Small-scale portable rainfall simulators are an essential research tool for investigating the process dynamics of soil erosion and surface hydrology. There is no standardisation of rainfall simulation and such rainfall simulators differ in design, rainfall intensities, rain spectra and research questions, which impede drawing a meaningful comparison between results. Nevertheless, these data become progressively important for soil erosion assessment and therefore, the basis for decision-makers in application-oriented erosion protection.

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Summary Spiking is a useful approach to improve the accuracy of regional or national calibrations when they are used to predict at local scales. To do this, a small subset of local samples (spiking subset) is added to recalibrate the initial calibration. If the spiking subset is small in comparison with the size of the initial calibration set, then it could have little noticeable effect and a small improvement can be expected. For these reasons, we hypothesized that the accuracy of the spiked calibrations can be improved when the spiking subset is extra‐weighted. We also hypothesized that the spiking subset selection and the initial calibration size could affect the accuracy of the recalibrated models. To test these hypotheses, we evaluated different strategies to select the best spiking subset, with and without extra‐weighting, to spike three different‐sized initial calibrations. These calibrations were used to predict the soil organic carbon (SOC) content in samples from four target sites. Our results confirmed that spiking improved the prediction accuracy of the initial calibrations, with any differences depending on the spiking subset used. The best results were obtained when the spiking subset contained local samples evenly distributed in the spectral space, regardless of the initial calibration's characteristics. The accuracy was improved significantly when the spiking subset was extra‐weighted. For medium‐ and large‐sized initial calibrations, the improvement from extra‐weighting was larger than that caused by the increase in spiking subset size. Similar accuracies were obtained using small‐ and large‐sized calibrations, suggesting that incipient spectral libraries could be useful if the spiking subset is properly selected and extra‐weighted. When small‐sized spiking subsets were used, the predictions were more accurate than those obtained with ‘geographically‐local’ models. Overall, our results indicate that we can minimize the efforts needed to use near‐infrared (NIR) spectroscopy effectively for SOC assessment at local scales.

Restoring the native vegetation is one of the most effective ways to control soil degradation in Mediterranean areas, especially in very degraded areas. In the initial months after afforestation, vegetation cover establishment and soil quality could be better sustained if the soil was amended with an external extra source of organic matter. The goal of this study was to test the effect of various organic amendments on select soil properties [soil organic carbon (SOC), pH, and electrical conductivity (EC)] over a 24‐month period. Four amendments were applied in an experimental set of plots: straw mulching (SM), mulch with chipped branches of Aleppo Pine (Pinus halepensis L.; PM), sheep manure compost (SH), and sewage sludge (RU). Plots were afforested following the same spatial pattern, and amendments were mixed with the soil at the rate 10 Mg ha−1. Organic amendments helped maintain SOC over the initial 6 months after the afforestation. However, only the SM and PM treatments had increased SOC values after 24 months. Decreases in EC were found after the addition of SM, PM, and SH amendments. However, RU increased EC values 24 months after the afforestation. Variations in pH values were not sufficient to establish differences among the various treatments. Furthermore, the results show that forest soils with or without organic amendments responded similarly to the seasonal changes in Mediterranean conditions. Copyright © 2014 John Wiley & Sons, Ltd.

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