Investigating the effect of biochar on microbial properties in the soil

Soil amendment with biochar has been widely described as a suitable approach to improve soil fertility, sequester carbon and reduce greenhouse gas (GHG) emissions to mitigate climate change. The purported benefits of biochar addition to soils include improved soil physical properties and nutrient retention as well as changes in microbial composition and abundance which in turn affect nutrient cycling in the biochar amended soils. However, the impacts of different types of biochar on biological properties of soil have received less attention and need to be explored. The aim of this thesis was to investigate the impact of biochar application on biological properties of soil. This thesis focuses on understanding the behaviour of soil microbes in relation to soil biological processes that occur following biochar application and attempts to assess the relationship between soil microbes and the chemical properties that are altered in soil matrices after biochar application. Four (4) different agricultural residues (vine pruning residue, tomatoes residue, clove residue and banana plantation residue) pyrolyzed at two different temperature (300 and 500 OC) to obtained biochars were used to conduct this experiment. The biochar types or treatments were identified according to the final temperature as Vinyard biochar-300 oC (BB300), Vinyard biochar-500 oC (BB500), Tomato biochar-300 oC (DB300), Tomato biochar-500 oC (DB500), Clove biochar-300 oC (KB300), Clove biochar-500 oC (KB500), Banana biochar-300 oC (MB300) ve Banana biochar-500 oC (MB500). A greenhouse pot experiments with lettuce (lactuca sativa crispa) as a test crop was conducted for two growing periods within the year 2019. The experimental design consisted of a randomized complete block design with five replications and 9 treatments. The trial consisted of a total of 45 pots (4 agricultural waste × 2 pyrolysis temperature × 5 replications) + 5 controls). Initial soil properties were determined before the establishment of the experiment. In the greenhouse, bulk soil samples were taken during plant growth stages at a normal interval (0, 2nd, 4th, 6th and 8th week) and were analyzed for biological parameters (urease, alkaline phosphatase, β-glycosidase, dehydrogenase, nitrification, denitrification activities and a number of bacteria) while the rhizosphere soil was sampled at harvest for a similar purpose. Furthermore, soil samples were taken at the end of each experiment for chemical analysis (macro-micro nutrient). Quality parameters and yield measurements of lettuce were carried out after the harvest. Biochar addition increased soil chemical properties (i.e. pH, EC, organic C, available P and K) in both seasons and decreased total N content of the soil. Biochar additions affected the microbial properties in soil depending on the type of biochar and growing period applied. Generally, enzyme activities under Clove (KB500) and Banana (MB300 and MB500) biochar treatments were observed to be higher in the bulk soil than other treatments in the first growing period. However, biochar applications had no impact on enzyme activities in the second growing period. Similarly, mesophilic aerobic bacteria count in the soil was not affected by biochar additions in both growing periods. Furthermore, strong positive correlations were observed in chemical properties and microbial properties in both growing periods. Generally, soil pH, EC and biological properties significantly increased in the rhizosphere after biochar additions. The application of Tomato (DB300) and Banana (MB500) biochars increased plant height by 15.2% and 10.2% respectively in the second growing period. Other quality parameters and yield were unaffected by biochar additions in both growing periods. These results remark how biochars have different interactions with soil, depending on their intrinsic physical-chemical characteristics. Also, this thesis emphasizes the importance of future work focused on formulating guidelines to biochar applications to the soil.