Uncompacted Soil Research Articles

Comprehensive lumped parameter and multibody approach for the dynamic simulation of agricultural tractors with tyre–soil interaction

AbstractModern agricultural tractors are complex systems, in which multiple physical (and technological) domains interact to reach a wide set of competing goals, including work operational performance and energy efficiency. This complexity translates to the dynamic, multi‐domain simulation models implemented to serve as digital twins, for rapid prototyping and effective pre‐tuning, prior to bench and on‐field testing. Consequently, a suitable simulation framework should have the capability to focus both on the vehicle as a whole and on individual subsystems. For each of the latter, multiple options should be available, with different levels of detail, to properly address the relevant phenomena, depending on the specific focus, for an optimal balance between accuracy and computation time. The methodology proposed here by the authors is based on the lumped parameter approach and integrates the models for the following subsystems in a modular context: internal combustion engine, hydromechanical transmission, vehicle body, and tyre–soil interaction. The model is completed by a load cycle module that generates stimulus time histories to reproduce the work load under real operating conditions. Traction capability is affected by vertical load on the wheels, which is even more relevant if the vehicle is travelling on an uncompacted soil and subject to a variable drawbar pull force as it is when ploughing. The vertical load is, in turn, heavily affected by vehicle dynamics, which can be accurately modelled via a full multibody implementation. The presented lumped parameter model is intended as a powerful simulation tool to evaluate tractor performance, both in terms of fuel consumption and traction dynamics, by considering the cascade phenomena from the wheel–ground interaction to the engine, passing through the dynamics of vehicle bodies and their mass transfer. Its capabilities and numerical results are presented for the simulation of a realistic ploughing operation.

Cultivar-dependent differences in tuber growth cause increased soil resistance in potato fields.

Since soil compaction of potato fields delays shoot emergence and decreases total yield, the causes and effects of this compaction need to be better understood. In a controlled environment trial with young (before tuber initiation) plants, roots of cv. Inca Bella (a phureja group cultivar) were more sensitive to increased soil resistance (3.0 MPa) than cv. Maris Piper (a tuberosum group cultivar). Such variation was hypothesized to cause yield differences in two field trials, in which compaction treatments were applied after tuber planting. Trial 1 increased initial soil resistance from 0.15 MPa to 0.3 MPa. By the end of the growing season, soil resistance increased three-fold in the upper 20cm of the soil, but resistance in Maris Piper plots was up to twice that of Inca Bella plots. Maris Piper yield was 60% higher than Inca Bella and independent of soil compaction treatment, whilst compacted soil reduced Inca Bella yield by 30%. Trial 2 increased initial soil resistance from 0.2 MPa to 1.0 MPa. Soil resistance in the compacted treatments increased to similar, cultivar-dependent resistances as trial 1. Maris Piper yield was 12% higher than Inca Bella, but cultivar variation in yield response to compacted soil did not occur. Soil water content, root growth and tuber growth were measured to determine whether these factors could explain cultivar differences in soil resistance. Soil water content was similar between cultivars, thus did not cause soil resistance to vary between cultivars. Root density was insufficient to cause observed increases soil resistance. Finally, differences in soil resistance between cultivars became significant during tuber initiation, and became more pronounced until harvest. Increased tuber biomass volume (yield) of Maris Piper increased estimated mean soil density (and thus soil resistance) more than Inca Bella. This increase seems to depend on initial compaction, as soil resistance did not significantly increase in uncompacted soil. While increased soil resistance caused cultivar-dependent restriction of root density of young plants that was consistent with cultivar variation in yield, tuber growth likely caused cultivar-dependent increases in soil resistance in field trials, which may have further limited Inca Bella yield.

Evaluation of Soil Infiltration Variability in Compacted and Uncompacted Soil Using Two Devices

Infiltration is defined by the expression of the hydraulic conductivity of the soil, which we decided to monitor on an experimental field applying a modern system of land management (control traffic farming). The present study compared two different methods of monitoring the hydraulic conductivity of soil on a selected 16 ha plot of land in the suburbs of the village Kolíňany (Slovak Republic). During the growing seasons, crops such as oilseed rape, winter wheat, spring barley, winter barley, spring peas, and maize alternated in individual years. In addition to the study of hydraulic conductivity, a long-term experiment is underway to investigate the influence of technogenic factors on soil degradation using a system of controlled movement of machines in the field. A mini disk infiltrometer (method one) was used to evaluate the unsaturated hydraulic conductivity of the soil, and a double ring infiltrometer (method two) was used to measure the saturated hydraulic conductivity. Monitoring changes in soil infiltration capacity within the compacted and uncompacted lines required 26 monitoring points (20 for method one and 6 for method two). The first longitudinal line was compacted by an agricultural machinery chassis, and the second line remained uncompressed. The research also created transverse compacted lines at eight monitoring points (six for method one and two for method two). The results did not show a statistically significant difference when examining the effect of soil infiltration monitoring (compacted p = 0.123; uncompacted p = 0.99). When evaluating the statistical dependence on the compression caused by machinery in the track line, the hypothesis of significance was not confirmed (p = 0.12, at the level of 0.05). However, the results showed variability in the value of the difference factor between the two methods, ranging from 0 to 0.24. On average, it can be concluded that the results achieved using the double ring infiltrometer were 4.16 times higher than those measured with the mini disk infiltrometer. The variability of hydraulic conductivity was demonstrated not only in the compacted but also in the non-compacted part of the plot. In some places, the phenomenon of water repellency appeared, which could be caused by the drier location of the targeted plot.

Integrity Assessment of Wall Distorted of Buried Gas Pipeline

In the oil and gas industry, the pipeline is the main mode to transport the product and can be applied for long-distance transportation; hence some pipe segments may be buried underground. Buckling as the main cause of pipeline deformation and failure is often found at the in-service buried pipeline during inspection activity. Changes in laying conditions such as design and operational parameters, human activity and geological movement can affect the redistribution of deformation that may lead to pipe buckling. This paper presents a methodology that integrates inspection results and finite element analysis for the distorted wall of the pipeline. Inspection reported anomaly cases of wall distorted at buried gas pipeline, and the result will be used to do stress analysis using finite element analysis. Three different conditions within the different treatment of bedding conditions were assessed: pipe buried on uncompacted soil, pipe buried with rock bedding, and pipe buried in compacted soil. The result shows that the deteriorated pipe can be considered acceptable when buried in compacted soil. This condition may be used for further action and consideration, such as a mitigation strategy to maintain the safety and integrity of the deteriorated pipe.

Soil Compaction under Different Traction Resistance Conditions—A Case Study in North Italy

Tractive efficiency is essential in tillage operations to optimise traction performance. In this field experiment, the tractor performance was measured under different traction resistance conditions. This study quantified the soil stress, soil bulk density, soil moisture, soil cone index, soil surface disturbance, rolling resistance and slip rate under different numbers of passes and traction conditions. The actual power used under different soil and traction conditions was collected. Fuel consumption and savings were calculated between uncompacted soil, compacted soil and the permanent traffic lane. The results show that soil stress increases in each location as traction and the number of passes increase. Soil’s physical properties increase, such as the soil bulk density, soil cone index and soil surface disturbance. Additionally, the slip rate increases with traction in each soil condition as uncompacted soil, compacted soil and the permanent traffic lane. The results show that the permanent traffic lane has a lower slip rate under different traction conditions than the uncompacted and compacted soil. Furthermore, the permanent traffic lane has less energy consumption with the same traction resistance. The permanent traffic lane saved 25.50%, 29.23% and 42.34% fuel compared to the uncompacted field in 7.85, 14.71 and 24.52 kN traction conditions, respectively. Our results confirm that dynamic factors such as traction and rolling resistance should be considered in soil compaction research rather than static weight only. In practice, the controlled traffic farming (CTF) system or driving the tractor more frequently on the permanent traffic lane should be considered to improve working efficiency and reduce energy consumption.

Performance of Tef [Eragrostis tef (Zucc) Trotter] Varieties Influenced by Soil Compaction and Sowing Dates in Toke Kutaye District in Ethiopia

Tef is the most cultivated crop in terms of area and second most produced crop after maize in Ethiopia. Soil compaction, inaccurate sowing date and shortage of high-yielding varieties are crucial problems in the study area. Therefore, this experiment was carried out during the main cropping season of 2021 to study the effects of soil compaction, sowing dates and tef varieties on yield and yield components of tef in Toke Kutaye district. The treatments included soil compaction (compacted and un-compacted soil), three sowing dates and three tef varieties such as [Dedefe (as standard check), Quncho and Dagim]. Treatments were factorially arranged and laid out in randomized complete block design with three replications. Analysis of the data indicated that days to 50% emergence, days to 50% panicle emergence, days to 90% physiological maturity and number of productive tillers of tef were significantly (P<0.05) influenced by main effect of soil compaction, sowing dates and varieties. Plant height, panicle length, total number of tillers, above-ground biomass yield, grain yield and straw yield of tef were significantly affected by the interaction of three factors. Highest plant height (124.26 cm), panicle length (36.26 cm), above-ground biomass yield (7.47 t ha-1), and grain yield (2.8 t ha-1) were recorded from un-compacted soil, in early sown Dagim variety. Therefore, farmers in the study area are advised to grow Dagim variety with July 15 sowing date without trampling the soil to improve tef production and yield. However, the experiment has to be repeated across locations and seasons to provide a reliable recommendation for improved tef production for similar agroecology.

Effect of Soil Compaction and Sowing Dates on Growth and Yield of Three Tef [Eragrostis tef (Zucc) Trotter] Varieties in Toke Kutaye District, Ethiopia

Tef is a highly valued crop in Ethiopia as tef flour used to prepare Injera which is the most popular food of the country. However, its production and productivity are constrained by a number of problems, out of which soil compaction, inappropriate sowing time, and limited use of improved varieties are the most important. Hence, a field experiment was conducted during the 2021 main cropping season to evaluate the effect of soil compaction, sowing dates and tef varieties on yield and yield components of tef in Toke Kutaye district. Treatments were factorially arranged and laid out in randomized complete block design with three replications. Analysis of the data indicated that days to 50% emergence, days to 50% panicle emergence, days to 90% physiological maturity, and number of productive tillers of tef were significantly (P<0.05) influenced by main effect of soil compaction, sowing dates and varieties. Plant height, panicle length, number of total tillers, biomass yield, grain yield and straw yield of tef were significantly affected by the interaction of three factors. Highest plant height (124.26cm), panicle length (36.26cm), above ground biomass yield (7.47 t ha-1), and grain yield (2.8 t ha-1) were recorded from un-compacted soil, from early sown Dagim variety. Therefore, it can be recommended that farmers of the study area can grow Dagim variety early third week of july without trampling the soil to enhance the tef production and productivity.

Mitigation of Greenhouse Gas Emissions with Biochar Application in Compacted and Uncompacted Soil

Biochar may offer a substantial potential as a climate change mitigation and soil improvement agent; however, little is known about its effects in fertile soils subjected to standard agricultural practices. The aim of this short-term (60 days) lab experiment, under controlled temperature and soil moisture regimes, was to investigate the interaction between soil compaction and fertiliser and biochar addition in relatively fertile Luvisol. Three different biochar types and two soil compaction levels were investigated to describe their interactive effect on soil greenhouse gas emission (GHG). A very strong effect of soil compaction on N2O emission (+280%) and an interaction with biochar were found. The cumulative N2O emissions from the compacted soil were higher (from +70 to +371%, depending on the biochar type) than the uncompacted soil. Soil compaction resulted in a faster onset and a faster decrease of N2O production. Biochar did not affect the temporal dynamics of N2O evolution from either soil. The addition of digestate/crop biomass biochar has resulted in a significant increase in CO2 evolution both in compacted and uncompacted soils, compared to softwood from spruce (mixture of branches and wood chips) and wood pallets from softwood (spruce without bark) biochar. In the compacted soil, NH4+ availability was positively related to N2O efflux, and CO2 emission was positively correlated to both NH4+ and SOC content. An increase in GHGs as a result of an increase in NH4+ availability was seen both in compacted and uncompacted soils, while the rates of N2O emission were modified by biochar type. Our results show a strong interaction between biochar and soil conditions and a strong effect of biochar type on GHG emissions from agricultural soils.

Active scour monitoring using ultrasonic time domain reflectometry of buried slender sensors

Local scour is a growing cause of bridge failure in the United States and around the world. In the next century, the effects of climate changes will make more bridges susceptible to scour failure more than ever before. This study aims to harness the spatially continuous monitoring capabilities of ultrasonic time-domain reflectometry to detect a soil interface for the purposes of scour monitoring. In this study, a long, slender plate is coupled with two flexible piezoelectric devices that propagate Lamb waves along the length of the plate to form the scour sensor. The sensor was tested for sensitivity to external pressure using metal weights and was able to detect the position of the pressure up at a length of up to ∼20 feet. The sensor was tested under simulated scour conditions, being buried in sand at various depths. The results show that the Lamb wave scour sensor is capable of reliably detecting a soil interface at 1 ft intervals. The scour sensor was also able to detect uncompacted soil interfaces, which is important considering the issue of scour hole refill following an extreme event.

Soil Water Movement of Mining Waste Rock and the Effect on Plant Growth in Arid, Cold Regions of Xinjiang, China

Understanding the water movement in reconstructed soil and its efficacy on local vegetation is critical for the ecological reclamation of mine lands. This study employed field experiments and a numerical model to investigate the water movement in reconstructed soil and evaluate the effects of mining waste rock on plant growth in an arid and cold region of Xinjiang. Water contents and matrix potentials were monitored over 1-year period. A numerical model was established based on the observed data to calculate soil water balance and irrigation demand. The results show that the soil water content at a shallow depth could be more vulnerable to the climate variability in uncompacted and compacted soil. The water content at the depth of 50 cm with 30 cm-thick covering soil was the lowest; meanwhile, the barrels with 50 cm- and 70 cm-thick covering soil without compaction had the highest water content. Moreover, the water content of the uncompacted soil could be lower than that of the counterpart attributed to the variation in soil porosity. To maintain the water content as an optimized value to grow a certain plant species in the long run, irrigation could be implemented according to the water balance over time in mine lands.

A numerical study into effects of soil compaction and heat storage on thermal performance of a Horizontal Ground Heat Exchanger

The good capacity of the numerical simulations makes possible to bring some further responses on the backfill soil selection and its installation depth in the Horizontal Ground Heat Exchanger (HGHE). Therefore, a well-known backfill soil was considered to be used as substitutive material. The hydrothermal properties of the backfill material were estimated in laboratory and then injected in a numerical framework considering the atmosphere-soil-HGHE interaction. Numerical simulations were performed for a HGHE installed in the compacted backfill soil and the local natural soil. The simulation results showed that the compacted backfill soil improves by 8.5% the HGHE performance compared to local uncompacted soil. Two heat storage scenarios at three different installation depths were also investigated. The results showed that an inlet fluid temperature of 50 °C in summer increased highly the system performance by 13.7%–41.4%, while the improvement was less significant (0%–4.8%) for the ambient inlet temperature scenario. A deeper installation depth of HGHE increased also the system performance, the more energy could be stored and extracted.

Enhancing pyromorphite formation in lead-contaminated soils by improving soil physical parameters using hydroxyapatite treatment

During chemical immobilization in soil, enhancement of insoluble phases is required to prevent toxic metal from leaching into the surrounding environment. Understanding the effects of physicochemical parameters of soil on the reaction between lead and hydroxyapatite is important to enhance the formation of the insoluble pyromorphite-lead phase. However, the combined effect of soil physical parameters on pyromorphite formation and compressive strength has not been reported. This study aimed to investigate the relationship between soil texture and pyromorphite formation, as well as unconfined compressive strength in lead-contaminated soils treated with hydroxyapatite under different compaction states and moisture conditions. Our findings showed that in compacted soil, >20% of lead was formed as pyromorphite compared with 10% of lead in uncompacted soil. In particular, low porosity and a high saturation ratio of soil under the unsaturated moisture condition were favorable for pyromorphite formation. Under the saturated moisture condition, the addition of hydroxyapatite enhanced pyromorphite formation compared with that under the unsaturated moisture condition. In addition, the leaching of soluble lead into the surrounding environment could be suppressed to <0.05% of lead in soil. The addition of hydroxyapatite also increased compressive strength of the compacted soil with increased curing period despite the soil texture. Our results suggest that treatments such as compacting and seepage control with hydroxyapatite may simultaneously increase pyromorphite formation and compressive strength. Furthermore, when performing soil recycling with hydroxyapatite at sites in the groundwater zone, the soluble lead in the soil is prevented from leaching to the surrounding environment. Hydroxyapatite could be used to enable the reuse of lead-contaminated soil for lead immobilization and to increase compressive strength.

Soil density and oscillation frequency effects on viscoelasticity and shear resistance of subtropical Oxisols with varying clay content

Soil density and oscillation frequency are some of the main factors affecting soil micromechanical behavior, but their role in the oscillatory amplitude sweep test (AST) is not yet well understood. Current studies use either a reference density, i.e. field density or a density based on texture and/or organic matter content or opt for a common density for all samples, while oscillation frequency may be relevant in simulating agricultural traffic speeds and affects coupled hydraulic-mechanical processes. We analyzed the effect of soil density and AST oscillation frequency at different matric potentials of three weathered Oxisols from southern Brazil that were repacked to different densities, namely different levels of compaction, no compaction and field density. Higher density, probably due to increased cohesion and friction, increased rheological shear stress parameters: shear stresses at the end of the linear viscoelastic range (LVR), τL; and at the yield point (YP), τYP; and storage and loss moduli (G’ and G”, respectively) at the YP, G’, G”YP. However, viscoelasticity parameters: strain at the end of LVR γL; strain at the YP γYP; and the integrated zone Iz, were negatively affected at low densities with increasing magnitude at higher density levels. Uncompacted soil resulted in densities similar to field density, and delimitated a soil state where density does not interfere with friction. This suggests a methodology for the comparison of distinct soils or where information on field density is missing or unavailable. Frequency alterations from 0.25 to 1.0 Hz had low impact and only increased few rheological parameters, mainly in some soils drained at −6 kPa, but neither reduced data accuracy nor affected the samples' evaporation. Hence, rheological tests can be executed at a higher frequency than 0.5 Hz (at least up to 1.0 Hz) to increase sample output. For both density and frequency, (i) drainage increased soils micromechanical resistance due to water menisci; and (ii) soil resistance showed the order: Typic Hapludox (clayey brown-reddish Oxisol) > Rhodic Kandiudox (clayey red Oxisol) > Rhodic Hapludox (sandy red Oxisol), mainly due to the cohesive effect of clay and Fe oxides, as well as the aggregating effect of soil organic matter.

Study on Compaction Effect and Process of Reclaimed Soil of Nonmetallic Mines in Xinjiang, China

Reclaimed soil is the key substrate for land reclamation and ecological restoration in the mine areas. The change of the density of reclaimed soil of the nonmetallic mines in Xinjiang during the land reclamation process was studied in this paper. Firstly, the in situ test method of static load was used to simulate the compaction of reclaimed soil with different thickness of overlying soil by different compaction times of mines reclamation machinery, and field in situ test compaction data were obtained. Then, the numerical simulation method was used to simulate the variation process of displacement and porosity at different depths for different thickness of the reclaimed soil under different compaction conditions. The numerical simulation and the in situ test results verified each other to acquire the compaction process and results of reclaimed soil under different compaction. The results showed that the numerical simulation results were consistent with the in situ test. The reclaimed soil thickness and compaction times were crucial factors affecting the compaction effect of the soil. The difference between the three times compaction and the uncompacted soil was obvious, and the effect of single compaction was weakened with the increase of compaction times. Under the same compaction action, the thicker the soil was, the less obvious the compaction effect would be. In the process of reclamation, the compaction effect of the surface part (at the depth of 10 cm) was visible, and the amount of compression and springback was larger. The research results can provide a reference to the land reclamation of nonmetallic mines in Xinjiang, China.

Soil Compaction Affects the Growth and Establishment of Street Trees in Urban Australia

Growing conditions for street tree roots are generally harsh with restricted space and soils compacted from streetscape infrastructure. Allocasuarina littoralis, Corymbia maculata, Cupressus sempervirens var. stricta, Eucalyptus polyanthemos, Lophostemon confertus, Olea europaea, Quercus palustris, and Waterhousea floribunda were grown in compacted and uncompacted soils for 20 months in experimental blocks. The bulk density and penetrative resistance of the soils and height, canopy spread, trunk diameter, leaf area, and chlorophyll fluorescence were measured regularly. Root and shoot biomass were determined after harvesting. Since the bulk density of compacted compared to uncompacted soil was root growth limiting, it was hypothesised that species would have reduced growth in compacted soils. However, C. maculata and E. polyanthemos grew better, C. sempervirens, Q. palustris, and W. floribunda grew well, and A. littoralis, L. confertus, and O. europaea were the worst performing in compacted soil. E. polyanthemos, L. confertus, and Q. palustris had higher canopy:root ratios in compacted soil. Q. palustris had greater mass below ground than above, which has implications for its use in confined sites. In a field study, C. maculata, E. polyanthemos, L. confertus, O. europaea, and Q. palustris growing as street trees were surveyed to determine their rates of establishment and growth under urban conditions. In addition to the soil and tree parameters mentioned above, a Visual Tree Assessment (VTA) was undertaken. E. polyanthemos had the largest trunk diameter, height and canopy spread, indicating its potential for rapid establishment in streets. It was the only species with a larger mean leaf area in compacted soil. E. polyanthemos and O. europaea were the only species classed as healthy from chlorophyll fluorescence but there was no significant difference in fluorescence between compacted and uncompacted soils. VTA showed that C. maculata and O. europaea performed best and that E. polyanthemos, L. confertus, and Q. palustris had reduced but acceptable growth in compacted soil. Soils ranged from non-saline to moderately saline and were slightly to strongly acidic. All soils were compacted to some degree and penetrative resistance was at root limiting levels. The results suggest that careful species selection and soil amelioration for species prone to the effects of compaction would facilitate street tree establishment.

Changes in soil bacterial community as affected by soil compaction, soil water content and plant roots

The present study assessed the effects of compaction on temporal dynamics of soil microbial communities and whether these changes were influenced by the presence of plant roots and soil water content. A pot trial comprised three levels of compaction (1.1 gcm-3 – un-compacted; 1.25 gcm-3 – moderately-compacted; 1.4 gcm-3 – heavily-compacted), two levels of irrigation regimes (60 and 80% FC), and two soil conditions (planted soil versus free root soil) was established. Soil microbial attributes investigated included bacterial activity and diversity, which were obtained from five sampling times (5; 10; 15; 20; 30 days). The results showed that bacterial activity and diversity changes over time and were higher in un-compacted soil treatment at day-20. Bacterial activity and diversity were higher in moderately-compacted soil with high soil moisture level (80% FC). Microbial activity and diversity were weakly correlated with the presence of plant roots particularly when soil was heavily compacted. Given the changes of microbial communities that followed changes in soil moisture availability, it was, therefore, concluded that management of the timing of irrigation inputs is needed in order to maintain microbial communities in soil.

Suspended pavement systems as opportunities for subsurface bioretention

Trees supply numerous ecosystem services to the urban environment, including mitigating the urban heat island, improving air quality, and providing habitat for wildlife. However, due to the structural stability requirements of infrastructure such as sidewalks, roadways, and parking areas, urban soils are commonly characterized by high compaction levels, low porosity, and nutrient deficiency, often to the detriment of urban tree health. By transmitting surface loads to a compacted subbase, suspended pavement systems create a matrix of uncompacted soil that promotes tree health through increased root access to oxygen, water, and nutrients. Recently, interest has grown in making suspended pavement systems multi-functional by designing them to act as subsurface bioretention practices in ultra-urban areas where space may be limited due to concentrated development and high land costs. Despite this interest, only one study has tested suspended pavement systems in this application. Further, the study utilized lined installations to allow a controlled water quality assessment; however, this negated the ability to fully quantify runoff reduction. Two unlined suspended pavement systems designed to function as subsurface bioretention practices were installed in Knoxville, Tennessee, USA, in 2015 and monitored over 27-months. During that period, over 99% of runoff volumes were reduced by the free-drained north system, which completely captured runoff from 79% of storms. The underdrained south system reduced influent runoff by over 88% and captured all runoff from 83% of events during the study. Influent TSS concentrations were significantly reduced by the south suspended pavement system, though no other significant differences between influent and effluent pollutant concentrations were observed, presumably due to low influent concentrations. This study demonstrates the viability of field-scale suspended pavement systems in a stormwater management application and illustrates the hydrologic and pollutant removal capabilities of these systems to manage urban stormwater runoff.

Soil Compaction and Soil Amendments on the Growth and Biomass Yield of Maize (Zea mays L.) and Soybean (Glycine max L.)

Two factorial pot experiments arranged in a Completely Randomised Design (CRD) with three replications were carried out to assess the impact of different levels of soil compaction and fertilizer amendments on root growth and biomass yield of maize (Zea mays L.) and soybean (Glycine max L.) plants. The treatments were different rates of bulk densities – 1.3, 1.5 and 1.7 Mg m-3 and fertilizer amendments comprising 100% poultry manure (applied at 15 g/plant), 100% 15:15:15 NPK fertilizer (applied at 2.89 g/plant) and 50% rate each of poultry manure and NPK fertilizer (applied at 7.5 g poultry manure + 1.45 g NPK/plant), and control (no fertilizer amendments). Soil compaction reduced the heights of maize and soybean plants. Increasing soil compaction resulted in the accumulation of most of the root biomass in the uncompacted soil above the compacted layer. Application of soil amendments increased the relative root biomass of maize plants in the uncompacted soil, while that in the compacted soil was reduced. In the case of soybean plants, although the relative root biomass in the uncompacted soil was relatively greater than that of maize plants, application of soil amendments tended to slightly decrease the relative root biomass to that of the control. The shoot biomass of both crops decreased with increasing soil bulk density. All the applied soil amendments significantly increased the shoot biomass of maize and soybean plants over the control. The magnitude of response of the crops to the soil amendments was greater in soybean than in maize plants. Soil compaction and amendments significantly influenced root/shoot ratio of both crops. The root/shoot ratio decreased with increasing compaction from 1.3 to 1.5 Mg m-3, however, at 1.7 Mg m-3, the root/shoot ratio increased. The fertilizer amendments significantly influenced the root/shoot ratio of maize but not soybean plants. The fertilizer amendments increased the biomass of both roots and shoots, being higher in the former than in the latter. The fertilizer amendments x compaction interactions showed that the root/shoot ratio was influenced by the type of crop, and the confounding effects of factor interactions on the relative increases/decreases in shoot and root growth. Overall, soil compaction accounted for 52 to 100% of the variations in the magnitude of the measured parameters of maize plants, and 62 to 98% for soybean plants. The ideal bulk density for shoot biomass production of both crops should, therefore, be within the range of 1.3 – 1.5 Mg m-3. At soil bulk density of 1.5 Mg m-3 and above, soil amendment should be added to ameliorate the negative impact of soil compaction.

Root Growth Responses of Maize (Zea mays L.) and Soybean (Glycine max L.) to Soil Compaction and Fertilization in a Ferric Acrisol

Mechanical impedance to root growth is one of the most important factors determining root elongation and proliferation within a soil profile. Two pot experiments were conducted at the Department of Horticulture, KNUST, Kumasi, Ghana, to determine the impact of subsurface compaction and different fertilizer amendments on the root growth of maize (Zea mays L.) and soybean (Glycine max L.). The experiments were arranged in a factorial Completely Randomized Design (CRD) with three replications. Maize and soybean varieties, “Obaatanpa” and “Anidaso” were sown in 72 plastic buckets (36 for each crop) of 12 L volume filled with a Ferric Acrisol. The treatments were different levels of compaction, using bulk density as proxy – 1.3, 1.5 and 1.7 Mg m-3, and fertilizer amendments of 100% poultry manure (15 g/pot), 100% NPK fertilizer (2.89 g/pot) and 50% each of poultry manure (7.5 g/pot) and NPK fertilizer (1.45 g/pot). The highest root growth occurred in the uncompacted soil and along the periphery of the soil core. The applied soil amendments significantly increased the root penetration ratio (RPR) of both crops in relation to the control. The shoot biomass of both crops decreased with increasing soil bulk density. All the applied soil amendments significantly increased the shoot biomass of maize and soybean over the control. The magnitude of response of the crops to the soil amendments was greater in soybean than in maize.

Study on Compaction of Reclaimed Soil of Nonmetallic Mining Area in Northern Foothills of Tianshan Mountains in Xinjiang, China

This study focused on the changes of the compaction of the reclaimed soil after the reclamation process and the one-year maintenance period of the nonmetallic mines in north foothills of Tianshan Mountains in Xinjiang. The plate load experiment method was employed to simulate the compaction effect of various times of compaction from the reclamation machine on a different thickness of the reclaimed soil. The experimental data were analyzed by multivariate statistical analysis. The experimental results showed both compaction frequency and thickness of the reclaimed soil were key factors affecting the compaction of the reclaimed soil, and the interaction between them had a dramatic impact on the soil compaction. The difference of the porosity between the three-time compacted soil by the compaction machine and the noncompacted soil was significant. The effect of a single compaction dampened with the increasing times of compaction. The porosity of the 50 cm and 70 cm thick topsoil continuously decreases with the increasing times of compaction at the depth of 10 cm from the surface soil. The porosity at the 30 cm depth of the 50 cm and 70 cm thick topsoil decreased first and then increased with the increasing times of compaction. At the end of the one-year maintenance period, samples from different depths of the reclaimed soil of various thicknesses were collected to investigate the changes of porosity. The results showed the porosity of the reclaimed soil at different depths was changed due to irrigation. The porosity of the uncompacted soil decreased progressively from the surface to the deep region. The porosity of the compacted soil at the 10 cm depth was lower than that at the 30 cm depth due to soil sealing, whereas the porosity decreased with the increasing depth in the deeper region. The results from this study could provide a fundamental reference for the reclamation of nonmetallic mines in northern foothills of Tianshan Mountains in Xinjiang, China.