Soybean producers across Michigan identified soybean planting rates as one of the highest-rated topics they wanted to see evaluated by the SMaRT (Soybean Management and Research Technology) program in on-farm replicated trials. When asked if they wanted us to evaluate the effect of higher planting rates or lower planting rates, the producers overwhelmingly voted for low planting rates.
There are two main factors driving the interest in reduced soybean planting rates: seed costs and white mold. Soybean seed is typically the highest variable cost in producing soybeans and reduced planting rates have the potential to reduce yield losses associated with white mold.
To evaluate the effect of low soybean planting rates on yield and income, 11 planting rate trials were conducted each year from 2015-2017. Four target planting rates (80,000, 100,000, 130,000 and 160,000 seeds per acre) were compared each year. A complete, three-year summary of the planting rate trials, including final plant stands and essential background information for each location, is available in the “2017 SMaRT Research Report – Part 1.”
Projected market prices ($9.20 per bushel) and conservative seed costs ($60 per 140,000 seeds for 2015 and 2016, and $64 per 140,000 seeds in 2017) were used to determine the income (gross income – seed cost) produced by the four planting rates. The figure below summarizes the average yields and income produced by the four planting rates in 2015, 2016 and 2017.
In 2015, the lowest two planting rates generated more income per acre than the higher two planting rates. In 2016 and 2017, the lowest three planting rates were more profitable than the highest planting rate. When all 33 sites were combined and analyzed, the highest planting rate was the least profitable.
There are several factors that contributed to the success of the reduced planting rates in these trials. The varieties planted in all the trials had the medium bush to bush type growth habit. This enabled the plants to produce robust branches at the lower planting rates (see photo). The second reason the lower planting rates may have performed so well was that complete seed treatments were applied in all but four of the locations.
I want to be clear that Michigan State University Extension does not recommend reducing planting rates to 80,000 or 100,000 seeds per acre. However, it is impressive how consistently well the 130,000 planting rate performed across 33 trials and three growing seasons. It produced higher yields than the 160,000 rate at two locations and produced a lower yield than the 160,000 rate in only one trial.
The 130,000 rate also increased income by $13 per acre over the 160,000 rate when all 33 sites were combined. Producers are encouraged to compare their planting rates to those evaluated in the trials to see if they have an opportunity to increase farm income by reducing planting rates in 2018.