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Organisationseinheit der BAM
Pot experiments are often performed to analyze the plant-availability of phosphorus (P) in P-fertilizers. However, these experiments do not determine the P compounds present in the soil which are responsible for the yield increase. In order to better understand the results of pot experiments we analyzed the soils by P K-edge X-ray absorption near-edge structure (XANES) spectroscopy to determine the P species and unravel transformation processes. We carried out pot experiments with maize testing different waste water derived recycling P-fertilizers on an acidic and a neutral soil. Soils samples before sowing and after harvest were collected and prepared for analysis. A combination of macro- and µ-XANES spectroscopy was used to determine the chemical state of the overall soil P and to identify P compounds in P-rich spots localized by micro-X-ray fluorescence (µ-XRF). P K-edge macro-XANES spectroscopy detected organic P and/or P sorbed onto organic matter or other substrates in the unfertilized and fertilized soils. In addition, µ-XRF mapping in combination with P K-edge µ-XANES spectroscopy evidenced that some P phases present in recycling P-fertilizers (magnesium phosphate and calcium sodium phosphate) react with co-fertilized ammonium nitrate and form highly plant-available ammonium phosphates in the soil. In opposite, apatites were not affected by the presence of ammonium. Thus, for a boost of the plant-availability of P in recycling P-fertilizers these fertilizers should be directly co-fertilized with nitrogen (N) sources that contain a high amount of ammonium instead of nitrate. Possibly, a specific preparation of NP-fertilizers by granulation of recycling P-fertilizers with ammonium compounds and a nitrification inhibitor could enhance the plant-availability of the produced fertilizer whereby they become more competitive to commercially available NP-fertilizers based on phosphate rock.
A wide range of methods are used to estimate the plant-availability of soil phosphorus (P). Published research has shown that the diffusive gradients in thin films (DGT) technique has a superior correlation to plant-available P in soils compared to standard chemical extraction tests. In order to identify the plant-available soil P species, we combined DGT with infrared and P K- and L-edge X-ray adsorption near-edge structure (XANES) spectroscopy. This was achieved by spectroscopically investigating the dried binding layer of DGT devices after soil deployment. All three spectroscopic methods were able to distinguish between different kinds of phosphates (poly-, trimeta-, pyro- and orthophosphate) on the DGT binding layer. However, infrared spectroscopy was most sensitive to distinguish between different types of adsorbed inorganic and organic phosphates. Additionally, also intermediates of the time-resolved hydrolysis of trimetaphosphate in soil could be analyzed. Furthermore, infrared and XANES microspectroscopy make it also possible to analyze P compounds on the binding layer with a lateral resolution down to 1 µm2. Therefore, P species of a spatial soil segment (e.g. rhizosphere) can be mapped and analyzed.
Specific co-fertilization of nutrients can enhance their plant-availability and thus the yield of plants. To investigate this effect, we performed a pot experiment with three different P-fertilizers and ammonium nitrate sulfate as a co-fertilizer, without and with a nitrification inhibitor (NI), and analyzed the form of nitrogen (N) in the soil via novel X-ray spectroscopic method. The application of NI with the N fertilizer led to a higher dry matter yield of maize. Novel N K-edge micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy identified that the application of a NI promotes the temporary formation of a non-exchangeable N in detectable hot-spots in the soil. The subsequent slow release and prolonged availability of N during plant growth leads to higher yield. It can be concluded that NIs lead to a temporary fixation of ammonium-N in a pool that can be accessed by plant roots. Those types of available nutrient pools meet the idea of so-called “next generation fertilizers” as plants have access to nutrients according to their current demand.
Thermal Treatment of Chromium (III) Oxide with Carbonates Analyzed by Far-Infrared/THz Spectroscopy
(2015)
Phosphorus (P) fertilizers from secondary resources became increasingly important in the last years. However, these novel P-fertilizer can also contain toxic pollutants e.g. chromium (Cr) in the hexavalent state (Cr(VI)), which is regulated with low limit values in agricultural products (German fertilizer ordinance limit: 2 mg/kg Cr(VI)). The determination of Cr(VI) in these novel fertilizer matrices can be hampered by redox processes that lead to false results with the standard wet chemical extraction method (German norm DIN EN 15192). Therefore, we analyzed Cr(VI) in various P-fertilizers with the DGT technique. DGT devices equipped with a APA (polyacrylamide) diffusion layer and Cr(VI) selective N-methyl-D-glucamine (NMDG) binding layer were used for the study. After a 24 h conditioning period of the fertilizer at 60% of the water holding capacity (WHC), the fertilizers were brought to 100% WHC, transferred onto the DGT devices and deployed for 24 h at 25°C. The extraction of Cr from the DGT binding layer was carried out with 1 M HNO3 for 24 h. The Cr-concentrations of the extract were determined by means of ICP-MS. We found a good correlation between the standard wet chemical extraction and the DGT method for the whole range of P-fertilizers. However, partly soluble Cr(VI) compounds cannot be detected in full extent by the DGT method that is best suited for mobile Cr(VI). Furthermore, Cr K-edge XANES spectroscopy showed that the Cr(VI)-selective DGT binding layer also adsorbs mobile Cr(III) compounds from acid treatment of phosphates which can therefore cause an overestimation of Cr(VI). The DGT method was very sensitive and in most cases selective for the analysis of Cr(VI) in P-fertilizers made from recycled materials. However, the results of certain types of P-fertilizers containing mobile Cr(III) or partly immobile Cr(VI) show that still some optimization of the method is required to avoid over- or underestimation of Cr(VI).
Phosphorus (P) resource availability is declining and the efficiency of applied nutrients in agricultural soils is becoming increasingly important. This is especially true for P-fertilizers from recycled materials which often have a lower plant-availability compared to commercial P-fertilizers but are expected to play an increasingly important role into the future (Kratz et al. 2019). One promising way to increase the plant-availability of the fertilizer P is a co-fertilization with specific nitrogen (N) forms which can enhance the P uptake and make P-fertilizers from recycled material more competitive to commercial phosphate rock-based P-fertilizers (Rahmatullah et al. 2006; Vogel et al. 2018). To investigate this effect, we performed a pot experiment with three different P-fertilizers (sewage sludge-based, phosphate rock and triple superphosphate) and ammonium nitrate sulfate as a co-fertilizer, without and with a nitrification inhibitor (NI), and analyzed the form of N and P in soil via a suite of chemical and novel X-ray spectroscopic methods. The application of NI with the P and N fertilizers led to a higher dry matter yield and a higher P uptake of maize. Novel N K-edge micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy identified that the application of a NI promotes the temporary formation of a non-exchangeable N in detectable hot-spots in the soil. The subsequent slow release and prolonged availability of N during plant growth leads to higher yield and nutrient uptake. It can be concluded that NIs lead to a temporary fixation of ammonium-N in a pool that can be accessed by plant roots. Those types of available nutrient pools meet the idea of so-called “next generation fertilizers” as plants have access to nutrients according to their current demand.
Bottom ash (BA) from municipal solid waste incineration (MSWI) contains harmful substances such as heavy metals, chloride and sulfate which are mobilized in contact with water. Standardized leaching tests are used to measure the extent of mobilization. It is known that fresh bottom ash displays elevated concentrations of various heavy metals such as lead or zinc due to the formation of hydroxo complexes as a result of high pH values of 12 and above. Storage of BA is accompanied by ageing processes, mainly the reaction of CaO and Ca(OH)2 with CO2 leading to lower pH values in contact with water around 11. Usually heavy metals concentrations are minimum at these conditions. Knowledge of the long-term leaching behavior of potentially harmful substances is crucial for the assessment of the environmental compatibility of reusing municipal solid-waste incineration bottom ash (MSWI BA) in construction, i.e., as a road base layer. BA fractions obtained from wet-processing aiming at the improvement of environmental quality were used to investigate the mobility of relevant substances. Eluates from laboratory-scaled leaching procedures (column percolation and lysimeters) were analyzed to learn about the long-term release of substances. Unsaturated conditions and artificial rainwater were used in the lysimeter tests to simulate field conditions. In addition, batch test eluates were generated at usual liquid-to-solid ratios (L/S) for compliance testing purposes. A variety of cations and anions was measured in the eluates. The wet treatment reduces the leaching of chloride and particularly sulfate by more than 60%. The release of typical contaminants for the treated MSWI BA such as the heavy metals Cu and Cr was well below 1% in the conducted leaching tests. An increase in the Sb concentration was observed in the lysimeter experiments starting at L/S 0.75 L/kg and in the column experiment at L/S 4 L/kg is assumed to be related to decreasing concentrations of Ca and thus to the dissolution of sparingly soluble calcium antimonate. The same leaching mechanism applies with V, but the concentration levels observed are less critical regarding relevant limit values. However, on the long term the behavior of Sb could be problematic for the application of MSWI BA as secondary building material.
Per- and polyfluoroalkyl substances (PFAS) are a large group of organofluorine surfactants used in the formulations of thousands of consumer goods, including aqueous film-forming foams (AFFF) used to suppress aviation fires in training scenarios, non-stick cookware, fast-food wrappers, water-repellent fabrics, medical equipment, and plastic and leather products. As a result of the perpetual use of PFAS containing products, effluents and sewage sludge from wastewater treatment plants (WWTPs) have been observed to be an important pathway for PFAS into the environment. In Germany, phosphorus and other nutrients from sewage sludge and wastewater should be recycled in WWTPs of cities with a large population. However, it is not clear if PFAS contamination from wastewater and sewage sludge end up in novel wastewater-based fertilizers. Normally, PFAS are analyzed using PFAS protocols typically with time-consuming extraction steps and LC-MS-MS quantification. However, for screening of PFAS contaminations in sewage sludge or wastewater-based fertilizers also passive sampler based on the Diffusive Gradients in Thin-films (DGT) technique can be used for the PFAS extraction. Afterwards, combustion ion chromatography (CIC) can be applied to analyse the “total” amount of PFAS on the passive sampler. Here, we show results from the DGT method in comparison to those of the extractable organic fluorine (EOF) method for a variety of wastewater-based fertilizers. Additionally, we analysed the adsorption of PFAS on the weak anion exchanger (WAX) based DGT passive sampler binding layer by infrared and fluorine K-edge X-ray adsorption near-edge structure (XANES) spectroscopy.
The amount of plant-available phosphorus (P) in soil strongly influences the yield of plants in agriculture. Therefore, various simple chemical extraction methods have been developed to estimate the plant-available P pools in soil. More recently, several experiments with the DGT technique have shown that it has a much better correlation to plant-available P in soils than standard chemical extraction methods (e.g. calcium-acetate-lactate (CAL), Colwell, Olsen, water) when soils with different characteristics are considered. However, the DGT technique cannot give information on the plant-available P species in the soil. Therefore, we combined DGT with solution 31P nuclear magnetic resonance (NMR) spectroscopy. This was achieved by using a modified DGT device in which the diffusive layer had a larger pore size, the binding layer incorporated an adsorption material with a higher capacity, and the device had a larger exposure area. The spectroscopic investigation was undertaken after elution of the deployed DGT binding layer in a NaOH solution. Adsorption tests using solutions of known organic P compounds showed that a sufficient amount of these compounds could be adsorbed on the binding layer in order for them to be analyzed by solution 31P NMR spectroscopy. Furthermore, various intermediates of the hydrolysis of trimetaphosphate in soil could be also analyzed over time.