North Dakota State University has a long tradition of recommending the establishment of a soybean population of 150,000 plants per acre across row spacings. This recommendation continues to exist across the state to optimize soybean seed yield.
NDSU has conducted numerous field trials during recent years to examine the impact of planting rates and row spacings on soybean production. With the large amount of data available from across the state, the opportunity existed to re-evaluate the current recommendation and provide a more precise soybean planting rate and row spacing recommendations.
Data generated by NDSU soybean planting rate and row spacing field trials was conducted from 2008 through 2019. A total of 390 data points (observations) comprise the database. Planting rates in the data set ranged from 80,000 to 220,000 pure live seeds (PLS). Row spacings in the data set ranged from 7- to 30-inches wide. Seed yield was normalized for each trial by comparing the treatment average to the overall trial mean. The treatment average within each individual trial was divided by the trial mean and multiplied by 100 to get the relative yield in percent (the trial mean was set at 100%). With all yield data on the same scale (relative percent), data were evaluated across trials.
The compiled data set concluded the following:
Across North Dakota and row spacings, the planting rate of about 170,000 PLS per acre optimized soybean seed yield, while optimum yield occurred with 180,000 and about 140,000 PLS per acre in eastern and western North Dakota, respectively.
In eastern trials, 8% of planted PLS per acre did not develop into viable soybean plants. Assuming 8% of PLS does not result in established plants across North Dakota, and using 170,000 PLS per acre, about 155,000 plants per acre would be expected to maximize yield.
Across North Dakota or by regions, narrow rows (less than 15 inches) consistently provided greatest soybean yield.
In eastern North Dakota, the combination of narrow rows (12 to 14 inches) and planting rates of about 170,000 PLS per acre provided optimum yield. If planting in wide rows (24 to 30 inches), planting rates to reach the optimum yield were about 190,000 PLS per acre.
In western North Dakota, the combination of narrow rows (7 to 10 inches) and planting rates of about 150,000 PLS per acre provided optimum yield.
A new publication, “Soybean Response to Planting Rates and Row spacing in North Dakota (A1961)”, was published this spring that explains the compiled data set in more detail. A copy can be found online or if you would like a hard copy, please contact the Stutsman County Extension office. For more information, contact Alicia Harstad at the Stutsman County Extension office at firstname.lastname@example.org or 701-252-9030.