"We've seen more soil erosion in western and southwest Iowa this year than we've seen in probably 15 or 20 years," says Clarke McGrath, Iowa State University Extension field agronomist located at Harlan. "I think the biggest reason it happened is these unpredictable wild swings in the weather. Rainfall amounts have been heavy. Just the other night we had 6 inches of rain in a three hour timeframe. It seems like we're getting more of these rains that come hard and fast the past few years."
The other thing that's aggravating the situation is "too much tillage." There's been more tillage done this year than in any year McGrath can remember. "If you do any tillage on these highly erodible soils, it will loosen that soil up and make it very susceptible to erosion," he emphasizes. "It's hard to maintain a no-till system if once every four or five or six years we go out there and tear it up. It's going to have to be long-term no-till. Farmers who have fields with erosion damage this spring are going to have to go in there and make repairs and try to rebuild the damage that's been done."
Spring rains come with unexpected amounts and force—what can you do?
Rain in the spring can fall in greater amounts and with more force that you realize—what can you do? Spring is the most critical time for soil erosion because of degraded crop residue, tillage in preparation for planting and the lack of crop canopy. Residue cover is not only good for preventing soil erosion, but it will cut down sediment transport to water bodies and contribute to the improvement of water quality, says McGrath.
The use of a well-designed conservation system can limit exposed soil and rain-splash soil erosion, notes Mahdi Al-Kaisi, an ISU Extension soil management specialist. An effective conservation system also depends on the planning, observation and timing of field operations. Spring is a good time to make observations of what's happening with regard to soil erosion in your fields and develop a new, more comprehensive conservation system.
Manage your soil conservation system to reduce raindrops' effect
Tillage and cropping management systems are critical components for reducing raindrop impact on soil particles due to the availability of crop residue to protect the soil surface, says Al-Kaisi. Excessive tillage can damage soil structure, leading to increased soil sealing and soil erosion. Conservation systems promote soil aggregates, infiltration, and soil tilth. Additionally, the improved soil structure of no-tillage and other conservation tillage systems stands up better against raindrops. A conservation system that includes high amounts of crop residue such as corn or fall cover crop traditionally provide abundant residue cover to protect the soil surface from spring rains.
Farmers are encouraged to assess residue cover since last fall's harvest and ask themselves the following questions:
* Was surface residue enough to prevent soil erosion? Is the surface residue cover distributed evenly across the field?
* Is there enough residue cover left after winter decomposition?
If these questions can be answered no, then fall tillage passes and fall manure or anhydrous application need to be considered based on the amount of crop residue and the residue distribution in the field. Remember--spring is the best time to evaluate conservation systems for their impact on improving soil and water quality.
Options for adjusting crop residue management to spring field operations
With spring weather and the most susceptible field conditions for water erosion here, what options remain before planting? Farmers should consider the effect of any additional tillage on remaining crop residue, advises Al-Kaisi. If residue cover should fall below 30%, adjust your field operations to minimize potential soil erosion due to early spring rain. Options for steep slope areas include growing cover crops, using permanent vegetation such as seeding that highly erosive area down or grass or hay, strip cropping, and planting on the contour--all of which can reduce the speed of water runoff and slow soil erosion. If soil crusting occurs, consider using a rotary hoe to allow seedling emergence to occur unrestricted. The faster the crop is growing, the sooner a crop canopy will develop; a partial crop canopy is better than none at all.
Conservation structures such as terraces, grassed waterways and field buffers are good components of a conservation system and help in slowing water flow, settling out sediments and directing water away from the field to a suitable outlet, says Al-Kaisi.
Remember that your field observations in the spring can help you in developing a more comprehensive conservation plan--one that greatly improves soil and water quality.