Abstract
It is unclear if additional inoculation with Bradyrhizobia at varying soybean [Glycine max (L.) Merr.] growth stages can impact biological nitrogen fixation (BNF), increase yield and improve seed composition [protein, oil, and amino acid (AA) concentrations]. The objectives of this study were to evaluate the effect of different soybean inoculation strategies (seed coating and additional soil inoculation at V4 or R1) on: (i) seed yield, (ii) seed composition, and (iii) BNF traits [nodule number and relative abundance of ureides (RAU)]. Soybean field trials were conducted in 11 environments (four states of the US) to evaluate four treatments: (i) control without inoculation, (ii) seed inoculation, (iii) seed inoculation + soil inoculation at V4, and (iv) seed inoculation + soil inoculation at R1. Results demonstrated no effect of seed or additional soil inoculation at V4 or R1 on either soybean seed yield or composition. Also, inoculation strategies produced similar values to the non-inoculated control in terms of nodule number and RAU, a reflection of BNF. Therefore, we conclude that in soils with previous history of soybean and under non-severe stress conditions (e.g. high early-season temperature and/or saturated soils), there is no benefit to implementing additional inoculation on soybean yield and seed composition.
Highlights
It is unclear if additional inoculation with Bradyrhizobia at varying soybean [Glycine max (L.) Merr.] growth stages can impact biological nitrogen fixation (BNF), increase yield and improve seed composition [protein, oil, and amino acid (AA) concentrations]
Characterizing amino acids (AAs) composition is an important factor for formulating balanced diets, with this requirement varying between animal species and within categories of the same specie[6]
AAs are classified as essential (EAA; AAs with carbon skeletons not synthesized by animals), including arginine, cysteine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine; and non-essential AA (NEAA; AAs that can be synthesized by animals) including alanine, aspartic acid, glutamic acid, glycine, proline, serine, and tyrosine[5,7,8]
Summary
It is unclear if additional inoculation with Bradyrhizobia at varying soybean [Glycine max (L.) Merr.] growth stages can impact biological nitrogen fixation (BNF), increase yield and improve seed composition [protein, oil, and amino acid (AA) concentrations]. The objectives of this study were to evaluate the effect of different soybean inoculation strategies (seed coating and additional soil inoculation at V4 or R1) on: (i) seed yield, (ii) seed composition, and (iii) BNF traits [nodule number and relative abundance of ureides (RAU)]. A study conducted across 187 site-years in the US indicated that overall yield increase due to seed inoculation was 60 kg ha−1 (1.7%)[21] These authors indicated that seed inoculation is a profitable practice, providing economic benefits. A recent study conducted in Brazil indicated that additional inoculation to the soil at different soybean stages increased nodulation and, in some situations, seed yield[22]. We hypothesized that additional inoculation can improve soybean N nutrition promoting yield increase and improving seed protein composition (greater protein and AAs concentrations)
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