Nutrient Removal by Grain in Modern Soybean Varieties

Abstract

Knowing the nutrient removal by soybean grain harvest in different varieties, locations, and over time is essential to correctly adjust agronomic recommendations, update farmers' practices, and increase nutrient use efficiency. A field-based research trial was carried out to assess macronutrients [nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), and sulfur (S)] removed in grain by modern soybean varieties from southern Brazil introduced between 2007 and 2016. We examined changes between our set of modern varieties and a dataset of historical values encompassing a wide range of varieties introduced before 2007. Moreover, we undertook a synthesis analysis using scientific literature published after 2007 to investigate nutrient removal by grain among modern Brazilian soybeans and a dataset that included field trials from Argentina, United States, and India. There were no yield gains across the years for modern soybean varieties introduced among 2007 and 2016 in Brazil, although the grain N and Mg concentrations decreased. Modern Brazilian soybeans increased nutrient removal compared with that by soybeans historically planted in Brazil, with 11.1, 26.9, 45.0, and 31.6% more N, P, K, and Mg removed, respectively. Our results indicated that soybean growing in Brazil removed 4.3% less N relative to the values reported in the literature dataset, whereas K removal was 21.4% greater. A significant difference was also recorded for high-yield soybean varieties, and Brazilian varieties removed 11.8% less N and 8.6% more K than varieties in the literature dataset. No differences were found among locations for P removal, averaging 4.9 kg Mg^-1 grain. In conclusion, this study indicates that the amounts of nutrients removed by modern soybean varieties were greater relative to the historical values recorded in Brazil, excluding Ca and S. Nonetheless, in the middle to long term (10 years), a significant impact of plant breeding on grain nutrient concentration was recorded only for N and Mg. The difference in nutrient removal patterns between Brazil and other countries indicates an integrated effect of management, genotype, and environment on nutrient removal. These findings provide guidance for optimal nutrient management and specific information for plant breeding programs to understand nutrient variability.

Keywords: calcium; cultivars; magnesium; nitrogen; nutrient concentration; phosphorus; sulfur.

FIGURE 1

(A) Relationship between the years of varieties’ releases and yield, and (B) box plot diagrams of yield indicating the variability outside the upper and lower quartiles across years (n = 192).

FIGURE 2

Relationship between the years of varieties’ releases and grain nutrient content of soybean or amount of nutrient removal in the current study (n = 192): (A) nitrogen, (B) phosphorus, (C) potassium, (D) calcium, (E) magnesium, and (F) sulfur. ns = not significant. *Significant at 5% and ***significant at < 0.001%.

FIGURE 3

Pearson correlation coefficient r values among grain nutrients (g 100 g^–1). Positive correlations are displayed in blue, and negative correlations are displayed in red. The color intensity and arc length of each slice are proportional to the correlation coefficients. **Significant at 0.01% and ***significant at < 0.001%.

FIGURE 4

Linear functions to describe N, P, and K removal relative to grain yield (A, D, G, respectively). Differences among the datasets were tested through an F test (p < 0.05). When no differences were found between the study and literature, a single model was pooled (indicated with a black line). Box plots (B, E, H) display the data distribution of the overall yield for N, P, and K removal by harvest. Box plots (C, F, I) display the distribution of yield data above 4 Mg ha^–1 for N, P, and K removal by harvest. ***Significant at < 1%.

FIGURE 5

Linear functions to describe (A) Ca, (D) Mg, and (G) S removal relative to grain yield. Differences among the datasets were tested using an F test (p < 0.05). The box plots display the data distribution of the overall yield for (B) Ca, (E) Mg, and (H) S removal by harvest. Box plots (C), (F), and (I) display the distribution of yield data above 4 Mg ha^–1 for (C) Ca, (F) Mg, and (I) S removal by harvest.

FIGURE 6

Relative change in nutrient removal as a function of (A) relative yield and (B) relatively high yield for the current study and model built from historical values. (C) Relative change in nutrient removal (N, P, and K) as a function of relative yield and (D) relatively high yield for the current study and literature data. The vertical and horizontal bars indicate the standard error for the x and y variables, respectively.