| Biochar is carbon rich byproduct of biomass pyrolysis in an oxygen-depleted environment. It is also regard as a low-risk and low-cost method of soil carbon sequestration. Climate change is one of the major challenge to human beings. One of climate change's consequences is extreme hydrological processes, such as prolonged drought and frequent wet-dry cycles. We conducted experimental researches focused on the impact of biochar application in agricultural soil on soil water, environmental behavior of agricultural chemicals, soil organic matter dynamics, soil microbial community and soil water-stable aggregates in the context of climate change. The connections between the impact of biochar with biochar characteristics, soil characteristics, soil microbial community and climate conditions were also investigated in this research.Soil water retention characteristics are critical to both crops and microbes in soil. We investigated the impact of biochar on water holding capacity of two kinds of agricultural soil using pressure plate. The impact of biochar kind, biochar dose and biochar particle diameter were also investigated. Our results indicated that high surface area biochar can increase field capacity of sandy soil, while low surface area biochar had no significant impact. Both biochars had no impact on field capacity of high clay content soil. Biochar with higher particle diameter can increase field capacity more than smaller particles. High surface area biochar didn't impact soil wilting point. Thus, it can increase plant available water in soil by only increase field capacity.To better understand the water distribution in biochar amended soil during drying processes, we applied neutron imaging method in our research to investigate moisture content inside biochar and in the material around biochar particle. Our results indicated that biochar can hold more water than surrounding material. Biochar can release water to the surrounding material during the drying processes. Biochar moisture content always higher than surrounding material. Generally, the moisture distribution in the viii biochar amended sample was inside biochar > biochar surface > surrounding material. The impact area of biochar can reduce over time since the moisture content of biochar reduced over time.In this research, the impact of biochar on agricultural chemicals was also investigated. Five biochars(Enhanced Biochar, Hog Waste, Turkey Litter, Walnut Shell and Wood Feedstock) and an agricultural soil(Yolo silt loam) were used in this research. The sorption behavior of three widely used phenylurea herbicides(monuron, diuron and linuron) on biochar and soil were investigated using a batch equilibration method. Sorption isotherms of herbicides to biochars were well described by the Freundlich model(R2=0.93-0.97). The adsorption KF values widely ranged(6.94-1306.95 mg kg-1) and indicated that the sorption of herbicides to biochars and Yolo soil was in the sequence of linuron > diuron > monuron and walnut shell biochar > wood feedstock biochar > turkey litter biochar > enhanced biochar > hog waste biochar > Yolo soil. The results indicated that the sorption of herbicides to biochar can have both positive(reduced off-site transport) and negative(reduced herbicide efficacy) impacts. Specific biochar properties such as H/C ratio and surface area can be used to consider together with soil properties, climate characteristics in biochar applications to achieve both environmental and agricultural benefits.Soil water extractable organic carbon(WEOM) is a small portion of soil organic matter, however soil water extractable organic carbon can be highly involved in many microbial activities. We investigate the interrelationships among soil moisture history, biochar and biosolid amendment on WEOM in California agricultural soil. A soil incubation experiment was carried out for 52 weeks with three soil moisture treatments: simulated wet, dry, and wet-dry cycles, three biochar amendment treatments of 0, 0.5, 1% biochar(w:w) and two biosolid amendment treatments of 0, 0.5% biosolid(w:w) under each of the soil moisture treatments. Biochar and biosolid amendments increased the amount of WEOM, as did dry and wet-dry cycle treatments. Specific Ultraviolet Absorption and carbon stable isotope analysis indicated that, on a per unit basis, biochar can release more WEOM than soil(up to 4.61 times), and biochar amendment can increase WEOM from agricultural soil(52.88 to 87.86%). In the extreme soil moisture treatments, biochar can enhance WEOM release increase due to water treatments, which can benefit soil microbial communities, but also increase the risk of SOM loss. This impact of biochar on SOM mobility needs to be considered in biochar soil amendment and deserves further research.ix Microbial activities are highly involved in nutrient cycling processes, including greenhouse gas emissions. To understand the responses of microbial community to biochar and biosolid amendments in the context of different soil moisture conditions and mechanism behind, we conducted a 12-week incubation experiment to look at microbial community response to different level of biochar(0, 0.5, 1%) and biosolid amendment(0, 0.5%) under different soil moisture condition(wet, dry, or wet-dry cycles). Our results indicated that drought and wet-dry cycles can strongly influence soil microbial community. The microbial community can response faster than total microbial biomass to environmental stress. Gram-positive to gram-negative bacteria ratio can be an effective index to characterize soil moisture stress in short term. Biochar can have both positive and negative impact on microbial community depend on biochar dose and soil nutrient condition. Soil nutrient amendment can help diminish negative impact of extreme soil moisture conditions on microbial communities.Soil water-stable aggregates is critical to soil organic matter dynamics, soil water conductivity and plant root development. Soil microbial activity can play an important role in soil aggregate formation. We conducted both field study(2 years) and lab incubation experiment(12 months) to investigate the impact of biochar amendment on soil aggregation, microbial community and their interactions. The field study with 0, 0.5% walnut shell biochar amendment and mineral fertilizer or compost management was conducted. There is no significant difference observed between biochar treatments since soil aggregation can be also impact by crop and climate conditions. In the lab incubation experiment, we investigated the impact of biochar amendment on soil chemical properties, microbial communities and soil aggregation within two California agricultural soils under laboratory conditions. Our results indicated that both biochars can influence soil p H, EC and soil organic carbon composition. Biochar can impact soil aggregation and soil microbial community through multiple mechanisms. Both biochars can increase soil water-stable aggregates in Yolo soil, while most biochar treatments didn't impact aggregations in Vina soil. Uncarbonized organic residue in biochar can be additional carbon source to microbial community and increase soil microbial biomass. The aromatic carbon in biochar can influence the capacity of microbes to metablize aromatic carbon. Simultaneously, biochar carbon can also increase the overall aromaticity of soil organic matter to influence soil aggregation. Our results indicated that, biochar can improve the physical protection of soil organic matter by improving soil aggregation. This impact can benefit the carbon sequestration effect of biochar itself.In the application of biochar to agriculture soil, soil and biochar properties need to be considered in regard to agricultural management proposes. As a long term strategy, it's important to consider the impact of biochar on soil water characteristics, soil structure, soil organic matter and soil microbial community in the context of extreme climate conditions to maximize environmental and agricultural benefits of using biochar. |
PDF Full Text Request