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Reduce soybean planting populations and save $10 to $18 per acre
Nebraska Increasing input costs are forcing producers to evaluate every decision they make. With soybean seed costs on the rise, producers in south central Nebraska wondered if they could reduce their soybean populations while maintaining yields and saving money. On-farm research was conducted in farmer plots and at the South Central Agricultural Laboratory near Clay Center. The research, which was conducted in field scale, randomized and replicated plots from 2006 to 2008, proved producers could reduce planting populations and still maintain yields. Since 2006, planting rates of 90,000; 120,000; 150,000; and 180,000 seeds per acre have been planted in 12 irrigated soybean fields in 30-inch rows. Prior to this research, most of these producers planted 160,000 to 180,000 seeds per acre. The 90,000 low rate was determined based on University of Nebraska-Lincoln research recommending not to replant a hailed soybean stand if at least 90,000 plants per acre remained in the field. In 2008, cooperating producers used these same rates to plant soybeans at five sites with 20 replications. Planting dates ranged from April 29 to June 3. In the end, there was little difference in percentage stand and yield among the four planting rates (see Table 1). The 120,000; 150,000; and 180,000 yields were statistically the same (only a 0.3-bushel difference between the 120,000 and 150,000 rates) and were significantly better than the 90,000 seed-per-acre plots; however, note that the 90,000 plot yielded only 1.7 bushels per acre less than the 150,000 plot. All data was statistically analyzed to determine the yield differences due to the various treatments. The findings are similar to the 2006 and 2007 studies. In 2006, yield results ranged from 65.5 bushels per acre at 90,000 to 67.4 bushels per acre at 180,000. In 2007 yield results were 59.4, 59.6, 59.4, and 60.2 bushels per acre for 90,000; 120,000; 150,000; and 150,000, respectively, with no statistical difference. Most likely, these results are indicative of soybean's ability to compensate for reduced populations. Soybeans will have increased plant branching at lower populations compared to less plant branching at higher populations. This characteristic was observed in all fields regardless of variety. Also observed in 2008 were two additional nodes per plant at the 90,000 population compared to the 180,000 population. Nodes are just as important as flowers and pods, and ultimately yield is influenced by the number of nodes. A dryland field in Nuckolls County also showed interesting results. This field was hailed at the cotyledon stage, so planted populations of 100,000, 130,000, and 160,000 became average actual stands of 74,417; 89,417; and 97,917 plants per acre. August rains in 2006 helped deliver yields of 38.6, 40.6 and 42.7 bushels per acre, respectively. Recommendation: Plant soybeans at 120,000 seeds per acre. Based on three years of consistent research results, UNL specialists recommend reducing planting populations from an average of 160,000 seeds per acre to 120,000 seeds per acre in 30-inch rows. This reduction of 40,000 seeds per acre results in a savings of $10.66 to $18.57 per acre based on seed costs of $40 and 65 a bag. For three years producers were able to achieve a 90 percent stand and have not seen a statistical yield variance from 150,000 or even 180,000 seeds per acre. With soybean seed costs increasing, reducing soybean planting populations is another way producers can survive high input costs of crop production. For more on-farm research information or to get involved with on-farm research, please check out the UNL Farm Research website at farmresearch.unl.edu.
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