Recent rains have brought another challenge for farmers, especially in fields that were conventionally tilled last fall or early this spring. In addition to potential soil erosion and the damage to soil structure that heavy rainfall can cause, there are after-effects of the rain when the soil surface starts to dry. The potential problem is soil crusting.
Soil crusting is a product of a weak soil structure and the absence of crop residue or a cover crop to protect the soil surface from the intensity of rainfall. Iowa State University Extension soil management specialist Mahdi Al-Kaisi, and ISU Extension ag engineer Mark Hanna, provide the following information and recommendations.
Crusting causes numerous problems--poor emergence, growing conditions
This crusting could occur especially in intensively tilled fields where crop residue cover is not adequate, as well as with fine texture soils and soils with low organic matter content. These conditions could increase the potential for soil crust formation. Residue cover plays a significant role in reducing soil crusting by absorbing the impact of rain drops that destroy soil surface structure. The destruction of soil structure impacts plant germination and seedling emergence for both corn and soybeans.
Soil crusting can also result in poor growing conditions and reduced water infiltration. Soybean seedling emergence can be a problem if a dense surface crust forms. In this situation, the hypocotyl of the crop plant is broken when pushing up against a solid crust. You should monitor high-risk fields for soil crusting, especially where plant emergence has not yet occurred, in order to take action to avoid damage to seedlings.
When should you use a rotary hoe? Timing is critical, don't hurt the crop
The quick-relief solution to such a problem is the use of a rotary hoe. This tool is commonly used in treating soil crusting to improve seedling emergence. However, the timing is critical in order to achieve the intended results and to prevent seedling damage from the hoe. The rotary hoe is a potentially good tool to use to break up soil crust, but make sure you've got a crust that is actually sealing the soil surface before using it.
To minimize the damage to the seedlings and to increase your success with hoeing, you should rotary hoe at a time when the soil surface is at the right moisture conditions. This will require frequent field scouting to ensure that soil surface moisture is just above field capacity. Field capacity is the point when a handful of soil will crumple easily in your hand under minimum pressure, leaving a trace of moisture on your palm. This moisture condition will ensure less damage to emerging crop seedlings and less soil compaction during the hoeing process.
Get off the tractor, check to see if rotary hoeing is damaging crop seedlings
You should pull the rotary hoe at high field speeds (8 to 10 miles per hour) unless safety is a concern. However, if soybeans are the crop that is emerging, make sure both cotyledons aren't broken off by the hoe. Corn will likely be the crop emerging from rains that occurred in Iowa this past weekend. You should expect to see a minor stand loss (approximately 1% to 2%) from hoeing, but this small loss should be insignificant if the corn is truly having difficulty breaking through a crust.
Getting off the tractor and checking for stand loss is a good idea when starting to rotary hoe a field. If the crop plant loss seems excessive (greater than 3% to 5% loss), you may want to slow your travel speed to be less aggressive with the tool.
Remember, it is very important to check early-planted fields periodically, especially those that were conventionally tilled and have fine soil texture and low organic matter. Timing is important to manage soil crusting at the proper moisture conditions.