Increasing Soil Depth Research Articles

Variation of Physico-Chemical Properties among Different Soil Orders under Different Land Use Systems of the Majha Region in North-Western India

The impact of different soil orders and land use systems on the distribution of physico-chemical properties is the most critical matter to address in order to maintain sustainable agricultural production. Hence, the present investigation was carried out to study the variation in the physico-chemical characteristics of soil in diverse land use systems (LUSs), i.e., agriculture, horticulture, and forestry, under major soil orders (entisol, inceptisol, and alfisol) in the Majha region of Punjab. A total of 225 depth-wise (at 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm and 80–100 cm) soil samples were collected from three land-use systems under different soil orders. The mean values of the physico-chemical properties ranged from 6.80–7.50, 7.64–8.34 and 6.94–7.87 for pH; 0.13–0.42, 0.19–0.54 and 0.19–0.46 dS m−1 for EC; 0.14–0.99, 0.21–0.69 and 0.15–0.72% for OC; 0.75–2.07, 1.07–3.32 and 0.93–2.29% for CaCO3; 7.77–41.84, 10.56–40.23 and 7.24–39.51 kg ha−1 for P; and 98.37–334.68, 94.51–230.18 and 93.01–367.39 kg ha−1 for K under different land uses in soil orders entisols, inceptisols and alfisols, respectively. Soil parameters including pH, CaCO3, and phosphorus (P) distribution differed significantly among soil orders; however, soil EC, organic carbon (OC) and available potassium (K) did not. The inceptisols under the agricultural land use system (ALUS) had the highest soil pH, EC, and CaCO3 values. The highest soil OC content was found in entisols under forest land use systems (FLUS), followed by horticultural land use systems (HLUS). The highest values of soil-available phosphorous (P) were found in FLUS under inceptisols, while the highest amounts of soil-available potassium (K) were found in entisols and alfisols under ALUS and FLUS, respectively. Thus, the distribution of physico-chemical properties under different LUSs in each soil order is highly variable and does not follow any particular trend. In general, soil properties such as OC, P, and K content decreased with an increase in soil depth, while pH and CaCO3 values increased with depth in all land uses and soil orders. There was a positive correlation between soil OC and EC, as well as available P and K in the soils investigated. The available P and K are negatively correlated with soil pH and CaCO3 content in the soil. The principal component analysis (PCA) revealed that soil pH and OC were the most variable soil parameters, which influence the availability of other physico-chemical properties under different soil orders and land use systems. Therefore, it is suggested that the land use systems play an important role in the distribution of physico-chemical properties of soil in different soil orders. The results of the study will help students, researchers, and agricultural management staff in managing different land uses for maintaining soil fertility and productivity in alluvial soils of North-western India.

Partial least square regression based machine learning models for soil organic carbon prediction using visible–near infrared spectroscopy

Monitoring and assessment of soil organic carbon (SOC) are critical for maintaining and enhancing the productivity of agricultural soils. The SOC is commonly determined through soil sampling and subsequent laboratory analysis using chemical methods. This method though very precise is time-consuming, labour-intensive and expensive. Contrarily, visible and near-infrared reflectance spectroscopy (VNIRS) may be utilised to estimate SOC in a quick, labour-saving, and cost-effective manner. In this study, 72 soil samples were collected for SOC estimation and spectra collection. This current work proposes to investigate the use of PLSR scores in place of raw spectral reflectance to increase both the computation and model efficiency by reducing the number of input variables while retaining the maximum information present in the original data. With the existing indices, ratio and normalized difference indices were calculated in all possible combinations and were regressed to SOC content to identify the best-performing indices. Ten different multivariate models were evaluated for SOC estimation using full-spectrum and partial least squares regression (PLSR) scores. The results revealed that reflectance gradually increased with increasing soil depth and decreasing SOC. The prediction models developed using existing indices were observed to be poor in predicting the SOC with the R2 values ranging from 0.009 to 0.34. The best spectral indices for estimating SOC were RI (R1888, R2015) and NDI (R1888, R2015) with R2 of 0.60, 0.61 and 0.39, 0.43 for calibration and validation datasets, respectively. The PLSR score-based multivariate models outperformed solo multivariate and optimized index-based models. Our study suggested that VNIRS with PLSR combined multivariate models can reliably be used for fast and non-invasive estimation of SOC.

Spatial Variation in Soil Base Saturation and Exchangeable Cations in Tropical and Subtropical China

In the last 30 years, severe soil acidification has been found in China due to acid deposition and nitrogen fertilizer overuse. Understanding the spatial pattern and vertical variations in base saturation percentage (BSP) and exchangeable cations (Ca2+, Mg2+, K+, Na+, H+ and Al3+) can directly benefit fertilization management and ecological protection. Here, 1253 soil profiles were surveyed in tropical and subtropical regions in China to investigate the spatial variations in BSP and exchangeable cations at three soil depths of 0–20 cm, 20–50 cm and 50–100 cm. The spatial distributions were interpolated by using advanced machine learning techniques. We found that the exchangeable Ca2+ (Exch. Ca), Mg2+ (Exch. Mg) and BSP were significantly higher in paddy fields and uplands than in forests and gardens, regardless of soil depth, while the exchangeable K (Exch. K) did not significantly differ between various land-use types. The Exch. Ca and BSP in Anthrosols were significantly higher than those in Ferrosols, Argosols and Cambosols in the three soil layers. The spatial prediction results indicated that exchangeable cations and BSP were generally characterized by strong heterogeneity, and the Exch. Ca, Exch. K and exchangeable H+ (Exch. H) contents and BSP declined with increasing soil depth. This study helps us understand the spatial variation in BSP and exchangeable cations in the study area and benefits fertilization management and environmental protection.

Effect of Shrub Components on Soil Water and Its Response to Precipitation at Different Time Scales in the Loess Plateau.

Water shortages have become the major limiting factor for ecological protection and sustainable development in the Loess Plateau. Few studies have focused on the effects of different plant components on soil water and its response to precipitation at different time scales. This study conducted an observation of shrub plants with three treatments (natural condition (NC), canopy + roots after removing the litter (CR), and only roots (OR)) to monitor the dynamics of soil water during the rainy season of an extreme drought year in 2015. The results showed that the soil moisture content (SMC) and soil water storage (W) had a trend of OR > CR > NC. The response of the SMC to precipitation was gradually decreased and delayed for longer with increasing soil depth. Daily precipitation >10 mm was the threshold to trigger an SMC response below 20 cm of depth. The thresholds of precipitation to increase W were 2.09-2.54 mm at the daily scale and 29.40-32.56 mm at the monthly scale. The effect of precipitation on W and its change (∆W) also depended on the time scales. At the daily scale, precipitation only explained 1.6%, 0.9%, and 2.4% of the W variation in NC, CR, and OR, respectively. However, precipitation was more important for ∆W, making a contribution of 57.6%, 46.2%, and 56.6%, respectively, and the positive ∆W induced by precipitation happened more easily and frequently at deeper depths in OR. At the monthly scale, the contribution of precipitation to ∆W increased to 75.0%, 85.0%, and 86%, respectively. The ∆W of the whole rainy season was OR > NC > CR. Precipitation of the monthly scale displayed higher contributions to soil water than that of the daily scale. Plant components had different influences on soil water and its response to precipitation, which was strengthened by the roots, weakened by the canopy, and neutralized by the litter. Regular cutting of the canopy at the single-shrub scale may help increase water storage, which is useful for vegetation management and hydrologic regulation.

Research on Deformation Law of Loess Layer with Buried Pipeline under Earthquake

Previous earthquake damage studies have shown that loess has strong seismic vulnerability under strong earthquakes, and the water pipelines buried in loess are prone to engineering disasters due to displacement around the soil. Therefore, it is necessary to study and analyze the deformation law of the loess layer with buried pipelines under earthquake. In this paper, based on the actual project of the water pipeline Hanjiang-to-Weihe River Water Diversion Project, using FLAC3D finite difference software, taking vertical dynamic displacement, dynamic stress, and dynamic acceleration as indexes, the deformation law of loess layer with water pipeline buried under earthquake is studied. The results show that: With the continuous attenuation of seismic wave energy, the dynamic displacement of the model gradually increases from bottom to top, and the maximum displacement is located at the top of the model. After the earthquake, the soil showed obvious uneven settlement, and the uneven settlement gradually decreased with the increase of soil depth. The overall dynamic stress of the model shows a trend of decreasing from top to bottom. Based on the above analysis results, this paper studies the influence of five factors, such as seismic amplitude, Young’s modulus of soil, cohesion, internal friction angle, and pipeline radius, on the seismic subsidence of loess with buried pipelines. The results show that the primary and secondary order of factors influencing seismic subsidence of loess is seismic amplitude, cohesion, internal friction angle, pipeline radius, and Young’s modulus.

Spatiotemporal variability and driving factors of the shallow soil moisture in North China during the past 31 years

To fully understand the dynamic change characteristics of soil moisture in North China, the spatiotemporal patterns of soil moisture anomalies (SMA) in the four active soil layers from January 1990 to December 2020 are analyzed based on the Global Land Data Assimilation System (GLDAS) model, then the driving factors and corresponding contribution rates (CRs) for SMA change are determined together with the meteorological, socioeconomic and land cover data. The results show that the SMA in the last three layers present decreasing trends, and the trend magnitudes increase in multiples with the increase of soil depth. The area with the most severe soil dry is clustered in the east-central plain, while the relatively wet areas are scattered in western Shanxi and northern Hebei. The annual, intra- and inter-annual cycles (1.0, 0.5, 4.3 and 7.3 yr) are the dominant frequency of the SMA time series, which are driven jointly by 6 natural-type factors and 6 human-type factors, especially the intensified evaporation and dramatically expanding urbanization. By combining principal component analysis (PCA) and grey absolute correlation degree, the reintegrated human and natural factors respectively account for 49.46% and 50.54% of mean CRs to SMA in the four layers, but the human factor dominates the change of the bottom SMA. On the other hand, the determined mean CRs by combining exploratory factor analysis (EFA) and grey absolute correlation degree are 53.46% and 46.44% for reintegrated positive and negative factors, but the negative factor has a greater effect on the bottom SMA. The results provide a clear clarification of the soil moisture dynamic change, which is conducive to shedding new light on water resources management, agricultural security and ecological sustainability.

Variation characteristics of microorganisms at different soil depths of typical forests in southwest China.

Microbial biomass and community structure play a significant role in soil carbon cycling. There is a large amount of organic carbon in the subsoil, but most studies on soil microbial community have focused on the surface soil. The changes and influencing mechanisms of microbial community in subsoil are unclear. We analyzed soil microbial biomass and community structure at different soil depths (0-20, 20-40, 40-60, 60-80, and 80-100 cm) in three typical forests in southwest China, Xishuangbanna tropical rain forest, Ailao Mountain subtropical broad-leaved forest, and Lijiang temperate coniferous forest, by using phospholipid fatty acid technology, to explore their variation characteristics and influencing factors in different forests and soil depths. The results showed that contents of soil organic carbon and total nitrogen decreased gradually, microbial biomass declined significantly. The ratio of Gram-positive bacteria to Gram-negative bacteria (G+:G-) reduced gradually, while the ratio of fungi to bacteria (F:B) increased with the increasing soil depth. Microbial community turned from G--dominated which adapted to eutrophic environment into G+-dominated which adapted to oligotrophic environment. The three forest types differed little in soil microbial biomass, but different significantly in microbial community structure. Ailao Mountain subtropical broad-leaved forest and Lijiang temperate coniferous forest had much higher F:B at 0-20 cm than Xishuangbanna tropical rain forest, while significantly higher G+:G- at 0-100 cm in Xishuangbanna tropical rain forest was observed. Results of the redundancy analysis showed that the contents of soil organic carbon and total nitrogen were the main factors determining microbial biomass, with combined explanation of 78.3%. Results of the stepwise regression analysis showed that C:N was the most important driving factor on F:B and G+:G-. The change in microbial community structure and the decrease in biomass along soil profile might strongly affect the dynamics of soil organic carbon in southwest China forests.

Responses of bacterial communities along vertical soil profile to the chromium-contamination stress

Driven by rainfall and agricultural irrigation, chromium slag causes serious pollution to the subsurface environment and damages the indigenous soil bacterial community. The study of the ecological responses of bacterial community to chromium pollution can provide support for bioremediation of chromium pollution. In this study, soil samples at different depths (0, 2, 5, 7 m) in a long-term chromium contaminated site were selected to analyze the vertical changes and responses of bacterial community structure using high-throughput 16S rRNA gene sequencing. Total Cr and soluble Cr(VI) concentrations were highest in topsoil and decreased with depth. Compared with the topsoil of uncontaminated land, the alpha-diversity in the contaminated topsoil was significantly reduced, and the bacterial community composition was altered. With increasing soil depth, the alpha-diversity decreased, and the species distribution became more uneven. Topsoil and subsurface soil showed different bacterial community structures, associated with the Cr concentration and physicochemical properties. Proteobacteria in all samples were dominant, and their relative abundances increased with depth. Bacterial community alpha-diversity and dominant taxa can be used as indicators of response to chromium pollution. The predicted metagenomic functional annotation (using Tax4Fun) showed that the relative abundance of chromate transporters (chrA, K07240) in the topsoil is 20–30 times of that in deeper soil, indicating potential bioremediation capability by topsoil bacterial community. The bioremediation feasibility of reducing Cr(VI) using indigenous bacterial community showed that Cr-polluted topsoil bacterial community has ability to reduce Cr(VI).

Grazing Regulates Changes in Soil Microbial Communities in Plant-Soil Systems

Soil microorganisms promote material transformation and energy flow in the entire ecological environment and play a key role in the stability and development of grassland ecosystems. Studies on the impacts of grazing on the soil microbial community and the establishment of a reasonable grazing intensity are crucial to improve our knowledge of the mechanisms underlying grassland degradation and to accurately assess the influence of grazing management on grassland functions and the nutrient cycle. Based on the grassland grazing control experimental platform, we compared the structure and diversity characteristics of soil microbial communities under six grazing intensities (0.00, 0.23, 0.34, 0.46, 0.69, and 0.92 AU ha−1) (1 AU = 500 kg of adult cattle) on the Hulunbuir Leymus chinensis meadow steppe. The results showed that soil microbial biomass carbon (MBC) and nitrogen (MBN) decreased with increasing soil depth. The 0–10 cm soil layer of G0.34 had the highest MBC and MBN, and the G0.92 treatment had the lowest MBC and MBN. Heavy grazing significantly decreased the MBC and MBN contents in the soil surface layer. The soil bacterial diversity under light grazing treatment (0.23 AU ha−1) was higher than that under heavy grazing, and the fungal diversity under the no-grazing treatment was higher than that under the grazing treatment. Overgrazing reduced the bacterial species in the soil. The plant belowground biomass significantly (p = 0.039) influenced the bacterial community structure, and the soil pH (p = 0.032), total nitrogen (p = 0.011), and litter (p = 0.007) significantly influenced the fungal community. The effects of grazing on microbial communities were primarily driven by vegetation productivity, litter mass, and soil geophysical and chemical characteristics. This study deepened our understanding of the impacts of grazing practices on soil microbial communities on the meadow steppe, suggesting that moderate-disturbance grazing can promote the sustainable development of grassland vegetation-soil microorganisms.

Soil microbial community diversity and distribution characteristics under three vegetation types in the Qilian Mountains, China

Qilian Mountains in Northwest China is a significant ecological security barrier due to its distinctive geographic setting, which has significant biological resource and gene pool. In order to assess the soil quality and ecosystem health in this area, we identified the structural characteristics and functional groups of soil microbial communities. This study focused on Amidongsuo, a typical watershed of the Qilian Mountains, and researched the vertical distribution and dominant populations of soil microorganisms in different habitats, and the relationship between soil microorganisms and environmental factors. Soil microorganisms from three grassland plots, five shrubland plots, and five forest plots in Amidongsuo were studied using high-throughput sequencing. The Venn diagram showed that the types of bacteria were fewer than those of fungi in Amidongsuo. Soil bacteria Acidobacteriota, Proteobacteria, and Methylomirabilota as well as fungi Basidiomycota, Ascomycota, and Mortierellomycota played dominant roles in Amidongsuo, according to the LEfSe (linear discriminant analysis (LDA) effect size) and community structure analyses. According to the ANOSIM (analysis of similarities) result, for both bacteria and fungi, R values of grassland and shrubland were small (R2=0.045 and R2=0.256, respectively), indicating little difference between these two ecosystems. RDA (redundancy analysis) showed a closer relationship between soil nutrients and fungi, and a gradually decreasing correlation between soil nutrients and microorganisms with increasing soil depth. Bacteria were mainly affected by pH, nitrogen (N), and potassium (K), while fungi were mainly affected by K. Overall, fungi had more effect on soil quality than bacteria. Therefore, adjustment of soil K content might improve the soil environment of Amidongsuo in the Qilian Mountains.

The quality and quantity of SOM determines the mineralization of recently added labile C and priming of native SOM in grazed grasslands

Continuous and pulsed inputs of labile organic carbon (LOC) into soil are common. However, because soil microbial responses to LOC input are rapid, the relative contributions of respiration derived from LOC to total microbial respiration and their influencing factors remain elusive. Furthermore, although numerous studies have explored the priming effect (PE) of soil organic matter (SOM) mineralization induced by LOC addition, few studies have focused on its short-term effects. There are some indications that the response of soil microbes to LOC input depends on the microbial demand of nutrients, especially C and N. Therefore, variations in soil C and N characteristics may further influence microbial response processes to LOC inputs and the decomposition of LOC and SOM, but a comprehensive understanding of this is lacking. To address this gap, 13C-labeled glucose was added to six temperate grassland soils with different C/N ratios (9.98–12.0), which were collected from areas with different grazing exclusion durations and at different soil depths. The microbial respiration was measured at 9-min intervals across a 105-h period. We found that soil microbes responded rapidly to LOC input, and microbial biomass controlled by soil organic C (SOC) and C/N was the most important factor directly influencing the intensity of the microbial response to LOC input. Grazing and deeper soil layers decreased the respiration derived from LOC and their relative contribution to total respiration, mainly attributed to variations in soil C/N and fungal/bacterial ratio (Fu/Ba). LOC addition stimulated SOM decomposition in all soils and increased respiration of SOM by 11.3–92.4 mg C/g SOC, equivalent to 18.7–266.1 % priming. Grazing and increased soil depth resulted in a greater PE and soil C loss, with soil C/N and SOC content being the most important regulators. Overall, this study revealed the important influence of LOC on soil C fluxes and highlighted the important role of SOM quality and quantity in regulating grassland soil C cycling.

Long-term combined organic manure and chemical fertilizer application enhances aggregate-associated C and N storage in an agricultural Udalfs soil.

Little information is known on whether carbon (C) and nitrogen (N) immobilization is synchronized in different sizes of aggregates under different agricultural management practices. Carbon and N concentrations and the C/N ratios in different sizes of aggregates down to 40 cm depth were determined after long-term application of chemical fertilizers combined with manure or without manure in a wheat-rice cropping system. Manure application usually produced significantly (P < 0.05) higher C and N concentrations and lower C/N ratios in bulk soil and in different sizes of aggregates down to 20 cm depth than the other treatments, and the 1.5 MNPK treatment at 0-10 cm depth had the highest SOC concentration of 26.3 g/kg. The C and N concentrations in bulk soil and all aggregate fractions decreased markedly with increasing soil depth. Among water stable aggregates in all soil depths, the highest C (48.2-66.4%) and N (47.8-68.3%) concentrations as a percentage of SOC were found in the small macroaggregates (2000-250 μm, SM). Manure application significantly (P < 0.05) increased the mass and C and N concentrations of SM and SM fractions down to 20 depth. The mean C/N ratios of silt-clay within large and small macroaggregates (inter-SC) were 1.57 and 1.46 units lower than those of silt-clay particles, respectively, indicating that inter-SC had relative high N availability. Moreover, the C and N content of SM down to 40 cm depth tended to saturation with increasing C input rate. Overall, manure application effectively improved soil structure, SM were the dominant particles involved in soil C and N storage, and inter-SC were the main particles responsible for N availability.

Carbon Pool Dynamic and Soil Microbial Respiration Affected by Land Use Alteration: A Case Study in Humid Subtropical Area

Alterations of soil characteristics frequently accompany adaptations of pristine areas to different land uses, and these shifts have an impact on the overall ecosystem. Soil carbon stores and atmospheric CO2 emissions are directly affected by those adaptations in farming management and land usage. To comprehend the mechanisms involved in the carbon pool, this study was conducted in a subtropical region by considering six contiguous land uses; pasture, rice land, kiwi orchard, tea land, woodland, and uncultivated land. A CO2 trap was used to quantify CO2 emissions for six weeks, and the obtained data were used to analyze CO2 respiration. In comparison to other land uses, the pasture and woodland showed the best results in soil microbial respiration (SMR), significantly higher than other land uses, with values of 2561.2 and 2334.8 mg CO2-C kg−1 soil, respectively. Tea land and uncultivated land demonstrated considerably increased microbial metabolic quotients (MMQ) compared to other land uses. Whereas with an increase in soil depth, the MMQ significantly increased in tea and uncultivated lands, other land uses did not show significant changes with depth. Compared to other land uses, pasture, and forest areas boosted soil organic carbon (SOC) and microbial biomass carbon (MBC) both in the top and subsoil. It is reasonable to assume that the amount of SOC and MBC in the soil significantly dropped when the land was converted from pasture and woodland to other land uses.

Hydrological Properties of Soil and Litter Layers of Four Forest Types Restored in the Gully Erosion Area of Latosol in South China

Litter and soil play an important role in influencing hydrological processes and the global water cycle. Artificial afforestation, as a part of vegetation restoration, was constructed in the gully erosion areas of latosol with the objective to prevent erosion. Variations in the hydrological properties in soils that have undergone vegetation restoration from gully erosion are not well understood. In this study, we examine the variations in the litter thickness and mass, soil structure and porosity, and hydrological properties of four forest types (eucalyptus–grass forest, bamboo–grass forest, acacia–grass forest, and shrub–grass forest). The results show that the total litter thickness varied from 1.71 to 3.74 cm and was highest in the acacia–grass forest. The total litter mass for the acacia–grass forest, 3.49 ± 0.06 t·ha−1, was significantly higher than that for the other forest types. The mass of the undecomposed litter (UL) layer was significantly lower than that of the semi-decomposed litter (SL). (2) The maximum water-retention capacity (Wmax) and effective water-retention capacity (Weff) of the SL layer were greater than those of the UL layer. The Wmax and Weff for the acacia–grass forest were markedly larger than those of the eucalyptus–grass, bamboo–grass, and shrub–grass forests. The water absorption rates of the SL and UL layers were highest during the onset of the immersion experiment, declined exponentially with time, and declined rapidly in the first 2 h. (4) The soil bulk density ranged from 1.46 g·cm−3 to 1.54 g·cm−3, and the total porosity ranged from 32.06% to 37.13%. The soil bulk density increased with the increasing soil depth, while the total porosity decreased gradually. The soil water-holding capacity of the soil layer of 0–60 cm in the acacia–grass forest (301.76 t·ha−1) was greater than that of the other forest types. A comprehensive evaluation of the water conservation capacity by the entropy weight method showed that the water conservation capacity was greatest in the acacia–grass forest. The higher water-holding capacity of the acacia–grass forest may be more effective in enhancing rainfall interception, minimizing splash erosion, and decreasing surface runoff. Here, the results indicate that acacia–grass forest restoration can mitigate soil erosion by favoring soil and water conservation, improving the environment in the gully erosion area of latosol.

Soil Moisture Regulation under Mulched Drip Irrigation Influences the Soil Salt Distribution and Growth of Cotton in Southern Xinjiang, China.

Water deficiency, together with soil salinization, has been seriously restricting sustainable agriculture around the globe for a long time. Optimal soil moisture regulation contributes to the amelioration of soil water and salinity for crops, which is favorable for plant production. A field experiment with five soil water lower limit levels (T1: 85% FC, T2: 75% FC, T3: 65% FC, T4: 55% FC, and T5: 45% FC, where FC is the field capacity) was conducted in southern Xinjiang in 2018 to investigate the responses of soil water-salt dynamics and cotton performance to soil moisture regulation strategies. The results indicated that in the horizontal direction, the farther away the drip irrigation belt, the lower the soil moisture content and the greater the soil salinity. In the vertical direction, the soil moisture and soil salinity increased first and then decreased with an increase in soil depth after irrigation, and the distribution was similar to an ellipse. Moreover, the humid perimeter of soil water and the leaching range of soil salt increased with a decrease in the soil moisture lower limit. Though more soil salt was leached out for the T5 treatment at the flowering stage due to the higher single irrigation amount, soil salinity increased again at the boll setting stage owing to the long irrigation interval. After the cotton was harvested, soil salt accumulated in the 0-100 cm layer and the accumulation amount followed T3 > T5 > T1 > T2 > T4. Moreover, with a decline of soil moisture lower limit, both plant height and nitrogen uptake decreased significantly while the shoot-root ratio increased. Compared with the yield (7233.2 kg·hm-2) and water use efficiency (WUE, 1.27 kg·m-3) of the T1 treatment, the yield for the T2 treatment only decreased by 1.21%, while the WUE increased by 10.24%. Synthetically, considering the cotton yield, water-nitrogen use efficiency, and soil salt accumulation, the soil moisture lower limit of 75% FC is recommended for cotton cultivation in southern Xinjiang, China.

Wetland‐type conversion drives the C, N and P stoichiometry change of soil in river plain of lower of the Yellow River

AbstractLand use conversion on river plain has profound impacts on soil characteristics and elemental stoichiometry. Four wetland types (Riparian lower‐beach wetland [RLW], Riparian higher‐beach wetland [RHW], Cultivated wetland [CW] and Mesophytic wetland [MW]) were selected in the lower Yellow River area to investigate the consequence of wetland type conversion on soil carbon (C), nitrogen (N) and phosphorus (P) stoichiometry. The results demonstrated that wetland conversion induced significant spatio‐temporal variations in soil C, N and P stoichiometry and physicochemical characteristics in soil. Frequent agricultural activities (fertilizer input) raised the nutrient content of natural wetland, particularly in surface soil (0–30 cm). Soil volumetric water content (VWC), soil bulk density (SBD), pH and soil enzyme activity varied significantly in different wetlands. Total carbon (TC) and total nitrogen (TN) contents in MW decreased with increasing soil depth (&lt;40 cm layers), as did TN and total phosphorus (TP) contents in CW. On the other hand, TC, TN and TP contents in RLW and RHW did not change significantly with soil depth. However, the contents of TOC, and Fe/Al‐P, etc., varied among soil layers and among wetland types. Furthermore, the stoichiometric characteristics changed significantly in some soil layers, with mean values being less than the Chinese average. Statistically, significant positive correlations were determined between TC and TN (r = .56), TDC and TP (r = .62), N:P and pH (r = .57) (p &lt; .05) and and pH (r = .66, p &lt; .01). VWC was negatively correlated with pH (r = −.56, p &lt; .05), while C/P was negatively associated with soil temperature (ST) and SBD (r = −.55, r = −.64, p &lt; .05). TDC, IP, TN, Fe/Al‐P and ST were identified as the dominant factors, with the percentage of variance 41%, 20%, 12%, 9% and 6% respectively. These findings have a great scientific significance for the ecological conservation of wetlands in the lower Yellow River area.

Implication of land use shifting on land degradation and restoration potential of conservation agriculture in India's North-West Himalayan region

The soil organic matter is a crucial factor in determining soil characteristics and productivity; however various land management practices degrade or aggrade the soil health. The objective of this study was to look at the influence of land-use conversion on soil health by using the concept of stratification ratio (SR) of soil organic carbon (SOC) and total nitrogen (TN) and appraise SR as a predictor of SOC and TN stock and soil health for India's North-West Himalayan region. The research is oriented toward assessing the consequences of various land use regimes' impacts on SOC and TN depth distribution, storage, and stratification and, hence, identifying appropriate sustainable tillage techniques for the region. The research was accomplished in 2020–21 in the long-term experimental plot with four land uses, namely control [natural sal forest (Shorea robusta L.), conventional tillage (CT), reduced tillage (RT), and zero tillage (ZT)] in a rainfed system of north-western Indian Himalayas. A decrease of 79% in the mean weighted diameter of CT was observed after conversion from forest land to CT; however, the decrease was only 50% in the case of the adoption of ZT. Further, the surface soil (0–5 cm) SOC was significantly different from each other, with forest soil having the highest SOC (27.5 ± 0.21 g kg−1) and CT having the lowest SOC (11.0 ± 0.09 g kg−1). The stock of SOC and TN increased significantly with increment in soil depth, and among landuses, the highest SOM was observed with forest and the lowest with CT. Among the treatments, forest (56.56 ± 1.90 Mg ha−1) had significantly higher SOC storage than conservation agriculture (CA) (42.84 ± 0.27 Mg ha−1, ZT, and 41.41 ± 1.84 Mg ha−1, RT) and CT (41.33 ± 1.19 Mg ha−1) based on equivalent soil mass approach. For forest land use, except the surface layer (0–5:5–10), all the soil layers had SR >2, whereas, for ZT, the bottom two layers (0–5:20–25 and 0–5:25–30) had SR >2 and for RT, only the bottom layer (0–5:25–30) was having SR > 2. It was observed that the conversion of land use to CT reduced the SR of SOM drastically; however, by adopting CA, the SR had been restored to near normal in forest land use. The carbon pool index (CPI) was used to determine the effects of soil tillage and residue incorporation on soil quality improvement with respect to a sal forest. The CPI value increased significantly with an increase in soil depth for three land uses, and also, at each soil depth, the CPI followed the ZT > RT > CT trend. Thus, CA may be considered a viable alternative to CT for improving soil physicochemical parameters.

Microorganisms carrying nosZ I and nosZ II share similar ecological niches in a subtropical coastal wetland

Nitrous oxide (N2O) reducers are the only known sink for N2O and pivotal contributors to N2O mitigation in terrestrial and water ecosystems. However, the niche preference of nosZ I and nosZ II carrying microorganisms, two divergent clades of N2O reducers in coastal wetlands, is not yet well documented. In this study, we investigated the abundance, community structure and co-occurrence network of nosZ I and nosZ II carrying microorganisms and their driving factors at three depths in a subtropical coastal wetland with five plant species and a bare tidal flat. The taxonomic identities differed between nosZ I and nosZ II carrying microorganisms, with nosZ I sequences affiliated with Alphaproteobacteria and Betaproteobacteria while nosZ II sequences with Gemmatimonadetes, Verrucomicrobia, Gammaproteobacteria, and Chloroflexi. The abundances of nosZ I and nosZ II decreased with increasing soil depths, and were positively associated with salinity, total carbon (TC) and total nitrogen (TN). Random forest analysis showed that salinity was the strongest predictor for the abundances of nosZ I and nosZ II. Salinity, TC and TN were the major driving forces for the community structure of nosZ I and nosZ II carrying microorganisms. Moreover, co-occurrence analysis showed that 92.2 % of the links between nosZ I and nosZ II were positive, indicating that nosZ I and nosZ II carrying microorganisms likely shared similar ecological niches. Taken together, we provided new evidence that nosZ I and nosZ II carrying microorganisms shared similar ecological niches in a subtropical estuarine wetland, and identified salinity, TC and TN serving as the most important environmental driving forces. This study advances our understanding of the environmental adaptation and niche preference of nosZ I and nosZ II carrying microorganisms in coastal wetlands.

Water competition among the coexisting Platycladus orientalis, Prunus davidiana and Medicago sativa in a semi-arid agroforestry system

Agroforestry has been widely used for the ecological restoration construction of semi-arid regions of the Chinese Loess Plateau. Investigating plant water sources is crucial for understanding the key ecohydrological processes of plant root water uptake and the water relations between coexisting plants. Clarifying the plant water use strategies can help to assess the sustainability of the vegetation restoration in agroforestry systems and provide references for the vegetation management. Thus, we investigated the water use characteristics of plants in an agroforestry system consisting of Platycladus orientalis, Prunus davidiana and Medicago sativa. The δD and δ18O of plant stem water and soil water in the 0–300 cm layer were measured. The MixSIAR model and proportional similarity (PS) were used to quantify the proportion of soil water absorbed by the plants in each layer and the hydrological niche overlap of plants. The results showed that the combined effects of rainfall recharge and evapotranspiration (ET) loss resulted in a decrease in soil water content (SWC) for the agroforestry system with increasing soil depth, and the SWC of the deep layer (80–300 cm) had minor variability (6.1–7.1%) throughout the study period. During the study period, due to the deep soil desiccation, P. orientalis, P. davidiana and M. sativa mainly utilized water from shallow (0–80 cm) soil layers, with a contribution rate of 65.4 ± 8.3%, 64.9 ± 7.7% and 73.0 ± 0.2%, respectively. The three coexisting plants relied on the unstable shallow soil water (recharged by rainfall) while the water use proportion of the deep soil layer was consistently low. This implies that the three plants were less resistant to drought stress, thus posing a threat to the stability and sustainability of the agroforestry system. Moreover, even in July and September with the high SWC in agroforestry, the partitioning of soil water among the three coexisting plants did not increase with increased ET loss. The three coexisting plants showed strong competition for soil water use, as indicated by the high values (0.69–0.97) of PS. Overall, the hydrological niche overlap of the coexisting plants in the agroforestry system resulted in low ecosystem stability. Density reduction or selection of suitable species is required to achieve sustainable vegetation restoration.

Insight into influence of roots on hydrothermal properties of alpine meadow in Tibetan Plateau

The physical and mechanical behavior of alpine meadow in Tibetan Plateau is now attracting widespread attention. In this paper, a series of experiments were conducted to study the influence of roots on hydrothermal behavior of alpine meadow located at Nangqian district, in the east of Tibetan Plateau, China. Root biomass, physical properties and hydrothermal properties were measured at a soil depth of 0–25 cm. The results showed that the root biomass within the depth of 0–15 cm accounts for 86% of the total root biomass. With the increase of soil depth, the root biomass shows a decreasing trend. The hydraulic conductivities and thermal conductivities of alpine meadow soil increase with the decrease of root biomass. There are lower hydraulic conductivity and thermal conductivity of swallow soil (0–5 cm) than that of deep layer soil. For the bottom soil layer, swallow alpine meadow acts as a “cap” and plays a function of ecological barrier of reducing water infiltration and heat transfer. Under the background of global warming, this insight is helpful to understand the relationship between soil hydrothermal properties and natural disasters in Tibetan Plateau.