Do Cover Crops Help Reduce Soil Compaction?

Soil compaction management requires "All hands on deck". You cannot rely on a single practice to manage compaction. A compaction management plan involves improvingsoils' resistance to compaction, using practices like reduced tire inflation pressure to avoid compaction, and practices to alleviate soil compaction and restore soil porosity.

Cover crops are an important hand in reducing the threat of soil compaction. They help soil resist compaction by transpiring water when alive, while the living root system improves the stability of soil aggregates. By lowering soil water content and improving soil structure cover crops improve trafficability. When soil is in the 'plastic condition', it is most compactible. You can test this with the 'ball test': grab a handful of soil, mold it in your hand, and if it is possible to make a ball the soil is in the plastic condition. Cover crops help reduce the number of days the soil remains in this highly compactable state. Cover crops with fibrous root systems, such as rye or annual ryegrass, tend to be the most effective. They need to be vigorous cover crops, not puny-looking, to make a difference. This means they should have been planted as early as possible after the fall crop was harvested, and they need to be alive. Once the cover crop is sprayed and lays dead on the soil surface, the mulch preserves soil moisture, and this actually decreases trafficability.

Next, cover crop roots restore porosity when alive. When equipment traffic or animal hoofs cause compaction the living roots will assist in creating new pores. Many farmers have testified to me that they had trouble managing compaction in permanent no-tillage until they started using a cover crop. Understanding their critical role in no-till systems should encourage us to pay more attention to picking the right species, planting them in a timely manner, and not killing them too early.