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Ministry of Agriculture, Food and Rural Affairs

Compaction - soil diagnostics

Crops grown in compacted soils often have a restricted root system. This leads to poor nutrient uptake, stunted growth, a general lack of vigour, and reduced yields. Compaction affected plants are also more susceptible to disease and insect pressure.

The root systems of affected plants often show signs of a physical barrier. The root tips may become stunted and club-like, or the plant may produce a proliferation of horizontal secondary roots, in an attempt to outgrow the compaction. Transplanted crops grown on compacted soils often fail to leave the root plug, or they may develop a corkscrew-shaped taproot.

Compaction may be assessed using several inexpensive tools, such as a tile probe, plot flags or a shovel. Take note of any resistance or barriers when probing the soil and assess the depth at which the resistance is felt. Consider soil moisture levels when probing. Soil strength increases as soils dry out, consequently a dry soil will exhibit more resistance than a very wet soil. Assessments of potential soil compaction should be performed on moist soils.

Types of Compaction

  • Crusting is common on soils with poor structure and low aggregate stability. Moderate to intense rain events after planting shatter the soil aggregates causing the finer textured particles to bind together and fill any open pores on the soil surface. As the soil dries, a thick and impermeable crust forms. Soils with a heavy crust will often exhibit poor crop emergence and increased seed decay and root rots. Excessive secondary tillage during seedbed preparation makes soils more prone to crusting. Crusting is more commonly found on soils with a finer texture (i.e. loams to clays).
  • Sidewall Compaction is caused when planting activities take place on wet soils. The planter’s disk openers cause the soil to smear, effectively sealing it, limiting both root growth and nutrient uptake. The emerging plants will often exhibit flattened roots and may have a proliferation of secondary roots growing horizontally along the planter trench. Under moist soil conditions the growing crop may be able to grow past the barrier. Sidewall compaction is more commonly found on soil types with high proportions of silt and clay.
  • Plow Pans are hard, compacted layers occurring 15- 30 cm (6- 12 in.) below the soil surface. Wet harvest seasons and long-term intensive vegetable crop-oriented rotations can result in the formation of a plow pan. The effects of a plow pan are most obvious in extremely wet or extremely dry years. In wet years, the compacted zone may cause drainage problems and waterlogged soils. In dry years, the compaction-confined root system is unable to access soil water below the plow pan. Plow pans and tillage pans can be found on any soil type including coarse sands and sandy loams.

Management Notes

  • Rotation with deep rooted crops, such as corn or alfalfa, or fibrous rooted crops, such as wheat will help to loosen compacted soils. They will also improve the soil structure, making it less susceptible to compaction in the future.
  • If possible, avoid working in wet fields, particularly with heavy equipment. The carrying capacity of dry soil is much greater than that of moist soil. Ensure tillage operations are performed when the soil is at proper moisture conditions at the tillage depth. Alternate tillage depth so that tillage pans are not created.
  • Use radials, large tires or tracks that create a long narrow footprint to restrict compaction. Reduce the tire pressure to reduce the force on the surface of the soil. This will only be effective with radial tires. The tires must be large enough to carry the equipment at reduced pressures. Check with the manufacturer to confirm that the tires are rated to operate at low pressures.
  • Avoid high axle loading, which will cause compaction in the subsoil, even with low tire pressure. Keep equipment weight and loads as low as practical (below 4.5 tonnes/axle or 5 tons/axle). Limit traffic with heavy equipment to laneways or harvest rows rather than tracking the entire field.
Effects of compaction on roots
Tractor ruts in muck soil Tire ruts and compaction
Click to enlarge.