Initial Soil Research Articles

Converting croplands into perennials may contribute to the deep soil nitrogen (N) accumulation in N‐limited region: Evidence from the arid and semi‐arid Chinese Loess Plateau

AbstractConverting degraded croplands into perennials has been proposed as an effective method of soil N sequestration, however, the dynamics of deep soil N (>100 cm) following cropland conversion are not well understood. In this study, we synthesized 3049 observations to detect the changes in deep soil N content following cropland conversion on the arid and semiarid Loess Plateau. Our results showed that converting croplands into perennials significantly increased the soil N content by an average of 57.4%, 23.1%, and 29.5% in the surface (0–20 cm), subsurface (20–100 cm), and deep (100–200 cm) layers, respectively. The extent of the increase was influenced significantly by the land‐use conversion types and tree species. Specifically, the conversion of croplands into deep‐rooted forests or shrubs, particularly Robinia pseudoacacia and Caragana microphylla, exhibited higher advantages in deep soil N sequestration. Moreover, deep soil N sequestration increased significantly with time since cropland conversion (p < 0.001), and the rates in deep soils were approximately 26.1% and 66.7% of that in 0–20 and 20–100 cm soils, respectively. In the long term, converting croplands into forests and shrubs showed higher potential for deep soil N sequestration. Linear regression analysis showed that the changes of deep soil N sequestration were influenced significantly by initial soil N content (p < 0.001) and humidity index (p < 0.001), with the slopes in >100 cm layers being 2 to 3 times than that in the top meter, indicating higher sensitivity in deep soils. Overall, this study provides evidence that converting degraded croplands into perennials may contribute to deep soil N accumulation in N‐limited regions, which could potentially alleviate N limitation and sustain long‐term ecosystem carbon sequestration.

Effects of municipal waste compost on microbial biodiversity and energy production in terrestrial microbial fuel cells

Microbial Fuel Cells (MFCs) transform organic matter into electricity through microbial electrochemical reactions catalysed on anodic and cathodic half-cells. Terrestrial MFCs (TMFCs) are a bioelectrochemical system for bioelectricity production as well as soil remediation. In TMFCs, the soil is the ion-exchange electrolyte, whereas a biofilm on the anode oxidises organic matter through electroactive bacteria. Little is known of the overall microbial community composition in a TMFC, which impedes complete exploitation of the potential to generate energy in different soil types. In this context, an experiment was performed to reveal the prokaryotic community structure in single chamber TMFCs with soil in the presence and absence of a municipal waste compost (3% w/v). The microbial community was assessed on the anode and cathode and in bulk soil at the end of the experiment (54 days). Moreover, TMFC electrical performance (voltage and power) was also evaluated over the experimental period, varying the external resistance to improve performance. Compost stimulated soil microbial activity, in line with a general increase in voltage and power. Significant differences were observed in the microbial communities between initial soil conditions and TMFCs, and between the anode, cathode and bulk soil in the presence of the compost. Several electroactive genera (Bacillus, Fulvivirga, Burkholdeira and Geobacter) were found at the anode in the presence of compost. Overall, the use of municipal waste compost significantly increased the performance of the MFCs in terms of electrical power and voltage generated, not least thanks to the selective pressure towards electroactive bacteria on the anode.

Evaluating soil water movement and soil water content uniformity under sprinkler irrigation with different soil texture and irrigation uniformity using numerical simulation

Water movement and its distribution uniformity in the soil are essential for the design of sprinkler irrigation systems. They are both crucial factors influencing nutrient migration and the productivity of crops. In this study, a new numerical simulation method was proposed to investigate the soil water movement in sprinkler irrigation under nonuniform infiltration boundary conditions using COMSOL software. Besides, two soil tank experiments were conducted to test the reliability of the simulation model. Finally, the model was applied to evaluate the effects of sprinkler irrigation uniformity, soil texture, and initial soil water content on soil wetting patterns and soil water content uniformity. The results showed that the COMSOL-2D predictions of the vertical wetting fronts were in good agreement with the experimental data. The soil texture and initial soil water content influenced the soil wetting pattern and the risks of surface runoff and deep percolation in sprinkler irrigation systems. When the water application rate was 11.35 mm h−1 with an irrigation duration of 10 h, it was easy to cause surface runoff in silty clay loam while deep percolation in loamy sand. Additionally, when the initial soil water content is high, it should be better to avoid irrigation or cut down the irrigation duration to prevent percolation. The water within the soil was more uniformly distributed than that applied through a sprinkler irrigation system. The uniformity coefficient of soil water content distribution (CUs) increased from 87.75 % to 95.56 %, as the uniformity coefficient of sprinkler irrigation (CU) increased from 40.74 % to 82.41 %. Although a higher initial soil water content brought a higher soil CUs value, it also led to a higher risk of percolation. The experimental and simulation results indicated that the COMSOL-2D model could be used to accurately simulate soil water movement in sprinkler irrigation and determine the suitable operation mode of low-pressure sprinklers.

Exploring an intelligent adaptation method of hydrological model parameters for flood simulations based on the light gradient-boosting machine

Traditional hydrological modeling methods use a set of parameters to simulate flood processes with complex causes and variable intensity, which can easily lead to parameter instability. To address the problem of parameter instability, this study proposes an approach integrating the hydrological model with Intelligent Adaptation Parameters (IAP), whose intelligent adaptation relationship is established by the light gradient-boosting machine (LightGBM) based on individual calibration parameters by each flood event and flood characteristics including flood-caused rainstorm information and initial soil moisture. A widely used hydrological model, Xin 'anjiang (XAJ) model, is chosen to be integrated with IAP (XAJ-IAP) in this study, which has a relatively complex structure and a total of 15 model parameters. The obtained findings demonstrate that: (1) recalibrating the sensitive runoff concentration and separation parameters with a single flood leads to a notable enhancement in simulation accuracy, while simultaneously considering the model's physical significance; (2) the XAJ overestimates large floods and underestimates small floods. Compared with the XAJ, the XAJ-IAP has a better rain-flood response relationship and simulation accuracy for floods of different magnitudes, solving the problem of parameter instability that exists in XAJ; and (3) evaluated in terms of information gain, sensitive parameters contribute the most to the establishment of the intelligent adaptation relationship in the LightGBM compared to flood-caused rainstorm information and initial soil moisture, indicating that sensitive parameters are the most important input features of the LightGBM. It can be concluded that the intelligent adaptation system can not only solve the problem of parameter instability that exists when traditional hydrological models simulate complex and changeable floods, but also further reveal the relationship between the model and floods.

Combined Application of Filter Cake and Macadamia Husk Compost Affects Soil Fertility and Plant Mineral Content of Orange-Fleshed Sweet Potatoes

A greenhouse pot experiment was conducted to investigate the influence of the combined application of filter cake and macadamia husk compost (FC+MHC) on the soil fertility and dry matter partitioning of Beauregard and 199062.1 cultivars of orange-fleshed sweet potato. The effects of the two organic wastes on the mineral nutrients in the leaves and the storage roots of the 199062.1 cultivar were also investigated. In addition to FC+MHC, four other treatments—filter cake only (FC), macadamia husk compost only (MHC), inorganic fertilizer only (IF), a combination of filter cake and inorganic fertilizer (FC+IF), a combination of macadamia husk compost and inorganic fertilizer (MHC+IF), and a control (CONT)—were included in the investigation for the purpose of comparison. To achieve this, 1 kg of compost was homogenized with 20 kg of soil and filled into graduated 25 L buckets. The experimental design was completely randomized. The plants were grown for 4 months. The results indicated that all treatments altered the soil fertility positively. There were indications that both filter cake and macadamia husk compost inhibited the absorption of iron (Fe), copper (Cu), and aluminum (Al). Also, zinc (Zn) and phosphorus (P) deficiencies in the initial soil were corrected after the application of the organic wastes. In terms of yield, FC+MHC was better than all other treatments. The outcome of this study will no doubt greatly benefit the resource-poor farmers of Northern KwaZulu-Natal who are involved in the production of orange-fleshed sweet potatoes.

Determining the Stabilised Subfoudation Soil Deformation Modulus According to the Plate Load Tests and Geotechnical Monitoring Data

Introduction. The subsiding soils, which are widely spread in the south of Russia, create a number of problems and hazards due to the high probability of subfoundations subsidence in case of exceeding the values of initial soil moisture and initial pressure for subsidence. This is an important phenomenon to be considered at all life cycle stages of a building or structure, especially at the stage of design, when the scientifically justified design and technological solutions must be developed to ensure the reliable operation of facilities in the complicated engineering and geological conditions being studied hereby. The present article analyses the acting federal and regional regulatory and technical documentation in the field of buildings and structures design on the subsiding soils. Based on the numerical experiment, the incorrectness of the results sometimes received upon following the normative methodology is shown. A new calculating methodology based on determining the stabilised subfoudation soil deformation modulus according to the plate load tests and geotechnical monitoring data is proposed.Materials and Methods. The research comprised:– analysis of the existing approaches and methodologies for the subfoundations and foundations design on the subsiding soils;– numerical experiments, including calculations according to the normative methodology, which implied variation of the original data of both the initial properties of soils and technological parameters of stabilisation, as well as statistical processing of the results;– analysis of the carried out earlier by the authors geotechnical monitoring results of the buildings built on the stabilized soils and experimental study of the deformation properties using a patented device;– determining the main factors having influence on the design solutions for the subfoudation soils and building foundations strengthening under a complicated set of operational loads and establishing a new dependence of the stabilised soil deformation modulus on the initial soil deformation modulus and percentage of soil reinforcement.Research results. It has been established that the existing methodologies for calculating the stabilised subfoudation soils are not enough precise for determining the forecastable subsidence of buildings and structures, and the obtained design values do not always correspond to the factual deformations of subfoundations and foundations. The dependence of the stabilised subfoudation soil deformation modulus on the initial soil deformation modulus and percentage of soil reinforcement with the cement-sand mortar has been traced. A new calculating methodology has been developed based on determining the stabilised subgrade soil deformation modulus according to the data of the plate load tests using a patented device and geotechnical monitoring.Discussion and conclusion. It has been established that the deformation modulus of the soil mass stabilised by the cementation method depends non-linearly on percentage of soil reinforcement with the cement-sand mortar and the initial soil deformation modulus, and this dependence is described by a second-order surface equation of a general form. It is recommended to apply the discovered dependencies for designing the technological parameters of the subsiding soils stabilisation in the Rostov region conditions.

The Microbiomes of Various Types of Abandoned Fallow Soils of South Taiga (Novgorod Region, Russian North-West)

More than 30 years have passed after the collapse of the Soviet Union, and huge areas of soil were left in a fallow state. The study of the microbiological status of fallow soils is an extremely urgent task because fallow soils represent the “hidden” food basket of Eurasia. In this context, we studied the influence of land use type (pasture, vegetable garden, hayfield, or secondary afforestation) on key agrochemical parameters and parameters of soil microbial biodiversity. All anthropogenically transformed soils included in the analysis showed increased humus content and pH shift to a more neutral side compared to the mature soil; the same seemed to be the case for all nutrient elements. It was established that the key factor regulating soil microbiome composition shift was the duration and degree of irreversibility of an agrogenic impact. The key phyla of soil microorganisms were Pseudomonadota, Acidobacteriota, Verrucomicrobiota, Bacteroidota, and Actinobacteriota. The proportion of other phyla was quite variative in soils of different land use. At the same time, all the 30-year-old abandoned soils were more similar to each other than to mature reference soil and 130-year-old soils of monoculture vegetable gardens. Thus, the first factor, regulating soil microbiome composition, is a continuation of soil agrogenic transformation. The second factor is the type of land use if the soil age was equal for fallow territory in the case of one initial podzol soil and one type of landscape. Thus, 30-year-old abandoned soils are intermediate in terms of microbial biodiversity between pristine natural podzols and plaggic podzol. It could be suggested that in the case of secondary involvement of soils in agriculture, the composition of the microbiome may turn to mature soil or to plaggic soil under intensive amelioration.

Impact of straw return combined with different fertilizations on soil organic carbon stock in upland wheat and maize croplands in China: A meta-analysis

Straw return is a vital soil amendment practice in Chinese upland soils, aiming to improve the soil organic carbon (SOC) stock. However, its impact on SOC stock depends on various fertilizer practices, leading to inconclusive results. To address this, we conducted a meta-analysis of 121 peer-reviewed publications to evaluate the effect of straw return combined with different fertilization practices including balanced NPK (BFS), unbalanced NP, NK, PK, or N fertilization (UFS), and no fertilization (NFS) in the wheat-maize cropping system. The results showed that straw return with BFS led to the highest increase in SOC stock (13.3%), followed by UFS (11.4%) and NFS (6.12%), compared to straw removal under the same fertilization conditions. BFS also significantly increased the soil C (15.9%), N (9.62%), and P (6.21%) contents, as well as the C:N (2.48%) and C:P (11.4%) ratios. In contrast, UFS resulted in higher C:N ratios (6.47%) and soil acidification, affecting the SOC stock during straw return. A structural equation model revealed that the presence of BFS positively influenced the association between SOC stock and soil stoichiometry (P ​< ​0.05) compared to UFS, which was influenced by climate and initial soil properties. Additionally, the impact of BFS on SOC stock was more significant in the double cropping system (14.5%) than in the single wheat (8.32%) and single maize (10.8%) cropping systems. A lower initial SOC (<6 ​g ​kg−1) also showed a greater response to BFS compared to a higher initial SOC (>12 ​g ​kg−1). Based on C sequestration efficiency, implementing straw return with BFS could lead to a higher rate of increase in SOC sequestration.

Transferred communities of arbuscular mycorrhizal fungal persist in novel climates and soils

Symbiotic mycorrhizal fungi strongly influence plant establishment and growth particularly in harsh environments, whereby sympatric, presumably co-adapted symbionts are considered particularly beneficial. However, the response of transferred sympatric mycorrhizal fungal communities to new environments remains largely ignored. We therefore studied the relative importance of initial inoculum, soil and climatic conditions on the composition, diversity and root colonization ability of arbuscular mycorrhizal fungal (AMF) communities. To do so, we analyzed the AMF communities in an extensive experiment with two ecotypes of Bouteloua gracilis planted in their sites of origin and in four new sites differing in climate and soil properties.After three seasons of growth, the sympatric AMF communities were little changed by the new abiotic conditions. The composition of the AMF communities in plant roots was most strongly determined by the initial inoculum, while the contribution of divergent soil and climatic conditions was an order of magnitude smaller. The levels of root colonization by AMF, in contrast, were significantly influenced by climatic and soil conditions and did not differ among communities of different origins. Their pattern indicates that mycorrhiza formation is facilitated in the plant's sympatric soil and climatic conditions, but also that transferred AMF communities adjust mycorrhiza formation to new abiotic conditions.

Phytoremediation of Lead, Arsenic and Chromium Polluted Soil Using Opuntia spp. (Dilang-Baka)

Phytoremediation capabilities of Opuntia spp. were tested on heavy metal polluted soil collected in a metallurgical factory in Carmona Cavite. Initial soil testing shows traces of Arsenic: 8.48 mg/Kg, Chromium: 116 mg/Kg, and Lead: 79 mg/Kg. pH and moisture are neutral and dry. Opuntia was compared to A. vera, within two months. Final results show both can decrease concentrations of Arsenic and Lead but Chromium from Opuntia have increased concentration might be due to the reduction of Cr(VI) to Cr(III).

A sensorless, Big Data based approach for phenology and meteorological drought forecasting in vineyards

A web-based app was developed and tested to provide predictions of phenological stages of budburst, flowering and veraison, as well as warnings for meteorological drought. Such predictions are especially urgent under a climate change scenario where earlier phenology and water scarcity are increasingly frequent. By utilizing a calibration data set provided by 25 vineyards observed in the Emilia Romagna Region for two years (2021–2022), the above stages were predicted as per the binary event classification paradigm and selection of the best fitting algorithm based on the comparison between several metrics. The seasonal vineyard water balance was calculated by subtracting daily bare or grassed soil evapotranspiration (ETs) and canopy transpiration (Tc) from the initial water soil reservoir. The daily canopy water use was estimated through a multiple, non-linear (quadratic) regression model employing three independent variables defined as total direct light, vapor pressure deficit and total canopy light interception, whereas ETS was entered as direct readings taken with a closed-type chamber system. Regardless of the phenological stage, the eXtreme Gradient Boosting (XGBoost) model minimized the prediction error, which was determined as the root mean square error (RMSE) and found to be 5.6, 2.3 and 8.3 days for budburst, flowering and veraison, respectively. The accuracy of the drought warnings, which were categorized as mild (yellow code) or severe (red code), was assessed by comparing them to in situ readings of leaf gas exchange and water status, which were found to be correct in 9 out of a total of 14 case studies. Regardless of the geolocation of a vineyard and starting from basic in situ or online weather data and elementary vineyard and soil characteristics, the tool can provide phenology forecasts and early warnings of meteorological drought with no need for fixed, bulky and expensive sensors to measure soil or plant water status.

Is green manure a viable substitute for inorganic fertilizer to improve grain yields and advance carbon neutrality in paddy agriculture?

Green manure is a widely applied to increase grain yield, while it also attributes to greenhouse gas (GHG) emissions in agriculture ecosystems. Combining green manure with inorganic fertilizer inputs is a common practice that can influence soil GHG emissions and grain yield, however, its impacts on grain yield and global warming potential (GWP) under different initial soil conditions before rotating experiments and agronomic management in paddy fields remain unclear. We synthesized 508 data pairs to evaluate the responses of CO2 emissions, CH4 emissions, N2O emissions, and grain yield to combined inputs of green manure plus inorganic fertilizer compared with only inorganic fertilizer application. Our findings indicate that both inorganic fertilizer plus extra green manure (GM-E) and green manure substitutes for inorganic fertilizer (GM-S) could increase CO2 emissions (22.5 %−76.8 %), CH4 emissions (100 %−103 %), N2O emissions (29.8 %−50.9 %), and yield (2.21 %−19.6 %). Except for GM-E, which showed a non-significant increase in grain yield. The initial soil properties before rotating experiments, the types and timing of green manure application were key drivers of GHG emissions and yield, and extra green manure applied in areas with low initial soil pH and high C:N can increase GWP and yield. Overall, the mixed green manure application had greater impact than leguminous or non-leguminous green manure applied alone. The responses of GHG emissions and yield to GM-S were modulated by mean annual precipitation and initial soil properties before rotating experiments, and green manure substitutes for inorganic fertilizer in areas with high initial soil pH and low C:N can increase GWP and yield. Meanwhile, excessive precipitation caused a reduction in yield and a significant increase in GWP intensity. Our results showed that extra green manure applications of less than 68.1 kg N ha−1 would not significantly increase GWP. Therefore, an effective green manure strategy can achieve a win-win situation for the dual challenge of agricultural production and climate change mitigation.

Construction of Temporary Landfill Shield by Utilizing MICP Stabilized Water Treatment Plant Sludge Waste

The addition of Bacillus Subtilis bacteria to the mud soil at IPAM (Integrated Wastewater Treatment Plant) Perumda Tirta Manuntung Km.8 in Balikpapan City aimed to enhance its suitability as a temporary cover layer in places like landfills. Initial mud testing revealed key characteristics: Chemical Characteristics: The mud's specific chemical composition was identified, providing a foundation for a deeper understanding of its properties. Physical Characteristics: The mud falls into the fine-grained soil category, with 63% of particles passing through a No. 200 sieve. Moisture content is high at 42.54%, primarily composed of silt (39.8%) and clay (25%). Mechanical Characteristics: Standard proctor tests yielded a maximum dry unit weight of 1.099 gr/cc and an optimum water content of 33.65%. Initial soil permeability met temporary landfill cover criteria, with a permeability value of 5.04×10-4 cm/s. Further research demonstrated that by introducing Bacillus Subtilis bacteria at varying concentrations and incubation periods, mud permeability could be altered. The highest permeability, 4.27×10-4 cm/s, was achieved with an 8% bacteria concentration and a 7-day incubation period, while the lowest permeability, 1.19×10-5 cm/s, resulted from an 8% bacteria concentration and a 28-day incubation period. These findings suggest that Bacillus Subtilis addition can modify mud permeability, making it more suitable as a temporary landfill cover. This presents a potential solution for more effective IPAM management.

A Novel Analytical Solution for Ponded Infiltration With Consideration of a Developing Saturated Zone

AbstractPonding at the soil surface exerts profound impacts on infiltration. However, the effects of ponding depth on infiltration, especially the development of a saturated zone below the soil surface, have yet to be considered in present infiltration models. A new general Green‐Ampt model solution (GAMS) was derived for a one‐dimensional vertical infiltration problem under a uniform initial moisture distribution with ponding on its surface. An expression was included in the new solution for simulating the saturated layer developed below the soil surface as long as the pressure head at the surface is sufficiently high to saturate the soil. The GAMS simulates the infiltration processes closer to the numerical solution by HYDRUS‐1D than the traditional and the recently improved Green‐Ampt model. Moreover, an inversion method to improve the estimates of soil hydraulic parameters from one‐dimensional vertical infiltration experiments that is based on the GAMS was suggested. The effect of ponding depth (hp), initial soil moisture content, soil texture, and hydraulic soil properties (saturated hydraulic conductivity Ks, water‐entry suction hd and shape coefficient n of soil water retention curve) in the saturated zone was also evaluated. The results indicate that the saturated zone length increased at a comparable rate with the unsaturated wetted zone length during infiltration. Generally, a larger saturated zone was found for soils with higher initial soil moisture contents, coarser texture, higher Ks values, greater n, and lower −hd. Our findings reveal that including the saturated zone in the infiltration model yields a better estimate of the soil hydraulic parameters. The proposed GAMS model can improve irrigation design and rainfall‐runoff simulations.

Effect of Liquid Biofertilizers on Productivity, Quality and Soil Biota of Fodder Sorghum

The field experiment was conducted during Rabi season of 2022 on sandy clay loam soils at wetland farm of the S.V. Agricultural College, Tirupati, Andhra Pradesh, India, to study the effect of liquid biofertilizers on productivity, quality, and soil biota of fodder sorghum. The treatments were allocated in randomized block design and replicated thrice. The soil was neutral in reaction (6.9 pH), low in available nitrogen (115 kg ha-1), medium in available phosphorus (29 kg ha-1) and low in available potassium (156 kg ha-1) status. The initial soil contains bacteria (13.08 X 107 CFU g-1 soil), fungi (4.04 X 104 CFU g-1 soil) and actinomycetes (1.54 X 103 CFU g-1 soil). The results revealed that the maximum green (32.1 t ha-1) and dry (13.0 t ha-1) fodder yield as well as crude protein (7.3%) were obtained with the application of 75% RDF + Azospirillum + PSB + KSB (Both seed &amp; soil application). Furthermore, this treatment produced a significantly higher soil bacterial (23.2 X 107 CFU g-1 soil), fungal (13.7 X 104 CFU g-1 soil) and actinomycetes (10.3 X 103 CFU g-1 soil) population at harvest.

Impact of Spectral Resolution and Signal-to-Noise Ratio in Vis–NIR Spectrometry on Soil Organic Matter Estimation

Recently, considerable efforts have been devoted to the estimation of soil properties using optical payloads mounted on drones or satellites. Nevertheless, many studies focus on diverse pretreatments and modeling techniques, while there continues to be a conspicuous absence of research examining the impact of parameters related to optical remote sensing payloads on predictive performance. The main aim of this study is to evaluate how the spectral resolution and signal-to-noise ratio (SNR) of spectrometers affect the precision of predictions for soil organic matter (SOM) content. For this purpose, the initial soil spectral library was partitioned into to two simulated soil spectral libraries, each of which were individually adjusted with respect to the spectral resolutions and SNR levels. To verify the consistency and generality of our results, we employed four multiple regression models to develop multivariate calibration models. Subsequently, in order to determine the minimum spectral resolution and SNR level without significantly affecting the prediction accuracy, we conducted ANOVA tests on the RMSE and R2 obtained from the independent validation dataset. Our results revealed that (i) the factors significantly affecting SOM prediction performance, in descending order of magnitude, were the SNR levels &gt; spectral resolutions &gt; estimation models, (ii) no substantial difference existed in predictive performance when the spectral resolution fell within 100 nm, and (iii) when the SNR levels exceeded 15%, altering them did not notably affect the SOM predictive performance. This study is expected to provide valuable insights for the design of future optical remote sensing payloads aimed at monitoring large-scale SOM dynamics.

Estimation of Sensor-based site specific variable rate fertilizer application for maize (Zea mays L.) crop

Optical spectrometry sensors in crops offer a remarkable technological breakthrough in the field of variable-rate nitrogen fertilization. A field study was conducted during rainy (kharif) season of 2021 at the research farm of the Agricultural Engineering College and Research Institute Tamil Nadu Agricultural University Coimbatore to estimate maize crop nitrogen (N), Normalized Difference Vegetation Index (NDVI) value and chlorophyll content in hybrid maize COH (M) 8. Fertilizers were administered to the plots following the recommendations (250:75:75 kg NPK ha-1) given under Soil Test Crop Response, with a goal yield of 9t ha-1 predicted based on the initial soil available N, P, and K values. The experimental findings revealed a significant impact of nitrogen rate (P&lt;0.001) on the percentage of nitrogen content in the leaves (% N leaf content). Additionally, there was a decrease in maize leaf chlorophyll content index over time, with ranges of 32.96 to 50.57, 28.78 to 41.78, 24.81 to 35.86, 22.12 to 28.54, and 14.34 to 20.56. On the contrary, the NDVI experienced an increase throughout the season, with ranges of 0.32 to 0.49, 0.30 to 0.55, 0.28 to 0.66, 0.46 to 0.88, and 0.56 to 0.84. The study will help foster sustainability within modern intensive farming practices by emphasizing the importance of reducing environmental pollution caused by applying Sensor-based site-specific nitrogen fertilizer for maize crop.

Variation in sprinkler irrigation droplet impact angle on the physical crusting properties of soils

The angle at which a droplet impacts determines its shearing and compaction effects on soil, which in turn affects the formation and properties of the physical soil crust. To investigate the effect of the droplet impact angle on soil physical crusting, this study considered droplet quantity, quality, and velocity and proposes an energy-weighted method for calculation of the equivalent droplet impact angle. Droplet information was acquired using a spraying platform with a controllable droplet impact angle and two-dimensional video disdrometer (2DVD). Six groups (38.10°, 49.43°, 58.77°, 68.88°, 76.81° and 84.10°) of droplet impact angles were established to obtain the parameters of the soil physical crust characteristics at different droplet impact angles by indoor soil tank tests. The results show that: 1) the stable values of crack length density (CLD), crust thickness (Ct), soil bulk density (BD), cohesion force (Cf), and internal friction angle (IfA) are strongly positively correlated with droplet impact angle; 2) the stable value of the crack area ratio (CAR) is strongly negatively correlated with the droplet impact angle, with maximum and minimum values of 6.94% and 5.57%, respectively; 3) the content of macro aggregates (MAA) tends to increase and then decrease with the increase in droplet impact angle, and the content of MAA has a maximum value of 50.2% at the impact angle of 68.88°. The content of micro aggregates (MIA) tends to decrease and then increase with the increase in the drop impact angle, with a minimum value of MIA of 20.4% at the impact angle of 58.77°; 4) the maximum soil bulk density of 1.99 g·cm−3 at an impact angle of 84.10° is significantly greater than the initial soil bulk density (1.35 g·cm−3); 5) the energy-weighted equivalent droplet impact angle takes into account the effects of both large and small droplets and characterises the overall impact angle of the sprayed droplet from an energy perspective. The results of this study provide new ideas for determining suitable sprinkler irrigation parameters to reduce soil erosion and promote the sustainable development of irrigated agriculture.

Experimental Investigation on the Post-liquefaction Behavior of Sands in Simple Shear Conditions

Abstract Experimental evidence shows that earthquake induced liquefaction can occur more than once in sandy soils. Moreover, despite an increase in soil density caused by the dissipation of the excess pore pressure induced by earthquakes, the liquefaction resistance of soils that have experienced liquefaction may be lower than that of virgin soils. This paper offers insight into this topic starting from the analysis of the undrained monotonic behavior of post-liquefied sands by means of tests performed with a simple shear cell equipped with flexible boundaries, which maintains a constant diameter to guarantee the “K0-condition.” The control system of cyclic, reconsolidation, and monotonic phases is described in detail. The experimental results show that neither the relative density, effective confining stress, cyclic stress ratio, nor the direction of shear strain play important roles in the monotonic behavior of post-liquefied soils. Moreover, the comparison between the monotonic response of virgin and post-liquefied soils (prepared by moist tamping technique) shows that it is not affected by the stress–strain history experienced by soils. It can be explained through a microstructural interpretation. According to which, the initial soil fabric generated with the moist tamping method and that formed during liquefaction remain almost unchanged because of the rotation of principal stress directions occurring during simple shear tests. A further confirmation is given by the results of tests performed on specimens prepared by air pluviation method.

Effects of Water Control and Nitrogen Addition on Functional Traits and Rhizosphere Microbial Community Diversity of Haloxylon ammodendron Seedlings

Water and nitrogen sources have always been the primary limiting factors for vegetation growth in arid and semi-arid regions and play an important role in the physiological ecology of vegetation. In this work, we studied the effects of water deficit and nitrogen addition on the physiological traits and rhizosphere bacterial microbial community of Haloxylon ammodendron seedlings in sterilized and non-sterilized soil habitats. A pot experiment was conducted to control the water and nitrogen sources of H. ammodendron seedlings. The water deficit treatment was divided into two groups based on gradient: a normal water group (CK, 70% field water holding capacity) and water deficit group (D, 30% field water holding capacity). The nitrogen addition treatment was divided into a no addition group (CK, 2.8 mg·kg−1) and addition group (N, 22.4 mg·kg−1). At the end of the growing season, the biochemical indexes of H. ammodendron seedlings were measured, and the rhizosphere soil was subjected to 16S rDNA-high-throughput sequencing to determine the rhizosphere bacterial community composition of H. ammodendron seedlings under different treatments. The results showed that the root-to-crown ratio of H. ammodendron seedlings increased significantly (p &lt; 0.05) under the water deficit treatment compared to the control and nitrogen addition treatments, indicating that H. ammodendron seedlings preferred to allocate biological carbon to the lower part of the ground. In contrast, plant height and root length were significantly lower (p &lt; 0.05) under water deficit treatment compared to the control, and no significant change was observed under water deficit and nitrogen addition compared to the control, indicating that water deficit inhibited the growth of H. ammodendron seedlings and nitrogen addition mitigated the effect of water deficit on the growth of H. ammodendron seedlings. Under sterilized soil conditions, both water deficit and nitrogen addition significantly increased the abundance and diversity of bacterial communities in H. ammodendron seedlings (p &lt; 0.05). Conversely, under non-sterilized conditions, both inhibited the diversity of microbial bacterial communities, and the microbial characteristic species under different controls were different. Therefore, in the short-term experiment, H. ammodendron seedlings were affected by water deficit and allocated greater quantities of biomass to the underground part, especially in the non-sterile microbial environment; different initial soil conditions resulted in divergent responses of rhizosphere bacterial communities to water deficit and nitrogen addition. Under different initial soil conditions, the same water deficit and nitrogen addition treatment will lead to the development of distinct differences in rhizosphere bacterial community composition.