in spring. The combination of tillage under fairly wet conditions using large, powerful and heavy tractors can contribute to soil compaction. Alternative cropping practices may be better for the soil but they may be less profitable, at least in the short term. Research has demonstrated that compaction does not occur when soils are worked under proper moisture conditions.

Measurements of Compaction

Several methods are used to measure soil compaction and five of the more popular ways were used in this study: visual observations of a combination of factors; bulk density determinations, hand and cone penetrometer measurements and detailed descriptions of soil peds and pores (tubular and planar).

Statistical Analysis

The degree of compaction was assessed using various statistical procedures to establish relationships among measured and observed soil properties. A visual compaction rating proved to be a good measurement, although it is subjective. Resultant ratings into slight, moderate and severe compaction categories using this approach gave essentially the same results as using a combination of all measurement techniques.

A point transect method was used to locate study sites throughout the area in an attempt to obtain unbiased estimates on the extent of compaction.

Soil compaction measurements were statistically compared to various agronomic management practices to identify significant linkages. Items examined included different measurements of soil compaction, tractor size, crops, rotations, tillage practices, fertilization methods, weed control practices, harvesting, number of passes, and others.


Soil compaction is a serious problem in southwestern Ontario. Statistical analysis indicates that about 50 to 70 percent of the clay to clay loam soils in the counties of Middlesex, Lambton, Essex, Kent and Elgin are affected. Of this total, about 25 percent are severely compacted and 75 percent are moderately affected. Impacts of compaction are estimated to be the following:

  Moderately Compacted Severely Compacted
Crop Yield Reduction 12% 25%
Increased Soil Erosion 17% 39%
Increased Phosphorus Loadings to Great Lakes (kg/yr) 35,000 39,400

In terms of dollars, decreased yields represent by far the greatest shortfall on returns. Increased soil erosion is very important in that it is a hidden cost to the farmers and contributes sediments and nutrients to streams. However, from the farmers' viewpoint these costs are minor compared to yield losses. The phosphorus loadings to the Great Lakes attributable to compaction are in the order of 10 to 15 percent of the total phosphorus loadings from agricultural lands. It is noteworthy that soil husbandry practices undertaken to minimize or ameliorate the compaction problem to increase yields will simultaneously reduce the harmful environmental impacts.

Important factors considered to be contributing to compaction include:


Size of tractor - Increasing compaction related to bigger tractors
Number of passes - More passes, especially when soils are wet
Crops grown - Forages < small grains < row crops < silage corn and tomatoes

Natural amelioration of subsoil compaction through freeze-thaw and wetting-drying cycles is a slow process and is not practical in an agricultural time frame. Subsoiling using heavy duty chisel plows and subsoilers may be helpful but results to date are mixed. Further work is needed to determine the most effective methods of mechanically ameliorating compaction. Management practices that farmers can implement to minimize or prevent compaction include:

  • reduce vehicle weights below critical limits (dependent on soil conditions and tires)
  • avoid traffic on wet or very moist fields
  • limit the number of passes and control traffic
  • utilize cropping systems which facilitate the above
  • reduce tire pressures, unknown how beneficial duals are with respect to subsoil compaction
  • use practices which maintain soil flora and fauna


Several questions arise from this study that should be answered in order to help farmers deal with the compaction problems. These include:

  • refinement of visual methods for quickly assessing seriousness of compaction and compaction hazard considering soil characteristics and moisture conditions.
  • better understanding of the role of rotations vs. monoculture, including crop yield and compaction relationships.
  • research into the use of different tires (radials, duals, flotation tires, loading vs. slippage)
  • development and application of computer models to make better estimates of the effects of compaction on erosion and phosphorus removal
  • development of an integrated, holistic model for soil compaction which would allow a farmer to chose the best combination of cropping practices, machinery and tires for his soil conditions and farming operation.


Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)

Five methods were used to assess compaction: visual observations, bulk density, hand and cone penetrometer measurements, and detailed descriptions of soil peds and pores. The visual assessment which considered layering, structural deformation, rooting patterns, number and continuity of pores, void characteristics, observed differences between horizons and consistency within a field was a useful method for assessing compaction problems.

The study determined that 50-70% of the clay and clay loam soils in Middlesex, Lambton, Essex, Kent and Elgin are affected by compaction. Of this total, 25% were severely compacted and 75% were moderately affected.

Farmer opinion (from interviews) was that compaction caused reduced yields of 12% for moderately compacted soils and 25% for severely compacted soils. Increased soil erosion and phosphorus loadings as a result of compaction were estimated using the USLE and census data.

Factors found to contribute to compaction were the size of the tractor, number of passes and the crops grown (silage corn and tomatoes < row crops < small grains < forages).


This report contains a good literature review on compaction.

The study considered compaction only below the plow layer, in the 15-30 cm depth. The effect of manure application was not specifically considered (although axle loads were considered).

Associated SWEEP/LSP Research:

  • SWEEP Report #16 - Effects of Subsoiling on Corn Yields and Soil Conditions in Southwestern Ontario
  • SWEEP Report #24 - Investigation of Soil and Crop Response to Fall Subsoiling in Southwestern Ontario
  • LSP 7002 - Management of Fine Textured Poorly Drained Soils for Intensive Agriculture
  • LSP 7006/LSP 7007 - Management of Fine Textured Poorly Drained Soils for Intensive Agriculture: Characterization of a Forage Factor - Part I & II
  • LSP 7012 - Improving the Degraded Structure of Fine Textured Soils with Deep Tillage and Grass and Legume Crops
  • LSP 7013 - Improving the Degraded Structure of a Clay Loam Soil with Deep Tillage and Grass and Legume Crops
  • LSP 7015 - Crop Production with a No-Traffic Tillage System
  • LSP 7019 - Impact of Soil Compaction on the Production of Processing Vegetables and Other Cash Crops

Future Research: ( ) indicates reviewers suggestion for priority, A - high, C - low.

(C) Refinement of visual methods for quickly assessing the extent of compaction and compaction hazard. Compaction research trials evaluating the actual extent of yield reduction in corn and soybeans.




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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 12:55:09 PM