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The aim of this study was to develop visible and near-infrared spectroscopy (Vis-NIRS) calibration models for predicting the content of organic carbon (OC), total nitrogen (N), clay + silt, and pH values in soils from Argentina, employing different mathematical preprocessing techniques for spectral data. A total of 154 soil samples with contrasting physicochemical characteristics was selected, dried, and sieved to 2 mm prior to the analysis of OC, N, pH, and clay + silt using reference methods. Subsequently, the Vis-NIR spectrum (400 to 2500 nm) of each sample was obtained in reflectance mode. The sample set was randomly divided into two groups: one for calibration model development (80%) and the other for model validation (20%). Eight preprocessing techniques for spectral information were employed, and the best one for each parameter studied was selected based on the criteria of achieving the minimum standard error of cross-validation (EECV), maximum coefficient of determination of cross-validation (R2cv), and maximum residual predictive deviation (RPD). Calibration models were obtained using modified partial least squares regression (MPLS) and five-fold cross-validation. The best models for predicting OC and N were obtained with the raw spectra (RPD=4.69 and 3.65 respectively); for pH, the best model was obtained using the standard normal variate preprocessing technique with the second derivative (RPD=2.27), and for clay + silt, the best model was obtained with multiple scattering correction and second derivative (RPD=2.83). The performance of the models applied to the calibration and testing groups was similar. The results indicate that the appropriate choice of spectral data preprocessing technique can optimize calibration for the prediction. Vis-NIRS is a valuable tool for soil monitoring in Argentina, complementing traditional analysis methods. [ABSTRACT FROM AUTHOR]

Hops (Humulus lupulus) is a plant with potential for cultivation in the Center-South region of Paraná, Brazil. However, there are no official Brazilian recommendations for production of seedlings or fertilization and liming. The aims of this work were to evaluate the production of hop seedlings and verify the development of hop plants grown in soil with different pH values and K2O rates, in the Center-South region of Paraná, Brazil. Three experiments were carried out: i) cuttings of a plant were dipped in a 1% indole-3-butyric acid (IBA) solution and placed in different substrates - the sprouting and survival of the hop seedlings was verified; ii) hop seedlings were transplanted to a soil with different pH values (4,5; 5,5; 6,0 and 6,5) - the development and nutrients uptake by the plants was evaluated; iii) hop seedlings were transplanted to a soil with different K2O rates added - the development and K uptake by the plants was assessed. The substrate for seedling production did not influence the sprouting of hop cuttings, but the presence of IBA reduced sprouting and growth up to 41 days. The pH 5,5 value in the soil provided the best hop development by increasing the production of fresh and dry biomass in comparison with pH 4,5. Hop plants in soil with pH 6,0 and 6,5 showed lower chlorophyll content, but maintained the same nutrient uptake. The production of dry biomass of hop plants and the K content of the roots increased with the K2O rates added to the soil, However, K was not transferred to the aerial part of the plants in the initial phase of development. [ABSTRACT FROM AUTHOR]