Soil Salt Content Research Articles

Soil-geochemical assessment of salinization of the territory adjacent to the Kuchuk salt deposit (Altai Krai)

A soil geochemical analysis was conducted to assess the impact of the exploitation of the Lake Kuchuk salt deposit on the salinization of the soils in the adjacent areas. The specific characteristic of the soil forming in the Kulunda steppe is the wide distribution of salinization processes. Solonetzes soils are distributed in the impact zone of the deposit exploitation; therefore, as background soils, we considered also Solonetzes. Background soils are located at a considerable distance (2–10 km) from industrial facilities. The results of the chemical analysis of the soil-water extracts showed that the area of the most intense salinization is concentrated in the eastern and southeastern parts of the depression of the former lake. Nowadays, a salt evaporation pond and an open salt storage, which are the main industrial sources of sodium sulfate dust, occupy the bottom of the lake. The maximum salt content (over 1%) was found in these parts of the basin and is associated with the prevailing wind direction in the study area. With an increase in the hypsometric level of the surfaces and the distance from the open technological sources of dust, as well as on the opposite slope of the basin, there was a sharp (2–3 times) decrease in the salt content. The total salt content in the background soils ranged from 0.3 to 0.6%. The specificity of the chemistry of soil salinization in the impact zone was the dominance of sulfates and sodium in the composition of the soil-water extract, and thenardite, which is a dehydration product of mirabilite, in the composition of salt crust minerals and salt efflorescences. In the background Solonetzes, the participation of soda in the chemical composition became more noticeable, which is a natural halogen geochemical feature of the Kulunda steppe. In the surface salt crusts in the background areas, a greater variety of minerals were noted, among which there were typical minerals of the evaporite association (gypsum, halite, calcite, dolomite, mirabilite) and their rare species (konyaite, wedellit).

Global Soil Salinity Estimation at 10 m Using Multi-Source Remote Sensing

Salinization is a threat to global agricultural and soil resource allocation. Current investigations of global soil salinity are limited to coarse spatial resolution of the available datasets (>250 m) and semiqualitative classification rules (five ranks). Based on these two limitations, we proposed a framework to quantitatively estimate global soil salt content in five climate regions at 10 m by integrating Sentinel-1/2 remotely sensed images, climate, parent material, terrain data, and machine learning. In hyper-arid and arid region, models established using Sentinel-2 and other geospatial data showed the highest accuracy with R 2 of 0.85 and 0.62, respectively. In semi-arid, dry sub-humid, and humid regions, models performed best using Sentinel-1, Sentinel-2, and other geospatial data with R 2 of 0.87, 0.80, and 0.87, respectively. The accuracy of the global models is considerable with field validation in Iran and Xinjiang, and compared with digitized salinity maps in California, Brazil, Turkey, South Africa, and Shandong. The proportion of extremely saline soils in Europe is 10.21%, followed by South America (5.91%), Oceania (5.80%), North America (4.05%), Asia (1.19%), and Africa (1.11%). Climatic conditions, groundwater, and salinity index are key covariates in global soil salinity estimation. Use of radar data improves estimation accuracy in wet regions. The map of global soil salinity at 10 m provides a detailed, high-precision basis for soil property investigation and resource management.

Quantifying the spatial water salinity threshold of saline water irrigation by applying distributed WAVES model

CONTEXTSaline water irrigation presents a viable solution to alleviate freshwater scarcity. However, it's crucial to consider the threshold of salinity, as excessive levels can adversely affect crop yield, crop productivity and soil sustainability. Additionally, due to varying surface conditions and management practices at the regional level, a distributed approach to saline water irrigation management is necessary. OBJECTIVEThe primary goal of this research was to develop a regional agro-hydrological crop model. The validated regional model was then employed to identify the spatial water salinity threshold for saline water irrigation. METHODSIn this research, we utilized the WAVES (WAter Vegetation Energy and Solute model), which was adapted for mulching environment and validated in severely arid and saline fields. To account for spatial variations, we applied a distributed method to upscale the WAVES to the regional level. Multisource and multiscale data were used for regional model validation. Different scenarios of salinity levels for saline water irrigation were simulated, and a comprehensive criterion to determine water salinity threshold was proposed considering cotton yield, water productivity and soil salt accumulation. RESULTS AND CONCLUSIONSModel evaluation indicated a high level of accuracy for the developed regional model. The comparison between simulated and measured values for soil salt content, soil water content, cotton leaf area index, measured lint yield, and statistical yield resulted in indices of agreement of 0.90, 0.71, 0.93, 0.58, and 0.70, respectively. The validated regional model was employed to simulate various saline water irrigation scenarios. The findings revealed that under identical irrigation water salinity, cotton cultivation on sandy loam soil is more productive but has a larger yield reduction percentage compared to silty loam soil. Moreover, the research indicates a groundwater depth of 1.5 m is associated with higher cotton production. Additionally, a spatial pattern of the irrigation water salinity threshold for saline water irrigation was determined, suggesting that the water salinity in most areas of the Tarim Irrigation District should not exceed 6 g L−1. Notably, in the current practice of pumping groundwater in situ for irrigation, approximately 46% of the areas are at risk, indicating that it's not suitable for saline water irrigation. SIGNIFICANCEThis study developed a distributed model under a typical irrigation district characterized by mulching, severe drought and salinization and defined the distributed spatial threshold for saline water irrigation. These research results hold significant implications for guiding regional-scale saline water irrigation and groundwater extraction.

Exogenous γ-Aminobutyric Acid Can Improve Seed Germination and Seedling Growth of Two Cotton Cultivars under Salt Stress.

Excessive salt content in soil has adverse effects on cotton production, especially during the germination and seedling stages. γ-aminobutyric acid (GABA) is an important active substance that is expected to improve the resistance of plants to abiotic stresses. This study focused on two cotton cultivars (Gossypium hirsutum L.: Tahe 2 and Xinluzhong 62) and investigated the impact of exogenous GABA (0, 1, 2, 3, and 4 mM) on seed germination, seedling growth, and related morphological, physiological, and biochemical indicators under salt stress (150 mM NaCl). The results showed that salt stress significantly reduced the germination rate and germination index of cotton seeds (decreased by 20.34% and 32.14% for Tahe 2 and Xinluzhong 62, respectively), leading to decreased seedling height and biomass and causing leaf yellowing. Salt stress induced osmotic stress in seedlings, resulting in ion imbalance (marked reduction in K+/Na+ ratio) and oxidative damage. Under salt stress conditions, exogenous GABA increased the germination rate (increased by 10.64~23.40% and 2.63~31.58% for Tahe 2 and Xinluzhong 62, respectively) and germination index of cotton seeds, as well as plant height and biomass. GABA treatment improved leaf yellowing. Exogenous GABA treatment increased the content of proline and soluble sugars, with varying effects on betaine. Exogenous GABA treatment reduced the Na+ content in seedlings, increased the K+ content, and increased the K+/Na+ ratio (increased by 20.44~28.08% and 29.54~76.33% for Tahe 2 and Xinluzhong 62, respectively). Exogenous GABA treatment enhanced the activities of superoxide dismutase and peroxidase, and reduced the accumulation of hydrogen peroxide and malondialdehyde, but had a negative impact on catalase activity. In conclusion, exogenous GABA effectively improved cotton seed germination. By regulating osmoprotectant levels, maintaining ion homeostasis, and alleviating oxidative stress, GABA mitigated the adverse effects of salt stress on cotton seedling growth.

Decision of Straw Deep Burial and Aluminum Sulfate Drip Irrigation in Soda Saline Soil Based on Grey Relation Analysis and TOPSIS Coupling

To investigate the impact of combining aluminum sulfate with straw and irrigation water to enhance soil quality in soda saline–alkali soil, in this study a field experiment was conducted in Tongliao City, Inner Mongolia Autonomous Region, China. With beet IM1162 as the indicator crop, four levels of aluminum sulfate dosage (30, 60, 90, 120 g m−2) and four levels of drip irrigation water quota (225, 270, 315, 360 m3 ha−1) were set. The study examined the impact of varying levels of aluminum sulfate and irrigation water on soil water salt and crop yield. Next, using a comprehensive evaluation method, the optimal quantities of aluminum sulfate and irrigation water needed for effective soil improvement were determined. The research findings indicate that the most effective treatment (W2S3) involved an aluminum sulfate dosage of 90 g m−2 and an irrigation quota of 270 m3 ha−1. This treatment resulted in significant improvements compared to the control (CK) group. Specifically, in the 0–50 cm soil layer, the following improvements were observed: the water storage capacity (SWS) increased by 51.7%; evapotranspiration (ET) increased by 16.2%; water use efficiency (WUE) increased by 55.0%; and irrigation water use efficiency (IWUE) increased by 98.1% (p < 0.05). These results emphasize the importance of optimizing the combination of aluminum sulfate dosage and irrigation water quota to improve soil conditions and crop performance. It is worth nothing that this study highlights the potential for enhancing water use efficiency and crop yield in agricultural practices, which can contribute to sustainable and efficient farming practices. The study results revealed significant improvements in soil quality and crop yield when compared to the control group (CK). Specifically, in the 0–50 cm soil layer: the soil salt content decreased by 19.8%, soil pH increased by 8.7%, and exchangeable sodium percentage (ESP) decreased by 34.0%. Moreover, the crop yield in the treatment group increased significantly, by 32.1%. These findings indicate the positive impact of the intervention on soil health and agricultural productivity. The study employed the game theory combination weighting method to comprehensively evaluate soil water, salt, and various yield indicators. The results showed that the sustainability weight for crop yield reached 0.116, emphasizing the aim of soil improvement: the sustainable enhancement of crop yield. This approach underscores the importance of balanced soil management practices to ensure long-term agricultural productivity and environmental sustainability. The comprehensive evaluation results of grey relation analysis and the TOPSIS coupling model showed that the soil improvement effect score was the highest when the dosage of aluminum sulfate was 61.7–120.0 g m−2, and the irrigation quota was 250.4–319.4 m3 ha−1, which was the recommended range for the local area. The research findings discussed in the provided sources contribute to the theoretical basis for soil improvement in soda–saline–alkali land.

Determination of salt tolerance level of Araz wheat (Triticum aestivum L.) cultivar concerning germination and growth parameters

As a result of climate change, an increased reliance on irrigation will be necessary for more arable lands. This will lead to elevated soil salinity levels, which will subsequently have a detrimental impact on both seed germination and plant growth. The primary aim of this research is to establish the threshold of salt tolerance in the Araz wheat cultivar (Triticum aestivum L.), using it as a representative example to delineate salt tolerance levels in other agricultural crop varieties. Araz is a widely cultivated wheat variety in Iraq and Kurdistan, and its salt tolerance was assessed by subjecting it to three different salt solutions: 0.01, 0.02, and 0.05 mol L-1, which corresponded to 0.9, 1.82, and 4.6 EC (dS m-1), respectively. The findings demonstrated notable impacts of the 0.01 mol L-1 salt concentration on germination and associated seedling parameters, with the exception of seed water uptake. The results indicated no discernible differences between the effects of 0.01 mol L-1 and 0.02 mol L-1 salt levels on the radicle's fresh weight. However, as salt levels increased to 0.05 mol L-1 , the adverse effects on growth became more pronounced. A salinity level of 4.6 EC (dS m-1) was found to significantly inhibit both germination and seedling growth, indicating that the Araz variety is sensitive to this level of soil salt concentration. This suggests that the recommended soil condition for cultivating Araz should have an electrical conductivity (EC) of less than 4.6 dS m-1.

Estimating and mapping the dynamics of soil salinity under different crop types using Sentinel-2 satellite imagery

Soil salinization is one of the main factors contributing to land degradation, affecting ecological equilibrium, environmental health, and the sustainable development of agriculture. Due to the spatial and temporal heterogeneity of soil properties and environmental conditions in a large-scale region, the monitoring accuracy of soil salinization can be challenging. This study investigated whether the classification of diverse crop types on a time series can improve the prediction accuracy of regional soil salinity levels. Specifically, we evaluated the changes in soil salt content (SSC) under diverse vegetation cover over time in the Hetao Irrigation District (HID) using multi-phase Sentinel-2 imagery and ground-truth data collected from June to September 2021 and 2022. Focused on sunflower and maize fields, this study analyzed the impact of classifying these two crop types and examining four distinct time series on the accuracy of SSC estimation. Five indices were selected as characteristic parameters from a pool of 17 vegetation indices (VIs) and 13 soil salinity indices (SIs) derived from satellite images. Moreover, three machine learning algorithms were used to establish SSC estimation models. The findings underscored the efficacy of classifying crop types and considering different time series in enhancing the response sensitivity of spectral indices to SSC and improving modeling accuracy. Among the spectral indices, VIs made more contributions to the SSC estimation model than SIs, achieving the highest coefficient of determination (R2) of 0.71. The artificial neural networks algorithm outperformed the other two machine learning algorithms in terms of accuracy and stability, yielding an optimal R2 of 0.72 and a Root Mean Square Error (RMSE) of 0.15%. This study proposed a modeling and mapping approach that considers crop types and various time series, offering valuable insights for accurately assessing soil salinization, guiding strategies for its prevention and remediation.

Biochar drives changes in soil bacterial communities and cotton growth by improving nutrients availability under saline conditions

AbstractApplying biochar to saline soil is a novel strategy for improving soil quality. However, how biochar addition amount affects soil nutrients, bacterial communities, and cotton growth at different stages remains unclear. Three biochar treatments, no biochar (BC0), 1% biochar (BC1, w/w), 3% biochar (BC3), and two cotton varieties, salt‐sensitive (SS) and salt‐tolerant (ST), were used in pot experiments, analyzing biochar effects on saline soil nutrients, bacterial communities, and cotton growth. The study found that biochar increased only organic carbon (SOC), total nitrogen (TN), and available potassium (AK) at the seedling stage. However, at the flowering‐boll stage, biochar also increased nitrate () and available phosphorus (AP) and reduced soil salt content. Biochar did not affect α‐diversity at the seedling stage, but BC3 reduced α‐diversity at the flowering‐boll stage. The principal coordinate analysis revealed changes in the soil bacterial community composition that were closely associated with biochar added. From the redundancy analyses, SOC and AK were the leading environmental factors for soil bacterial community composition changes. SOC, TN, and AK correlated positively with Proteobacteria, which increased their relative abundance through biochar addition and correlated negatively with Bacteroidetes, Chloroflexi, and Acidobacteria, which decreased their relative abundance due to biochar. Furthermore, the random forests analysis showed that SOC, Shannon index, and β‐diversity were significant predictors of cotton biomass. In summary, biochar drives changes in bacterial communities in saline soils by increasing nutrients such as SOC and AK, which affect cotton growth. This study provides data to support the application of biochar on saline soils.

Development and application of a monthly water and salt balance model for seasonally frozen agricultural and non-agricultural areas with shallow groundwater table

Long-term water and salt predictions in seasonally frozen arid agricultural regions with shallow groundwater tables are important for water conservation and soil salinity control. In this study, we developed a monthly water and salt balance model. The water balance model was built to obtain the water flux in the vertical layers and the water exchange between agricultural and non-agricultural areas. In the frozen period, the upward water flux from the groundwater was calculated using a function which considered the water table depth and the negative accumulated temperature, and the volume of groundwater entering the root zone was estimated by the thickness of the root zone and frozen depth. With regards to frozen soil, the model considered salt diffusion and expulsion as well as convection. Only four additional parameters were required to estimate the water and salt processes during the freeze–thaw period. Soil salinity and water table depth data from 1999 to 2018 were used to calibrate and validate the model in a seasonally frozen agricultural district in the Hetao Irrigation District (HID), China. The mean relative error (MRE) of water table depth and averaged soil salt content was −4.29 % and 8.65 %, and the root mean square error (RMSE) was 0.38 m and 0.02 g/100 g during the validation period of 2010–2018. The validated model was used to simulate future long-term soil salinity under different autumn irrigation. The results showed that increasing autumn irrigation water can decrease root zone soil salinity during the autumn irrigation period, but it has a limited effect on long-term annual average soil salinity. The groundwater table becomes shallower with increasing irrigation water in autumn, which results in greater upward salt in the adjacent freeze–thaw and crop-growing periods. This study offers a new perspective on reducing autumn irrigation in HID.

The Effect of Salt-dissolving Growth-promoting Rhizobacteria on the Growth of Pepper

Soil salinization is increasing, which seriously threatens the local ecological environment security and affects the development of social economy. Plant growth-promoting rhizobacteria (PGPR) is the bacterial population isolated from rhizosphere soil that has a growth-promoting effect on plants, which is of great significance for improving salt stress. In this study, pepper was used as the research object, and the effect of salt-dissolving and growth-promoting bacteria on pepper plants was studied by pot experiment. A total of 7 treatments were set up, 0 % salt sterility ( CK-0 % ), 0.5 % salt sterility ( CK-0.5 % ), 0 % salt-hydrolyzed salt-promoted strains ( C-0 % ), 0.5 % salt-hydrolyzed salt-promoted strains ( C-0.5 % ), 1 % salt-hydrolyzed salt-promoted strains ( C-1.0 % ), 2.0 % salt-hydrolyzed salt-promoted strains ( C-2.0 % ), 5.0 % salt-hydrolyzed salt-promoted strains ( C-5.0 % ). The results showed that : ( 1 ) The germination rate of pepper seeds inoculated with salt-dissolving and growth-promoting strains was significantly increased, and the salt concentration in the soil had no significant effect on the germination rate of pepper seeds. ( 2 ) Inoculation of salt-solubilizing growth-promoting strains and salt concentration in soil also had no significant effect on the plant height of pepper seeds. ( 3 ) The fresh weight and dry weight of pepper plants inoculated with salt-solubilizing and growth-promoting strains were significantly increased. This study has important scientific and theoretical significance for the more rational application of Plant growth-promoting rhizobacteria.

Effect of Continuous Cropping on the Physicochemical Properties, Microbial Activity, and Community Characteristics of the Rhizosphere Soil of Codonopsis pilosula

Effects of continuous cropping on rhizosphere soil physical and chemical properties, soil microbial activity, and community characteristics of Codonopsis pilosula were investigated. The C. pilosula plot(CK) fallow for five years and C. pilosula fields with different years of continuous cropping were studied using Illumina high-throughput sequencing technology combined with soil physical and chemical properties analysis. The response of rhizosphere soil physical and chemical properties, microbial activities, and microbial community characteristics to continuous cropping years of C. pilosula were investigated. The results were as follows:the contents of organic carbon, total phosphorus, total nitrogen, and salt in rhizosphere soil of C. pilosula increased with the extension of continuous cropping years. However, soil pH value decreased with the extension of continuous cropping years. Compared with that in the CK treatment, rhizosphere soil organic carbon content of C. pilosula in continuous cropping for one, two, three, and four years increased by 11.1%, 80.5%, 74.9%, and 78.2%, respectively. Total phosphorus content increased by 11.8%, 52.9%, 66.7%, and 78.4%, and total nitrogen content increased by 31.3%, 68.8%, 52.1%, and 56.3%, respectively. Soil salt content increased significantly under continuous cropping of three and four years, and soil conductivity increased by 54.2% and 84.7% compared with that in the CK treatment, respectively. The C/N ratio of microbial biomass in rhizosphere soil exhibited an increasing trend with the extension of continuous cropping years. Soil respiration entropy and microbial entropy showed a decreasing trend. With the increase in continuous cropping years, the diversity and abundance of bacteria in soil decreased, whereas the diversity and abundance of fungi increased. In addition, with the increase in continuous cropping years, the antagonistic effect between bacterial communities was enhanced, whereas the synergistic effect between fungal communities was mainly observed. Correlation analysis showed that soil total phosphorus, available potassium, carbon to nitrogen ratio of microbial biomass, soil respiration entropy, microbial biomass carbon, and electrical conductivity were the main factors affecting the changes in soil bacterial community characteristics. Soil total nitrogen, available potassium, available phosphorus, and soil respiration entropy were the main factors affecting the changes in fungal community characteristics. In conclusion, continuous cropping significantly changed the physical and chemical properties of soil and microbial activity and affected the abundance and diversity of bacteria and fungi in soil. This changed the interaction between microorganisms, which disrupted the stability of microbial communities in the soil.

Estimation of Soil Salt Content at Different Depths Using UAV Multi-Spectral Remote Sensing Combined with Machine Learning Algorithms

Soil salinization seriously affects the sustainable development of agricultural production; thus, the timely, efficient, and accurate estimation of soil salt content (SSC) has important research significance. In this study, the feasibility of soil salt content retrieval using machine learning models was explored based on a UAV (unmanned aerial vehicle) multi-spectral remote sensing platform. First, two variable screening methods (Pearson correlation analysis and Grey relational analysis) are used to screen the characteristic importance of 20 commonly used spectral indices. Then, the sensitive spectral variables were divided into a vegetation index group, a salt index group, and a combination variable group, which represent the model. To estimate SSC information for soil depths of 0–20 cm and 20–40 cm, three machine learning regression models were constructed: Support Vector Machine (SVM), Random Forest (RF), and Backpropagation Neural Network (BPNN). Finally, the salt distribution map for a 0–20 cm soil depth was drawn based on the best estimation model. The results of experiments show that GRA is better than PCA in improving the accuracy of the estimation model, and the combination variable group containing soil moisture information performs best. The three machine learning models have achieved good prediction effects to some extent. The accuracy and stability of the model are considered comprehensively, the prediction effect of 0–20 cm is higher than that of 20–40 cm, and the validation set coefficient of determination (R2), Root-Mean-Square-Error (RMSE), and Mean Absolute Error (MAE) of the best inversion model are 0.775, 0.055, and 0.038, and the soil salt spatial map based on the optimal estimation model can reflect the salinization distribution in the study area. Therefore, this study shows that a UAV multi-spectral remote sensing platform combined with machine learning models can better monitor farmland soil salt content.

Inversion of soil water and salt information based on UAV hyperspectral remote sensing and machine lear-ning.

Accurate diagnosis of water and salt information in saline agricultural lands is crucial for long-term soil quality improvement and arable land conservation. In this study, we extracted field-scale vegetation canopy spectral information by UAV hyperspectral information, transforming the reflectance (R) to standard normal variate transformation (SNV), multiplicative scatter correction (MSC), first derivative of reflectance (FDR) and second derivative of reflectance (SDR). We determined the optimal spectral transformation forms of soil water content (SWC), soil pH, and soil salt content (SSC) by the maximum absolute correlation coefficient (MACC), and extracted the feature bands by competitive adaptive reweighted sampling (CARS). We constructed an inversion model of soil water and salt information by partial least squares regression (PLSR), random forest (RF), and extreme gradient boosting (XGBoost). The results showed that R, FDR and MSC were the best spectral transformation types for soil water content, soil pH, and soil salt content, and the corresponding MACC were 0.730, 0.472 and 0.654, respectively. The CARS algorithm effectively eliminated the irrelevant variables, optimally selecting 16-17 feature bands from 150 spectral bands. Both soil water content and soil pH performed best with XGBoost model, achieving determination coefficient of validation (Rp2) 0.927 and 0.743, and the relative percentage difference (RPD) amounted to 3.93 and 2.45. For soil salt content, the RF model emerged as the best inversion method with Rp2 and RPD of 0.427 and 1.64, respectively. The study could provide a reference solution for the integrated remote sensing monitoring of soil water and salt information in space and sky, serving as a scientific guide for the amelioration and sustainable management of saline lands.

Effects of Three Long-Term Land Use Patterns on Soil Degradation in the Yellow River Delta: Evidence from Ecological Stoichiometry

The irrational land use patterns in the Yellow River Delta (YRD) have resulted in an imbalance in ecological stoichiometry, leading to secondary salinization and soil degradation. However, there is limited knowledge about the long-term response of soil and enzyme stoichiometry to land use. This hampers our ability to optimize land use in the YRD to alleviate nutrient limitation and thus promote ecological stoichiometric balance. We investigated the stoichiometry of soil and enzyme carbon (C), nitrogen (N), and phosphorus (P) in three land use patterns (Alfalfa artificial grassland, AG; wheat–maize rotation field, WM; native grassland, PC) established for 19 years in the YRD. The results showed that the soil stoichiometry of the three land uses in the YRD was lower than the world and Chinese averages, indicating lower C and N levels. Nutrient limitations of soil microorganisms were C and P due to an enzyme C:N ratio greater than 1:1 and vector angle greater than 45°. The three land use patterns have different advantages in alleviating nutrient limitations in the YRD. AG promotes soil macroaggregate formation, reduces soil salt content, improves nutrient availability, and mitigates N limitation. This makes AG more conducive to improving the poor soil structure, high soil salinity, and stoichiometric imbalance in the YRD to mitigate local soil degradation and be suitable for long-term continuous cultivation. WM is beneficial for increasing soil total C content due to straw return. However, WM does not reduce soil salinity. WM is more suitable for intercropping or crop rotation to improve soil C content in the YRD. Although PC can alleviate soil microbial C limitation due to its significantly lower vector length than AG and WM, the low nutrient levels hindered its ability to alleviate local soil nutrient limitation. In conclusion, our study provides a theoretical basis for rational land use in the YRD to mitigate soil degradation.

Remotely sensed estimation of root-zone salinity in salinized farmland based on soil-crop water relations

Accurate monitoring and evaluation of root-zone soil salt content (SSC) are critical for sustainable development of irrigated agriculture in arid and semi-arid areas. Based on soil-crop water relations and farmland evapotranspiration (ET) fused through remote sensing data, this study developed an inversion method to estimate root-zone SSC using a case study from cotton fields under film mulched drip irrigation (CFFMDI) in the Manas River Basin (MRB) over 21 years (2000–2020). Two hypotheses were set as: (1) relative transpiration can be approximated by relative ET; and (2) the soil water stress response function is linearly proportional to the ratio of relative water supply. Measured data from a field experiment and collected data from regional survey and literature retrieval were used to optimize parameters and verify the hypotheses and method. The method was then applied to analyze the spatial and temporal distribution characteristics and cumulative effects of root-zone SSC. Results showed that the hypotheses and the method were reasonable and reliable in estimating root-zone SSC (with coefficient of determination R2 > 0.50). Along with the popularization of film-mulched drip irrigation and the expansion of CFFMDI over the past 21 years, regional-scale root-zone SSC declined significantly with an annual attenuation rate of about 0.09 g kg−1. Due to the gradual reduction of irrigation amount per unit area, the decline was more rapid before 2011 (0.18 g kg−1), but slightly slowed down or even reversed at the end of the second decade (2015–2020). By 2020, the mean regional root-zone SSC reached 3.93 g kg−1. At the beginning of this century, MRB was mainly composed of mildly- (59.8%) and moderately-salinized CFFMDI (39.9%). However, by 2020, non- (69.7%) and mildly-salinized cotton field (28.2%) dominated the basin. The inversion method of root-zone SSC fully considers the water consumption mechanism of soil-crop system, thus shows great potential in effective planning and management of soil and water resources in arid salinized areas such as MRB.

Soil Quality Improvement with Increasing Reclamation Years in the Yellow River Delta

The saline soils in the Yellow River Delta are primarily affected by seawater intrusion resulting from the intersection of land and sea, which exhibit variations in salinity. The quality of these soils is also influenced by anthropogenic reclamation, including fertilization and irrigation. This study quantitatively evaluated the distinct soil properties and soil quality characteristics of the Yellow River Delta during different reclamation years (i.e., 0a, 1a, 5a, 10a, and 20a) using principal component analysis (PCA) and the Soil Quality Index (SQI). The findings indicated that the soil salt content (SSC) significantly decreased (p < 0.05) from 6.60 g/kg in the initial reclamation year (0a) to 1.63 g/kg in the 10th year (10a) and then slightly increased to 2.85 g/kg in the 20th year (20a). Consequently, the soil salinity level shifted from saline soil to slight salinity and then increased to medium salinity. Ammonium nitrogen (NH4+-N) notably increased by 8.31 mg/kg during the first five years of reclamation (0a to 5a) and gradually decreased by 2.56 mg/kg in the 20th year (20a). On the other hand, nitrate nitrogen (NO3−-N) experienced a significant decrease of 2–5 times after reclamation but continued to increase by 8.96 mg/kg with subsequent reclamation years. The available nitrogen (AN), available phosphorus (AP), and soil organic carbon (SOC) exhibited a significant increase of 24.87 mg/kg, 10.11 mg/kg, and 6.76 g/kg, respectively, with increasing reclamation years. However, available potassium (AK) gradually decreased after reclamation and then increased in the 20th year (20a). The values of SQI for different reclamation years were 0.307 for 0a, 0.339 for 1a, 0.320 for 5a, 0.318 for 10a, and 0.327 for 20a, indicating an increasing trend with increasing reclamation years. It was discovered that long-term reclamation significantly reduced soil salinity and improved soil quality, leading to the sustainable development of reclaimed saline soils in the Yellow River Delta.

Genetic diversity and salt tolerance assessment of 51 alfalfa (Medicago sativa) varieties under saline soil conditions

IntroductionSalt stress significantly impacts plant growth worldwide. Although alfalfa exhibits some tolerance to salt-alkali soils, the specific salt tolerance levels across different alfalfa varieties remain inadequately understood. For this purpose, we conducted a study to investigate the diversity of agronomic traits of alfalfa (Medicago sativa) under different soil environments in order to elucidate the salt tolerance of 51 alfalfa varieties.MethodsWe chose three different soil conditions for our study: normal conditions in Yantai as control, saline conditions in Yantai with soil salt concentrations ranging from 0.25 to 0.33%, and saline-alkali conditions in Dongying with soil salt concentrations ranging from 0.28 to 0.32%. We chose 51 alfalfa varieties from different sources as our experimental materials. Planting was conducted following a completely randomized block design with three replicates for each variety. Harvesting was performed when the plants reached 50% flowering, cutting them at a height of 5 cm above the ground. Comprehensive assessments encompassed 10 parameters, namely fresh weight, dry weight, stem-leaf ratio, branch count, plant height, crude protein content, crude fat content, acid detergent fiber, neutral detergent fiber, and ash content.ResultsOur findings revealed that the 51 studied alfalfa varieties displayed significant generalized heritability and coefficient of variation, indicating a high level of genetic diversity. Using principal component and cluster analyses, we categorized the varieties into three distinct clusters based on their agronomic traits. Grey correlation degree analysis revealed the commendable performance of Ying st, PI 672734, and Mei zuo across diverse environments. Genotype emerged as a predominant determinant of all parameters, except crude fat, acid detergent fiber, and neutral detergent fiber. Through the application of membership function analysis, PI 672768 emerged as a variety that demonstrated strong tolerance in both saline soil contexts.DiscussionDespite extensive previous studies indicating Zhong Mu No. 1 as a salt-tolerant alfalfa variety, its performance in this experiment did not distinguish itself. The findings of this study provide a fundamental basis for improving the management of saline-alkali lands and advancing alfalfa cultivation practices.

The effect of soil salt content and ionic composition on nitrification in a Fluvisol of the Yellow River Delta

Soil salinization is a common cause of land degradation and a major constraint on global food production. However, the effects that different salts have on soil biogeochemical processes such as nitrification are not fully understood. An incubation experiment was conducted with two different salt treatments applied at varying concentrations (sodium chloride addition, NaCl1: 2.06, NaCl2: 4.12, NaCl3: 5.00 g kg−1; sodium sulphate addition, NaS1: 5.00, NaS2: 6.07, NaS3:12.14 g kg−1). A Fluvisol soil was used as incubation medium and urea was supplied as the nitrogen source. Results showed that urease activities were reduced (28–76%) in salt treated soils on day 1, but recovered over time and finally surpassed that of the control on day 56. Moreover, the average urease activity of Na2SO4 treatments was 1.26 times higher than that of NaCl treatments on day 56. In addition, increasing soil salinity levels simultaneously reduced hydrolysis and nitrification rates, which led to the temporary accumulation of ammonium (NH4+-N) in soils for up to 14 days. The maximum contents of NH4+-N accumulation in NaCl3 and NaS3 were 1.64 and 1.48 times higher than those of NaCl1 and NaS1, respectively. Nitrification rates were inhibited more severely in soils dominated by Cl-. Low soil salt contents (less than 7.79 g kg−1) only delayed nitrification without reducing the total amount of nitrate (NO3--N) produced during the incubation. However, high salt contents (NaS3) significantly decreased the total NO3--N production. Our results indicate that nitrite oxidation process may also limit the speed of nitrification in salt-affected soils. Additionally, a new model is introduced to better simulate the dynamics of nitrification in salt-affected soils. In conclusion, soil salt content is the primary factor that inhibits nitrification. Anions affect the inhibitory strength of salinity on nitrification in soils with similar salinity levels, where Cl- is more suppressive than SO42-.

Study on Mechanical Properties of Sulfate Saline Soil Improved by CLI-Type Polymer Active Agent

Large amounts of soluble salts in a soil enhance the soil sensitivity to changes in its properties induced by changes in environmental conditions, such as easy dissolution in water and easy occurrences of salt heaving in low-temperature environments, which make the soil volume swell rapidly, leading to a series of engineering disasters. Moreover, the growth and development of surface vegetation will be inhibited due to excessive salinity, resulting in a gradual decline in the ecological functionality of the area. A polymer active agent (CLI) was selected for the ecological improvement of sulfuric acid saline soils. Triaxial compression tests and a test on the soluble salt content of the treated soil were carried out to investigate the effects of polymer active agent content and maintenance time on the mechanical properties and soluble salt content of sulfate saline soils. The results showed that the addition of CLI can improve the soil strength by increasing the cohesion of the specimen, and the improvement increases significantly with the content of CLI and the curing age. Meanwhile, the calcium ions in CLI can react with sulfate ions in sulfate-salted soils to produce calcium sulfate precipitation to alleviate soil salinization. The scanning electron microscopy (SEM) images indicated that an appropriate content of CLI (about 8%) can strengthen the soil structure through an excellent chelating ability, enhancing the strength of the soil.

Stoichiometric ratios in soil are relevant to the abundance of constructive species in reed-dominated saline-alkaline marshes

Ecological stoichiometry is an important mediator of the feedback between plant and soil systems, which greatly affects ecosystem processes and functions. However, how carbon (C), nitrogen (N) and phosphorus (P) stoichiometry in plants and soils influence helophytes’ performance to environmental changes remain unclear. In this study, the saline-alkaline marsh dominated by Phragmites australis in the Western Songnen Plain of China was investigated, and soil and plant samples along a saline-alkaline and flooding gradient were collected in 22 marsh sites. The results showed that C, N and P contents of leaf and soil and soil C:N:P stoichiometric ratios decreased significantly with increasing soil salt content (p < 0.05), but increased significantly with increasing flooding depth (p < 0.05). Soil C:N:P ratios decreased by 24.6 %–47.1 % in severely salinised sites (>5 g kg−1) than in unsalinised sites (<1 g kg−1), and they increased by 11.0 %–99.0 % in deeply flooded sites (>5 cm) than in shallowly flooded sites (<5 cm). Changes rates of foliar C:N:P ratios were remarkedly smaller than those of soil C:N:P ratios. Foliar N and P contents increased with increasing soil N and P contents, but foliar C:P and N:P ratios had negative associations with soil C:P and N:P ratios. The abundance of P. australis was explained by soil C:N:P stoichiometric ratios more than individual contents of C, N and P, in which soil N:P ratio played the largest role. These results suggest that maintaining the balances amongst C, N and P in soil is critical when restoring degraded marsh ecosystems.