The potential of Sesbania rostrata as green manure: nitrogen fixation and the relative contributions of root and stem nodules to fixation in Morogoro, Tanzania

Journal of Agriulture. 1998 Vol. 7 : 5-11The legume plant Sesbania rostrata, an important green manure plant in some parts of Asia, occurs also in Tanzania where its manurial value is not exploited. In order to assess its potential as green manure in Tanzania, a glasshouse study was undertaken to evaluate the ability of S. rostrata to fix nitrogen (N) under Morogoro conditions. The S. rostrata seeds, and nodules for the Rhizobium inoculum, were obtainedfrom the Dodoma area of Central Tanzania. The seeds were grown in a Vertic Ustifluvent soil in 20-litre plastic pots. The split-plot design was used. Waterlogged and drained soil conditions were imposed as main-plot treatments. The sub-plots were the control, seed inoculation, stem inoculation, and seed + stem inoculation. By 60 days ofplant growth, root nodule weights were higher (P=O.05) in the inoculated treatments in the waterlogged soil. Stem nodule weights were not significantly different between the moisture regimes, though numbers were higher (P=O.OI) in the drained soil. Stem inoculation resulted in higher (P=O.OI) nodulation compared to that under seed inoculation or control. Put together, nodule weights at 60 days after emergence were lower (P=0.05) in the drained soil. Overall, inoculation increased the level of nodulation over that in the controls. Consequently, N2fixation was greater (P=O.05) in the waterlogged than in the drained soil. Inoculation resulted in more N,fixation than that in controls. Stem nodules contributed significantly (P=O.05) to total nodulation and N2fixation. The higher level of Nsfixation followtng inoculation as compared to that in the controls indicates feasibility of improving the N content of S. rostrata plants/manure through inoculation. The poorer performance under drained soil conditions was attributed 10 infestation of the plants by root-knot nematodes in that moisture regime