Should an Early Relative Maturity (RM) Soybean Crop Be Planted Before Corn?​​

Planting a soybean crop earlier than traditional planting dates is a strategy that has helped increase soybean yield potential.1 As an example, average soybean yields for the past four years in southwestern Iowa for early planted soybean crops have been some of the highest I have heard reported by farmers doing the practice.

Many agronomists recommend planting the fullest relative maturity (RM) soybean suited for early planting which can help maximize the number of nodes developed before flowering. While this certainly can help produce higher potential yields, many soybean producers have moved to planting a half RM product earlier than what is common for the area for several reasons. In most farming operations, planting and harvest are the two bottlenecks that hinder profitability if the optimum window is sacrificed due to labor, weather or machinery constraints. Some farmers have realized they can better utilize each window if they can plant an early soybean field or two first. Fall-tilled corn ground going to a soybean crop is usually ready to plant one to two days earlier than soybean stubble scheduled for a corn crop. Yields have been impressive for an early planted soybean crop for several reasons including being potentially too early for late-season diseases such as charcoal root rot and Diaporthe. Sudden death syndrome (SDS) can be more of an issue in an early planted soybean crop; however, to help minimize SDS infection, soybean products with higher degrees of tolerance or resistance to SDS should be planted. Additionally, ILeVO® fungicide can help minimize SDS infections.

Harvest tends to be simpler because an early planted soybean crop can be ready for harvest in mid- September. This can allow farmers to cut the crop when there is more daylight and working time. Many times, soybean fields planted during the traditional planting period are ready for harvesting right or soon after the harvesting of the early planted fields. A second trend that naturally follows the planting and harvesting of an early soybean crop is the ability to plant fuller RM corn. In general, selecting adapted fuller-season RM corn products may allow for excellent late-season standability, greater yield potential and drought tolerance.

An early planted soybean crop may help with weed management because weeds can be controlled before they grow too tall. The Roundup Ready® Xtend Crop System for weed control can be applied after Roundup Ready 2 Xtend® soybeans are planted. Canopy and row closer tend to be better when soybean plants can spend more time in the vegetative stages of growth because of early planting. Quicker canopy closure can also help suppress late weed flushes.

The application of a foliar fungicide on an early planted soybean can help extend the life of the soybean plants about 10 days verses non-fungicide-treated acres. Early RM soybeans lessen that inconvenience of waiting for those soybeans to reach maturity.​

Figure 1. Early planted soybean field ready for harvest two weeks prior to most fields in the area.

1Pedersen, P. Soybean planting date. Iowa State University Extension. Additional information: Early soybean planting considerations. Agronomy ADVICE. Effects of seeding rate and maturity group on yield, lodging, and profitability of soybeans. 2015 Demonstration Report. Monsanto Learning Center at Huxley, Iowa. Websites verified 9/25/18. ​​​

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