@misc{GypserSchuetzeFreese, author = {Gypser, Stella and Sch{\"u}tze, Elisabeth and Freese, Dirk}, title = {Single and binary Fe- and Al-hydroxides affect potential phosphorus mobilization and transfer from pools of different availability}, series = {Soil Systems}, volume = {5}, journal = {Soil Systems}, number = {2}, doi = {10.3390/soilsystems5020033}, pages = {1 -- 21}, abstract = {Phosphorus (P) fixation is a global problem for soil fertility and negatively impacts agricultural productivity. This study characterizes P desorption of already fixed P by using KCl, KNO3, histidine, and malic acid as inorganic and organic compounds, which are quite common in soil. Goethite, gibbsite, and ferrihydrite, as well as hydroxide mixtures with varying Fe- and Al-ratio were selected as model substances of crystalline and amorphous Fe- and Al-hydroxides. Especially twoand multi-component hydroxide systems are common in soils, but they have barely been included in desorption studies. Goethite showed the highest desorption in the range from 70.4 to 81.0\%, followed by gibbsite with values in the range from 50.7 to 42.6\%. Ferrihydrite had distinctive lower desorption in the range from 11.8 to 1.9\%. Within the group of the amorphous Fe-Al-hydroxide mixtures, P desorption was lowest at the balanced mixture ratio for 1 Fe: 1 Al, increased either with increasing Fe or Al amount. Precipitation and steric effects were concluded to be important influencing factors. More P was released by crystalline Fe-hydroxides, and Al-hydroxides of varying crystallinity, but desorption using histidine and malic acid did not substantially influence P desorption compared to inorganic constituents.}, language = {en} } @misc{SchuetzeGypserFreese, author = {Sch{\"u}tze, Elisabeth and Gypser, Stella and Freese, Dirk}, title = {Kinetics of phosphorus release from vivianite, hydroxyapatite, and bone char influenced by organic and inorganic compounds}, series = {Soil Systems}, volume = {4}, journal = {Soil Systems}, number = {1}, issn = {2571-8789}, doi = {10.3390/soilsystems4010015}, pages = {1 -- 20}, abstract = {The availability of P is often insuffcient and limited by accumulation in soils. This led to the necessity of solutions for the recovery as well as recycling of secondary P resources. Batch experiments were conducted with CaCl2 and citric acid to characterize P release kinetics from vivianite, hydroxyapatite, and bone char. While the P release during the CaCl2 treatment was so low that only vivianite and hydroxyapatite showed a slightly higher release with increasing CaCl2 concentration, the increase of dissolved P was more pronounced for citric acid. The application of citric acid resulted in a 32,190-fold higher P release for bone char. Fourier-transform infrared spectroscopic data suggested higher instability of hydroxyapatite than for bone char. The kinetic data showed that bone char, especially at a lower particle size, had a higher long-term P release than hydroxyapatite or vivianite. The suitability of hydroxyapatite and bone char as a poorly soluble, but sustainable P source is better than that of vivianite. However, the efficiency as a P fertilizer is also dependent on present soil P mobilization processes. The results underline the importance of the accessibility of fertilized or naturally bound P for plant roots to benefit from the excretion of organic acids.}, language = {en} } @misc{DimitrovaRepmannFreese, author = {Dimitrova, Tsvetelina and Repmann, Frank and Freese, Dirk}, title = {Degradation of ferrocyanide by natural isolated bacteria}, series = {International Journal of Phytoremediation}, volume = {Vol. 22}, journal = {International Journal of Phytoremediation}, number = {1}, issn = {1522-6514}, doi = {doi:10.1080/15226514.2019.1633996}, pages = {20 -- 28}, abstract = {This study aims at investigating the iron cyanide (CN) degradation potential of two natural bacterial isolates with the purpose of their application in iron CN phytoremediation. The strains were isolated from contaminated soil and incubated over 4 months with 50 mg L-1 CN (as ferrocyanide) as the sole iron and nitrogen source. Unlike previous reports, the study provides control for bacterial growth, biotic and abiotic CN losses. Bacterial growth, CN, ammonium, and nitrate concentrations were monitored regularly. Both strains grew less rapid with iron CN compared with the positive control. However, the growth was diauxic. The CN concentration in the media decreased with 20\% and 25\% respectively, while that in the sterile controls remained stable. Ammonium was detected in the media of both strains implying that a fraction of the initially applied ferrocyanide has been converted. The nitrogen lost from the system evened out with that in the cells at the end of the experiments. These results showed that the investigated strains were undoubtedly able to grow on iron CN as an alternative nitrogen source, but contrary to some previous findings, the iron CN utilization is much slower and takes place only after complete exhaustion of the cellular nitrogen reserves.}, language = {en} }