Soybean planting dates: Is earlier a good idea?
In recent years, there has been renewed interest in early soybean planting dates. Much of that interest is based on relatively recent work done in Nebraska, Iowa and Indiana. In Kansas, planting dates and variety maturity combinations are often chosen to avoid having soybeans flower or fill seed during the most stressful times of year. Does early planting achieve this under Kansas conditions? If you planted your soybeans in late April or this first week of May, did you do the right thing? If you still have soybeans to plant, how long should you wait?
First, we should review the research results.
Recent research in other states
In the Nebraska research, yields of irrigated soybean decreased somewhat when planting was delayed past May 1. This research was done at one location, for two years. The early planted beans had more pod-bearing nodes. It should be noted that with irrigated soybeans, the potential for adverse environmental conditions during bloom and grain fill is greatly reduced. In these trials, a fungicide and insecticide seed treatment was used to minimize the effects of planting early into cool, wet soils.
In Iowa, the research was done under dryland conditions – but dryland in Iowa is not quite the same as dryland in Kansas, except possibly northeast Kansas. The research done in Iowa, consisting of 24 tests, found that yields were higher 79% of the time when soybeans were planted in late-April or early May than when planted about May 20. The greatest response to early planting was in high-yield environments.
In Indiana, research at one location in 2006 and 2007 also found that soybean yields were higher when planted in late April or early May than at later dates. Earlier planting was associated with more pods per unit area.
click image to zoomFigure 1. Effect of planting date and seed treatment on soybean yields at Manhattan, Belleville, and Scandia. Average of two years. Untreated = raw seed, Treated = CruiserMaxx. Kansas research
The most recent research to examine planting date effects was conducted in north central and northeast Kansas. It was embedded in a study funded by the Kansas Soybean Commission designed to determine the relative importance of seed treatments at early and late planting dates. Results from this series of studies conducted in 2009 and 2010 indicated a 2 to 9 bushel yield reduction when planting was delayed from late April or early May to early June. The advantage for early planting was greatest with treated seed (Figure 1).