Most soil compaction from equipment traffic occurs where tires contact soil during the first pass over soil. Farmers can reduce compaction by limiting traffic to interrows that have already been trafficked.

Soil compaction is a persistent problem in fields across North Carolina and remains a serious concern for farmers because of the many soil and plant growth problems it creates. These problems include reduced infiltration, stunting of roots, and drought stress, all of which reduce yield. Research indicates that farm equipment traffic is one of the main causes of soil compaction. This traffic is the result of critical operations, such as tillage, planting, spraying, and harvesting. However, by managing the traffic patterns created by equipment of different widths, farmers can greatly affect the amount of soil driven over and thereby compacted.

Farm equipment tires cause soil compaction in just one pass over a field area. The amount of soil compacted can be reduced by managing field traffic.

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Farm equipment tires cause soil compaction in just one pass over a field area. The amount of soil compacted can be reduced by managing field traffic.

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We investigated traffic patterns in three different North Carolina crop management systems (conventional-till corn, strip-till cotton, and conventional-till organic corn) to quantify the field area trafficked in one season with typical field operations for each system. Using Global Positioning System (GPS) equipment and geographic information system (GIS) software, we mapped the path of every farm vehicle (including tractors, combines, and sprayers) used in each field. Cumulative traffic covered between 50 and 85 percent of the field area for these systems (Figure 1).

Other studies have shown that the first pass of equipment produces most of the compaction that can occur on a given soil (Botta, Becerra, & Toum, 2008; Soane, Dickson, & Campbell, 1982). In fact, almost two-thirds of the compaction can occur in the first pass over a ‘loose’ soil (Slowińska & Domźal, 1989). Up to 85 percent of the surface area in our study was driven over at least once, which shows that compaction occurred on much of each field.

Portions of these fields were driven over more than once (Figure 2). Because most compaction occurs during the first pass, field operations that cover areas already traveled help to limit soil compaction. Trafficking an area more than once keeps compaction confined to a relatively small area because limited additional impact occurs when an area is driven over more than once. In the organic corn system, traffic occurred on 85 percent of the field area, but 32 percent of the field was driven over only once.

Much of the soil compaction occurs from driving over different areas only once when growers use unique traffic patterns for equipment of different widths. Using a controlled traffic pattern that relies on multiple passes confined to a smaller total area can greatly reduce the trafficked percentage of the field.

Figure 1. Percentage of field area traveled by equipment tires in one season for three different cropping systems.

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Figure 1. Percentage of field area traveled by equipment tires in one season for three different cropping systems.

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Figure 2. The number of passes and the field area covered by traffic in a conventional-till organic corn production system.

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Figure 2. The number of passes and the field area covered by traffic in a conventional-till organic corn production system.

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Controlling traffic patterns by driving equipment over the same area and in the same direction confines compaction to a relatively small area.

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Controlling traffic patterns by driving equipment over the same area and in the same direction confines compaction to a relatively small area.

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The three crop scenarios we investigated reflect only a small portion of the diverse cropping systems in North Carolina. Even if your system does not match one of these, some useful practices can limit the traffic on your fields:

• Enter the field in the same set of rows each time, and move across the field in the same direction (left to right, right to left) each time. This ensures that traffic patterns for a given vehicle will match the pattern used last.
• Match equipment widths where feasible. For example, if a sprayer is 3 or 5 times as wide as your planter, it will travel on soil already driven over during the planting operation.
• GPS and precision farming technology allow growers to control traffic with highly accurate real-time kinematic (RTK) GPS and guidance systems. This technology is now implemented on many tractors. It allows traffic patterns to be repeated within an accuracy of a few inches.

Apart from traffic pattern management, these key recommendations can help to prevent compaction:

• Stay off wet soil. Moist soil is more susceptible to compaction. Very wet soil is also prone to rutting and degradation of other soil physical properties.
• Use flotation tires on equipment. Flotation tires reduce the pressure per square inch on the soil.
• Maintain the appropriate tire pressure for your equipment. Tires with higher pressures exert compaction forces deeper into the soil than tires with lower pressures. Check with your equipment and tire manufacturer about appropriate tire pressures.

Botta, G. F., A. T. Becerra, and F. B. Tourn. 2008. Effect of the number of tractor passes on soil rut depth and compaction in two tillage regimes. Soil Tillage Research, 103:381- 386.

Slowińska, A., and H. Domźal. 1989. The structure of the cultivated horizon of soil compacted by the wheels of agricultural tractors. Soil Tillage Research, 19:215-226.

Soane, B. D., J. W. Dickson, and D. J. Campbell. 1982. Compaction by agricultural vehicles: A Review. III. Incidence and control of compaction in crop production. Soil Tillage Research, 2:3-36.