Will your disk bury too much crop residue this spring? How about your field cultivator? What if you chisel plowed the field last fall—have you already done too much tillage to meet residue requirements?
"Each spring, you have to look at each field and assess how much crop residue is left on the surface and also consider the erosion potential," says Mark Hanna, an Iowa State University extension ag engineer.
Hanna ISU Extension agronomist Mahdi Al-Kaisi have made that job easier for you. Farmers who have a computer and access to the Internet can go on-line and find a crop residue calculator that Al-Kaisi and others at ISU have designed.
Using the on-line calculator as a "soil saver"
Do you know for sure how much crop residue you are leaving on the field surface?
To help answer that question, Hanna and Al-Kaisi suggest farmers get the ISU Extension publication Conservation Tillage: Adjustment and Operation of Tillage Equipment in Systems with High Levels of Surface Residue (PM-1492k). It is available at www.abe.iastate.edu/machinery.
They also recommend farmers use a special residue calculator on the ISU Soil Management Web site. This tool calculates the impact of tillage operations on residue levels and potential erosion from Iowa soils.
When you are at that Web site, you plug your variables (crop, field trips, type of tillage equipment, slope of land) into the calculator and the program will give you an estimate of the amount of crop residue remaining.
A similar calculation can be made to estimate erosion, but you have to use a separate online calculator program.
To use the residue calculator, you go to the ISU Web site (previously listed). Click on either the residue button or the erosion control button. The computer model and programming then take over and make the process easy for you.
The case for cutting down on tillage
The two calculators were first put online a year ago. "They give farmers the chance to estimate crop residues in fields and the soil erosion possibilities under different tillage scenarios," explains Al-Kaisi.
The two ISU specialists remind farmers to check tillage equipment and set it properly to leave enough crop residue. They point out that doing the job right the first time means fewer repeat tillage passes, more residue left on the soil surface and less erosion in Iowa farm fields.
"Leaving less than 30% crop residue on the soil's surface after planting puts most Iowa soils at risk for soil erosion," says Al-Kaisi. "So before choosing tillage, there are several key questions that need to be answered.
- What will tillage accomplish?
- What effect will spring tillage have on the 30% residue goal?
- What are the risks of turning over or disturbing residue?
"The key issue is to know when tillage is warranted and also how to do the job right," emphasizes Al-Kaisi.
Rising fuel costs are consideration too
You don't need to use the same tillage on all your land, says Hanna. Also, you don't need to treat the land the same every year. For example, if last year was dry, you may try to reduce field trips to preserve soil moisture. Of, if you have a problem with soil compaction in a field, you might need to do a deep tillage operation to break up the compacted layer of soil.
With fuel prices recently rising to high levels, some farmers are looking to reduce the number of tillage trips across fields. "Using the online calculators might help you determine how to change your system to reduce those passes," he notes.
Crop residue is important in controlling soil loss from fields. "Many farmers and agronomists use 30% as a basic figure for the amount of crop residue to have remaining on the soil surface after planting," says Al-Kaisi. "But a flat field might be protected by less than that amount while a field with steep slopes or long slopes might require 50% or 60% cover."
Timing of tillage is also important
Doing tillage in the fall buries residue before winter, which leaves the ground exposed for a longer period. However, spring tillage tends to remove more residue from the field because the residue is more decomposed.
That's where the calculator comes in handy. "The crop residue calculator lets you plug in the data and conditions for your field so you can see what the different spring tillage options might do to your residue levels," says Al-Kaisi.