Here are Farm Journal Field Agronomist Ken Ferrie’s recommendations for early-planted soybeans:
1. Because the critical photoperiod comes sooner as maturities get longer, plant your fullest-season varieties first when you plant early. This is the opposite of normal planting.
2. Do not plant shorter-season maturity groups than those rated for your natural environment. Shorter-season varieties will go through their reproductive stages too rapidly, resulting in a shorter plant with fewer nodes, which ripens too early.
3. Planting soybeans ahead of corn requires planning. If you use tillage, fields must be level enough to plant as you come into spring. Trying to prepare fields for corn and soybeans at the same time might cause you to miss corn’s optimum planting window.
4. Soybeans planted in March and early April are subject to cool, wet conditions for a long period. Soil-applied herbicides from Group 14 (PPO inhibitors) can cause stunting in these conditions. Seed treatments are essential, especially if you farm in a physical environment subject to Sudden Death Syndrome.
5. Early-planted soybeans will reach the reproductive stages earlier than normal. Base post-emergence herbicide application on the stage of soybean growth, not on plant height or calendar days from planting. Failing to do so could cause plants to abort flowers.
6. Inform seed suppliers, landowners, farm managers and retailers of your plans to plant early.
7. If conditions are right to plant corn, then plant corn, rather than soybeans, if you are unable to plant both crops at the same time. Soybeans, unlike corn, can tolerate marginal planting conditions. In fact, days when you know you are pushing the envelope for corn planting are good days to plant soybeans.
8. Plant only as many acres as you are comfortable with because a freeze in May could kill all your early-planted soybeans.
Risks and Rewards
The goal of early soybean planting is to get plants to flower before the summer solstice on June 21. At the unifoliate stage (two leaves on opposite sides of the stem, across from each other), the plant begins to sense night length. If the nights are long enough (that is, sufficient hours of darkness), the plant’s internal clock tells it to start flowering, the beginning of the reproductive, or grain-fill, stage. Flowering shifts back into normal or low gear after the solstice.
Here’s an example based on a Maturity Group 3.5 variety and conditions in central Illinois. To start flowering before the summer solstice, June 21, plants must reach the unifoliate stage by May 17.
“It all comes down to the natural environment,” says Ken Ferrie, Farm Journal Field Agronomist. “A warm April makes this much easier to accomplish. With a cold April and first half of May, we might not get enough Growing Degree Days to reach the unifoliate stage before the critical photoperiod passes.”
