Soil Compaction and its Effect on Corn Growth

• Soil compaction reduces the size and amount of pore space which decreases vertical water movement, soil aeration and oxygen movement.
• Compaction layers in the soil can alter plant rooting depth, causing issues later in the season.
• There are several types of soil compaction, including tillage pan/plow layer, planter side-wall compaction and deep compaction.
• The use of proactive measures is typically the most effective way to mitigate soil compaction long-term.

Figure 1. Compaction layer from tillage on wet soils.

The temptation to begin field work or planting before soil conditions are ideal happens almost every year, but it is even worse when cool, wet springs cause delays. However, running across fields with planters or tillage implements when the soil is too wet can cause soil compaction issues that will impact growth and development of corn throughout the year.

Effect of Compaction on Soil

Compaction increases bulk density of the soil, creating an impenetrable layer of soil that will break apart in flat pieces when digging (Figure 1). Compaction reduces the size and amount of pore space in the soil, which decreases vertical water movement throughout the soil profile and increases water runoff. Less soil pore space also reduces soil aeration and oxygen movement, which is important for root respiration and nutrient uptake.

Soil compaction depletes the soil of oxygen, throwing off the balance of “healthy soil.” Soil should be about 25% air. Lower ratios of oxygen within soil reduce soil mineralization rates, resulting in reduced nitrogen, phosphorus and potassium availability to the crop through normal microbial processes.

Figure 1. Compaction layer from tillage on wet soils.

Soil compaction can also alter and reduce rooting depth, which can cause trouble later in the growing season when water becomes scarce and plants are not able to mine the full soil profile for water and mobile soil nutrients.

3 Common Types of Compaction

1. Tillage pan or plow layer – Tillage is mainly used to manage residue from prior crops and prepare an even surface for planting. If similar tillage practices are used across years, soil profiles will begin to form a hard, compacted layer across fields at the depth the tillage equipment was run. Disks or field cultivators will form a layer closer to soil surface due to their operating depth, whereas moldboard plowing creates similar layers at deeper depths. Tillage in wet soil conditions only worsens the effects of tillage pan or plow layers. The resulting layer will restrict water movement and root growth to needed depths for accessing nutrient and moisture.

2. Planter sidewall compaction – When the openers on a planter “smear” the sides of the seed trench, they create a layer of soil that restricts outward root growth. This “smearing” of the sidewalls of the seed furrow will restrict the root growth through the seed furrow, leading to the development of “mohawk” roots on the corn plant.

3. Deep compaction – As the name implies, deep compaction forms at a deeper depth in the soil profile and is therefore much harder to eliminate with tillage. Deep compaction typically forms in areas with high traffic with implements loaded to maximum axle weights. The most common cause is grain cart or truck traffic lanes within fields or on end rows. This type of compaction is often the most visible, as the restricted rooting depth can dramatically reduce crop growth (Figure 3).

Corn plant roots will grow and develop the best in a porous soil that is free of compaction. A healthy root system that spreads out and penetrates into the soil profile will have large amounts of surface area. This large root surface area allows for efficient uptake of nutrients and water and in addition to helping anchor the plant into the soil, decreasing the risk of lodging throughout the growing season.

Figure 3. Deep compaction from grain cart traffic the prior fall.

​​​​Compaction restricts root growth and affects nutrient and water uptake throughout the growing season, even if the proper rates of nutrients have been applied to the field and soil moisture is adequate. This leads to plants cannibalizing stalks and increases the  risk of late season lodging because the roots cannot fully develop enough to anchor the plant.

Determining When Soil is Ready for Field Work

A dry soil surface doesn’t necessarily mean that the field is ready for tillage. Purdue University recommends digging 1” below the depth of tillage, taking a handful of soil and rolling it into a “worm” shape. If the soil can be rolled into a “worm” that is longer than 5” and does not break apart, the soil is too wet for tillage.

Farmers may be tempted to use vertical tillage tools to work the top 2-3” of soil to “dry out” the soil to plant sooner. This is not recommended as it will create a tillage pan just below where the seeds will be placed and can restrict water movement through the soil profile. That water will accumulate at the same depth as the seeds and can cause injury or death to the germinating and emerging seedlings.

Managing Compacted Soils

Preventing soil compaction is the best way to manage soils. However, minimizing or controlling soil compaction are the next best options since farmers often need to be in the field in less than ideal soil conditions. Consider controlling traffic in fields, managing axle loads and tire pressure, and selecting the right equipment for the job. Before deciding on a compaction management tool, it is important to diagnose the existence and depth of current compaction.

During the early growing season, corn growing in compacted soils should be monitored for nutrient deficiency symptoms and corrected, if possible. For sidewall compaction, cultivation may be considered to help promote more root growth and help standability. For a tillage pan, a cultivator pass or sidedress N application can help break up the layer if it can be made deep enough.

For late season management, monitor the fields for any potential stalk or root lodging, and plan to harvest those fields early to help minimize losses. To help break up compaction in a field, a deep tillage pass at an angle to the normal cropping rows may be considered in the fall. This will help restore oxygen to the soil profile. In a no-till environment, consider planting an aggressively growing cover crop, such as tillage radish, to break compaction layers. The most important resource to growing a healthy and profitable crop is your soil, so consistent management of compaction is necessary.

For more information on soil compaction management, contact your local Golden Harvest Seed Advisor.

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