Effects of Soil Compaction on Corn Productivity

Basics of Soil Compaction

Soil moisture and texture are both important influences on soil compaction. Medium- and fine-textured soils can be vulnerable to compaction when they are at or near field capacity, defined as the amount of water a soil can retain against gravity after excess water has drained away. This is the point at which the pore space surrounding soil particles is completely filled with water, and this state can make fields more vulnerable to compaction because, on the microscopic level, the water in the soil pores holds soil particles together without allowing air between them.¹

Water is not compressible, so when too much weight is applied to soils—and particularly to soils at or near field capacity that contain the most water a soil can hold—the weight squeezes the particles as close together as they can be pressed, while the adhesive force of the water keeps the particles stuck together. High pressure applied by the weight of heavy machinery traffic in a field can cause soil aggregates to become compacted (tightly packed together), and farm machinery has become heavier every decade since the 1950s.^1,2 Previous studies have found that conventional tillage can result in heavy machinery traffic over the entire field area during a single cropping cycle—sometimes multiple times.³

Soil compaction can be measured using the soil’s bulk density, expressed as grams per cubic centimeter (g/cm³). A soil’s ideal bulk density varies depending on its texture. A productive soil composed primarily of silt and clay will typically have a bulk density of about 1.2 to 1.3 g/cm³. A compacted soil of the same textural class may have a bulk density around 1.6 to 1.7 g/cm³. Coarse soil textures will have higher bulk density, ideally around 1.7 to 1.8 g/cm³. Within a given textural class, higher bulk density may indicate limited pore space is available for air or water in the soil.¹

Soil compaction degrades land at a global level that, if not addressed, can lead to long term negative effects on crops.

Corn Response to Soil Compaction

Corn Emergence and Stand Counts.

As compaction increases a soil’s bulk density, the corresponding reduction in pore space often results in restricted plant root growth and poorer water infiltration (Figure 1). Additionally, increased machinery traffic may both compact soil and create uneven planting surfaces that make planting depths more variable, causing delays and variability in corn seedling emergence.⁴

Changing the type of tire used on machinery wheels and the pressure within the tires can help reduce the effects of compaction on corn emergence and stand. A study conducted in Pennsylvania found that fields trafficked with floatation tires at 36 psi (pounds per square inch) had higher plant counts than fields trafficked with road tires at 100 psi.⁴ Reducing tillage can also help reduce compaction. However, just like compaction, residue remaining from previous corn crops can cause uneven emergence (Figure 2). While reducing tillage passes preserves soil structure and helps mend compaction, doing so may require planters to have row-cleaner attachments to prepare seedbeds.

Corn Plant Height.

Compaction can reduce the height of corn plants, as seen in the results of a 2006 study (Table 1). In this study, corn grown on non-compacted soil was 21% taller than corn grown in soil with annual road tire compaction six weeks after planting. Height differences were still noticeable at harvest, and grain yield tended to be lower with plants shortened by compaction.⁵

Table 1. Soil compaction effects on corn height (inches) six weeks after planting and at harvest.

Ear Development and Corn Yield Potential

The effects of soil compaction on ear development and yield potential tend to be inconsistent across fields, likely due to interactions between the many factors that influence yield potential and corn’s ability to produce larger ears with lower stand counts. However, two studies from Purdue University both found a negative effect of compaction on yield.⁴ Severe subsoil compaction can occur in a single pass. Studies have shown that subsoil compaction from a load of 10 tons per axle can affect yields for up to seven years, while the effects of a 20-ton axel load can affect yields for 12 years.¹

Potential Remedies to Alleviate Soil Compaction

Deep-Ripping Implements.

This type of tillage tool is designed to break compaction in the subsoil to a depth of about 16 inches. However, deep-ripping results in positive crop responses only about 25% of the time.⁶ The benefits of deep-ripping are largely dependent on subsoil moisture conditions—the drier the better.

Winter Freeze-Thaw Cycles and Summer Cracking.

Alleviating deep soil compaction can begin naturally through drying during the summer months. Soils crack as they dry, potentially to several feet below the surface, and this shrink-swell process is one way that clay-type soils become less compacted. Winter freezing can also provide a remedy for compaction, but only in the top few inches of soil.⁴ Several dozen freeze-thaw cycles on fields with high soil moisture (greater than 85% of pore space filled with water) are needed to break up compaction. In most years, the North Central corn-growing area experiences only one to two freeze-thaw cycles per year reaching below a six-inch depth.⁶

Cover Crops.

Cover crops can provide an alternative to machinery for breaking up compaction. For example, the large, deep taproots of tillage radish can repair soils by stabilizing aggregates, creating pore spaces for the infiltration of water and air, and breaking through plow pans. Cover crops planted on acres with compaction issues help drain wet soils and create root channels which commodity crops can grow through. These beneficial soil services are unique to cover crop growth.

How to Prevent Soil Compaction

Take Steps to Build Soil Organic Matter.

Building organic matter (OM) can help to improve soil structure and can provide a means for reducing soil compaction even in higher soil-moisture conditions.¹

Establish Controlled Traffic.

When unconsidered and unchecked, the machinery traffic used in conventional tillage can cover the entire field—even overlapping itself to spread wheel tracks across 145% percent of the planting area.³ Up to 80% of soil compaction occurs during the first pass across the field and even a single pass can be damaging for years to come.¹ Changing to controlled traffic pathways may take several, but doing so can result in more efficient field operations that require less machine power. Consider the following to reduce wheel impacts:

• Consider taller, narrower tires on new machinery.
• Grain carts are the heaviest machinery (carrying more than 2,000 bushels) and should be the first equipment considered when planning pathway control (Figure 2).⁴
• Avoid moving diagonally crossing fields.
• Properly inflate tires to reduce surface compaction. Proper tire pressure for field work is about one-fourth to one-third the pressure used for road conditions.⁶ Consult with the tire or equipment manufacturer for proper pressure settings to avoid over-inflating tires.
• Eliminate tillage passes, especially if the intention is to dry out fields.

Be Aware of Axle Loads.

Grain combines and grain carts are the two most common types of farm equipment with the highest axel loads (Figure 4). For example, modern combines can range from 20 to as high as 44 tons per axle (tons/axle) when grain tank capacity and header weight is taken into consideration. A single-axle grain cart with about 700 bushel capacity may have an axle load of about 22 tons/axle while a 1,200-bushel grain cart will have nearly twice that amount of axle load.¹ High axle loads combined with over-inflated tires can create ruts with double the soil compaction compared to ruts made by the same equipment with proper tire pressure adjustment.⁶ Deep compaction (two to three feet) runs vertically and horizontally from ruts. If axle loads are kept under 10 tons, compaction zones can be localized to the top six to 10 inches of soil but, as mentioned, severe subsoil compaction can occur in a single pass with a load of 20 tons per axle.

Soil compaction cannot be entirely avoided but steps should be taken to minimize and control it as much as possible.

Sources

¹DeJong-Hughes, J. and Daigh, A. 2022. Upper Midwest soil compaction guide. University of Minnesota Extension. https://hdl.handle.net/11299/263301
²Duiker, S.W. 2005. Effects of soil compaction. PennState Extension. https://extension.psu.edu/effects-of-soil-compaction/
³Duttmann, R., Malte, S., Nolde, M., and Horn, R. 2014. Predicting soil compaction risks related to field traffic during silage maize harvest. Soil Science Society of America Journal. 78: 408–421. https://acsess.onlinelibrary.wiley.com/doi/10.2136/sssaj2013.05.0198
⁴DeJong-Hughes, J. 2018. Soil compaction. University of Minnesota. https://extension.umn.edu/soil-management-and-health/soil-compaction#sources-1200560
⁵Sidhu, D. and Duiker, S.W. 2006. Soil compaction in conservation tillage: Crop impacts. Agronomy Journal. 98(5): 1257–1264. https://doi.org/10.2134/agronj2006.0070
⁶Daigh, A.L.M. and Bly, A. 2020. Compaction reaction: Soil compaction and ruts following a wet harvest. Crops & Soils. 53(3): 24–28. https://www.sciencesocieties.org/publications/crops-soils/2020/may-june/compaction-reaction-soil-compaction-and-ruts-following-a-wet?q=publications/crops-soils/2020/may-june/compaction-reaction-soil-compaction-and-ruts-following-a-wet/
Web sources verified 6/26/26. 1217_118601