Inoculation effects on growth, nodulation, cytosol components and nitrogen fixation of narrowleaf and hairy vetch

Abstract

Underutilized indigenous legumes have potential for enhanced nitrogen fixation when properly managed. Many species have unusual tolerance and adaptive capabilities to survive when intensively grazed, and to continue vigorous regrowth on sites with very low soil productivity under extremes of climatic stress. The objective of these studies was to determine effects of specific inoculation compared to intrinsic soil Rhizobium on growth, nodulation, nitrogenase (C₂H₂ red.) and associated nodule components of narrowleaf vetch (Vicia angustifolia L.). Responses were determined for soil fertility treatments and evaluated with comparative responses of hairy vetch (Vicia villosa, Roth). Field evaluations for availability of fixed nitrogen by these vetch species was determined as fertilizer nitrogen equivalence (NH₄NO₃) with Maton rye (Secale cereale L.).

Top growth of both vetch species at anthesis significantly increased with inoculation. Narrowleaf growth was approximately one third or less of hairy vetch with comparable treatments. However, both nodule mass and corresponding nitrogenase activity (C₂H₂ red.) of narrowleaf plants were approximately the same or greater than hairy vetch plants with ATCC 10314, Rhizobium leguminosarium Frank, inoculations. This interrelationship was also true for nodule cytosol components with total ureides at 0.63–0.95 mmol g^‐1 noninoculated and 1.14–1.75 mmol g^‐1 inoculated, KG ranged in content 0.08–0.13 mmol g^‐1 noninoculated and 0.14–0.21 mrnol g^‐1 inoculated. Nodule cytosol enzyme activity levels of narrowleaf recurrently exceeded those of hairy vetch with the same inoculation treatments. Ranges as IU g^‐1 fresh nodule, noninoculated and inoculated; were glutamine synthetase (GS), 10.3–21.4 and 28.1–35.6; aspartate aminotransferase (AST) 8.4–11.4 and 12.3–20.7; glutamate synthase (GOGAT 0.8–1.3 and 1.1–1.5; glutamate dehydrogenase (GDH) 0.43–1.27 and 1.27–1.73. Growth of narrowleaf increased significantly only with K levels to 100 mg/kg soil. However, both nodule mass and corresponding nitrogenase levels (CpH,, red.) continued to significantly increase near linearly to 300 mg K/kg soil. Fertilizer nitrogen equivalence (FNE) as increased rye yields were: narrowleaf 15 kg N noninoculated and 68 kg N/ha inoculated, and from hairy vetch 34 kg N noninoculated and 64 kg N/ha inoculated. Residual increased available soil N (FNE) following vetch‐rye mixtures were: narrowleaf 17 kg N noninoculated and 36 kg N/ha inoculated; for hairy vetch 18 kg N noninoculated and 29 kg N/ha inoculated. High levels of symbiotic nitrogen fixation were attained by narrowleaf vetch when effectively nodulated and with favorable soil fertility levels. Nodulation by indigenous soil rhizobia may have reduced nitrogen fixation compared to results with specific, improved inoculation.

Key words:

• Rhizobium leguminosarum Frank
• Vici angustifolia L
• Vici villosa Roth
• Secale cereale L
• nitrogen fertilizer equivalence

Notes

Professors, Agronomy and Statistics, respectively. Journal article 3940, Oklahoma Agricultural Experiment Station, Stillwater, OK 74078. Received______________, 1982.