Soil Water Content Characteristics Research Articles

Effects of vegetation on the spatiotemporal distribution of soil water content in re-vegetated slopes using temporal stability analysis

The temporal stability of soil water is a critical state variable affecting hydrological process and structural stability of slopes. In this study, the effect of vegetation on the spatiotemporal characteristics of soil water content (SWC) was assessed via temporal stability analysis. Three types of re-vegetated slopes (grass, shrub, and grass-shrub) were constructed to explore the spatiotemporal distribution of the SWC at depths of 0–100 cm. Then, the effects of different vegetation covers on the SWC were explored. The coefficient of variation, the Spearman rank correlation coefficient, the mean relative difference, and the index of temporal stability were utilized to demonstrate the temporal stability of the SWC. Finally, a method of estimating the soil water status of re-vegetated slopes based on representative locations was developed. The results revealed that soil water dynamics were considerably governed by vegetation and rainfall. The vegetation cover considerably reduced the similarity of the spatial distribution pattern of the soil water, which tended to be more stable under grass cover. The weight-based prediction method developed in this study can more accurately estimate the overall soil water state of re-vegetated slopes. It provides a theoretical basis for the reasonable layout of SWC monitoring points and guidance for the ecological restoration of engineering slopes.

Characterization of Soil-Plant Leaf Nutrient Elements and Key Factors Affecting Mangoes in Karst Areas of Southwest China

Baise city is one of the largest producers of mangoes, with this agricultural industry located in the karst region of Southwest China. However, calcium-rich and alkaline soils, severe soil fragmentation, and poor water and fertilizer retention capacity contribute to low mango yields and are key issues that limit the development of the mango industry in karst areas. Our study objectives were to identify the soil factors that limit mango growth and yield in the karst region of Southwest China, and to determine how these growth- and production-limiting conditions vary between landscape positions. This study analyzed the differences in soil nutrient and element contents in mango leaves, and used a Random Forest algorithm to calculate the eigenvalues of the mango leaf and soil elemental indices in the different geomorphic parts (slopes, transition zone, passes, high-yielding depressions, and low-yielding depressions) of the karst peak-cluster depressions. The key factors affecting the mango leaves and soil were screened based on the diagnostic results and the eigenvalues. The results showed that for the elemental contents of Fe, Mg, Ca, and Mn in the mango leaves in the different geomorphic parts of the karst, the peak-cluster depressions were generally deficient and varied significantly. The contents of available B (AB), soil organic matter (SOM), pH, total nitrogen, available Fe, available Mn, alkaline hydrolysis nitrogen, exchangeable Ca (Caex), exchangeable Mg, and other indices in the soils differed significantly, and AB, available Zn, and available K (AK) showed low or very low content levels. In addition, the key soil factors limiting mango yield in the karst areas were AB, fulvic acid, SOM, Fe, Mn, Caex, soil water, and AK; and the key mango leaf factors were Ca, Mn, Fe, Zn, and Mg. Consequently, the characteristics of soil water content, pH, and soil organic matter may be the main drivers affecting the differences in the mango yield and the elemental characteristics. These findings suggest that the addition of organic fertilizer could improve the quality and yield of mangoes in karst areas.

Effects of Warming and Increased Precipitation on Soil Respiration of Abandoned Grassland in the Loess-Hilly Regions

Clarifying the changing trends and driving factors of soil respiration in fragile habitats under the background of climate change is of great significance for understanding the regional carbon cycle and the conversion of ecosystem carbon source and sink functions. This research focused on grasslands that had been naturally abandoned and restored for 12 years in the loess hilly region of northern Shaanxi, using an open top chamber (OTC) and artificially increased natural rainfall to simulate climate warming and precipitation increase and their interaction. Furthermore, we used a combination of field monitoring and indoor analysis to explore soil water content, temperature, and nutrient characteristics and the response characteristics of soil respiration rate to warming and increased precipitation and further analyzed the key factors driving changes in soil respiration. The results showed that:① warming (W) significantly increased the 5 cm soil temperature, with an average increase of 1.34℃ throughout the sampling year, whereas the increased precipitation (P50%) treatment significantly reduced the 5 cm soil temperature, reducing the average 5 cm soil temperature during the entire sampling year by 0.88℃ and increasing the soil water content (SWC) at the same time. The SWC was 13.12% and 16.45% higher than that in the control (CK), respectively. In addition, compared with that in the CK, the treatment of warming and increased precipitation (WP50%) not only increased soil temperature but also increased SWC; in general, the increase in temperature and precipitation played an antagonistic effect on the influence of soil temperature and humidity. ② P50% significantly increased the content of soil organic carbon, dissolved organic carbon, and labile organic carbon, causing changes in the soil stoichiometric ratio and the distribution characteristics of labile-recalcitrant carbon components, whereas W did not have a significant impact on organic carbon. In addition, soil total nitrogen and phosphorus and available nitrogen and phosphorus nutrients were not significantly different between treatments. ③ P50% significantly increased the Rs rate, and the effect of W on the soil respiration rate mainly depended on the seasonal precipitation and temperature. It was demonstrated that warming in winter and seasons with abundant rainfall had a significant promotion effect on the soil respiration rate. The exponential fitting of soil respiration rate and 5 cm soil temperature found that the soil respiration temperature sensitivity (Q10) was the highest under the precipitation treatment, reaching 1.68, whereas the Q10 was the lowest under the warming treatment (1.50). ④ Linear regression analysis showed that soil organic carbon, dissolved organic carbon, and labile organic carbon were all significantly positively correlated with soil respiration rate. Variation partitioning analysis showed that soil temperature, SWC, and nutrient characteristics explained 64.43% of the variation in soil respiration rate. The soil temperature and SWC were the main controlling factors of the change in soil respiration rate, with an explanation degree of 31.16%. Correlation analysis also showed that there was a significant correlation between SWC, soil temperature and respiration rate, soil organic carbon, dissolved organic carbon, labile organic carbon, C:N, and C:P. In summary, the climate prediction of abandoned grassland tending toward warm temperatures and high humidity in the loess hilly region will significantly affect the regional hydrothermal environment and nutrient characteristics, change the distribution ratio of soil labile and recalcitrant carbon, and promote regional soil carbon emissions. The analysis results showed that the key factor driving the change in soil respiration rate of abandoned grassland in the loess hilly region was soil temperature and SWC characteristics.

The characteristics of seedling regeneration and its influencing factors of Pinus tabuliformis under different wildfire severity of Liaoheyuan Nature Reserve

PurposeThis paper studies the characteristics of the seedling regeneration, stand structures, undergrowth biomasses, litter amounts and soil water contents of planted forests of Pinus tabuliformis in the Liaoheyuan Nature Reserve after a fire disturbance in 2014 and analyzes the significant factors affecting seedling regeneration to offer a scientific basis for the ecological restoration of vegetation in burned areas. MethodsPlots of forest stands that experienced different fire severities (high severity, moderate severity, low severity) and control sample plots were used to study the significance of differences in seedling regeneration, stand structure, undergrowth biomass, litter amount and soil water content characteristics among stands under the effects of different fire severities by using single element variance analysis. The major factors affecting seedling regeneration characteristics were also analyzed here by using correlation and principal component analyses. Results(1) There was no significant difference in the density and growth characteristics (base diameter, plant height and crown diameter) of regenerated seedlings of Pinus tabuliformis under the different fire severities (P ​> ​0.05), and the spatial distribution of regenerated seedlings fit the aggregated distribution pattern. (2) There was no significant difference in diameter at breast height (DBH), plant height or crown diameter of Pinus tabuliformis under different fire severities (P ​> ​0.05), but there were highly significant differences in scorch height, biomass of undergrowth woody plants, biomass of undergrowth herbs, undecomposed litter amount, semidecomposed litter amount and soil water content under different the fire severities (P ​< ​0.01). (3) According to the correlation and principal component analyses, the results indicate that the characteristics of regenerated seedlings of Pinus tabuliformis are significantly affected by stand structure, undergrowth plants and litter and soil factors in burned areas but not by stand density. ConclusionIn the 5th year after a fire disturbance, the seedling regeneration of Pinus tabuliformis in a burned area was influenced by factors such as the stand structure, undergrowth plants, litter and soil. Low- and moderate-severity fires promote the natural regeneration of stands and are conducive to the stable balance of ecosystems.

Predicting soil water content using support vector machines improved by meta-heuristic algorithms and remotely sensed data

ABSTRACT Soil water content characteristics included field capacity (FC) and permanent wilting point (PWP) are key soil indicators to study permeability, soil water retention capacity, drainage, irrigation, plant water stress and solute movement. It is necessary to use an appropriate model for predicting these characteristics because of the hardness of their measurement. The present research shows a comparison of intelligent models included ANN, ANFIS, SVM and SVM optimised by firefly and particle swarm meta-heuristic algorithms (SVM-FFA and SVM-PSA) to predict soil water content at −33 and −1500 kPa matric potentials in agricultural soils. Results showed that the SVM-PSA and SVM-FFA hybrid models presented the best performance rather than the others, with predictor variables included geometric mean diameter (dg) of soil particles, bulk density, organic carbon, NDVI and NSMI and the values of R2 and NRMSE in validation dataset, 0.94, 0.081, 0.96 and 0.077 for FC and PWP in SVM-PSA, respectively, and 0.96, 0.079, 0.97 and 0.075 for FC and PWP in SVM-FFA model. Therefore, these intelligent machines are preferable for accurate prediction and could be used to predict soil water content of soils with different soil textures in other regions of Iran or even the world.

Laboratory characterization of sandy soil water content during drying process using electrical resistivity/resistance method (ERM)

Drought-induced evaporation can reduce soil water content and significantly alter soil hydro-mechanical behavior. Understanding the temporal and spatial distribution characteristics of soil water content during evaporation is of great significance for evaluating the encountered geotechnical and geo-environmental problems in arid or semi-arid regions. In this study, an electrical resistivity/resistance method (ERM) with a high spatial resolution of centimeter-level was developed for a small-scale laboratory test and applied to quantitatively characterize the evaporation-induced water content variations along a depth gradient. A total of 8 groups of initially saturated sandy soil columns (84 mm in diameter and 290 mm in height) were prepared, and eight pairs of mini electrodes (3.5 mm in diameter) were installed in each soil sample with a vertical distance of 30 mm. The soil columns were subjected to continuous drying. The changes in soil electrical resistance at different depths were monitored by the electrode couples. The gravimetric water contents at different depths were also measured at the end of drying. It is found that soil water content decreases exponentially with increasing electrical resistance. Based on the obtained data, a calibration relationship between soil gravimetric water content and corrected electrical resistance was well established with consideration of temperature effect. This relationship was validated successfully by the experimental results, indicating the feasibility of the developed ERM to characterize the soil water content dynamics during the drying process. Besides, the drying process with the movement of the evaporation front was discussed. The results of this study demonstrate the good performance of ERM in the estimation of temporal and spatial variations of soil water content and its potential application in arid or semi-arid regions with frequent droughts.

Spatiotemporal characteristics and temporal stability of soil water in an alpine meadow on the northern Tibetan Plateau

The spatiotemporal characteristics of soil water content (SWC) have a significant influence on vegetation degradation and growth in alpine meadow ecosystems. The spatiotemporal variability and temporal stability (TS) of SWC, however, have rarely been studied on the northern Tibetan Plateau owing to the rugged and hostile sampling environment. The objective of this study was to analyze the spatiotemporal variability and the TS of SWC in various layers of the soil, to a depth of 50 cm in a 33.5 hm2 plot, with the data obtained from 113 measuring locations collected on 22 sampling occasions during the growing seasons of 2015 and 2016. The SWC was moderately variable both in time (two consecutive growing seasons) and horizontal space (plot). The variabilities, however, did not vary consistently with increasing depth for the various dominant influencing factors. The SWC in the undeveloped, shallow, and stony alpine meadow soil was temporally stable; TS did not depend on depth due to disturbances by grass roots...

Long-term temporal variations of soil water content under different vegetation types in the Loess Plateau, China

The temporal characteristics of soil moisture are critical for the stability and sustainability of rebuilt ecosystems. In China's Loess Plateau (CLP), large areas of unsuitable croplands were restored to forest or grassland in order to control soil and water loss. Thus, knowledge of the temporal pattern and its controlling factors of soil moisture in revegetated areas over long-term is indispensable. In this study, four plots with different land uses (shrubland, grassland, fallow land and cropland) were set up on a loess slope in northern CLP. The profile soil moisture in the 0–4m soil layer was measured from 2004 to 2015. Semivariogram models were established to analyze the profile temporal characteristics of soil water content (SWC) over 12years of revegetation. The results suggested that: temporal stability of SWC under cropland was better than that under the three types of revegetated lands. Among the three types of revegetated lands, fallow land had stronger stability and higher value of SWC and was thus recommended as the best revegetation type. Generally, variation of SWC decreased with the increase of soil depth under shrubland, fallow land and cropland. However, under grassland, an inverse trend of SWS variation was observed and huge water absorption by deep grass roots was responsible for this trend. The temporal variation in SWC was under the joint influence of land use, soil depth and slope position, and land use was regarded as the dominant one. The study provided wider insight into scientific and reasonable vegetation restoration strategies in CLP region.

Temporal and spatial characteristics of soil water content in diverse soil layers on land terraces of the Loess Plateau, China

Soil water content (SWC) plays a significant role in land surface hydrological processes (e.g., evapotranspiration, infiltration and runoff) and the spatial and temporal distribution of vegetation in arid and semi-arid regions. The aim of this study was to analyze the temporal stability of the SWC distribution pattern and to examine the primary factors that influence SWC temporal stability over a year and during the rainy season at different soil depths in terraces. The SWCs in eight soil depths at intervals of 0.2m down to a depth of 1.6m were measured at 21 locations in terraces containing jujube trees (Ziziphus jujuba Mill.) over two periods (over a year and during the rainy season). The results showed that the mean SWC over a year was larger than that for the rainy season in the corresponding layers. The mean SWC was highest in the lower slope. Soil depth significantly affected the SWC distribution over time and space. Water uptake mainly occurred between 1.0 and 1.2m soil depth in both the rainy season and over the whole season. Moreover, the SWC demonstrated moderate spatial variability and was normally distributed at each depth. The temporal stabilities of SWC spatial patterns were strong for both the year period and the rainy season. The number of SWC representative locations varied depending on the soil depth. The SWCs measured at the best representative locations correctly represented the mean SWCs. Soil particles were the primary influencing factor affecting the mean relative difference, and root density was the primary influencing factor affecting the standard deviation of the relative differences. In conclusion, the SWC in the terraces showed stronger temporal stability during the rainy season compared to the year period.