Soil Compaction Danger remains – HIGH!

Anne Verhallen, Soil Management Specialist

“Only YOU can prevent soil compaction!” This misquote of Smokey the Bear was in a recent Penn State Field Crop News by Sjoerd Duiker, a Soil Management Specialist. But he is certainly right. He notes that with moisture content at or above field capacity in the entire soil profile, soil is highly sensitive to compaction from traffic, animals or tillage. We are in prime planting time for many crops and everyone feels the clock ticking. However, we do need to keep the threat of compaction in mind – it can hurt yields significantly. Many of our vegetable crops are not aggressive in their root development. At some point the rain will turn off – root systems that have been restricted by compaction will not fare well under hot dry conditions that we can expect about mid summer.

Soil compaction can take several forms:

Surface compaction (<12″ deep) is caused by high contact pressures. Road tires inflated to 100 psi cause high contact pressures. Surface compaction can cause very high yield losses the year immediately following the act. Using flotation tires or tracks helps reduce surface compaction. Reducing the number of trips over the area can also help.

Subsoil compaction below 12″ depends on axle load, not on contact pressure. This means that reducing soil contact pressure by using flotation tires or tracks will not reduce subsoil compaction, although it helps to reduce surface compaction. If you traffic soil that is really too wet with axle loads of 10 tons or higher, you’re likely causing subsoil compaction below 20 inches. Freeze-thaw and wetting-drying cycles will not remove this compaction, nor will biological forces such as earthworms, roots, or microbial activity. The key to subsoil compaction avoidance is to reduce axle load.

It is hard to avoid compaction completely, particularly in vegetable rotations but it is well worth the effort to reduce the impact as much as possible. Prevent soil compaction by:

• Staying off the field until soil has dried out sufficiently OR in the case of spray operations in perennial crops like apples – allow the soil to drain as much as possible
• Not tilling soil when it is too wet
• Using flotation tires, duals, or tracks to reduce surface compaction – remember to use lowest allowable inflation pressure in flotation tires or duals.
• Using cover crops – the root mass acts like a shock absorber making the soil resist compaction better
• Adopting no-till where possible and as long as possible – the increased biological activity creates a soil that is full of macropores (thousands of little drain tiles) and covered with a layer of residue that acts as a bit of a buffer for traffic.

Adapted from The Soil Compaction Danger Level for today is HIGH – Sjoerd Duiker, Soil Management Specialist, Penn State Field Crop News Vol 11:06 April 19, 2011