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2006 Annual Report: Planting Populations in Soybeans

Objective

Soybean planting population demonstration emergence rates
Table 1 - 2006 Soybean planting population demonstration emergence rates

With the increasing cost of seed and the ever fluctuating market, producers are trying to reduce their inputs as much as possible to maximize their net profit. One such input that can be varied is the seed population at planting. This demonstration is designed to help producers make decisions on planting rates taking into account conditions in Northwest Missouri.

Methods and Materials

This demonstration consisted of plots 250-feet long each with 12 rows on 30-inch spacing. The seed was no-till planted on May 19, 2006 into corn stubble and harvested on November 7, 2006. The six different planting populations used were:

2006 Soybean planting population demonstration yield data
Table 2 - 2006 Soybean planting population demonstration yield data
  • Plot #1 - 243,000 seeds/acre
  • Plot #2 - 218,000 seeds/acre
  • Plot #3 - 189,000 seeds/acre
  • Plot #4 - 178,000 seeds/acre
  • Plot #5 - 151,000 seeds/acre
  • Plot #6 - 130,500 seeds/acre

Results

All of the soybeans emerged at approximately the same time regardless of the planted population. Emergence varied from 94.0% to 95.5% as summarized in Table 1.

Five-year emergence averages for the soybean planting population demonstration
Figure 1 - Five-year emergence averages for the soybean planting population demonstration

Yields ranged from 50.5 to 54.9 bu/acre. The yield data is shown in Table 2. With an average of 53.2 bu/acre and a standard deviation of 1.7 bu/acre, there was no significant difference between the different planted populations.

This is the fifth year for this demonstration so we can draw some conclusions from the data that has been collected. Figure 1 shows the average emergence for each of the six planting populations over the past five years. The five year average is 94.7% with a 1.9% standard deviation.

Soybean Planting Population Emergence 5-Year Averages

Gross income per acre minus seed costs over a five year period
Table 4 - Gross income per acre minus seed costs over a five year period

Previous research had suggested that planting approximately 180,000 seeds/acre would provide the best net return for seed planted. This demonstration has shown no significant yield increases beyond a planted population of 189,000 and supports the earlier research.

Five-year yield averages for the corn planting population demonstration
Table 3 - Five-year yield averages for the corn planting population demonstration

One of the goals of this project was to look at the relative cost savings that could be incurred by using the optimum planting population. Seed costs can vary tremendously.

The more traits you purchase, the higher the cost of the seed. For this comparison, we used $65 per unit for seed and 3000 seeds per pound. We also used $5.50 per bushel for the price of soybeans.

The results of this economic comparison are shown in Table 4. As the planting population rises past 151,000 seeds/acre, the yield gain is not sufficient to offset the increase in seed cost.

Five year yield averages for the soybean planting population demonstration
Figure 2 - Five year yield averages for the soybean planting population demonstration

Looking at the five-year results, one can make the case for the optimum planting population begin between 151,000 and 189,000. The 180,000 seeds/acre appears to be a good rule of thumb.

Individual hybrids as well as field conditions can also have an effect on these numbers. We would suggest varying the population on your farm to achieve the optimum population using this data as a starting point. You can also consult your seed representative for their recommendations based on the variety and the field conditions.