Cyanobacteria are amongst the first colonizers of disturbed lands and their activities are reported to improve soil conditions by the addition of fixed atmospheric nitrogen, by aggregation of soil particles, and by the enhancement of seed germination and establishment. Seedling establishment may also be improved by the presence of soil crust disturbances such as cracks and irregularities in the microtopography. In this study, we report the results of experiments in a field situation and in controlled greenhouse conditions in which a bulk culture of the nitrogen-fixing cyanobacterium, Nostoc commune, was sprayed onto the soil surface. Three replicates of four treatments were used: soil surface inoculated with Nostoc and surface disturbed by trampling, soil surface inoculated and surface undisturbed, soil surface not inoculated and disturbed, and soil surface not inoculated and undisturbed.
After a period to allow for growth of Nostoc, seeds of Poa compressa, Canada bluegrass, (field study) and
Schizachyrium scoparium Little bluestem, (greenhouse study) were sown on all surfaces. Results from the field and greenhouse studies differed greatly. Soil aggregate size and nitrogen content were not significantly different among treatment groups in the field plots, however, in the greenhouse significantly larger aggregates were produced in inoculated trays, and a significant interaction was found among all treatments for the NH, form of soil nitrogen. In the field, disturbance enhanced seedling emergence and early establishment significantly, though this effect was not evident in the greenhouse trials.