Biochar and Compost-Based Integrated Nutrient Management: Potential for Carbon and Microbial Enrichment in Degraded Acidic and Charland Soils

Soil acidification and charland formation through alluvial sand deposition are emerging threats to food security in Bangladesh in that they endanger crop production in about 35% of its territory. The integrated plant nutrient system (IPNS) is a globally accepted nutrient management approach designed to revive the damaged soils’ fertility level. Total organic carbon (TOC) in soil is a composite index of soil quality that has consequences for agricultural productivity and natural soil ecosystems. This study assesses the impacts of using biochar, compost, poultry litter, and vermicompost-based IPNS approaches on labile and TOC pools, TOC stocks, lability and management indices, and microbial populations under different cropping patterns after 2 years in acidic and charland soils. The application of IPNS treatments increased microbial biomass carbon (MBC) by 9.1–50.0% in acidic soil and 8.8–41.2% in charland soil compared to the untreated soil, with the largest increase in poultry manure biochar (PMB). Microbial biomass nitrogen (MBN) rose from 20 to 180% in charland soil compared to the control, although no effect was observed in acidic soil. Basal respiration (BR) rose by 43–429% in acidic soil and 16–189% in charland soil compared to the control, exhibiting the highest value in PMB. IPNS treatments significantly improved SOC and POC but did not affect POXc and bulk density in both soils. The PMB and organic fertilizer (OF, compost)-based IPNS wielded the greatest influence on the lability index of MBC in acidic soils and the management index of MBC in both soils. This is despite the fact that IPNS did not affect the lability and management indices of active carbon (AC). IPNS treatments increased the stocks of SOC and MBC in both the soils and POC stock in acidic soil. IPNS treatments significantly boosted the bacterial and fungal populations in both soils, despite having no effect on phosphorus-solubilizing bacteria (PSB). Thus, PMB and OF (compost)-based IPNS may be a better nutrient management practice in degraded acidic and charland soils. This is especially the case in terms of soil quality improvement, soil carbon sequestration, and microbial enrichment.

Biotic and Abiotic Biostimulation for the Reduction of Hexavalent Chromium in Contaminated Aquifers

Hexavalent chromium is a carcinogenic heavy metal that needs to be removed effectively from polluted aquifers in order to protect public health and the environment. This work aims to evaluate the reduction of Cr(VI) to Cr(III) in a contaminated aquifer through the stimulation of indigenous microbial communities with the addition of reductive agents. Soil-column experiments were conducted in the absence of oxygen and at hexavalent chromium (Cr(VI)) groundwater concentrations in the 1000–2000 μg/L range. Two carbon sources (molasses and EVO) and one iron electron donor (FeSO4·7H2O) were used as ways to stimulate the metabolism and proliferation of Cr(VI) reducing bacteria in-situ. The obtained results indicate that microbial anaerobic respiration and electron transfer can be fundamental to alleviate polluted groundwater from hazardous Cr(VI). The addition of organic electron donors increased significantly Cr(VI) reduction rates in comparison to natural soil attenuation rates. Furthermore, a combination of organic carbon and iron electron donors led to a longer life span of the remediation process and thus increased total Cr(VI) removal. This is the first study to investigate biotic and abiotic Cr(VI) removal by conducting experiments with natural soil and by applying biostimulation to modify the natural existing microbial communities.

Prediction of California Bearing Ratio from Consistency and Compaction Characteristics of Fine-grained Soils

Soil’s characteristics are essential for the successful design of projects such as airports runway and flexible pavement. CBR (California Bering Ratio) is one of the significant soil characteristics for highways and airports projects. Thus, the CBR property can be used to determine the subgrade reaction of soil through correlations. Many of the soil geotechnical parameters such as compaction characteristics (Maximum Dry Density, MDD; Optimum Moisture Content, OMC), and consistency parameters (Liquid Limit, LL; Plastic Limit, PL; Plasticity Index, PI) can be in charge of changes that happen in soil CBR value. Soaked and/or non-soaked conditions of soils also affect CBR value. Hence, testing soils in a laboratory for CBR calculation is time-consuming that needs notable effort. Therefore, this study aims to generate some useful correlations for soil’s CBR with compaction and consistency parameters for 85 samples of fine-grained soils. The study trials were applied on natural soil samples of various places in Sulaimani Governorate, Northern Iraq. Statistical analysis has been carried out by using SPSS software (Version 28). Soaked CBR is counted, which is important for conditions such as rural roads that remain prone to water for few days. Based on the statistical analysis, there is a significant correlation between LL, PL, PI, MDD, and OMC with CBR as the dependent variable as a single variable equation with R2 of 0.7673, 0.5423, 0.5192, 0.6489, and 0.51, respectively. In addition, the highest value of R2 correlation was obtained between CBR value with consistency and compaction properties as a multiple regression equation with R2 of 0.82. The obtained equations for correlation purposes are successfully achieved and can be used, notably, to estimate CBR value.

Efficiency of application of mineral fertilizers and bacterial preparations on winter barley in the conditions of the Lower Don

Field experiments on ordinary black soil were conducted in 2018-2021 in the Rostov region. The object of research was a variety of winter barley Master. The predecessor is corn for grain. Bacte-rial preparations developed at the All-Russian Institute of Agricultural Microbiology (VNIISHM) in St. Petersburg contain strains of associative microorganisms-nitrogen fixators: Mizorin, Ri-zoagrin, Extrasol. They were applied to barley seeds in the pre-sowing period. It was found that the use of Mizorin (600 g /ha) for seed treatment before sowing against the background of a near-sowing application of nitrogen-phosphorus fertilizer in the form of a mixture of ammophos and ammonium nitrate at a dose of N30P30, nitrogen fertilization by a scattered surface method with ammonium nitrate at a dose of 30 kg/ ha of the active substance increased the increase in grain yield on average for 3 years compared with the control variant by 0.71 t/ ha or by 14.4%. The use of the biological preparation Mizorin without mineral fertilizers against the background of natural soil fertility increased the yield compared to the control variant by 0.31 t /ha or by 6.3%. On av-erage, in 2019-2021, the protein content in winter barley grain in the control variant was 10.7%, which provided a protein harvest equal to 528 kg/ha. Against the background of nitrogen-phosphorus fertilizers at a dose of N30P30 and nitrogen fertilizing at a dose of 30 kg / ha, the max-imum increase in protein content was obtained in the variant with the use of Mizorin, which compared to the control variant was 1.1%, while the protein harvest increased by 138 kg/ha or 26.1%. Keywords: WINTER BARLEY, ORDINARY BLACK SOIL, BACTERIAL PREPARATIONS, MINERAL FERTILIZERS

The effect of toxic metal As on the Matricaria Chamomilla L. medicinal plant

The paper presents an experimental laboratory study of the bioaccumulation of the toxic metal arsenic in the medicinal plant chamomile (Matricaria Chamomilla L.). The study makes a comparison regarding the bioaccumulation capacity of the chamomile plant in which arsenic is found as a unique contaminant, as well as in mixtures of 2, 3, or 4 toxic metals (Cd, Ni and Pb) on a natural soil enriched with metals, compared to the chamomile plant developed on an unpolluted substrate. The tests followed the effects of soil pollution with metals on the germination and development of chamomile. The experimental results indicated that arsenic does not bioaccumulate in the chamomile plant, remaining in the soil. The experiment that was an exception is the one with arsenic as the only contaminant (E1) in which at 90 days, the arsenic content in the chamomile plant was 3.58 mg/kg arsenic, the value that is within normal limits, below the phytotoxic value of 5 mg/kg, but was higher than that determined in the plant from the control test experiment (<0.75 mg/kg). The bioaccumulation factor (BCF) after 90 days, in all experiments, either by a combination of metals or a single contaminant had values lower than 1, indicating that the plant does not accumulate arsenic. The total chlorophyll from the results obtained indicates that the toxicity in the E1 experiment is higher than in the metal mixture.

Activation of Cadmium Under Simulated Solar Illumination and Its Impact on the Mobility of Cd in Flooded Soils

In waterlogged paddy soils, cadmium (Cd) can be precipitated as cadmium sulfide (CdS) under reductive environment, thereby limiting the absorption of Cd by plants. Multiple environmental factors (such as water, pH, Eh, etc.) played a role in the control of Cd mobility and bioavailability. In this study, we investigated the influence of the solar irradiation on the photo-dissolution of synthetic CdS-montmorillonite composites (CdS-M) in solution and the stability of Cdin natural soil. The release kinetic of Cd2+ showed that after the irradiation of simulated sunlight, CdS-M composites became less stable compared to the dark control. The solar irradiation seemed to enhance the release of Cd2+ from CdS significantly and continuously. Electron paramagnetic resonance (EPR) and quenching experiments confirmed that the photogenerated holes, O2·- and •OH were possibly involved in the photo-induced release of Cd2+, while the holes was primarily responsible for the reaction.Irradiation under alkaline solution or the presence of DOM, PO43-, CO32- and urea markedly inhibited the photodissolution process of CdS. The photo-mediated activation of Cd was further confirmed in paddy soil under natural sunlight, with a nearly 3-fold increase in concentration of extractable Cd during the 15 days irradiation. This study highlights the importance of photochemical transformation of Cd in the environmental water and soil.

The Combined Use of Remote Sensing and Wireless Sensor Network to Estimate Soil Moisture in Golf Course

In gardening, particularly in golf courses, soil moisture management is critical for maximizing water efficiency. Remote sensing has been used to estimate soil moisture in recent years with relatively low accuracies. In this paper, we aim to use remote sensing and wireless sensor networks to generate soil moisture indexes for a golf course. In the golf course, we identified three types of soil, and data was gathered for three months. Mathematical models were obtained using data from Sentinel-2, bands with a resolution of 10 and 20 m, and sensed soil moisture. Models with acceptable accuracy were obtained only for one out of three soil types, the natural soil in which natural vegetation is grown. Two multiple regression models are presented with an R2 of 0.46 for bands at 10 m and 0.70 for bands at 20 m. Their mean absolute error was lower than 3% in both cases. For the modified soils, the greens, and the golf course fairway, it was not feasible to obtain regression models due to the temporal uniformity of the grass and the range of variation of soil moisture. The developed moisture indexes were compared with existing options. The attained accuracies improve the current models. The verification indicates that the model generated with band 4 and band 12 is the one with better accuracy.

On a Data-Driven Approach for Detecting Disturbance in the Brazilian Savannas Using Time Series of Vegetation Indices

Remote sensing of disturbance in the savannas from Brazil is challenging, especially due to confounding effects of the vegetation phenology and natural soil exposure on the detection of clearing and fire events. In this study, we investigated the detection of disturbance over this global hotspot of biodiversity using seven vegetation indices (VIs) calculated from the Landsat time series (2017–2019) and the Continuous Change Detection and Classification (CCDC) algorithm. The selected VIs represented distinct biophysical characteristics of the savannas. We evaluated the effects of disturbance on these VIs and assessed the accuracy of CCDC-detection in 2019, considering individual VIs, ensemble VIs, and the type of disturbance (savanna clearing and fire). Finally, we analyzed the possible existence of seasonal patterns of disturbance in a study area located at the new agricultural frontier of the Cerrado biome. The results showed that the overall accuracy of CCDC detection of total disturbance ranged from 51.2% for the Green-Red Normalized Difference (GRND) to 65.9% for the Normalized Burn Ratio (NBR2). It increased to 71.2% for ensemble VIs, whose multivariate approach reduced the omission errors in the analysis when compared to the use of single VIs. For detecting events of savanna clearing and fire, the most important VIs used near-infrared and shortwave infrared reflectance bands on their formulations (NBR2, NBR, and Moisture Stress Index—MSI). The CCDC accuracy was generally higher for detecting clearing than for mapping burned areas. In contrast, the recorded date of disturbance occurrence was less precise for detecting clearing than for recording events caused by fire, especially due to the existence of some gradual processes of vegetation degradation until complete clearing. Our findings showed also the existence of a seasonal pattern of disturbance occurrence. Savanna clearing predominated in the transition from the rainy to the dry season (April to July) to open new areas for agriculture. It preceded most events of fire disturbance between August and October that occurred near the consolidated areas of agriculture and extended into the native vegetation areas. Results reinforce the importance of data-driven approaches for generating early warning alerts of disturbance in the Cerrado to be further checked in the field.

Efficacy of Cicer arietinum L. & Vigna mungo L. in remediation of Hexavalent Chromium

Hexavalent Chromium is a major soil pollutant; thus, its remediation from soil deserves due attention. Phytoremediation is an area of active current research which is eco-friendly and economic. Use of leguminous plants for phytoremediation will improve soil quality, fertility and nutrient balance and would help in restoration of natural soil ecosystem. The present study focuses on the use of two commonly growing legumes; Cicer arietinum (RP1) and Vigna mungo (RP2) to explore their remediation potential towards Cr(VI) with concentration ranging from 100-900 mg kg−1 with the growth up to three weeks and were assessed for remediation potential and toxicity parameters. Higher percentage of decrease in root and shoot length was observed in RP2 as compared to RP1. Chlorophyll content was also found to be decreasing with increasing Cr stress in both the species. RP2 recorded higher BCF than RP1. Highest bioaccumulation factor 4.32 was observed in RP2 at 400 mg kg−1 concentration. Translocation factor >1 was observed in both the plants with highest as 1.67 at 600 mg kg−1 in RP2 and 1.93 at 400 mg kg−1 in RP1. Remediation percentage of 72.25% in RP2 at 600 mg kg−1 and 73.13% at 400 mg kg−1 in RP1 was observed. Both the plants showed high tolerance and remediation potential towards Cr(VI) therefore has a great phytoremediation prospect, however, RP2 can be preferred over RP1.