Effect Of Rhizobial Inoculation Research Articles

A 2-year pot experiment testing the use of sewage sludges as fertilizers for subclover plants was carried out under greenhouse conditions. Two limed soil samples (leptosol and Luvisol) and two anaerobically digested sewage sludges (Evora and Belmonte) were used at the rates of 5, 10, 20 and 60 t ha −1, together with a standard mineral fertilizer-treated (PK) sample and an untreated control. Half the pots with the Leptosol received sludge from Evora and the other half sludge from Belmonte. The soils in all pots were inoculated with a mixture of two indigenous selected Rhizobium leguminosarum bv. trifolii strains. The Luvisol was amended with the sludge from Evora, soil in half of the pots being inoculated with the Rhizobium inoculum. In the first year, the number of nodules and dry weight of shoots increased with lower rates of sludge amendments but decreased with the highest rate (60 t ha −1), except dry weights on the Luvisol. With the standard mineral fertilization, the number of nodules and dry weight of shoots were always significantly superior to the other treatments. On the Luvisol, the number of nodules and the dry weight of shoots of the inoculated pots of all treatments were significantly superior to the uninoculated pots. In the second year, the number of nodules and dry weight of shoots increased with all rates of sludge amendments. The harmful effects of the highest rates of sludges disappeared at 60 t ha −1 and the number of nodules and dry weight of shoots were superior to the standard mineral fertilization. The effect of rhizobial inoculation still remained, but to a smaller extent, probably due to an increase of the rhizobial population and breakdown of soil organic matter. Both sludges can be used as organic fertilizers. The sludge from Evora however, was superior to that from Belmonte, probably as a result of larger amounts of nutrients associated with a higher pH value.

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