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ARS Home » Midwest Area » Morris, Minnesota » Soil Management Research » Research » Publications at this Location » Publication #372569

Research Project: Stewardship of Upper Midwest Soil and Air Resources through Regionally Adapted Management Practices

Location: Soil Management Research

Title: Soil mineralization of microalgal biomass: An incubation experiment on nitrogen and phosphorus release in an arable soil

item ALVAREZ DE LA HOZ, ADRIANA - University Of Minnesota
item Weyers, Sharon
item GARDNER, ROBERT - University Of Minnesota

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/11/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Agriculture needs to increase productivity and minimize the environmental footprint. Microalgae provide a promising platform to improve soil fertility while protecting the soil resource base. Unlike chemical fertilizers, microalgae are a source of carbon and enhance soil health. Mineralization of microalgal biomass into plant-available forms of nitrogen (N) and phosphorus (P) was compared to chemical fertilizers (urea and triple superphosphate, TSP) in aerobic incubations conducted at 25°C for 42 days. The cyanobacteria Anabaena cylindrica (1611) and a local green alga (SLS1) were grown in bag reactors and the biomass was harvested, washed and mixed with soil (arable mollisol). Treatments for N mineralization used a fixed N application rate of 0.78 g N·kg soil-1, treatments for P mineralization reflected algal-P. Treatments were: (T1) unfertilized control; (T2) 100% urea-N; (T3) 75% urea-N + 25% 1611-N at 0.02 g algal-P·kg soil-1; (T4) 75% urea-N + 25% SLS1-N at 0.07 g algal-P·kg soil-1; (T5) 100% 1611-N at 0.09 g algal-P·kg soil-1; (T6) 100% SLS1-N at 0.28 g algal-P·kg soil-1; (T7) 75% 1611-N + 25% SLS1-N at 0.14 algal-P·kg soil-1; (T8) 0.09 g TSP-P kg soil-1; (T9) 0.28 g TSP-P·kg soil-1; and (T10) 0.09 g SLS1-P·kg soil-1. Net N mineralized was greatest at day 3 and declined over time for most treatments. It was highest in treatments with urea (T2, T3 and T4) than with algae only, and higher with the cyanobacteria (T5) than with the green alga (T6 and T7). For all treatments, N mineralization started with active ammonification in days 3-7, followed by gradual nitrification. At day 42, 71%, 50% and 39% of the total applied N in T2, T5 and T6, respectively, was mineralized, illustrating a slower rate of mineralization for algal N. Soil available P decreased over time for most treatments indicating an increased biological demand. Treatments T6 and T9 showed the greatest P availability at the end of the incubation period (90-96 mg·kg soil-1). Available P was higher for TSP (T9) than for the green alga (T6) in the first 21 days which may translate into lower P losses from soil fertilized with the green alga. Available P from algal treatments of a lower P fertilization rate (T5 and T10) did not differ from TSP (T8) during the incubation period. These results advance our knowledge for future developments of algae-based agricultural solutions.