Managing Flooded Soybean Fields

  • Flooding delays emergence in soybeans, slows growth, and results in stand loss.   
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  • Saturated soils can inhibit root growth, leaf area expansion, and the photosynthetic process. 
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  • It is important to scout fields entirely before making the decision to replant. 
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Saturated and Flooded Fields

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Along with soil temperature, adequate soil moisture and high soil oxygen concentrations are favorable for seed germination and plant growth. Saturated soils, which may include flooded or ponded soils, can have a negative effect on emergence. The main side effects include plant growth restriction and decreased oxygen availability to the plant. Young plants may develop yellow leaves due to slowing of photosynthesis and plant growth. Lack of oxygen because of a prolonged period of saturated soil can reduce germination and emergence. In addition, portions of roots may die as a result of no oxygen. However, there is still a chance for survival unless the growing point is damaged.   

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The longer an area remains saturated, the higher the risk of plant death and higher air temperatures can shorten the number of days of survival.1 According to University of Minnesota Extension, yield losses are not typically noted in soybean fields flooded for 2 days or less. Four days or more of flooding can stress the crop, delay plant growth, and cause shorter plants with fewer nodes. Six days can cause significant yield loss while flooding for a week or more can result in loss of the entire stand.2 

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Figure 1. Submerged soybean plants.
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Soil Crusting

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Soil crusting can occur when a wet field dries and a crust layer forms on the soil surface. The crust layer can delay or prevent seedling emergence. In addition, soybean hypocotyls can easily be broken when trying to push through the crust. Crusting may be more common in fields with fine textured soils, low organic matter, and little surface residue, especially where excessive tillage has taken place.3 A rotary hoe can break up the crust and aid seedling emergence. Timing is essential and breaking the crust as soon as possible is most beneficial to plant growth.  

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Scouting and Replanting Options

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It is important to scout fields within 4 to 7 days after the water has receded.  Stand counts need to be taken to see if a desirable plant stand survived. Count intact plants with buds or expanded leaves.  Research across the Midwest shows that yield decreases by 2 to 6% for every 10% reduction in stand counts. A final stand count of 73,000 or more plants/acre consistently yield 90% of optimum, and it is not recommended to replant the field.4  Soybean plants usually compensate well and fill in small gaps by branching out. If there are numerous gaps larger than 2 feet in diameter, consider replanting as surrounding plants cannot fill in these larger gaps.4  

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If replanting with soybeans, minimum or no tillage is recommended to maintain efficacy of any herbicides and/or soil insecticides already applied to the field. Plant soybeans 1 to 1.75 inches deep and not deeper than two inches. Planting too deep can burn energy that could be used later by plants. In addition, planting too deep can inhibit emergence in stressful situations, such as soil crusting and compaction.   

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 Table 1. Percent yield potential at an established density of 4 and 8 plants per row foot.
 
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 Stand Reduction (%)
 Percent Yield Potential
 4 Plants Per Foot of Row
 8 Plants Per Foot of Row
 0
 95
 100
 10
 93
 98
 20
 91
 96
 30
 88
 93
 40
 83
 89
 50
 78
 84
 60
 73
 78
 Source: University of Illinois cited within Soybean Replant Decisions, Iowa State University Extension, 2000.
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