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Soil Compaction

By Wayne Cords

My knowledge in soil compaction deals more with a 14,000-pound tractor and a 25,000-pound combine and the effect they have on corn and soybeans. But, hopefully will stimulate some thinking on part by pumpkin growers.

First, there are four types of compaction:

Surface crusting, this type of compaction occurs in the top two inches of the soil and is usually occurs because of heavy rains. Can severely effect water absorption of later rainfalls and result in more runoff.

Surface compaction occurs from the surface down to the bottom of the tillage depth. The cause of surface compaction is the usual: the weight of people, animals, implements, etc. The degree of surface compaction is determined by the moisture content of the soil and the ground contact pressure of equipment or animals. Normal tillage will usually fix this type of compaction

Subsoil compaction occurs just below the depth of tillage and usually is the result of implements having an axle load of over 5 tons. Hard to eliminate, usually requires the area to be "subsoiled or ripped" to a depth of 18"

Plow pan (hard pan) compaction lies directly below the normal tillage depth. It develops when the depth of tillage is the same from year to year.

Subsoil compaction is never beneficial but light to moderate surface compaction has been shown to be beneficial to SOME crops (when I say light to moderate compaction I am talking of a medium-texture soil having a bulk density of around 1.2 grams per cubic centimeter, which is not much). The reasoning for this is: increases seed to soil contact; decreases water loss by evaporation; promotes root branching and secondary root formation; allows the root to be in more contact with nonmobile nutrients such as phosphorus.

Each plant reacts differently to compaction (and I am not sure how pumpkins react) corn for example is sensitive to deep compaction but less affected by surface compaction. As a matter of fact I have pressure wheel on my planter which I can adjust to apply compaction to the soil at planting time. However, soybeans are just the opposite, they are sensitive to surface compaction and not really affected by deep compaction.

With that said, how can you deal with or prevent compaction. Some of these are common knowledge but bear repeating:

  • Stay off the soil when it is wet. Wet soil compacts easier and will "transmit" the compaction to a deeper depth.
  • Increase your organic matter in the soil. Soils with high OM tend to "bounce" back better after compaction
  • Leave mulch on the soil surface. This absorbs the impact of rain and prevents the crusting of soil.
  • Increase your worm population. Worms are one of the best soil conditioner there is. Make sure you are not killing off your worm population with your pesticide applications.
  • Break up your plow pan compaction. If you do not have access to tillage implements for this, use a wide tine pitchfork (I call them potato forks I know there are different names). Push the fork in to the soil 8-12" and rock back and forth to create holes in the plow pan, root growth will take over from there opening up the holes wider. The more holes you provide the better.
  • Incorporate your nonmobile fertilizers (P and K) down to 3 to 6 inches that way if there is compaction on the surface it will not affect your roots ability to seek out these nutrients. Plus it will promote root growth away from the surface making it less prone to drought conditions.

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