Soil Solution Research Articles

Water security threats and solutions in the Grande River basin – One of the Brazilian agricultural frontiers

This paper evaluates the effectiveness of sustainable agricultural management solutions at a farm level to mitigate water security threats in one of Brazil's agricultural frontiers – the Grande River basin. The paper addresses future challenges to water security in the river basin and explores how effective solutions are at a farm level to mitigate current and future water security threats at a basin scale. Based on the assessment of multiple drivers, higher future water security threats in the region are predicted in 2040 due to climate change, land use modification and corresponding changes in water use. The paper finds that the Formosa do Rio Preto region, which is not currently water-insecure, may turn into a water security hotspot area by 2040. The effective response index for water security (ERI-WS), based on the qualitative assessment of the impact at the farm scale, is used to evaluate the effectiveness of current sustainable management practices in addressing water security challenges. The water security dimensions approach of the ERI-WS shows that >50 % of the sites have technologies that can have positive impacts on the “Drinking water and human well-being”, “Economic activities and development”, “Ecosystem” and the “Resilience” dimensions. The paper finds that 66 % of the farms have efficient soil, land, and water management solutions (ERI-WS > 0.5) to address current and future water security issues. These solutions range from sustainable grazing land management to integrated plant nutrition management to enhanced soil productivity. However, 15 % of the farms located in vulnerable areas of the municipalities of São Desidério, Barreiras and Catolândia have lower effectiveness. Results also indicate that 36 % of the sites, distributed in 8 municipalities, employ nature-based solutions to mitigate water security threats, mainly those related to water quality conditions in downstream areas, indicating the relevance of these practices in the region.

Straw incorporation induces rice straighthead disease in As-contaminated paddy soil

Rice straw incorporation is globally recognized as a viable alternative to incineration. However, it might lead to arsenic (As) methylation in soils, resulting in increased accumulation of methylated As in rice plants, potentially contributing to the emergence of rice straighthead disease. To evaluate the effect of straw incorporation on the As transformation in the paddy field system, we conducted a pot experiment for rice cultivation in two paddy soils with different As background levels and also characterized the response of the soil microbial community to straw incorporation. The results showed that straw incorporation elevated the total and methylated As concentration within the soil solution and rice plants, which in turn reduced rice seed setting rate and yield, and caused straighthead disorder in rice cultivated in soils with high As levels. 16S rRNA-based sequencing demonstrated reduced abundance and diversity of microorganisms upon adding straw. Notably, the dominant phylum, Bacteroidetes, exhibited a significant increase in abundance due to straw integration, while the abundance of Proteobacteria and Acidobacteria decreased. At the family level, the prevalence of Rikenellaceae increased only in soils contaminated with As following straw incorporation. Redundancy analysis showed positive associations between Rikenellaceae and levels of methylated As present in both soil porewater and rice husks, suggesting a potentially pivotal role of Rikenellaceae in the As methylation process after straw integration. These findings collectively emphasize that including straw can reshape the soil's microbial community and amplify As methylation in the soil, thereby promoting the uptake and accumulation of methylated As in rice and inducing straighthead disease in As-contaminated soil.

Life in the dark: Impact of future winter warming scenarios on carbon and nitrogen cycling in Arctic soils

The high Arctic region is warming faster than other areas globally, with widespread decreases in snow cover and longer growing seasons. This is expected to greatly influence plant-microbial carbon (C) and nitrogen (N) cycling and thus ecosystem functioning, particularly when soils remain unfrozen during the dark winter period and no photosynthesis is possible. To better understand this response, we studied the effects of different winter warming scenarios on soil C and N dynamics. We collected intact soils cores from two contrasting biomes from Svalbard, namely a moss-dominated peat mire and purple saxifrage-dominated dry tundra heath. In the laboratory, we used an Arctic annual light regime and three contrasting winter temperature regimes to simulate a range of climate scenarios: (i) current climate in which the soils were frozen in winter and thawed in the summer, (ii) a year 2050 regime in which the soils were both frozen and thawed in winter, and (iii) a year 2100 regime in which the soils remained unfrozen during winter. We monitored greenhouse gas (GHG) emissions (CO2, CH4 and N2O) and nutrients in soil solution (DOC, NO3−, NH4+, P) over a one-year period. In the peat mire, warmer winters increased CO2 emissions due to increased microbial activity but had little effect on methane or N2O fluxes. Warmer winters also decreased dissolved organic carbon and nutrients in soil solution. In the dry tundra heath, warmer winters increased nitrate availability but did not greatly alter CO2, CH4 or N2O gas fluxes or other nutrients. Warming in the dry tundra health induced earlier spring flowering and shifts in vegetation composition. Overall, we present clear evidence that warmer winter conditions are likely to alter C and N cycling in Arctic soils, with implications for plant productivity and vegetation community composition.

Урожайность и содержание белка в семенах сортов среднерусской однодомной конопли при разных нормах высева в Среднем Предуралье

The article presents the results of scientific research for 2020-2022 on the study of the content and harvesting of protein with the yield of cannabis varieties depending on the seeding rate in the soil and meteorological conditions of the Middle Urals. The soil of the experimental plots in the years of laying the experiments differed in the agrochemical characteristics of the arable layer: low and medium humus content, high and elevated – mobile phosphorus, elevated and very high – mobile potassium. The soil solution had a strongly acidic, medium acidic and close to neutral reaction. On sod-medium-podzolic medium loamy soil, the Vera variety stood out in terms of seed yield, providing seed productivity of 71 g/m2 in 2020, 193 g/m2 in 2021 and 128 g/m2 in 2022 with a crude protein content of 21.6%, 20.2%, 22.4%, respectively, by year. On average, over the years of research, the collection of raw protein with a yield of 291 and 303 kg/ha of the Nadezhda and Vera varieties had 1.2 million units/ha at the seeding rate, Surskaya hemp formed more raw protein in a yield of 273 kg/ha at a seeding rate of 0.8 million units/ha. The seeding rate of 0.4 million units/ha provided the highest 22.0–25.7% crude protein content in hemp seeds. Keywords: HEMP, VARIETY, SEEDING RATE, CRUDE PROTEIN, YIELD, SEEDS

Investigation of iron-reducing and iron-oxidizing bacterial communities in the rice rhizosphere of iron-toxic paddy field: a case study in Burkina Faso, West Africa

ABSTRACT Iron (Fe) toxicity in rice is one of the serious problems in some paddy fields in West African areas. Microbial community structures involved in the redox cycle of Fe have not been revealed in the Fe-toxic paddy fields. The present study investigated the bacterial community structure and the abundance of Gallionellaceae, Geobacteraceae, and Anaeromyxobacteraceae, as the representative indicator bacteria of Fe oxidizers and reducers, in the bulk and rhizosphere soils and rice roots of a Fe-toxic paddy field in Burkina Faso (BF)in 2017–2019. Thosein a paddy field in Anjo, Japan (AN) were also analyzed for comparison. The amplicon sequencing analysis revealed that the BF rhizosphere soil was characterized by typical anaerobic bacterial groups like Firmicutes and Deltaproteobacteria, including several potential Fe reducers. The relative abundance of Gallionellaceae, lithotrophic Fe oxidizers, in the BF rice roots was significantly lower than that in the AN rice roots. Quantitative PCR analysis showed that the ratios of Gallionellaceae to Geobacteraceae and to Anaeromyxobacteraceae were higher in the rice roots than in the soils irrespective of the fields. However, the ratios of Gallionellaceae to Geobacteraceae were lower in the BF soils and roots than in the AN soils and roots. The ratios of Gallionellaceae to Anaeromyxobacteraceae in the BF soils were also lower than those in the AN soils. These findings indicated the relative predominance of Geobacter- and Anaeromyxobacter-related Fe reducers over Gallionellaceae-related Fe oxidizers in the rice rhizosphere of the BF field, corresponding well to the circumstances of Fe-toxic soil: higher Fe(II) amounts in the soil. Since Fe(II)-oxidizing activity at rice roots is an important factor as a primary defense system against Fe(II) in the soil solution, the ratios of Gallionellaceae to Geobacteraceae and to Anaeromyxobacteraceae may serve as an indicator of potential Fe(II)-oxidizing activity of rice rhizosphere. Further studies focusing on the activity of Fe oxidizers and Fe reducers at rice roots under effective cultivation practices and in various types of Fe-toxic paddy fields will help to promote a better understanding of the Fe-toxic soil circumstances and to establish sustainable rice cultivation in the Fe-toxic soils.

Effects of Deep Vertical Rotary Tillage Management Methods on Soil Quality in Saline Cotton Fields in Southern Xinjiang

A long-term high-saline soil environment will limit the improvement of soil quality and cotton yield. Modified tillage management measures can improve soil quality, and the establishment of a soil quality evaluation system will facilitate evaluation of the soil quality and land production potential in southern Xinjiang. The objective of this study was to determine the effects of different tillage management methods on soil quality in saline cotton fields in southern Xinjiang. A three-year experiment was conducted in Tumushuke, Xinjiang, with different deep vertical rotary tillage depths (DTM20, 20 cm; DTM40, 40 cm; DTM60, 60 cm) and conventional tillage (CTM, 20 cm). The soil quality index (SQI) under different tillage management methods was established by using the full dataset (TDS) with a scoring function for eight indicators, including physicochemical properties of the soil from 0 to 60 cm, to evaluate its impact on the soil quality of the saline farmland in southern Xinjiang. The results of the study showed that deep vertical rotary tillage management can effectively optimize soil structure; reduce soil bulk density (BD), soil solution conductivity (EC), and pH; and promote the accumulation of soil organic carbon (SOC) and total nitrogen (TN) in the soil. However, the average diameter of soil water-stable aggregates (MWD) in a 0–60 cm layer becomes smaller with an increasing depth of tillage. This does not reduce crop yields but does promote soil saline leaching. In addition, the significant linear relationship (p < 0.001) between seed cotton yield and soil quality indicated that improving soil quality was favorable for crop yield. The principal component analysis revealed BD, MWD, pH, and EC as limiting sensitive indicators for seed cotton yield, while SOC and TN were positive sensitive indicators. The soil quality index (SQI) values of DT40 and DTM60 were significantly higher than that of CTM by 11.02% and 15.27%, respectively. Overall, the results show that DTM60 is the most suitable tillage strategy to improve soil quality and seed cotton yield in this area, and this approach will provide a reliable theoretical basis for the improvement of saline farmland.

A controlled experiment to verify the effect of magnesium fertilizers on soil pH and available soil nutrients in acid soil of Nilgiris, India

An incubation experiment was conducted in laboratory conditions for 60 days to observe the impact of different Magnesium fertilizers on soil chemical properties, i.e. pH, available nitrogen, phosphorus, potassium, and DTPA extractable micronutrient cations. A complete factorial complete randomized block design (FCRD)with two replications and six levels was selected as the experimental layout. The levels included were (L0) Absolute control (L1) soil + Mg @ 10 kg ha-1, (L2) soil + Mg @ 20 kg ha-1, (L3) soil + 30 kg ha-1, (L4) soil + 40 kg ha-1, (L5) soil + 50 kg ha-1. Findings revealed that applying magnesium fertilizers to soil significantly (p ≤ 0.05) affects soil parameters. The impacts of magnesium fertilization on soil pH altered with sources and incubation period. The application of CaMg(CO3)2 @ 50 kg ha-1 recorded significantly (p ≤ 0.05) higher soil pH (5.67) as compared to MgCO3 @ 50 kg ha-1 that increased the pH up to 5.57 due to the impact of carbonate ion whereas MgSO4.7H2O decreased the soil up to 4.80 because of dissolution of SO42- ions to the soil solution. Applying CaMg(CO3)2 significantly (p ≤ 0.05) influenced soil available N, P, K, Fe, Mn, and Cu content which is due to the decrease in acidity, which indirectly enhanced the nutrient availability. The positive effects persisted throughout the experimental duration, indicating the potential long-term benefits of magnesium fertilization in acid soil management. This study contributes to the current body of knowledge by providing novel insights into applying magnesium fertilizers as an effective strategy for addressing soil acidity and improving nutrient availability in acid soil.

Lysimeter Sampling System for Optimal Determination of Trace Elements in Soil Solutions

Understanding trace element (TE) composition and behavior in soil solution is extremely important for assessing ecological and human health impacts. Using lysimeters to collect soil solution with minimum alteration to the in situ phase distribution and concentration of TEs will facilitate a more accurate assessment. However, different lysimeter materials and sampling conditions may lead to vastly different results, demonstrating the need for the optimal choice of lysimeter depending upon environmental conditions. There is no general agreement or overview discussing the best lysimeter type and sampling system to use under various conditions. This review provides a critical summary of various lysimeters that can be used to collect soil solutions for the analysis of TEs and thereby provides key guidance for developing the best lysimeter sampling system for conditions and research questions of interest. This includes a range of aspects related to lysimeters, such as different types and materials, the basic principles of design and operation, advantages and disadvantages, challenges and limitations, techniques for cleaning and pretreatment, correct installation procedures, the influence of soil physical and chemical properties on sampling, and existing research gaps within this field.

Point of Zero Charge of Soils - It’s Dynamics under Fertilizer Management Practices and Nutrient Availability

Aims: To study the dynamics of point of zero charge of different soil types and determine the availability of nutrients under the influence of specific fertilizer management practices.
 Study Design: Completely Randomized Design.
 Place and Duration of Study: Department of Soil Science, Assam Agricultural University, Jorhat, Assam; between March 2020 and December 2021.
 Methodology: We estimated the point of zero charge (PZC) components, i.e., the point of zero salt effect (PZSE) and point of zero net charge (PZNC) in six surface soil samples [black soil (Vertisol), laterite soil (Alfisol), red soil (Alfisol) of Odisha, and alluvial soils belonging to Entisol, Inceptisol, and Alfisol of Assam, India] through potentiometric titration and ion retention methods respectively. The soils were subjected to four specific fertilizer management practices under laboratory incubation, viz., FYM @ 5 t ha-1 (T1), NPK @ 80:40:40 for Odisha soils and 60:20:40 for Assam soils (T2), T1 + T2 (T3) and T3 + Lime requirement/ Gypsum requirement (T4). The PZC components and availability of nutrients were determined at 15 and 30 days after incubation.
 Results: The PZSE values of the soils ranged from 2.18 to 4.70, while PZNC values were achieved at relatively lower pH ranging from 2.03 to 4.10. Highest values of PZSE and PZNC were recorded under treatment T2 followed by T3, T4 and T1 for all the incubated soil samples, however there was a decrease in the PZC values with increase in days of incubation. Comparatively, the treatment T4 resulted as the most ideal fertilizer management practice. Besides providing optimum amount of primary and maximum amount of secondary nutrients, T4 regulated the PZC values favouring minimal loss of nutrients and enhanced nutrient use efficiency. The availability of nutrient ions is influenced by the difference between soil solution pH and PZC values of the soil, which recorded to be highest for Vertisol (OS1), followed by Entisol (AS1), Inceptisol (AS2), and Alfisol (AS3, OS2, OS3) soil orders.
 Conclusion: The exchange and availability of cationic nutrients get enhanced due to higher CEC in soils with high clay and organic matter percentage. The pH of these soils must therefore be regulated for better availability of anionic nutrients. Highly weathered soil of Alfisol order exhibit optimal CEC over a narrow pH range, favouring better availability of anionic nutrients and hence simultaneously require frequent fertilizer application along with organic manures for the enhanced retention, mobility and availability of nutrients in soil.

Bioavailability of Cd in Agricultural Soils Evaluated by DGT Measurements and the DIFS Model in Relation to Uptake by Rice and Tea Plants

The elevated accumulation of cadmium (Cd) in rice (Oryza sativa L.) and tea (Camellia sinensis L.) grown in agricultural soils may lead to a variety of adverse health effects. This study collected and analyzed crop samples along with paired rhizosphere soil samples from 61 sites in Cd-contaminated regions in Anhui Province, China. The findings revealed that both the diffusive gradients in thin-films (DGT) and soil solution were capable of effectively predicting Cd contents in crops. Conventional chemical extraction methods were inappropriate to evaluate the bioavailability of Cd. However, the effective concentrations (CE) corrected by the DGT-induced fluxes in soils (DIFS) model exhibited the strongest correlation with crop Cd contents. Except for CE, various measurement methods yielded better results for predicting Cd bioavailability in tea compared to rice. Pearson’s correlation analysis and the random forest (RF) model identified the key influencing factors controlling Cd uptake by rice and tea, including pH, soil texture, and contents of zinc (Zn) and selenium (Se) in soils, which antagonize Cd. To reduce the potential health risk from rice and tea, the application of soil liming and/or Se-oxidizing bacteria was expected to be an effective management strategy.

The structure of beta-diversity explains why the relevance of phytoindication increases under the influence of park reconstruction

Urbanization causes the highest local extinction rates and often leads to the loss of the vast majority of native species. Plant communities are sensitive to urban expansion and are therefore indicators of human land use. A city park, part of which has undergone reconstruction, was studied. The study found that the changes in ecological conditions caused by the reconstruction of a city park can be detected using phytoindication. The informativeness of phytoindication scales was shown to increase under conditions of anthropogenic load. The phytoindication scales are a reliable source of information for assessing the state of the vegetation cover of park plantations. The ecological regimes were assessed based on descriptions of the vegetation cover using Didukh's phytoindication scales. The phytoindication approach allows one to identify changes in ecological regimes that occur as a result of park reconstruction and to separate them from ecological regimes of natural origin. The study showed that the reconstruction of the park significantly affects the conditions of the park and the diversity of vegetation. The ratio of useful phytoindicative information compared to information noise in the structure of beta-diversity of the park's plantations increases significantly as a result of the park's reconstruction. The reconstruction of the park has led to changes in the spatial organization of the vegetation cover. The results obtained indicate a decrease in soil moisture as a result of the park's reconstruction. The park’s reconstruction leads to a significant change in the light regime of the park’s plantings, which leads to changes in the park’s vegetation and soils. Reducing the density of plantations as a result of their pruning during the reconstruction process also decreases the amount of fallen leaves that form leaf litter. A significant increase in the variability of the moisture regime under the influence of the park reconstruction was found. The phytoindication revealed a decrease in the acidity of the soil solution as a result of the reconstruction. The changes in soil acidity are accompanied by an increase in phytoindication estimates of carbonate content in the soil. The observed increase in carbonate content estimates may be an artifact when representatives of another ecological group also have related ecological properties that can be misinterpreted as indicators of certain regimes. The phytoindication also revealed trends in the variability of microclimatic conditions in the park as a result of reconstruction. The reconstruction of the park leads not only to a change in the modal levels of ecological regimes, but also to the formation of specific patterns of their spatial distribution. The heterogenization of the ecological space under the influence of reconstruction has been established. This heterogenization is evident in the fact that areas with homogeneous vegetation cover are decreasing. The accuracy of the description of the spatial process was found to have decreased after the park reconstruction procedures. Smooth spatial structures of the park’s vegetation cover without reconstruction are changing into rough spatial structures of the park after reconstruction. The park’s reconstruction obviously disrupts the course of long-term processes that structure the vegetation cover, which leads to temporal and spatial desynchronization of the dynamics of ecological processes. The spatial variation of variables that indicate soil processes can best be described. In contrast, the phytoindication scales that indicate climatic factors are much less spatially structured. The best variogram model to describe the spatial process is also changing under the influence of reconstruction. The significant consequences of the park reconstruction are time variability and spatial heterogeneity of ecological processes.

Assessing Soil Dynamics and Improving Long-Standing Irrigation Management with Treated Wastewater: A Case Study on Citrus Trees in Palestine

Irrigation with Treated Wastewater (TWW) is a well-known agricultural practice in Palestine. The long-term use of irrigation with TWW, a source of water and nutrients, can affect plant development, soil, and groundwater quality. Consequently, the frequency and the intervals of irrigation events should be adequately scheduled, especially when nutrients (TWW-N) cannot be separated from the water. Achieving good water quality implies its immediate reuse in irrigated agriculture. In contrast, long-term soil and groundwater quality conservation is marked by the complex mechanisms that correlate the soil, water, plant, and atmosphere. Therefore, monitoring and modeling (MMA) are combined to retrieve the soil water and nitrate fluxes and identify a proper irrigation management plan in a case study in Beit Dajan-Palestine, where a schedule adapted to conventional water was applied to a 6-year-old citrus orchard continuously irrigated with TWW. Soil nitrogen concentration and water content data were collected from March to August 2021 to calibrate the Hydrus-1D model under the (1) farmer demand (F) scenario, where irrigation volumes are delivered according to the farmer experience, and to define an optimal irrigation management strategy with TWW according to the (2) model demand (M) scenario, based on the irrigation frequency. The latter respects the allowable thresholds of soil solution electrical conductivity, σe, assuming an average soil salinity profile and estimated leaf nitrogen concentrations tolerance as reference; 2021 was taken as a calibration year to retrieve water and nitrate fluxes for 2019 and 2020. In 2021, the measured soil electrical conductivity, σe, showed no salinity risk with an average value of 1.07 dS m−1 (low salinity < 2 dS m−1) but with a leaf nitrogen deficit. Although an acceptable level of available soil nitrogen was observed (ranging between 10 and 35 mg kg−1, whereas the standard value is 10–40 mg kg−1), critical concentrations were observed in the leaves (below 1%) in scenario (F) compared to scenario (M) (ranging between 1.7 and 1.9%). The latter also showed a decrease in nitrate leaching by 33% compared to the former. Overall, the comparison between the simulated and measured soil variables shows that the 1D-Hydrus model could follow the temporal variation in the monitored data, with some overestimation of the measured data during the simulation period. The simulations demonstrate that by modulating the salt tolerance threshold, the M scenario achieved better results in terms of root water and N uptake despite the stress inevitably experienced by citrus with long-term TWW irrigation. Moreover, the optimum threshold values used to assess the soil quality and citrus response under conventional water irrigation were inadequate for TWW practices. Therefore, MMA could be an alternative strategy to schedule proper TWW irrigation.

Transport and Model Calculation of Microplastics Under the Influence of Ionic Type, Strength, and Iron Oxide

Microplastics (MPs) in soil have attracted extensive attention as an emerging pollutant, and the transport of MPs is affected by their own physical and chemical properties, the chemical composition of soil solutions, and soil minerals. However, in the presence of oxides, the underlying mechanism for the transport of MPs in different ionic types and ionic strengths is still not fully understood. In this study, the effects of ionic type, ionic strength, and iron oxide on the transport of polystyrene microplastics (PSMPs) with different functional groups were investigated through stability experiments and transport experiments. The colloid transport model, CD-MUSIC model, and DLVO theory were used to explore the transport mechanism. The results showed that normalized concentrations (c/c0) of PSMPs were 0.99 in the NaH2PO4 background and 0.94 in the CaCl2 background, respectively, which indicated that the strongest stability of PSMPs was observed in the former and the weakest in the latter. Different ionic types had different effects on the transport of PSMPs. For the cations Na+ and Ca2+, Ca2+ strongly inhibited PSMPs transport in pure quartz sand because of the bridging effect and strong charge neutralization effect; the recovery rate of the PSMPs in the effluent was (43.83±1.71)%, and a first-order retention coefficient on the second kinetic Site-2 (k2a) was 1.54 min-1. The presence of iron oxide enhanced the inhibition, the recovery rate of the PSMPs in the effluent decreased to (6.04±0.40)%, and k2a increased to 5.33 min-1. For the anions Cl- and PO43-, the transport of PSMPs in pure quartz sand was dominated by surface electronegativity of PSMPs, and PSMPs exhibited lower electronegativity under Cl- background and thus showed higher recovery[(92.95±0.63)%] and lower k2a (0.19 min-1). However, in the presence of iron oxides, the Zeta potential of the quartz sand surface was the controlling factor for PSMPs transport. According to results of the CD-MUSIC model, PO43- could be easily adsorbed on the iron oxide surface to form innersphere complexes, which reduced the surface electronegativity of the iron-loaded quartz sand and enhanced the transport of PSMPs, higher recovery[(76.22±1.39)%], and lower k2a (0.66 min-1). Moreover, the species of the formed innersphere complex was controlled by the PO43- concentration, and different species of innersphere complexes had distinct negative surface charges. Higher surface electronegativity of the iron-loaded quartz sand was observed under higher PO43- concentration, which was not conducive to the transport of PSMPs. Further, the transport ability of PSMPs decreased with the increase in ionic strength. Finally, the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to calculate the variation in the primary barrier between PSMPs and the collector under the conducted experimental conditions, which helped better elucidate the transport behavior of PSMPs. The variation in the primary barrier was consistent with the transport ability of PSMPs, and a higher primary barrier indicated a larger repulsion between PSMPs and the collector, which was in favor of PSMPs transport.

Chemical features and biological effects of degradation products of biodegradable plastics in simulated small waterbody environment

A plethora of research has focused on the biosafety of biodegradable plastics (BPs), including their microplastic formation and additives leaching; however, relatively fewer studies have explored biodegradation products. This study aims to investigate the biological effects and chemical features of degradation products from three kinds of BPs, namely polyglycolic acid (PGA), poly (butylene adipate-co-terephthalate) (PBAT), and the blends of PGA/PBAT without the addition of additives, in a simulated small waterbody environment with extracted soil solution for three months. Results showed that exposure to the whole degradation remnants of three BPs had no lethal effects on zebrafish at the current BP environmental concentrations (from 0.24 to 12.72 mg plastic/L) in small waterbodies. However, from the calculated BPs environmental concentrations (from 0.57 to 43.82 mg plastic/L) in 2026, PGA and PGA/PBAT blends may cause adverse effects on the cardiovascular system such as heartbeat rate suppression in zebrafish embryos, and also lead to reduced body length and pericardial edema and spinal curvature in fish larvae. We further qualitatively analyzed the composition of degradation products, and quantitatively measured four dominant degradation monomers (glycolic acid (GA), adipic acid (A), 1,4-butanediol (B), and terephthalic acid (T)) in the degradation remnants. It was found that the observed toxicities were probably due to the presence of GA, A, and T monomers, and their concentrations can reach 0.776, 0.034, and 0.6 mg/L under the calculated future scenario, respectively. It is worth mentioning that either GA or T monomers at the above concentrations were found to cause suppressed heartbeat rate in zebrafish embryos. Collectively, though the degradation products of BPs are temporarily safe at current environmental concentrations, they may lead to non-negligible toxicity with increasing production and continual improper recycling and/or BP waste management.

Effects of blast furnace slag on the immobilization, plant uptake and translocation of Cd in a contaminated paddy soil

The potential toxicity of Cd to soil and rice plant severely threaten human health. This study was conducted to investigate the remediation effects of blast furnace slag (BFS) on the bioavailability of Cd in a contaminated paddy soil from a perspective of soil solution chemistry. Batch experiments, pot culture experiments, and principal analysis (PCA) were used to study the effects and mechanisms of BFS addition changing Cd chemical behavior and Cd toxicity. Results indicated that BFS facilitated Cd adsorption in soils, increased pH, Eh, and EC values in soil solution, whereas reduced dissolved Cd content. BFS amendment was efficient in decreasing root Cd intake and Cd upward transport in rice plant, with the Cd translocation factor in brown rice decreased by ∼ 75% (BFS treatment, 6‰ wt) relative to Cd treatment, which in turn increased rice biomass and grain yield. PCA indicated that the dissolved Cd concentration had a close relationship with soil pH and metal concentration in soil solution. Results from this study indicated that BFS had potential ability for either immobilization or remobilization of Cd in soils, and the findings have important implications for Cd-polluted soil remediation or other resource utilization with slag-based materials.

Short‐term phosphorus sorption and desorption in contrasting cropped Vertisols

AbstractVertisols are important cropping soils in tropical and subtropical areas, but in many regions, decades of cropping has substantially reduced concentrations of plant‐available phosphorus (P), especially in the subsoil layers. Phosphorus behaviour in P‐depleted Vertisols has received comparatively little attention, and the availability of P following the addition of inorganic P fertilisers at different concentrations is poorly understood. In this study, we evaluated short‐term P sorption and desorption behaviour in cropped Vertisols in relation to specific soil physical and chemical properties. We collected the surface and subsurface of 15 Australian soils with a broad range of physical and chemical properties, comprising nine Vertisols, three Ferralsols, two Lixisols and one Calcisol. For each soil, we generated sorption and desorption curves (fitted with a Freundlich equation), determined soil physical and chemical properties likely to influence P sorption and evaluated the relationships between the measured soil properties and the Freundlich equation sorption coefficients. The P sorption curves differed drastically between soils, with the sorption equation coefficients (aS × b) significantly correlated with the P buffering index (PBI) and clay content. Clay content itself was correlated with citrate‐extractable Fe and Al oxides and BET surface area. Vertisols formed on basaltic parent materials had greater Fe and Al oxide concentrations, resulting in an overall greater P sorption capacity. Sorption and desorption hysteresis were mostly small. The reacting materials in these soils probably had limited ability to continue to react with P. The Vertisols differed in their capacity to replenish P in the soil solution by desorbing different proportions of previously sorbed P, although the proportion of desorbable P generally increased with greater concentrations of sorbed P. These results suggest that for fertiliser management in these soils, smaller volumes of P enrichment combined with higher P concentrations may result in a greater P recovery by the crop.

Release of glucose from dissolved and mineral‐bound organic matter by enzymatic hydrolysis

AbstractSorption of dissolved organic matter (DOM) by poorly crystalline minerals during their formation may protect large amounts of carbon in soils from mineralization. We investigated the bioavailability of carbohydrates in DOM and after co‐precipitation with short‐range ordered aluminosilicates. Carbohydrates originated from soil solutions collected in situ at two depths of a Dystric Cambisol, and from litter extracts. Quantification of substrate‐specific degradability was achieved by the addition of β‐glucosidase at an optimal concentration and subsequent determination of glucose release. Depending on DOM composition, 0.6–41.4 mg g−1 C−1 of glucose was enzymatically released from dissolved carbohydrates. Co‐precipitated carbohydrates were partially accessible, resulting in a glucose release of 0.7–5.2 mg g−1 C−1. Restricted enzymatic depolymerization due to co‐precipitation may contribute to accumulation of easily degradable substrates in soils.

Effect of Different Irrigation Managements on Infiltration Equations and Their Coefficients

The main aim of this paper was to analyze the sensitivity of the five infiltration equations (Kostiakov, Kostiakov–Lewis, Philip, Horton and SCS) and their coefficients to various ponding depths and initial soil moisture under different irrigation managements. The treatments included three qualities of water (electrical conductivity = 6, 3 and 0.6 dS/m), two managements of irrigation (intermittent irrigation and daily irrigation) and three irrigation periods (100, 45 and 8 days). The HYDRUS-1D model was calibrated to simulate infiltration in various initial soil moistures and ponding depths. Evaluating the performance of infiltration equations showed that the Horton and Kostiakov–Lewis had better accuracy and Kostiakov and SCS had less accuracy than the other equations. The empirical coefficients of SCS and Kostiakov had the most and least sensitivities, respectively. Furthermore, Horton was the most sensitive equation, while SCS was the least sensitive one. The output parameters under daily management were the most sensitive to variations in infiltration coefficients, especially when the salinity and sodium contents of water and soil were higher. The results also showed that the effect of the initial soil moisture on the infiltration coefficient in high permeable soil (arising from daily management) was greater; but in low permeable soil (arising from intermittent management), the ponding depth was more effective. It is concluded that the infiltration equations (specifically the SCS equation) and their coefficients (specifically coefficient c) should be calibrated relative to the initial soil moisture, ponding depth, soil solution and water irrigation quality. Particularly in areas with high permeable soil (in the daily management), the calibration of the infiltration equation should be conducted with the initial soil moisture. In these areas, the irrigation period should be controlled. In areas with low permeable soil (in intermittent management), calibration should be carried out relative to the ponding depth. In these areas, the inflow rate should be controlled.

The Mixture of Legumes and Gramineous as Green Manure and Its Effect on Nutrient Efficiency and Soil Solution Characteristics in Three Successive Crops

The Mixture of Legumes and Gramineous as Green Manure and Its Effect on Nutrient Efficiency and Soil Solution Characteristics in Three Successive Crops

Sorption, leaching, and degradation of dicamba in two Brazilian soils: A study into soil layers

Understanding the behavior in soil of soluble and mobile herbicides, such as dicamba, is essential for efficient weed management. Thus, the objective of the research was to understand the sorption, leaching and degradation processes of dicamba along the profile of two Brazilian soils (Oxisol and Ultisol). The Oxisol collected is a very deep soil, the A horizon was collected in a layer of 0.10 m deep, the B horizon 2.0 m and the C horizon ranging from 5.0 to 6.0 m. In contrast, the Ultisol presents a difference between the most superficial horizons, the A horizon was collected at a depth of 0.10 m, the B horizon at around 1.0 m depth and the C horizon at a depth of 2.0–3.0 m. A High-Performance Liquid Chromatography (HPLC) was used to determine the herbicide in the soil solution. The Freundlich sorption coefficient (Kf) values of dicamba ranged from 0.53 to 0.88 mg (1-1/n) L1/n kg−1 in Oxisol and 0.25–0.69 mg (1-1/n) L1/n kg−1 in Ultisol, indicating a low sorption capacity of the herbicide in all profiles. The dicamba mobility index was higher in the Ultisol, ranging from 4.22 to 65.8 compared to the Oxisol, which ranged from 0.46 to 8.10. The degradation half-life time (DT50) of dicamba was short (∼4 days) in the A horizon of both soils compared to the other horizons. Moreover, persistence in the B and C horizons was higher in Oxisol (182 and > 250 days) compared to Ultisol (85.6 and 52.1 days, respectively). The sorption and mobility index of dicamba showed a correlation with soil pH and DT50 values, depending on the organic matter (OM) content. The recommendation of use of dicamba should consider the physical and chemical attributes of the soil as an alternative to reduce the risk of environmental contamination.