Plant Available Phosphorus From Bone Char And Biochar Additions In A Phosphorus-Fixing Soil

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Managing phosphorus (P) plant availability in soils and efficient usage of P fertilizers are essential for agricultural sustainability worldwide. Since P is an immobile nutrient, preventing Pdeficiency in crops becomes especially challenging in highly weathered, acid soils that are prone to strong P adsorption. With the rapid depletion of global P reserves, finding alternatives to rock phosphate-dependent fertilizers and management practices that enhance P availability in agricultural ecosystems will become even more critical. Recycling P from slaughterhouse waste into bone char fertilizers through pyrolysis could make human P usage more sustainable and affordable. Animal bone is rich in calcium phosphates (CaP), but many of its uses are banned due to the risk of Bovine Spongiform Encephalopathy (BSE). Charring bone could overcome this problem through heat sterilization. Bone char has been used as P fertilizer for centuries; however, little is known about how pyrolysis production conditions influence the chemical P characteristics of bone fertilizers. Applying organic matter in form of biomass or biochar as strategy to enhance P availability and reduce P adsorption to mineral oxides also warrants further investigation. Moreover, few studies address soil management and plant foraging strategies to improve P accumulation simultaneously and little is known about how plants with different rooting strategies obtain access to P sources with varying solubility. The study discussed in the first chapter of this thesis used X-ray Absorption Near-Edge Structure (XANES) spectroscopy and wet-chemistry extractions to determine (1) how pyrolysis temperature and biomass additions influence P chemistry in bone char and (2) how CaP crystallinity affects the fertilizer potential of bone char. The second chapter discusses an abiotic incubation and pot trial with maize (Zea mays L., variety B73) designed with the objectives (1) to test the P fertilizer characteristics of bone char in comparison to TSP fertilizer in a P-fixing soil, (2) to determine the effect of co-pyrolyzed biochar on P availability, and (3) to analyze how maize roots with varying soil exploration capacity access different P sources. Olsen-extractions and anion-exchange resins (AER) were used to determine P availability in incubated soils. Maize mutants without root hairs and arbuscular mycorrhizae (AM, Glomus clarum, strain WV235) inoculants were used to alter the soil exploration capacity of maize. Morphological characteristics of roots were quantified after scanning using the software package WinRHIZO Pro 2007d. Results show that increasing pyrolysis temperature enhances CaP crystal formation. Copyrolysis with biomass reduces CaP crystallization. Higher CaP crystallinity is associated with lower water-soluble P and higher formic acid-extractable P. Charring bone at 350°C results in a 67% increase in resin-P when incubated in a P-fixing soil. The addition of wood biochar decreases resin-P by 14-26%, while uncharred wood increases resin-P by 23%. This may indicate that pyrolysis reduces the potential of wood biomass to enhance P availability. The 1319% increase in Olsen-P from co-pyrolyzed rendered bone and wood biochar is explained by a decrease in CaP crystallinity by wood biomass during pyrolysis. When associated with AM, maize had similar access to P from rendered bone char and TSP fertilizer. Maize receiving copyrolyzed rendered bone-wood char application demonstrated lower plant P accumulation, suggesting that wood biochar may have had a negative effect on AM colonization. Future research should concentrate on optimizing the effects of biochar on P availability from bone char during pyrolysis and in soils. In addition, P availability from bone char in different soil environments should be tested.

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phosphorus; soil; bone char; biochar; maize rooting strategies; XANES; arbuscular mycorrhizae; P adsorption


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Lehmann, Christopher Johannes

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Bauerle, Taryn L.

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Soil and Crop Sciences

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M.S., Soil and Crop Sciences

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Master of Science

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dissertation or thesis

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