International Soil and Water Conservation Research最新文献

Climate change alters the intensity and frequency of drought and rewetting (D/W) events; however, the influence patterns of D/W on soil N₂O efflux in the water-limited area were not fully understood. Therefore, the impacts of D/W cycles varying in different extent of rewetting and frequency to N₂O efflux in two kinds of soil on the Loess Plateau were investigated. The incubation conditions consisted of 1) D/W treatments with four 7-day cycles from 10% water holding capacity (WHC) to 60%WHC or 90%WHC, 2) constant moisture of 60%WHC and 90%WHC. The pulse of N₂O efflux rate under 10−60%WHC treatment was higher than that under 10−90%WHC treatment in calcic cambisols, while opposite trend was observed in earth-cumuli-orthic anthrosols. Meanwhile, the pulse of N₂O efflux rate decreased as cycle number increased for different wetting intensities and soil types. The direct N₂O efflux under 10−60%WHC and 10−90%WHC treatments were 5.49 and 1.89 μg N₂O–N g⁻¹ soil in calcic cambisols, with those being 1.92 and 10.85 μg N₂O–N g⁻¹ soil in earth-cumuli-orthic anthrosols, respectively. The N loss in earth-cumuli-orthic anthrosols was approximately 5.74 times greater than that in calcic cambisols under 10−90%WHC treatment, whereas the N loss under 10−60%WHC treatment was about 2.86 times greater in calcic cambisols than that in earth-cumuli-orthic anthrosols. This study suggested that extreme rainfall events can enhance the N₂O efflux and N loss in agricultural soils on the Loess Plateau in terms of soil type and wetting intensity, which should not be ignored in the N fertilizer management.

To avoid soil degradation, adapt to climate change and comply with the Sustainable Development goals 2030 (UN General Assembly), establishing the quality/fertility of the agricultural soils of the Mediterranean region and evaluate how these evolve with time is mandatory. This enables adequate management practices to be implemented. The Mediterranean calcareous region has received little attention in this sense, in spite its soil particularities. So, 24 different representative calcareous agricultural soils of the Mediterranean region, including the main management strategies of agricultural soils (rainfed and irrigated), were sampled from the island of Mallorca; and their physical, chemical and biological properties determined. The values obtained for most of the soil characteristics allowed to establish an initial approach to the reference values for the type of calcareous agricultural soils considered, and to clearly distinguish the effect of rainfed or irrigation management practices on soils properties and dynamics. Some enzyme activities were not stimulated by the irrigation conditions assayed or they were only in dry conditions, suggesting optimum enzyme activities could be obtained when alternating dry and humid soil conditions. Soil organic carbon, calcium carbonate and active lime revealed of significant importance in the collection of soils. Finally, the results obtained clearly indicate the heterogeneity of the region and its implications on the different soil characteristics. Therefore, this study could serve as a starting point to adequately establish the quality (fertility) for Mediterranean calcareous agricultural soils and their reference values by conducting further research in this region and including more type of soils.

Physical soil crust (PSC), a key component of surface soil structure, exists extensively in loess areas. PSC is considered to have a significant effect on soil detachment processes. However, the long-term effects and the corresponding mechanisms of PSC on soil detachment by overland flow are still not well understood, especially in natural environments. To investigate temporal variation in soil erosion resistance and the underlying factors during PSC formation, an 8 × 8-m soil plot was exposed to natural conditions in the Loess Plateau over a 524-day period spanning two rainy seasons and a winter between them. A flume test was conducted to determine soil detachment capacity (D_c) under six designed flow shear stress levels (5.66–22.11 Pa) using crusted (SC) and non-crusted (NSC) soil samples at different PSC development stages. Subsequently, two soil erosion resistance parameters, rill erodibility (K_r) and critical shear stress (τ_c), were calculated. Over time, in the SC and NSC treatments, K_r decreased from 0.516 to 0.120 s m⁻¹ and 0.521 to 0.223 s m⁻¹, respectively, while τ_c increased from 0.49 to 4.42 Pa and 0.26–2.46 Pa, respectively. Variation in soil erosion resistance was rapid in the first one to two months, and then slowed down, with slight fluctuations afterwards. In the SC treatment, K_r was 42% lower and τ_c was 67% greater than those in the NSC treatment. Soil properties changed greatly for both treatments. SCT increased from 0 to 7.09 mm in the SC treatment. Coh increased from 2.91 to 9.04 kPa and 3.01–4.78 kPa in SC and NSC treatments, respectively. Both soil erosion resistance parameters could be well predicted by SCT and Coh in the SC treatment (R² ≥ 0.82), while their best predictor was Coh in the NSC treatment (R² ≥ 0.90). The results demonstrate that PSC formation enhances soil erosion resistance in the soil detachment process in the loess region under natural conditions. Our study revealed the important role and complexity of PSC in the process of soil erosion, and provided theoretical and data support for accurate understanding and prediction of soil erosion.

An inventory of topographic modifications is essential to addressing their impacts on hydrological and morphological processes in human-altered watersheds. However, such inventories are generally lacking. This study presents two workflows for semi-automatic detection of linear earthen runoff and erosion control berms in rangelands using high-resolution topographic data. The workflows consist of initial object identification by applying either morphological grayscale reconstruction (MGR) or the Geomorphon (GEO) method, followed by identification refinements through filters based on objects’ horizontal and vertical information. Three sites were selected within the Altar Valley, Arizona, in the southwestern United States. One site was used for developing workflows and optimizing filter thresholds, and the other two sites were used to validate workflows. The results showed that: 1) The MGR-based workflow methodology could produce final precision and detection rates of up to 92% and 75%, respectively, and take less than 5 s for a 10.1 km² site; 2) The workflow based on the MGR method yielded greater identification accuracy than did the GEO workflow; 3) Object length, orientation, and eccentricity were important characteristics for identifying earthen berms, and are sensitive to general channel flow direction and berm shape; 4) Manual interrogation of topographic data and imagery can significantly improve identification precision rates. The proposed workflows will be useful for developing inventories of runoff and erosion control structures in support of sustainable rangeland management.

Identifying the nitrogen (N) fate is complicated and a great challenge in karst watersheds because of the co-existence of natural pools and anthropogenic sources. The objective of the study was to use stable isotopic composition of dual-isotope (δ¹⁵N_Nitrate and δ¹⁸O_Nitrate) and LOADEST model approaches to trace N sources, pathways in karst watershed. The study was conducted in the Houzhai watershed, which is a typical agricultural karst watershed from July 2016 to August 2018, to reveal the N fate and the coupled carbon(C)–N processes occurring in the riverine-watershed with agricultural activities. We found that the wet deposition of total nitrogen (TN) flux was 33.50 kg hm⁻²·a⁻¹ and dissolved nitrogen (DN) flux was 21.66 kg hm⁻²·a⁻¹. The DN runoff loss was 2.10 × 10⁵ kg·a⁻¹ and the loss of DN during the wet season accounted for 95.4% over a year. In the wet season, NO₃⁻-N daily efflux was 977.62 ± 516.66 kg ha⁻¹·day⁻¹and 248.77 ± 57.83 kg ha⁻¹·day⁻¹ in the dry season. The NH₄⁺-N efflux was 29.17 ± 10.50 kg ha⁻¹·day⁻¹ and 4.42 ± 3.07 kg ha⁻¹·day⁻¹ in the wet and dry seasons, respectively. The main form output load of N was NO₃⁻-N which was more than 30 times as much as NH₄⁺-N output loss. The NO₃⁻-N caused by rainfall contributed 11.82%–53.61% to the export load. Nitrate from soil contributed over 94% of the N to Houzhai river caused by N leaching. In addition, manure and farmland soil were the main sources of groundwater in the Houzhai watersheds, the contribution rates were 25.9% and 22.5%. The chemical N fertilizers affected carbonate weathering strongly, and the HCO₃⁻ flux caused by nitrification due to N fertilizers application in soil accounted for 23.5% of the entire watershed. This study suggested that carbonate weathering may be influenced by nitrogen nitrification in the karst watershed.

Present global maps of soil water retention (SWR) are mostly derived from pedotransfer functions (PTFs) applied to maps of other basic soil properties. As an alternative, ‘point-based’ mapping of soil water content can improve global soil data availability and quality. We developed point-based global maps with estimated uncertainty of the volumetric SWR at 100, 330 and 15 000 cm suction using measured SWR data extracted from the WoSIS Soil Profile Database together with data estimated by a random forest PTF (PTF-RF). The point data was combined with around 200 environmental covariates describing vegetation, terrain morphology, climate, geology, and hydrology using DSM. In total, we used 7292, 33 192 and 42 016 SWR point observations at 100, 330 and 15 000 cm, respectively, and complemented the dataset with 436 108 estimated values at each suction. Tenfold cross-validation yielded a Root Mean Square Error (RMSE) of 6.380, 7.112 and 6.485 10⁻²cm³cm⁻³, and a Model Efficiency Coefficient (MEC) of 0.430, 0.386, and 0.471, respectively, for 100, 330 and 15 000 cm. The results were also compared to three published global maps of SWR to evaluate differences between point-based and map-based mapping approaches. Point-based mapping performed better than the three map-based mapping approaches for 330 and 15 000 cm, while for 100 cm results were similar, possibly due to the limited number of SWR observations for 100 cm. Major sources or uncertainty identified included the geographical clustering of the data and the limitation of the covariates to represent the naturally high variation of SWR.

Sustainable vegetable production especially during the dry season requires adequate conservation of soil water. This study was conducted to evaluate the sole and interactive effects of mulching (M) and poultry manure (PM) application on soil temperature (ST), crop evapotranspiration (ETc) and water use efficiency (WUE) of okra. The experiment was a Randomized Complete Block Design (RCBD) with three replicates. The treatments were M at 0 and 6 t ha⁻¹ and PM at 0, 10 and 20 t ha⁻¹. Soil temperature was measured using digital thermometer while ETc was determined by water depletion method using a Time Domain Reflectometer. Irrigation at field capacity was applied manually at 2-day intervals. Independent application of mulch significantly lowered ST while joint application of 20 t ha⁻¹ PM (PM20) and M significantly (p ≤ 0.05) reduced ST at 5 cm and 10 cm soil depth compared with the unmulched plots in both seasons. Application of 10 t ha⁻¹ PM (PM10) without M recorded the highest ETc (43.7 mm), while joint application of PM20 and M reduced ETc by about 93% compared with PM10 only. Okra used water most efficiently when PM20 was applied under mulched plot. There was 62.2% increase in WUE under mulched plots compared with the control while the residual effect of PM10 and M significantly increased WUE by 65.5%. It was evident that M alongside application of PM is a good strategy for regulating ST, moderating ETc and increasing okra WUE, especially during dry season farming.

In slopes of Mediterranean mid-mountain areas, land use and land cover changes linked to the abandonment of cropland activity affect soil quality and degradation and soil redistribution; however, limited attention has been paid to this issue at catchment scale. This paper evaluates the effects of cropland abandonment and post-land abandonment management (through natural revegetation and afforestation) on soil redistribution rates using fallout ¹³⁷Cs measurements in the Araguás catchment (0.45 km², Central Spanish Pyrenees). A total of 52 soil core samples, distributed in a regular grid, from the first 30–40 cm and 9 sectioned reference samples were collected across the catchment and soil properties were analysed. Fallout ¹³⁷Cs was measured in a 5 cm sectioned references samples and in bulk grid samples. ¹³⁷Cs inventories were used to estimate soil erosion and deposition rates across the catchment. Results show that the highest erosion rates were recorded under sparsely vegetated sites in the badland area, while the lowest rates were found in the afforested area, but no significant differences were observed between the different uses and covers in soil redistribution rates likely due to a long history of human intervention through cultivation in steep slopes and afforestation practices. However, the recovery of the soil organic matter in afforested areas suggest that afforestation can reduce soil degradation at long-term scale. The information gained achieve a better understanding of soil redistribution dynamics and provide knowledge for effective land management after cropland abandonment of agroecosystems in Mediterranean mountain areas.

Orchards have a high potential for carbon sequestration. However, little research is available on the spatial variability at catchment scale and on the difference between the tree area and the lanes. We analyzed theik spatial variability of soil organic carbon stock, SOC_stock at 90 cm depth in an 8-ha catchment in Southern Spain with olives on a vertic soil. Results showed higher soil organic carbon concentration, SOC, in the tree area as compared to the lane up to 60 cm depth, but its impact on SOC_stock was negligible since it was compensated by the higher soil bulk density in the lane. SOC at different depths was correlated with that in the top 0–5 cm. The overall SOC_stock of the orchard was 4.14 kg m⁻², ranging between 1.8 and 6.0 kg m⁻². This SOC_stock is in the mid-lower range of values reported for olive orchards, measured at smaller scale, and similar to those other intensive field crops and agroforestry under comparable rainfall conditions. The spatial variability in SOC_stock was correlated to several geomorphological variables: elevation, cumulative upstream area, topographic wetness index, sediment transport index, and tillage erosion. Differences in SOC and SOC_stock are driven by the sediment redistribution downslope, mainly by tillage erosion, and higher soil water availability in lower areas allowing higher biomass production. These topographic indexes and the correlation between SOC in the topsoil and SOC_stock up to 90 cm should be further explored in other typology of olive orchards for facilitating the mapping of SOC_stock.

Mollisols are rich in organic matter, which makes them suitable for cultivation and for enhancing global food security. Mollisols are experiencing severe soil erosion due to overfarming and a lack of maintenance. Thus, suitable soil and water conservation measures (SWCMs) are needed to protect Mollisols. However, how SWCMs respond to changes in slope gradient and rainfall and their effective application area remain ambiguous. Using a long-term field observation dataset, meta-analysis, and statistical test methods, we reveal the typical erosion reduction effect of SWCMs and their responses to changes in slope gradient and rainfall. Next, we calculated a coupling factor, P·S, by slope gradient and rainfall in flood season to determine the effective SWCMs application threshold. Compared with bare land, no-tillage (NT), contour ridge tillage (CT), ridge hedgerows (RH), and terraced fields (TF) had an average erosion reduction coefficient of 91.5%. There was a significant exponential increase in the correlation between P·S and the soil erosion amount in plots with typical measures. According to this correlation and soil loss tolerance (200 t/km²), the upper limits of P·S (NT: 564 mm; CT: 885 mm; RH: 1135 mm) were determined and utilized to determine the effective application areas (NT: 311.40 10³ km²; CT: 320.86 10³ km²; RH: 323.72 10³ km²) at the plot scale. In wet years, the applicable area of SWCMs declined toward the low-elevation foothills and flat terrain. All the results are applicable when slope length within 20 m. These results provide a basis for the precise allocation of SWCMs in Mollisols area and promote the scientific utilization of Mollisols resources.