Soybean Replanting Decisions

We are midway  in the planting of soybeans but I have seen several stands planted back in early April that are beginning to be rowed and populations can be conducted now.  To illustrate this here is a table with the relative impact on yield by planting date as the season progresses. This illustrates the ability of the soybean to respond to varying planting date.
                                              1.       May 10 – 100%

Replanting is one of those thankless jobs in farming, so it pays to take time to evaluate stands carefully before replanting.  Consider some of these issues in deciding to replant. 1.  Soybeans have a tremendous capability to recover from reduced stands.  Data from various states would indicate that near maximum yields are possible with stands at 100,000 plants per acre.  At 70,000 plants, yields will still be in the range of 90-95% of optimum.  The Pa On Farm Soybean Network has studied the impact of reduced soybean stands over the past three years.  The table below represents the impact of reduced populations on stands and supports replant decisions that if a uniform stand that is above the 80,000 ppa population yields will be maintained without replanting.  The key in those plots were uniform stands. 2. Soybeans cannot compensate for large gaps in the stand.  Many Pennsylvania fields with varying soil types are prone to uneven soil conditions which could lead to many gaps in the rows.  More gaps in the stand lead to a lower yield potential.  In a field with 40% gaps, at 70,000 plants, we’d estimate the yield to be 83% of optimum. Where large gaps are or in fields where large patches occurr replanting might be the best option. 3. It is important to identify the cause of poor emergence before replanting.  Seed depth, crusting, dry seedbeds, cold wet seedbeds, seedling disease insects, hail or seed quality are possible culprits. Stands with significant number of injured seedlings may have limited yield potential. 4. The one great aspect of soybean replanting is that one does not have to eliminate the existing stand. It can be replanted directly with only slight differences in seed set at the end of the season.  I had a grower a few years ago that we had just shy of 60,000 ppa in the field so he chose to replant with an additional 100,000 seed drop per acre and at the end of the season he had about 120,000ppa final stand and  70 bu/acre yields.

So what should you do to conduct a stand assessment?

First you will need to determine the population as it stands in the field. To do this utilize the following table below. Otherwise there is a simple method I use to estimate populations.  To determine populations you must first know the width of planting. 6”, 7”, 8” for small grains 7”, 15” or 30” for beans and 15” or 30” for corn.

1. Now to determine population you simply convert the row width from inches to feet by dividing by 12.
2. Then divide the square feet per acre(43560) by the foot of row. This gives you linear feet
3. Then, take the number of plants you find per foot in the field and multiply by the linear feet number to get the ppa.
4. For an example. Thirty-inch rows divided by 12 is 2.5 feet. 43560 square feet in an acre divided by 2.5 gives us 17424 linear feet. Now if you get 3 plant in a foot you have 17,424 plants per acre. If you get 2 then you have 34,848. To simplify this you could now take 17424 and divide by 1000 to get the number of feet you need to represent 1/1000th of an acre. In this case it would be 17.4 feet. So you could go to the field measure 17.4 feet count the plants multiply by 1000 and you will have your plants per acre. Do this in several places and you could find the average of the field.

• ²Full season = 150,000 plants/A; double crop = 200,000 plants/A
• * Double-crop beans should be planted in row widths of 15 inches or closer.