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Estimating yield potential of soybean by planting date
Author: Jeremy Ross, Extension Agronomist - Soybeans

With the wet weather conditions we have been experiencing this spring, many soybean growers are concerned about the late start we have this year compared to the 2012 spring.  Below is a study using historical data from the Soybean Research Verification Program (SRVP) to estimate optimum planting date to maximize soybean yield.

Until recently, data from the SRVP has only been subjected to analyses based upon the current year’s results.  Observed data from 1983 to 2007 was analyzed to estimate yield potential by planting date for the SRVP.  Estimation results revealed the expected yield potential based on planting dates measured as “week of the year” (WOY).

Data for this study comes from the SRVP during the previous 25 years.  The SRVP has been conducted on 445 commercial soybean fields in 41 soybean production counties in Arkansas.  The SRVP collects a range of data from yields, inputs, soil textures, machinery use, planted date, emergence date, to harvest date.  This study used yields and planted dates to estimate yield potential.

Figure 1 presents the frequency of planning throughout the 25 years of the SRVP.  Week 21 (3rd week of May) was the most frequently planted for soybean.  Observational data was normalized across weeks of the year and time to more accurately reflect the impact of planting date on yield potential.  A base week was sought to compare yields across weeks planted within a given year.

Farm management decisions are made in the presence of risk and uncertainty, with weather risk being a leading source.  Each cropping year is different with respect to the number of days that farm equipment can be operated in a field, however an expected number of day suitable can be estimated.  Figure 2 presents soybean yield potential by planting date with the expected number of day suitable per week that Arkansas farmers are expected to be able to work in the field.

Although crops tend to be planted earlier in the year than they were in the past decade, risk of not having sufficient days suitable for fieldwork should be considered before making crop allocation decisions.

The data suggests that yield potential is maximized for soybean between the 17th (4th week of April) and 23rd week (1st week of June), after which yield penalties are expected, although early planting may have greater environmental risk.  The seven week planting window without large yield penalties generally allows producers sufficient time to complete planting operations assuming that their equipment complement and other crop acreage allocation is appropriately matched to the local days suitable for field work.  The general trend is that earlier planting for soybean results in higher yields with plantings in the 18th week (1st week of May) having the highest yield potential.

Figure 1. Frequency of fields planted by week of the year in SRVP.

Figure 1. Frequency of fields planted by week of the year in SRVP.

Figure 2. Soybean yield potential relative to expected days suitable for fieldwork.

Figure 2. Soybean yield potential relative to expected days suitable for fieldwork.

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