Recently the Faculty Council of the Faculty of Agriculture and Forestry, University of Helsinki, decided to afford the pioneering doctoral thesis of Mina Kiani the highest grade, pass with distinction. We are very happy for such a high recognition to our work!
Mina's doctoral thesis "Closing the phosphorus cycle by recycling lake sediments in agriculture" data collection work started in 2017 under the supervision of Dr. Priit Tammeorg, Dr. Olga Tammeorg, Dr. Asko Simojoki and Dr. Petri Penttinen. The work came to the grande finale on 21 April 2023 with the public defense where Professor Giancarlo Renella, University of Padua, served as the opponent. We enjoyed very much the discussions, both before, during and after the defense, with Prof. Renella sharing his insights to (history of) soil science but also with his latest experiences with biochars and sediments in Italy.
In this work, Dr. Mina Kiani found a sustainable solution for closing the leaking agricultural #phosphorus (P) cycle by #recycling P-rich lake #sediments back to the agriculture. It is globally the first study covering the effects of lake sediment recycling both to lake and to the plants on the shore of the lake over four-year field experiment. What is more, first time ever also the environmental aspects of recycling lake sediments to agriculture were reported over several years.
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| Mina Kiani's doctoral theis was graded with Pass with distinction |
We learned that the sediment-based growing media sustained grass biomass yield in the field condition, even though yield enhancement in field experiment was less obvious compared with our previous lysimeter experiment. Sediment from Lake Mustijärv was rich in organic matter and was a good source of several essential nutrients, including P, in plant-available form. In addition to P, the sediment had high solubility of essential plant nutrients including sulfur (S), calcium (Ca), magnesium (Mg), boron (B), zinc (Zn), and a fair supply of copper (Cu). Also, the sediment continuously provided a moderate supply of N to the plants over the four-year field experiment, which was likely due to mineralization of the organic reserves of the sediment.
Considering the environmental impacts, the sediment-based growing media had higher carbon dioxide (CO2) emissions yet broadly similar nitrous oxide (N2O) emissions compared with the soil surrounding the lake. Also, applying a thick layer of excavated sediment (~2000 t ha−1) increased the risk of P and mineral N leaching. The application of biochar increased the amount of N taken up by the plants but did not significantly reduce emissions or leaching.
In addition, sediment-based growing media had different bacterial and fungal community compositions compared with soil. This could result in different mineralization pathways in soil and sediment-based treatments. The bacterial phyla associated with solubilizing P, including Proteobacteria and Chloroflexi, were more abundant in the sediment material than in Soil. This is while the relative abundances of Actinobacteria and Planctomycetes, with the potential to accumulate bioavailable P fractions, were higher in Soil.
We wish Mina all the best for her career in science and beyond, currently she works for the Natural Resources Institute Finland and continues the ongoing work in AgriChar group as a visiting post-doctoral researcher.
