Mineral nitrogen impairs the biological nitrogen fixation in soybean of determinate and indeterminate growth types

ABSTRACT

Soybean (Glycine max Merrill) crop production in Brazil relies mainly on biological nitrogen fixation (BNF) for nitrogen (N) supply. Recent adoption of indeterminate growth-type genotypes has raised doubts on the need for supplemental mineral N that might negatively affect the BNF. We assessed the effects of mineral N on BNF attributes of soybean genotypes grown in central and southern Brazil. Genotypes were inoculated with Bradyrhizobium sp. and/or received mineral N in three sets of experiments. In the first set, two genotypes received increasing rates of mineral N in nutrient solution, which consistently reduced the BNF. In the second set, mineral N applied at sowing and/or topdressing reduced nodulation and ureides-N in determinate and indeterminate growth-type genotypes. In the third set, mineral N applied at R5.3 stage, foliar or as topdressing, did not increase grain yield in four field experiments. Mineral N impaired BNF irrespective of the growth type and had no effect on grain yield.

KEYWORDS:

• Glycine max
• ureides
• nitrogen fertilization
• mineral N
• nodulation

Acknowledgments

To CAPES for providing Master fellowship to D.F. Saturno. To Carlos Alberto Arrabal Arias (Embrapa Soja) and Luiz Carlos Miranda (Embrapa Produtos e Mercado) for providing seeds of different growth-type soybean genotypes. M. Hungria and M.A. Nogueira are research fellows of CNPq.

Funding

This work was partially supported by Embrapa (project 02.13.08.003.00.05.002). This paper was approved for publication by Editorial Board of Embrapa Soja as manuscript number 15/2015.