Soil

How should ruts be repaired in crop fields?

Dr. Mark Hanna, an extension agricultural engineer in Iowa State University’s Department of Agricultural and Biosystems Engineering provided this response to our request for information after a wet fall in 2009. Although the topic focuses on combines at harvest, the recommendation are appropriate.

“Wet conditions have caused ruts to form in some fields as combines work to harvest crops. About three-fourths of combine mass and virtually all of loaded grain tank weight are carried on the combine’s front axle. With good yields, grain tank extensions, and a 12- row head, front axle load can be 18 to 20 tons. Compacted soil created beneath the rut might interfere with subsequent crop rooting. In addition, ruts deeper than about two inches can interfere with maintaining seed depth during planter operation next spring unless they are leveled.

Soil loosening by using tillage to relieve compaction requires soil to be dry enough so that soil shattering is effective. Because soil moisture has re-filled the top 12 to 24 inches of the soil profile, deep tillage with a chisel plow or subsoiler this fall or next spring will use fuel and time but is unlikely to loosen soil effectively between tillage shanks. The full soil moisture profile in upper layers will however aid freeze/thaw cycles to help loosen soil during winter depending on air temperatures and snow cover.

Ruts deeper than planting depth will need to be leveled before planter operation. A good strategy might be to wait until a week or two before planting next spring and use a light tillage pass such as with a field cultivator, light disk, harrow or soil finisher. If only a portion of the field is rutted, consider tilling only that area to avoid re-compacting subsoil in other parts of the field. Waiting until warmer weather next spring allows potential for some drying of the top two or three inches of soil and avoids further compaction of wet, plastic soil on the surface that would be done with a tillage pass this fall. If compaction effects are observed during the 2010 growing season and soil is dry after harvest, tillage next fall might be considered deep enough to break through the compacted layer.”

— Answer by Bill Wiebold

What is fallow field syndrome?

Sometimes, but not in every incidence, crops planted in a field in which no crop was planted (or died from flooding) the previous year grow and perform poorly. The Missouri crop most often affected is corn. Visual symptoms appear similar to phosphorus deficiency, and often the symptoms appear in fields that test high for P.

The cause of fallow field syndrome (FFS) is unknown, but it might be related to beneficial fungi called mycorrhizae. These fungi grow in and around roots and increase phosphorous uptake, and are dependent on host plants to complete their life cycle. If plants are not grown in a field, mycorrhizal growth and spores are substantially reduced. Plants grown the next year might be slow to be infected because of the relatively low number of spores in the soil.

Planting a cover crop in prevented planting fields might decrease the potential for FFS next year. Almost any cover crops species, except members of the radish family, will be helpful.

— Answer by Bill Wiebold