Date of Graduation

5-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Larry C. Purcell

Committee Member

Richard E. Mason

Second Committee Member

Dan Poston

Third Committee Member

Curt R. Rom

Fourth Committee Member

Nathan A. Slaton

Keywords

Biological sciences; Glycine max; High; Maximum; Nutritional; Physiological; Soybean; Yield

Abstract

Soybean [Glycine max (L.) Merr.] grain yields greater than three times the national average have been reported in yield contests. Characterization of soybean in a maximum yield environment is necessary to provide empirical data to support those yield claims and to provide an understanding of the physiological processes at that yield level. From 2011 to 2013, research characterized biomass and N accumulation rates, radiation use efficiency (RUE), leaf N dynamics, the rate of harvest index increase (dry matter allocation coefficient, DMAC), seedfill period (SFP), and grain yield components from Mr. Kip Cullers' contest fields and in small plots at the University of Arkansas in Fayetteville. The greatest cultivar mean yield was 7953 kg ha-1, which occurred in 2013 when biomass and N accumulation rates and RUE values as high as 64.3 g m-2 d-1, 2.08 g N m-2 d-1, and 1.89 g MJ-1 were observed, respectively. These observed crop growth characteristics were near or above the maximum values previously reported in the literature. The DMAC and SFP values were also abnormally slow and long, respectively. This coupled with the enhanced growth rates provide empirical data and insights into the production of yields >6419 kg ha-1 (100 bushels acre-1).

Additional research in Fayetteville evaluated the yield effects of several of Mr. Cullers' alternative management practices. Management practices evaluated included various seed treatments, intentional herbicide injury, uniform plant spacing and emergence, lodging prevention, and a proprietary foliar-applied product. None of these alternative practices were effective in increasing yields beyond the high input practices utilized within this maximum yield environment.

The feasibility of several of these high input maximum yield management practices in large production fields in eastern Arkansas were evaluated. Enhanced management including

additional inputs of poultry litter, irrigation, supplemental N, and pest control were evaluated on the field scale. Two cultivars had average yields of 6931 and 6986 kg ha-1 at the England location in 2013. Economic analysis suggested that even this scaled down maximum yield management was less profitable than the growers' normal production practices.

Finally, a simple soybean crop model was used to simulate crops grown within maximum yield environments at Fayetteville and Mr. Cullers' contest fields. Sensitivity analyses were also conducted to examine the effects of varying values of RUE, N accumulation, specific leaf N (SLN), and DMAC. The most accurate dataset was for Fayetteville in 2012 and 2013 and the default parameters in the model predicted yields 34.0% less than observed over all cultivars. Modifying the model with the observed parameters for RUE, N accumulation, and SLN resulted in yield predictions that averaged 3.4% greater than the observed for all the cultivars in Fayetteville in 2012 and 2013. Sensitivity analyses indicated that yield could be increased with decreased DMAC values, increased RUE values, increased SLN values when coupled with greater N accumulation rates, and with increasing N accumulation when coupled with increasing RUE values.

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