Deeper Soil Layers Research Articles

LESSONS LEARNT FROM SOIL IMPROVEMENT CASE STUDIES

In Saudi Arabia two methods of soil improvement have been customarily employed. They are soil improvement by means of stone columns, and soil improvement by means of controlled modulus columns, that is CMC. Each of these methods have their own challenges to offer. Experience has shown that the sub-surface geology of the coastal areas of Saudi Arabia are marked with deep layers of poor soil termed locally as sabkha soil. Test results have determined that sabkha soil is known to have low shear strength, high soil compressibility, and high concentration of chlorides and sulphates which are corrosive to concrete, steel, and other construction materials. Design of foundations over a sabkha deposit remains a challenge and requires soil improvement. The CMC installation utilizes reverse flight augers, which displaces the soil laterally. However, it offers a huge challenge of post-operation trimming and cutting of CMCs. for stone columns, soil is removed during the drilling operation creating environmental issue. It also offers challenges as the huge impact during its operation are likely to damage the underground utilities. The environmental issues thus created can pose yet other challenge. This research paper is a case study that collates the experiences of soil improvement methods employed on a project in Saudi Arabia – vis-à-vis their advantages and the challenges encountered.

LESSONS LEARNT FROM SOIL IMPROVEMENT CASE STUDIES

In Saudi Arabia two methods of soil improvement have been customarily employed. They are soil improvement by means of stone columns, and soil improvement by means of controlled modulus columns, that is CMC. Each of these methods have their own challenges to offer. Experience has shown that the sub-surface geology of the coastal areas of Saudi Arabia are marked with deep layers of poor soil termed locally as sabkha soil. Test results have determined that sabkha soil is known to have low shear strength, high soil compressibility, and high concentration of chlorides and sulphates which are corrosive to concrete, steel, and other construction materials. Design of foundations over a sabkha deposit remains a challenge and requires soil improvement. The CMC installation utilizes reverse flight augers, which displaces the soil laterally. However, it offers a huge challenge of post-operation trimming and cutting of CMCs. for stone columns, soil is removed during the drilling operation creating environmental issue. It also offers challenges as the huge impact during its operation are likely to damage the underground utilities. The environmental issues thus created can pose yet other challenge. This research paper is a case study that collates the experiences of soil improvement methods employed on a project in Saudi Arabia – vis-à-vis their advantages and the challenges encountered.

Research on bearing capacity of piles with negative skin friction based on field test

There are extensive deep soft soil layers in the coastal areas of China, and the drainage consolidation method is widely adopted for foundation pretreatment in these areas. However, there are still dozens of centimeters of post construction settlement, which may produce negative skin friction on the pile foundation. To accurately estimate the magnitude of negative skin friction, two prestressed high strength concrete pipe piles with different pile end holding layers were used to conduct field tests. The development law of negative skin friction of pile foundation with soil consolidation is studied by simulating different pre-load height conditions of soil around pile. The monitoring results of field tests indicate that with the soil settlement around the pile, the dragload increases gradually and the neutral point moves downward. When the relative displacement between the pile and soil is 87 cm, the neutral point position of the end bearing pile is approximately 44.6-m deep, and the dragload is about 3640 kN, while the friction pile is 30 m and 2160 kN. The analysis shows that if the pile foundation construction is carried out during the foundation pretreatment, the dragload is considerably large, and this may lead to excessive settlement and damage of the pile.

Soil Organic Matter Input Promotes Coastal Topsoil Desalinization by Altering the Salt Distribution in the Soil Profile

Organic amendment is an effective method to reclaim salt-affected soil. However, in coastal land with shallow saline groundwater, it is limited known about the mechanism of organic amendment on soil desalinization. Thus, to examine the effect of topsoil organic matter content on soil water/salt transport and distribution, two-year field observations in Bohai coastal land, North China, and soil column experiments simulating salt accumulation and salt leaching were conducted, respectively. There were different organic fertilizer amendment rates in 0–20 cm topsoil, 0% (CK), 50% (OA 0.5), and 100% (OA 1.0) (w/w) for soil column experiments. Field observation showed that after organic amendment (OA), the soil’s physical structure was improved, and less of the increase in topsoil salt content was observed, with more salt accumulated in deep soil layers during the dry season. In addition, OA greatly promoted salt leaching during the rainy seasons. The results of the soil column tests further indicated that OA treatments significantly inhibited soil evaporation, with less salt accumulated in the topsoil. Although there was no difference in soil water distribution between the CK and OA 0.5 treatment, the topsoil EC for the OA 0.5 treatment was significantly lower than that for CK. During soil water infiltration, the OA 0.5 and OA 1.0 treatments significantly increased the infiltration rates, enhanced the wetting front, and promoted salt leaching to deeper soil layers, compared with CK. The improvement of soil organic amounts could make the soil more self-resistant to the coastal salinization. The findings of this study provide some insights into soil water/salt regulation in heterogeneous soil masses and on the permanent management of coastal saline farmland.

The dimensions of deep-layer soil desiccation and its impact on xylem hydraulic conductivity in dryland tree plantations

Abstract. In water-limited areas, planted trees can extract substantial amounts of soil water from deep layers (> 200 cm) to meet their high water demand, resulting in deep soil desiccation, which influences not only regional water cycling but also the sustainability of trees per se in drylands. However, the specific dimensions of deep soil desiccation in relation to both the soil moisture limitation and the maximum root water uptake (RWU) depth are still not well determined. Whether the dimensions depend on tree species and how they will affect trees' xylem hydraulic conductivity are also unclear, restricting our ability to predict the fate of dryland tree plantations. Therefore, we studied the spatiotemporal distribution of deep soil moisture deficit (DSMD) for two typical planted trees, apple (Malus pumila Mill.) and black locust (Robinia pseudoacacia L.), based on published data and multiple field samplings on China's Loess Plateau. The results indicated that the lowest deep soil moisture (DSM; units of gravimetric percent, i.e., grav-%) occurred under the planted trees aged 24–28 years at all sites. The lowest DSMD varied around −0.6, which was close to the DSMD at the permanent wilting point (PWP, grav-%), regardless of tree species and site, although shallow (< 200 cm) soil moisture was not reduced to the point of limitation. This suggests that PWP is a reliable indicator of the moisture limitation of deep-layer soil desiccation for the tree species examined. The corresponding depth of soil moisture use reached 18.0–22.0 m for these old planted trees at different sites, while it was more than 25 m for R. pseudoacacia in the drier site of Mizhi. Furthermore, the mean values of native percentage loss of hydraulic conductivity of planted trees' branches xylem reached 74.9 %–96.5 % in the plantations sampled in this study, indicating that tree mortality may occur. The findings help predict the sustainability of planted trees in semi-arid regions with a thick vadose zone.

Soil Moisture Profiles of Ecosystem Water Use Revealed With ECOSTRESS

AbstractWhile remote sensing has provided extensive insights into the global terrestrial water, carbon, and energy cycles, space‐based retrievals remain limited in observing the belowground influence of the full soil moisture (SM) profile on ecosystem function. We show that this gap can be addressed when coupling 70 m resolution ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station retrievals of land surface temperature (LST) with in‐situ SM profile measurements. These data sets together reveal that ecosystem water use decreases with depth with 93% of sites showing significant LST coupling with SM shallower than 20 cm while 34% of sites have interactions with SM deeper than 50 cm. Furthermore, the median depth of peak ecosystem water use is estimated to be 10 cm, though forests have more common peak interactions with deeper soil layers (50–100 cm) in 37% of cases. High spatial resolution remote sensing coupled with field‐level data can thus elucidate the role of belowground processes on land surface behavior.

Tree water uptake patterns across the globe.

Plant water uptake from the soil is a crucial element of the global hydrological cycle and essential for vegetation drought resilience. Yet, knowledge of how the distribution of water uptake depth (WUD) varies across species, climates, and seasons is scarce relative to our knowledge of aboveground plant functions. With a global literature review, we found that average WUD varied more among biomes than plant functional types (i.e. deciduous/evergreen broadleaves and conifers), illustrating the importance of the hydroclimate, especially precipitation seasonality, on WUD. By combining records of rooting depth with WUD, we observed a consistently deeper maximum rooting depth than WUD with the largest differences in arid regions - indicating that deep taproots act as lifelines while not contributing to the majority of water uptake. The most ubiquitous observation across the literature was that woody plants switch water sources to soil layers with the highest water availability within short timescales. Hence, seasonal shifts to deep soil layers occur across the globe when shallow soils are drying out, allowing continued transpiration and hydraulic safety. While there are still significant gaps in our understanding of WUD, the consistency across global ecosystems allows integration of existing knowledge into the next generation of vegetation process models.

Evaluation of soil water content and bulk electrical conductivity across the U.S. Climate Reference Network using two electromagnetic sensors

AbstractSoil bulk electrical conductivity (BEC) was evaluated alongside soil volumetric water content (VWC) and soil temperature measurements using the HydraProbe (model HydraProbe, Stevens Water Monitoring Systems, Inc.) (hereafter called HP) with accuracy range of BEC ≤ 0.3 S m−1, and the time domain reflectometry (TDR)‐315L Probe (model TDR‐315L, Acclima, Inc.) (hereafter called AP) suitable for BEC up to 0.6 S m−1, at 23 stations of the U.S. Climate Reference Network. Previous evaluations revealed inconsistent performance of both sensors in some clay soils using manufacturer‐recommended calibrations in converting dielectric permittivity measurements to VWC. Here, we found that hourly values of BEC reached 0.6 S m−1 in high clay content soils and exceeded 2 S m−1 in high saline soils, and these high values of BEC were associated with poor performance and failures of both HP and AP sensors. Large values of BEC occurred in predominantly saturated soils where VWC values reached about 0.5 m3 m−3 for saline soils and about 0.7 m3 m−3 for clay soils, while low magnitudes of BEC were associated with low soil water content and seldomly saturated soils. Low hourly BEC values of less than 0.1 S m−1 were observed in wide variety of soil types, where sensor performance was typically excellent. The most influential factor on BEC was high soil water content conditions. Although dielectric permittivity measurements in estimating the soil water content were sensitive to BEC as some high clay content and high salinity soils increased BEC, the impact of large BEC on dielectric permittivity measurements was smaller in the well‐drained top soil layers than in deep soil layers that remained near saturation. Soil temperature had only a small impact on BEC. With high clay content and high salinity, the specific area of clay minerals was also associated with the magnitude of BEC.

Water Use Strategies and Shoot and Root Traits of High-Yielding Winter Wheat Cultivars under Different Water Supply Conditions

Drought is the most important factor limiting winter wheat yield in the North China Plain (NCP). Choosing high-yielding cultivars is an important measure to minimize the negative effects of drought stress. Field studies were conducted with 10 cultivars in the 2020–2022 seasons under three irrigation treatments (I0, without irrigation; I1, irrigated at jointing stage; I2, irrigated at jointing and anthesis stages) in the NCP to examine the water use strategies and root and shoot traits of high-yielding cultivars under different water supply conditions. The results showed that yield variation among cultivars was 21.2–24.6%, 23.7–25.9% and 11.6–15.3% for the I0, I1 and I2 treatments, respectively. Under water deficit conditions (I0 and I1), high-yielding cultivars reduced water use during vegetative stages and increased soil water use during reproductive stages, especially water use from deeper soil layers. Those cultivars with higher root length density (RLD) in deep soil layers exhibited higher water uptake. Each additional millimeter of water used after anthesis from the 100–200 cm soil layers increased grain yield by 23.6–29.6 kg/ha and 16.4–28.5 kg/ha under I0 and I1, respectively. This water use strategy enhanced dry matter accumulation after anthesis, decreased canopy temperature (CT) and increased relative leaf water contents (RLWC), which ultimately improved grain yield. For winter wheat grown under I2, cultivars that decreased water use after anthesis had higher water productivity (WP). Root length (RL), root weight (RW) and root:shoot ratio were each negatively correlated with grain yield, while above-ground biomass was positively correlated with grain yield. Therefore, higher dry matter accumulation and smaller root systems are two important traits of high-yielding cultivars under sufficient water supply conditions (I2) in the NCP.

Rare‐earth element phytoextraction efficiency in southern Chinese mines under different clipping intensities using a co‐cropping system (Dicranopteris pedata and Pinus massoniana)

AbstractOur understanding of how varying clipping intensities affect the efficiency of phytoextraction remains limited, particularly with co‐cropping systems. This study focuses on assessing the effects of different clipping intensities on phytoextraction efficiency within co‐cropping systems dominated by the key species Dicranopteris pedata and Pinus massoniana in rare‐earth mines of southern China. Our results confirmed the following. Firstly, the compensation index, dry aboveground biomass, and rare‐earth elements (REE) accumulation of clipped D. pedata per unit area were highest under 100% clipping (p < 0.05). Meanwhile, the bioabsorption coefficient, bioconcentration factor, and translocation factor of P. massoniana were less than 1. Secondly, the soil catalase, sucrase, and α‐diversity indices of bacteria and fungi separately indicated no significant variation between the clipping treatments and control. The REE content in tree rings increased, and the total REE contents in thicker tree rings were higher than those in the thinner tree rings of P. massoniana from 1997 to 2016. Additionally, the soil erosion intensity diminished significantly in the growth area of P. massoniana from 1995 to 2019. Thirdly, both D. pedata and P. massoniana, when subjected to 100% clipping, could effectively remove excess REEs from the 0–20 cm soil layer within 18.57–61.19 years. In contrast, P. massoniana alone achieved a removal rate of excess REEs in the 20–60 cm layer, within 923.16–1899.62 years. Thus, D. pedata with 100% clipping can phytoextract the maximum amount of REEs. It is noted that P. massoniana cannot be used for REEs phytoextraction or phytostabilization. Co‐cropping with 100% clipping would have a less negative impact on growth and REEs extraction, and the co‐cropping system can phytoextract excess REEs from the surface soil within decades. However, it is not efficient for the phytoextraction of excess REEs from deep soil layers.

Soil water dynamics and deep percolation in an agricultural experimental area of the North China Plain over the past 50 years: Based on field monitoring and numerical modeling

The unregulated irrigation systems used in the late 20th century have led to increasingly severe deep percolation (DP) in the agricultural irrigation areas of the North China Plain. This has become an important factor limiting the efficient utilization of water resources and sustainable environmental development in these irrigation areas. However, the thick vadose zone is hydrodynamically exceptionally complex. The soil hydrological cycle is constantly changing under the influence of major climate change and human activity, thereby causing changes in DP that are difficult to quantify accurately. Here, the Luancheng Agricultural Irrigation District in North China was selected for a continuous 20-year in situ experiment. Soil-water dynamics were monitored using neutron probes and tensiometers, to determine the complete annual soil-water cycle and the hydrodynamic properties of the thick vadose zone irrigation district. For 1971–2021, DP was simulated using the HYDRUS-1D model and was verified by fitting observed values. Soil water content (SWC) exhibited similar trends in years that differed in terms of the amounts of irrigation and precipitation. The 0–100 cm soil layer was significantly affected by precipitation and other factors, and recharge >60 mm/d caused percolation. DP occurred mostly after irrigation or during the period of intensive precipitation in July–October. The maximum percolation rate was 16.9 mm/d under the present irrigation method. The main factors leading to DP were soil water storage capacity (R2 = 0.86) and precipitation (R2 = 0.54). Under the evolution of irrigation measures in the last 50 years, the average DP has gradually decreased from 574.2 mm (1971–1990) to 435.5 mm (2005–2021). However, a substantial amount of precipitation and irrigation water infiltrated the soil and percolated into the deep soil layer without being utilized by the crop. Therefore, there is an urgent need to consider measures to reduce DP to improve water-use efficiency in agriculture.

How Does Irrigation with Wastewater Affect the Physical Soil Properties and the Root Growth of Sugarcane under Subsurface Drip?

Studies on the development of the root system can provide important information about responses to different management strategies, such as the use of lower quality water, also evaluating the interaction between plants and the physical properties of the soil. This study tested the hypothesis that irrigation with treated sewage effluent (TSE) supplies the water needs of sugarcane plants, increasing root growth and improving the physical properties of the soil. We evaluated the effects of subsurface dripping with TSE or surface reservoir water (SRW) on the root development of first ratoon cane (Saccharum officinarum L.) and the physical properties of dystrophic red latosol. Irrigation treatments were applied at 20 and 40 cm and soil properties were evaluated at soil depth layers of 0–20, 20–40, 40–60, and 60–80 cm. We verified that under irrigation with TSE and SRW, shallower soil layers present better porosity, soil aggregation, and aggregate stability conditions, parameters that improve the root system development and plant growth. On the other hand, deeper soil layers have lower macroporosity and higher total clay volume, indicating the possibility of compaction and greater limitations for sugarcane root growth. These results are important for understanding soil quality and provide significant information for agricultural management and for the implementation of sustainable soil conservation practices. This study shows the efficiency of TSE as an alternative water source for sugarcane crops.

Estimating deep soil water depletion and availability under planted forest on the Loess Plateau, China

Deep soil water (DSW) plays a pivotal role in tree growth, susceptibility to drought-induced mortality, and belowground carbon and nutrient cycling. Assessing DSW depletion is essential for evaluating the resilience and sustainability of planted forests. But, due to the poor accessibility of deep soil layers, little is known about large scale DSW depletion. In this study, we leverage the concept that “plants are reliable indicators of deep soil water” to estimate DSW depletion in planted forests within the arid and semi-arid regions of the Chinese Loess Plateau (CLP). Our approach involves establishing a model that correlates forest age with DSW depletion. We then employ this model to estimate DSW depletion across the region, utilizing readily available data on the distribution of forest age and utilize the boundary models to consider the variability of DSW depletion estimated with forest age. Our results indicate that the model effectively estimates DSW depletion in planted forests, demonstrating a strong fit with an R2 of 0.71 and a low root mean square error (RMSE) of 332 mm. Notably, a substantial portion of the planted forest areas on the CLP has experienced DSW depletion from 800 mm to 1600 mm, and totaling 2.41 × 1010 m3 DSW depletion from 1995 to 2020 based on the general model. However, the available DSW in the existing planted forests on the CLP is estimated at only 1.73 × 1010 m3 by 2038. This suggests that there is potential risks and unsustainability for further afforestation efforts and carbon sequestration on the CLP under the current continuous afforestation measures. Our study holds significant implications for sustainable regional ecological management and quantifying water resources for carbon trading through afforestation.

Rainfall–runoff modeling using an Adaptive Neuro-Fuzzy Inference System considering soil moisture for the Damanganga basin

ABSTRACT Rainfall is the major component of the hydrologic cycle and it is the primary source of runoff. The main purpose of this study was to estimate daily discharge by employing an Adaptive Neuro-Fuzzy Inference System (ANFIS) model using rainfall and soil moisture data at three different depths (5 cm, 100 cm and bedrock) for the Damanganga basin. The length of the data for the study period 1983–2022 is 39 years. The model employed nine membership functions for each variable of soil moisture, rainfall, discharge and 30 rules were optimized. The results were compared considering a range of model performance indicators as correlation coefficient (R2) and Nash–Sutcliffe efficiency (NSE) coefficient. The model application results shows that soil moisture at bedrock gives more precise value of daily discharge with (R2) and NSE value as 0.9936 and 0.9981, respectively, as compared to the soil moisture at depths of 5 and 100 cm. The better results obtained for the measurement of soil moisture in the deeper soil layer are consistent with the hydrological behavior anticipated for the analyzed catchment, where the root-zone soil layer is the driver of the runoff response rather than the surface observations. This study can be helpful to hydrologists in selecting appropriate rainfall–runoff models.

Quantitative estimation of dust transport in the desert region of northwest China by plutonium isotopes

Dust is an important source of atmospheric pollution, and quantitative estimation of desert dust transport is crucial for air pollution control. In this study, five typical sandy soil profiles in the Tengger Desert were collected and analyzed for 239,240Pu concentration and 240Pu/239Pu atomic ratios in order to identify the source of 239,240Pu in this area and explore the sedimentary characteristics of dust in different profiles. The results revealed that the concentrations of 239,240Pu in the soil profiles were between 0.002 and 0.443 mBq/g with an exception of the deep layer soil at one site. The measured atomic ratios of 240Pu/239Pu are at the global atmospheric fallout level with a mean of 0.184 ± 0.020, indicating that global fallout is the dominant source of plutonium in this region. The total inventories of 239,240Pu in the reference sites in this area were estimated to be 39.2–44.6 Bq/m2, this is in agreement with the value from the global fallout of atmospheric nuclear weapon tests at the similar latitude (30–40 °N: 42 Bq/m2). The estimated erosion rate in the erosion profile utilizing soil erosion intensity mode is 2491 t/km2/yr and the soil erosion depth is 9.86 cm, While, the stacking rate of the accumulation profile is 1383 t/km2/yr, and the depth of accumulation is estimated to be 5.48 cm. The difference between the erosion and accumulation profiles indicated that approximately 1107 t/km2/yr of dust was exported from the Gobi landform area of the Tengger Desert, which might be transported long distance in the downwind direction.

No-tillage with straw mulching restrained the vertical transportation of chemical fertilizer N and reduced its leaching loss in Northeast China

Intensified by the pursuit of food security, nitrogen (N) source pollution caused by excessive chemical N fertilizer application has emerged as a major environmental threat, especially through nitrate N (NO3--N) leaching. While no-tillage with straw mulching is recognized for mitigating NO3--N leaching from chemical fertilizer N, its efficacy in deep soil layers remains unclear. Thus, employing the 15N isotope labeling technique in Northeast China's black soil, we investigated the impact of no-tillage and/or straw mulching on the transformation, vertical transport, and leaching loss of fertilizer N under five treatments: conventional ridge tillage (RT), and no-tillage with varying straw coverages (NT-0, NT-33, NT-67, and NT-100). Our results revealed that over 98.3% of fertilizer-derived mineral N in the soil was NO3--N, with substantial downward movement beyond 120 cm, posing a leaching risk. Three years after N fertilizer application, no-tillage and/or straw mulching with varying coverages significantly reduced fertilizer-derived NO3--N by averaging 36.3% in 0–300 cm soil profile, compared to RT with 18.36 kg ha−1 fertilizer-derived NO3--N in soil. Notably, no-tillage and/or straw mulching of 33%, 67%, and 100% coverages effectively decelerated the vertical transport of fertilizer-derived NO3--N to 140–220 cm soil deeper layers by averaging 48.4%, where NO3--N accumulates in large quantities. The percentages of fertilizer-derived NO3--N leached to applied fertilizer N varied from 3.7% to 7.2% after three years of vertical migration. No-tillage with different straw coverages remarkably decreased this leaching percentage by 42.7% and 21.9% compared with RT and NT-0, respectively. Furthermore, we found that no-tillage with straw mulching enhanced fertilizer N utilization efficiency (NUE) and crop yields with NT-33, NT-67, and NT-100 demonstrating higher accumulative NUE of 58.4%, 56.2%, and 58.8% and average yields of 13.90, 13.48, and 13.21 Mg ha−1, respectively. Therefore, we preliminarily suggest that implementing no-tillage and straw mulching with 33% and 100% coverages in Northeast China holds promise for simultaneously enhancing crop yields and NUE, and mitigating N fertilizer leaching in the form of NO3--N. These findings offer valuable insights for optimizing field management and mitigating N pollution in agriculture, contributing to the achievement of sustainable agricultural development.

Ridge-furrow planting patterns with film mulching improve water use efficiency by enhancing arbuscular mycorrhizal fungi in the rhizosphere and endophyte of summer maize

In a rainfed agroecosystem with limited water resources, the symbiotic interactions between crop-arbuscular mycorrhizal fungi may have a significant impact on field productivity and water absorption and utilization. However, the interaction between AMF characteristics of root endophyte and rhizosphere soil and water use patterns of summer maize has not been studied under ridge-furrow with film mulching planting patterns (RFPM) in dry farmland. Based on a field experiment, we aimed to reveal the effects of different RFPM planting patterns (i.e., ridge/furrow ratio of 40:70 cm (RF40:70), ridge/furrow ratio of 55:55 cm (RF55:55), and ridge/furrow ratio of 70:40 cm (RF70:40)) on the root water use patterns of summer maize, the distribution characteristics of AMF in root endophyte and rhizosphere soil, and their interaction relationship by using the water isotope (δD and δ18O) tracer technique, the high-throughput sequencing technology, MixSIAR model, and the structural equation models. As a result, compared to flat planting without mulching (FP), RF40:70, RF55:55, and RF70:40 significantly increased grain yield by 29.74%, 35.24%, and 45.53%, and water use efficiency by 23.13%, 35.99%, and 50.25%, across the two growing seasons, respectively (P < 0.05). The root characteristic parameters of summer maize decreased with the increase in soil depth, and were mainly distributed in the shallow layer (0–20 cm) and middle layer (20–60 cm). Compared with FP, the distribution ratio of root surface area density, root length density, and root dry weight density in shallow soil layer was significantly increased by 5.03%, 7.46%, and 9.70% averaging the different RFPM treatments, respectively (P<0.05). Besides, compared to FP, the AMF abundance and diversity in rhizosphere soil and root endogenous averaged RFPM treatments increased by 32.32% and 29.66% and 5.88% and 28.43% respectively, in which the abundance and diversity gradually increased with the increase of the ratio of ridge-furrow. The PLS-PM results found that the larger ridge-furrow ratio could significantly increase the yield and WUE of summer maize mainly by increasing the root surface area density, root length density, and the abundance and diversity of AMF in the root endophyte and rhizosphere soil, which increased the water use of the middle and deep layer soils. In summary, the large ridge-furrow ratio can significantly increase the yield and WUE of summer maize by extending the hyphal network of maize root symbiotic AMF, which increases the water uptake of middle and deep layer soil.

Effects of the conversion of natural tropical rainforest to monoculture rubber plantations on soil hydrological processes

AbstractRubber plantations have increased significantly under unprecedented economic growth in tropical areas, which leads to soil degradation and thereby alters soil hydrological processes. However, our understanding of how forest conversion affects soil hydrological processes remains unclear. Here, we collected soil samples from secondary forests (SF) and rubber plantations (RP) to determine the soil hydrological characteristics. We found the topsoil (0–20 cm) water retention in SF was higher than that of RP but displayed the contrast pattern in a deeper soil layer (20–60 cm). Meanwhile, the soil infiltration rates among the two vegetation types decreased significantly with infiltration time, with higher stable soil infiltration rates in SF than those in RP. Moreover, soil properties were also impacted by the forest conversion, such as the topsoil capillary porosity (CP) and total porosity (TP) in SF were higher than those of RP but contrasted in a deep soil layer. In comparison, the topsoil bulk density (BD) in SF was lower than that of RP, but contrasted in the deep soil layer and reached a significant level in the 0–10 and 40–50 cm (P &amp;lt; 0.05). Overall, the soil water retention was mainly determined by the CP, which could explain 31.56% of the total variance in soil water retention, followed by TP (26.57%) and soil BD (26.47%), whereas soil texture exerts a weak effect on soil water retention. Therefore, we can conclude that the conversion of tropical rainforest into rubber plantations may accelerate soil erosion owing to its lower topsoil water retention and soil infiltration rates.

Biogeochemistry of dissolved organic matter and inorganic solutes in soil profiles of tropical pasturelands

Tropical soils play a critical role in the global biogeochemical cycles and are essential for maintaining the Earth's carbon balance. Understanding the dynamics of dissolved organic matter (DOM) is paramount due to its implications for ecosystem functioning and nutrient cycling. This study comprehensively evaluated the origin, distribution, and composition of DOM and inorganic solutes in Brazilian tropical agricultural soils. Multiple analytical techniques were utilized to assess DOM from soil profiles (0–100 cm depth) across a spectrum of land uses, including a native Atlantic Forest, a degraded pasture, as well as intensive grazing, extensive grazing, and silvopastoral systems. Inorganic elements were quantified to assess the coupling between the organic and inorganic biogeochemical cycles. The dominance of C4 carbon in topsoil layers suggested substantial contributions of organic matter from grasses to the soil organic matter pool. However, with increased depth, C3 carbon inputs became more prominent, indicating the influence of forest vegetation that existed prior to the implementation of agricultural managements. DOM concentrations decreased with soil depth due to reduced carbon inputs, sorption to minerals, or oxidation. DOM composition did not show significant changes among different land use and managements. Lignin was identified as the primary contributor to oxidized DOM with increasing soil depth. The composition of DOM exhibited a shift from more aromatic and higher molecular weight compounds in topsoil layers to smaller, more aliphatic compounds in subsoil layers. Our key findings revealed that aliphatic compounds, particularly fatty acids, tend to accumulate in deeper soil layers. This phenomenon was consistent in pastures dominated by grasses but not in soils near treed vegetation. Overseeding (from C3 plants) did not significantly impact DOM compositions, emphasizing the persistence of C4 plants in these systems. The presence of inorganic elements in soil water extracts showed minimal impact on DOM dynamics, suggesting decoupled organic and inorganic biogeochemical cycles in tropical pasturelands.

Determining Water Use Patterns for the Betula platyphylla in the Southern Greater Khingan Mountains and Its Adaptation to Drought

Due to global climate change, seasonal droughts have intensified and become more frequent in certain semi-arid regions, and plants often adjust their water uptake depths to adapt to shifting environmental conditions. The southern Greater Khingan Mountains have a large natural secondary forest area and act as an important ecological barrier. This study focused on examining the water use patterns of the primary plant species, Betula platyphylla, within the natural secondary forest of the southern Greater Khingan Mountains. The investigation utilized oxygen stable isotope techniques and covered a timeframe spanning from July 2019 to September 2020. The findings indicate that the adaptable water utilization strategies and rapid response to precipitation could facilitate plants fully utilizing water from all depths, thereby enabling them to better adapt to arid environments. When the rainfall was low (390.4 mm in the growing season of 2019), the developed shallow roots quickly absorbed shallow soil water (0–20 cm, with a utilization ratio of 40.4% for the entire root depth), but when the rainfall increased (501.5 mm in the growing season of 2020), Betula platyphylla gradually transitioned to extracting soil water from deeper soil layers (40–60 cm) and deepened its root system (with a utilization ratio of 39.4%), indicating its adaptability to semi-arid environments. Therefore, the flexible water use strategy of Betula platyphylla in the same habitat may give it a competitive advantage during low rainfall periods. The findings are important for the protection of natural forests and water management in the southern Greater Khingan Mountains.