Sample collection and measurement of soil bulk density (BD) are often labor-intensive and expensive in large regions. Conversely, soil spectra are easy to measure and facilitate BD prediction. However, the literature suggests that the damage to the physical structure of soil during scanning spectra on the ground and/or sieved samples might hinder the capacity of spectral technology to accurately predict BD. In addition, because some soil properties that have high correlations with BD, such as the soil organic matter (SOM), are routinely measured and available in most soil databases, coupling them with soil spectra may improve BD prediction compared to using soil properties or spectra. Therefore, in this study, we propose a novel spectral pedo-transfer function (spectral PTF) that couples the measured visible and near-infrared spectra of soils on intact samples and other soil properties to accurately predict the BD (BD = f (soil spectra, soil properties)), which is different from the traditional PTF that uses only soil properties (BD = f (soil properties)) or spectra alone (BD = f (soil spectra)). In this study, we collected topsoil (0-20 cm) and subsoil (20-40 cm) samples from 586 sites in Northeast China, covering a large area of 1.09 million km(2) characterized by black soils with high SOM contents. Five routinely measured soil properties were selected: SOM, moisture content (MC), Sand, Silt, and Clay, and various spectral PTFs with one, two, and three soil properties were calibrated using the partial least square regression. The cross-validation results show that the traditional PTF can only predict BD for subsoil with an R-2 of 0.51 and an RMSE of 0.11 g center dot cm(-3) when using SOM + MC + Silt or SOM + MC. Compared to subsoil, topsoil and all layers (topsoil + subsoil) had a lower BD prediction accuracy, and a saturation effect was observed for BD values above 1.5 g center dot cm(-3). Unexpectedly, the soil spectra did not provide a higher BD prediction accuracy than traditional PTFs, although the spectra were measured on intact samples. However, adding soil properties to the spectral PTF improved the prediction accuracy and saturation effect for high BD values. The optimal spectral PTF with a single soil property (MC) showed an acceptable BD prediction performance with R-2 >= 0.49, RPD>1.4, and RPIQ>1.7 regardless of whether the sample was topsoil, subsoil, or all layers. Furthermore, the spectral PTF with two or three soil properties yielded a slightly better prediction performance and a more stable prediction among different combinations of soil properties. These results indicate that soil properties and spectra are irreplaceable for BD prediction. Our study demonstrates the potential of spectral PTFs for the accurate prediction of BD and offers insights into the prediction of other soil properties using soil spectra.

Context Plant roots can increase soil shear strength and reinforce soil. However, wetting and drying alternation (WD) could lead to soil structure destruction, soil erosion and slope instability.Aims This study tried to explore the effects of wetting and drying alternation on shear mechanical properties of loess reinforced with root system.Methods Direct shear testing was conducted on alfalfa (Medicago sativa L.) root system-loess composites with three soil bulk densities (1.2 gcm-3, 1.3 gcm-3 and 1.4 gcm-3) under 0, 1, 2 and 3 cycles of wetting and drying alternation (WD0, WD1, WD2 and WD3).Key results The morphological integrity of the root-loess composites was obviously better than the non-rooted loess after WD. Under the three soil bulk densities, negative power-law relationships were observed between the shear strength, cohesion and internal friction angle and the cycles of WD. WD deteriorated the soil shear strength. The most obvious decrease in soil shear strength occurred under WD1, which was 13.00-22.86% for the non-rooted loess and 17.33-25.09% for the root-loess composites. The cohesion was decreased more than the internal friction angle by WD.Conclusions The most obvious damage to the soil was under WD1. The roots inhibited the deterioration effect of WD on the shear property of loess, and the inhibition by the roots decreased with the cycles of WD.Implications The results could provide new insights into the mechanical relationship between plant roots and loess under WD, and provide a scientific basis for the ecological construction in the loess areas. Wetting and drying alternation (WD) on the mechanical properties of root-soil composites is not clear at present, or if roots can inhibit the deterioration of soil under WD. This paper investigated the effect of WD on the shear strength of root-loess composites. WD was found to deteriorate soil shear strength and cohesion, while roots inhibited the deterioration of WD on the shear property of loess. The results provide a scientific basis for ecological construction in loess areas.

Cryosols contain roughly 1700 Gt of Soil organic carbon (SOC) roughly double the carbon content of the atmosphere. As global temperature rises and permafrost thaws, this carbon reservoir becomes vulnerable to microbial decomposition, resulting in greenhouse gas emissions that will amplify anthropogenic warming. Improving our understanding of carbon dynamics in thawing permafrost requires more data on carbon and nitrogen content, soil physical and chemical properties and substrate quality in cryosols. We analyzed five permafrost cores obtained from the North Slope of Alaska during the summer of 2009. The relationship between SOC and soil bulk density can be adequately represented by a logarithmic function. Gas fluxes at -5 degrees C and -5 degrees C were measured to calculate the temperature response quotient (Q(10)). Q(10) and the respiration per unit soil C were higher in permafrost-affected soils than that in the active layer, suggesting that decomposition and heterotrophic respiration in ciyosols may contribute more to global warming. (C) 2014 Published by Elsevier B.V.