Suitability of charcoal-amended mineral soil as carrier for Rhizobium inoculants

Abstract

The use of peat as a currier for Rhizohium inoculants in many countries is hindered by its unavailability or high cost. The capability of soil to support survival of rhizobia implies that mineral soils, particularly if amended with organic carbon, could substitute for peat. This paper reports the ability of two soils, with or without amendments of wood charcoal, to support prolonged rhizobial growth as compared to high quality Australian peat. In a series of three experiments, soil amended with charcoal proved equally effective to peat in maintaining high ( > 10 °g −1) populations of rhizobia nodulating chickpea (Cicer arietinum L.) for periods of 105–126 days. After storage for 280 days, two Rhizobium strains differing in growth rate maintained viable numbers in the soil-charcoal mixture above 108 g−1, indicating the suitability of this material as an inoculant carrier. The results imply that quality Rhizohium inoculants may be produced with some mineral soils and locally obtained materials where peat is not available.