Agronomic Performance and Economic Value of High‐Seed‐Protein Soybean (1993)

The long‐term trend in relative value of soybean [ Glycine max (L.) Merr.] protein and oil is toward greater value of protein, thus furthering interests in the potential for increasing seed protein concentration in soybean. If a change in U.S. soybean breeding strategy for improving seed protein levels is required, it should be based on sound economic and biological principles. This research was conducted to: (i) develop high‐protein soybean germplasm adapted to Mid‐Atlantic latitudes; and (ii) compare agronomic performance, economic value, and stability of performance of resulting genotypes with that of normal‐protein soybean cultivars. Fifty‐two high‐protein soybean lines were developed and evaluated in field tests in 1988 and 1989. Seven of the highest yielding high‐protein lines, seven advanced commercial lines, and ‘Essex’ were evaluated in 11 field tests in 1990. All lines in all tests were evaluated for seed protein and oil, seed yield, and other agronomic characters. High‐protein lines were: (i) superior for seed protein concentration and approximate processed value (APV) per bushel; (ii) inferior for seed yield and oil concentration and APV per acre; and (iii) less able to use environmental yield potential, with a decreased seed protein and increased seed oil, as compared with commercial cultivars. Extensive regional testing, including environments with very high seed yield potential, will be required to more precisely describe the biological and economic trade‐offs for high‐protein vs. normal‐protein soybeans. Research Question There is continuing interest in increasing seed protein concentration in soybean. This research was conducted to: (i) develop high‐protein soybean lines adapted to Mid‐Atlantic latitudes; and (ii) compare agronomic performance, economic value, and stability of performance of high‐protein genotypes with that of normal‐protein soybean cultivars. Literature Summary For more than half a century, U.S. soybean breeding has produced improved, higher yielding cultivars. Seed of current cultivars average approximately 41% protein and 21% oil on a dry weight basis. Seed protein and oil are highly negatively correlated in soybean, and seed protein usually is negatively correlated with seed yield. The approximate processed value (APV) per bushel of soybean can be estimated from the soybean's protein and oil concentration and prices for oil and 44% meal. Environmental factors that influence soybean seed yield and protein include soil fertility, N nutrition, temperature, water stress, and soil pH. Stability of performance of a line, the ability to exhibit minimum interaction with the environment, can be determined by regressing the seed yield or other character of each line for each environment on the mean yield of all lines in those environments. Study Description Fifty‐two high‐seed‐protein soybean lines were developed from 18 crosses of high protein × high protein germplasm via phenotypic selection at Beltsville, MD, for plant maturity, lodging resistance, seed yield, and seed quality. These 52 lines were compared with the two best adapted high‐protein parental lines in two 1988 field tests. In 1989, these 54 high‐protein lines and six commercial, normal‐protein cultivars were evaluated in six Mid‐Atlantic field tests, cooperatively with state agricultural experiment stations. In 1990, private industry coordinated the evaluation of the seven highest yielding high‐protein lines, seven advanced commercial lines, and ‘Essex’ in six Mid‐Atlantic and five Mid‐Mississippi Valley field tests. All field tests were evaluated for seed yield, protein, and oil and other agronomic characteristics via conventional soybean plot technique. Applied Questions How does the agronomic performance of high‐protein soybean lines developed for Mid‐Atlantic latitudes compare with that of current cultivars? The high‐protein lines were comparable for lodging resistance and seed quality but were not as high yielding as Essex or other commercial lines. In 16 field tests, the highest yielding high‐protein line averaged 90% of the seed yield of Essex, 48 vs. 53 bu/acre. In 1990, the mean yields of seven high‐protein lines ranged from 40 to 49 and averaged 43 bu/acre. Commercial lines ranged from 54 to 59 and averaged 56 bu/acre. What is the potential value of high‐protein soybean, assuming the values of $0.20/lb for oil and for protein? The seven highest yielding, high‐protein lines evaluated at 11 locations in 1990 averaged 50.3% seed protein and 15.5% seed oil, compared with the mean of 41.2% protein and 20.7% oil for eight commercial lines. The APV per bushel of these high‐protein lines ranged from $6.71 to $7.03, compared with $6.42 to $6.53 for commercial lines. The APV per acre (APV/bu × bu/acre) of these high‐protein lines ranged from $270 to $326, compared with $348 to $382 for commercial lines. Do high‐protein soybean lines respond to high yield environments as well as commercial lines? In 1989, mean seed yields of the 54 high‐protein lines and of commercial lines increased ≈ 1.0 and 1.5 bu/acre, respectively, with each 1.0 bu/acre increase in mean seed yield of environments. In 1990, the high‐protein lines and commercial lines increased 0.93 and 1.06 bu/acre, respectively, with each 1.0 bu/acre increase in mean seed yield of environments. In 1990, the mean seed yields of environments ranged from 33 to 64 bu/acre. The estimated changes in seed yield, protein, and oil per 31 bu/acre increase in seed yield over environments are summarized in Table . Compared with commercial lines, the high‐protein lines had less seed yield response, greater drop in protein, and an increase rather than a decrease in oil in higher yielding environments. We conclude that high‐protein soybean lines probably differ from normal‐protein lines in response to increasing seed yield potential of field environments. Recommendations More accurate estimates must be obtained to provide conclusive evidence on stability of high‐protein vs. normal‐protein soybean. Comparisons of higher yielding, high‐protein (> 50%) vs. commercial, normal‐protein lines should be made in a great number of environments ranging in yield from U.S. average to highest attainable yields. Changes in soybean breeding strategies to improve seed protein levels should be based on: (i) the econometrics of maximizing net returns to soybean producers; and (ii) known and rational interrelationships among seed yielding ability of genotypes and their protein, oil, and residual fractions of the seed. Estimated changes in seed yield, protein, and oil of commercial and high‐protein soybean lines per 31 bu/acre increase in mean seed yield of environments. Changes in Mean of: Yield Protein Oil bu/acre ‐‐‐‐‐‐ % ‐‐‐‐‐‐ 8 commercial lines +33 −0.7 −0.6 7 high‐protein lines +29 −1.8 +0.5