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Soybean Row Spacing and Seeding Rate (05/07/20)

North Dakota soybean seeding rate and row spacing varies across the state. In 2017 and 2018, eight soybean seeding rates (starting at 80,000 and increasing by 20,000 live seeds per acre increments) and row spacing (12 and 24 inch) were evaluated in 15 eastern North Dakota environments to quantify established plant densities, seed yield, and plant loss occurring during the season.

North Dakota soybean seeding rate and row spacing varies across the state. In 2017 and 2018, eight soybean seeding rates (starting at 80,000 and increasing by 20,000 live seeds per acre increments) and row spacing (12 and 24 inch) were evaluated in 15 eastern North Dakota environments to quantify established plant densities, seed yield, and plant loss occurring during the season. Planting at 12 inch row spacing yielded 2.7 bushel per acre greater than 24 inch row spacing and provided $33 per acre greater net profit on average. Following plant establishment, 6.6% in season plant loss occurred on average (Table 1). Using 180,000 to 200,000 live seed per acre had higher yields compared to seeding rates of 120,000 or less (Table 2).

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Seed cost affects the seeding rate at which the maximum net profit is observed. Quadratic regression between live seeding rate and net profit was performed to identify maximum partial net profit. Seed costs were obtained from Sebesta (2020), Plastina (2019), and Haugen and Swenson (2020) who estimated herbicide tolerant seed prices to be $33 (NDSU GT soybean Foundation Seed), $50.80, and $57.80 per soybean unit (140,000 seeds per acre), respectively. Price per individual seed was calculated and multiplied by live seeding rate. Partial net profit was computed by subtracting live seed cost from gross revenue (yield multiplied by estimated market price of $9 per bushel) and only takes seed cost into consideration. The quadratic regression analysis show there is a specific maximum net profit for each of the three seed costs. Based on the quadratic regression equation, net profit maximizes at higher seeding rates as the seed cost is lower (green line in Figure 1). Economic returns based on seed cost suggest opportunities to increase producer profit with slightly lowering seeding rates when using seed with higher unit costs (red and blue lines in Figure 1). As market prices increase, the benefit of lower seeding rates will diminish. North Dakota’s current recommendation of 150,000 established plants per acre is in the range to optimize yield but will likely not optimize profit based on high seed costs and current market values.

 Fortunately for North Dakotans, there are possibilities to obtain less expensive (than used in Figure 1) certified soybean seed of NDSU’s conventional or glyphosate tolerant varieties, which would also change the calculated partial profit. Although slightly lower seeding rates can optimize net profit for more expensive seed sources, research on North Dakota’s iron deficiency chlorosis (IDC) prone soils has shown that reducing seeding rate will increase IDC expression and lower yields when IDC is present.

On a farm scale, higher production with higher seeding rates will likely reduce the harvest cost per bushel. The lower harvest costs per bushel may offset additional seed costs when higher seeding rates are used. In this article, we analyzed the yield based on live seeding rate. Not all live seed planted will develop into an established plant. If producers can increase their planting accuracy and have a better establishment rate, the amount of live seed needed for an optimal stand could be reduced.

For more information, see Schmitz PK, Stanley JD, Kandel, H. Row spacing and seeding rate effect on soybean seed yield in North Dakota. Crop, Forage and Turfgrass Management. 2020;6:e20010.

https://doi.org/10.1002/cft2.20010

 

 Hans Kandel

Extension Agronomist Broadleaf Crops

 

Peder Schmitz

NDSU Research Assistant

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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