Plant and soil responses to a commercial blue-green algae inoculant

Abstract A commercial blue-green algae inoculant (Genesis II) for improving the N content of soils was applied to basalt and pumice soils in a greenhouse pot test with orchardgrass, pinegrass, Douglasfir, and ponderosa pine. Treatments were control (deionized water), live algae, killed algae, live algae plus P, K and S and P, K and S only. Plant biomass yields with live inoculant generally were significantly greater than with the control treatment but were the same as with killed inoculant. Live algae plus P, K and S further enhanced productivity. P, K and S alone produced no increase over the control treatment. Response to the inoculant compared to the control appears to be a result of addition of nutrients present in the inoculant stock solution. Further biomass increases with the P, K and S plus live algae treatment compared to live and dead algae treatments occurred because these nutrients became limiting as N was added. Total organic-N and total C in surface soils were similar in all treatments. When the stock solution was sampled via culture methods, the most prominent species found was Chlorella , a green alga. Anabaena , an N 2 fixing blue-green alga, produced less than one colony per plate on the average. Phormidium , a blue-green alga not found in the inoculant, was dominant on the soil surface at the end of the test suggesting a soil origin for this species. Results indicate that Genesis II probably has very limited potential to enhance blue-green algal populations and, consequently, N of the forest soils used in this test.