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The study comparatively analyzed the variability of some agrochemical indices related to agricultural and forest land, in the area of the “Cenad Forest Protected Area”, Timis County, Romania. Within the agrochemical indices, the soil reaction (pH), total nitrogen content (TN %), phosphorus content (P, ppm), potassium content (K, ppm), calcium content (Ca, ppm) and magnesium content (Mg, ppm) were determined. The ANOVA test confirmed the presence of the variance and the statistical safety of the data (F> Fcrit, p <0.001; Alpha = 0.001). The correlation analysis showed some correlations and their statistical significance between TN and pH (r = -0.993**), between K and pH (r = -0.963*), between Ca and pH (r = 0.963*), and between K and TN (r = 0.974*). The variation of the mineral elements was described by polynomial equations, in different conditions of statistical safety: TN variation in relation to the soil reaction (pH) in conditions of R2 = 0.986, p = 0.117; variation of potassium (K) in relation to the soil reaction (pH) under conditions of R2 = 0.993, p = 0.080; variation of calcium (Ca) in relation to soil reaction (pH) under conditions of R2 = 0.978, p = 0.147; variation K in relation to TN under conditions of R2 = 0.997, p = 0.0531. Based on the coefficient of variation, the agrochemical indices presented differentiated values, CVTN = 50.4183, CVCa = 40.0339, CVK = 22.9719, CVP = 21.9803, CVMg = 12.0496, CVpH = 3.1064. In the PCA, correlation matrix, PC1 explained 71.422% of variance, and PC2 applied 26.357% of variance. The regression analysis evaluated the variation of P in relation to the soil pH and the Ca content, respectively the Mg content and found models in the form of equations, as well as 3D graphic and in the form of isoquants models. From the analysis of the 3D models of variation of P in relation to the considered indices, it was found differentiated situations, respectively the decrease of the P availability in relation to Ca and the increase of the P availability in relation to Mg, at the same pH range.
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