Abstract:
With a view to study the biomass productivity and nutrient accumulation of Sesbania rostrata, a field experiment was initiated at college of Agriculture, Vellayani during summer of 1988-’89. The investigation was carried out as two separate experiments. The objective of Experiment I was to assess the biomass productivity and nutrient accumulation of Sesbania rostrata in relation to other green manures, viz. Sesbania aculeata and Crotolaria juncea. The second experiment was intended to determine the effect of Rhizobium inoculation, Liming and phosphorus application on the biomass productivity of Sesbania rostrata. The experiment (s) were laid out in randomized block design with three replications. The soil of the experimental site(s) was sandy clay loam, low in available nitrogen and phosphorus and medium in available potassium. An abstract of the results is given below.
Optimum time of harvest of the green manures during the third crop season in rice fallows was at flowering stage(50 DAS), since all the parameters investigated showed a maximum value at this period. Among the green manures tried, Crotolaria juncea proved to be superior in terms of green matter yield, dry matter yield and nutrient up take followed by Sesbania aculeata. At final harvest (50DAS) Crotolaria juncea plant, yielded 14.98 t/ha of biomass, 5.36t/ha of dry matter and yielded 103.78kg/ha, nitrogen. The performance of Sesbania rostrata was not at all satisfactory under the agro-climatic conditions of Trivandrum during the summer season. The present study indicated the superiority of Crotolaria juncea as a green manure under Trivandrum conditions during the summer, as compared with the other two green manures tried.
Highest level of lime application (500kg/ha) tried in the experiment together with inoculation positively influenced the growth parameters, nutrient uptaken , soil content of nitrogen, phosphorus, calcium and Rhizobium population . Net returns and cost-benefit ratio also showed higher values for the said treatments. Though phosphorus application at 30kg/ha positively influenced the said parameters, its effect was negligible and greatly nullified by the cost of fertilizer which resulted in a lower net profit and cost-benefit ration. Thus, it is revealed from the present study that phosphorus application is not absolutely necessary for growth of Sesbania rostrata under the agro-climatic conditions of Trivandrum district.