By Angie Rieck-Hinz
As I write this article in mid-October, we are facing a period of several consecutive days with little to no harvest activity in some parts of the state due to wet conditions. Soil conditions are highly variable across Iowa at this point, and anxiety to start harvest, let alone complete harvest, is high. As harvest is delayed, that also tends to delay opportunities for fall tillage and manure application, and can sometimes lead to decisions that may have lasting repercussions when it comes to the impact on the soil.
After harvest is complete, ask yourself if tillage is even necessary. There are good reasons to do fall tillage, but often our decision to do tillage is related to boredom after harvest or the desire to keep people busy.
Reasons to consider fall tillage is lack of time in the spring and potential to have wetter soils in the spring, both which may hamper timely planting if tillage is delayed to spring. Another possible consideration for fall tillage is to manage crop residue. Management of residue should start with good distribution of residue coming out of the combine. Reasons for not choosing tillage may include vulnerability to erosion, additional input costs of equipment use, labor and fuel, and damage to soil, such as reduced water infiltration and organic matter.
Recognize, prevent and alleviate compaction
If the fall continues to be wet, damage to soils will increase from harvest activities. Because such damage, mainly compaction, has happened, take steps to recognize the damage, and prevent and mitigate it as needed.
Topsoil compaction is mainly caused by ground contact pressure. If this is the case, a freeze-thaw cycle may help mitigate this type of compaction and tillage may not be warranted. If tillage is to be done, a light, shallow tillage operation should suffice. Care should be taken to make sure soils are not too wet during tillage; tilling wet soils may lead to other challenges.
If compaction occurs in the topsoil and the upper subsoil, this is likely caused by both contact pressure and axle load. Compaction in the lower subsoil is related to axle load only, and is often not totally mitigated by deep tillage, nor is it economical. If soil freezes and thaws to 6 to 12 inches deep during a couple of cycles over the winter, the ice expansion will be more effective at loosening soil than subsoiling when the soil is wet this fall. Axle-load and contact pressure need to be managed at harvest, so take a look at what happened during harvest 2017 and plan ahead for harvest 2018 if conditions are similar.
Things to consider when doing fall tillage:
• Don’t till when it is too wet. Soils receiving significant rainfall in October will likely remain wet and will have a plastic consistency below the field surface. Wet soil resists fracturing and loosening by deep tillage. Just because you don’t get the tractor stuck doesn’t mean the soil is suitable for tillage when wet. Tilling wet soils can lead to more compaction and smearing. Make a 2-inch ball of soil with your hands, toss it in the air and let it fall to the ground. If the ball stays intact upon impact, it is too wet.
• Conduct tillage in limited areas. If you must do tillage, do it only on the headlands and high-trafficked areas, to reduce further complications and to retain crop residue.
• Avoid tillage or use reduced tillage. This is a good idea especially on sloping soils or where water or wind erosion can cause soil loss. Erosion is still the primary concern causing water quality issues in Iowa. Crop residue can absorb raindrop impact, lessening the threat for soil particle detachment and subsequently movement of soil particles or erosion.
• Wet soils slow intake of manure and water. The capacity of wet soils to hold liquid is already used and they are prone to compaction and surface runoff. Consider hauling loads of manure to lighter, well-drained soils that will better support manure application equipment until other areas dry. To limit the weight, don’t completely fill tanks. Be sure to check tire inflation for better distribution of weight.
Avoiding compaction concerns should be considered with any field activity, but let’s hope fall activities of 2017 do not lead to issues with planting and crop production in 2018.
The ISU Crops Team would like to recognize and thank Dr. Mark Hanna for his 44 years of service to Iowa State University. Hanna, who is retiring, has been our “go-to” equipment engineer and has done a lot of research on tillage systems, distribution of anhydrous, and research with planters and combines. Mark, we wish you well!
Rieck-Hinz is the ISU Extension field agronomist for north central Iowa. Contact her at [email protected].