We're really proud for the success of our group member, Subin, who has completed doctoral studies and defended his doctoral thesis on 2 September 2022. The discussions with the opponent Professor Claudia Kammann were excellent (as was inspiring her talk on 1 September)!
Subin has been working with us since 2017, and has been extremely hardworking and smart on finding the mechanisms behind biochar-soil nutrients interactions. His first paper investigated plant growth response to biochar addition. Over the 8 years in two soils, biochars increased plant growth in only 2 cases when the previous growing seasons were planted with legumes. For more details, please see:
Kalu,
S., Simojoki, A., Karhu, K., & Tammeorg, P. (2021). Long-term
effects of softwood biochar on soil physicalproperties, greenhouse gas
emissions and crop nutrient uptake in twocontrasting boreal soils. Agriculture,
Ecosystems & Environment. 316: 107454.
Second paper showed that biochars increased the loss of ammonium ions and increased the retention of nitrate ions in the soil whereas increased the plant availability of N derived through mineralization of soil organic nitrogen. See:
Kalu, S., Oyekoya, G. N., Ambus, P.,
Tammeorg, P., Simojoki, A., Pihlatie, M., & Karhu, K. (2021).
Effects of two wood-based biochars on the fate of added fertilizer nitrogen—a 15 N tracing study. Biology and Fertility of Soils, 57, 457-470.
His third paper, biochars' abilities to reduce nitrogen leaching were tested in clayey soil. Out of two biochars, the one with the large surface area reduced the leaching of nitrate. See more:
Karhu, K., Kalu, S., Seppänen, A.,
Kitzler, B., & Virtanen, E. (2021). Potential of biochar soil amendments to reduce N leaching in boreal field conditions estimated using the resin bag method. Agriculture, Ecosystems & Environment, 316, 107452.
And in his fourth paper (actually just three are required for doctoral degree, so exceptional achievement) found that biochars increased crop yield even after seven years of application in sandy soil. Biochars can decrease N2O emissions mostly during the peak emission period.
See: Kalu, S., Kulmala, L., Zrim, J.,
Peltokangas, K., Tammeorg, P., Rasa, K., ... & Karhu, K. (2022).
Potential
of biochar to reduce greenhouse gas emissions and increase nitrogen use
efficiency in boreal arable soils in the long-term. Frontiers in Environmental Science. https://doi.org/10.3389/fenvs.2022.914766
And of course, the latest biochar doctoral thesis can be found here helda.helsinki.fi/handle/10138/3.
Update: on 18 Oct 2022, the Faculty Council confirmed the grade as "accepted with distiction"!
Well done, Subin, the doctoral sword is well deserved!
