EFFECT OF DIFFERENT WATER SALINITY LEVELS ON GROWTH, NODULATION, AND N₂-FIXATION BY DHAINCHA AND ON GROWTH OF SUNFLOWER USING A ¹⁵N-TRACER TECHNIQUE

ABSTRACT

The effect of different salinity levels of irrigation water (EC _w range 1.1 to 33 dS/m) on the nodulation, dry matter production and N₂ fixation by dhaincha (Sesbania aculeata Pers.) was investigated in a pot experiment. The same effect on the growth of sunflower (Helianthus annuus L.), which was also utilized as a reference crop for measuring N₂-fixation by the legume crop using the [¹⁵N]isotope dilution method, was also investigated. Irrigation with water having EC _w of more than 4.03 dS/m reduced plant growth, and the reduction was more pronounced in S. aculeata than in H. annuus. High levels of water salinity caused more inhibition in shoot than in root growth of both plant species. The indigenous rhizobial strains could form nodules on S. aculeata grown under different salinity levels of irrigated water, except for those irrigated with high level of ground water salinity (EC _w 33 dS/m) where nodulation and N₂ fixation were completely inhibited. However, %N₂ fixation was significantly enhanced by a moderate salinity level (EC _w of 4.03 dS/m) in irrigated water, whereas small effects were obtained with higher water salinity levels (up to 12.3 dS/m). The results indicated that S. aculeata and H. annuus grown in saline soils can be irrigated either with saline water up to 8.03 dS/m and 12.3 dS/m, respectively, or with gradually increased levels of salinity for both of them.

ACKNOWLEDGMENTS

The authors would like to thank Professor I. Othman, General Director of AECS, for his support, and Dr. A.F. Asfari and Dr. M.F. Al-Rabbat for their remarks.