Rolling Soybean Fields and
Soybean Replant Decisions

Rolling soybean fields after planting is generally conducted to conserve moisture and to prepare the field for harvest. Rolling can help level the soil and push rocks into the ground making it possible to do a better job combining. Many producers roll immediately after planting while others wait until the soybeans have emerged. Rolling immediately after planting provides improved seed-to-soil contact and reduces the likelihood of plant injury. However, rolling right after planting increases the chance of soil crusting which hinders soybean emergence. Soybean fields that are not rolled after the drill often emerge more quickly and uniformly. Limited University research has shown that rolling soybeans after emergence does not reduce yields. If rolling is delayed until soybeans have emerged keep these points in mind:

1) Roll during the heat of the day to ensure that soybeans are limp. Soybeans are the most turgid (stiff) during the morning hours and rolling during that time will result in more plant injury.

2) Do no roll soybeans that are in the hook stage! Soybeans that are just emerging out of the ground are more vulnerable to being broken off. Wait until all soybeans have fully emerged before rolling.

3) The best time to roll soybeans is during the unifoliate stage since all beans will have emerged by then. Rolling can be completed successfully until the first trifoliate leaf stage. Waiting beyond the first trifoliate to roll soybeans will increase plant losses.

Poor Soybean Emergence!

Soybean emergence across the province has generally been acceptable and in many cases excellent. In a few fields seed corn maggot and root rot diseases have destroyed seed and replanting has been required. Unfortunaltey, some areas have been extremely dry and soybeans have not had adequate moisture for proper germination and emergence. In these fields emergence has been spotty and thin. In no-till fields seeds may have been planted too shallow for this year's conditions. In conventionally tilled fields the ground may have been dry 3 to 4 inches down so it was impossible to plant into moisture. If the beans imbibed enough moisture to swell up (beans became soft and rubbery) but then stopped development for 4 - 7 days they will not emerge once it rains. These beans will usually rot.

Deciding to Replant:

In many fields stands are acceptable and fields should not be replanted. Studies and field experience have shown that soybeans have a tremendous ability to compensate for missing plants. Existing plants will branch and produce more pods to fill in gaps. The uniformity of the existing crop is more important than having a high population. Soybean plants can fill spaces up to 30 cm (12 inches) within or between rows with relatively little yield reduction. Research has shown that a 60-70% stand provides 95-100% yield potential under good growing conditions. This will be dependent on the remaining plants being healthy and distributed evenly throughout the field. It's also important that plants be kept free of weed competition, or yield reductions will occur. On lighter soils fields with a plant stand of more than 100 000 plants/acre should not be replanted. Heavier clay soils will require more plants per acre. The minimum number of plants on heavy clay soils is approximately 100 - 120 000 plants/ac. Table #1 shows the yield potential of reduced stands under good growing conditions for soybeans planted at a normal planting time.

Table 1 - Expected Yield of Soybeans in Optimum and Reduced Stands¹

¹Results of trials conducted at Huron and Kemptville research station, University of Guelph
1 hectare = 2.47 acres

Replanting Options:

If replanting is required there is no need to destroy the existing stand of soybeans. Simply plant the same variety on top of the existing stand. If moisture is present to a depth of 2.5 inches plant seed into moisture. Make sure that seed is planted into moisture and not sitting on top of the moisture. If the drill will not go that deep consider using a no-till planter and plant up to 2.5 inches deep. Do not plant deeper than 3 inches. If no moisture is to be found to a depth of 2.5 - 3 inches plant only 1.5 inches deep. These beans will emerge after a good rainfall. This is still better than trying to plant after the next rainfall. Too much time will be lost at this late date.

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