Mean Soil Water Content Research Articles

Evaluation of subsurface soil water content estimate methods: Maximum entropy vs. exponential filter

Profile soil water content (SWC) is a vital variable in the atmosphere-vegetation-soil system. Although remote sensing currently can provide reliable surface SWC data (∼5 cm depth), acquiring accurate subsurface SWC data from existing reanalysis products remain challenging. In this study, we evaluated two widely used methods in estimating subsurface SWC, namely the exponential filter (ExpF) and the principle of maximum entropy (POME). The evaluation is carried out in two distinct areas on the Tibetan Plateau using ground observations collected from two monitoring networks: the Maqu network area characterized by cold humid climate and grassland and the Shiquanhe network area characterized by cold arid climate and bare ground. The results indicate that POME generally performs better than ExpF in both areas, particularly in deeper soil layers. Specifically, the accuracy of estimated SWC using the ExpF method decreases with depth, while it increases with depth using the POME method. Additionally, both methods achieve commendable performance at a depth of 10 cm in both areas. The deficiency of ExpF is mainly reflected in underestimations for dry cases, which is amplified with increasing depth. Dry cases account for 51 % in the humid area and 68 % in the arid area throughout the study period. Consequently, the ExpF method yields higher root mean square differences (RMSD) by 30 % and 113 % in the humid area at depths of 20 and 40 cm, respectively, compared to the POME method. Similarly, it results in higher RMSD values by 220 % and 200 % in the arid area. As expected, the superior performance of POME in deeper soil layers is primarily attributed to the incorporation of additional bottom and profile mean SWC observations. However, it also potentially introduces uncertainties when integrated with satellite-based data, which inherently contains errors compared to ground observations. To assess the potential of these two methods in large-scale applications combined with satellite-based datasets, this study conducted further evaluation of both methods with required input data derived from the soil moisture active and passive mission (SMAP). The results demonstrate that the performance of both methods in estimating subsurface SWC is acceptable in both humid and arid areas, although some bias is transferred from the input data. They achieve average RMSD values of 0.034 and 0.055 m3/m−3(−|−) in the humid area for the ExpF and POME methods, respectively, and 0.021 and 0.014 m3/m−3(−|−) in the arid area.

Spatio-temporal variability of soil water content across plot scales within a vineyard

Understanding spatio-temporal variability of soil water content (SWC) at different scales is of great importance for designing monitoring networks and assimilating observed data in hydrological modeling. The objective of the study was to examine spatio-temporal variability of SWC for different soil layers at different extent scales within an agricultural field. Spatio-temporal variability of SWC and the relationship between variability and mean were investigated at three extent scales for different soil layers of 0–100 cm in different years within an intensively irrigated vineyard. Nested sampling grids were used, and at each scale, there was a total of 16 points distributed regularly at the grids. The distance between any two adjacent sampling points was 25-m, 50-m, and 75-m for the three scales respectively. Overall, there was no consistent pattern regarding the change of mean, standard deviation (SD), and coefficient of variation (CV) with scales during the three years. For the surface soil layer, mean SWC was similar between scales, while SD was closely related to soil clay content at the sampling locations of each scale. For subsurface soils, the overall magnitude of variability of SWC was greater, whereas the difference in the variability between scales was lower than that of the soil texture of the corresponding soil layer. The proportional decrease of CV with increasing mean was found to be largely consistent between different years for all soil layers excluding 20–40 cm, but variable between scales and soil layers. For subsurface soil layers, the CV vs. mean relationship differed between relatively wet and dry years, indicating that factors controlling SWC dynamics for the layers below the surface layer were different depending on climatic conditions. Variance partitioning analysis showed that spatial variance accounted for at least 57 % of total variance for all cases, and the temporal variance at different scales fluctuated within a narrow range for subsurface soils for the three years. The results could benefit soil water content monitoring network design, calibration of soil moisture related parameters and assimilation of observed soil moisture data into field soil water modeling.

Importance of stemflow to soil water replenishment in a montane forest of Popa Mountain Park, Myanmar

Stemflow (SF), rainwater that reach the ground by flowing down along the branches and trunk, is important in maintaining soil water content (SWC) and recharging groundwater in a forest. This study aims to investigate the importance of SF to soil water replenishment in a montane forest. Measurements of gross rainfall, SF at 9 trees, SWC at two different points for two soil depths and infiltration rates at the two points were carried out in Popa Mountain Park (PMP) in 2019. SF rates in PMP were high ranging from 4.0% to 18.8% of total gross rainfall. Mean SWC near the tree were 18.5% at 5 cm depth and 21.7% at 15 cm depth, respectively, while those outside the canopy area were 11.4% and 9.0%, respectively. SWC near the tree were significantly higher for both soil depths. Similarly, significant higher infiltration rate was found near the tree. Near the tree, infiltration rate exceeded the amounts of individual rain events helped to store more rainwater as SWC in deeper soil layers. In PMP, thus, vegetative cover particularly forested areas are expected to have hydrological advantages in restoring rainwater through a large amount of infiltrated SF into the soil.

Effects of conventional soil and water conservation measures on soil moisture of sloping land in the loess region

ABSTRACT Traditional soil conservation measures were widely recognized for their excellent ability to promote rainwater infiltration in the loess region. However, little is known about how these measures affect the soil moisture variations under natural rainfall conditions. To compare their effects on soil water content, four different treatments were conducted at runoff plots, i.e., super absorbent polymer amendment (SCR), ridge–furrow rainwater harvesting with plastic mulching (CRP), the same measure with CRP but without mulching (CRN), and flat planting (FSN, control), soil moisture at multiple slope positions and depths were periodically measured. The results showed that in the top 0- to 30-cm soil, SCR and CRN relatively greatly varied with time, yet CRP and FSN changed less. The mean soil water content of these treatments generally followed the pattern of CRN > SCR > CRP > FSN. Responding to a heavy rainfall event, the recharge and depletion rates of soil water storage generally showed similar patterns of SCR > CRN > CRP > FSN in the topsoil, yet in the deeper soil they followed the patterns of CRP > CRN > FSN > SCR. It suggested that SCR and CRN could improve the water accumulation and infiltration performances in the topsoil, and thus may be more suitable for rain-fed crop planting on sloping farmlands of the loess region.

Spatial variability and forecast of soil water in the ultra‐deep loess profile across a south–north transect of the Chinese Loess Plateau

AbstractKnowledge of the spatial variability and forecast of soil water in the ultra‐deep (>21 m) loess profile are important for understanding the chemical, physical, and biological processes in the CZ. In this study, we regularly monitor soil water content (SWC) in deep soil profile along regional transect on the Loess Plateau. Descriptive statistical analysis found that the coefficient of variation (CV) of mean SWC in Ansai and Shenmu were 16.036% and 13.606%, respectively, indicating moderate variability. The CV of mean SWC in Yangling, Changwu, and Fuxian were 4.111%, 7.951%, and 6.117%, respectively, showing low variability. Geo‐statistical analysis indicated that mean SWC showed strong spatial dependence. Wavelet analysis showed that the approximative trend of mean SWC in five sampling sites showed an increased trend along depth series. In addition, a good fit line equation (R2 = 0.329) was established by using observed values and ANN‐forecast of three sites (Yangling, Fuxian, and Shenmu). And the RMSE values of five sample sites, respectively, were 1.302, 4.546, 2.662, 6.231, and 4.293. This study fills the gap in research' ultra‐deep (>21 m) soil water changes and forecast, evidence from soil borehole data. At the same time, our research provides valuable information for the vegetation restoration and modelling of deep soil water.

SOIL PHYSICAL QUALITY INDICES OF MINING-INDUCED DISTURBANCES IN SOIL WITHIN THE LOESS REGION OF WESTERN CHINA

Soil sampling and in situ measurements were conducted at 24 locations at three time points from May 2015 to April 2016. The statistical analysis showed that the variabilities of soil water content and soil penetration were moderate, while particle size and soil saturated hydraulic conductivity varied considerably. Rainfall before measurements contributed positively to the mean soil water content and negatively to particle size. This was mainly due to the soil aggregates and large soil particles being broken into smaller particles from rain splash. The detached small-sized soil particles could coalesce into larger-sized ones and even soil aggregates. Stressors in zones differ, resulting in variations between soil physical quality indices. The point-to-point comparisons indicated that the mean measured soil water content and soil saturated hydraulic conductivity were similar, if the measurements for these two indices were conducted under similar weather conditions during the same period between years. The investigation on the relationships among soil physical quality indices showed a negative relationship between the measured soil water content and soil saturated hydraulic conductivity. A positive correlation was also found between soil particle size and soil saturated hydraulic conductivity. Lower soil strength resulted in higher soil saturated hydraulic conductivity.

Effects of long-term afforestation on soil water and carbon in the Alxa Plateau.

Plantations in dry and semi-arid areas significantly affect the soil's ability to store carbon and maintain a stable water balance. It is yet unclear, though, how planted trees in these regions might impact the soil's carbon and water levels. As a forest ages, it is unknown how soil water and soil carbon interact with one another. In order to conduct this study, four Saxaul plantations in the Alxa Plateau were chosen, with the neighboring mobile sandy (MS) ground serving as a control. The ages of the plantations ranged from 5 to 46 years. The major topics of the study included the relationship between soil water and soil carbon, changes in the 0-300 cm soil layer's soil water content (SWC), soil organic carbon (SOC), and soil inorganic carbon (SIC) following afforestation. The findings demonstrated that, in comparison to MS, afforestation considerably increased SOC and SIC stocks. In comparison to MS, the SIC grew by 4.02 kg m-2, 4.12 kg m-2, 5.12 kg m-2, and 6.52 kg m-2 throughout periods of 5 years, 11 years, 22 years, and 46 years, respectively. SOC increased relative to MS by 2.55 kg m-2, 2.91 kg m-2, 3.53 kg m-2, and 4.05 kg m-2. Afforestation, however, also contributed to a considerable decline in deep SWC and an increase in the soil water deficit (SWD). In comparison to MS, the mean SWC values were lower at 5 years, 11 years, 22 years, and 46 years, respectively, by 0.48%, 1.37%, 1.56%, and 4.00%. The increase in soil carbon pool caused by sand afforestation actually came at the expense of a reduction in soil water due to a large negative association between deep SWC, SOC, and SIC. To limit SWC losses and encourage sustainable forest land development, we advocate suitable harvest management practices on forest land.

Contrasting Land and Atmospheric Controls on the Generalized Complementary Relationship of Evaporation Over Grasslands and Forests

AbstractThe generalized complementary relationship (CR) rooted on land–atmosphere coupling has been widely used to study evaporation over various ecosystems. Evaporation estimation models based on CR usually contain two parameters. The first one controls the shape of CR, and the second one is related to potential evaporation (Epo). Previous studies have found substantial variations in these parameters, but how they are affected by land surface and/or the atmosphere under conditions with varying land–atmosphere coupling remains unclear. In this study, the land and atmospheric controls for the generalized CR were comparatively investigated focusing on the two parameters of the sigmoid type function by using the data of 24 grassland and 19 forest flux sites and by considering the contrasting land–atmosphere coupling strength. The strong coupling to the outer atmosphere at the forest sites resulted in a large variation in the Epo‐related parameter and its significant correlation with the mean relative humidity. The shape parameter had a large variation at the grassland sites due to the weak coupling with the outer atmosphere and was significantly correlated with the mean soil water content. The simple parameterizations for the two parameters based on the correlations improved the predictions of monthly actual evaporation compared with the parameterizations for the fixed parameters corresponding to ecosystem types. The effects of land surface wetness and local advections on the generalized CR over grasslands and forests were also discussed respectively.

Precipitation consistently promotes, but temperature oppositely drives carbon fluxes in temperate and alpine grasslands in China

Temperate grassland (TG) and alpine grassland (AG) are two distinct grassland types with different climatic backgrounds and adaptation patterns. Little is known about the universal and divergent responses of TGs and AGs to climate change, particularly with regard to the carbon (C) fluxes. The large-scale responses of the C fluxes in different grasslands to climate change remain unclear, with only a few comparative studies of distinct responses of the C fluxes in TGs and AGs to climate change hinders our understanding of this subject. In this study, we conducted a large-scale transect study across the Mongolian, Loess, and Tibetan Plateaus in China to reveal the similarities and differences in the responses of the C fluxes in TGs and AGs to climate change. We used C flux data measured by eddy covariance from ChinaFLUX and published literature, covering the period from 2003 to 2020. The results showed that TGs and AGs in China were weak C sinks. Net ecosystem productivity in TGs and AGs exhibited opposite trends with increasing latitude, longitude, and altitude. Elevated water (mean annual precipitation and soil water content) consistently increased the C fluxes. Conversely, increased temperature (mean annual temperature and mean annual soil temperature) reduced the C fluxes in TGs and increased the C fluxes in AGs. The water factors promoted the C fluxes in both TGs and AGs by improving the leaf area indices. Conversely, the temperature factors had a strong direct, negative effect on the C fluxes in TGs and a weak direct, positive effect on the C fluxes in AGs, emphasizing the divergent patterns of the C fluxes in TGs and AGs and their responses to climate change. Overall, this study enhances our knowledge on C sinks and various grassland hydrothermal sensitivities.

Effect of Autumn Irrigation on Salt Leaching under Subsurface Drainage in an Arid Irrigation District

Non-growing season irrigation and farmland subsurface drainage play a crucial role in salt leaching and salinization control in arid irrigation areas. This study aimed to investigate the reduction of autumn irrigation quotas and drainage discharge while maintaining soil moisture retention and reducing soil salinization. Field experiments were conducted with different autumn irrigation quotas (160 mm for SD1, 180 mm for SD2, and 200 mm for SD3) combined with subsurface drainage (1.5 m drain depth and 45 m spacing). A control treatment (referred to as CK) without subsurface drainage received 200 mm of irrigation. The results showed that, after 31 days of autumn irrigation, the groundwater depth in all three subsurface drainage plots stabilized to 1.5 m, with the CK being 0.2–0.3 m shallower compared to the SD plots. The mean soil water content in the 0–150 cm soil layer of the SD1, SD2, SD3, and CK after autumn irrigation was 0.36, 0.39, 0.41, and 0.42 cm3cm−3, respectively. The combination of autumn irrigation and subsurface drainage significantly reduced the soil salt content. The mean desalination rates in the root zone (0–60 cm) soil layer were 57.5%, 53.7%, 51.9%, and 45.1% for the SD3, SD2, CK, and SD1, respectively. The mean desalination rate of 60–150 cm was not significantly different between the SD2 and SD3 (p > 0.05), and both were significantly higher than that of the SD1 and CK (p < 0.05). The drainage discharge was 31, 36, and 40 mm in the SD1, SD2 and SD3, respectively. The amount of salt discharge through the drain pipe increased with increasing irrigation quota, which was 1.22 t/ha, 1.41 t/ha, and 1.50 t/ha for the SD1, SD2, and SD3, respectively. Subsurface drainage is an effective way to prevent salt accumulation in the soil, and an autumn irrigation quota of 180 mm is recommended for leaching of salinity in the Hetao Irrigation District. These findings provide valuable insights into optimizing irrigation practices and managing soil salinization in arid regions.

Greenhouse gas emissions and environmental drivers in different natural wetland regions of China

Wetlands sequestrate carbon at the highest rate than any other ecosystems on Earth. However, the spatial and temporal dynamics of GHGs emissions from the wetland ecosystems in China are still elusive. We synthesized 166 publications that contain 462 in situ measurements of GHGs emissions from the natural wetlands in China, and further analyzed the variability and the drivers of GHGs emissions in eight subdivisions of China's wetlands. The results show that the current studies are mainly concentrated in the estuaries, Sanjiang Plain, and Zoige wetlands. The average CO2 emissions, CH4 fluxes and N2O fluxes from Chinese wetlands were 218.84 mg·m−2·h−1, 1.95 mg·m−2·h−1 and 5.8 × 10−2 mg·m−2·h−1, respectively. The global warming potential (GWP) of China's wetlands was estimated to be 1881.36 TgCO2-eq·yr−1, with CO2 emissions contributing more than 65% to the GWP value. The combined GWP values of Qinghai-Tibet Plateau wetlands, coastal wetlands and northeastern wetlands account for 84.8% of GWP of China's wetlands. Correlation analysis showed that CO2 emissions increased with the increasing mean annual temperature, elevation, annual rainfall, and wetland water level, but decreased with soil pH. CH4 fluxes increased with the mean annual temperature and soil water content but decreased with the redox potential. This study analyzed the drivers of GHGs emissions from wetland ecosystems at the national scale, and GWP values of eight wetland subregions of China were comprehensively assessed. Our results are potentially useful for the global GHGs inventory, and can help assess the response of GHGs emissions of wetland ecosystem to environmental and climate change.

Bamboo species, size, and soil water define the dynamics of available photosynthetic active solar radiation for intercrops in the Brazilian savanna biome

Bamboo has many potential applications in agroforestry systems. This study evaluated the photosynthetic active solar radiation available (PAR) to intercrops in three bamboo species as a function of estimated soil water content in the Brazilian savanna biome (tropical savanna climate with dry winters and rainy summers). The study was conducted from 2019 to 2021 (three to five years after planting), with clumps spaced at 8 × 5 m. PAR was measured below the bamboo at 0900, 1200, and 1500 h in the central, in-row, and inter-row positions. The estimated soil water balance was used to define the water available in the soil, which was correlated with the fraction of available PAR. The lowest value for the available PAR fraction occurred at the end of the maximum soil water content, being lower than 0.20 for Dendrocalamus asper and Dendrocalamus strictus and 0.80 for Guadua angustifolia. D. asper and D. strictus showed an inverse response rate of 0.50% and 0.75%, respectively, in the change in the available PAR fraction for each percentage change in the estimated mean soil water content 60 days prior to the PAR measurement date. G. angustifolia did not show any significant effect because of the smaller size of the culms and clump. The available PAR was correlated with estimated soil water content and species rate response. This information can be used to plan the cutting of bamboo culms to maximize the amount of PAR based on intercrop demand.

Detecting the impact of the “Grain for Green” program on land use/land cover and hydrological regimes in a watershed of the Chinese Loess Plateau over the next 30 years

To increase vegetation coverage and improve ecosystem services, the government has promulgated and implemented the “Grain for Green” policy since 1999. How and where vegetation cover increases and how land use/land cover (LULC) changes determine regional water resources and hydrological regimes. On the Chinese Loess Plateau (LP), an arid and semiarid area with fragmented topography and the transitional vegetation nature, accurately predicting LULC and vegetation change is particularly important. We employed a simple habitat analogy approach, and the Soil and Water Assessment Tool (SWAT) to predict potential vegetation restoration and LULC change and investigated their impact on the hydrological regime in a watershed of Liujiahe. Results showed that the maximum recoverable vegetation cover of the Liujiahe watershed is 71.1%, of which 9.2% still has potential for vegetation cover and 36.4% of the area vegetation continued to improve in the future. Future suitable afforestation areas are limited to 46.06 km2, which will result in cropland will decrease by 47.4%, and grassland and forestland will increase by 15.8% and 0.7%, respectively. However, SWAT results showed that vegetation restoration between the 1980 s and 2020 s has already reduced the annual mean runoff and soil water content (SW) by 44.2% and 43.9%, respectively, while evapotranspiration (ET) has increased by 12.6%; LULC changes in the next 30 years will further reduce runoff and SW by 15.6% and 11.1% respectively, and increase ET by 1.2%. Overall, large-scale vegetation restoration has greatly affected hydrological regimes on the LP. The area still has potential for vegetation enhancement; however, considering the limited rainfall and water-carrying capacity, the vegetation restoration of this watershed should be based on natural restoration or low water consumption grasses and shrubs to avoid a water resource crisis. These results provide a perspective for modelling LULC changes in areas with fragmented terrain and highly influenced by human activities, and provide an important basis for sustainably managing natural resources on the LP under long-term ecological restoration.

Experimental design of open-field temperature and precipitation manipulation system to simulate summer extreme climate events for plants and soils

Extreme climate events are expected to occur very frequently and intensively with climate change, and such extreme events can induce irreversible damage to plants and soils, as well as ecosystems. Accordingly, there is a need to understand the effects of extreme climate events on ecosystems. Here, we designed a temperature and precipitation manipulation system to simulate extreme climate events of heat, drought, and heavy rainfall. We constructed three soil surface temperature manipulation levels (control, 3 °C, and 6 °C increases) and three precipitation manipulation levels (control, drought, and heavy rainfall) with six replicates, and operated these from day of year (DOY) 195 to 233 in 2020. Infrared heaters increased the soil surface temperature during the extreme heat treatments. For precipitation manipulation, the automatic rainout shelter excluded ambient rainfall to produce drought conditions and an artificial rainfall simulator with spray nozzles produced heavy rainfall conditions. As a result, the soil surface temperature (°C ± one standard deviation) was higher in the 3 °C and 6 °C heated treatments than in the control by 2.7 ± 0.2 and 5.7 ± 0.5, respectively. The mean soil water content (vol. %) was 12.9 ± 8.6 in the drought treatment, 14.1 ± 7.8 in the control, and 16.1 ± 8.3 in the heavy rainfall treatment during the precipitation manipulation period. The results showed that the system design and operation were as expected. The designed system can be effectively utilized to investigate the responses of plants and soils to extreme climate events.

宁夏草地土壤有机碳空间特征及其影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 宁夏草地土壤有机碳空间特征及其影响因素 DOI: 10.5846/stxb202201040022 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（42061037） Spatial characteristics of soil organic carbon in grassland of Ningxia and its influencing factors Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:草地是重要的碳汇资源库，在陆地生态系统碳循环中扮演着重要角色。探明草地土壤有机碳的空间分布格局及其影响因素对于推动区域生态系统碳汇管理，实现"双碳"目标和绿色高质量发展具有重要意义。以宁夏三种主要草地类型为研究对象，基于野外样点调查，采用结构方程模型，分析了草地土壤有机碳的空间分布特征及其影响因素。结果表明：不同类型草地土壤有机碳含量表现为草甸草原高于典型草原，荒漠草原最低，垂直剖面上均随土壤深度的增加而降低。草甸草原和荒漠草原有机碳空间变异自表层向下逐渐增大，典型草原在20-40 cm土层变异系数达到最大。有机碳分布在区域上从南部六盘山山地向中部干旱风沙带逐渐降低。路矩分析发现，海拔高度、地上生物量、降水量、温度和土壤含水量可解释土壤有机碳空间变异的91.4%。海拔高度对土壤有机碳总效应最大（作用系数为0.78），海拔高度引起的降水和温度等要素区域分异间接影响土壤有机碳含量；地上生物量对土壤有机碳的直接正向效应最大（0.559）；降水量对土壤有机碳效应分为直接效应和作用于生物量及土壤含水量的间接影响；温度表现为通过生物量对土壤有机碳间接产生负向效应（-0.259）。宁夏草地土壤有机碳的空间分布主要受降水量和与其密切相关的生物量的支配作用。近20年来降水量增多和草地人为干扰减少，宁夏草地碳汇作用显著。 Abstract:Grasslands are important contributors of carbon sequestration among terrestrial ecosystems, which play an important role in the global biogeochemical cycle and energy exchange. Based on field surveys in July-August 2021, soil samples of meadow steppe, typical steppe and desert steppe in Ningxia were collected. The organic carbon contents, bulk density, total nitrogen, and pH of these soil samples were measured. We also monitored factors affecting carbon distribution such as altitude, annual precipitation, annual mean temperature, aboveground biomass and soil water content. Results indicated that content of the soil organic carbon decreased along the vertical soil profile, the average organic carbon content followed the order of meadow steppe > typical steppe > desert steppe. The distribution of grassland soil organic carbon gradually decreased from the Liupan Mountains in the south to the dry sand belt in the middle along the altitude. Soil organic carbon was significantly positively correlated with aboveground biomass, annual precipitation, altitude and soil total nitrogen density, and significantly negatively correlated with annual mean temperature (P<0.001), positively correlated with soil water content, and negatively with soil bulk density (P<0.01), and no obvious correlation with soil pH. Amos structural equation model was applied to evaluate the combined effects of environmental factors on grassland soil organic carbon. The most important factors affecting organic carbon was altitude (r=0.78), which mainly caused regional differentiation of precipitation and temperature to affect soil organic carbon indirectly; followed by aboveground biomass (r=0.559); then annual precipitation (0.539), which not only directly but also indirectly affected the soil organic carbon by altering aboveground biomass and soil water content positively. Annual mean temperature indirectly affected organic carbon negatively by influencing aboveground biomass (r=-0.259). The spatial distribution of grassland organic carbon in Ningxia was dominated by precipitation and aboveground biomass closely related to precipitation. In the past 20 years, with the increase of precipitation and the reduction of grassland anthropogenic disturbance, grassland ecosystem in Ningxia had a very significant carbon sink function. 参考文献 相似文献 引证文献

Soil moisture dynamics near a gully head in relation to the trigger of collapse in granite red soil slope in southern China

Gully head collapse is caused by the combined action of water and gravity, resulting in the loss of soil and water in granite soil slope of southern China. However, the soil moisture dynamics near a gully head and the mechanism triggering collapse are still unclear. A five-year high-time-resolution soil water content (SWC) dataset was obtained from soil moisture sensors that were buried at four to seven depths at three positions near a typical gully head on a hillslope in Hubei Province. From 2016 to 2020, two large collapse events were recorded in June in 2016 and 2017. The results showed that the soil moisture regimes were relatively heterogeneous in terms of spatial variation near the gully head: the closer to the gully head, the lower the SWC; the closer to the surface, the greater the SWC variation. This was attributed to the different texture and hydraulic properties of the soil layers. Moreover, the SWC showed obvious periodic dynamics on a seasonal and annual basis, which was consistent with the seasonal precipitation pattern. Although single heavy rainfall events increased the SWC at the surface, high SWC at deep sandy soil layers (≥130 cm) occurred only late in the rainy season after a long period of infiltration during the wet years of 2016 and 2017. Only when the antecedent SWC reached a certain threshold at the deep soil (0.37 m3 m−3, 0.22 m3 m−3, and 0.30 m3 m−3 at 130 cm, 210 cm and 270 cm depth, respectively), the additional heavy rain (53.6 mm in 9 h) triggered the gully head collapse. The exact time of collapse was indicated by a specific instantaneous variation in SWC near the gully head, when the mean SWC in the soil profile increased to high level, whereas the standard deviation of SWC was low during the heavy rainfall. The results confirm that gully head collapse is driven by rainfall and a high SWC in the deep sandy soil layer, as well as provides a useful reference for soil and water conservation control.

Simulation and evaluation of soil water and salt transport under controlled subsurface drainage using HYDRUS-2D model

Controlled drainage is an important measure to improve salinized soil in arid and semi-arid areas. However, free drainage during the growth period leads to excessive water loss, and crops lack water in the later growth period, resulting in crop yield reduction. Therefore, in arid and semi-arid areas, soil salts should be leached during the non-growing period, and drainage should be controlled during the growing period to ensure that crops have adequate water absorption and utilization, improve soil water availability for optimal water supply and salinity control. In this study, through field trials in 2020 and 2021, 3 treatments were set up. The depth of free drainage (FD) is common subsurface pipe drainage and the controlled drainage in the growth period were 40 cm (CWT1) and 70 cm (CWT2), respectively, and the drainage depth in the non-growing period was 100 cm. Using the HYDRUS-2D model to simulate the dynamic changes of soil water and salts in the 0–100 cm range, the calibration and validation of the HYDRUS-2D model were performed using the measured soil water and salt content values of 2020 and 2021. The results showed that the simulated soil water and salt contents agreed well with the measured contents. Controlled Drainage (CD) is a new agricultural drainage management practice that involves periodically increasing the outlet elevation of subsurface drainage pipes, CD significantly increased the water content of the 0–100 cm soil layer—especially at 0–40 cm depth—after growth stage irrigation. Under FD, CWT1, and CWT2, the 2-year mean soil water content of the 0–40 cm soil layer after growth stage irrigation in 2020 and 2021 was respectively 0.263, 0.278, and 0.267 cm3 cm−3, with the latter two values being higher by 5.70 % and 1.52 % than the former value, respectively. Soil water uptake by sunflower after irrigation mainly occurred in the 0–40 cm soil layer, which contributed 55.88–78.51 % of the total soil water uptake. Soil re-salinization occurred in the late growth stage (the flowering stage) under different treatments, with a mean re-salinization rate (relative to the period before spring irrigation) of 29.29 %, 33.48 %, and 30.34 % under FD, CWT1, and CWT2, respectively. Although the re-salinization rate was relatively high under CWT1 and CWT2, it had a low effect on crop growth as well as crop yield. HYDRUS-2D simulation was performed to compare different drain depths in the growth stage in order to determine the optimal drain depth for sunflower in moderately saline soils. To this end, the following metrics were considered for the main root zone (0–40 cm): soil water content, soil salt content, soil de-salination rate during spring irrigation, and soil re-salination rate in the late growth stage. Reduce soil salt content during spring irrigation, increase soil water content after irrigation during growth period, and minimize soil salt return rate in late growth stage, that is, to provide suitable water conditions for crop growth and minimize salt stress. The optimal drain depth during the growth stage was ultimately determined to be 50 cm.

Optimizing irrigation for winter wheat to maximize yield and maintain high-efficient water use in a semi-arid environment

Optimizing irrigation scheduling is vital in maintaining high crop yield and sustainable water use in water-limited regions worldwide. In this study, a 4-year field experiment (2016–2020) was conducted to evaluate the effect of six irrigation schedules on the grain yield performance, soil water content, plant evapotranspiration, and irrigation water use efficiency of typical winter wheat production system in the North China Plain. The six irrigation schedules involved irrigation at different growth stages, including one critical growth stage (60 mm per stage, I60), two stages (I120), three stages (I180), four stages (I240), and five stages (I300). No irrigation was performed in the control field (I0). The results showed that the plant height and yield components of winter wheat (spike number per hectare, kernels per spike, thousand-kernel weight) increased with the increase in annual irrigation amount. The grain yield in each study year increased quadratically (P < 0.05) with the annual irrigation amount. The soil water content in the 0–90 cm soil layer (where the wheat roots are mainly distributed) increased significantly during the growing season with the increase in annual irrigation amount. In I240, the mean soil water content (0–90 cm) during the growing seasons (17.3–22.6 %) was 61.7–80.8 % of the field water holding capacity, sufficiently favoring wheat growth. The average soil water storage (0–90 cm) during the wheat growing season ranged from 241.1 to 283.2 mm in the irrigation applied treatments, which were 21.7–63.8 mm (9.9–29.1 %) higher than in no irrigation treatment (I0, 219.4 mm). The 4-year averages of wheat grain yield did not differ significantly between I240 (7909.1 kg ha-1) and I300 (7868.6 kg ha-1); however, the average irrigation water use efficiency decreased from 33.0 kg ha-1 mm-1 in I240 to 26.2 kg ha-1 mm-1 in I300. Therefore, we recommend an irrigation scheduling at the regreening, jointing, flowering, and filling stages (I240, 60 mm per stage, 240 mm in total) to maintain high grain yield and sustainable soil water use for winter wheat production in the North China Plain and similar semi-arid regions.

What explains the year-to-year variation in growing season timing of boreal black spruce forests?

Amplified climate warming in high latitudes is expected to affect growing season timing of the vast boreal biome. It is unclear whether the presence of permafrost (perennially frozen ground) might have an influence on changes in growing season timing. This study examined how different environmental variables explained, either directly or indirectly, the variation in growing season timing of boreal forest stands with and without permafrost. We expected that environmental variables explaining the variation in growing season timing differed or had different explanatory power depending on permafrost presence or absence. The growing season was delineated from daily gross primary productivity (GPP) time series derived from 40 site-year data of net ecosystem carbon dioxide exchange measured with eddy covariance techniques over five black spruce (Picea mariana [Mill.])-dominated boreal forest stands in North America. In permafrost-free forest stands, a combination of start in canopy ‘green-up’ in spring and the timing of air and soil temperature increasing above freezing explained the start-of-season (SOSGPP). Results from commonality analysis and structural equation modeling suggest that canopy ‘green-up’ and air temperature directly affected SOSGPP in permafrost-free forest stands. In addition, soil temperature acted as mediator for an indirect effect of air temperature on SOSGPP. In contrast, none of the environmental variables, or their combination, explained the variation in SOSGPP in forest stands with permafrost. The explanatory power of environmental variables was more consistent regarding the end-of-season (EOSGPP). In both, forest stands with and without permafrost, EOSGPP was directly explained by mean soil water content in the fall and the first day of continuous snowpack formation. A better understanding how environmental variables control SOSGPP and EOSGPP in forest stands with and without permafrost will help to refine parameterizations of the boreal biome in Earth system models.

Spatial–temporal dynamics and recovery mechanisms of dried soil layers under Robinia pseudoacacia forest based on in‐situ field data from 2017 to 2020

AbstractPlanting Robinia pseudoacacia in water‐limited regions can promote soil and water conservation and ecological service functions. However, it can cause the formation of below ground dried soil layers (DSLs), causing land degradation and tree mortality. To ascertain the spatial–temporal dynamics and recovery processes of DSLs, we monitored the deep soil water content (SWC) to a depth of 500 cm at 27 sites on a typical R. pseudoacacia forest from 2017 to 2020 and calculated the evaluation indices of DSLs based on plant‐available SWC (PASWC) and stable field capacity (SFC). Compared with PASWC‐identified DSLs, the degree of SFC‐identified DSLs was more severe, although the spatial–temporal characteristics were similar. Severe soil desiccation was identified as 79% of the 500 cm profile dried out below 101 cm. The mean thickness of DSL and mean SWC within a DSL were 396 cm and 9.0%, respectively, and the quantitative index reached Grade III (severe) DSLs. All DSL indices demonstrated weak or moderate variability in space and strong variability in time. The heterogeneity of rainfall events and microtopographic positions explain the spatial–temporal variation of DSL indices well. A heavy rainfall event (&gt;50 mm) triggered the disappearance of DSLs at some sites, indicating the possibility of DSLs recovery based on field observations under natural condition. Microtopography (such as the swales) provides advantageous conditions to the recovery of DSLs by redistributing rainfall flow at the local scale. These results provide insights into DSLs recovery, which is useful for land development and rehabilitation in planted forests.