Soybean Planting Analyzed Across Decades

The U.S. Department of Agriculture’s National Agricultural Statistics Service has reported Wisconsin soybean-planting progress on a weekly basis since 2000. We explore the Wisconsin historical soybean-planting-progress data and provide insights into trends in planting dates and their effects on yields. According to recent UW-Madison research, soybean yield is likely to increase when planted earlier in the season. This article seeks to explore whether Wisconsin soybean growers have been shifting their planting dates forward across the course of more than two decades, and how this trend might affect potential yield. We provide an analytical overview of soybean planting progress in Wisconsin, along with the possible yield effects.

Figure 1 shows weekly estimates of Wisconsin soybean-planting progress – represented by solid dots – from the service for four notable years in the past – 2004 = red, 2012 = black, 2019 = green and 2021 = blue. Planting progress was modeled by the Logistic Equation – illustrated in the figure text boxes – with Sigmoid S-shaped – curve, which illustrates planting progress across Wisconsin from the start – 0 percent – to the end – 100 percent. The sigmoid curves illustrated in Figures 1 and 2 characterize the slow initial progress of planting that gradually increases in pace until it reaches a midway point of 50 percent progress – represented by a thick black horizontal line – and then slows as it nears completion.

Using the equation we computed the Logistic Xm value for each curve, which represents the specific spring date when the planting progress reached 50 percent. The vertical lines in different colors in the figure indicate the Day of Year – bottom axis – and Month-Day – top axis. In addition we computed a Logistic k rate value for each curve, which is a numerical measure of the pace at which planting progress took place. The greater the Logistic k rate, the more rapid the ascent of the curve – e.g., 2012 curve [k = 0.20] indicating rapid planting progress, while a slower k rate generates a flatter curve – e.g., 2004 curve [k = 0.09]. The shaded area characterizes the 95 percent confidence interval – CI – for the regression planting-progress error estimation.

The four curves depicted in Figure 1 correspond to the most rapid – black line; slowest – red line; earliest – blue line; and latest – green line; soybean-planting-progress data observed during the 23-year period to date. For instance the earliest 50 percent of soybean progress was attained in 2021 – May 13 – whereas the latest 50 percent date was attained in 2019 – June 6. The 50 percent soybean progress in 2021 outpaced that of 2019 by 23 days.

Source: agupdate.com

Photo Credit: Flickr - United Soybean Board