Study shows higher soybean yields with early planting across most locations
A new study from Purdue University shows that planting soybeans early can help farmers achieve greater yields, even when crops experience slight stand reductions or minor herbicide injury.
Researchers conducted field trials during 2024 and 2025 at three Purdue Agricultural Centers located across northern, central, and southern Indiana. The goal was to evaluate how planting date and herbicide programs affect soybean performance and weed management.
The study found that early-planted soybean fields produced higher yields than mid- and late-planted fields in nearly every location. The only exception occurred at one southern Indiana site in 2024, where unusually cold temperatures after planting caused significant stand loss and reduced yields.
While early planting resulted in somewhat lower plant populations compared to later planting dates, these reductions rarely affected yield. Researchers also reported that residual herbicides caused only minor crop injury, typically between 5% and 10%, and did not reduce soybean production.
Another key finding involved weed management. Early planted fields had more weeds present when postemergence herbicides were applied. Higher weed populations were recorded both during the growing season and at harvest compared to later-planted soybean fields.
The study also found increased numbers of common lambsquarters, giant ragweed, and waterhemp in early planted soybean fields. These weeds can become more difficult to control over time and may increase the risk of developing herbicide-resistant populations.
Although earlier planting improved crop growth and canopy development, the additional canopy cover did not significantly improve weed suppression.
Researchers concluded that early soybean planting remains a strong strategy for maximizing yield potential. However, farmers may need to pay closer attention to weed management practices to reduce future challenges from difficult-to-control weeds and herbicide resistance.
The findings suggest that early planting can deliver important production benefits, but successful weed control programs remain essential for protecting long-term soybean productivity.
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