Now is optimal soybean planting time

“Early planting” has taken on a new definition for many farmers this spring as unusually warm, dry weather allowed them to finish planting corn in record time. It’s also causing some farmers to question how early to plant soybeans.

Benefits of early planted soybeans, defined as late April or early May planting, have shown to outweigh potential risks in some university studies. Research by Iowa State University shows the optimal planting dates for soybeans – if soil conditions are suitable – in the southern 2/3 of the state is the last week of April and the first week of May for the northern 1/3 of Iowa. Seventy-nine percent of the time planting in late April or early May resulted in higher yields than soybeans planted around May 20.

When determining how early to plant, the potential benefit of yield gain must be weighed against the potential risks. Planting seeds in cool soils can delay emergence and predispose soybean plants to seedling diseases. The ideal soil temperatures for soybeans is 77 degrees Fahrenheit; germination may be delayed by three weeks if the soil temperature at two inches is about 50 degrees. Cool soil temperatures may also slow root development and make seedlings more susceptible to root rotting pathogens that can cause “damping off”.

Early planting may also predispose soybean plants to infection by Sudden Death Syndrome (SDS). To reduce the risk of SDS infection, choose soybean varieties with good tolerance to that disease. Also be aware of whether the field in which the soybeans will be planted has a history of SDS.