Variations In Soil Moisture Content Research Articles

Spatial mapping of soil moisture content using very-high resolution UAV-based multispectral image analytics

Assessing soil moisture content (SMC) is necessary for managing water at a spatial scale. Remote sensing technologies provide a robust approach for detecting the spatial-temporal fluctuations of SMC. The aim of this study was to estimate SMC at different soil depths using very high-resolution unmanned aerial vehicle (UAV)-based multispectral (MS) images and machine learning algorithms and generate spatial maps of SMC using the best-performed machine learning (ML) algorithm. The UAV-based multispectral images of bare soil were captured at 40 m altitude with a very high spatial resolution (2.89 cm) during the rabi 2021/22 season. At the same time, the soil samples were collected from different soil depths, and the gravimetric SMC was measured. Five machine-learning algorithms (Linear Regression (LR), K-Nearest Neighbors (KNN), Random Forest (RF), Decision Tree (DT), and Support Vector Regression (SVR)) were used to train the model between SMC and MS data (MS band reflectance and vegetation indices). The soil with high SMC has low spectral reflectance and soil with low SMC shows high spectral reflectance. For the prediction of surface SMC, the linear regression (R2 = 0.89; RMSE = 2.80 %) and 5 cm depth SMC, the SVR (R2 = 0.64; RMSE = 3.03 %) were performed well compared to other ML algorithms. For surface SMC, blue band reflectance, and 5 cm depth SMC, the Ratio Vegetation Index (RVI) correlated well compared to others. All models failed to predict the SMC at the deeper soil depths. The spatial SMC mapping described the visual color variations in SMC within the field. Crop irrigation scheduling can be significantly improved through the insights this spatial SMC estimation approach provides, making it a valuable tool for farmers and irrigation planners.

Effects of Soil Moisture Content Variations on Fruit Quality and Tree Stress in Satsuma Mandarin ‘Miyagawa Wase’ during Porous Sheet Mulching Cultivation

Effects of Soil Moisture Content Variations on Fruit Quality and Tree Stress in Satsuma Mandarin ‘Miyagawa Wase’ during Porous Sheet Mulching Cultivation

Effects of road- vs. field-recommended tyre inflation pressures and small variations in soil moisture content on traffic-induced soil compaction during seedbed preparation

Soil compaction has become one of the most common forms of soil degradation, with associated negative effects on the functioning of agricultural soils. Decades of research have led to publication of several practical measures that mitigate risk of soil compaction, yet adoption among European farmers remains limited. To improve adoption by farmers, experiments under practical conditions using common operations should be performed. A field experiment was set up to evaluate the effects of road- (200 kPa) vs. field- (140 kPa and 100 kPa) recommended tyre inflation pressure and soil moisture content (0.24 g g−1 vs. 0.22 g g−1) on traffic-induced compaction of a silt loam soil during seedbed preparation. The various tyre inflation pressures were tested using two tyre types (standard radial tyre at 200 kPa and 140 kPa; VF tyre at 100 kPa) of similar dimensions mounted onto the same tractor. Variation in experimental soil moisture content was achieved by performing the seedbed preparation on two dates in spring (early, March 30th, vs. late, April 14th). In this one-year study, reducing the standard-tyre inflation pressure from road- (200 kPa) to field-recommended (140 kPa) pressure did not prevent soil compaction. The use of VF tyres at field-recommended (100 kPa) tyre inflation pressure resulted in significant reductions in vertical contact stress and mean normal stress as compared to 200 kPa. Although non-significant, the pressure reduction from 200 kPa to 140 kPa did result in a 4 % increase in in-track dry matter sugar beet yield while a reduction from 200 kPa to 100 kPa resulted in an 11% increase. Lower tyre inflation pressure showed no significant effect on fuel consumption and penetration resistance. Seedbed preparation under slightly drier (0.22 g g−1) soil conditions negatively affected fuel consumption (+11 %) and resulted in an in-track dry matter sugar beet yield increase of 11 %. For both tested prevention strategies, the impact of soil compaction was better observable by sugar beet yield than by most of the measured soil physical parameters.

Spatial variability of soil resistance penetration in forest areas converted for agricultural uses in the Amazon, Brazil

The knowledge of the spatial variability of soil attributes has been characterized as an important step for an adequate management to be carried out. Thus, the aim of this study was to evaluate spatial variability of soil resistance to penetration in areas under forest and converted to agricultural uses in the Amazon, Brazil. The study was carried out in Typic Hapludultsin the San Francisco Settlement located in the municipality of Canutama, Amazonas, Brazil. Four areas were selected. The collections proceeded at the crossing points of the grids, under the layers of 0.00-0.05; 0.05-0.10; and 0.10-0.20 m, making a total of 80 sample points in each area. Physical soil analyzes were carried out, with the criterion of determining the texture, soil resistance penetration and soil moisture. The variation in soil moisture content remained constant in all evaluated layers. The PR and soil moisture showed a spatial dependence structure that made it possible to analyze the influence on the different conditions of use and evaluated layers, since the scope of spatial dependence was preponderant to evaluate the scales of spatial variation, mainly in verifying the possible effects and factors that most affect these variables analyzed.

Load-Settlement Analysis of Axially Loaded Piles in Unsaturated Soils

Unsaturated soil covers a significant part of the world, and studying the behavior of deep foundations in this medium is an important step in increasing accuracy and economic efficiency in geotechnical studies. This paper presents an analytical solution to investigate the load-carrying characteristics of single piles embedded in unsaturated soils, accounting for the effect of groundwater level on the pile’s response. For this purpose, relationships for shear modulus and Poisson’s ratio for unsaturated soils were collected from the literature to consider their effects as key parameters on pile performance. A parametric study was conducted to evaluate the effect of soil moisture content on the behavior of the pile-soil system for different soil types, and the effect of pile slenderness on its load-settlement behavior was studied for varying soil moisture contents. The results indicate that the pile stiffness increases as the soil suction increases while below a critical slenderness value, hence increasing the pile load capacity. However, this improvement occurs within a limited range of soil suction that is narrower for coarse-grained soils. The pile settlement corresponding to soil failure was also evaluated by modifying the existing solutions for unsaturated soils. The developed solutions were verified against the predictions of published solutions as well as the results of finite element analysis and pile load tests. It was found that the system stiffness decreases by 50% when the water table rises from the pile toe level to the ground surface in the studied soil.

900-Days long term study of plant microbial fuel cells and complete application for powering wireless sensors

Plant microbial fuel cells (PMFCs) are electrochemical systems capable of producing electrical energy from plant growth. Despite their limited power density, PMFCs hold pomise as power source for wireless sensor, without using embedded battery, especially in isolated locations. In this study, a complete wireless system was presented, with Cyperus papyrus-based microbial fuel cell. The Cyperus papyrus system was studied over 900 days. Although there was a slight decrease in power output attributed to anodic decreasing performance, the reduction at the cathode remained stable. This stability is likely due to biocatalyst activity, supported by the oxygen transport from the plant to the roots. Although performance of Cyperus papyrus microbial fuel cell were lower than those found in literature, these plants were stacked to power a microcontroller equipped with a temperature/humidity sensor. This microcontroller transmitted measurements wirelessly to a web server every 2 h. The web server, accessible via a web interface, provided real-time data to users on the local network. Finally, the intervals between measurements could serve as indicators of environmental stress, such as variations in soil moisture content.

Soil Moisture Distribution and Time Stability of Aerially Sown Shrubland in the Northeastern Margin of Tengger Desert (China)

Considering the importance of soil moisture in hydrological processes, it is crucial to understand the water distribution and time stability of different aerial shrub soils. There are few studies on the soil moisture of aerial vegetation in the northeastern margin of the Tengger Desert. Based on long-term monitoring data from the aerial seeding area in the northeastern margin of the Tengger Desert, the distribution characteristics of soil moisture and the temporal stability of soil moisture were studied. From June to October 2022, the soil moisture monitoring instrument WatchDog was used to monitor the long-term soil moisture changes (0–200 cm) in the four aerial afforestation plots of Hedysarum scoparium, mixed forest land (Hedysarum scoparium dominant species), mixed forest land (Calligonum mongolicum dominant species), and Calligonum mongolicum. The Spearman rank correlation coefficient was used to study the temporal stability of soil moisture in the four plots. Rainfall data were collected through small weather stations. The results show that the average soil water storage of four kinds of aerial shrub land in the study area was the highest in August, and the average soil water storage of different forest lands was different. The soil water content of the surface layer (0–30 cm) fluctuated the most in different months. The variation in soil water content in the shallow layer (30–100 cm) was smaller than that in the surface layer. The fluctuation of soil water content in the middle layer (100–150 cm) and deep layer (150–200 cm) was relatively stable. There was no strong variability in soil moisture content, and the temporal variation coefficient of surface soil moisture was the highest (31.44–39.8%), which showed moderate variability. The temporal variation coefficient of soil moisture in the shallow, middle and deep layers of all kinds of plots was significantly reduced, and the soil moisture stability of different aerial shrub land was the same. Spearman rank correlation analysis showed that the spatial pattern of soil water content in the surface layer (0–30 cm) and deep layer (150–200 cm) was more stable over time, that is, the temporal stability of soil water content was higher, and the temporal stability of soil water content in the middle and shallow layers of different types of shrub land was different. The research results help us to understand the soil hydrological process in the aerial seeding afforestation area in the northeastern margin of Tengger Desert, rationally arrange soil moisture monitoring points, efficiently manage and utilize water resources in the aerial seeding area, and provide a theoretical basis for local vegetation restoration and the optimization of the ecological environment.

Screening of cacao clones for drought tolerance by assessing predawn leaf water potential, growth, and leaf gas exchange

Drought in cacao-producing regions worldwide is causing a decrease in yield and, in severe cases, leading to plant death. This primarily affects small farmers who lack sufficient financial resources or water availability to irrigate their plantations. This study aimed to test 83 cacao clonal genotypes for drought tolerance by evaluating their physiological and morphological features. These genotypes, referred to as drought-tolerant cacao (DTC) genotypes, were selected through mass selection from regions of Bahia, Brazil, severely affected by prolonged droughts. Seedlings of the DTC clonal genotypes and two control clones (CCN 51- drought-intolerant and CEPEC 2002 – drought-tolerant) were obtained from rooted cuttings of plagiotropic branches and evaluated under greenhouse conditions. Three experiments (EXP 1, 2, and 3) were conducted using a randomized block design, with three replications each and two plants per replication of each clonal genotype to test for drought tolerance. Data analyses were conducted using univariate and multivariate statistical analysis. DTC and control clones were subjected to varying soil moisture contents [70, 60, 50, 40, and 30 % of field capacity (FC)] and their controls (maintained close to 100 % of FC) for approximately 40 to 60 days. The results revealed significant statistical differences in growth variables before the plants were subjected to drought. They were categorized based on vigor into three, four, and three groups for EXP 1, 2, and 3, respectively during cluster analysis. DTC and control clones subjected to drought (70, 60, 50, 40, and 30 % of FC) exhibited significant statistical differences in physiological traits compared to the traits of their respective controls (100 % of FC). However, plant growth remained largely unchanged under drought stress (30 or 40 % of FC). DTC clonal genotypes 15, 17, 23, 41, 61, 66, 90, 91, 92, and 93 were more efficient in maintaining net photosynthesis (A) with decreases in soil moisture, showing greater changes only at 40 % of FC. DTC clonal genotypes 14, 32, 41, 61, 69, 70, 88, 89, 92, 95, and 108 maintained stomatal conductance (gs) values similar to those of their controls. Twenty-three DTC clonal genotypes maintained values of A, gs, E, Ci, A/gs, and A/E close to their respective controls, suggesting that these genotypes present features for drought tolerance.

Research on Landslide Hydrology and Hydrogeological Disaster Monitoring

The triggering of landslides is strongly related to hydrological processes, as variations in soil moisture content and pore water pressure affect variations in soil mechanical properties [...]

Ensemble Learning Methods for Shear Strength Prediction of Fly Ash-Amended Soils with Lignin Reinforcement

For industrial applications in cold regions, a fly ash-amended soil with lignin reinforcement is introduced here. Predictive models were developed for soil shear strength based on two ensemble learning algorithms, to facilitate understanding soil properties with limited prior knowledge. First, over 270 unconsolidated undrained triaxial tests were conducted on the stabilized soil with varying soil moisture contents, percent lignin fiber, confining pressures, and curing conditions (uncured, 15 days curing, and 15 days curing along with freeze-thaw actions). Extreme gradient boosting (XGBoost) and random forest (RF) were then applied to develop the predictive models for the specimens. A parallel genetic algorithm optimized the hyperparameters of both the XGBoost- and RF-based models. Next, monotonicity and sensitivity analyses were carried out with these models, to compare and assess their generalization capabilities. Finally, the peak shear strengths of the specimens finally correlated across different curing conditions. Given different training sample sizes, the XGBoost-based model consistently outperformed the RF-based model, particularly when half of the samples were fed as input. The root-mean-squared error (RMSE), mean absolute percentage error (MAPE), and coefficient of determination (R2) values of the XGBoost-based model on the test set are approximately 105−135, 5%−7%, and 0.85, respectively. Some essential features that are overlooked by conventional analysis have been identified with ensemble learning. This study demonstrates the potential of ensemble methods to tackle regression and prediction issues arising in civil engineering with less experimental data.

Near-Surface Soil Moisture Characterization in Mississippi’s Highway Slopes Using Machine Learning Methods and UAV-Captured Infrared and Optical Images

Near-surface soil moisture content variation is a major factor in the frequent shallow slope failures observed on Mississippi’s highway slopes built on expansive clay. Soil moisture content variation is monitored generally through borehole sensors in highway embankments and slopes. This point monitoring method lacks spatial resolution, and the sensors are susceptible to premature failure due to wear and tear. In contrast, Unmanned/Uncrewed Aerial Vehicles (UAVs) have higher spatial and temporal resolutions that enable more efficient monitoring of site conditions, including soil moisture variation. The current study focused on developing two methods to predict soil moisture content (θ) using UAV-captured optical and thermal combined with machine learning and statistical modeling. The first method used Red, Green, and Blue (RGB) color values from UAV-captured optical images to predict θ. Support Vector Machine for Regression (SVR), Extreme Gradient Boosting (XGB), and Multiple Linear Regression (MLR) models were trained and evaluated for predicting θ from RGB values. The XGB model and MLR model outperformed the SVR model in predicting soil moisture content from RGB values. The R2 values for the XGB and MLR models were >0.9 for predicting soil moisture when compared to SVR (R2 = 0.25). The Root Mean Square Error (RMSE) for XGB, SVR, and MLR were 0.009, 0.025, and 0.01, respectively, for the test dataset, affirming that XGB was the best-performing model among the three models evaluated, followed by MLR and SVR. The better-performing XGB and MLR models were further validated by predicting soil moisture using unseen input data, and they provided good prediction results. The second method used Diurnal Land Surface Temperature variation (ΔLST) from UAV-captured Thermal Infrared (TIR) images to predict θ. TIR images of vegetation-covered areas and bare ground areas of the highway embankment side slopes were processed to extract ΔLST amplitudes. The underlying relationship between soil surface thermal inertia and moisture content variation was utilized to develop a predictive model. The resulting single-parameter power curve fit model accurately predicted soil moisture from ΔLST, especially in vegetation-covered areas. The power curve fit model was further validated on previously unseen TIR, and it predicted θ with an accuracy of RMSE = 0.0273, indicating good prediction performance. The study was conducted on a field scale and not in a controlled environment, which aids in the generalizability of the developed predictive models.

No-tillage with straw mulching promotes wheat production via regulating soil drying-wetting status and reducing soil-air temperature variation at arid regions

Straw returning is a technical measure of crop production widely adopted in arid and water-deficient areas. However, the mechanism by which straw returning drives spatio-temporal changes in soil moisture and temperature to improve crop productivity remains unclear. So, a three-year field experiment was conducted with four various straw returning treatments for wheat production: 1) no-tillage with straw mulching (NTSM), 2) no-tillage with straw standing (NTSS), 3) conventional tillage with straw incorporation (CTS), and 4) conventional tillage without straw returning (CT, control). The spatio-temporal variations of soil moisture content and soil temperature were assessed. It will provide the basis for selecting the appropriate way of straw returning to increase wheat yield and clarifying its hydrothermal regulation mechanism. NTSM and NTSS were effective in maintaining soil moisture and regulating soil temperature, and had a greater effect on grain increase, than CTS and CT. Meanwhile, NTSM had a relatively higher yield than NTSS through better regulation of soil hydrothermal characteristics. NTSM had higher soil moisture content in the 0–120 cm depth by 9.8–10.2%, 6.7–8.2%, 6.5–10.2%, and 6.9–7.4% at sowing to jointing, jointing to booting, booting to early-filling, and early-filling to maturing stages of wheat, respectively. NTSM decreased evapotranspiration modulus coefficient (ETMC) and evapotranspiration intensity (ETI) at jointing to early-filling stage of wheat, but increased both indexes from early-filing to maturing stage of wheat, which is helpful to adjust the contradiction of soil moisture demand for wheat in different growth stages. Additionally, NTSM had 9.8–10.2%, 6.7–8.2%, 6.5–10.2%, and 6.9–7.4% lower soil temperature in the 5–25 cm depth than CT, at the four aforementioned wheat growth stages, respectively. The difference of soil temperature was mainly reflected at the 5–15 cm depth by analyzing the difference on soil temperature in various soil depths. The treatment on NTSM had little variation and stabilized soil temperature, according to the difference between air and average soil temperature of 5–15 cm depth. NTSM allowed wheat to grow a suitable thermal environment across their growth period, which is a significant regulatory mechanism for wheat to maintain better growth and development. Thereby, NTSM boosted wheat grain yield by 18.6–27.3% as compared to CT. Collectively, the NTSM treatment had better effect on regulating soil drying-wetting status and reducing soil-air temperature variation, which could be used as a recommended measure to improve wheat productivity at arid conditions.

Genome-wide association study of agronomical and root-related traits in spring barley collection grown under field conditions.

The root system is a key component for plant survival and productivity. In particular, under stress conditions, developing plants with a better root architecture can ensure productivity. The objectives of this study were to investigate the phenotypic variation of selected root- and yield-related traits in a diverse panel of spring barley genotypes. By performing a genome-wide association study (GWAS), we identified several associations underlying the variations occurring in root- and yield-related traits in response to natural variations in soil moisture. Here, we report the results of the GWAS based on both individual single-nucleotide polymorphism markers and linkage disequilibrium (LD) blocks of markers for 11 phenotypic traits related to plant morphology, grain quality, and root system in a group of spring barley accessions grown under field conditions. We also evaluated the root structure of these accessions by using a nondestructive method based on electrical capacitance. The results showed the importance of two LD-based blocks on chromosomes 2H and 7H in the expression of root architecture and yield-related traits. Our results revealed the importance of the region on the short arm of chromosome 2H in the expression of root- and yield-related traits. This study emphasized the pleiotropic effect of this region with respect to heading time and other important agronomic traits, including root architecture. Furthermore, this investigation provides new insights into the roles played by root traits in the yield performance of barley plants grown under natural conditions with daily variations in soil moisture content.

Studies on Controlling Variables of the Conveying Unit of a Power Tiller Operated Groundnut Digger

A power tiller operated groundnut digger was designed and developed in the Dept. of Farm Machinery and Power Engineering, CAET, OUAT, Bhubaneswar during 2021–22. The objective of this project was to optimize the operational parameters of the digger's conveying unit using the RSM technique. The study analysed the effects of soil moisture content and conveyor speed, on the conveying efficiency and soil separation efficiency with two different types of peg geometries. The central composite rotatable design (CCRD) method with a quadratic model was utilized to correlate the independent parameters with the conveying and soil separation efficiencies. The results indicated that variations in soil moisture content and conveyor speed had a significant impact on the conveying and soil separation efficiencies. The optimum parameters for the conveying unit of a power tiller operated groundnut digger were found to be a soil moisture range of 9.0-12.0%, a conveyor speed of 1.0 m/s and straight shank with bending tip pegs, resulting in a conveying efficiency and soil separation efficiency of 89.45% and 71.45%, respectively.

Моделирование процесса приема собственного радиотеплового излучения земной поверхности

The receiving model of the own soil radiothermal radiation by a bipolarized microwave radiometer when remote sensing the soil moisture from an unmanned aerial vehicle on low altitude is considered. The simulation is carried out taking into account the receiving antenna pattern with side lobes. The height, speed of the carrier and the main lobe axis angle are taken into account. The main parameters of the microwave radiometer for remote determination of portraits of moistened soils are given. The Earth's surface is modeled by a two-dimensional distribution function of the soil permittivity on the thickness of the near-surface layer and a deeper layer with a different permittivity value. The two-dimensional permittivity distribution function represents as "checkerboard" with a periodic change in the permittivity of the soil by "cells". Both the proper radiothermal radiation of the soil and the relict sky radiation of the celestial sphere, re-reflected by the earth's surface, are taken into account. The perspective of using the simulation results to optimize the parameters of the radiometer and remote sensing system according to the criterion of maximum sensitivity of the system to variations in soil moisture content is analyzed.

Spatial distribution characteristics of soil moisture in different slopes on Loess Gully Region

AbstractThe spatiotemporal changes of soil moistures under different rainfall events and slope positions in the loess hilly and gully area were assessed in this study using the positioning monitoring method. According to the three positions with different distances from the top of the slope, set the three treatments of “top of the slope” (TS), “middle of the slope” (MS), and “bottom of the slope” (BS). The results demonstrated a certain degree of influence of rainfall and slope position on the vertical change of soil moisture at different soil depths in the study area. Before intense rainfall, soil moisture at different slope positions revealed a vertical distribution pattern and increased with increasing soil depth. In addition, soil moisture contents below the 60‐cm depth at different sites were significantly higher than those observed above the 60‐cm depth (p < .05), while soil moisture contents below the 120‐cm depth were extremely significantly higher than those observed above the 120‐cm depth (p < .01). On the other hand, no significant variation in soil moisture content was observed between different depths after intense rainfall events (p > .05). The above studies show that soil moisture in the loess hilly and gully area has a certain hysteresis effect. The hysteresis of soil flow allows us to effectively collect and use soil moisture, which can provide a theoretical basis for the intensive and economical use of soil moisture in this area.

Failure mode of rainfall-induced landslide of granite residual soil, southeastern Guangxi Province, China

Abstract. Granite residual soil landslides are widely distributed in the southeast of Guangxi, China. They pose threats to local communities, economic development and ecological restoration. To understand the failure mode, the landslide can provide a scientific basis for early warning and prevention. In this study, we conducted artificial flume model tests to investigate the failure mode of granite residual soil landslide. The macroscopic phenomena of landslides were observed and summarized. The response and variations of soil moisture content and pore water pressure were analyzed. And the discrepancies in landslide initiation were explored. The results had three aspects: (1) the response of volume moisture content was not synchronized with that of pore water pressure. Their variations were influenced by initial dry density, slope angle and rainfall intensity. The fluctuation of pore water pressure depended on soil mechanical behavior and its diffusion. (2) The differences in the formation process of granite residual soil landslides included the initiation time and mode. The starting time of landslide was delayed with increasing initial dry density and slope angle but shortened with increasing rainfall intensity. The failure mode could be changed from a sudden type to a progressive type due to the increase in initial dry density. (3) There are five stages in the landslide mobilization as follows: rain infiltration and crack generation, soil slide at the slope toe, occurrence of surface runoff and soil erosion, formation of steep-free surface, and soil slide at the upper slope. This research can provide valuable reference for the prevention and early warning of granite residual soil landslide in southeastern Guangxi.

Effects of Supplementary Irrigation on Soil Respiration of Millet Farmland in a Semi-Arid Region in China

Carbon dioxide (CO2) is recognized as key part of evaluating the soil environment, and the soil respiration rate is an effective indicator of CO2 emission. To explore the influence and coupling mechanism of irrigation on the soil respiration of millet farmland in the Northern Shanxi Province in China, conventional rainfed (CK) and supplementary irrigation (W1) at the late jointing stage were conducted. The soil respiration rate and carbon emission flux in millet farmland under different treatments were observed. The relationship between soil respiration rate and soil physical–chemical properties and the crop growth index was further analyzed. The result showed that the soil respiration rate and carbon emission flux of W1 were higher than those of CK treatment. The comparison of the linear regression correlation between soil respiration rate and soil physical–chemical properties revealed that the major regulating factors of the soil respiration rate were soil moisture (<10.6%) followed by soil pH, soil moisture (>10.6%), soil temperature, and finally soil organic matter content. There are uncertainties regarding the soil moisture content variation range in soil respiration. Moreover, supplementary irrigation promoted the growth indexes, yield, and irrigation water use efficiency in millet farmland. Further research with less irrigation treatment is necessary for exploring an optimization model of water use efficiency and low carbon dioxide emissions in millet fields, which would be helpful to realize agricultural water utilization and a “carbon peak” in the sense of farmland.

Analysis of Spatial Variability of Plough Layer Compaction by High-Power and No-Tillage Multifunction Units in Northeast China

In this study, we addressed the problem of the spatial variability of plough layer compaction by high-power and no-tillage multifunction units in the management of maize planting in the Great Northern Wilderness in China. A comprehensive field experiment involving high-power and no-tillage multifunction units for 165 acres of maize was conducted and analyzed using GIS. Firstly, the test area was divided into four areas, and points were set at equal horizontal distances to collect data on the compactness, water content, porosity and fatigue of the plough layer at different depths. Secondly, the GIS kriging difference method was used to analyze the impact of longitudinal compaction of the plough layer profile at each depth in different test areas. Thirdly, the GIS kriging difference method was used to analyze the lateral spatial distribution of plough layer compaction. Finally, the spatial longitudinal and transverse variabilities of the plough layer were summarized, and the effect of the high-power and no-tillage multifunction units on the physical ecology of the soil in the plough layer was investigated. The results show that the physical properties of the plough layer can be significantly affected by compaction after spreading in the middle tillage period. The surface soil was most affected, with the greatest change in compactness and porosity; the rate of change of soil compactness reached 143.49% and the rate of change of soil porosity reached 40.57%. With the increase in soil depth, the rate of change of soil compactness and porosity gradually decreased. The greatest variation in soil moisture content was found in the middle layer and reached a maximum of 13.78% at a depth of approximately 20 cm. The results of the spatial variability analysis show that the mean values of c0/(c0 + c) for the spatial semi-variance functions of compactness, water content and porosity of the tilled soil in the longitudinal space of each test area before compaction were approximately 15%, 19% and 20%, respectively; after compaction, the mean values were approximately 33%, 23% and 30%, respectively; the mean values of c0/(c0 + c) for the spatial semi-variance functions of compactness, water content and porosity change of the tilled soil were approximately 24%, 14% and 12%, respectively. The mean values of c0/(c0 + c) for the spatial semi-variance functions of compactness, water content and porosity of the soil at each depth in the lateral space before compaction were approximately 80%, 71% and 78%, respectively, and after compaction the mean values were approximately 40%, 23% and 24%, respectively, with the mean values of c0/(c0 + c) along the east–west direction being approximately 8%, 27% and 18%, and the mean values of c0/(c0 + c) along the north–south direction being approximately 9%, 0% and 20%. The results show that compaction by high-power and no-tillage multifunction units led to a decrease in the spatial variability of soil physical parameters at each depth of tillage in the black soil layer in the longitudinal space, while the spatial variability of the soil physical parameters at each depth of tillage in the black soil layer in the transverse space increased. Moreover, the degree of influence of compaction by high-power and no-tillage multifunction units on soil physical parameters was higher in both vertical and horizontal spaces. This study can provide a theoretical reference for the analysis of the impact of large units on the compaction of black soil layers from the perspective of GIS.

Long-term watermelon continuous cropping leads to drastic shifts in soil bacterial and fungal community composition across gravel mulch fields

Despite the known influence of continuous cropping on soil microorganisms, little is known about the associated difference in the effects of continuous cropping on the community compositions of soil bacteria and fungi. Here, we assessed soil physicochemical property, as well as bacterial and fungal compositions across different years (Uncropped control, 1, 6, 11, 16, and 21 years) and in the watermelon system of a gravel mulch field in the Loess Plateau of China. Our results showed that long-term continuous cropping led to substantial shifts in soil bacterial and fungal compositions. The relative abundances of dominant bacterial and fungal genera (average relative abundance > 1.0%) significantly varied among different continuous cropping years (P < 0.05). Structural equation models demonstrated that continuous cropping alter soil bacterial and fungal compositions mainly by causing substantial variations in soil attributes. Variations in soil pH, nutrient, salinity, and moisture content jointly explained 73% and 64% of the variation in soil bacterial and fungal compositions, respectively. Variations in soil moisture content and pH caused by continuous cropping drove the shifts in soil bacterial and fungal compositions, respectively (Mantel R = 0.74 and 0.54, P < 0.01). Furthermore, the variation in soil bacterial and fungal composition showed significant correlation with watermelon yield reduction (P < 0.01). Together, long-term continuous cropping can alter soil microbial composition, and thereby influencing watermelon yield. Our findings are useful for alleviating continuous cropping obstacles and guiding agricultural production.