Physical and mechanical behavior of fine soil according to the content of multispecies diatoms

The physical response and geotechnical properties of diatomaceous soils are not fully understood, data are sparse, and do not account for the effects of single and multispecies frustule content, origin, type, and variability. The main physical problem lies in the irregular response of diatomaceous soils due to micro and nano scale causes and its unexpected effects on the macro scale. This research compared the characteristics of a multispecies diatomaceous soil sample (North American origin) with other diatomaceous single-species soils. Six artificial soil mixtures were prepared, dosed by weight, in order to determine the influence of the content of frustules. The results show that the liquid limit of the samples is lower than that of the monospecies samples for any content of frustules. The pore areas of the monospecies samples are found to be 4 to 7 times larger than those of the North American soil. Void ratios and compressibility ranges are higher as the diatom content increases. The internal friction angle of diatomaceous soils varies in a non-linear tendency with respect to fossil content. For the studied soil at 100% fossil concentration, the internal friction angle reached 38.32°, a magnitude that is lower than the values reported for most of the monospecies contrast samples.

Technology and tools for strip tillage in the energy-saving system of agriculture in Volgograd region

The article highlights the results of research in strip farming. The method of minimum soil tillage, a resource-saving working body ROPA and a soil tillage tool for strip ripping OMPO-5.6, which are designed to perform fine soil tillage with strip deepening, are proposed. Adjustment of loosening depth from bit is achieved within the range of 0.25-0.4 m and is selected taking into account the crop grown in the farm. Availability of undercutter tine allows to regulate parameters of continuous ripping zone. Parameters of treated and untreated strips are regulated by location of undercutter paw. The design of the tool provides a smooth adjustment mechanism by which the width of the cultivated strip can be changed within 0.25-0.35 m. This makes it possible to use the implement for different tilled crops. The technological process carried out by this working body helps to reduce the wounding effect on the soil through a simple technical solution. Installation of side undercutting discs allows cultivating the soil within a given strip, and the process of cutting the soil in a blocked environment improves the quality of treatment.

Performance characteristics of low carbon waste material to stabilise soil with extremely high plasticity

The application of low-carbon and natural materials to mitigate the undesired properties of difficult soils is considered as a sustainable solution to the issues regarding these soils. Selecting some natural materials, of low carbon type, from the rubble of demolished buildings or debris from the construction of new buildings and recycling them in a poor or weak soil stabilisation process is a very little explored field of research in Iraq. This paper investigated the geotechnical characteristics of extremely high plasticity soil (EHPS) improved with a low-carbon building stone debris (BSD). Five dosages from coarse and fine soil-size ((BSDC) and (BSDF)) of BSD have been prepared to use in the EHPS-BSD mixtures. The laboratory tests included Atterberg limits, linear shrinkage, unconfined compression, consolidation, and swelling. The effect of the BSD on the time to zero-water content and the maximum swell was included. The efficiency of the BSD was proved by the amelioration of the compressibility and strength, and by reducing the shrinkage, swell pressure, and the potential of swelling. The shrinkage, compressibility, and swelling properties of the EHPS were reduced depending on the gradation and content of BSD. The gradation of BSD had a major role in strength development and controlling the time required to reach the final shrinkage and maximum swell stage.

Are agricultural plastic covers a source of plastic debris in soil? A first screening study

Agricultural plastic covers made from polyethylene (PE) and polypropylene (PP) offer increased yields and an improved crop quality. However, such covers are suspected of partially breaking down into smaller debris and thereby contributing to soil pollution with microplastics. To scrutinize this, we randomly sampled 240 topsoil cores (0–5 cm) from eight fields covered with fleeces, perforated foils, and plastic mulches for less than two years. Samples from the field periphery (50 m perimeter) served as reference. Visual plastic debris > 2 mm was analyzed by Fourier transformed infrared spectroscopy with attenuated total reflection (FTIR–ATR). Smaller, soil-associated plastic debris was dispersed from 50 g of fine soil (≤ 2 mm) using sodium hexametaphosphate solution and density-separated with saturated NaCl solution. The collected PE, PP, and polystyrene (PS) debris was selectively dissolved in a mixture of 1,2,4-trichlorobenzene and p-xylene at 150 °C and quantified by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). We counted six PE and PS fragments > 2 mm in two out of eight fields. By contrast, Py-GC/MS analysis revealed PE, PP, and PS contents > 1 µg g−1 in seven fields (17 % of all samples). In three fields, PE levels of 3–35 µg g−1 were associated with the use of thinner and less durable perforated foils (40 µm thickness). This was slightly more pronounced at field edges where the plastic covers are turned and weighted down. By contrast, 50 µm thick PE films were not indicated to emit any plastic debris. PP contents of 5–10 µg g−1 were restricted to single observations in the field centers of three sites. On one site, we found expanded PS particles >2 mm that concurred with elevated PS levels (8–19 µg g−1) in the fine soil. Both PP and PS were distributed indistinctly across sites so that their source remained unresolved. In addition, the extent to which plastic contents of up to 7 µg g−1 in the field periphery of some sites were attributed to wind drift from the covered fields or from external sources needs to be investigated in future studies. Yet, our results suggest that the short-term use of thicker and more durable plastic covers should be preferred to limit plastic emissions and accumulation in soil.

Soil properties and carbon stock along the toposequence of Lalmai hill ecosystem of Bangladesh

A study was carried out in the Lalmai hill ecosystem of Bangladesh regarding their soil properties and soil organic carbon (SOC) stocks. The Lalmai hill ecosystem consists of three toposequence arrangements as hills, piedmonts, and floodplains. Forty-five soil samples covering nine soil profiles were selected to conduct the present study. Soil samples were collected at five different depths of 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm and 80-100 cm intervals from each pit of the study sites. Soil pH, percent SOC, percent total nitrogen (TN), bulk density, cation exchange capacity (CEC), particle size distribution, and SOC storage (kg/m2) dataset indicates that piedmont deposits and floodplain soils are more enriched than the upper hill soils. Regarding SOC storage, the post hoc test indicates that hill soils are significantly different from the other two physiographic units, but there is no significant difference between piedmont deposits and floodplain soils. The soil property varies differently depending on their depth level at different physiographic units. Estimation on SOC stock revealed that 2.01Tg, 21.75Tg, 12.68Tg carbon remains in the hill soils, piedmont soils, and estuarine floodplain soils, respectively. The total SOC stock was estimated at 36.44 Tg in the Lalmai hill ecosystem of Bangladesh, where piedmont deposits contained the highest level of SOC stock. It is assumed that more clay-organic substances are washed in at the foot of piedmont units due to the well-drained nature of upper Pleistocene hill soils. Thus, fine soil textural nature, diverse land and land cover accelerates to sequester more carbon in piedmont zone rather than hill or floodplain zones. Dhaka Univ. J. Biol. Sci. 30(2): 331-343, 2021 (July)

Perennial grasses for sustainable tillage and soil quality optimization of highlands

Основные исследования выполнены в стационарном полевом опыте М-01-18-ОП, который был заложен осенью 1980 года профессором И. С. Кочетовым на экспериментальной базе учебно-опытного хозяйства «Михайловское» в Московской области. История ведения опыта включает два периода. В первый период (1980–1989 годы) проводился трёхфакторный опыт. Во второй период (с 1990 года) с учётом дальнейшего совершенствования систем земледелия, комплексного изучения принципов и приёмов обработки почвы, построения на этой основе принципиально новых ландшафтных систем земледелия для эрозионно опасных территорий полевой опыт был модернизирован в двухфакторный. Показано, что при разработке и освоении севооборотов на склоновых территориях в рамках адаптивно-ландшафтных экологически сбалансированных систем земледелия необходимо в максимальной степени учитывать зональные особенности природных ландшафтов (климат, микроклимат, рельеф, почвенный и растительный покровы и другие факторы). При этом крайне важно учитывать средообразующую и почвозащитную способность каждой полевой культуры, её реакцию на степень эродированности почв, экспозицию и крутизну склонов, а также условия перезимовки, особенно на фоне современных изменений климата в сторону потепления. Самый высокий почвозащитный эффект при интенсивном использовании пашни склоновых земель в условиях наиболее активного развития эрозионных процессов (склон 8º) получен при возделывании бобово-злаковой смеси 1-го года пользования. Хорошо раскустившиеся с осени, с высоким проективным покрытием и закреплением почвы корневой системой, на фоне относительно благоприятных инфильтрационных свойств почвы травы обеспечили минимальные потери мелкозёма (0,12 т/га) в сравнении с другими культурами севооборота. Однако с возрастом с учётом указанных выше негативных обстоятельств почвозащитная (0,22т/га) и стокорегулирующая (22 мм) роль многолетних трав снижается. В этой связи возникает необходимость оптимизации состава травосмеси на принципах соответствия её компонентов местообитанию и устойчивости к неблагоприятным погодным воздействиям зимних периодов. The field trial (M-01-18-OP) was started by I. S. Kochetov in 1980 at the research farm “Mikhaylovskoe” in the Moscow region. In the period of 1980–1989 the effects of three factors were analyzed. Starting from 1990 the trial was modified into the two-factorial one due to the new improved farming systems and tillage techniques for low-quality soil. Crop rotation on highlands should be performed considering climate, environment, local topography, soil, plant cover etc. It is important to take into account habitat-forming and soil-conserving ability of each crop as well as its response to soil damage, landscape and winter conditions particularly under current global warming. Cultivation of legumes and gramineous together for 1 year had significant positive effect on highly damaged soil (plot 8º). Grasses showed good tillering capacity, soil coverage and root formation minimizing the loss of fine soil (0.12 t ha-1) on the background of favorable soil structure. However, soil-conserving (0.22 t ha-1) and flow-regulating capacities (22 mm) of perennial grasses decrease with the time. Therefore, optimal plant composition of such mixtures are of great importance with regard to plant tolerance to abiotic and biotic stresses.

Using of recycled clay brick/fine soil to produce sodium hydroxide alkali activated mortars

In the study, the recycled clay brick powder/fine soil powder-based sodium hydroxide alkali-activated mortar (AAM) specimens were prepared by mixing different percentages (100/0, 80/20, 60/40, 40/60, 20/80, and 100/0, respectively) to investigate the mechanical and durability performance of sustainable AAM specimens for the possible utilization instead of OPC. The constant ratio of glass powder was used in the production of AAM to increase the alkalinity and improve the mechanical properties of alkali-activated mortar. Also, the influences of sodium hydroxide molarity concentrations (8, 10, 12, 14, and 16 M) on the performance of AAM specimens were studied. The compressive strength, water absorption, and water sorptivity tests were conducted on the AAM specimens and the relationships between the investigated parameters were analyzed. The obtained results revealed that the fine soil powder replacement with clay brick powder improved the compressive strength, and reduced water absorption and water sorptivity up to 80% replacement ratios, and the superior mechanical and durability performance was obtained in the 80% fine soil powder-based AAM specimens. For the higher fine soil powder replacement ratio (100%), the performances of the AAM specimens were found to be adversely affected. Besides, the concentration of NaOH solution significantly influenced the material performances of the fine soil powder-based AAMs and 12 M NaOH concentration performed superior mechanical and durability performance. The strength enhancement of the AAMs was found to be significant after 90 days of ambient curing period.

Soil-water retention behaviour of fine/coarse soil mixture with varying coarse grain contents and fine soil dry densities

An interlayer soil identified in the French conventional rail track corresponded to a mixture of fine soil and coarse grains. To investigate the role of fines in the soil-water retention property of such mixture, different coarse grain contents fv and dry densities of fine soil ρd-f were considered. The filter paper method was applied to measure the matrix suction. Mercury intrusion porosimetry tests were performed for the microstructure observation of fine soil. In terms of gravimetric water content of fine soil wf with matrix suction Ψ, the soil-water retention curve (SWRC) was significantly affected by ρd-f for Ψ < 715 kPa, while independent of ρd-f for Ψ > 715 kPa. Interestingly, this threshold Ψ corresponded to a delimiting pore diameter of bi-modal microstructure of fine soil, which separated micro-pores from macro-pores. In terms of degree of saturation Sr with Ψ, the SWRC was significantly affected by ρd-f in the full suction range, while independent of fv. These findings help better understand the results on samples with the dry density of mixture ρd kept constant: an increase of fv resulted in a decrease of ρd-f and the suction changed accordingly. In that case, both fv and Ψ affected the mechanical behavior.