How To Treat Compacted Soils
Wait
If you stop compacting the soil, yields will probably return gradually to pre-compaction levels. The process of rehabilitating compact soils is not well understood. Researchers have seen yield recovery even when physical measurements (such as bulk density) have not returned to pre-compaction levels. Medium to heavy soils are more susceptible to severe compaction and take longer to recover.
You cannot rely on frost action to relieve compaction each year. It may have some effect on surface compaction, but does little to ease deep compaction. Subsoil usually goes through only one freeze/thaw cycle each winter.
USDA researchers compacted soil at the Waseca Experiment Station in 1981 by using ten-and twenty-ton axle load equipment. For the first 2 to 3 years, corn yields on the compacted plots were less than those on the non-compacted plots. During
the next decade, the one-time compaction event caused reduced yields during years of very high or low rainfall, but not under optimal moisture conditions.
Loosen the soil
Normal tillage relieves surface compaction.
Roots are invaluable for loosening soil. Deep tap-rooted plants will grow through hardpans (such as tillage pans) and deep compaction. When they die, the root channels become conduits for water and other roots. There has been minimal research linking yield improvements with crops used to loosen compaction, so there is little guidance about which plants to use and how to grow and manage them. The strong tap roots of alfalfa and sweet clover are thought to be useful in treating subsoil compaction. These plants may need three or more years to be effective. Other useful antidotes to deep compaction may include red clover, lupines, soybeans, reed canarygrass, burdock and dandelion. Any grass (especially quackgrass) loosens surface compaction.
Earthworms and other soil invertebrates loosen soil and create channels for root growth and water movement. Attract earthworms by regularly adding organic matter.
Subsoiling (or deep tillage) is sometimes helpful, but has not been found to be a reliable cure for deep compaction in the upper-Midwest. If you think it might help on your farm, consider these guidelines.
- Be sure compaction is the problem. Explore your fields with a shovel or probe to learn where it is compacted and how deeply.
- It may be most cost effective to deep-till only the worst areas, such as headlands.
- Be sure soil is dry so it fractures. Cutting through moist soil will have little effect.
- Plan to avoid future compaction. One pass with a heavy implement will wipe out your investment in deep tillage.
Compensate for decreased nutrients and water
If you know what is causing a yield loss, it may be possible to partially compensate by increasing fertilizer or irrigation inputs. For example, it may be necessary to use split applications of nitrogen to minimize denitrification losses, or to use row applications of phosphorus and potassium to improve availability. Keep in mind that these short-term fixes may aggrevate compaction problems. They increase traffic and may reduce the extensiveness of root growth.
Soil Management Sections:
Introduction |
Soil Manager |
Soil Scientist |
What's Next |
Acknowledgments
