A Hint for Growing Sesbania rostrata

The stem-nodulating tropical legume S. rostrata has recently shown promise as a green-manure crop in rice-farming systems due to its high N-fixation potential, fast growth and tolerance for flooding. Results from one trial in Senegal indicated approximately 270 kg n was fixed by S. rostrata within 45 days. Unfortunately S. rostrata is limited to use in the long-day period of the year due to its photoperiod sensitivity. Its extremely hard seed coat requires acid immersion (30 min. bath in H2SO4) or scarification. The seed's small size makes it difficult for farmers to handle, and the high seeding rates and stand establishment required to obtain good results are quite demanding. Furthermore, the S. rostrata seeds are in short supply and their quality varies.

Vegetative propagation of S. rostrata appeared to be an attractive alternative to seeding S. rostrata. The scheme seemed probable since nodulation sites on the stems of S. rostrata also serve as the origins of adventitious roots, which are able to grow even in waterlogged fields.

Researchers from IRRI and the Justus Liebig University of Germany participated in the GTZ funded investigation. They compared the performance of seeded S. rostrata to that of planted stem-cuttings and ratooned plantings. Ratooning is the practice of cutting a plant at or near the base and allowing it to re-grow.

After 6 weeks both ratooned and cut stems had produced more biomass and accumulated more n than the seeded S. rostrata. Although cuttings and ratooned plants produced fewer plants per m2 than the seeds, they grew one to three branches apiece and developed faster than the seeded plants. Ratoonedplants started growing 2 to 3 days after cutting. They grew faster and showed 2 to 2.5 times more biomass and N accumulation after 6 weeks than the seeded plants did.

Sesbania can be grown outside the paddy all year and reproduced by ratooning for planting in the paddy. Thus ratooning may have two advantages over seeding: 1) no additional cost for the growth of S. rostrata in the paddy field since it is not necessary to purchase seed every season, and 2) a continuous and abundant supply of "biofertilizer" due to the vigor and robust N fixation they exhibit.

The maximum biomass produced by cuttings of S. rostrata by dry weight after 67 weeks was 887 g/m. The cuttings tested were 15 cm and 30 cm long. 100 of them were planted in a square meter. Stem cuttings began to grow after 3 days and produced 1.5 to 2.5 times more biomass and accumulated 1.3 to 2.2 times more N than the seeded plants. The short cuttings of 15 cm grew more slowly and branched less than the 30-cm cuttings. A 65% increase in biomass and N accumulation may be obtained by using the longer cuttings. An increase from 50 to 100 cuttings per m2 increased the biomass yield by 15% and the amount of accumulated N by 10%.

The vegetative propagation of S. rostrata by ratooning and the use of cuttings presents a practical alternative to the use of seeds for propagation. These alternative methods may make it more available, and its benefits more widely acceptable to farmers. If you have had any experiences reproducing this plant or any other with such a method, please write and share your experiences with other readers.

Becker, M., J.K. Ladha, I. Watanebe, and J.C.G. Ottow (1988) Seeding vs. vegetative propagations of the stem-nodulating green manure Sesbania rostrata. Biology and Fertility of Soils 6:279-181.

For more information contact:

Dr. M. Becker
Dept. of Soil Microbiology
P.O. Box 933, Manila