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Elevated CO2 and drought are key consequences of climate change and affect soil processes and plant growth. This study investigated the effects of elevated CO2 and drought on the microbial biomass and enzymatic activities in the rhizospheres of Bothriochloa ischaemum and Medicago sativa in loess soil. Drought exerted significant species-specific negative effects on root and shoot biomass and microbial properties except for the soil basal respiration in the rhizospheres of B. ischaemum and M. sativa. Increased CO2 exerted weak effects on plant biomass and enzymatic activities but demonstrated significant effects on the amounts of carbon and nitrogen in soil microbial biomass, basal respiration, substrate-induced respiration, and the metabolic quotients in the rhizospheres of M. sativa and B. ischaemum. The rhizosphere soil microbial index was a good aggregative indicator of the general state of the microbial properties of the rhizospheres. The interactive effects of elevated CO2 and drought on plant growth and microbial properties significantly differed, indicating that elevated CO2 significantly alleviated the effects of drought stress on the microbial properties of the rhizosphere. In addition, the effects of elevated CO2 and drought on microbial biomass and enzymatic activities considerably varied between the two selected species. M. sativa generally experienced a better ameliorative effect than B. ischaemum.

Wind erosion potential can be assessed using the Threshold Friction Velocity (TFV) of the soil, which is not always easy to measure, especially on regional and global scales. To overcome this difficulty, the spectroscopy technique can provide a useful approach in estimating the TFV as an alternative for time-consuming wind tunnel studies in the field. In this study, we evaluated the potential of Vis-NIR spectroscopy in predicting the TFV and some TFV-related soil properties using Partial Least Square Regression (PLSR) and the Support Vector Regression (SVR). We also developed a Point Spectrotransfer Function (PSTF) using Multiple Linear Regression (MLR) to predict the TFV based on diagnostic wavelengths and compared it to the derived Pedotransfer Function (PTF). For this purpose, 300 in-situ wind tunnel tests were performed in the Fars Province, Iran and the spectral reflectance of soil samples were analysed using a spectrophotometer apparatus. The 10 best key wavelengths resulting from the correlation analysis between the TFV and the spectral reflectance were 750, 1342, 1446, 1578, 1746, 1939, 2072, 2162, 2217, and 2338 nm which were mostly located in the short-wavelength infrared (SWIR) area. The derived PSTF performed better than the PTF for the TFV estimation (R2 = 0.94, RMSE = 0.71). Results of the predictive models revealed that machine learning using the SVR had a significantly (P < 0.01) higher prediction accuracy for the TFV estimation (R2 = 0.85, RMSE = 0.45, RPD = 2.50, and RPIQ = 4.06) than the PLSR (R2 = 0.68, RMSE = 1.01, RPD = 1.72, and RPIQ = 2.64). The same results were obtained for the soil moisture, clay and CaCO3 content. This study proved that reflectance spectroscopy coupled with the machine learning algorithm is a promising technique for large-scale assessment of wind erosion.

Forest management practices are commonly used in plantation forestry to obtain renewable energy and harvest biomass, in addition to maintaining the ecological environment, by changing the flow of carbon (C) and nutrients in the food webs of terrestrial ecosystems. To identify which forest management practices, alleviate soil nutrient limitation and impact stoichiometric homeostasis in relation to microbes, we used a Pinus tabuliformis plantation in the Loess Plateau where forest management practices were conducted since 1999. Five forest management practices were implemented: two at the forest level (P. tabuliformis with and without ground litter, CK, LRL) and three of different vegetation restorations after clear-cutting (P. tabuliformis seedlings (SPL), grass land (GL), and shrub land (SL)). Generally, the threshold elemental ratios for carbon:nitrogen (TERC:N; 7.77) and carbon:phosphorus (TERC:P; 44.37) were lower than the ratios influenced by forest management practices. The forest management practices significantly influenced ecoenzymatic activity and the ratios of ecoenzymes; however, the scale of the ecoenzyme activities for acquiring both organic N and organic P to that for acquiring C still follow the global pattern. The regression coefficients of C:N and C:P between the soil and microbial community at 0–20 cm and 20–40 cm depths were also influenced by these practices. Thus, the influence of forest management practices on the soil microbial community was limited by N and P in the Loess Plateau. The soil microbial community changed ecoenzymatic activities and ratios of ecoenzymes and even changed microbial community in order to balance elemental limitations in the soil. Finally, forest management practices have a minimal impact on the stoichiometric homeostasis of the microbial community at our study site.

Dryland agriculture in Cabo Verde copes with steep slopes, inadequate practices, irregular intense rain, recurrent droughts, high runoff rates, severe soil erosion and declining fertility, leading to the inefficient use of rainwater. Maize and beans occupy > 80% of the arable land in low-input, low-yielding subsistence farming. Three collaborative field trials were conducted in different agroecological zones to evaluate the effects of water-conservation techniques (mulching of crop residue, a soil surfactant and pigeon-pea hedges) combined with organic amendments (compost and animal or green manure) on runoff and soil loss. During the 2011 and 2012 rainy seasons, three treatments and one control (traditional practice) were applied to 44- and 24-m2 field plots. A local maize variety and two types of beans were planted. Runoff and suspended sediments were collected and quantified after each daily erosive rainfall. Runoff occurred for rainfalls ≥ 50 mm (slope < 10%, loamy Kastanozem), ≥ 60 mm (slope ≤ 23%, silt–clay–loam Regosol) and ≥ 40 mm (slope ≤ 37%, sandy loam Cambisol). Runoff was significantly reduced only with the mulch treatment on the slope > 10% and in the treatment of surfactant with organic amendment on the slope < 10%. Soil loss reached 16.6, 5.1, 6.6 and 0.4 Mg ha− 1 on the Regosol (≤ 23% slope) for the control, surfactant, pigeon-pea and mulch/pigeon-pea (with organic amendment) treatments, respectively; 3.2, 0.9, 1.3 and 0.1 Mg ha− 1 on the Cambisol (≤ 37% slope) and < 0. 2 Mg ha− 1 for all treatments and control on the Kastanozem (< 10% slope). Erosion was highly positively correlated with runoff. Mulch with pigeon-pea combined with an organic amendment significantly reduced runoff and erosion from agricultural fields on steep slopes, contributing to improved use of rainwater at the plot level. Sustainable land management techniques, such as mulching with pigeon-pea hedges and an organic amendment, should be advocated and promoted for the semiarid hillsides of Cabo Verde prone to erosion to increase rainwater-use and to prevent further soil degradation.

Post-fire land degradation is to a large degree determined by what happens to soil properties and ground cover during and after the fire. To study fire impact in relation to fire intensity and post-fire soil exposure, a 9-ha Portuguese shrubland catchment was burned by experimental fire in the 2008/9 winter season. Previous studies reported on the significant increase in erosion after this fire, and discussed the role of reduced canopy interception and changed soil water repellency dynamics. Our objective was to assess whether fire-induced changes in soil physical properties and soil surface characteristics may have played an additional role in the increase in runoff and erosion observed after the fire. We sampled these properties before, immediately after, and up to one year after fire, and monitored soil temperatures during the fire using thermocouples. Despite the locally high fire intensity (> 15.000 kW m − 1 in some places), soil physical changes were not observed: topsoil bulk density, organic matter, porosity and saturated conductivity did not significantly change, likely because soil temperatures stayed low with the 0.5 cm depth not exceeding 32.5 °C. Soil surface characteristics did change: Manning's n and random roughness both decreased, increasing the risk and erosivity of overland flow. Results indicate that soil physical changes unlikely contributed to the increase in post-fire erosion observed in the catchment and that a high-intensity winter burn does not necessarily lead to severe soil changes. Nevertheless, soil surface changes during and after fire contribute to an increase runoff and erosion risk in these areas.

The Chinese Loess Plateau is one of the most rapidly eroding regions in the world. The purpose of this study is to find out to which extent soil erosion on the Loess Plateau is driven by sunspot activity. We analyzed the relation between annual sediment discharge (from 1919 to 2010) from the Loess Plateau and the relative sunspot number, using Complex Morlet wavelets. We divided sediment discharge into 2 periods: before and after 1980 the year where the large-scale implementation of soil and water conservation techniques started. Before 1980, sediment discharge followed a 6 and 11-year period, the 11-year period being the most important one within a 25-year scale. After 1980, the impact of soil and water conservation techniques on the soil erosion in the Loess Plateau became obvious. The period of sediment discharge changed to, 4, 7 and 12-year periods, the 12-year period dominating the record. Similar analyses were conducted for the sunspot relative number, with an 11-year period dominating the record from 1919 to 2010. In different periods, the population, farm land area, land use/cover patterns and other factors have changed significantly. Although this has certainly affected sediment magnitudes, solar activity remains a clear (indirect) forcing factor for soil erosion in the Loess Plateau throughout the period of analysis. This underlines that solar activity influences Earth processes and argues for a more complete analysis of the pathways through which this happens.

Water repellency is a soil property which temporally changes in severity and is most pronounced when soils are dry. In the past, numerous researchers air- or oven-dried soil samples in the laboratory to determine the potential water repellency. However, measurement on air- and oven-dried samples can overestimate as well as underestimate the conditions occurring in the field under prolonged drought conditions. To reveal and determine realistic and potentially the highest persistence, we studied the influence of dehydration upon repellency in a dune sand grassland between 11 April and 5 September 2002, by artificially sheltering the soil. The shelter was built to protect the soil from getting wetted by precipitation during this period. The soil was sampled eight times in vertical transects over a distance of 75 cm to a depth of 33 cm during the dehydration period. On each sampling date soil water contents were measured and the persistence or stability of actual water repellency was determined in 120 field-moist samples collected at 8 depths. At the start of the dehydration experiment the mean volumetric soil water contents in the transect varied between 5 and 10.5%. At the end of the dehydration process the grass cover was wilted and yellow-brown and the soil profile dried-up to volumetric water contents between 1 and 2.5%. During the dehydration period, the average water storage in the upper 33 cm of the soil (total of 8 layers) decreased from 22 mm to less than 5 mm. Slightly water repellent and wettable dune sand layers at depths of 7 to 19 cm on 11 April were found to be altered into extremely water repellent soil within eight days of dehydration. The most extreme soil water repellency, with water drop penetration times of more than 6 h, was detected in large parts of the five soil layers sampled between depths from 9.5 to 33 cm on 4 June, 11 July and 5 September, 2002. The maximal water repellency was found to be evidently less in the organic rich surface layer in comparison with the organic poor deeper layers. For each soil layer the relation between soil water content and actual water repellency was determined. This resulted into three distinguished zones: a) a water repellent zone; b) a transition zone and c) a wettable zone. The threshold values of the volumetric water content that describe the transition zone varied per depth.

Wetting front instability resulting in fingered flow has been found in both wettable and nonwettable soils. Understanding how and when this phenomenon occurs under field conditions is greatly limited. Laboratory research has resulted in a number of expressions for finger diameter. In this paper we test the applicability of one of these equations for three different soils in the Netherlands where detailed soil sampling of moisture content was done earlier. In addition, information needed for finger prediction, such as the main wetting and drying loops of the soil moisture characteristic curves and the unsaturated and saturated soil conductivities, were measured in the laboratory. Results show that predicted finger diameters for the two sandy soils agreed well with the observed moisture patterns, while for the loess soil the wetting front was flat as predicted. The finger diameters in dry soil were based on the main wetting loop and in the wet soils were dependent on the main drying loop.