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Soil nitrogen undergoes a series of chemical and biological transformations, which influence their availability to plants and the leaching losses. Methods for measuring various forms of nitrogen in soil are important in order to improve N management and to minimize losses of essential nutrients in soils.  In the present study 0.01 M CaCl 2 extraction was used to determine the concentrations of ammonium, nitrate and N-organic forms, as these are closely related to the N mineralization potential of the soil and play a major role in nitrogen availability to plants. Improving the precision of nitrogen requirement estimation is essential for increasing the efficiency and minimizing potential losses of nitrogen in agricultural production. A better knowledge of the plant-availability of nitrogen may help improve the efficient use of fertilizers and organic manure. In the present study the amounts of N-NO 3 , N-NH 4 and N organic were studied in Westsik's crop rotation experiment. The crop rotation experiment was established in 1929, and is the best known and most remarkable example of continuous production in Hungary, enabling the study of the long-term effects of organic manure treatment, the development of models and the prediction of the probable influences of different cropping systems on soil properties and crop yields in the Nyírség (sandy soil) region of Hungary.  The study aimed the optimization of the fertilizer recommendation system by considering the soil N-organic content as a measurement of site-specific mineralization potential. The 0.01 M CaCl 2 extraction method measures soluble organic N compounds that are related to the mineralization of organic nitrogen in the soil.  The introduction of this concept can possibly result in a more environment-friendly nitrogen fertilization, without negative effects on the yield or the quality of produced crops. Taking practicability and costs into consideration, the 0.01 M CaCl 2 extraction method is suitable for the routine analysis of measuring easily available organic nitrogen. 

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An incubation experiment was set up to investigate the effects of NPK fertilizers, wheat straw and food waste compost in combination with Phylazonit MC biofertilizer on the changes in 0.01 M CaCl 2 extractable nitrogen forms (NO 3 + -N, NH 4 + -N, organic-N fraction) of three types of soils. The quantities and changes in CaCl 2 -NH 4 + -N mainly depended on the adsorption capacity of soils. Higher CaCl 2 extractable NH 4 + -N values were measured in the calcareous chernozem and sandy soil with the application of NPK treatment, while in case of the chernozem soil with loamy texture no significant differences were found between the NPK and control treatments. NH 4 + immobilization appeared in pots given straw treatment. The quantity of CaCl 2 -NH 4 + -N changed within the incubation period, the direction and extent of the change were dependent of the production rates and consumption processes. In all soils the 0.01 M CaCl 2 extractable NO 3 - -N was the largest pool for plant nutrition. The highest CaCl 2 -NO 3 - -N values were found in pots given NPK and combined NPK+straw treatments, while the lowest values were measured in straw-treated pots. Wheat straw, with higher C/N ratio caused a temporary immobilization, followed by remineralization. Food waste compost, with lower C/N ratio, proved to have a good N supplying capacity. The contrasted effect of straw and compost was more conspicuous in sandy soil, in which the original NO 3 - -N content was the lowest. Higher CaCl 2 -organic N values were measured for pots treated with straw and with compost, as compared to the control. During the incubation period the amount of soluble organic-N changed, the direction and extent of the change depended on the soil type and treatments. The effect of Phylazonit MC was on the quantity of CaCl 2 extractable N fractions was not really expressed, and the significancy of the effect varied and was dependent of the soil type. Biofertilizer amendment increased the extractable NO 3 - -N in sandy soil, decreased the negative effect of wheat straw, and it also might help in decomposing wheat straw and food waste compost. The application of Phylazonit MC in the calcareous chernozem caused a significantly higher amount of organic-N, especially in straw-treated pots.

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. 161. (4) 409 – 424. Lazányi, J. & Loch, J., 2006. Evaluation of 0.01 M CaCl 2 extractable nitrogen forms in a long-term experiment. Agrokémia és Talajtan. 55. 135 – 144

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