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Evaluating Soybean Emergence

The spring of 2007 has been one of the best planting seasons in recent memory. Dry conditions have made timely planting possible and emergence has been excellent in most fields. The majority of soybeans were planted by the 25th of May. So far most of the crop is in good condition. However, there have been some emergence problems especially on clays soils and fields planted between May 8 and 15th. There are numerous reasons for poor stands. The most common reasons this year include:

1. Soil Crusting - Clay soil planted on May 15, 2007

2. Insufficient Moisture for Germination. Seed planted to a depth of 2.0" was planted into moisture. Seed planted at 1.0" was not planted in moisture.

3. Insect and Slug Feeding. Seed corn maggot feeding in a field where manure was applied.

Make sure that all the beans are up before making a decision. Fields with a plant reduction of up to 50% do not need to be replanted, if plant loss is uniform and the remaining stand is healthy. Numerous studies and field experience have demonstrated that keeping an existing stand is often far more profitable than replanting. If the stand reduction is due to slugs or insects remaining damaged seedlings are often weak and will not perform well. If the problem is due to seed corn maggots consider using Cruiser insecticide seed treatment if replanting is required. Yield results will depend 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, while heavier clay soils may require more plants per acre for success -- a minimum of 100,000 - 120,000 plants/acre. Graph 1 shows the effect of plant stand on soybean yield.

Graph 1. shows the effect of plant stand on soybean yield. Results from 28 Ontario soybean population trials conducted in 2005 and 2006. Source: Bohner, Earl.

One of the quickest ways to determine a soybean stand is the "Hula Hoop" method. For example for the hoop below 15 plants = 100 000 plants/acre. Once the number of plants per hoop has been calculated to plants per acre from Table #1 write these numbers on the side of the hoop for future reference. (ie. 15 = 100 000, etc) Take at least 10 hoop counts and average the results.

Figure 4. "Hula Hoop" method can help determine your soybean plant stand population.

Table 1 - Plant Populations Using the "Hula Hoop"

The alternative method is to measure the length of 1/1000th of an acre, count the number of plants and multiply by 1000 to get the number of plants per acre.

Table 2 - Length of Row Required for 1/1000th of an Acre

For more details on replanting please see last year's article entitled "Thickening Thin Soybean Stands" (Link available below).

Related Links:

• CropPest Article May, 2006 - Thickening Thin Soybean Stands

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