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The application of natural fertilizer mixtures that improve nutrient retention ability of soils has attracted considerable attention in recent years. In addition to rock phosphate (RP), the basic components of these mixtures are zeolites modified with selected cations, such as the ammonium ion. The NH4-zeolite serves as a carrier of nutrients as well as a soil conditioner, and it promotes the RP dissolution in all soil types. The purpose of the present work was to prepare costeffective NH4-zeolite supplement, using 32 full factorial experimental designs, with concentration of modifier and processing time as variables. Saturation processes were carried out on two types of natural zeolites, K- clinoptilolite (K-Cp) and Ca-clinoptilolite (Ca-Cp). The Response Surface Method (RSM) was applied for evaluation of cation exchange, suggesting an effective NH4+ modification of natural zeolite at lower quantities of modifier than commonly found in other studies on the topic. Using Principal Component Analysis (PCA), differences between samples relative to the process variables were clearly outlined and correlated with concentrations of the exchanged cations. The best results were obtained for the K-Cp type modified with 1.5 M solution of ammonium sulfate (at a Cp/NH4+ stochiometric ratio 1:7.5) for all three processing intervals. By optimizing the modification process parameters, an experimental design of partially saturated NH4-Cp supplement that has the potential to supply all major plant nutrients was proposed.
Loess deposits in the Vojvodina region, northern Serbia, are among the oldest and most complete loess-paleosol sequences in Europe to date. These thick sequences contain a detailed paleoclimatic record from the late Early Pleistocene. Based on the correlation of detailed magnetic susceptibility (MS) records from Vojvodina with the Chinese loess record and deep-sea isotope stratigraphy we here reconfirm and expand on a stratigraphic model of the Vojvodinian loess-paleosol chronostratigraphic sequence following the Chinese loess stratigraphic system.
Variations in MS, dust accumulation rates, and the intensity of pedogenesis demonstrate evidence for a Middle Pleistocene climatic and environmental transition. The onset of loess deposition in Vojvodina also indicates a direct link between dust generation in Europe and that in the interior of Eurasia since the Early Pleistocene. The youngest part of the Early Pleistocene and oldest part of the Middle Pleistocene is characterised by relatively uniform dust accumulation and soil formation rates as well as relatively high magnetic susceptibility values. In contrast, the last five interglacial-glacial cycles are characterised by sharp environmental differences between high dust accumulation rates during the glacials and low rates observed during soil development. The data presented in this study demonstrate the great potential of Vovjodina's loess archives for accurate reconstruction of continental Eurasian Pleistocene climatic and environmental evolution.
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