Response of Soybean Varieties to Advanced Weathering

Poor seed quality from a variety contained in the MSU OVT in Stoneville, MS. Purple seed stain and Phomopsis seed decay (white seed) are evident in this harvested sample along with numerous other seed quality maladies.

By: T.H. Wilkerson and T.W. Allen

Since 2008/2009, seed quality issues have continued to plague soybean farmers in Mississippi and much of the Mid-southern U.S. During 2018, seed quality has been a much larger issue with reports of poor quality stretching north into Wisconsin.  Even though environment plays a large part in the occurrence of quality losses, one of the main issues is delayed harvest.  Soybean simply will not sit in the field forever and wait on the combine if the environment remains wet for a prolonged period of time.  But, there are situations when the environment simply will not cooperate for timely harvest, we all remember 2009.

Between 2009 and 2011, a Mississippi Soybean Promotion Board funded project considered the role of fungicide and insecticide applications at specific growth stage timings alone and tank mixed. As a portion of the objectives of that project, applications were made at R1, R3, R5, and R6 in addition to multiple applications including a treatment at all four timings.  The take home message from that project appeared to be: If the environment gets really bad it doesn’t matter how much fungicide you apply seed quality losses will still occur.  Bottom line, a fungicide can only provide so much benefit.  For more specific results from these studies see: https://www.mississippi-crops.com/2017/08/19/protecting-soybean-seed-quality/

Even though trials were conducted during the above mentioned research project to consider the differences between a subset of commercial varieties, little if any information exists regarding the differences in seed quality as it relates to soybean varieties. Therefore, we invested some time into determining the differences between a portion of the commercially available varieties included in the OVT.

Explanation of the Data Set

Since quality continues to be a big issue an opportunity presented itself with a set of the entries in the MSU OVT. Harvest across the state has been delayed, most notably due to wet weather.  On October 2, the OVT location in Stoneville on the silt loam soil was harvested by the OVT coordinator.  Following harvest, the remaining two rows (rows 1 and 4) of each plot remained in the field and were exposed to a continued period of environmental conditions.  Between October 2 and October 11, 0.4 inches of rain fell on the trial.  On October 11 we were able to begin harvesting one row of each of the plots to tentatively harvest all of the entries (MG IV early and late; MG V early and late) to determine the quality of the grain remaining in the field.  The MG IV early were harvested October 11, the MG IV late were harvested October 12 and it rained again delaying the harvest of the MG V entries for an additional week.  The MG V entries were harvested on October 19 and received 1.4 inches of rain between October 2 and October 19.

From each remaining two rows, a single row was harvested (with a one-row plot combine) and grain was evaluated in the field after each plot to speed the process and reduce the need to store grain samples with poor quality. Grain was evaluated for the incidence of purple seed stain and a general category “total damage” that included ALL of the potential characteristics of poor quality (purple seed stain, Phomopsis covered grain and any grain exhibiting discoloration).

A larger data analysis will be done this winter to take into account some of the variables that were not included in the more basic statistical analysis. We were working to provide the information as fast as possible rather than spending another month analyzing all of the variables involved.

For the purposes of this blog post and the initial data analysis, the planting date was entered into the Soymap which is a decision based spreadsheet tool that can be used to plan based on soybean maturity. The spreadsheet is distributed by the University of Arkansas (see: https://agribusiness.uark.edu/decision-support-software.php#soymap).  Soymap was developed through years of trials conducted at multiple locations with multiple soybean varieties within different relative maturities sponsored by the United Soybean Board.  The tool itself is a downloadable Excel file that can be used to provide data based on the environment at the given locations and provide a specific harvest date window based on a maturity group relative maturity of a particular relative maturity and how that particular variety could potentially yield.  By entering the planting date of the variety trial (April 19, 2018), the earliest harvest date or R8 value was determined to arrive at a rough approximation for the duration of time that each soybean variety remained in the field based on the assigned values from the spreadsheet for each relative maturity (included in the attached tables).  These values were then considered in some initial trend analysis.  Over the years, multiple entities have stated that leaving soybean in the field for a greater duration can increase the seed rotting.  Essentially, and based on the initial analyses conducted, the duration of time that these particular varieties remained in the field ranged from 32-50 days after physiological maturity.  Initially, and when we began harvesting plots, we didn’t think there would be any difference between varieties based on the duration the plots remained in the field.

Based on the initial analysis, pod color, pubescence color, hilum color, and seed size (considered as a result of # of seed/pound) were not determined to suggest a trend would relate to seed quality.  However, in general, differences were observed between both the amount of purple seed stain as well as overall total damage.  Even though this is a single location and only the result of one year of data we think the results suggest a large amount of variability between commercially available varieties when it comes to the ability to maintain quality during periods of inclement weather.

Maturity group IV early (MG IV early quality table)

Maturity group IV late (MG IV late quality table)

Maturity group V early (MG V early quality table)

Maturity group V late (MG V late quality table)