Nitrogen Mineralization Potential of Cyanobacterial Fertilizers Compared to Traditional Organic Fertilizers Applied to Clayey and Sandy Soils.

Nitrogen Mineralization Potential of Cyanobacterial Fertilizers Compared to Traditional Organic Fertilizers Applied to Clayey and Sandy Soils

Abstract

Arina S. Sukor, Heather Storteboom, Mary E. Stromberger, and Jessica G. Davis

Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO 80523-1170

Organic farmers require organic sources of N fertilizer. Cyanobacteria can be grown on site and may be an effective N fertilizer, but N mineralization potentials of this material needs evaluation. The N mineralization potential of cyanobacteria (in liquid and solid form) was compared with traditional organic fertilizers (fish emulsion and composted manure) in two soils with contrasting textures. Two soils with four organic fertilizer treatments were incubated in the lab at constant temperature (25^oC) and moisture content (60% water-filled pore space). The experimental units were arranged in a Randomized Complete Block Design. Organic fertilizers were applied at the field application rate of 50 kg N ha^-1. Soils were destructively sampled over the course of  140 days and analyzed for NH₄⁺-N, and NO₃^--N. Nitrogen  mineralization percentage, total C, total N, soil organic C, soil microbial biomass C were analyzed at the end of the incubation study. In all treatments, soil NH₄⁺-N was the highest at day 56 and decreased from day 56 to 140 due to the formation of soil NO₃^--N.  Soil NO₃^--N was significantly higher with fish emulsion (57.49 mg NO₃^--N kg^-1 in clayey soil and 33.31 mg NO₃^--N kg^-1 in sandy soil) compared to other treatments. Microbial biomass was lowest in sandy soils. Manure significantly increased soil microbial biomass C (207.50 mg C kg^-1 soil)  compared to fish emulsion (115.42 mg C kg^-1 soil) in sandy soil. Nitrogen mineralization percentage was 10.07% significantly greater with fish emulsion than liquid cyanobacteria, and was 5.64% significantly greater with solid cyanobacteria than composted manure. Solid cyanobacteria N was mineralized more rapidly than composted manure, whereas fish emulsion N was mineralized more rapidly than liquid cyanobacteria. Further field studies need to be conducted to optimize cyanobacteria use as biofertilizers.