Tag: population

Soybean Populations, Row Spacings, and Planting Dates

Jarrod Miller1, Agronomy Extension Specialist | jarrod@udel.edu and Nicole Fiorellino2, Agronomy Extension Specialist
1University of Delaware |2University of Maryland, College Park

15″ (right) vs. 30″ (left) soybeans.

Soybean Row Spacing and Population Studies

Modern soybean varieties can tolerate lower seeding rates and still produce good yields, providing there are no other issues with stand loss or stress. In southern Delaware two studies (2022 and 2023) observed no yield difference when planting full season beans (MG 4.2, late May planting date) when planted between 60,000 to 180,000 seeds per acre (Figure 1). You may consider dropping your seeding rates, considering your regional weather, planting date, and soil conditions.

Figure 1. Soybean yields by a) population, row spacing, and irrigation in 2022 (average yields below the legend) and b) irrigated yields by population and row spacing in 2023. Soybeans were planted in a coastal southern- Delaware climate.

Over both years, 15” row spacing provided an 8-to-10-bushel advantage compared to 30” rows. A narrower row spacing helps soybeans canopy faster, providing more leaf area per acre to increase yields. Water is consistently a major yield limiting factor, where irrigation boosted yields by 26 bushels in 2022. All these yield differences were statistically significant

Maryland and Delaware Planting Date Studies

Planting soybeans earlier can provide more vegetative growth before flowering commences, closing the canopy earlier and providing more nodes for pods. In years prior, soybeans would be planted after corn, so that early planting usually referred to May. Now we may consider late April to be early, and many mid-western studies have observed yields steadily decline as soybeans are planted later into May. Even when you choose to plant earlier, colder soils (<50°F) and saturated conditions can limit germination and growth. What is considered early for the Mid-Atlantic though, where our climates range from Coastal to Appalachian?

Between 2020-2022, University of Maryland and University of Delaware performed planting date trials for soybeans from lower Delaware (Georgetown) to the mid-shore (Wye Rec, MD), piedmont (Clarksville, MD), and Ridge & Valley (Keedysville). All planting dates were at least two weeks apart, typically starting in mid-April (weather and field conditions permitting) and the final planting date in mid to late May (Table 1).

Table 1. Planting dates for each site and year of the study for early, mid, and later planting dates.

Site Year Early (1) Mid (2) Late (3)
Delaware 2020 8-May 21-May 4-Jun
  2021 12-Apr 28-Apr 10-May
  2022 13-Apr 26-Apr 11-May
Wye 2021 23-Apr 12-May 28-May
  2022 2-May 23-May 7-Jun
Clarksville 2021 21-Apr 5-May 19-May
  2022 18-Apr 2-May 28-May
Keedysville 2021 11-May 28-May 7-Jun
  2022 28-Apr 11-May 31-May

Although earlier planting (April) did produce earlier canopy closure and sometimes earlier flowering, yields were only statistically different at two site years, the Wye and Clarksville in 2021 (Figure 3). The latest planting date at the Wye (May 28th) did have the lowest yields, compared to either April 23 or May 12, 2021. In Clarksville, yields were higher on the latest planting date of May 19th, compared to April 21st or May 5th. This could be due to the timing of rainfall or temperature conditions during early stages that season, as there was a lot of variability for the first two planting dates in yield.

For the other seven site by year combinations, there was no benefit to planting earlier, but there was also no yield penalty (Figure 3). In fact, we purposely did not apply a seed treatment to provide a more suitable environment for disease pressure. At the UD site in 2021, one row unit planted too deep in April, but yields remained similar to May planting. Freeze damage at UD in 2022 cause the death of some leaf and cotyledon tissue, but the soybeans recovered and matched later planted yields.

As there was no clear benefit to planting in mid to late April for soybeans, planting decisions can be made based on field suitability, disease presence, or tillage and soil temperatures. As noted in the population studies above, these decisions should be matched with local knowledge of yield potential, planting dates, and potential freeze damage.

Figure 3. Soybean yields based on early (1), mid (2), and later (3) planting dates for soybeans in Delaware (UD), the Wye Rec, MD, Clarksville Rec (CV), MD, and Keedysville Rec (KV), MD.

Effects of Planting Population on Yield in Full Season Soybeans

Kelly Nichols, Agriculture Agent Associate & Matt Morris, Agriculture Agent
University of Maryland Extension, Frederick County

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)

 % Germination Initial Population (1000 ppa)

% Germination
80

63

 79 71

88
100

85

 85 88

88
120

95

 79 117

98
140

123

 88 124

88
160

135

 84 153

96

 

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

 

Yield (bu/A)

Net $/A
Planted Population (1000 plants per acre)

Thurmont Farm

Tuscarora Farm

Both Farms

Thurmont Farm

Tuscarora Farm
80

67

61

64

 596.92

548.18
100

68

 63 65 598.19

554.78
120

69

 64 66 595.33

560.13
140

69

 63 66 581.39

542.89
160

70

 61 65 581.71

515.76