Browsing by Author "Liu, Zuolin"

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    Biochar particle size, shape, and porosity act together to influence soil water properties
    (Public Library of Science, 2017) Liu, Zuolin; Dugan, Brandon; Masiello, Caroline A.; Gonnermann, Helge M.
    Many studies report that, under some circumstances, amending soil with biochar can improve field capacity and plant-available water. However, little is known about the mechanisms that control these improvements, making it challenging to predict when biochar will improve soil water properties. To develop a conceptual model explaining biochar’s effects on soil hydrologic processes, we conducted a series of well constrained laboratory experiments using a sand matrix to test the effects of biochar particle size and porosity on soil water retention curves. We showed that biochar particle size affects soil water storage through changing pore space between particles (interpores) and by adding pores that are part of the biochar (intrapores). We used these experimental results to better understand how biochar intrapores and biochar particle shape control the observed changes in water retention when capillary pressure is the main component of soil water potential. We propose that biochar’s intrapores increase water content of biochar-sand mixtures when soils are drier. When biochar-sand mixtures are wetter, biochar particles’ elongated shape disrupts the packing of grains in the sandy matrix, increasing the volume between grains (interpores) available for water storage. These results imply that biochars with a high intraporosity and irregular shapes will most effectively increase water storage in coarse soils.
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    Biochar-Induced Changes in Soil Hydraulic Conductivity and Dissolved Nutrient Fluxes Constrained by Laboratory Experiments
    (Public Library of Science, 2014) Barnes, Rebecca T.; Gallagher, Morgan E.; Masiello, Caroline A.; Liu, Zuolin; Dugan, Brandon
    The addition of charcoal (or biochar) to soil has significant carbon sequestration and agronomic potential, making it important to determine how this potentially large anthropogenic carbon influx will alter ecosystem functions. We used column experiments to quantify how hydrologic and nutrient-retention characteristics of three soil materials differed with biochar amendment. We compared three homogeneous soil materials (sand, organic-rich topsoil, and clay-rich Hapludert) to provide a basic understanding of biochar-soil-water interactions. On average, biochar amendment decreased saturated hydraulic conductivity (K) by 92% in sand and 67% in organic soil, but increased K by 328% in clay-rich soil. The change in K for sand was not predicted by the accompanying physical changes to the soil mixture; the sand-biochar mixture was less dense and more porous than sand without biochar. We propose two hydrologic pathways that are potential drivers for this behavior: one through the interstitial biochar-sand space and a second through pores within the biochar grains themselves. This second pathway adds to the porosity of the soil mixture; however, it likely does not add to the effective soil K due to its tortuosity and smaller pore size. Therefore, the addition of biochar can increase or decrease soil drainage, and suggests that any potential improvement of water delivery to plants is dependent on soil type, biochar amendment rate, and biochar properties. Changes in dissolved carbon (C) and nitrogen (N) fluxes also differed; with biochar increasing the C flux from organic-poor sand, decreasing it from organic-rich soils, and retaining small amounts of soil-derived N. The aromaticity of C lost from sand and clay increased, suggesting lost C was biochar-derived; though the loss accounts for only 0.05% of added biochar-C. Thus, the direction and magnitude of hydraulic, C, and N changes associated with biochar amendments are soil type (composition and particle size) dependent.
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    Effect of freeze-thaw cycling on grain size of biochar
    (Public Library of Science, 2018) Liu, Zuolin; Dugan, Brandon; Masiello, Caroline A.; Wahab, Leila M.; Gonnermann, Helge M.; Nittrouer, Jeffrey A.
    Biochar may improve soil hydrology by altering soil porosity, density, hydraulic conductivity, and water-holding capacity. These properties are associated with the grain size distributions of both soil and biochar, and therefore may change as biochar weathers. Here we report how freeze-thaw (F-T) cycling impacts the grain size of pine, mesquite, miscanthus, and sewage waste biochars under two drainage conditions: undrained (all biochars) and a gravity-drained experiment (mesquite biochar only). In the undrained experiment plant biochars showed a decrease in median grain size and a change in grain-size distribution consistent with the flaking off of thin layers from the biochar surface. Biochar grain size distribution changed from unimodal to bimodal, with lower peaks and wider distributions. For plant biochars the median grain size decreased by up to 45.8% and the grain aspect ratio increased by up to 22.4% after 20 F-T cycles. F-T cycling did not change the grain size or aspect ratio of sewage waste biochar. We also observed changes in the skeletal density of biochars (maximum increase of 1.3%), envelope density (maximum decrease of 12.2%), and intraporosity (porosity inside particles, maximum increase of 3.2%). In the drained experiment, mesquite biochar exhibited a decrease of median grain size (up to 4.2%) and no change of aspect ratio after 10 F-T cycles. We also document a positive relationship between grain size decrease and initial water content, suggesting that, biochar properties that increase water content, like high intraporosity and pore connectivity large intrapores, and hydrophilicity, combined with undrained conditions and frequent F-T cycles may increase biochar breakdown. The observed changes in biochar particle size and shape can be expected to alter hydrologic properties, and thus may impact both plant growth and the hydrologic cycle.
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    Impacts of biochar concentration and particle size on hydraulic conductivity and DOC leaching of biochar-sand mixtures
    (Elsevier, 2016) Liu, Zuolin; Dugan, Brandon; Masiello, Caroline A.; Barnes, Rebecca T.; Gallagher, Morgan E.; Gonnermann, Helge
    The amendment of soil with biochar can sequester carbon and alter hydrologic properties by changing physical and chemical characteristics of soil. To understand the effect of biochar amendment on soil hydrology, we measured the hydraulic conductivity (K) of biochar–sand mixtures as well as dissolved organic carbon (DOC) in leachate. Specifically, we assessed the effects of biochar concentration and particle size on K and amount of DOC in the soil leachate. To better understand how physical properties influenced K, we also measured the skeletal density of biochars and sand, and the bulk density, the water saturation, and the porosity of biochar–sand mixtures. Our model soil was sand (0.251–0.853 mm) with biochar rates from 2 to 10 wt% (g biochar/g total soil × 100%). As biochar (<0.853 mm) concentration increased from 0 to 10 wt%, K decreased by 72 ± 3%. When biochar particle size was equal to, greater than, and less than particle size of sand, we found that biochar in different particle sizes have different effects on K. For a 2 wt% biochar rate, K decreased by 72 ± 2% when biochar particles were finer than sand particles, and decreased by 15 ± 2% when biochar particles were coarser than sand particles. When biochar and sand particle size were comparable, we observed no significant effect on K. We propose that the decrease of K through the addition of fine biochar was because finer biochar particles filled spaces between sand particles, which increased tortuosity and reduced pore throat size of the mixture. The decrease of K associated with coarser biochar was caused by the bimodal particle size distribution, resulting in more compact packing and increased tortuosity. The loss of biochar C as DOC was related to both biochar rate and particle size. The cumulative DOC loss was 1350% higher from 10 wt% biochar compared to pure sand. This large increase reflected the very small DOC yield from pure sand. In addition, DOC in the leachate decreased as biochar particle size increased. For all treatments, the fraction of carbon lost as DOC ranged from 0.06 to 0.18 wt% of biochar. These experiments suggest that mixing sandy soils with biochar is likely to reduce infiltration rates, holding water near the surface longer with little loss of biochar-derived carbon to groundwater and streams.
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    Interactions between Biochar, Soil, and Water
    (2016-09-08) Liu, Zuolin; Dugan, Brandon; Masiello, Caroline A
    Biochar has been proposed as an approach for carbon sequestration and soil amendment. Biochar impacts soil carbon cycling, and in addition, the interaction between biochar and soil water can affect the soil hydrologic cycle as well as plant growth. For instance, after being applied into soil, biochar releases dissolved organic carbon (DOC) through leachate into ground water. This may influence the global carbon cycle. In addition, Biochar’s grain size and shape evolve due to natural processes which will then have feedback on the hydrologic properties of soil. Therefore, it is important to understand the effect of biochar on soil hydrologic properties as well as how the properties of biochar change in soil. Through laboratory experiments and numerical modeling, I investigated the effect of biochar on soil hydraulic conductivity and soil water retention. Meanwhile, I studied change of biochar in soil. For example, I measured DOC as a way of biochar carbon transport in the leachate of biochar-sand mixtures. Also, I tested how biochar’s grain size was altered by freeze and thaw cycling. Coupled with the mechanisms driving these changes, we can better understand the effect of biochar amendment to soil on our living environment. My results show that biochar’s effect on soil hydraulic conductivity (K), soil water retention, and DOC release vary with biochar grain size. Fine mesquite biochar changed K the most (72 ± 2% decrease), medium mesquite biochar did not cause significant change of K, and coarse mesquite biochar decreased K decreased by 15 ± 2%. Hydraulic conductivity also decreased with biochar concentration increase, by up to 72 ± 3% from 0-10 wt% mesquite biochar addition. Fine mesquite biochar did not affect plant available water significantly. The addition of medium and coarse mesquite biochar, however, increased plant available water by 75% and 125%, respectively. DOC in the leachate decreased as mesquite biochar particle size increased. The fraction of carbon lost as DOC ranged from 0.06 to 0.18 wt% of mesquite biochar. I propose that the decrease of K through the addition of fine biochar was because finer biochar particles filled spaces between sand particles which increased tortuosity and reduced pore throat size of the mixture. The decrease of K associated with coarser biochar was caused by the bimodal particle size distribution of biochar-sand mixture, resulting in more compact packing and increased tortuosity. The volume of pores inside biochar (intraporosity) and the shape of biochar particles control the observed changes in water retention. Intraporosity drives the increase in water retention of biochar-amended soils at more negative soil water potential values. At less negative soil water potential values, biochar particles’ elongated shape increases water retention by reducing the efficiency of particle packing, creating large gaps where water can be stored. My results show that biochar grain size plays an important role in controlling soil hydrologic properties and DOC leaching. However, the effect may not stay the same over a long term because biochar grain size can be changed by freeze and thaw cycling. The effect of freeze and thaw cycling on biochar grain size varies with biochar feedstock type. For instance, median grain diameter of pine biochar decreased by up to 28.8%, median grain diameter of miscanthus biochar decreased by up to 45.8%, and median grain diameter of mesquite biochar decreased by up to 32% from 0 to 20 freeze and thaw cycles. However, there was no significant change in grain size observed for sewage waste biochar after five freeze and thaw cycles. These results suggest that mixing sandy soils with biochar is likely to reduce infiltration rates, holding water near the surface longer, increase soil water storage with little loss of biochar-derived carbon to groundwater and streams. However, the reduction of biochar grain size by freeze and thaw cycling will drive changes in soil properties such as hydraulic conductivity and soil water retention.