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Rutted fields and soil compaction

What are the best ways to alleviate damaged fields in the spring?

Persistent rains with cold, damp conditions in September and October made harvest last fall even more stressful that usual for many farmers. Trucks, grain carts and combines in wet fields have left moderate to severe ruts in fields across the Prairie. Ruts must be fixed before spring planting. Many farmers are also worried about soil compaction below the ruts.

Avoid spring deep ripping

Think twice if you are tempted to deep rip rutted areas this spring. Fields with ruts will likely still have relatively high soil moist levels. This means the rutted areas should not be deep ripped this spring.

Ripping can be beneficial to fracture compacted soils and reduce the soil compaction. But, ripping is only beneficial and effective when soils are relatively dry. A soil moisture content less then 40 per cent of field capacity is best. Then, ripping can fracture the soil and reduce the compaction. When ripping is used on very moist or wet soils, fracturing does not occur. When soils are wet and are higher in silt or clay, ripping will cause the soil to smear resulting in more problems and no fracturing will occur.

Soil penetrometers can probe rutted and unaffected areas in the field to determine if and where the compaction layer is located within the soil profile.
photo: Ross McKenzie

Effects of rutting

When soils are rutted, the weight of field equipment causes soil particles at the base and sides of the rut to be smeared and compressed together. This reduces soil pore space and increases the bulk density of the soil at the base and sides of the ruts.

Often, the winter freeze-thaw and wetting-drying processes help alleviate some soil compaction. Light tillage is needed to fill in the ruts. You will need to do some field assessment to determine if significant soil compaction may have occurred below the ruts.

To better understand rutting and soil compaction, we need to understand differences in soil moisture. Soil saturation occurs when all soil pores are filled with water. Soils are at field capacity, after gravity has pulled away free or excess water from the larger soil pores within the rooting zone. Soil macro-pores will be mostly filled with air and some water, and smaller soil pores are mostly filled with water.

During last year’s wet fall, trucks, grain carts and combines in wet fields left moderate to severe ruts in fields across the Prairie. These ruts must be fixed before spring planting, and there may be soil compaction below the ruts.
photo: Ross McKenzie

Soils are most susceptible to compaction when soil moisture is near field capacity. The proportion of soil pores filled with both air and water is ideal for compaction to occur. The weight of field equipment displaces the air and causes pore spaces to collapse. Depending on equipment weight and soil conditions, soil compaction may penetrate downward 12 to 24 inches below the ruts.

When soils are near saturation and pores are mostly filled with water, soils are much less susceptible to subsoil compaction. This is hard to believe, but remember that water is not compressible. When soil pores are mostly filled with water, there is very little air to be displaced and water cannot be compressed, so very little compact will occur. But, soils that are at or near saturation still very prone to rutting.

So, if your fields were rutted during harvest last fall, tillage is necessary to fill in ruts. But, don’t automatically assume there is significant subsoil compaction below the ruts.

Rut management this spring

This spring, some form of tillage is needed to eliminate the ruts and to prepare a good, uniform seedbed. For ruts of up to five inches:

  • Use light tillage that will shift soil sideways to fill in the ruts.
  • Till just below the depth of the ruts to lift and fracture the soil below.
  • Use caution if soils are fairly wet below the ruts; tillage could induce more compaction. Just focus on filling in the ruts in the spring.
  • When tilling in the ruts, make sure to track your travel pattern in the field with GPS. If future deeper tilling for soil compaction problems is needed, you will have the exact location pattern of the ruts.

Ruts deeper than five inches may penetrate below the top soil layer (the A soil horizon) and extend down into the B soil horizon. If this is the case, still use lighter tillage passes to fill in the ruts but do not till into the B horizon as this may cause mixing of the A and B horizons, which will reduce soil quality. A deeper tillage, using vertical tillage may be necessary at a later time, when soils are drier.

Summer observation

After ruts are filled, soils are levelled out and fields are seeded, carefully watch in spring and summer to see if the residual effects of the ruts may be affecting crop emergence and growth. Hopefully, no significant differences are observed in crop growth between rutted areas and unaffected areas.

But, if crop differences are observed, dig some soil pits to 24 inches to physically check the soil profiles for compaction and root penetration. Consider contacting an experienced agronomist with a soil penetrometer to probe the rutted and unaffected areas in the field to determine if and where the compaction layer is located within the soil profile. This information is needed to determine how much compaction has occurred, if ripping might be necessary and to determine the correct depth for effective ripping. If compacted soils are present and depressed crop growth is observed, then after harvest next fall, ripping could be considered, but only if soils are relatively dry. When ripping, follow the same travel path used when tilling in the ruts. Ideally, ripping is only needed in the areas that were rutted. Avoid unnecessary deep tillage of unaffected areas in the field.

During last year’s wet fall, trucks, grain carts and combines in wet fields left moderate to severe ruts in fields across the Prairie. These ruts must be fixed before spring planting, and there may be soil compaction below the ruts.
photo: Ross McKenzie

About the author

Columnist

Ross H. McKenzie, PhD, P. Ag., is a former agronomy research scientist. He conducted soil and crop research with Alberta Agriculture for 38 years. He has also been an adjunct professor at the University of Lethbridge since 1993, teaching four-year soil management and irrigation science courses.

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