Ground rolling soybean fields can be a useful practice for preparing the field for harvesting, but it also poses agronomic, economic and environmental risks that farmers need to consider.
While rolling can help to push rocks down into the soil, shatter corn root balls, and smooth the seedbed, it can also cause potential plant injury, soil sealing, erosion and added expense.
One important question for farmers is how late soybeans can be rolled without cutting into yield. According to a three-year University of Minnesota Extension research study, soybeans may be safely rolled up to the third trifoliate growth stage, or V3, when bean plants are about three inches tall. Rolling at or after V3 is not recommended because of the greater potential for stem injury, goose-necking and lodging. It is also important to note that wheel tracks cause more plant damage to emerged soybeans than the rollers themselves.
In wet years, stem injuries caused by rolling could make plants more susceptible to soil-borne diseases. Additionally, the most serious environmental disadvantage of soybean rolling is its effect on soil quality. Rolling crushes surface soil aggregates, increasing the potential for soil crusting, runoff and erosion. To minimize this problem, leaving approximately 40% residue on the field will protect the otherwise exposed soil.
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Standing water between the rows of rolled plots after moderate or heavy rains has also been observed in northern Iowa research fields, indicating that water infiltration may be slower in rolled fields. Reduced infiltration leads to more surface runoff after rainfall, contributing to soil and nutrient losses and water pollution. Rolling also increases the risk of both wind and water erosion, especially on susceptible soils or sloping terrain. After rolling, residue may come loose from the soil, reducing the soil conservation benefits of less tillage.
If farmers decide to roll their soybean fields, they should consider these guidelines to minimize potential risks:
- Confine rolling to rocky fields and flat fields with low erosion risk.
- Roll before plants reach the third trifoliate growth stage, or about 3 inches tall. If rolling after emergence, expect some plant injury.
- If rolling erosion-prone fields, roll pre-plant or post-emergence, rather than right after planting, when erosion risk is greatest.
- After emergence, roll in the afternoon, during the heat of the day when soybeans are limp. Avoid rolling in the morning or evening when plants are most rigid.
- Roll only when field conditions are favorable. To reduce the risk of crusting or sealing, do not roll when the soil is moist.
- After emergence, avoid rolling when plants are damp because they will stick to the tool bar and be pulled out of the soil.
In summary, while rolling can provide improved harvesting conditions and peace of mind for farmers, it is important to consider the potential damaging effects on soil quality and additional expenses.
By following these guidelines, farmers can make informed decisions about when and how to roll their soybean fields. For more information visit http://z.umn.edu/rolling.