Research Note: Nodulation and Nitrogen Fixation of Stylosanthes hamata in Response to Induced Drought Stress

Abstract

In the north of Senegal, the average annual rainfall has fallen to 300–400 mm because of the occurrence of drought. In addition, the soils are impoverished, with particularly low nitrogen content—less than 0.20 g N kg⁻¹. Stylosanthes (Stylosanthes hamata) is a forage legume cover crop with high nitrogen fixing potential when inoculated with elite Bradyrhizobium strains such as strains ISRA 97 and ISRA 674 already selected in West Africa MIRCEN rhizobial culture collection. This species was used as a test plant to study the effect of drought stress on nodulation and nitrogen fixation, aiming at the recommendation of its cultivation in the north of Senegal. Use of S. hamata could therefore reach the objective to increase and to sustain soil productivity. A pot experiment was carried under greenhouse conditions to estimate the fixed nitrogen in stylosanthes after induced drought stress using the ¹⁵N isotope dilution technique. Maximum of fixation occurred when stylosanthes was inoculated with Bradyrhizobium strain ISRA 97 and watered every 2 days with 100 ml of distilled water. The strain ISRA 674 should be used, however, to inoculate S. hamata in view to maximize the process of biological nitrogen fixation for sustaining agriculture in north and central regions of Senegal. Indeed, no effect of drought was observed up to watering once every 4 days when this strain ISRA 674 was used for inoculating S. hamata.

Keywords:

• drought stress
• nitrogen fixation
• nodulation
• ¹⁵N isotope dilution
• Stylosanthes hamata

This work was done at the MIRCEN/Laboratoire Commun de Microbiologie IRD-ISRA-UCAD within the framework of “Jeune Equipe Associée ERES.” It was supported by the International Atomic Energy Agency (IAEA) through the fellowship contract no. ETH/01006R for Wassie Haile Woldeyohannes. The authors thank Oumar Toure for his valuable technical assistance.

Notes

∗Significant at p = 0.05

In each column, values followed by the same letter do not differ significantly at p = 0.05.