Agronomic Performance and Stability of Soybean Varieties Grown in Three Maturity Zones of Minnesota

Soybeans [Glycine max (L.) Merr.] grown in the northern latitudes generally have lower protein concentrations than in the southern latitudes, reducing the value of northern grown soybeans. The objectives of this research were to: (i) study maturity zones within Minnesota for soybean seed yield, protein concentration, and oil concentration; (ii) compare performance of soybean varieties grown in producers' yield-contest fields with University of Minnesota research plots; and (iii) analyze seed yield, protein concentration, and oil concentration means and stability statistics for 30 soybean varieties. Yield, protein, and oil data were collected from University of Minnesota research trials across 15 environments from 1991 to 1995. Producer data were collected from the Minnesota Soybean Grower's Association Yield Contest from 1991 to 1995. The general trend was a decrease in yield and protein concentration from southern to northern Minnesota, with higher yield and protein concentration among the same varieties grown in central Minnesota compared with northern Minnesota. Yields were highest in producers' yield-contest fields, but no protein and oil concentration differences were noted between yield-contest fields and research plots. Seed yield, protein concentration, and oil concentration means, as well as three stability statistics, differed among 30 varieties grown in 15 environments. The three stability statistics consisted of two nonparametric statistics based on variety ranks and Kang's yield-stability statistic. These results suggest that stability statistics, in addition to variety means, could be used by consultants, variety testing personnel, and breeders to recommend the most appropriate varieties for maximum yield and protein concentration. Research QuestionSoybeans grown in the northern latitudes generally have lower protein concentrations than those grown in southern latitudes. There have been concerns over lower protein concentrations because crushing companies and foreign markets desire higher protein concentrations. Lower protein concentrations have resulted in lower prices paid for northern grown soybeans, resulting in decreased profits for northern soybean producers. The purpose of this research was to compare seed yield, protein concentration, and oil concentration of several Minnesota adapted soybean varieties grown in small research plots and large, optimal production fields in either the northern, central, or southern maturity zones of Minnesota. In addition to means analyses, three stability statistics were calculated among 30 varieties for potential use as an additional statistic in variety selection. Literature SummarySoybeans grown in Minnesota average 1.1 percentage points less protein and 0.7 percentage points more oil than the U.S. average at 13% moisture. There are concerns about these discrepancies, but the reasons why northern latitude soybeans are lower in protein concentration are not well defined. An important research goal is the development of high yielding soybean varieties with improved protein concentration and good stability of production characteristics. To reach this goal, an improved understanding of the relationship between varieties, environmental conditions, and variety × environment interaction are needed. Additionally, an understanding of the relationships between small research plots and large production fields are needed in order to make recommendations for high yielding, high protein varieties. Variety stabilities, in addition to variety means, have to be analyzed in order to understand the above relationships. Two nonparametric stability measures based on variety ranks and Kang's yield-stability statistic are three examples of stability statistics that can easily be computed and compared among varieties adapted to a specific growing region. Study DescriptionYield, protein, and oil data from the University of Minnesota's public and private tests were analyzed and compared with data from the same varieties grown in producers’ yield-contest fields. The data from the yield-contest fields were collected by the Minnesota Soybean Grower's Yield Contest from 1991 to 1995. These data were used to determine whether University of Minnesota research plots could reasonably predict the relative performance of these varieties under large, optimal production field conditions. Data from varieties grown in both the northern and central maturity zones, and the central and southern maturity zones of Minnesota were used to determine whether protein concentrations changed from southern to northern Minnesota. Finally, data from the University of Minnesota research plots were used to determine stability characteristics of varieties grown in all 5 yr at three locations per maturity zone. Applied QuestionsDo soybean seed yields and protein concentrations decrease from southern to northern Minnesota, and, if so, are they due to environmental or varietal differences? Yield and protein concentration tended to decrease from southern to northern Minnesota. Significantly higher yields and protein concentrations were found among the same varieties grown in the central vs. northern maturity zones, and in the southern vs. central maturity zones suggesting that environmental conditions played an important role in determining yield and protein concentrations. However, some varieties were higher yielding and had higher protein concentrations than others under similar environmental conditions, demonstrating a large variety effect. Do varieties perform similarly under small research plot conditions and optimal, large production conditions? Yields from the Minnesota soybean producer's yield contests were higher than those from research plots, but protein and oil concentrations were not different between research plots and the yield contest fields. Yields obtained from the Minnesota Soybean Growers' Yield Contest were some of the highest in Minnesota, and it would be expected that small research plot yields would be very high due to their intensive management. No variety interactions were found between small research plots and producers' yield contest fields, suggesting that research plots can reasonably predict the performance of varieties under optimal, large-scale production conditions. However, the average Minnesota soybean yield from 1991 to 1995 was 10 to 15 bu/acre less than the average yield under either small research plot or producers' yield contest conditions. Do varieties differ in their level of production and production stability? Varieties in all three maturity zones differed for yield, protein concentration, and oil concentration, as well as for three measures of production stability for yield, protein concentration, and oil concentration. The stability measures, in addition to variety means, could be used by consultants, variety testing personnel, and breeders to help recommend the most appropriate varieties for specific regions of Minnesota to maximize yield and protein concentrations. The stability measures would be most useful when varieties do not differ in seed yield, protein concentration, and oil concentration. For example, if three varieties had the same mean yield, protein concentration, and oil concentration, but differed in stability, then the variety with the greatest stability should be recommended to the producer.