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Effects Of Planting Population On Yield In Full Season Soybeans

By Andrew Kness
 
Soybean population plots were planted on two farms in Frederick County near Thurmont and Tuscarora on June 4 and 7, respectively. Planted populations were 80, 100, 120, 140, and 160 thousand plants per acre (ppa). The Thurmont plots were planted on 30-inch spacing with three replications. The Tuscarora plots were drilled on 7.5-inch spacing with four replications.
 
On July 1, initial population counts were taken at both farms. At the Thurmont farm, plots ranged from 79 to 88 percent germination. At the Tuscarora farm, plots ranged from 88 to 98 percent germination (Table 1). This is consistent with the germination percentage of the seed.
 
Plots were harvested on October 3 and October 24 at the Tuscarora and Thurmont farms, respectively. The average yield for each farm individually and combined were calculated (Table 2). Yield ranged from 61 to 70 bu/A. Overall, yield differences between the populations were within three bu/A. While a complete statistical analysis has not been conducted, the trend of the data indicates that planting at a lower population, such as 120,000 or 100,000, would allow for reduced seed costs while still maintaining optimum yield.
 
The variety used at the Thurmont farm was Pioneer P37A69, which retails for $71.00 per unit of 140,000 seeds. The variety used at the Tuscarora farm was Hubner 38-27R2X, which retails for $59.00 per unit of 140,000 seeds. (Note that these costs do not include any discounts or seed treatments.) At the time of harvest, soybeans were $9.51/bu on the Chicago Board. The net dollar amount was calculated by subtracting the seed cost from the gross amount per acre. At the Thurmont farm, the 100,000 planting population had the highest net per acre at $598.19, while the 140,000 and 160,000 populations had the lowest net, around $581/A (Table 2). At the Tuscarora farm, the 120,000 planting population had the highest net per acre at $560.13, while the 160,000 population had the lowest net at $515.76/A.
 
Planting at lower populations, around 100 to 120 thousand ppa, may not reduce yield or net per acre, indicating that this is a potential for cost savings on farms. We are planning to conduct this study again next year at more locations around the state. To stay up to date with this research project, visit https://go.umd.edu/FCagresearch.
 
Table 1. Initial Population Counts, July 1.
 
 

Thurmont Farm

Tuscarora Farm

Planted Population

 

(1000 plants per acre [ppa])

Initial Population (1000 ppa)

% GerminationInitial Population (1000 ppa)

% Germination

80

63

7971

88

100

85

8588

88

120

95

79117

98

140

123

88124

88

160

135

84153

96

Table 2. Average Yield at 13.5% Moisture and Net Profit in $/A.
 

Thurmont Farm

Tuscarora Farm

Planted Population

 

(1000 plants per acre [ppa])

Initial Population (1000 ppa)

% GerminationInitial Population (1000 ppa)

% Germination

80

63

7971

88

100

85

8588

88

120

95

79117

98

140

123

88124

88

160

135

84153

96

 

Source : umd.edu