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This study aimed at examining effective sample treatments and spectral processing for an alternate method of soil nitrate determination using the attenuated total reflectance (ATR) of Fourier transform infrared (FTIR) spectroscopy. Prior to FTIR measurements, soil samples were prepared as paste to enhance adhesion between the ATR crystal and sample. The similar nitrate peak heights of soil pastes and their supernatants indicated that the nitrate in the liquid portion of the soil paste mainly responded to the FTIR signal. Using a 0.01-M CaSO4 solution for the soil paste, which has no interference bands in the characteristic spectra of the analyte, increased the concentration of the nitrates to be measured. Second-order derivatives were used in the prediction model to minimize the interference effects and enhance the performance. The second-order derivative spectra contained a unique nitrate peak in a range of 1,400–1,200 cm−1 without interference of carbonate. A partial least square regression model using second-order derivative spectra performed well ( R2 = 0.995, root mean square error (RMSE) = 23.5, ratio of prediction to deviation (RPD) = 13.8) on laboratory samples. Prediction results were also good for a test set of agricultural field soils with a CaCO3 concentration of 6% to 8% ( R2 = 0.97, RMSE = 18.6, RPD = 3.5). Application of the prediction model based on soil paste samples to nitrate stock solution resulted in an increased RMSE (62.3); however, validation measures were still satisfactory ( R2 = 0.99, RPD = 3.0). [ABSTRACT FROM AUTHOR]

To calculate critical acid loads or to predict element concentrations in the soil solution, information on weathering rates is essential. Several studies have taken place in the Netherlands to obtain weathering rates for non-calcareous sandy soils. Recently information on weathering rates in less vulnerable loess and clay soils have become available. However, up to now no system is available to estimate weathering rates on a regional scale by relating them to regionally available soil properties. To obtain weathering rates of loess and clay soils on a regional scale for the Netherlands, the applicability of a statistical regression model and the process based PROFILE model have been evaluated. Both models were calibrated on a set of laboratory experiments. To evaluate their predictive power, both methods were validated on a number of sites for which field weathering rates were available. Predictions with the statistical model, for the individual base cations, were generally within a factor 2 of the calculated historical weathering rates, except for Ca, which was overestimated, by a factor 3 to 4. PROFILE strongly overestimated all weathering rates using both standard parameters and in particular after calibration on the laboratory rates. However, PROFILE predicted weathering rates of the loess soils quite good after calibration on historical weathering rates, indicating that the downscaling procedure used in PROFILE to translate laboratory to field weathering rates is inadequate for the considered soils. The statistical model was applied to predict weathering rates, for the Netherlands on a 1 × 1 km grid scale. Weathering rates at the present pH values in forested loess and clay soils ranged from 135 to 6000 molc ha-1 a-1 in loess soils and from 100 to 1750 molc ha-1 a-1 in clay soils. [ABSTRACT FROM AUTHOR]

To assess the impact of acid deposition on forested loess and clay soils in the Netherlands, changes in base saturation and soil solution concentrations were simulated with the dynamic soil acidification model ReSAM for 38 loess soils and 16 clay soils. The selected locations represent the range in geographical position and diversity in parent material occurring in forested loess and clay soils in the Netherlands. Two deposition scenarios were used for the period 1992–2050: a business as usual scenario (BAU) and a scenario in which deposition was reduced according to present Dutch policy plans (MV-3). A comparison of simulated and measured soil solution concentrations and base saturation in 1992/1993 showed that the model simulated concentrations and base saturation in the loess soils quite good. However, the model tended to overestimate acidification in the top (0–10 cm) of the clay soils. Despite the reasonable agreement between measured and simulated data some uncertainty in the validity of the model predictions remains because time trends to validate the model were not available. The model predicted a small but ongoing acidification during the BAU scenario in the loess soils as indicated by a decline in median base saturation and pH in the topsoil in 2050. Present policy plans (MV-3) lead to a slight recovery of the base saturation in 2050 and a decline in Al concentrations. In the clay soils a strong decline in base saturation is simulated in the topsoil, whereas an increase in base saturation is predicted for the subsoil. [ABSTRACT FROM AUTHOR]