University researchers around the Corn Belt have shown that early planting is critical to producing high soybean yields. The ideal planting time for soybeans is basically the same as for corn - the first week of May for the lower half of the Lower Peninsula. If soil conditions are favorable and producers manage the crop carefully, however, soybeans planted during the last week of April can perform as well as beans planted during the first week of May. Early planting has both risks and benefits.

One of the biggest advantages of early planting is that it extends the planting window for attaining maximum yields. Data from the University of Wisconsin and the Ohio State University indicate that beans planted on May 1 will yield about 7 bushels per acre higher than beans planted during the last week of May. Beans planted during the last week of April have produced slightly higher yields than those planted on May 1.

Mark Westgate, plant physiologist at Iowa State University, and Palle Pedersen, soybean agronomist at Iowa State University, are proponents of early planting because it extends the vegetative stage. This means more nodes per plant, and that translates into increased photosynthesis capacity in the crop canopy. Early planting also promotes more rapid crop growth during flowering and pod set and so increases seed number per acre, a key factor in producing high yields. Pedersen's data from Iowa show that early planting is potentially more beneficial in high-yield environments than in low-yield environments. University agronomists have also found that newer soybean varieties are more tolerant of adverse conditions and produce higher yields than

The primary risk of early planting is that emerged bean plants will be damaged by freezing temperatures as the growing point is exposed and vulnerable when the cotyledons emerge. This risk is mitigated to some degree by the fact that germination and emergence are delayed under cooler soil temperatures. Soybean tissue is also more resistant to freezing temperatures than corn tissue. Typically, temperatures must reach 28 degrees F for damage to occur.

Another risk to consider when planting early is poor germination and emergence. Cold soils slow bean emergence. The longer they are in the ground, the greater the risk from soil-borne diseases such as pythium and insect feeding. Early-planted soybeans that emerge uniformly and escape freeze injury also have a higher probability of experiencing damage from bean leaf beetles and sudden death syndrome (SDS) than soybeans planted later in the season.

If you decide to plant soybeans in the last week of April, consider the following recommendations.

Source: Soybean 2010 project. Soybean 2010 was developed to help Michigan growers increase soybean yields and farm profitability. Funding for Soybean 2010 is provided by Michigan State University Extension and the Michigan Soybean Promotion Committee. Additional information about increasing soybean yields and profitability can be found online at web1.msue.msu.edu/soybean2010.