Loess Plateau Of China Research Articles

An Optimised Region-Growing Algorithm for Extraction of the Loess Shoulder-Line from DEMs

The positive and negative terrains (P–N terrains) of the Loess Plateau of China are important geographical topography elements for measuring the degree of surface erosion and distinguishing the types of landforms. Loess shoulder-lines are an important terrain feature in the Loess Plateau and are often used as a criterion for distinguishing P–N terrains. The extraction of shoulder lines is important for predicting erosion and recognising a gully head. However, existing extraction algorithms for loess shoulder-lines in areas with insignificant slopes need to be improved. This study proposes a regional fusion (RF) method that integrates the slope variation-based method and region-growing algorithm to extract loess shoulder-lines based on a Digital Elevation Model (DEM) at a spatial resolution of 5 m. The RF method introduces different terrain factors into the growth standards of the region-growing algorithm to extract loess-shoulder lines. First, we employed a slope-variation-based method to build the initial set of loess shoulder-lines and used the difference between the smoothed and real DEMs to extract the initial set for the N terrain. Second, the region-growing algorithm with improved growth standards was used to generate a complete area of the candidate region of the loess shoulder-lines and the N terrain, which were fused to generate and integrate contours to eliminate the discontinuity. Finally, loess shoulder-lines were identified by detecting the edge of the integrated contour, with results exhibiting congregate points or spurs, eliminated via a hit-or-miss transform to optimise the final results. Validation of the experimental area of loess ridges and hills in Shaanxi Province showed that the accuracy of the RF method based on the Euclidean distance offset percentage within a 10-m deviation range reached 96.9% compared to the manual digitalisation method. Based on the mean absolute error and standard absolute deviation values, compared with Zhou’s improved snake model and the bidirectional DEM relief-shading methods, the proposed RF method extracted the loess shoulder-lines highly accurately.

Cropland abandonment mapping at sub-pixel scales using crop phenological information and MODIS time-series images

Cropland abandonment is a common land-use change with mixed impacts on the environment and rural economic development. Prevalent small family farms and excessive land fragmentation result in cropland abandonment processes that are often gradual and spatially dispersed. These difficulties limit the ability to apply previous remote sensing mapping methods of cropland abandonment to areas with complex underlying surfaces, where mixed pixels and spectral aliasing problems arise. To meet the demands of broad-scale and high-accuracy abandoned cropland mapping, we developed the PCRRSBS-CV model by combining the phenology-based cropland retirement remote sensing (PCRRS) model with the coefficient of variation (CV) and tilled soil fraction (BS). This method combines information regarding crop phenology with Moderate Resolution Imaging Spectroradiometer (MODIS) time-series images. The PCRRS model was used to estimate changes in spectral metrics parameters during the process of cropland abandonment. Additionally, the dead fuel index and normalized difference vegetation index (NDVI) were employed to estimate the BS in mixed pixels (according to crop type). We predicted that use of the BS as the weighting coefficient for the PCRRS model would reduce interference from the mixed pixel problem, while spatial heterogeneity could be reduced by dividing the research area into regional units. Use of the CV of the NDVI time series with phenological information highlights the volatility of crop growth periods and helps to eliminate disturbances associated with woodlands and grasslands. Finally, we demonstrated this method in the Loess Plateau of China and a portion of central Europe; we verified its accuracy using high-resolution images from Google Earth. Our algorithm demonstrated overall accuracy of 82.2 % and can extract cropland abandonment information as little as 20 % of a pixel. The overall root mean square error (RMSE) was controlled below 15 %. In summary, the high accuracy achieved by this method enables the monitoring of cropland abandonment dynamics on a large scale.

A Hybrid Time Series Model for Predicting the Displacement of High Slope in the Loess Plateau Region

The physical and mechanical properties of the loess differ from other kinds of soil due to its collapsibility, which has resulted in the complex displacement development law of the loess slope. Therefore, the accurate estimation of the displacement of high slopes in a loess gully region is critical for the safety of people and in construction activities. In the present study, to improve the accuracy of traditional methods, the original cumulative displacement curve was decomposed into trend and fluctuation terms using Empirical Mode Decomposition (EMD) and Wavelet Decomposition (WD). Subsequently, the results were estimated using the Support Vector Machine (SVR) and Long Short-Term Memory Network (LSTM) optimized by Biogeography-based Optimization (BBO), respectively. To select the most appropriate model, SVR, LSTM, EMD-SVR-LSTM, EMD-BBO-SVR-LSTM, and WD-BBO-SVR-LSTM were employed to predict the deformation of a loess slope in the Loess Plateau of China. According to the results, the displacement increases rapidly at the starting stage, and then gradually stabilizes, which is the same as the trend in reality. On comparing the predicted results with field data, it was found that the models with decomposition algorithms achieved higher accuracy. Particularly, the determination coefficient of the EMD-BBO-SVR-LSTM model reaches 0.928, which has better algorithm stability and prediction accuracy than other models. In this study, the decomposition algorithm was applied to the loess slope displacement innovatively, and the appropriate machine learning algorithm adopted for the displacement components. The method improves the accuracy of prediction and provides a new idea for instability warning of loess excavation slopes. The research has implications for urban construction and sustainable development in loess mountainous areas.

Evolution of the water–carbon relationship at basin scale under the background of a vegetation restoration program

AbstractVegetation restoration is an important means for regional climate change mitigation and terrestrial carbon sequestration. However, large‐scale vegetation restoration in arid and semiarid regions can excessively consume local water resources, thus threatening regional water supply safety. To explore the impact of vegetation restoration on the water–carbon relationship in the Loess Plateau in China before and after the implementation of the Grain‐for‐Green Program (GfGP), the regional hydro‐ecological simulation system (RHESSys) model was used to simulate the temporal and spatial evolution of key variables of the water cycle, including the actual evapotranspiration (ET) and the surface runoff (Rs), and that of the carbon cycle, including the net primary productivity (NPP) and the total carbon density (TC). In addition, statistical methods were applied to analyze the interaction between water and carbon cycles. Results show that the RHESSys model is capable of simulating the key ecohydrological elements. In the period of 1990–2019, ET and NPP both showed significant increasing trends at rates of 8.9 mm yr−1 and 6.9 g C m−2 yr−1, respectively. The TC also had a slightly increasing trend, with rates of 0.04 t C hm−2 yr−1 (land‐use in 1995), 0.07 t C hm−2 yr−1 (land‐use in 2005), and 0.08 t C hm−2 yr−1 (land‐use in 2015). In contrast, Rs decreased at the rate of 0.35 mm yr−1. As for spatial distribution, in the middle and southeastern parts of the Yanhe River basin with the vegetation well‐restored, ET, NPP, and TC showed significant increasing trends, while the Rs showed a decreasing trend. ET was also found to have a positive correlation with NPP and TC, while the Rs has a negative correlation with NPP and TC. Moreover, the correlation of Rs‐NPP and Rs‐TC was found to increase after the implementation of the GfGP, which indicates the reinforcing effect of vegetation restoration on the water–carbon trade‐off relationship. Therefore, it is critical to coordinate and regulate the interaction between water consumption and runoff in the context of vegetation restoration in the Yanhe River basin, as well as to promote the synergy between regional ecological restoration and social economic development for water security.

Spatiotemporal patterns of planted forests on the Loess Plateau between 1986 and 2021 based on Landsat NDVI time-series analysis

ABSTRACT Long-term and large scale spatiotemporal patterns of planted forests are essential for evaluating local plantation effectiveness and to promote sustainable afforestation. Satellite remote sensing data provide broad spatial coverage and increasingly long-term and large scale records for spatiotemporal analysis of planted forests. In this study, we developed a dynamic and conversion extraction (DCE) framework by combining the similarity of Landsat normalized difference vegetation index (NDVI) time-series with a change detection algorithm. This framework allows the analysis of spatiotemporal dynamics of planted forests. The proposed framework can be used to extract the planting year and conversion patterns of planted forests by performing the Mann-Kendall (MK) statistic test on the inter-annual Landsat NDVI time-series and measuring the similarity of the intra-annual time-series, respectively. Therefore, it can be applied to addressing the key questions on where, when, and how planted forests conversions have occurred. Took the Loess Plateau in China as an example, we applied the DCE framework to illustrate how planted forests have changed over time and space and have been converted from other land cover types from 1986 to 2021. The producer and user accuracies for the mapping of planted forests were 88.22% and 87.11% in 2021, respectively, and the accuracy of identifying planted forests conversions was 80.25%. The results showed that the newly planted forests experienced four phases: a slow rise from 1986 to 2000, a sharp increase during 2001–2004, a fluctuating pattern from 2005 to 2013, and a reduction until 2020, resulting in a total planted forest area of 7.13 Mha in 2021. In addition, 83.51% of the planted forest pixels underwent conversion from grasslands (58.19% or 4.15 Mha) or croplands (25.32% or 1.81 Mha) during 1986–2021. These results indicate the capability of the DCE framework to capture essential information (planting year and conversion patterns) to support the spatiotemporal analysis of planted forests at large scales.

Abandoned terrace recognition based on deep learning and change detection on the Loess Plateau in China

AbstractTerraces are an important cultivated land resource. Terrace abandonment affects the soil quality, soil and water conservation benefits, and biodiversity of terraces. Therefore, it is important to quantify the number and spatial distribution of abandoned terraces to protect cultivated land and food security. However, the traditional remote sensing method cannot identify small plots and make accurate assessment of abandoned farmland quickly in mountainous areas. To accurately identifying abandoned terraces, this study used semantic segmentation based on deep learning and change detection to identify abandoned terraces and their spatial distribution in a small watershed on the Loess Plateau in 2021. A comparative analysis of the accuracy of three deep learning models revealed that RefineNet is superior to DeepLabv3+ and DeepLabv3 for identifying abandoned terraces. The user's accuracy, producer's accuracy, overall accuracy, and appa values for RefineNet were 0.817, 0.894, 0.800, and 0.539, respectively. For change detection, the corresponding values were 0.821, 0.753, 0.731, and 0.426, respectively. In addition, semantic segmentation produced better recognition results than change detection in complex terrain and geomorphological areas. The abandoned terraces in the study area were mainly distributed in mountainous areas far from residential areas and more likely at high elevations with large slopes. This study provides a new method for recognizing abandoned terraces and spatial distribution information for managing and utilizing abandoned terraces.

A 1000‐Year Record of Temperature From Isotopic Analysis of the Deep Critical Zone in Central China

AbstractTemperature proxies for paleoclimate reconstruction have been made typically via ice cores, tree rings, stalagmites, and lake sediments. While extremely useful, these proxies can be limited spatially. Here we sampled a 98 m “soil core” from Loess Plateau of China and examined the relationship between pore water isotopic values and hydroclimate history. We extracted soil pore water for δ18O, δ2H, and 3H and measured chloride concentration. The 3H‐peak at 6 m and chloride mass balance were used to turn depth into calendar year. A 1000 year span was revealed. δ18O and δ2H values between 14–50 m were anomalously low—bracketing well the Little Ice Age period from 1420 to 1870. The identification was consistent with other standard proxies in the region and showed the same temporal dynamics of temperature anomalies. Our study shows the potential of stable isotopes of soil water for paleoclimate reconstruction in deep soils.

The role of ecosystem transpiration in creating alternate moisture regimes by influencing atmospheric moisture convergence.

The terrestrial water cycle links the soil and atmosphere moisture reservoirs through four fluxes: precipitation, evaporation, runoff, and atmospheric moisture convergence (net import of water vapor to balance runoff). Each of these processes is essential for sustaining human and ecosystem well-being. Predicting how the water cycle responds to changes in vegetation cover remains a challenge. Recently, changes in plant transpiration across the Amazon basin were shown to be associated disproportionately with changes in rainfall, suggesting that even small declines in transpiration (e.g., from deforestation) would lead to much larger declines in rainfall. Here, constraining these findings by the law of mass conservation, we show that in a sufficiently wet atmosphere, forest transpiration can control atmospheric moisture convergence such that increased transpiration enhances atmospheric moisture import and results in water yield. Conversely, in a sufficiently dry atmosphere increased transpiration reduces atmospheric moisture convergence and water yield. This previously unrecognized dichotomy can explain the otherwise mixed observations of how water yield responds to re-greening, as we illustrate with examples from China's Loess Plateau. Our analysis indicates that any additional precipitation recycling due to additional vegetation increases precipitation but decreases local water yield and steady-state runoff. Therefore, in the drier regions/periods and early stages of ecological restoration, the role of vegetation can be confined to precipitation recycling, while once a wetter stage is achieved, additional vegetation enhances atmospheric moisture convergence and water yield. Recent analyses indicate that the latter regime dominates the global response of the terrestrial water cycle to re-greening. Evaluating the transition between regimes, and recognizing the potential of vegetation for enhancing moisture convergence, are crucial for characterizing the consequences of deforestation as well as for motivating and guiding ecological restoration.

Runoff–Sediment Simulation of Typical Small Watershed in Loess Plateau of China

The implementation of measures such as check dams and terraces in the Loess Plateau of China has had a groundbreaking impact on water and sediment conditions. The question of how to accurately simulate the runoff–sediment process under complex underlying surface conditions has become key to clarifying the water cycle law. This study focused on the Chenggou River basin, a small watershed located in the Loess Plateau, to examine the effect of the underlying surface characteristics on the runoff production process, and the spatial distribution of the dominant runoff process in the runoff generation mechanism was determined according to the land application, slope and vegetation coverage of the watershed. A runoff–sediment model was constructed that was combined with the traditional hydrological physical mechanism and a deep learning algorithm. Different parameters were calibrated depending on the spatial distribution of the dominant runoff process and we then ran the runoff–sediment simulation model to very its serviceability in the typical watershed of the Loess Plateau. Different parameters were calibrated for each type of hydrological response unit (HRU), according to the division of each HRU and the actual flood process, to calculate the runoff yield of each HRU. An LSTM algorithm was used for flow routing and a CSLE algorithm was used to simulate soil erosion. The results show that there were 29 flood events in the Chenggou River basin from 2013 to 2017. The average runoff depth had an 8.86% margin of error, while the peak flow had a slightly higher 9.44% deviation. The Nash efficiency coefficient was 0.84, and the relative error of soil erosion was 14.45%. The model simulation effect is good and can be applied to the typical watershed of the Loess Plateau. The model can provide a scientific basis for the highly efficient and sustainable utilization of water resources, ecological environment construction and the sustainable development of agriculture.

Impacts of climate change on soil desiccation in planted forests with different tree ages: A case study in the Loess Plateau of China

Investigating the impacts of climate change on soil desiccation in planted forests is of theoretical and practical importance for water resource management and ecological restoration in the Loess Plateau. In this study, field experiments were conducted in four planted forests (Platycladus orientalis plots) with tree ages of 5, 12, 25, and 35a (abbreviated as T5, T12, T25, and T35 plots, respectively). Based on which, Hydrus–1D models were calibrated and validated to simulate soil water dynamics under preset climate change scenarios. Then, the soil desiccation index (SDI) in different soil layers was calculated and evaluated. The results showed that under historical climate scenarios, soil desiccation levels were slight or medium in T5, T12, and T25 plots but were mainly medium or severe in T35 plots. Future warming and drying climate would greatly increase the SDI in all plots, and its impacts increased with tree ages in the upper soil layers (0–40 cm) but decreased with it in lower layers (40–100 cm). However, it only had limited influence on the responses of soil desiccation to the climate in different hydrological years. Precipitation and vapour pressure deficit dominated soil desiccation in the upper and lower layers, respectively, and both showed linear relationships (p < 0.05) with the SDI in corresponding soil layers. The SDI in the lower layers should be given full attention when controlling soil desiccation, and its rapid increase thresholds of tree ages were 20.3a under historical scenarios, but were unexpectedly delayed to 22.8a under future climate conditions. Our study not only improved the scientific understanding of the soil water conditions and their responses to climate change, but also provided valuable guidelines for the management of water resources and the restoration of the ecological environment in the semi-arid Loess Plateau.

Effect of Nitrogen Application Rate on Grain Yield, Dry Matter and Nitrogen Accumulation and Remobilization in a Winter Wheat-Fresh Maize Cropping System

Three-harvest in two years is a traditional farming system in the Jinzhong Basin of Shanxi Province of the eastern Loess Plateau in China. Recently, an innovative farming system of winter wheat-fresh maize with two-harvest per year, making full use of temperature and light resources, is proposed. However, there is little known of the optimal nitrogen application rate for the innovative farming system to increase crop yield and improve ecological environment. In current study, six nitrogen application rates were carried out, consisting of winter wheat/fresh maize season 0/0 kg·ha-1 (N0, Control), 75/75 kg·ha-1 (N75), 150/150 kg·ha-1 (N150), 225/225 kg·ha-1 (N225), 300/300 kg·ha-1 (N300) and 375/375 kg·ha-1 (N375). The grain yield, dry matter and nitrogen accumulation and remobilization were analyzed to determine the optimal nitrogen application rate in the winter wheat-fresh maize cropping system in the Jinzhong Basin. The results showed that in the winter wheat and fresh maize season, compared with the N0, N75 and N375 treatments, total dry matter accumulation at winter wheat maturity and fresh maize harvesting increased significantly by 82.9%-94.5% and 26.1%-197.1%, respectively, and dry matter remobilization in leaves and stem+sheath (+tassel) increased significantly under the N150 treatment. Total nitrogen accumulations under the N150, N225 and N300 treatments increased significantly by 58.2%-162.9% and 55.7%-301.7% compared with those under the N0 and N75 treatments, respectively. Nitrogen remobilization in the kernel and stem+sheath (+tassel) under the N150 treatment increased significantly compared with the N0 and N75 treatments. In addition, nitrogen partial factor productivity of winter wheat and fresh maize under the N75 and N150 treatments increased significantly by 36.7%-534.1% and 45.2%-390.4% compared with the other nitrogen treatments, respectively, and nitrogen uptake efficiency also increased significantly by 79.1%-321.4% and 58.3%-239.5%, respectively. The yield of winter wheat and fresh maize under the N225 treatment was the highest, which significantly increased by 54.1% and 71.6% compared with that under the N0 treatment, respectively. In summary, nitrogen application rates of 150-225/150-225 kg·ha-1can be potential recommended use amounts with higher crop yield and nitrogen use efficiency in winter wheat-fresh maize cropping system in the Jinzhong Basin.

Disentangling the Impact of Event‐ and Annual‐Scale Precipitation Extremes on Critical‐Zone Hydrology in Semiarid Loess Vegetated by Apple Trees

AbstractThe extent and mechanisms by which precipitation extremes affect hydrological processes in the critical zone (CZ) of loess possessing a thick unsaturated zone remains poorly understood. To this end, we here employed a coupled liquid‒vapor‒heat‒airflow STEMMUS (simultaneous transfer of energy, mass, and momentum in unsaturated soil) model to investigate the impact of extreme precipitation, at both event and annual scales, on CZ hydrological processes within a semiarid loess site vegetated by apple trees on China's Loess Plateau. At the event scale, the vapor flux was two orders of magnitude lower than the liquid water flux. However, the thermal vapor flux penetrated to depths of 200 cm, whereas the isothermal liquid water flux only infiltrated to 100 cm during the study period, implying that thermal‐gradient‐driven vapor transfer is an important mechanism for deep‐layer recharge (DLR). At the annual scale, the DLR below 200 cm during extremely wet years was 6.5 times larger than that during extremely dry years. In contrast, extreme changes in climate had only limited impacts on evapotranspiration; the difference between extremely wet and extremely dry years averaged only 35 mm, much less than the difference in precipitation, which averaged 310 mm. However, the extremely dry years showed a higher ratio (0.58) between transpiration and evapotranspiration than did the extremely wet years (0.51). The findings reported here improve our understanding of CZ hydrological processes related to precipitation extremes in semiarid loess regions.

Effects of planting patterns plastic film mulching on soil temperature, moisture, functional bacteria and yield of winter wheat in the Loess Plateau of China

The yield of winter wheat is hindered by drought and low temperature in the Loess Plateau of China. Two common mulching methods to conserve soil moisture, ridge furrows with plastic film mulching (RP) and flat soil surfaces with plastic film mulching (FP) are helpful for wheat production. Our previous study indicated that FP could improve wheat yield more effectively than RP, but the reason remains unclear. The effect of mulching method on functional bacteria also needs to be further studied. In this study, winter wheat was employed to evaluate the impacts of mulching method on soil temperature, moisture content, microorganisms and grain yield. The results showed that FP had a warming effect when the soil temperature was low and a cooling effect when the temperature was too high. However, the ability to regulate soil temperature in the RP method was unstable and varied with year. The lowest negative accumulated soil temperature was found in the FP treatment, which was 20–89 and 43–99% lower than that of the RP and flat sowing with non-film mulching control (NP) treatments, respectively. Deep soil moisture was better transferred to topsoil for wheat growth in the FP and RP treatments than the NP treatment, which made the topsoil moisture in the two treatments (especially FP) more sufficient than that in the NP treatment during the early growing stage of wheat. However, due to the limited water resources in the study area, there was almost no difference between treatments in topsoil water storage during the later stage. The wheat yield in the FP treatment was significantly higher, by 12–16 and 23–56%, respectively, than in the RP and NP treatments. Significant positive correlations were observed among the negative accumulated soil temperature, spike number and wheat yield. The Chao1 and Shannon indices in the RP treatment were 17 and 3.9% higher than those in the NP treatment, respectively. However, according to network relationship analysis, the interspecific relationships of bacteria were weakened in the RP treatment. Phosphorus solubilizing, ammonification and nitrification bacteria were more active in the RP than in the FP treatment, and microbes with nitrate reduction ability and plant pathogens were inhibited in the RP treatment, which improved nutrient availability and habitat for wheat.

Spatial distributions of soil nutrients affected by land use, topography and their interactions, in the Loess Plateau of China

Soil nutrient availability and their spatial distributions are strongly related to land use and landscape morphology. This study aims to address the knowledge gap regarding the interaction between these factors and the underlying mechanisms. We selected five land uses (grassland with Artemisia gmelinii, woodland with Robinia pseudoacacia, shrubland with Caragana korshinskii and Hippophae rhamnoides, and apple orchard with Malus pumila) and nine slope positions across hillslopes in the Loess Plateau, China, to investigate their combined effects on the contents and stocks of soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP). Parametric and non-parametric statistical tests were conducted to determine the significant differences in the means or the medians of the soil nutrient variables. Results showed that the SOC and TN contents of shrubland with Caragana korshinskii were statistically significantly greater than those of the grassland (p < 0.05). SOC and TN contents generally decreased from the upper slope to the middle slope, and to the foot slope for the grassland, woodland and shrublands, and on the contrary, an increasing trend from the upper slope, to the middle slope, and to the foot slope was identified for the apple orchard. This study highlights that land use, slope position and their interaction have significant effects on the spatial distributions of soil nutrients. It provides essential empirical evidence for the identification of the optimal vegetation type and slope positions in land management and vegetation restoration activities.

Water use characteristics of the artificial forests black locust (Robinia pseudoacacia) and Chinese pine (Pinus tabulaeformis) on the Loess Plateau of China

AbstractThe broad leaf, deciduous black locust (Robinia pseudoacacia) and needle leaf, evergreen Chinese pine (Pinus tabulaeformis) are the major afforestation species on the Loess Plateau of China, accounting for 29.5% and 15.9% of the afforestation area, respectively. The decay of black locust and drying of the forest land soil in this region have caused serious concerns among scientific community and local management authorities. Understanding the hydrological characteristics of the afforestation plantation may provide clues for choosing proper species. However, previous studies demonstrated diverse or even contradictory understandings due to incomplete observations of the water balance. We used a model to reconstruct the water balance based on 5 years (2015–2019) of incomplete soil water and transpiration observations at the field for these two species. The R‐squares of linear regression analysis of simulated and observed soil water in black locust and Chinese pine plantations were 0.69 and 0.90, respectively; and transpiration was 0.62 and 0.69, respectively. Based on the reconstructed water balance components, we found that (1) black locust and Chinese pine had similar annual evapotranspiration in quantity. However, the Chinese pine transpired less and evaporated more water from the canopy than the black locust, with their ratios to the annual precipitation 50.7% and 69.7%, 26.3% and 17.2%, respectively; (2) the Chinese pine has higher evapotranspiration than the black locust in the non‐growing season, accounting for 19.5% and 9.2% of the annual evapotranspiration, respectively; and (3) the Chinese pine is more tolerable to soil water drought than black locust. The findings may suggest that the Chinese pine is a more favourable species for afforestation than the black locust from the point view of drought resistance in this region.

New archaeobotanical evidence for Tolai hare (Lepus tolai) millets-consumption on the Loess Plateau of China

This study presents the results of a preliminary investigation on micro-botanical remains preserved on Tolai hare (Lepus tolai) teeth recovered from Yangjiesha, a site located on the north of the Loess Plateau in China, dated circa. 4900B.P. The microscopic analysis reveal that starch grains from Triticeae, millets and their wild relatives as well as wood tissue fragments were identified in dental residues This implies that, in the context of the intensive development of millet farming at about 5000B.P., hares at Yangjiesha may have been active inside or near the agricultural settlement areas and formed long-term interactions with humans against the new agricultural ecology of the north Loess Plateau.

Responses of root water uptake to soil water dynamics for three revegetation species on the Loess Plateau of China

AbstractIn water‐limited ecosystems, soil water regulates root water uptake (RWU) strategies. However, RWU responses to soil water changes under different species are not well‐understood. We assessed RWU responses of three revegetation species [shrub (Hippophae rhamnoides Linn.), coniferous forest [Platycladus orientalis (L.) Franco], and broad‐leaved forest (Robinia pseudoacacia L.) during the dry (May to June) and rainy (July to August) seasons in 2020 on the Loess Plateau using stable isotope methods. We sampled soil and xylem for each species at approximately weekly intervals and used the MixSIAR model to quantify RWU contribution with stable water isotopes. The results indicated that soil water in the shallow (0–40 cm) and middle (40–200 cm) soil layers fluctuated more strongly than the deep soil layer (200–300 cm) due to precipitation and evapotranspiration. Before precipitation in the dry season, most of the RWU for H. rhamnoides and R. pseudoacacia (97% and 98%) came from the middle layer under limited soil water. After precipitation in the dry season, the three species had similar RWU responses to soil water changes. After precipitation in the rainy season, the RWU change of H. rhamnoides and R. pseudoacacia with deep soil drying was more sensitive to soil water change than P. orientalis with sufficient deep water on August 3 and 11, while, the RWU of H. rhamnoides was more sensitive to soil water change than R. pseudoacacia on August 11 and 19. Thus, by switching its water‐use strategy, H. rhamnoides adapted better to the soil water environment than P. orientalis and R. pseudoacacia. This finding will help in selecting the optimal revegetation species for water use in a changing climate environment.

Runoff and soil loss responses of restoration vegetation under natural rainfall patterns in the Loess Plateau of China: The role of rainfall intensity fluctuation

Vegetation restoration is effective at combating soil erosion. The intensity distribution within rainfall events (rainfall pattern) has undergone evident variations under global change, which was crucial for hydrological and erosive processes. However, the responses of runoff and soil loss to natural rainfall patterns under restored vegetation are not fully understood. In this study, the rainfall hyetograph, runoff and soil loss data from forestland, shrubland and grassland plots were collected during 2012–2016 in the Yangjuangou catchment, a typical hilly and gully catchment in the Loess Plateau of China. The roles of natural rainfall pattern on runoff and soil loss were explored, and the consistency of these effects among three land use types was examined. The erosive rainfall events were grouped into three rainfall patterns based on the occurrence time of the most intense rainfall, including the early-peak, center-peak and late-peak patterns. The results indicated that the early-peak pattern contributed to approximately 50 % of erosive events, which also yielded the significantly larger RC (runoff coefficient) (0.91 ∼ 3.07 %) and larger SLC (soil loss coefficient) (0.07 ∼ 0.13 g m−2 mm−1) compared to center-peak (0.08 ∼ 0.11 % and 0.005 ∼ 0.010 g m−2 mm−1) and late-peak pattern (0.14 ∼ 1.05 % and 0.003 ∼ 0.010 g m−2 mm−1). Generally, the influences of rainfall pattern on runoff and soil loss were consistent between the three land use types. The RC-SLC relationships were well described by a power function, and the early-peak (0.022) and center-peak pattern (0.027) showed larger magnitude term compared to the late-peak pattern (0.010), revealing larger capacity of runoff to produce erosion. This study shed light on the crucial role of natural rainfall pattern in yielding runoff and soil loss from vegetated hillslopes, and highlighted that the early-peak pattern may be responsible for triggering serious soil erosion in the semi-arid environment.

Optimizing nitrogen fertilizer application to improve nitrogen use efficiency and grain yield of rainfed spring maize under ridge-furrow plastic film mulching planting

Efficient nitrogen (N) fertilizer management strategies are integral components of rational farmland cropping systems. Ridge-furrow plastic film mulching (RFPM) is a widely used micro-catchment planting system in the rain-fed farming area of the Loess Plateau in China, there are still problems of excessive N fertilizer application and unreasonable application method under this system. In this study, we conducted a two-year field experiment with traditional flat planting (FP) as a control, to determine the effect of N application rate (180 kg ha–1, 240 kg ha–1, and 300 kg ha–1) on soil nitrate N, total N, grain yield and N fertilizer partial factor productivity (NFPF) of spring maize under RFPM with three ridge–furrow ratios (RF40–70 = 40 cm:70 cm; RF55–55 = 55 cm:55 cm; RF70–40 = 70 cm:40 cm). In addition, under N application rate of 240 kg ha−1, a micro-plot experiment was conducted to determine the fate of fertilizer N by applying N15-labeled urea on ridges and in furrows under RFPM, respectively. The results showed that compared with flat planting (FP), RFPM reduced the residue of NO3–-N (0–200 cm soil layer) and accumulation total N (0–100 cm soil layer) in the soil under three N application rates, especially under RF70–40. Reducing the N application rate decreased the accumulation of NO3–-N and total N under each ridge-furrow ratio. Compared with FP, RFPM increased the N accumulation, grain yield, NFPF for spring maize under all three N application rates. However, the N harvest index decreased as the N application rate increased under RFPM, thereby suggesting that the targeted N production could be improved for plants by optimizing the N application rate. By balancing the grain yield and NFPF, the optimal N application rates under FP, RF40–70, RF55–55, and RF70–40 were determined as 223 kg ha–1, 204 kg ha–1, 228 kg ha–1, and 207 kg ha–1, respectively, and these results also suggest that RFPM can lower the N input threshold compared with FP. In addition, N isotope tracing was used to clarify the fate of fertilizer N under RFPM, which showed that the contribution of fertilizer N to plants increased when N fertilizer was applied in furrows, and reduced the residual proportion of fertilizer N in soil. Therefore, our findings suggest that N fertilizer should be applied in the furrows after forming the ridges and furrows under RFPM.

Spatial variation in soil water on a hillslope with ephemeral gullies restored by different vegetation restoration modes on the Loess Plateau

Vegetation restoration in an ephemeral gully (EG) can alter the traits of soil, vegetation, and microtopography, and therefore likely influences soil water. Nevertheless, few results have been reported regarding the response of soil water regime to vegetation restoration modes in EGs in semiarid region. This research was designed to clarify the spatial variation in soil water in an EG with different restoration modes on the Loess Plateau of China. For the selected EG, the two banks of ephemeral gully were well restored by natural succession and artificial planting. Soil water content (θg) was quantified on the ephemeral gully floor (F), natural successional restored ephemeral gully top (NT), and artificial planted restored ephemeral gully top (AT) in both the vertical and longitudinal directions. A sloping farmland was selected as the control. The results revealed that θg increased significantly with soil depth (i.e., 0–1 m) and the distance from the ephemeral gully head (i.e., 0–60 m). In the vertical direction, the mean θg of the six test points of the ephemeral gully floor was 1.1 to 1.2 times greater than that of the control in each soil layer, while the mean θg of the six test points of NT and AT decreased by 12.3 % to 15.6 % and 29.2 % to 29.9 % compared to the control in each soil layer. Along the longitudinal direction, the θg (i.e., 0–1 m soil layer) abided by the pattern of F > NT > AT. The difference in θg between the three ephemeral gully units and their variations in the vertical and longitudinal directions were mainly driven by the variations in soil clay content, bulk density, organic matter content, plant root density, plant litter density, and the distance from the ephemeral gully head. The findings are useful to clarify the spatial variation in soil water and to select a reasonable vegetation restoration mode on hillslopes in semiarid regions.