Exopolysaccharide of Nostoc muscorum (cyanobacteria) in the aggregation of soil particles

The effects on a saline-sodic soil of exopolysaccaride isolated from Nostoc muscorum or the addition of a cyanobacterial mass proliferation were evaluated in a greenhouse experiment. By day 180 the exopolysaccharide increased soluble C by 100%, microbial activity by 366% and the amount of water-stable aggregates larger than 250 mu m by 12 times. Inoculation with living cyanobacterial mass increased at the end of 365 days oxidizable C by 11%, soluble C by 66%, microbial activity by 73% and aggregates larger than 250 mu m by 66%. A slimy film 3-5 mm thick, with N. muscorum predominating, covered all the surface of inoculated soils. The higher soil aggregate stability produced by both treatments is a consequence of increased microbial activity and concentrating the soil polysaccharide. The high percentage of clays favours the creation of firm and long-lasting slime-mineral joints. Addition of isolated exopolysaccharide produces a faster and higher increase in soil aggregate stability than cyanobacterial mass inoculation.