Nitrogen assimilation traits and dinitrogen fixation in soybean and common bean

• Published in: Agronomy journal Vol. 84; no. 6
• Main Authors: George, T. (University of Hawaii, Paia, HI), Singleton, P.W
• Format: Journal Article
• Language: English
• Published: 01.11.1992
• Subjects: ABONOS NITROGENADOS; ABSORCION DE SUBSTANCIAS NUTRITIVAS; ABSORCION DE SUSTANCIAS NUTRITIVAS; ABSORPTION DE SUBSTANCES NUTRITIVES; ALTITUD; ALTITUDE; ANABOLISME; ANABOLISMO; AZOTE; DISPONIBILIDAD DE NUTRIENTES; DISPONIBILITE D'ELEMENT NUTRITIF; ELEMENT NUTRITIF DISPONIBLE; ENGRAIS AZOTE; ENSAYO; FACTEUR EDAPHIQUE; FACTORES EDAFICOS; FERTILIDAD DEL SUELO; FERTILITE DU SOL; FIJACION DEL NITROGENO; FIXATION DE L'AZOTE; GENOTIPOS; GENOTYPE; GLYCINE MAX; NITROGENO; PHASEOLUS VULGARIS; SIMBIOSIS; SYMBIOSE; TESTAGE
• ISSN: 0002-1962; 1435-0645
• DOI: 10.2134/agronj1992.00021962008400060022x

Nitrogen derived from symbiotic and mineral sources by a legume is determined by the interactions between mineral N supply, plant N demand, and N assimilation traits. These interactions need to be understood to maximize legume N2 fixation and yield, and to identify plant traits supporting high N2-fixation. These interactions were examined in inoculated soybean [Glycine max Merr. (L.)] and common bean (Phaseolus vulgaris L.) by varying N supply (9, 120, and 900 kg N ha-1) at two field sites. Nitrogen fixation was measured by 15N dilution method. Plants were sampled at full bloom (R2), 21 to 25 d from R2, and physiological maturity (R7). Total N of both legumes at R7 was 25% greater with 900 than 9 kg N ha(-1). With 900 kg N ha(-1), soybean N accumulation at R7 (271 kg N ha-1) was 42% more than common bean but was 22% less at R2 (78 kg N ha-1). Applied N had the largest impact on N accumulation rates before R2 and from the second sampling to R7, both periods of minimal N2 fixation. Rate of N accumulation by common bean (0.19 g N m(-2) d-1) was more uniform over the growth cycle than by soybean (0.26 g N m(-2) d-1) which peaked (0.58 g N m(-2)d-1) between R2 and the second sampling. This peak also coincided with maximum N2 fixation rate. Our 15N uptake and extractable soil N data indicate that common bean derived more N from the mineral source than soybean because of more efficient uptake. Greenhouse data indicated greater root weight and uptake of mineral N per unit root weight for common bean than soybean. Maximizing both N2 fixation and yield might entail timing the mineral N supply during early vegetative and late reproductive phases. The limited N2 fixation capacity of common bean might be due to N assimilation traits favoring mineral N uptake