Soil Physical Conditions Research Articles

Prediction of soil solution concentrations and leaching losses of cadmium in agricultural soils.

Cadmium (Cd) leaching is often estimated in Cd balance models using the product of drainage water (precipitation excess) and soil solution Cd concentration. However, Cd concentrations are seldom available but rather predicted using empirical models. Despite the availability of empirical models that estimate soil solution Cd concentrations, they have limitations for use in New Zealand where total Cd in agricultural soils is low and organic matter (OM) high. This study derived a Freundlich-type model from desorption data and a soil-liquid partitioning coefficient (KD ) model based on sorption data to predict soil solution Cd concentrations from commonly measured soil parameters that could be used to calculate Cd leaching fluxes. Independent soil solution Cd concentrations and Cd fluxes measured in drainage water from field trials were used to validate the predictive capacity of the models. It was found that soil pH and OM content were the most important factors controlling soil solution Cd, along with total Cd. Both models explained 83% of the variation in measured soil solution Cd concentrations in an independent dataset. Comparisons between Cd fluxes predicted using the Freundlich-type model and measured fluxes were within 25% of each other at 6 of 19 field sites studied. However, physical and chemical nonequilibrium conditions in soils and uncertainty in measured values likely contributed to differences between predicted and measured Cd fluxes at other sites. To unravel the impact of nonequilibrium and soil physical conditions on Cd concentrations in drainage water, more data are required on Cd concentrations collected under field conditions. This will allow better validation of the approach used in Cd balance models to calculate Cd leaching from soils.

Phosphorus and Potassium in Aggregates of Degraded Soils: Changes Caused by Biochar Application

AbstractThe low capacity of degraded soils to provide phosphorus (P) and potassium (K) to plants makes cultivation unviable in these areas. Biochar can increase nutrients availability and improve the physical conditions of soil to maintain their availability over time, including within soil macroaggregates, where P and K are less susceptible to losses. The aim of this study is to understand, how biochar application can change P and K availability in aggregates of degraded soils. The experiment is carried out under controlled conditions following the factorial scheme 2 × 3 × 5 × 2 + 4, corresponding to two classes of soil, three biochars produced from different raw materials (including stems of elephant grass, EGB, and two types of agricultural wastes: eucalypt stalks, ESB, and sugarcane bagasse, SBB), five rates of biochar, two times and four control treatments. At the end of each time, soil aggregates are divided into two classes by size (macroaggregates and microaggregates) and then P and K availability are measured. The results show that biochar can be a powerful tool to increase P and K availability in soil aggregates. EGB is the most efficient biochar to increase P and K availability, followed by SBB and ESB biochars.

Effects of soil compaction on grain yield of wheat depend on weather conditions

The use of heavy farm machinery has resulted in widespread soil compaction in many regions of the world. Compacted soil limits the access of crops to soil water and nutrients and is expected to reduce crop productivity, but the influence of weather conditions on the interactions between compacted soil and crop productivity is unclear. Furthermore, early vigor has been regarded as a promising trait for improving the yield of crops grown under edaphic stress such as soil compaction. We aimed to assess the combined effects of soil compaction and contrasting weather conditions on growth and grain yield of spring wheat, and to evaluate the association between early vigor and grain yield under temporal variations of the soil physical conditions. Nine spring wheat genotypes were grown on compacted and non-compacted soils during two cropping seasons with contrasting weather conditions in Central Sweden. Compared to the non-compacted treatment, soil compaction increased the relative growth rate of shoot biomass from sowing to stem elongation, and from stem elongation to flowering in the drier year (2018), but decreased the same traits in the wetter year (2019). The contrasting effects of soil compaction on shoot growth in the two years could be explained by soil moisture and penetration resistance associated with the interactive effects of soil compaction and weather condition. Higher early vigor, here indicated by higher relative growth rate from sowing to stem elongation, was associated with reduced grain yield under the progressively drying and hardening soil conditions during the entire cropping season of both years. We conclude that the interactive effects of soil physical and weather conditions need to be considered when evaluating the impact of soil compaction on crop growth and productivity. The potential of early vigor to increase grain yield is strongly influenced by the temporal dynamics of soil physical conditions.

The possibility of reclamation criteria success in Indonesia: soil condition, vegetation structure and species composition

There are two regulations for mine reclamation success in the forestry area in Indonesia, namely Minister of Forestry Regulation No. P.60/Menhut-II/2009 and Minister of Energy and Mineral Resources Decree No. 1827.K/30/MEM/2018. Both regulations rule vegetation and soil success. This study aims to analyse criteria parameters from both regulations in the mine reclamation and compare them to the surrounding secondary natural forest (SNF). This study was conducted in 6 six types of mine reclamation stand structures: 1, 4, 6, 9, 11-year-old plantation and SNF using 1 hectare of the circular plot each (total 6 ha). Soil samples were collected from 40 cm depth to analyse physical, biological and chemical conditions. Mine reclamation areas had almost similar physical, biological and chemical soil conditions with SNF. Nevertheless, due to the potential acid-forming (PAF) material from overburden, the 1-year-old plantation had pH = 3.23-3.27. The highest diversity index and the number of species and families in all reclamation areas were H’ = 1.82 (11-year-old); 14 species (9-year-old); and 11 families (9-year-old), comparing with SNF were H’ = 3.48; 67 species, and 31 families. Conversely, vegetation structure parameters in mine reclamation areas were higher than SNF (diameter at height breast (DBH; 1.3 m) = 28.42 cm; tree density = 469/ha; basal area = 35.04 m2/ha; and total height = 16.85 m). Compared to the SNF, vegetation structure and soil conditions are mostly possible for mine reclamation success. Still, species composition needs to be considered further as a standard interval to meet the criteria.

Global meta-analysis suggests that no-tillage favourably changes soil structure and porosity

Role of soil to meet global food security, sustainable intensification and food nutritional quality has got renewed attention with a larger focus on soil physical condition. No-tillage (NT) practice can essentially contribute to develop a sustainable, low carbon and resource efficient agriculture, and encourage the use of crop residues for added soil benefits. Soil aggregation and pore size distribution, two most important soil physical factors controlling the mass and energy transport processes within the soil and between soil and environment, were evaluated under the NT through a global meta-analysis of 5065 pairs of data points from 419 peer-reviewed studies. Compared to conventional tillage (CT), NT increased mean weight diameter of aggregates, water stable aggregates, and macroaggregates by averages (0–30 cm) of 25, 10 and 22%, respectively, although predominantly in 0–10 and/or 10–20 cm layers, with an accompanying reduction in microaggregates. A small but significant 3% decrease in total porosity, a large reduction (20–32%) in macroporosity and a moderate increase (4–7%) in microporosity were realized under NT up to 20 cm soil depth. Bulk density remained stable, although a very large decrease (70% change over CT) in saturated hydraulic conductivity was recorded in 10–20 and >30 cm soil layers. Years of adoption of NT had an additive effect on mean weight diameter and macroaggregates, and the total and macroporosity. Increase in latitudes favoured soil aggregation and micropore volume under NT, while clay content was unfavourable to macro- and water stable aggregate contents. Improvement in structure and water retention properties relate to long-term sustainable development of soils by following no-till practice, which has far-reaching implications beyond the boundaries of agronomy.

Short‐term effects of alternative cultivation practices on putting green infiltration rates

AbstractCore aerification iscommonly used to manage organic matter and improve soil physical conditions of putting greens. Most methods of core aerification are labor intensive and temporarily reduce the playability of greens. Less invasive cultivation techniques are available, but their specific effects on playability and drainage properties of greens are often less understood. The objective of this study was to assess the short‐term effects of air‐injection cultivation (AIC), sand‐injection cultivation (SIC), and hollow‐tine cultivation (HTC) on playability characteristics and soil physical properties of putting greens. A field study was conducted at the Oklahoma State University Turfgrass Research Center in Stillwater, OK, on a creeping bentgrass (Agrostis stolonifera L. ‘Penncross’) green from September 2017 to September 2019. Cultivation type and timing of application were arranged in a split‐plot design with four replications. Cultivation type was defined as either AIC, SIC, or HTC, and each was applied in spring, summer, and fall. Compared with the control, HTC reduced surface firmness by 5% at 28 d after cultivation event (DACE), increased infiltration by 87% at 28 DACE, reduced ball roll distance by 6% up to 14 DACE, and reduced normalized difference vegetation index (NDVI) by 10% up to 14 DACE. Neither AIC nor SIC had a detectable effect on measured variables. Results suggest a single application of AIC or SIC has minimal short‐term effects on soil physical properties or surface playability of putting greens.

Characterization of soil moisture dynamics in Colombian agricultural areas

Seasonal dynamics in edaphic humidity are influenced by different environmental factors, such as topography, physical and chemical soil conditions, type of vegetation cover and climatic classification. Data from 105 agrometeorological stations in the IDEAM network, distributed throughout Colombia, with records from January, 2001 to April, 2020, were studied. A non-parametric Spearman rank correlation test was used to evaluate the relationship between soil moisture and atmospheric variables. Simultaneously, the behaviors of seasonal dynamics were analyzed, along with their interaction with atmospheric, physical soil and vegetation cover variables. The results showed that soil moisture is more significantly influenced by frequency than by intensity of precipitation; this variable had a seasonal behavior, similar to that of precipitation. The physical variable texture was closely related to the behavior of the soil surface moisture (<10 cm deep). In addition, there was evidence of a surface moisture response to the physical conditions of the soil, topography and availability of plant cover. As the soil depth increased, the soil moisture had less variation because the influence of the atmospheric conditions was greater on the surface and persisted longer over time.

Parametric and Non-Parametric Suitability Evaluations of Rice Soils of Asu River Group Parent Materials in Ohaozara, Nigeria

The study was carried out in Ohaozara Southern Ebonyi State in Southeastern Nigeria. Study area was identified in a rice soil of about 120 hectares used for FGN/IFAD Value Chain Development program (VCDP). Three profile pits were dug on a transect line of about 100 – 200m apart for suitability evaluation study. The aim of the study was to use parametric and non – parametric suitability evaluation to study the rice soils under Asu River Group parent material. Parametric method is where each limiting characteristic was rated using information provided on factor ratings of land use requirements for wetland ricetable. In Nonparametric method, pedons were placed in suitability classes by matching their land characteristics with the agronomic requirements of rice. The index of productivity (IP) (actual and potential) was calculated using the equation: IP= A x √(B/100 x C/100 x D/100xE/100). Suitability evaluation results show that climate, soil physical conditions and wetness were optimum S1(95%) and moderately suitable S2(85%) while,fertility and toxicity parameters made the soil marginally suitable S3(60%). Parametric and non – parametric suitability evaluation revealed that the soils were mostly marginally suitable both potentially and currently. Major limitations of the investigated soils bother on fertility and Al toxicity.

English

Tillage is the physical manipulation of soil to improve physical soil conditions. In Pakistan, various tillage technologies such as primary and secondary tillage affect plant growth, incorporate organic matter residues into the soil, eradicate weeds, and prepare the bed for seed germination preventing soil erosion and preparing the ground for irrigation. Furthermore, tillage practices change soil water holding capacity, temperature, aeration, and the mixing of crop residues within the soil matrix. Today's real agricultural problems are resource depletion with declining production, decreased human resources, and rising prices and societal shifts due to different anthropogenic activities (tillage). These changes in the physical environment and the food supply of the organisms affect different groups of organisms in different ways. In addition, they are also affecting the environment health. Therefore, its management, including conservation tillage and other includes cover crop, organic residues, and direct sowing of rice seedling is necessary to mitigate the problems. The present review discusses the tillage systems effects on soil, plants, environment and their possible solutions.

Effect of Liquid Organic Fertilizers and Soil Moisture Status on Some Biological and Physical Properties of Soil

<p>This study was conducted to evaluate the effects of liquid organic fertilizers (LOFs) and soil moisture status on some biological and physical properties of postharvest soil of maize cultivation. For this purpose, a factorial greenhouse experiment was performed based on the completely randomized design with three replications. Treatments consisted of five levels of LOFs (control, vermicompost tea, vermiwash, plant growth-promoting rhizobacteria [PGPR] enriched vermicompost tea and PGPR enriched vermiwash) and three levels of soil moisture status (field capacity [FC], 0.8 FC and 0.6 FC). The results showed LOFs caused an increase of soil biological properties (soil microbial respiration, soil microbial biomass, dehydrogenase activity and the number of aerobic heterotrophic bacteria) and the improvement of soil physical condition. LOFs increased aggregate stability, hydrophobicity and total porosity, while decreased bulk density and soil penetration resistance. Increasing water stress levels reduced soil biological activity and made soil physical properties more unfavorable. In general, LOFs improved soil conditions by enhancing soil physical and biological properties and decreased the negative effects of water stress. In addition, results showed that LOFs enriched with PGPR could be more effective than non-enriched ones.</p>

Corn seedling root growth response to soil physical quality

AbstractPlant available water content or matric potential, particle size (texture), aeration, and penetration resistance are soil physical properties that influence soil structure, bulk density, aggregation, and several metabolic plant processes. Collectively they influence productivity and sustainability of agricultural practices, primarily through their impact on root development and growth. To simplify use of these parameters for assessing soil physical condition, the least limiting water range (LLWR) was developed as an integrated, comprehensive soil physical quality indicator. Our objective was to use the LLWR to evaluate corn (Zea mays L.) seedling root growth in soils with clay, sandy clay loam, or sand texture. Overall, root growth was affected by soil water content, aeration, and penetration resistance. Upper and lower LLWR boundaries were defined by a minimum air‐filled porosity and maximum soil penetration resistance for water contents between field capacity and permanent wilting point. Herein, the LLWR was calculated using a range of minimum air‐filled porosity (0.117–0.146 m3 m−3), field capacity (–2.2 to –5.3 kPa), and permanent wilting point or matric potential values (–461 to –6,516 kPa), and a restrictive penetration resistance value of 1.6 MPa as boundaries. The LLWR was sensitive to soil texture, decreasing from fine to coarse soils. The highest and lowest relative root growth measurements fell inside and outside the LLWR boundaries, proving that this index can successfully predict the optimum soil physical conditions for seedlings root growth and can therefore be used as a sensitive soil physical quality.

Is cassava yield affected by inverting tillage, chiseling or additional compaction of no-till sandy-loam soil?

Defining a suitable soil tillage option that provides adequate soil physical conditions for optimum cassava (Manihot esculenta Crantz) productivity has not been adequately researched in southern Brazil. This study aimed to evaluate, in an Argissolo Vermelho-Amarelo Distrófico (Acrisol or Hapludalf), three tillage methods – conventional (inverting) tillage, chiseling, and long-term no-tillage (without and with, additional soil compaction), as affecting soil hydro-physical properties and cassava yield, in southern Brazil. Undisturbed and disturbed soil samples were collected from row and interrow [...]

Estimate of Available Soil Water and The Physical Condition of Soil for Different Use Soils

Three sites of different soils have been identified. The soil of the first site is planted with a field crop (wheat plant), the soil of the second site planted with a horticultural crop (Loquat plant) and the soil of the third site (uncultivated) in Dhuluiya district of Salah al-Din Governorate. Many laboratory tests were conducted, represented by measuring : Moisture tensile, bulk density, texture, total porosity, gravimetric and volumetric humidity, electrical conductivity EC, degree of soil interaction PH, organic matter OM, estimation of bicarbonate and carbonate and after obtaining the data were treated with several mathematical programs: RETC, SAWcal in order to find several indications Physics such as PAW100, PAW330, and soil physical quality index (S), and the following results were obtained: The decrease in the bulk density values of the soil of the third site (not cultivated), as it reached 1.43, 1.29 and 1.23 g / cm3 compared to the soil of the first site (wheat) 1.55, 1.58 and 1.61 g / cm 3 and the soil of the second site (Loquat), which reached 1.6 And 1.6 and 1.6 g / cm3 due to the high clay content in the third site, which leads to a decrease in bulk density. The water holding capacity of soil, represented by the values of ready soil water at 1 bar and 0.3 bar, was higher in the soil of the third site compared to the first and second sites, due to the high values of water conductivity in the soil of the first site. The high values of the water conductivity in the soil of the third site (not cultivated), as it reached 0.015037, 0.015872 and 0.021653 cm / min compared to the soil of the first site (wheat), as it reached 0.008577, 0.007209 and 0.004241 cm / min, and the soil of the second site (Loquat) It was 0.003955, 0.00507, and 0.006741 cm / min. The physical quality of the soil obtained through the previous indicators showing that the soil of the first site (wheat) possesses a (good) physical quality, then the soil of the second site (Loquat) possesses a (good) physical quality as well while the soil of the third site (not cultivated) possesses (very good) physical quality

Reversible and irreversible root phenotypic plasticity under fluctuating soil physical conditions

Roots grow in a highly heterogeneous physical environment due to the spatial complexity of soil structure. Thereby, the root growth zone repeatedly experiences soil physical stress such as hypoxia or increased penetration resistance. To mimic the highly variable physical environment surrounding the root growth zone, we subjected pea and wheat seedlings to periodic soil physical stress. One day of soil hypoxia or increased penetration resistance reduced root elongation rate of both species by at least 20 %. Upon stress release, root elongation rate of pea could recover within one day, while no such recovery occurred in wheat. Similarly, the diameter of the root elongation zone in pea increased by 15 % and 20 % due to hypoxia and increased penetration resistance, respectively, but decreased again once the stresses were released. In contrast, the diameter of the elongation zone of wheat roots started to decrease with the onset of soil physical stress and this trend continued upon stress release. Hence, root responses to short-term soil physical stress were reversible in pea and irreversible in wheat, indicating reversible and irreversible root phenotypic plasticity, respectively. This suggests that strategies to cope with periodic soil physical stress may vary among species. The differentiation between reversible and irreversible phenotypic plasticity is crucial to advance our understanding on soil exploration, resource acquisition, whole plant growth, and ultimately crop yield formation on structured soil.

The impact of cattle grazing and treading on soil properties and the transport of phosphorus, sediment and E. coli in surface runoff from grazed pasture

ABSTRACT Contaminant loss from grazed pasture can negatively affect freshwater quality. There is, however, little data on the impact of different levels of grazing/treading on contaminant loss measured under field conditions. This study quantified phosphorus (P), sediment and Escherichia coli (E. coli) loss in surface runoff from plots grazed by cattle for 0, 16 or 28 h to create different pasture/treading damage. Results showed an increase in grazing/treading duration decreased soil macroporosity (30%) and saturated hydraulic conductivity (96%), and increased surface roughness (71%) and depression water storage capacity (388%). These changes in soil physical condition contributed to greater volumes of surface runoff in the 16 h (31%) and 28 h (55%) treatments. Contaminant concentrations and loads in runoff also tended to increase with grazing/treading, although the increases were not statistically significant. An exception was total P (TP) which increased from 0.323 to 1.222 kg ha−1, principally due to increased dissolved P, probably released from plants due to grazing and from the deposition of dung. Management of animals to minimise the number, duration and frequency of grazing wet soils that are vulnerable to physical damage are likely key factors to reducing TP, and probably SS and E. coli transport in surface runoff.

WITHDRAWN: Counterions, smectite, and palygorskite increase microstructural stability of saline-sodic soils

Abstract Saline-sodic soils are susceptible to wind and water erosion when the dispersive effect of sodium overcomes inter-particle bonds. Rheological parameters of viscoelasticity can help to quantify inter-particle attractive forces and account for the effect of salinity in these soils. The main objective of the present study was to investigate the viscoelasticity behavior of saline-sodic soils of the Sirjan playa in south-central Iran. Three representative pedons were excavated and described by horizon. Soil physicochemical properties and rheological properties were determined, namely the micromechanical parameters flow point (γf), loss factor tan δ, and integral z, with samples analyzed at three matric potentials (0, −6, and −15 kPa). Results showed that soil microstructural stiffness was mainly influenced by soil texture, clay minerals, gypsum, calcium carbonate equivalent (CCE), and matric potential. The dispersive effect of sodium, as indicated by low integral z and γf values, decreased with increasing gypsum content in − 6 and − 15 kPa matric potentials (0.6 0.8). However, greater microstructural stability (i.e., higher integral z and γf) was observed for fine-textured soils with relatively high amounts of smectite and palygorskite and low pH. Furthermore, integral z and γf increased with lower matric potentials due to the stabilizing effect of menisci forces. Therefore, the viscoelastic behavior of the saline-sodic soils was negatively associated with water content and high sodium concentration, while the presence of smectite, palygorskite, gypsum, and CCE improved the soil physical conditions and thus the rigidity of the porous system. These results demonstrate that rheological measurements can identify saline-sodic soils that have strongly degraded microstructural stability and would most benefit from active management and amelioration.

Untrafficked furrowed seedbed sustains soil physical quality in sugarcane mechanized fields

AbstractManagement strategies that reduce machinery traffic, such as creating seedbeds, could be adopted to preserve soil health and reduce soil physical restriction to sugarcane (Saccharum sp.) growth. Field experiments on clayey and sandy loam soils were conducted along four crop seasons (2013–2017) to investigate the changes in bulk density, soil penetration resistance, macroporosity and microporosity in the row and inter‐row positions, as well as sugarcane biomass production (root and stalk yield) under different machinery traffic treatments. The experimental areas were conducted in randomized block design with two treatments and four repetitions. The evaluated treatments were: (a) regular traffic, in which all operations were performed mechanically using regular machinery traffic; and (b) without traffic, in which all field operations (except those used for sunn hemp management and for opening the sugarcane planting furrow) were performed manually without machinery traffic. No critical values of physical properties were identified in either soil type in plots without machinery traffic, indicating the lowest density and soil penetration resistance values, as well as higher macroporosity, where sugarcane seedbed zones had been established. Our findings show that seedbeds resulted in greater root growth and development in the soil profile, mainly in inter‐row positions. Overall, sugarcane stalk yield was similar between the treatments in both soil types. This study reinforces the importance of the planting furrow in keeping suitable soil conditions for plant growth and concludes that sugarcane production in untrafficked seedbeds is an effective strategy to sustain soil physical conditions over the crop cycle, without the need for tillage operations during the (re)planting period.Highlights The use of seedbeds sustains soil physical quality along the crop cycle Most of root biomass were concentrated in the crop‐row Crop‐row position provides adequate soil physical conditions for root growth and plant development Untrafficked furrowed seedbed sustains soil physical quality and makes no‐tillage viable

Oil Palm Empty Fruit Bunch Alkaline Biochar Influences Total Soil Microbial Population, Number of Root Nodules and Soybean Growth in Wonosari Inceptisol

Alkaline biochar oil palm empty fruit bunches is the result of converting oil palm empty fruit bunch waste from the palm oil mill. The waste converted into resources that can be function to repaired / transformed edacid soils into agricultural land alkaline biochar oil palm empty fruit bunches is the result of converting oil palm empty fruit bunch waste from the palm oil mill. The waste converted into resources that can be function to repaired / transform acid soils into agricultural land. The purpose study is to examine the ability of Biochar Alkaline Oil Palm Empty Fruit Bunches and their effect on the total soil microbial population, the number of root nodules, and the growth parameters of soybean plants in the Inceptisol Tanjung Morawa Medan acid soil. The Screenhouse of the Faculty of Agriculture, University of HKBP Nommensen Medan conducted the greenhouse test phase research by using a completely randomized design research design. Field-testing confirmed by a Dessin factorial randomized trial design. Determination of Total Population of soil microbial cups at both stages of testing is to conduct at the Biology Laboratory of the University of North Sumatra, Meda. (The research method uses all statistical observations in the form of analysis of variance analysis (ANOVA). The results of the different parameter tests followed by Duncan's Multiple Range Test the results showed the influence of Biochar as acid amelioration for acid soil affected the total microbial population and the growth of soybean plants. The research (including chemical and physical properties) with various parameters of other plant elements proved that the alkaline biochar of the palm oil-palm bunches was able to replace agricultural lime (calcite) in repairing acid soils. Further research results show the use of biochar oil palm empty fruit bunches has a more diverse effect; because in addition to improving soil chemical properties such as pH and alkaline nutrient levels, this material also helps improve soil physical conditions in terms of porosity and acidic soil water systems, compared to agricultural lime only has a chemical effect. The advantages of biochar oil palm empty fruit bunches are renewable resources (replacing resources) replacing agricultural lime (calcite) which is a mining material that is classified as an unrenewable resource.

Soil Water Retention and Soil Compaction Assessment in a Regional-Scale Strategy to Improve Climate Change Adaptation of Agriculture in Navarre, Spain

The aim of this study was to evaluate the effectiveness of the different agricultural management adaptive strategies considered in the framework of a regional climate change adaptation roadmap in Navarre (Spain), from the point of view of soil physical indicators associated to soil compaction and water retention. These indicators were chosen as representative of the potential of these strategies to improve the soil physical condition. That for, the effectiveness of conservation agriculture (CA), crop rotations (ROT), additions of organic matter (ExO), irrigation (IRR) and innovative grassland management (GSS) was assessed by monitoring soil bulk density (BD) and soil available water holding capacity (AWHC) in a network of 159 agricultural fields across homogeneous agro-climatic zones in the region. A sampling protocol designed to compare groups of plots with or without adaptive practices, and with equal soil characteristics within each zone, allowed to determine the effect size of each strategy (measured as response ratios, RR, calculated as the relative value of BD and AWHC in fields with adaptive management vs. without). Both parameters responded to soil and crop management, although the observed effect was highly variable. Only the ExO strategy showed an overall positive effect on BD. ROT, IRR and GSS displayed no effect and, in the case of CA, the effect was negative. In terms of AWHC, although the results within the zones were heterogeneous, the overall effect associated to the strategies ROT, ExO, IRR and GSS was neutral, and only CA resulted in an overall negative effect. The observed variability in terms of the effectiveness of the five strategies tested in this region highlights the need to understand the complexity of interrelationships between management and dynamic soil properties at the regional scale.

Resilient modulus descriptive analysis and estimation for fine-grained soils using multivariate and machine learning methods

ABSTRACT The adoption of mechanistic-empirical approach to pavement design requires the use of resilient modulus of subgrade soils as a crucial input. The determination of in the laboratory is inexpedient due to the nature of the existing test protocols. This prompted the use of estimated values, which inadvertently has gained popularity lately. However, the accuracy of estimated values is questionable due to spatial variability of soil properties. This necessitated the aggressive search for robust and thorough approaches for predictive modelling of the . In the present study, a systematic approach was adopted for the descriptive analysis and estimation of . from routine soil properties using data from Long-Term Pavement Performance (LTPP) and considering the spatial variability of the soil properties. Descriptive analysis was executed using non-parametric correlation and principal component analysis (PCA), while the estimation was done using three machine learning methods which include gradient boosting regression (GBR), adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN). Based on the PCA, four factors which explained a total of 77.5% variance in the data had significant influence on the . These include the effect of moisture-induced changes on the soil consistency limits and physical condition, effect of the soil clay content, effect of the soil gradation and effect of the soil stress state. Various factors of the machine learning methods such as the learning rate, number of clusters and number of hidden layers had a significant effect on the prediction accuracy. The three machine learning methods were satisfactory for the prediction based on R 2 values which were generally above 0.9. Also, when considering spatial variability of routine soil properties, the GBR and ANFIS have a comparative advantage over the ANN, since they exhibited a high stability in the prediction for both the training and testing dataset.