Date of Award

Spring 5-5-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

Ling Li

Second Committee Member

Yongjiang Zhang

Third Committee Member

Jay Wason

Additional Committee Members

Yingchao Yang

Abstract

Maine wild (or lowbush) blueberries (Vaccinium angustifolium Ait.) continue to face challenges imposed by climate change. Reduced frequency of precipitation and increased drought conditions have negatively impacted this crop since it resides in sandy soils with limited retention of water and nutrients. The wild blueberry plants growing in water- and nutrient-poor sandy soils are likely to have poor resilience to drought, resulting in a decline in berry yield during drought years. Thus, there is an urgent need to find a drought management solution for wild blueberries. Compared with other drought management practices, such as irrigation systems, mulching, and adopting drought-resistant varieties, maximizing the water-holding capacity using biochar is a promising solution due to its other benefits, like providing nutrients, immobilizing heavy metals, and increasing carbon storage. Numerous studies revealed that the effects of biochar additions on the improvement of the water retention capacity of sandy soils are significantly greater than other soil types, such as clay soils. Currently, in Maine, biochar can be produced as a byproduct of bioenergy in a medium-sized forest biomass Combine Heat and Power (CHP) plant with a production capacity of approximately 1,000 tons of biochar per year going to the landfill. Using the locally available biochar to amend the sandy soil in the wild blueberry fields might be a cost-effective approach. However, the physical properties of this biochar, and its influence on soil texture, soil pH, and wild blueberry physiology need to be addressed. This study aimed to characterize the biochar recycled from the local CHP plant, test biochar pH modification effectiveness for use in the wild blueberry fields, and investigate the role of biochar in improving the resistance of wild blueberries to drought in terms of physiological performance. First, biochar physical and chemical characterization was conducted in the laboratory. Other biochar materials made of similar feedstocks showed comparable qualities to our biochar. Then the biochar was modified using an acid treatment method (acetic acid and citric acid with 1% to 3% concentrations) to reduce pH from 11.4 to 6.0, aiming to maintain an acidic soil pH for wild blueberries when used in the fields. We also quantified the water holding capacity of sandy soils (S) amended with untreated biochar (B) at four ratios of 100S:0B (control), 50S:50B, 30S:70B, 10S:90B without fertilizer (Type I) and with fertilizer (Type II). Based on the analysis results and economic consideration, we determined the 50S:50B mixing ratio of sandy soils and biochar to be used in the controlled drought experiments in the greenhouse. Untreated biochar and pH-modified biochar were applied to wild blueberry soils in 2021 and 2022, respectively. The results showed that adding biochar to the sandy soils aided the wild blueberry plants by delaying the onset of soil water deficits and leaf water stress in wild blueberries in the later summer drought in 2021. The midday leaf water potential (ψleaf), stomatal (gs) conductance, and photosynthetic electron transport rate (ETR) of plants in biochar treated soils declined slower compared to those in soils without biochar. However, in the early summer drought accompanied by unexpected heatwaves in 2022, there was limited effect of biochar applications in plant drought response. Plants in biochar treated soils (BA soils) did not show a significant delay in the decline in ψleaf compared with those in soils without biochar (NA soils), but BA soils aided in maintaining leaf chlorophyll concentrations after the heatwave. pH- adjusted biochar was applied to the soil in 2022 and was able to maintain a pH of 5.7, which was lower than the soil pH of 6.3 when untreated biochar was used in 2021. From this study, we concluded that 1) the biochar produced from the local CHP plant shows potential to be used as a soil amendment in wild blueberry fields; 2) as drought conditions continue to intensify and impact wild blueberries, amending proper biochar to sandy soils would be an effective method to mitigate the effect of rainfall shortages or climate drought.

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