Assessing Variation in US Soybean Seed Composition (Protein and Oil)

Abstract

Soybean [Glycine max (L.) Merr.] seed composition and yield are a function of genetics (G), environment (E), and management (M) practices, but contribution of each factor to seed composition and yield are not well understood. The goal of this synthesis-analysis was to identify the main effects of G, E, and M factors on seed composition (protein and oil concentration) and yield. The entire dataset (13,574 data points) consisted of 21 studies conducted across the United States (US) between 2002 and 2017 with varying treatments and all reporting seed yield and composition. Environment (E), defined as site-year, was the dominant factor accounting for more than 70% of the variation for both seed composition and yield. Of the crop management factors: (i) delayed planting date decreased oil concentration by 0.007 to 0.06% per delayed week (R ²∼0.70) and a 0.01 to 0.04 Mg ha^-1 decline in seed yield per week, mainly in northern latitudes (40-45 N); (ii) crop rotation (corn-soybean) resulted in an overall positive impact for both seed composition and yield (1.60 Mg ha^-1 positive yield difference relative to continuous soybean); and (iii) other management practices such as no-till, seed treatment, foliar nutrient application, and fungicide showed mixed results. Fertilizer N application in lower quantities (10-50 kg N ha^-1) increased both oil and protein concentration, but seed yield was improved with rates above 100 kg N ha^-1. At southern latitudes (30-35 N), trends of reduction in oil and increases in protein concentrations with later maturity groups (MG, from 3 to 7) was found. Continuing coordinated research is critical to advance our understanding of G × E × M interactions.

Keywords: crop environment; oil concentration; protein yield; seed quality; soybean management.

FIGURE 1

Partial map of the United States (US) showing the locations for all field trials conducted and utilized to create the soybean seed yield and quality (protein and oil) database. Geographical locations are presented as red circles.

FIGURE 2

Frequency distribution for individual data points and an overall distribution for soybean oil concentration (A), protein concentration (B), seed yield (C), and seed yield by latitude (D). Line data distributions were calculated by grouping values to the nearest whole number and adding the frequency of each of the grouped values to arrive at the frequency for the group.

FIGURE 3

Relationships between oil and protein concentration with seed yield (A), seed yield with oil and protein yield (B), and protein concentration and oil concentrations (C). Study numbers are in the order presented in Table 1.

FIGURE 4

Variation in oil concentration (A), protein concentration (B), and seed yield (C) across environments each ranked with respective variables and oil and protein concentration (D) across Es ranked with mean seed yield.

FIGURE 5

Minimum, mean, and maximum values of oil concentration (A–C), protein concentration (D–F), and seed yield (G–I) by latitude and at different planting weeks. There was no enough planting data variation for latitude >45 N. Regression equations are given for significant relation (P < 0.05^∗ or 0.001^∗∗∗) between mean response and planting week.

FIGURE 6

A detailed forest plot for the effect of improved tillage, seed treatment, rhizobium inoculation, foliar N application, foliar fungicide and insecticide application, corn-soybean, and spring wheat-soybean double crop rotation over conventional approaches on oil concentration, protein concentration, and seed yield. Light symbols with square box in mean difference represent factors with greater weight and black dot with a standard error bar represent factors with less weight. The weights of each factor and dotted line in mean difference were important points to discuss if an overall factor effect and comparison of factors was the objective, however, the intention of the current analysis is only to present the individual management (M) factor effect.

FIGURE 7

Exceedance probabilities for oil concentration (A), protein concentration (B), and seed yield (C) of soybean at different N rate. Exceedance probability here is defined as the probability (indicated in the y-axis) of obtaining oil, protein, or yield exceeding the indicated value (in the x-axis) for each fertilizer N rate category.

FIGURE 8

Minimum, mean, and maximum values of oil concentration (A–D), protein concentration (E–H), and seed yield (I–L) by latitude and different varieties maturity groups (MG).