Evaluating the effect of microalgal biomass on soil-plant-water systems

Authors: ALVAREZ, ADRIANA - University Of Minnesota; GARDNER, ROBERT - University Of Minnesota; Weyers, Sharon

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Exploring all possible applications of microalgal biomass is crucial to strengthen the current algal industry and reducing the environmental impacts of agriculture is a major global challenge. Microalgae can play a progressive role as they have the potential to improve soil structure, reduce erosion, improve microbial and nutrient dynamics, and enhance soil fertility. This study describes the effects of inoculating an arable mollisol soil with the nitrogen-fixing cyanobacteria Anabaena cylindrica UTEX1611, using one base experiment (Base) and two follow-up experiments. The cyanobacteria was grown in BG-11 medium without nitrogen (N). For the Base experiment, the cyanobacteria was applied directly on the surface of Hamerly soil at 70 lb N acre-1 in 6-in pots, and compared to non-inoculated controls. Pots were maintained in a plant growth chamber at 22 deg C, relative humidity 55%, and light intensity of 340 µmol photons m-2 s-1 in a 14:10 light-dark cycle. Samples from the soil surface (0-0.4 in depth) were analyzed for soil aggregation, nutrients, and microbial biomass carbon (C) and N. Experiment 2 compared Base treatments but subjected the pots to simulated rain events. Experiment 3 compared Base treatments with and without spring wheat. With inoculation, soil aggregate distribution changed and water stability of some of the aggregate size classes increased. The positive influence these changes had for soil erosion resistance were demonstrated by significantly reduced soil loss in runoff in experiment 2. Inoculation had a positive fertility effect, significantly increasing nitrate (NO3-), ammonium (NH4+), available phosphorus (P), and microbial biomass N. In addition, soluble total organic C increased, potentially indicating exopolysaccharide contributions from the algae. Experiment 3 established that soil NO3- was higher with algae with or without wheat, at 4 weeks. At 6 weeks, lower soil NO3- in algae with wheat treatments, than algae without wheat, suggested wheat plants potentially used the excess NO3- made available in the presence of the cyanobacteria. This study adds insights on the C, N and P dynamics and soil structural changes for advancing the development of microalgal biofertilizers. Isolation and testing of native soil strains with comparisons to chemical fertilizers are recommended for future studies.