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Ruhr-Universität Bochum (2018)

Biochar based soil amendments in West African urban agriculture : Effects on crop yields, nutrient leaching and soil biological properties

Werner Steffen

Titre : Biochar based soil amendments in West African urban agriculture : Effects on crop yields, nutrient leaching and soil biological properties

Auteur : Werner Steffen

Université de soutenance : Ruhr-Universität Bochum

Grade : Doktor der Naturwissenschaften (Dr. rer. nat.) 2018

Sommaire partiel
One of the main hypotheses of this thesis was that biochar can reduce pathogens from water in a filter system and later be used as fertilizer because of its large surface area and reactivity. It was concluded that waste water treatments with a biochar filter is possible. The mean path ogen reduction in the filter was 1.8 log units for E.Coli and enterococci but a loading of bio char with nutrients was not found. Especially Mg, K and P contents of biochar were reduced. However, when the treated water is used for irrigation the loss of nutrients from biochar into the water is not problematic. Despite the lower nutrient content of the filterchar, the crop yields were still significantly higher than the control treatments and not statistically different from the yields obtained when untreated biochar was used. The analysis of plant tissue showed that a direct P fertilizing effect of biochar was mainly responsible for the increases in crop yields. Other authors reported the loading of biochar with diary effluent or effluent from an anaerobic digester (Ghezzehei et al. 2014, Sarkhot et al. 2012, Streubel et al. 2012). It seems that the ability to recover nutrients with biochar from water is controlled by the nature and properties of the waste stream (form of nutrients) and the properties of biochar (sorption properties, surface area, etc.). Especially the properties of biochar can be very specific de pending mainly on feedstock for pyrolysis, the production method, degree of oxygen exclu sion and pyrolysis temperature (Enders et al. 2012, Rajkovich et al. 2011, Steiner 2016). Es pecially the rice husk biochar used in this study was produced at KNUST in Kumasi, Ghana. The custom made pyrolysis reactor allows only little monitoring and produces a very ash rich biochar (Atijah 2017). In addition, rice husk is a very unique feed stock because of its rela tively low carbon and high silica content (Yalçin und Sevinç 2001). Also in the lysimeter study, the rice husk biochar was not able to reduce nutrient leaching and has a low surface area compared to other biochars (Atijah 2017). This may explain why this biochar was not loaded with nutrients. Nevertheless, the hypothesis that biochar can be used in waste water filtration holds true. Although, biochar was not enriched with nutrients it still showed a significant beneficial effect on crop yields.

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Page publiée le 7 janvier 2019