The effects of microalgae-based fertilization of wheat on yield, soil microbiome and nitrogen oxides emissions

Abstract Overuse of agrochemicals is linked to nutrient loss, greenhouse gases (GHG) emissions, and resource depletion thus requiring the development of sustainable agricultural solutions. Cultivated microalgal biomass could provide such a solution. The environmental consequences of algal biomass application in agriculture and more specifically its effect on soil GHG emissions are understudied. Here we report the results of a field experiment of wheat grown on three different soil types under the same climatic conditions and fertilized by urea or the untreated biomass of fresh-water green microalga (Coelastrella sp.). The results show that neither soil type nor fertilization types impacted the aboveground wheat biomass, whereas, soil microbiomes differed in accordance with soil but not the fertilizer type. However, wheat grain nitrogen (N) content and soil N oxides emissions were significantly lower in plots fertilized by algal biomass compared to urea. Grain N content in the wheat grain that was fertilized by algal biomass was between 1.3%–1.5% vs. 1.6%–2.0% in the urea fertilized wheat. Cumulative soil nitric oxide (NO) emissions were 2–5 fold lower, 313–726 g N ha−1 season−1 vs. 909–3079 g N ha−1 season−1. Cumulative soil nitrous oxide (N2O) emissions were 2-fold lower, 90–348 g N ha−1 season−1 vs. 147–761 g N ha−1 season−1. The lower emissions resulted in a 4–11 fold lower global warming impact of the algal fertilized crops. This calculation excluded the CO2 cost from the algae biomass production. Once included algal fertilization had a similar, or 40% higher, climatic impact compared to the urea fertilization.