Effect Of Giant Reed Derived Biochar On Agricultural Soil Environment

Biochar, the carbon-rich product from heating biomass in a closed system underlimited oxygen supply, which is distinguished from charcoal by its use as a soilamendment and carbon sequestration, has generated great interest for scientists andpolicy makers. Less attention has been paid on the nutrient properties of biochars, theeffects of biochar on nitrogen （N） leaching and N₂O emissions from agricultural soils,and the antibiotics fates in soils, which are of importance for sustainable soilproductivity. Therefore, biochars produced from giant reed at different temperatureswere characterized and used to investigate their influence on these processes in anspecifi agricultural soil. The main results of this thesis are as following:（1） To investigate the effect of pyrolysis temperature on basic properties,biochars were produced from giant reed at300-600°C and characterized for theirphysical and chemical properties. With increasing temperatures, C content increased,while H and O content decreased. Ash content and pH aslo increased, whereas totalsurface acidic functional groups decreased.（2） Application of biochars to soils is suggested as an effective way forimproving soil quality. To investigate the effect of pyrolysis temperature on nutrientsvalue and release of N, P and K. With increasing temperatures, more N was lost andresidual N was transformed to heterocyclic nitrogen, whereas no P and K losses wereobserved. P was transformed less soluble minerals, resulting in available-P reductionfor high-temperature biochars. More NH₄⁺, PO₄^3-and K were released in water fromall the biochars at low pH （≤5）. These results indicate that pyrolysis atlow-temperatures may be optimal for producing biochar from giant reed to improvethe nutrient availability more suitably in acidic soils exhibiting N, P and/or Kdeficiency.（3） Adsorption of NH₄⁺, NO₃^-and PO₄^3-on biochars was also studied.Low-temperature biochars （≤400°C） showed appreciable NH₄⁺adsorption, whilehigh-temperature biochars （≥500°C） had limited sorption capacity for NO₃^-. No PO₄^3-could be adsorpbed by all the biochars.（4） Interest in the use of biochar from pyrolysis of biomass to improve soilproductivity has increased. N loss, retention and bioavailability in thebiochar-amended soils added with NH₄⁺-N and NO₃^--N fertilizers were studied.NO₃^--N leaching from the soils treated with NH₄⁺-N and NO₃^--N was significantlyreduced by biochar addition. NH₄⁺-N leaching from the NO₃^--N treated soil was alsosignificantly reduced by adding biochar, while no significant effect was observed forthe NH₄⁺-N treated soil. Greater reduction of NH₄⁺-N and NO₃^--N leaching from theNO₃^--N treated soil was obtained in the system of plant-biochar-soil. The mitigationof N leaching loss by biochar addition is mainly attributed to the increase of soil waterholding capacity （WHC）, NH₄⁺adsorption and enhanced N immobilization. Thebiochar addition stimulated the maize growth, including the increase of biomass andthe parameters of root morphology. The results showed that biochar additionincreased the the NUE （N utilization efficiency） maize but decreased NAE （Naccumulation efficiency）, indicating that biochar addition may improve Nbioavailability in agricultural soils. Therefore, reduction of N leaching, and increaseof N retention and bioavailability in agricultural soils could decrease the N fertilizerdemand for crop growth.（5） Extensive use of biochar to mitigate N₂O emission is limited by the lack ofunderstanding on the exact mechanisms altering N₂O emissions frombiochar-amended soils. Biochars （200-600°C） produced from giant reed werecharacterized and used to investigate their influence on N₂O emission from soil.Responses of N₂O emission varied with pyrolysis temperature, and the reductionorder of N₂O emission by biochar was: BC200≈BC600> BC500≈BC300≈BC350>BC400. The reduced emission was attributed to decreased denitrification in thebiochar-amended soils. The remaining PAHs in low-temperature biochars（300-400°C） played a major role in reducing N₂O emission, but not forhigh-temperature biochars （500-600°C）. Removal of phenolic compounds fromlow-temperature （200-400°C） biochars resulted in a surprising reduction of N₂Oemission, but the mechanism is still unknown. Overall, adding giant reed biochars could reduce N₂O evolution from agricultural soil, thus possibly mitigating globalwarming.（6） Sorption of sulfonamides antibiotics by biochars is poorly understood.Sorption of sulfamethoxazole （SMX） on biochars produced at300-600°C wasconducted as a function of concentration and pH, as well as the mineral fraction inbiochars. The sorption of neutral SMX on all the biochars was nonlinearity because ofthe dominant adsorption via hydrophobic interaction, π-π EDA interaction andpore-filling, not the conventional transition from partitioning-dominant at lowpyrolytic temperatures to adsorption-dominant at higher pyrolytic temperatures.Mineral fractions in the biochars showed different contribution to the total sorption,depending on the pyrolytic temperature. Minerals in the low-temperature biochars（e.g.,300°C） significantly enhanced SMX sorption, whereas decreased the sorptionin the high-temperature biochars （e.g.,600°C）, which could result from the differentforms and distribution of minerals in the biochars. Moreover, SMX sorption onbiochars was pH-dependent, reaching the highest sorption at about pH4.0. Below pH6, where neutral SMX was dominant, while the sorption of anion SMX increased andgradually dominant at pH>6possibly via a negative charge-assisted H-bond. Thisresult emphasized the importance of identifying the dominant mechanisms, speciesand the contribution of minerals in biochars for antibiotics sorption.