Nitrogen mineralization from biofertlizer Azolla mexicana compared to traditional organic fertilizers
Date
2018
Authors
Jama, Aisha, author
Davis, Jessica G., advisor
Stromberger, Mary, committee member
Uchanski, Mark, committee member
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Abstract
Organic agriculture has become an essential approach to meeting the growing global food production demand and long-term soil sustainability, as well as addressing environmental problems connected with the use of synthetic agrochemicals. As a result, biofertilizers (biological fertilizers) have become promising resources to meet the growing demands for healthy and safe food production. Biofertlizers supply nutrients and take advantage of microorganisms that contribute to sustainable practices. One such biofertilizer is the aquatic pteridophyte Azolla mexicana which can be found in both tropical and temperate climates. Azolla can multiply rapidly, ensuring year-round biomass, and has also been found to have fast and high rate of N fixation. Azolla strains have been successfully exploited as effective biofertilizers in Asia but strains native to the Great Plains have not. There is no literature that assesses N mineralization (Nmin) rates of Azolla mexicana compared to other organic fertilizers in Colorado soils. A laboratory soil incubation was conducted to determine the rates of Nmin, N availability and total C and N of Azolla mexicana applied to soils compared to commonly-used organic fertilizers. Then, a greenhouse study was conducted to assess the organic fertilizer and urea treatment responses on kale growth and yield, leaf and petiole N percentage, total N uptake and percentage N recovery. In this study, we hypothesized that Azolla biofertilizer application will enhance soil inorganic nitrogen (soil ammonium-N and nitrate-N) concentrations and that soil amended with Azolla will also enhance vegetable plant growth parameters (plant height, leaf and petiole N percentage, total N uptake and percentage N recovery). In the incubation study, soil NH4+-N for all treatments tended to increase until day 56 where they all peaked then subsequently decreased until the end of the incubation period. Compost treatment recorded higher initial soil NH4+-N while Azolla + Watanabe treatment recorded higher soil NH4+-N concentration towards the end of the study. The soil NO-3-N concentrations in all treatments increased throughout the 140-day study. The Azolla + Watanabe treatment showed highest average soil NO-3-N concentration at day 140 while the Control treatment had the lowest soil NO-3-N concentration throughout the experiment. The decline in soil NH4+-N concentration formed during ammonification was followed by an increase in soil NO-3-N concentration because of nitrification. In the greenhouse study, Azolla + Watanabe treatments had taller kale, significantly higher leaf fresh weight as well as significantly higher leaf dry weight. Both Azolla + Watanabe and Urea treatments recorded significantly higher yields compared to the other treatments. The Azolla + Watanabe and both Cyano treatments recorded significantly higher root dry weights compared other treatments. Control treatment had significantly higher root to shoot ratio. There were no significant differences in leaf N (%) among Azolla + Watanabe, Azolla, Cyano and Cyano + Moringa treatments. Azolla + Watanabe treatment also had significantly higher total N uptake among the organic fertilizers but was not significantly different from Azolla. Urea treatment recorded significantly higher N recovery and showed a similar pattern as the total N uptake whereby Azolla + Watanabe had significantly higher N recovery.
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Subject
cyanobacteria
Azolla
plant response
mineralization