CHANGES IN AGGREGATE STABILITY, NUTRIENT STATUS, INDIGENOUS MICROBIAL-POPULATIONS, AND SEEDLING EMERGENCE, FOLLOWING INOCULATION OF SOIL WITH NOSTOC-MUSCORUM

The potential of the N-2-fixing cyanophyte Nostoc muscorum for improving the aggregate stability of a poorly structured silt loam soil was studied in a greenhouse experiment. Inoculum rates 1.61x10(5) cells g(-1) soil dry weight (low rate) 4.04x10(5) cell g(-1) soil dry weight (high rate), approximately equivalent to a field application of 2 and 5 kg ha(-1) cells dry weight, respectively. N. muscorum numbers had increased 8-fold (low rate) and 10-fold (high rate) by 300 days after inoculation, indicating not only survival but proliferation. Increases in soil polysaccharides, determined as soil carbohydrate C, were 2.96-3.49 times the values in the non-inoculated soils and aggregate stability had incrased by an average of 18% on day 300. Inoculation with N. muscorum also had a pronounced effect on soil chemical and biological properties, with total C increasing by 50-63% and total N increasing by 111-120%. Increases in the soil indigenous microbial population were recorded, with numbers of bacteria 500, fungi 16, and actinomycetes 48 times the non-inoculated values on day 300 in the high-rate soil. The emergence of lettuce seedlings (Lactuca sativa var. Saladin) in undisturbed inoculated 300-day soils was 56% (low rate) and 52% (high rate) higher than in non-inoculated soils. However, homogenising soils and irrigating (to simulate ploughing and surface crusting) significantly reduced this increase in both treatments, although emergence in inoculated soils was still greater by 45% (low) and 24% (high). It is recommended that inoculated soils be left undisturbed prior to planting. The effects of N. muscorum on soil physical, chemical, and biological properties indicate the possible benefits of cyanobacteria