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Student Researches Recipe for Record-Setting Soybean Yields
Author: Arkansas Agricultural Experiment Station

Soybean Maximum Yield Research

By Ryan Van Roekel, Ph.D. Graduate Student; and Larry Purcell, Professor & Altheimer Chair for Soybean Research

Soybean producer Kip Cullers in southwest Missouri has reported yields of 139 (2006), 155 (2007), and 161 bu/A (2010), and these yields are substantially greater than any other reported maximum yields. For the past 3 years, we have made measurements in Mr. Cullers’ contest field with the intent of documenting crop growth characteristics that would result in these yields. Additionally, we wanted to examine the yield potential of soybean under intensive management on a large-scale with strip trials in eastern Arkansas.

Seedlings in England after heavy rain and wind washed away part of the beds. Photo taken May 5, 2011 (Photo courtesy Ryan Van Roekel)

Two strip trials were conducted in 2011, one near England, Ark., and another near Helena, Ark. Each strip trial contained five leading Pioneer Hi-Bred indeterminate varieties ranging from 4.4 to 5.1 relative maturities. Intensive management practices included treating seed with fungicide, insecticide, and inoculant, applying 2-3 tons/A of poultry litter, planting in mid-April, more frequent irrigation, and strict pest management including preventative fungicide applications at the R3 and R5 growth stage. Strips were approximately one acre in size and the varieties were randomized and replicated six times across the field.

Unfortunately, both locations experienced challenging weather soon after emergence. A heavy rain storm washed away part of the beds in England and a hail storm went through Helena. Growing conditions at both locations were hot and dry during the key reproductive stages of pod set and seed fill which suppressed yields.

Yields in England ranged from 74 to 69 bu/A when averaged over replication and yields in Helena ranged from 83 to 77 bu/A. In comparison, the 2010-2006 county-average irrigated yield for England (Lonoke Co.) was 37 bu/A and 44 bu/A for Helena (Phillips Co.). The highest yield reported for the 2011 Arkansas Soybean Association Yield Contest was 94 bu/A.

Soybean strip trial near Helena, Ark. Photo taken July 12, 2011. (Photo courtesy Ryan Van Roekel)

In other research, maximum yield experimental plots in Fayetteville, Ark., were characterized for growth and development and compared with measurements taken from Mr. Cullers’ contest field in southwest Missouri. Unusual characteristics found in Fayetteville and on Mr. Cullers’ farm included high growth and nitrogen accumulation rates and abnormally slow seed fill rates over a longer seed fill period. Mr. Cullers was able to win the Missouri Soybean Association Yield contest again this year with 109 bu/A. The highest replicated treatment yield in Fayetteville was 92 bu/A. In both cases, we believe that delayed planting (May 9th) in conjunction with high temperatures during the soybean reproductive stages reduced these yields. For example, a small yield sample was taken from within a border plot in Fayetteville and was found to have a yield of 137 bu/A! This small spot check is similar to those high yielding spots that a farmer can sometimes see on the yield monitor as the combine goes through a field. We cannot explain why this small spot had such high yield and we assume that this sample represented the maximum yield potential of this environment in 2011.

One-hundred-bushel-per-acre soybeans. Photo taken Oct. 5, 2011 (Photo courtesy Ryan Van Roekel.)

High Yield Soybean Management

Many of Mr. Cullers’ practices are focused on maximizing yield, that does not necessarily maximize profitability or sustainability. Of all the things Mr. Cullers is doing to maximize his yields, the main components attributing to his high yields which can be directly applied to Arkansas soybean production include: early planting, excellent pest management, timely irrigation, selecting the right varieties, and paying close attention to soil fertility and plant nutritional needs. If these five management goals are accomplished, we have demonstrated that yields can average over 80 bu/A across a whole field in our strip trial research.

When striving for and achieving high soybean yields, it is also important to take a look at fertility. An 80 bu/A soybean crop will uptake about 250 lbs/A of K2O. While over half of this is returned to the soil in the form of residue, having adequate potassium levels available in the soil is important for these high yields are to be realized. Additionally, high yielding soybean has a tremendous nitrogen requirement. An 80 bu/A soybean crop will uptake over 400 lbs/A of N and remove more than 300 lbs/A with the grain. However, based on recent research from the Purcell lab regarding soybean’s ability to fix N2 from the atmosphere, we believe that a well nodulated soybean crop does not need additional N fertilizer to reach 80 bu/A. Only when realized yields have plateaued around 80 bu/A and yield goals are over 100 bu/A should N fertilizer be considered and even then, the profitability of this practice is unlikely.

One unusual and widely discussed practice utilized by Mr. Cullers in the past was the use of a Cobra herbicide to burn the soybean crop early in the season. Previous research results on this practice have been unpredictable with inconsistent yield increases. While our first year data did show a potential yield increase, we do not recommend burning the soybean crop as part of a producer’s standard management practices.

Untreated soybean plot in comparison with a soybean plot purposefully burnt with Cobra herbicide plus crop oil concentrate (COC). Photos taken June 17, 2011. (Photo courtesy Ryan Van Roekel.)

We will continue to examine this practice and if a grower would like to experiment with this practice on their own on limited acres, we would recommend applications of broadleaf herbicides like Cobra, Aim, or Cadet be made early in the season (~V2 – V4) when the crop is NOT under stress. If the herbicide is not needed for additional weed control, we encourage the use of multiple untreated check strips across the field for yield verification with a combine yield monitor or weigh wagon. While it is possible that stressing the plants early can allow them to come back stronger, it is likely that the potential yield benefit will be small, as will be the chances of the success with this practice.

This research will continue in 2012 and 2013 and was partially funded by the Arkansas Soybean Promotion Board and Pioneer Hi-Bred.

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