Integrated Ca, Mg, Cu, and Zn supply upregulates leaf anatomy and metabolic adjustments in Eucalyptus seedlings

Adaptive responses to abiotic stresses such as soil acidity in Eucalyptus-the most widely planted broad-leaf forest genus globally-are poorly understood. This is particularly evident in physiological and anatomical disorders that inhibit plant development and wood quality. We aimed to explore how the supply of Ca and Mg through liming (lime), combined with Cu and Zn fertilization (CZF), influences physiological and anatomical responses during Eucalyptus grandis seedlings growth in tropical acid soil. Therefore, related parameters of leaf area and leaf anatomy, stomatal size, leaf gas exchange, antioxidant system, nutrient partitioning, and biomass allocation responses were monitored. Liming alone in Eucalyptus increased specific leaf area, stomatal density on the abaxial leaf surface, and Ca and Mg content. Also, Eucalyptus exposed only to CZF increased Cu and Zn content. Lime and CZF increased leaf blade and adaxial epidermal thickness, and improved the structural organization of the spongy mesophyll, promoting increased net CO2 assimilation, and stomatal conductance. Fertilization with Ca, Mg, Cu, and Zn positively affects plant nutrition, light utilization, photosynthetic rate, and antioxidant performance, improving growth. Our results indicate that lime and CZF induce adaptive responses in the physiological and anatomical adjustments of Eucalyptus plantation, thereby promoting biomass accumulation.

The enhanced weathering potential of a range of silicate and carbonate additions in a UK agricultural soil

Enhanced weathering (EW) is a carbon dioxide removal (CDR) technology which aims to accelerate silicate and/or carbonate weathering in agricultural land. At present, the rate and magnitude of CDR from EW remains uncertain. In this study, soil cores extracted from a typical UK agricultural site in Oxfordshire were used to geochemically assess the efficacy of EW while simulating field conditions. Six material "treatments" were applied to soil cores at a rate equivalent to 50 t ha-1: agricultural lime (aglime), basalt, cement kiln dust (CKD), olivine, steel slag, and volcanic ash. A range of chemical measurements were used to constrain the rate of dissolution, fate of dissolution products, and the CDR potential and environmental impact of treatment. After a single application, the CDR rates were, in decreasing order: steel slag (20 ± 4 kgCO2 ha-1 yr-1) > CKD (16 ± 4 kgCO2 ha-1 yr-1) > basalt (5 ± 3 kgCO2 ha-1 yr-1) > volcanic ash (3 ± 3 kgCO2 ha-1 yr-1) > aglime (2 ± 1 kgCO2 ha-1 yr-1) > olivine (0 ± 2 kgCO2 ha-1 yr-1). Despite its drawdown potential, steel slag addition is not advised because application raised the dissolved concentration of heavy metals in the soil. CKD application will be limited due to availability of this material. Liming of agricultural soil is normally considered a source of CO2, but this study indicates liming could cause CDR in some UK soil conditions. Extrapolating from this site to a wider scale supports the conclusions of recently published research which suggests 10 years of basalt application over UK cropland could remove 1.8 ± 0.9 MtCO2 yr-1. Given the low rates of CDR observed in this study, EW is only likely to be worthwhile, at least in soil and climate conditions common to SE England, where there are co-benefits beyond carbon uptake.

Mitigation effects of foliar supply of different sulfur forms on uptake, translocation and grain accumulation of Cd and As by paddy rice on basis of liming

Co-contamination of Cd and As in strongly acidic paddy soil has posed great challenges for remediation practice due to their distinct properties. Liming is a necessary but inadequate measure for normal growth of paddy rice and for Cd and As remediation in strongly acidic paddy soils rich in iron minerals. A greenhouse rice pot cultivation experiment was conducted to explore the efficiency and mechanisms of how foliar supply of different sulfur forms (K2S, K2SO4) could further mediate the uptake, translocation and grain accumulation of Cd and As by paddy rice on basis of liming. Results showed that compared to liming alone (CK), co-application of liming and foliar supply of K2S (L + FK2S) significantly reduced contents of Cd and As in brown rice by 44.4 % and 24.7 %, respectively. Contrastingly, co-application of liming and foliar supply of K2SO4 (L + FK2SO4) decreased Cd content of brown rice by 55.5 %, but had no effect on As content. Foliar supply of K2S and K2SO4 dramatically facilitated Cd upward transfer from roots to shoots by enhancing root Cd transfer from cell wall into trophoplast. On the other hand, both sulfur forms remarkably elevated sulfur contents in leaves and significantly inhibited Cd translocation from leaves to grain by enhancing vacuolar sequestration of Cd in leaves. Compared to CK and L + FK2SO4 treatment, it was by enhancing glutathione synthesis, cell wall deposition in roots and vacuolar sequestration of As in leaves that L + FK2S showed greater inhibiting effects on transfer of As from roots, stems and leaves to grain. Foliar supply of either sulfate or sulfide could efficiently decrease grain Cd of paddy rice, but only foliar supply of sulfide is effective in reducing grain As.

Improving fertilizer response of crop yield through liming and targeting to landscape positions in tropical agricultural soils

Nutrient management research was conducted across locations to investigate the influence of landscape position (hill, mid-, and foot slope) in teff (Eragrostis tef) and wheat (Triticum aestivum) yield response to fertilizer application and liming in the 2018 and 2019 cropping seasons. The treatments included 1) NPS fertilizer as a control treatment (42 N + 10P + 4.2S kg ha^-1 for teff and 65 N + 20P + 8.5S kg ha^-1 for wheat); 2) NPS and potassium (73 N + 17P + 7.2S + 24 K kg ha^-1 for teff and 103 N + 30P + 12.7S + 24 K kg ha^-1 for wheat) and 3) NPSK and zinc (73 N + 17P + 7.2S + 24K + 5.3Zn kg ha^-1 for teff and 103 N + 30P + 12.7S + 24K + 5,3Zn kg ha^-1 for wheat) in acid soils with and without liming. Results showed that the highest teff and wheat grain yields of 1512 and 4252 kg ha^-1 were obtained at the foot slope position, with the respective yield increments of 71% and 57% over the hillslope position. Yield response to fertilizer application significantly decreased with increasing slope owing to the decrease in soil organic carbon and soil water content and the increase in soil acidity. The application of lime with NPSK and NPSKZn fertilizer increased teff and wheat yields by 43-54% and 32-35%, respectively compared to the application of NPS fertilizer without liming where yield increments were associated with the application of N and P nutrients. Orthogonal contrasts revealed that landscape position, fertilizer application, and their interaction effects were significant on teff and wheat yields. Soil properties including soil pH, organic carbon, total N, and soil water content were increased down the slope, which might be attributed to sedimentation down the slope. However, available P is yet very low both in acidic and non-acidic soils. We conclude that crop response to applied nutrients could be enhanced by targeting nutrient management practices to agricultural landscape features and addressing other yield-limiting factors such as soil acidity and nutrient availability by conducting further research.

Can simultaneous immobilization of arsenic and cadmium in paddy soils be achieved by liming?

Liming acidic paddy soils to near-neutral pH is the most cost-effective strategy to minimize cadmium (Cd) accumulation by rice. However, the liming-induced effect on arsenic (As) (im)mobilization remains controversial and is called upon for further investigation, particularly for the safe utilization of paddy soils co-contaminated with As and Cd. Here, we explored As and Cd dissolution along pH gradients in flooded paddy soils and extracted key factors accounting for their release discrepancy with liming. The minimum As and Cd dissolution occurred concurrently at pH 6.5-7.0 in an acidic paddy soil (LY). In contrast, As release was minimized at pH < 6 in the other two acidic soils (CZ and XX), while the minimum Cd release still appeared at pH 6.5-7.0. Such a discrepancy was determined largely by the relative availability of Fe under overwhelming competition from dissolved organic carbon (DOC). A mole ratio of porewater Fe/DOC at pH 6.5-7.0 is suggested as a key indicator of whether co-immobilization of As and Cd can occur in flooded paddy soils with liming. In general, a high mole ratio of porewater Fe/DOC (≥ 0.23 in LY) at pH 6.5-7.0 can endow co-immobilization of As and Cd, regardless of Fe supplement, whereas such a case is not in the other two soils with lower Fe/DOC mole ratios (0.01-0.03 in CZ and XX). Taking the example of LY, the introduction of ferrihydrite promoted the transformation of metastable As and Cd fractions to more stable ones in the soil during 35 days of flooded incubation, thus meeting a class I soil for safe rice production. This study demonstrates that the porewater Fe/DOC mole ratio can indicate a liming-induced effect on co-(im)mobilization of As and Cd in typical acidic paddy soils, providing new insights into the applicability of liming practice for the paddy soils.

Panarchy suggests why management mitigates rather than restores ecosystems from anthropogenic impact

Panarchy, a model of dynamic systems change at multiple, interconnected spatiotemporal scales, allows assessing whether management influences ecological processes and resilience. We assessed whether liming, a management action to counteract anthropogenic acidification, influenced scale-specific temporal fluctuation frequencies of benthic invertebrates and phytoplankton assemblages in lakes. We also tested whether these fluctuations correlated with proxies of liming (Ca:Mg ratios) to quantify scale-specific management effects. Using an ecosystem experiment and monitoring data, time series analyses (1998-2019) revealed significant multiscale temporal (and thus panarchy) structure for littoral invertebrates across limed and reference lakes. Such patterns were inconsistent for sublittoral invertebrates and phytoplankton. When significant panarchy structure was found, Ca:Mg ratios correlated with only a few of the identified temporal fluctuation frequencies across limed and reference lakes. This suggests that liming effects become diluted in the managed lakes. The lack of manifestations of liming across the independent temporal fluctuation patterns suggest that this lake management form fails to create and enforce cross-scale interactions, a crucial component of ecological resilience. This interpretation supports liming as a mitigation effort rather than a tool to restore acidified lakes to a self-organizing system equivalent of circumneutral references.

Long-term trends in yield variance of temperate managed grassland

The management of climate-resilient grassland systems is important for stable livestock fodder production. In the face of climate change, maintaining productivity while minimizing yield variance of grassland systems is increasingly challenging. To achieve climate-resilient and stable productivity of grasslands, a better understanding of the climatic drivers of long-term trends in yield variance and its dependence on agronomic inputs is required. Based on the Park Grass Experiment at Rothamsted (UK), we report for the first time the long-term trends in yield variance of grassland (1965-2018) in plots given different fertilizer and lime applications, with contrasting productivity and plant species diversity. We implemented a statistical model that allowed yield variance to be determined independently of yield level. Environmental abiotic covariates were included in a novel criss-cross regression approach to determine climatic drivers of yield variance and its dependence on agronomic management. Our findings highlight that sufficient liming and moderate fertilization can reduce yield variance while maintaining productivity and limiting loss of plant species diversity. Plots receiving the highest rate of nitrogen fertilizer or farmyard manure had the highest yield but were also more responsive to environmental variability and had less plant species diversity. We identified the days of water stress from March to October and temperature from July to August as the two main climatic drivers, explaining approximately one-third of the observed yield variance. These drivers helped explain consistent unimodal trends in yield variance-with a peak in approximately 1995, after which variance declined. Here, for the first time, we provide a novel statistical framework and a unique long-term dataset for understanding the trends in yield variance of managed grassland. The application of the criss-cross regression approach in other long-term agro-ecological trials could help identify climatic drivers of production risk and to derive agronomic strategies for improving the climate resilience of cropping systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13593-023-00885-w.

Soil pH-increase strongly mitigated N2O emissions following ploughing of grass and clover swards in autumn: A winter field study

Emissions from crop residues contribute largely to the total estimated N₂O emissions from agriculture. Since low soil pH increases N₂O production by impairing the last denitrification step, liming has been suggested as a mitigation strategy; however, it may also increase N₂O emissions by enhancing mineralization and nitrification. To gain field-based empirical knowledge, we measured N₂O fluxes with an autonomous field-flux robot in limed and control plots before and after autumn ploughing of 3-year-old grass, clover grass or red clover swards under different N fertilization regimes. Dolomite applied before establishing the swards raised soil pH_CaCl2 from ~4.8 to ~5.8 in limed plots. Higher pH halved emissions from ploughed leys despite higher soil mineral N contents. It also reduced emissions before ploughing. We observed substantial N₂O fluxes after ploughing, with peaks during a relatively warm wet period after freezing and higher peaks during diurnal snow melt over frozen soil. Average N₂O fluxes were strongly positively correlated with high herbage yields in the preceding growing seasons rather than with the presence of clover. The yield-scaled average N₂O fluxes were strongest in low pH soils at all yield levels; this was a true effect of soil pH on N₂O, as herbage yields were not increased by liming. Here, yield-scaled flux was defined as the average N₂O flux after ploughing divided by the dry matter. Fluxes in red clover plots were similar to those in grass plots, despite the lower C/N ratio and higher total amount of N in clover residues. However, clover in mixtures with grass increased yields and N₂O emissions. This suggests that higher ley production enhanced microbial activity, including nitrifiers and denitrifiers, and that the pH effect on facilitating complete denitrification to N₂ overrode any effect on mineralization and nitrification, thus resulting in N₂O mitigation.

Combining sequential extraction and 3D fluorescence to investigate the behavior of antibiotic and polycyclic aromatic hydrocarbons during solar drying of sewage sludge

Solar drying and liming are commonly used for sludge treatment, but little is known about their efficiency on antibiotics and Polycyclic Aromatic Hydrocarbons (PAHs) removal. This study aimed to investigate the removal of antibiotics and PAHs during solar drying of Limed Sludge (LS) and Non-Limed Sludge (NLS). Thus, organic matter fractionation and 3D fluorescence were used to assess the accessibility and the complexity of organic matter. 2 experiments have been conducted using LS and NLS for 45 days of drying in a pilot scale tunnel. Physicochemical results indicated significant decrease of water content (90%) for both sludge samples within 15 days of drying. For both treatments, the removal of total organic carbon and total nitrogen was low and similar for both treatments. Through this study, it has been confirmed that liming and drying contributed to a strong modification of the organic matter quality with an increase of its accessibility. On the other hand, drying alone increased the less accessible compartments, while the presence of lime affected the interconnexion between the organic matter pools. 3D fluorescence confirmed the obtained results and indicated that LS leads to obtaining more simple molecules in the most accessible compartments, while NLS leads to obtaining more complex molecules in the less accessible compartments. In addition, solar radiations and leaching may contribute to the significant removal (p < 0.01) of roxithromycin, benzo(a)anthracene, chrysene, benzo[k]fluoranthene, benzo[a]pyrene, and benzo(g, h, i) perylene in the presence of lime. Furthermore, the evolution of organic matter pools in terms of accessibility and complexity may drive the bioavailability of these pollutants, leading to their significant removal.

Asbestos cement waste treatment through mechanochemical process with KH2PO4 for its utilization in soil pH correction and nutrient delivery

The manufacture of asbestos materials has been banished worldwide due to their toxicity, but discarding the existing wastes remains a challenge. We investigated an alternative mechanochemical method to treat asbestos-cement materials by loading them with potassium and phosphorus from KH₂PO₄ during the milling process to obtain a product used as liming and soil conditioner. The results showed total asbestos fibrous elimination after 7 to 8 h of milling. The materials showed a slow-release fertilizer profile. The liming property is maintained when the asbestos-cement weight proportion used is equal to or higher than KH₂PO₄. A comparative soil experiment with limestone also indicates that lower doses of the K- and P-enriched detoxified asbestos cement were required to reach similar liming effects. Maize cultivation (greenhouse) was used to evaluate its performance showing higher biomass production for the sample loaded with potassium and phosphorous.

Microbial biomass and activity dynamics in restored lands in a metal contaminated region

Soil microbial communities are important for biogeochemical processes, along with the cycling of nutrients in an ecosystem. Their enzymatic activities are key indicators of their responses to stress. The objective of this research was to assess the effect of land reclamation on microbial biomass and activities in soils impacted by metal contamination. Phospholipid fatty acid analysis (PLFA) (PLFA) results revealed a significant increase in total microbial biomass, fungi, actinomycetes, and bacteria when limed soils were compared to unlimed samples. This change in microbial biomass was associated with a significant increase of pH. The overall level of the β-glucosidase (BG), cellobiohydrolase (CBH), and aryl sulfatase (AS) activities was significantly higher in the dolomitic limestone treated soils than in the untreated samples. However, the activity of glycine aminopeptidase (GAP) was significantly lower in the limed soil than in unlimed samples used as reference. No significant differences (P ≥ 0.05) were observed between the two types of lands (limed vs unlimed) for other enzymes tested, which includes β-N-acetylglucosaminidase (NAGase), acid phosphatase (AP), alkaline phosphatase (ALP), leucine aminopeptidase (LAP), and peroxidase (PER). The levels of enzymatic responses also varied among sites. Overall, this study revealed for the first time the effects of liming on soil microbial activities in recently reclaimed sites damaged by metals.

Nitrous oxide fluxes from long-term limed soils following P and glucose addition: Nonlinear response to liming rates and interaction from added P

Liming of acidic soils to regulate pH for crop growth may decrease emissions of nitrous oxide (N₂O) due to direct effects of pH on the synthesis of N₂O reductases by denitrifying bacteria. However, liming also changes general pH-dependent soil properties, including availability of phosphorus (P), with a feedback on N₂O fluxes that remains largely unknown. Here we used a mesocosm approach to study the combined role of liming and P in regulating N₂O fluxes from denitrification in an arable coarse sandy soil where N₂O emissions under field condition coincided with rainfall events and irrigation, which facilitated anoxia. Soils from three long-term liming treatments (0, 4, and 12 Mg ha^-1) with resulting pH(CaCl₂) of 3.6, 4.7 and 6.3 were incubated at original bulk density first at 60% water filled pore space (WFPS) and successively at 75% WFPS with added nitrate, inorganic P (0 and 10 μg P g^-1 soil) and glucose as labile carbon. N₂O fluxes were measured during 28 days and were supplemented with measurements of CO₂ fluxes, microbial biomass, potential denitrification, and acid phosphatase activity. The results showed a nonlinear response of N₂O fluxes to liming rates, with highest fluxes at the intermediate liming level (4 Mg ha^-1). Furthermore, inorganic P stimulated N₂O fluxes only at the intermediate liming level. Assays of potential denitrification indicated that the N₂O/(N₂O + N₂) product ratio decreased consistently with increasing liming rates, but total N₂O fluxes responded nonlinearly likely due to combined effects on N₂O/(N₂O + N₂) product ratios and total denitrification rates. The results suggest that liming and P addition interact on microbial properties and N₂O emissions from acidic arable soils and may not follow linear trends. This makes it uncertain to predict and model the resulting net effect, which may depend on the actual pH range and P availability from the unlimed to the limed treatments.

Two-year and multi-site field trials to evaluate soil amendments for controlling cadmium accumulation in rice grain

Representing the staple crop for half of the world population, rice can accumulate high levels of cadmium (Cd) in its grain, posing concerns on food safety. Different soil amendments have been proposed to decrease Cd accumulation in rice grain by either decreasing soil Cd availability, introducing competitive ions on Cd uptake, or down-regulating the expression of transporters for Cd uptake. However, the effectiveness of soil amendments applied alone or in combinations needs to be tested under field conditions. Here, we present results of field trials with two rice cultivars differing in Cd accumulation grown at three field sites in southern China in two years, to investigate the effects of two Mn-containing soil amendments (MnO₂, Mn-loaded biochar (MB)), Si fertilizer (Si), limestone, and K₂SO₄, as well as interactions among MnO₂, Si, and limestone on decreasing Cd accumulation in rice grain. We found that single applications of MnO₂ or MB to acidic soils low in Mn decreased grain Cd concentrations by 44-53 % or 78-82 %, respectively, over two years without decrease in performance. These effects were comparable to or greater than those induced by limestone liming alone (45-62 %). Strong interactions between MnO₂ and limestone resulting from their influence on soil extractable Cd and Mn led to non-additive effects on lowering grain Cd. MB addition minimized grain Cd concentrations, primarily by increasing extractable and dissolved Mn concentrations, but also by decreasing Cd extractability in soil. In comparison, Si and K₂SO₄ amendments affected grain Cd levels only weakly. We conclude that the amendments that decrease labile Cd and increase labile Mn in soils are most effective at reducing Cd accumulation in rice grain, thus contributing to food safety.

Geochemical fingerprint of agricultural liming as a regular management practice in Modern-period Basque farming

The Modern period in Europe is marked by the introduction of deep agricultural changes. In the Basque Country (northern Spain), the implantation of an intensive crop rotation was made possible by the expansion of agricultural liming, although the extent and implications of this practice have not been previously explored in depth. The present paper proposes a multidisciplinary approach to this question, based on the combined analysis of archival sources, toponymy, visual prospection focused on the presence of limekilns, and agricultural soil coring in four local contexts of the Atlantic Basque Country. The results show, for the first time, evidence of concurrent and widespread liming in this territory at the edge of the 18th century, with strong implications for the model of agricultural management in the communities involved. The spreading of mineral fertilisation reflects an intensification in the forms of agricultural management, in the framework of a new relationship between land and labour that emerged after the introduction of American crops. Continuous liming for more than 200 years exerted a deep impact in the analysed soils, with interesting socio-economic and ecological implications that are representative of the potential short-term effects that changing relationship between humans and their socio-ecological environment may produce in agricultural soils.

Mediation effects of different sulfur forms on solubility, uptake and accumulation of Cd in soil-paddy rice system induced by organic carbon and liming

Liming is a safe and effective remediation practice for Cd contaminated acid paddy soil. The fate of Cd can also be strongly influenced by redox chemistry of sulfur. But it is unclear if, to what extent and how the combination of liming and sulfur mediation could further control Cd uptake by paddy rice. A rice cultivation pot experiment was conducted to evaluate the impact of different sulfur forms (S⁰ and SO₄^2- in K₂SO₄) on the solubility, uptake and accumulation of Cd in the soil-paddy rice system and how liming and reducing organic carbon mediate the process. Results showed that under neutral soil circumstances achieved by liming, co-application of K₂SO₄ and glucose significantly reduced brown rice Cd by 33%, compared to liming alone. They made it more readily for Cd²⁺ to be precipitated into CdS/CdS₂ or co-precipitate with newly formed FeS/FeS₂/iron oxides. The higher pH balancing capability of K₂SO₄ as well as liming kept the newly formed sulfide or iron containing minerals negatively charged to be more prone to adsorb Cd²⁺, that kept the porewater Cd²⁺ the lowest among all the treatments. Individual K₂SO₄ showed significant promoting effect on soil Cd solubility due to SO₄^2- chelation effect. Furthermore, K₂SO₄ had much weaker inhibiting effect on Cd translocation from root to grain, it showed no significant attenuating effect on brown rice Cd. S⁰ containing treatments displayed weaker or no attenuating effect on brown rice Cd due to its strong soil acidification effect. On the basis of liming, organic carbon induced sulfur (K₂SO₄) mediation showed great application potential for safe production on large areas of acid paddy soil contaminated by Cd.

Effectiveness of helminth egg reduction by solar drying and liming of sewage sludge

The present study is aimed at assessing the effectiveness of solar drying process in terms of helminth egg reduction in sewage sludge (SS) generated from an activated sludge wastewater treatment plant (WWTP) in Marrakesh city (Morocco). It is also engaged to highlight a synergic effect of liming (1% CaO) and solar drying on helminth egg reduction. The solar drying process was conducted for 45 days, in summer under a semi-arid climate in a pilot scale polycarbonate-based tunnel (2 m³). Before undergoing solar drying process, data showed an important load of helminth eggs including Ascaris sp., Schistosoma spp., Capillaria spp., Trichuris spp., Ankylostome spp., Toxocara spp., and Taenia spp. in limed sludge (LS) and non-limed sludge (NLS) (15.2 and 17.9 eggs/g, respectively). Ascaris eggs were the most abundant (11.2 and 13.5 eggs/g in LS and NLS, respectively). By the end of the solar drying process, a considerable removal of the total helminth eggs was recorded in LS and NLS (92.8% and 91.6%, respectively). A complete removal of Schistosoma spp., Capillaria spp., Trichuris spp., Toxocara spp. and Taenia spp. was noted in LS and NLS. In the case of Ankylostome spp., data showed a total removal in LS and 81% in NLS; however, the final load is in agreement with the standards (0.4 egg/g). As for Ascaris spp., neither liming nor solar drying process allowed a complete removal (91% and 90% in NLS and LS, respectively) and the final load (1.1 egg/g) does not fulfill the WHO requirements for an agricultural use. Principal component analysis (PCA) demonstrated a negative correlation between dry matter (DM) content (hence temperature) and helminth egg concentration. No significant synergic effect of liming and solar drying process was showed by statistical analysis. This is substantiating that temperature is the key parameter involved in helminth egg removal while undergoing solar drying of SS.

Producing Cd-safe rice grains in moderately and seriously Cd-contaminated paddy soils

Rice grains produced on cadmium (Cd) contaminated paddy soils often exceed the maximum permissible limit. A number of mitigation methods have been proposed to decrease Cd accumulation in rice grain in contaminated acidic soils, including altering water management regimes, liming, and genetic engineering. In the present study, we conducted a pot experiment to compare these methods for their effectiveness at decreasing grain Cd concentrations in both acidic (pH 5.1-5.2) and alkaline (pH 7.5-7.9) paddy soils that varied in the degree of Cd contamination. In moderately Cd-contaminated acidic soils (with Cd concentrations lower than the intervention value of Chinese soil standard, GB15618-2018), any of the three methods was effective, reducing grain Cd concentration by 80-90% to levels below the Chinese maximum permissible limit (0.2 mg/kg). However, in the highly Cd-contaminated soils (with soil Cd concentrations exceeding the intervention value) with elevated concentrations of extractable Cd, although both liming and alternation of the water management regime (continuous flooding) was effective at decreasing grain Cd accumulation, grain Cd concentrations still exceeded the Chinese limit. Genetic engineering of rice, such as knockout of OsNramp5 (encoding the plasma membrane transporter responsible for Cd uptake into root cells) or overexpression of OsHMA3 (encoding a tonoplast Cd transporter sequestering Cd into the vacuoles), produced dramatic decreases (≥90%) in grain Cd concentration. Even in seriously contaminated soils, overexpression of OsHMA3 alone produced grain with Cd concentrations below the Chinese limit, offering a highly effective approach to produce Cd-safe rice especially in seriously Cd-contaminated paddy soils without affecting grain biomass or the concentrations of essential micronutrients.

What is the effect of 19 years of restoration managements on soil and vegetation on formerly improved upland grassland?

Finding the best management strategies to restore grassland diversity and achieve a compromise between agricultural use and biodiversity protection is a global challenge. This paper reports novel data relating to the impacts of 19 years of restoration managements predicted to increase botanical diversity within reseeded upland temperate grassland common in less favoured areas in Europe. The treatments imposed were: continuous sheep grazing, with and without lime application; hay cutting only, with and without lime application; hay cutting followed by aftermath grazing, with and without lime application; and a control treatment continuing the previous site management (liming, NPK application and continuous sheep grazing). Defoliation type, irrespective of liming, was the key driver influencing plant species diversity (hay cutting followed by aftermath grazing > hay cutting > grazing). Grazing only managements supported grasses at the expense of forbs, and thus related plant species diversity significantly declined. Limed treatments had higher concentrations of Ca and Mg in the soil compared to those receiving no lime. However, no effects on species richness or plant species composition were found. Potassium was the only element whose plant-available concentration in the soil tended to decrease in response to cutting treatments with herbage removal. Postponing the first defoliation to the middle of the growing season enables forbs to reach seed production, and this was the most effective restoration management option for upland grassland (as hay cutting only, and as hay cut followed by aftermath grazing). Although continuous low-density sheep grazing is often adopted as a means of improving floristic biodiversity, deleterious effects of this on plant diversity mean that it cannot be recommended as a means of long-term maintenance or restoration management of European temperate grasslands.

Liming effects on dissolved and colloid-associated transport of cadmium in soil under intermittent simulated rainfall

Liming has been regarded as an effective measure to reduce the bioavailability and mobility of cadmium (Cd) in soil. However, its effect on Cd transport in colloid-associated form remains unclear. In this study, relative importance of dissolved and colloid-associated transport of Cd was explored in columns packed with moist soil aggregates (diameter <2 mm) under intermittent simulated rainfall of distilled water or 5 mmol L^-1 CaCl₂ solution. The Cd²⁺/Ca²⁺ exchange selectivity coefficient determined in column experiments displayed gradual decreases with decreasing ionic strength. It is proposed that the exchange selectivity coefficient determined by repeated batch extraction can be used to predict Cd discharge in dissolved form in column effluent. Colloid-associated Cd was the main Cd form in the first flushing effluent sample upon resuming infiltration of distilled water. Otherwise, Cd was transported mainly in dissolved form, accounting for 81-93 % and 54-72 % of total Cd discharge for unlimed soils and limed soils, respectively. Liming remarkably reduced dissolved Cd concentration but only slightly enhanced colloidal Cd transport. Cd was enriched on colloids, and the enrichment factor was enhanced by liming. Colloidal Cd transport through preferential pathways (e.g., macropores, shrinkage cracks, tile drains) should be paid due attention.

Disruptions and re-establishment of the calcium-bicarbonate equilibrium in freshwaters

During recent decades, increasing anthropogenic activities have affected natural ionic composition, including the strongest and most common relationship between ionic concentrations in the majority of natural global freshwaters, i.e., the Ca²⁺-ANC (acid neutralizing capacity) equilibrium. Using long-term monitoring data and MAGIC modelling, we evaluated effects of major present environmental stressors (synthetic fertilizers, liming, acidic deposition, forest disturbances, and climate change) on the Ca²⁺-ANC equilibrium. We evaluated the effects for three different types of terrestrial ecosystems, a circumneutral lowland agricultural catchment, two acid sensitive mountain forest catchments differing in forest health, and one acid sensitive alpine catchment. All catchments are in a region with the world-largest changes in fertilizing rates and acidic deposition in the 20^th century, with increasing impacts until the late 1980s, and their subsequent abrupt, dramatic decreases. These strong changes resulted in a substantial disruption, followed by continuing re-establishment of the Ca²⁺-ANC relationship in all study waters. The shape of the disruption and the following re-establishment of its new value were dependent on the intensity, duration, and combination of stressors, as well as on catchment characteristics (bedrock composition, soil amount and composition, vegetation status, and hydrology). We conclude that a new equilibrium may deviate from its natural value due to the (1) legacy of fertilizing, acidic deposition and liming, affecting the soil Ca²⁺ pools, (2) forest disturbances and management practices, and (3) climate change.

Sub-millimeter distribution of labile trace element fluxes in the rhizosphere explains differential effects of soil liming on cadmium and zinc uptake in maize

Trace element concentrations in the rhizosphere were quantified to better understand why soil liming often fails to reduce cadmium (Cd) uptake by plants. Maize seedlings were grown on a soil with natural background levels of Cd and zinc (Zn). Soil liming increased soil pH from 4.9 to 6.5 and lowered the soil solution free ion activities by factor 7 (Cd) and 9 (Zn). In contrast, shoot Cd concentrations were unaffected by liming while shoot Zn concentrations were lowered by factor 1.9. Mapping of labile soil trace elements using diffusive gradients in thin films (DGT) in combination with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) revealed an almost complete depletion of Cd in the rhizosphere in all soil treatments, showing that Cd uptake is controlled by diffusion. The flux of Cd from soil to the DGT, with direct contact between the soil and the binding gel, was unaffected by liming whereas it decreased by factor 3 for Zn, closely mimicking the contrasting effects of liming on Cd and Zn bioavailability. This evidence, combined with additional flux data of freshly spiked Cd and Zn isotopes in soil and with modelling, suggests that the diffusive transport of Cd in unsaturated soil is more strongly controlled by the labile adsorbed metal concentration than by its concentration in solution. This is less the case for Zn because of its inherently slower desorption compared to Cd.

Nitrogen induced DOC and heavy metals leaching: Effects of nitrogen forms, deposition loads and liming

Atmospheric nitrogen (N) deposition is believed to accelerate dissolved organic carbon (DOC) production and could lead to increased heavy metal mobility into water resources. We sampled intact soil cores from the Isle of Skye with low background N deposition history and having Serpentine rock known for its higher heavy metal concentrations including zinc (Zn), copper (Cu), nickel (Ni) and lead (Pb). The effects of 16 (16kgN) and 32 kg N ha^-1 year^-1 (32kgN), and liming with 32kgN (32kgN+Lime) on soil solution chemistry and heavy metal mobilization were investigated over the 15-month study. Nitrogen in deposition load was added at five ammonium (NH₄⁺) to nitrate (NO₃^-) ratios of 9:1, 5:1, 1:1, 1:5 and 1:9 along NO₃^-dominance. We found significant effects of load on Cu and NH₄⁺/NO₃^- ratio on pH, DOC and Zn in soil solution. However, under lime and ratio experimental factors, liming significantly influenced pH, DOC, Cu and Pb, and NH₄⁺/NO₃^- ratio pH, DOC, Ni and Zn whereas interactions between lime and ratio was significant for Ni and Cu. pH and DOC increased with N load, liming and NO₃^- dominance, and both correlated significantly positively. Liming under NH₄⁺ dominance enhanced DOC production due to supply of base cations in lime. Mobilization of Cu, Ni and Pb was driven by DOC concentrations and, therefore, increased with load, liming and NO₃^- dominance in deposition. However, in contrast, low pH and high NH₄⁺ dominance was associated with Zn mobilization in soil solution. On the contrary, despite of some patterns, heavy metals in soil HNO₃ extracts were devoid of any load, lime and NH₄⁺/NO₃^- ratio effects. Our study suggests that the effects of N load and forms in deposition on sites with high accumulated loads of metals need to be better quantified through soil solution partitioning models.

Process type is the key driver of the fate of organic micropollutants during industrial scale treatment of organic wastes

Organic micropollutants (OMPs) such as polycyclic aromatic hydrocarbons, nonylphenols and pharmaceutical products are ubiquitous in organic wastes generated by most human activities. Those wastes are mainly recycled by land spreading, most often after treatments, such as liming, dewatering, composting or anaerobic digestion. It has been shown essentially at lab scales that biological treatments have an effect on the removal of some OMPs. However, less is known on the role of each step of industrial treatment lines combining physico-chemical and biological treatments on the OMP fate and removal. The present study focuses on the impact of waste treatment on the fate of 53 OMPs along 10 industrial treatment lines treating urban, agricultural wastes or mixtures. The combination of studying a diversity of organic wastes and of OMPs with different characteristics (solubility, ionic charges, hydrophobicity etc.), sampling in situ industrial sites, quantifying native OMP concentrations and looking at each step of complete treatment lines allows for a global and representative view of the OMP fate in the French organic waste treatment sector. Less studied wastes, i.e. territorial mixtures, revealed intermediate OMP contents and compositions, between urban and agricultural wastes. Dewatering and liming, usually dismissed, had a noticeable effect on concentrations. Anaerobic digestion and composting had significant effects on the removal of all pollutant families. Combination of processes enhanced most OMP dissipation. Here we showed for the first time that the process type rather than the waste origin affects dissipation of organic micropollutants. Such data could be used to build and validate dynamic models for the fate of OMPs on solid waste treatment plants.

Field evaluation of one Cu-resistant somaclonal variant and two clones of tobacco for copper phytoextraction at a wood preservation site

A Cu-resistant somaclonal tobacco variant (NBCu 10-8-F1, C1), its BaG mother clone (C3), and the FoP tobacco clone (C2) were cultivated at a wood preservation site on Cu-contaminated soils (239-1290 mg Cu kg-1 soil range) and an uncontaminated control site (CTRL, 21 mg Cu kg-1) to assess their shoot DW yields and potential use for bioavailable Cu stripping. The Cu concentration in the soil pore water varied between 0.15 and 0.84 mg L-1. Influences of Cu exposure and soil treatments, i.e., untreated soil (Unt), soils amended with compost and either dolomitic limestone (OMDL) or zerovalent iron grit (OMZ), on plant growth and shoot ionome were determined. All transplants survived and grew even at high total soil Cu. Shoots were harvested after 3 months (cut 1). Subsequently, bottom suckers developed and were harvested after 2 months (cut 2). Total shoot DW yield (cuts 1 + 2) varied between 0.8 and 9.9 t DW ha-1 year-1 depending on tobacco cultivars, soil treatments, and soil Cu exposure. It peaked for all cultivars in the OMDL plots at moderate Cu exposure (239-518 mg kg-1 soil), notably for the C2 plants. Cut 2 contributed for 11-43% to total shoot DW yield. Increase in shoot DW yield diluted shoot Cu concentration. At low Cu exposure, total shoot Cu removal peaked for the variant. At moderate Cu exposure, shoot Cu concentrations were similar in all cultivars, but total shoot Cu removal was highest for the C2 plants. At high Cu exposure (753-1140 mg kg-1), shoot Cu concentrations peaked for the C2 plants in the Unt plots, the C1 and C2 plants in the OMZ plot, and the C3 ones in the OMDL plots. Shoot Cu removal (in g Cu ha-1 year-1) ranged from 15.4 (C2 on the CTRL soil) to 261.3 (C2 on moderately contaminated OMDL soils). The C2 plants phytoextracted more Cu than the C1 and C3 ones in the Unt plots and in the OMDL plots at moderate Cu exposure. In the OMDL plots with high Cu exposure, shoot Cu removal was highest for the C1 plants. Soil amendments improved shoot Cu removal through increase in either shoot DW yield (OMDL-3-fold) or shoot Cu concentration (OMZ-1.3-fold). Increased shoot Cu concentration induced an ionome imbalance with increased shoot Al, Fe, B, and Mg concentrations and decreased P and K ones. Copper concentrations in plant parts varied in decreasing order: roots > leaves > inflorescence (cymes including seeds) > stem, whereas Cu removal ranked as roots > stem = leaves > inflorescence.

Effects of liming on the flavor of kokuto-shochu, a spirit made from non-centrifugal sugar

Kokuto-shochu is a traditional Japanese spirit prepared from kokuto, a non-centrifugal brown cane sugar. When manufacturing kokuto, lime is added to the sugarcane juice to accelerate the crystallization of sucrose. Although the liming process differs depending on the manufacturer, the effects of liming on the quality of kokuto-shochu are unclear. Therefore, we investigated the flavor characteristics and volatiles present in kokuto-shochu prepared from kokuto with different liming degrees. Kokuto-shochu prepared from kokuto without liming had a pronounced kokuto-like flavor with a rich taste and contained higher contents of nerolidol, nonanal, acetoin, β-damascenone, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone compared to that prepared from kokuto with liming. On the other hand, kokuto-shochu prepared from kokuto with excess liming had a comparative grassy flavor. It contained higher esters, 4-vinylguaiacol, and pyrazines compared to other shochu. The levels nerolidol, isoamyl acetate, nonanal, and acetoin were affected by the mash pH during fermentation, and thus, liming would affect the formation of such volatiles via changing the mash pH. In contrast, pyrazines, 4-vinylguaiacol, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone were not affected by mash pH, and their levels in the kokuto-shochu were consistent with those in kokuto raw materials. These results suggested that the liming process affects the levels of volatiles in kokuto-shochu by changing the mash pH and volatile levels in kokuto raw materials.

Modelling long-term impacts of fertilization and liming on soil acidification at Rothamsted experimental station

Liming is widely used to reduce the impacts of soil acidification and optimize soil pH for agricultural production. Whether models can simulate the effect of liming on soil pH, and base saturation (BS), and thereby guide lime application, is still largely unknown. Long-term experimental data from a grassland (Park Grass, 1965-2012) and arable land (Sawyers Field, 1962-1972) at Rothamsted Research, UK, were thus used to assess the ability of the VSD+ model to simulate the effects of long-term fertilization and liming on soil acidification. The VSD+ model was capable of simulating observed soil pH and BS changes over time in the long-term liming experiments, except for a treatment in which sulphur (S) was added. Normalized Mean Absolute Errors (NMAE) and Normalized Root Mean Square Errors (NRMSE) of simulated and observed pH values, averaged over the observation periods varied between 0.02 and 0.08 (NMAE) and 0.01-0.05 (NRMSE). The acidity budget results for Park Grass suggest that nitrogen (N) transformations contributed most to acidity production, causing predominantly aluminium (Al) exchange in the topsoil (0-23 cm) followed by base cation (BC) release, but in the treatment with S addition, BC uptake had a nearly similar effect on acidity production. However, in Sawyers Field, the acidity budget suggested that BC uptake was the dominant cause of soil acidification, while the impacts of N transformations were limited. Liming was found to sufficiently replenish BC and decrease Al exchange in the topsoil layer. Overall, the VSD+ model can adequately reconstruct the impacts of fertilizer and liming applications on acid neutralizing processes and related soil pH and BC changes at the soil exchange complex.

Life cycle assessment of woody biomass ash for soil amelioration

The increasing use of forest biomass as a fuel for power plants due to environmental concerns will certainly increase the amount of woody biomass ash produced. Because of the environmental problems derived from woody biomass ash disposal, an important aspect for the sustainable development of the energy sector is the implementation of effective ash management strategies. The purpose of this study is to assess the environmental impacts of woody biomass ash landfarming for soil amelioration through a Life Cycle Assessment. The baseline scenario corresponds to the current most common practice of woody biomass ash management (landfilling), and two different landfarming alternatives were assessed: liming and fertilisation. Credits were given to the system due to the substitution of three traditional liming products and five traditional fertilisers. Woody biomass ash landfarming presented satisfactory performance in five impact categories under study in comparison to landfilling. When woody biomass ash was used for liming, the environmental savings were more pronounced when substituting hydrated lime. For potassium supply, the substitution of potassium nitrate by woody biomass ash presented the best environmental performance, while for phosphorus supply, the environmental savings were more pronounced substituting single superphosphate. However, in four impact categories, the environmental impacts of ash landfarming exceeded the impacts of ash landfilling, due to the emission to soil of nutrients and trace elements to soil. But this does not necessarily imply increased risks for the environment, as the potential pollutants leaching depends on their bioavailability in the soil.

Mitigation of N2O emissions from urine treated acidic soils by liming

Nitrous oxide (N₂O) is a devastating greenhouse gas mainly released from soils to the atmosphere. Pasture soils, particularly acidic in nature, are large contributors of atmospheric N₂O through deposition of urine-N. Devising strategies for reducing N₂O emissions in acidic soils are the utmost need of the time. Therefore, the present study was carried out to investigate the possible efficacy of dolomite application to reduce N₂O emissions from urine treated acidic soil. Application of urine to soil enlarged the production of NH₄⁺-N, NO₃^--N, microbial biomass C (MBC) and dissolved organic C (DOC), resulting in higher N₂O emissions as compared to the control (soil only). The highest N₂O emission rate (1.35 μg N₂O-N kg^-1 h^-1) and cumulative flux (408 μg N₂O-N kg^-1) occurred in urine only treated soil. Dolomite addition, especially higher application dose, greatly reduced N₂O emissions through improved soil pH. The results suggest that increasing pH of acidic soils is a good applicable approach for reducing N₂O emissions from urine-treated soils.

Effectiveness of simultaneous applications of lime and zinc/iron foliar sprays to minimize cadmium accumulation in rice

Due to the large area of Cd-contaminated paddy soils worldwide, low-cost measures to reduce the accumulation of Cd in rice plant are necessary. A field experiment was therefore conducted to investigate the reducing effect of lime combined with foliar applications of Zn (ZnSO₄) or Fe (EDTA·Na₂Fe) on Cd concentrations in brown rice on a Cd-contaminated paddy soil. The results indicated that liming alone or in combination with foliar sprays of Zn or Fe increased the soil pH by 0.27-0.63 units. However, limited effects of lime or lime combined with foliar applications of Zn/Fe on soil DTPA-extractable Cd, rice grain and rice straw biomass were observed. Liming alone significantly reduced the Cd concentration in brown rice and rice straw by 31.8% and 42.3%, respectively. The Cd concentrations in brown rice decreased by 25.5% and 65.4% and in rice straw by 53.0% and 68.1% after liming combined with foliar applications of Fe and Zn, respectively. In contrast, liming combined with foliar spraying of Fe significantly increased the transfer ratio of Cd from the rice straw to the grain. As a low-cost technique, lime application combined with foliar application of ZnSO₄ could be recommended for the remediation of Cd-contaminated paddy soils.

The influence of liming on cadmium accumulation in rice grains via iron-reducing bacteria

Cadmium (Cd) in soil is attracting worldwide attention, and many valuable measures and suggestions of minimizing the rice grain Cd are available. Among these methods, liming can increase the soil pH and decrease the rice grain Cd content. Here, we report that soil pH was negatively and significantly correlated with the concentration of soil extractable Fe and Cd. In addition, the iron concentration on root surface was significantly and positively associated with the available metals in soil and the rice grain Cd. However, the return of contaminated rice straw significantly increased the Cd accumulation in the rice grain, although the returned straw did not significantly influence the concentration of extracted soil Cd. Furthermore, an analysis of the functional microbe community was performed, and the response of iron-reducing bacteria (IRB) under the six treatments provides valuable insights for reducing the available Cd concentration in soil. A LEfSe (LDA coupled with effect size measurement for significant differences) analysis showed that the application of liming reduced the abundance of IRB. The results of a redundancy analysis (RDA) indicated that soil pH was significantly and negatively associated with the abundance of Proteobacteria and Geobacter and the concentration of bioavailable Fe and Cd in the soil, which could explain the reduced accumulation of bioavailable Cd in rice grain. Collectively, our results demonstrated that liming in Cd-polluted paddy soil is a reasonable strategy for minimizing rice grain Cd by increasing the soil pH, which reduces the soil available iron and Cd concentration by shifting the diversity and composition of IRB, thus ultimately resulting in decreased Cd in rice.

Liming induces carbon dioxide (CO2) emission in PSB inoculated alkaline soil supplemented with different phosphorus sources

Agricultural land is a major sink of global organic carbon (C). Its suitable management is crucial for improving C sequestration and reducing soil CO₂ emission. Incubation experiments were performed to assess the impact of phosphate solubilizing bacterial (PSB) inoculation (inoculated and uninoculated) and soil calcification (4.78, 10, 15, and 20% crushed CaCO₃) with phosphorus (P) sources [single superphosphate (SSP), rock phosphate (RP), farm yard manure (FYM), and poultry manure (PM)] in experiment 1 and with various rates of PM (4, 8, and 12 kg ha^-1) in experiment 2 on cumulative soil respiration. These experiments were arranged in three factorial, complete randomize design (CRD) with three replications. Interactively, lime with P sources (at day 1 and 3) and lime with PSB (at day 1) significantly expedited soil respiration. Mainly, PSB inoculation, liming, PM fertilization, and its various rates significantly enhanced soil respiration with time over control/minimum in alkaline soil at all incubation periods. Higher CO₂ emission was detected in soil supplemented with organic P sources (PM and FYM) than mineral sources (SSP and RP). CO₂ emission was noted to increase with increasing PM content. Since liming intensified CO₂ discharge from soil, therefore addition of lime to an alkaline soil should be avoided; instead, integrated approaches must be adopted for P management in alkaline calcareous soils for climate-smart agriculture.

Long-term leaching of nutrients and contaminants from wood combustion ashes

With increasing amounts of woody biomass being combusted for energy purposes worldwide, more wood ash is being generated and needs management. As an alternative to landfilling, residues may be utilised for liming and fertilising purposes on forest soils. Comprehensive evaluations of long-term leaching from these residues are needed in order to assess potential environmental impacts associated with their utilisation. Two Danish wood ash samples, one fly ash and one mixed ash (a combination of fly ash and bottom ash), were evaluated in long-term percolation column tests (up to L/S ∼2000 L/kg), in order to quantify the release of major, minor and trace metal(loid)s. While columns of three different lengths were used, the leaching of individual elements could be described as a function of the L/S ratio - irrespective of the column length. At L/S 1000 L/kg, the cumulative releases of K, S, Na, Ca and Rb were at 40-100% of their respective solid contents, followed by Ba, Cr, Sb, Sr and V at 15-40% and Al, Mg, Zn, Cd, Co, Fe, Pb, Tl, Mn and P at < 5%. Speciation calculations indicated that (i) the observed concentrations of Ca, Mg, Al, Ba, Si and sulphate from both ash types could be described through the dissolution/precipitation of a limited set of minerals and that (ii) leaching of silicates should be included in long-term assessment of alkalinity release from wood ashes. Non-equilibrium conditions were indicated by flow interruptions. However, the presence of non-equilibrium did not have significant effect on the calculated cumulative releases at high L/S ratios. Based on the assessment of cumulative releases at L/S 10 L/kg and L/S 1000 L/kg it is concluded that low L/S-based data may not provide sufficient background for prediction of long-term release from wood ash, in particular for Ba, Cr, Sb and V, and less critically also for As, Cd, Cu, Mo and Ni.

Modulation of hexavalent chromium toxicity on Οriganum vulgare in an acidic soil amended with peat, lime, and zeolite

Dynamics of chromate (Cr(VI)) in contaminated soils may be modulated by decreasing its phytoavailability via the addition of organic matter-rich amendments, which might accelerate Cr(VI) reduction to inert chromite (Cr(III)) or high-cation exchange capacity amendments. We studied Cr(VI) phytoavailability of oregano in a Cr(VI)-spiked acidic soil non-treated (S) and treated with peat (SP), lime (SL), and zeolite (SZ). The addition of Cr(VI) increased the concentrations of Cr(VI) and Cr(III) in soils and plants, especially in the lime-amended soil. The plant biomass decreased in the lime-amended soil compared to the un-spiked soil (control) due to decreased plant phosphorus concentrations and high Cr(VI) concentrations in root at that treatment. Oregano in the peat-amended soil exhibited significantly less toxic effects, due to the role of organic matter in reducing toxic Cr(VI) to Cr(III) and boosted plant vigour in this treatment. In the lime-amended soil, the parameters of soil Cr(VI), soil Cr(III), and root Cr(III) increased significantly compared to the non-amended soil, indicating that Cr(VI) reduction to Cr(III) was accelerated at high pH. Added zeolite failed to decreased Cr(VI) level to soil and plant. Oregano achieved a total uptake of Cr(III) and Cr(VI) of 0.275 mg in plant kg^-1 soil in a pot in the non-amended soil. We conclude that peat as soil amendment might be considered as a suitable option for decreasing Cr(VI) toxicity in soil and plant, and that oregano as tolerant plant species has a certain potential to be used as a Cr accumulator.

Effects of long-term grassland management on the carbon and nitrogen pools of different soil aggregate fractions

Common grassland management practices include animal grazing and the repeated addition of lime and nutrient fertilizers to soils. These practices can greatly influence the size and distribution of different soil aggregate fractions, thus altering the cycling and storage of carbon (C) and nitrogen (N) in grassland soils. So far, very few studies have simultaneously addressed the potential long-term effect that multiple management practices might have on soil physical aggregation. Here we specifically ask whether and how grazing, liming and nutrient fertilization might influence C and N content (%) as well as C and N pools of different soil aggregate fractions in a long-term grassland experiment established in 1991 at Silwood Park, Berkshire, UK. We found that repeated liming applications over 23years significantly decreased the C pool (i.e. gCKg^-1 soil) of Large Macro Aggregate (LMA>2mm) fractions and increased C pools within three smaller soil aggregate fractions: Small Macro Aggregate (SMA, 250μm-2mm), Micro Aggregate (MiA, 53-250μm), and Silt Clay Aggregate (SCA<53μm). Soil C (and N) accrual in smaller fractions was mainly caused by positive liming effects on aggregate fraction mass rather than on changes in soil C (and N) content (%). Liming effects could be explained by increases in soil pH, as this factor was significantly positively related to greater soil C and N pools of smaller aggregate fractions. Long-term grazing and inorganic nutrient fertilization had much weaker effects on both soil aggregate-fraction mass and on soil C and N concentrations, however, our evidence is that these practices could also contribute to greater C and N pools of smaller soil fractions. Overall our study demonstrates how agricultural liming can contribute to increase C pools of small (more stable) soil fractions with potential significant benefits for the long-term C balance of human-managed grassland soils.

Effect of pH and added slag on the extractability of Si in two Si-deficient sugarcane soils

The effects of increasing pH on the adsorption and extractability of Si in two Si-deficient Australian sugarcane soils was investigated and the effects of increasing rates of fertilizer Si (as blast furnace slag) on pH and extractable Si were also examined. Equilibrium studies showed that maximum adsorption of Si by the two soils occurred in the pH range 9-10. When soil pH was increased from 5.0 to 6.5, subsequent adsorption of Si by the two soils, as measured by adsorption isotherms, increased. After incubation with progressive lime additions there was a decline in CaCl₂- extractable Si due to its increased adsorption and an increase in acid (H₂SO₄^- and acetic acid)-extractable (mainly adsorbed) Si. The increase in acid extractable Si was greater than the decrease in CaCl₂^- extractable Si suggesting a supply from an additional source. Alkali (Na₂CO₃ and Tiron)-extractable Si decreased greatly with increasing pH suggesting dissolution of the amorphous (mainly biogenic) pool of silica was occurring with increasing pH. When increasing rates of slag were incubated with the soils, pH, CaCl₂^- and acid- extractable Si were all increased because upon dissolution slags release both silicic acid and OH^- ions. There was, therefore, a positive relationship between extractable Si and soil pH. However, Na₂CO₃^-and Tiron-extractable Si decreased with increasing slag rates (and increasing soil pH) suggesting dissolution of the biogenic pool of soil Si. It was concluded that future research needs to examine the desorption potential of adsorbed Si and the effects of liming on dissolution of the biogenic pool of soil silica under field conditions.

Can liming reduce cadmium (Cd) accumulation in rice (Oryza sativa) in slightly acidic soils? A contradictory dynamic equilibrium between Cd uptake capacity of roots and Cd immobilisation in soils

Cadmium (Cd) accumulation in rice is strongly controlled by liming, but information on the use of liming to control Cd accumulation in rice grown in slightly acidic soils is inconsistent. Here, pot experiments were carried out to investigate the mechanisms of liming on Cd accumulation in two rice varieties focusing on two aspects: available/exchangeable Cd content in soils that were highly responsive to liming, and Cd uptake and transport capacity in the roots of rice in terms of Cd accumulation-relative gene expression. The results showed that soil availability and exchangeable iron, manganese, zinc and Cd contents decreased with increased liming, and that genes related to Cd uptake (OsNramp5 and OsIRT1) were sharply up-regulated in the roots of the two rice varieties. Thus, iron, manganese, zinc and Cd contents in rice plants increased under low liming applications but decreased in response to high liming applications. However, yield and rice quantities were only slightly affected. These results indicated that Cd accumulation in rice grown in slightly acidic soils presents a contradictory dynamic equilibrium between Cd uptake capacity by roots and soil Cd immobilisation in response to liming. The enhanced Cd uptake capacity under low liming dosages increases risks to human health.

Pulsed corona discharge for improving treatability of coking wastewater

Coking wastewater (CW) contains toxic and macromolecular substances that inhibit biological treatment. The refractory compounds remaining in biologically treated coking wastewater (BTCW) provide chemical oxygen demand (COD) and color levels that make it unacceptable for reuse or disposal. Gas-phase pulsed corona discharge (PCD) utilizing mostly hydroxyl radicals and ozone as oxidants was applied to both raw coking wastewater (RCW) and BTCW wastewater as a supplemental treatment. The energy efficiency of COD, phenol, thiocyanate and cyanide degradation by PCD was the subject of the research. The cost-effective removal of intermediate oxidation products with addition of lime was also studied. The energy efficiency of oxidation was inversely proportional to the pulse repetition frequency: lower frequency allows more effective utilization of ozone at longer treatment times. Oxidative treatment of RCW showed the removal of phenol and thiocyanate at 800 pulses per second from 611 to 227mg/L and from 348 to 86mg/L, respectively, at 42kWh/m³ delivered energy, with substantial improvement in the BOD₅/COD ratio (from 0.14 to 0.43). The COD and color of BTCW were removed by 30% and 93%, respectively, at 20kWh/m³, showing energy efficiency for the PCD treatment exceeding that of conventional ozonation by a factor of 3-4. Application of lime appeared to be an effective supplement to the PCD treatment of RCW, degrading COD by about 28% at an energy input of 28kWh/m³ and the lime dose of 3.0kg/m³. The improvement of RCW treatability is attributed to the degradation of toxic substances and fragmentation of macromolecular compounds.

Changes in enzymatic activities in metal contaminated and reclaimed lands in Northern Ontario (Canada)

Metal and sulfur dioxide (SO₂) contaminations in Northern Ontario (Canada), especially in the Greater Sudbury Region (GSR) caused by mining activities have resulted in severe environmental degradations. A long term restoration program has led to significant landscape changes and healthy ecosystems. The objective of this study was to assess variation in enzymatic activities and soil respiration in metal contaminated and reclaimed ecosystems. Soil analysis revealed that respiration rates were higher in metal contaminated limed soils (65ppm) compared to adjacent unlimed areas (35ppm). The respiration rates in metal contaminated sites (55ppm) were significantly lower compared to reference (metal-uncontaminated) areas (90ppm). β-glucosidase (BG), cellobiohydrolase (CBH), β-N-acetylglucosaminidase (NAGase), aryl sulfatase (AS), acid phosphatase (AP), alkaline phosphatase (AlP), glycine aminopeptidase (GAP), and leucine aminopeptidase (LAP) activities were significantly higher in limed compared to unlimed sites. Metal contamination significantly reduced the activities of these enzymes with the exception of LAP. An opposite trend was observed for peroxidase (PER) activity that was lower in limed compared to corresponding unlimed areas. Likewise, PER activity values were significantly lower in metal contaminated than in uncontaminated reference sites.

The effect of pH, electrolytes and temperature on the rhizosphere geochemistry of phytosiderophores

BACKGROUND AND AIMS

Graminaceous plants are grown worldwide as staple crops under a variety of climatic and soil conditions. They release phytosiderophores for Fe acquisition (Strategy II). Aim of the present study was to uncover how the rhizosphere pH, background electrolyte and temperature affect the mobilization of Fe and other metals from soil by phytosiderophores.

METHODS

For this purpose a series of kinetic batch interaction experiments with the phytosiderophore 2'-deoxymugineic acid (DMA), a calcareous clay soil and a mildly acidic sandy soil were performed. The temperature, electrolyte concentration and applied electrolyte cation were varied. The effect of pH was examined by applying two levels of lime and Cu to the acidic soil.

RESULTS

Fe mobilization by DMA increased by lime application, and was negatively affected by Cu amendment. Mobilization of Fe and other metals decreased with increasing ionic strength, and was lower for divalent than for monovalent electrolyte cations at equal ionic strength, due to higher adsorption of metal-DMA complexes to the soil. Metal mobilization rates increased with increasing temperature leading to a faster onset of competition; Fe was mobilized faster, but also became depleted faster at higher temperature. Temperature also affected biodegradation rates of metal-DMA complexes.

CONCLUSION

Rhizosphere pH, electrolyte type and concentration and temperature can have a pronounced effect on Strategy II Fe acquisition by affecting the time and concentration 'window of Fe uptake' in which plants can benefit from phytosiderophore-mediated Fe uptake.

Influence of ameliorating soil acidity with dolomite on the priming of soil C content and CO2 emission

Lime or dolomite is commonly implemented to ameliorate soil acidity. However, the impact of dolomite on CO₂ emissions from acidic soils is largely unknown. A 53-day laboratory study was carried out to investigate CO₂ emissions by applying dolomite to an acidic Acrisol (rice-rapeseed rotation [RR soil]) and a Ferralsol (rice-fallow/flooded rotation [RF soil]). Dolomite was dosed at 0, 0.5, and 1.5 g 100 g^-1 soil, herein referred to as CK, L, and H, respectively. The soil pH_(H2O) increased from 5.25 to 7.03 and 7.62 in L and H treatments of the RR soil and from 5.52 to 7.27 and 7.77 in L and H treatments of the RF soil, respectively. Dolomite application significantly (p ≤ 0.001) increased CO₂ emissions in both RR and RF soils, with higher emissions in H as compared to L dose of dolomite. The cumulative CO₂ emissions with H dose of dolomite were greater 136% in the RR soil and 149% in the RF soil as compared to CK, respectively. Dissolved organic carbon (DOC) and microbial biomass carbon (MBC) increased and reached at 193 and 431 mg kg^-1 in the RR soil and 244 and 481 mg kg^-1 in the RF soil by H treatments. The NH₄^--N and NO₃^--N were also increased by dolomite application. The increase in C and N contents stimulated microbial activities and therefore higher respiration in dolomite-treated soil as compared to untreated. The results suggest that CO₂ release in dolomite-treated soils was due to the priming of soil C content rather than chemical reactions.

Effect of liming on nickel bioavailability and toxicity to oat and soybean grown in field soils containing aged emissions from a nickel refinery

Remediation of soils elevated in trace metals so that the soils may provide ecosystems services is typically achieved through pH adjustment or addition of sorbents. The present study aimed to generate higher-tier in situ toxicity data for elevated nickel (Ni) in soils with and without lime addition and to explore the effect of liming on soil chemistry and bioavailability of Ni to plants. A multiyear study of agronomic yield of field-grown oat and soybean occurred in 3 adjacent fields that had received air emissions from a Ni refinery for 66 yr. The soil Ni concentration in the plots ranged between 1300 mg/kg and 4900 mg/kg, and each field was amended with either 50 Mg/ha, 10 Mg/ha, or 0 Mg/ha (or tonnes/ha) of crushed dolomitic limestone. As expected, liming raised the pH of the soils and subsequently reduced the plant availability of Ni. Toxicity thresholds (effective concentrations causing 50% reduction in growth) for limed soils supported the hypothesis that liming reduces toxicity. Relationships were found between relative yield and soil cation exchange capacity and between relative yield and soil pH, corroborating findings of the European Union Risk Assessments and the Metals in Asia studies, respectively. Higher tier ecotoxicity data such as these are a valuable contribution to risk assessment for Ni in soils. Environ Toxicol Chem 2017;36:1110-1119. © 2016 SETAC.

Effects of soil acidification and liming on the phytoavailability of cadmium in paddy soils of central subtropical China

Intensive and paired soil and rice grain survey and multiple-field liming experiments were conducted to assess soil acidification in the past 30 years, quantify the relationships of Cd phytoavailability with soil acidity, and determine efficacies of liming on soil acidity and Cd phytoavailability in paddy soils of central subtropical China at a regional scale. Soil pH, total and extractable Cd (Cd_tot and Cd_ext), rice grain Cd were determined, and all measured data were analyzed separately in groups of 0.1 pH units intervals. Paddy soil pH averagely declined at 0.031 unit yr^-1 between 1980s and 2014 (P < 0.01). Piecewise means of log Cd transfer ratio kept around -0.062 between soil pH 4.0 and 5.5 and around -1.31 between pH 6.9 and 7.3, whereas linearly decreased by a factor of 0.76 with pH 5.5-6.9, and by a factor of 1.38 with pH 7.3-8.2 (P < 0.01), respectively. Similar responses to soil pH were observed for soil Cd_ext to Cd_tot ratio. However, the former exhibited a lag effect to soil acidification in the acidic soils and a leading effect in alkaline soils. Liming increased soil pH by 0.50 units, and decreased rice grain Cd by 35.3% and log Cd transfer ratio by a factor of 0.76 (P < 0.01). The piecewise relationship based on the survey precisely predicted the changes in Cd transfer ratio across the multiple-field liming experiments. In conclusion, soil acidification occurred and accelerated in the past 30 years, and piecewise-linearly increased Cd phytoavailability of paddy soils in central subtropical China. Mitigating soil acidification, i.e. liming, should be preferentially implemented to minimize Cd phytoavailability.

The effects of soil liming and sewage sludge application on dynamics of copper fractions and total copper concentration

The paper deals with effects of liming and different doses of municipal sewage sludge (5, 10, and 15 % of soil mass) on copper speciation in soil. In all samples, pH was determined together with total copper concentration, which was measured with the ICP-AES method. Concentration of copper chemical fractions was determined using the seven-step procedure of Zeien and Brümmer. In the soil treated with the highest dose of sludge (15 %), there was, compared to the control, a twofold increase in the concentration of copper and a threefold increase in the concentration of nitrogen. Copper speciation analysis showed that in the municipal sewage sludge the easily soluble and exchangeable fractions (F1 and F2) constituted only a small share of copper with the highest amount of this metal in the organic (F4) and residual (F7) fractions. In the soil, at the beginning of the experiment, the highest share was in the organic fraction (F4), the residual fraction (F7) but also in the fraction where copper is bound to amorphous iron oxides (F5). After 420 days, at the end of the experiment, the highest amount of copper was mainly in the organic fraction (F4) and in the fraction with amorphous iron oxides (F5). Due to mineralization of organic matter in the sewage sludge, copper was released into the soil with the share of the residual fraction (F7) decreasing. In this fraction, there was much more copper in limed soil than in non-limed soil.

Impact of sludge stabilization processes and sludge origin (urban or hospital) on the mobility of pharmaceutical compounds following sludge landspreading in laboratory soil-column experiments

This study aimed to determine the effect of sludge stabilization treatments (liming and anaerobic digestion) on the mobility of different pharmaceutical compounds in soil amended by landspreading of treated sludge from different sources (urban and hospital). The sorption and desorption potential of the following pharmaceutical compounds: carbamazepine (CBZ), ciprofloxacin (CIP), sulfamethoxazole (SMX), salicylic acid (SAL), ibuprofen (IBU), paracetamol (PAR), diclofenac (DIC), ketoprofen (KTP), econazole (ECZ), atenolol (ATN), and their solid-liquid distribution during sludge treatment (from thickening to stabilization) were investigated in the course of batch testing. The different sludge samples were then landspread at laboratory scale and leached with an artificial rain simulating 1 year of precipitation adapted to the surface area of the soil column used. The quality of the resulting leachate was investigated. Results showed that ibuprofen had the highest desorption potential for limed and digested urban and hospital sludge. Ibuprofen, salicylic acid, diclofenac, and paracetamol were the only compounds found in amended soil leachates. Moreover, the leaching potential of these compounds and therefore the risk of groundwater contamination depend mainly on the origin of the sludge because ibuprofen and diclofenac were present in the leachates of soils amended with urban sludge, whereas paracetamol and salicylic acid were found only in the leachates of soils amended with hospital sludge. Although carbamazepine, ciprofloxacin, sulfamethoxazole, ketoprofen, econazole, and atenolol were detected in some sludge, they were not present in any leachate. This reflects either an accumulation and/or (bio)degradation of these compounds (CBZ, CIP, SMX, KTP, ECZ, and ATN ), thus resulting in very low mobility in soil. Ecotoxicological risk assessment, evaluated by calculating the risk quotients for each studied pharmaceutical compound, revealed no high risk due to the application on the soil of sludge stabilized by liming or anaerobic digestion.

Reducing the infectivity and richness of ectomycorrhizal fungi in a calcareous Quercus ilex forest through soil preparations for truffle plantation establishment: A bioassay study

In the early years of a black truffle plantation, the field proliferation of the nursery-inoculated fungi can be hampered by native ectomycorrhizal fungi colonising the seedling roots. Reducing the soil ectomycorrhizal infectivity in the planting hole before introducing the inoculated seedling could be an effective strategy to reduce this problem. Three bioassays were conducted to evaluate the impact of several soil preparations on the ectomycorrhizal infectivity and richness of a Quercus ilex soil in a truffle-producing region. Microwaves, quicklime, and acetic acid significantly decreased the percent root colonisation and morphotype richness of the native ectomycorrhizal fungi. However, they also decreased seedling survival or growth. Peracetic acid, hydrogen peroxide, and sodium hypochlorite did not show a significant negative effect on the soil ectomycorrhizal community. The results support the potential of soil preparation for reducing the ectomycorrhizal infectivity of forest soils, thus being a promising strategy to reduce the early colonisation by native fungi in truffle plantations. However, the indications of damage to the seedling development must be addressed.

The geochemical transformation of soils by agriculture and its dependence on soil erosion: An application of the geochemical mass balance approach

Agricultural activities alter elemental budgets of soils and thus their long-term geochemical development and suitability for food production. This study examined the utility of a geochemical mass balance approach that has been frequently used for understanding geochemical aspect of soil formation, but has not previously been applied to agricultural settings. Protected forest served as a reference to quantify the cumulative fluxes of Ca, P, K, and Pb at a nearby tilled crop land. This comparison was made at two sites with contrasting erosional environments: relatively flat Coastal Plain in Delaware vs. hilly Piedmont in Pennsylvania. Mass balance calculations suggested that liming not only replenished the Ca lost prior to agricultural practice but also added substantial surplus at both sites. At the relatively slowly eroding Coastal Plain site, the agricultural soil exhibited enrichment of P and less depletion of K, while both elements were depleted in the forest soil. At the rapidly eroding Piedmont site, erosion inhibited P enrichment. In similar, agricultural Pb contamination appeared to have resulted in Pb enrichment in the relatively slowly eroding Coastal Plain agricultural soil, while not in the rapidly eroding Piedmont soils. We conclude that agricultural practices transform soils into a new geochemical state where current levels of Ca, P, and Pb exceed those provided by the local soil minerals, but such impacts are significantly offset by soil erosion.

Improving the mining soil quality for a vegetation cover after addition of sewage sludges: inorganic ions and low-molecular-weight organic acids in the soil solution

We assessed the effects of applying stabilized sewage sludge (SSL) and composted sewage sludge (CLV), at 5 and 10% to an acid mining soil. Limed soil (NCL) amended or not with SSL and CLV was incubated for 47 days. We studied the cations and organic and inorganic anions in the soil solution by means of ion chromatography. Liming led to big increases in Ca(2+) and SO4(2-) and to significant decreases in K(+), Mg(2+), NH4(+) and NO3(-). Addition of both organic amendments increased some cations (NH4(+), K(+), Mg(2+), Na(+)) and anions (Cl(-), NO3(-) only with CLV and PO4(3-) only with SSL) and provided a greater amount of low-molecular-weight organic acids (LMWOAs) (SSL more than CLV). Incubation led to decreases in all cations, particularly remarkable for Ca(2+) and Mg(2+) in SSL-10. A decrease in NH4(+) was associated with variations in NO2(-) and NO3(-) resulting from nitrification reactions. During incubation the LMWOAs content tended to decrease similarly to the cations, especially in SSL-10. Chemometric tools revealed a clear discrimination between SSL, CLV and NCL. Furthermore, treatment effects depended upon dose, mainly in SSL. Amendment nature and dose affect the quality of a mining soil and improve conditions for plant establishment.

Metal contaminated biochar and wood ash negatively affect plant growth and soil quality after land application

Pyrolysis or combustion of waste wood can provide a renewable source of energy and produce byproducts which can be recycled back to land. To be sustainable requires that these byproducts pose minimal threat to the environment or human health. Frequently, reclaimed waste wood is contaminated by preservative-treated timber containing high levels of heavy metals. We investigated the effect of feedstock contamination from copper-preservative treated wood on the behaviour of pyrolysis-derived biochar and combustion-derived ash in plant-soil systems. Biochar and wood ash were applied to soil at typical agronomic rates. The presence of preservative treated timber in the feedstock increased available soil Cu; however, critical Cu guidance limits were only exceeded at high rates of feedstock contamination. Negative effects on plant growth and soil quality were only seen at high levels of biochar contamination (>50% derived from preservative-treated wood). Negative effects of wood ash contamination were apparent at lower levels of contamination (>10% derived from preservative treated wood). Complete removal of preservative treated timber from wood recycling facilities is notoriously difficult and low levels of contamination are commonplace. We conclude that low levels of contamination from Cu-treated wood should pose minimal environmental risk to biochar and ash destined for land application.

Effects of calcite and magnesite application to a declining Masson pine forest on strongly acidified soil in Southwestern China

Liming of strongly acidified soil under a Masson pine (Pinus massoniana Lamb.) forest was studied through a seven-year field manipulation experiment at Tieshanping, Chongqing in Southwestern China. To distinguish between the individual effects of Ca(2+) and Mg(2+) addition, we separately applied calcite (CaCO3) and magnesite (MgCO3), rather than using dolomite [CaMg(CO3)2]. Both calcite and magnesite additions caused a significant increase in pH and a decrease in dissolved inorganic monomeric aluminium (Ali) concentration of soil water. Ecological recovery included increases of herb biomass (both treatments) and Mg content in Masson pine needles (magnesite treatment only). However, the growth rate of Masson pine did not increase under either treatment, possibly because of nutrient imbalance due to phosphorus (P) deficiency or limited observation period. In China, acid deposition in forest ecosystems commonly coincides with large inputs of atmogenic Ca(2+), both enhancing Mg(2+) leaching. Calcite addition may further decrease the Mg(2+) availability in soil water, thereby exacerbating Mg(2+) deficiency in the acidified forest soils of southern and southwestern China. The effect of anthropogenic acidification of naturally acid forest soils on P availability needs further study.

Impacts of simulated drought on pore water chemistry of peatlands

Northern peatlands are increasingly threatened by climate change and industrial activities. This study examined the impact of simulated droughts on pore water chemistry at six peatlands in Sudbury, Ontario, that differ in copper (Cu), nickel (Ni) and cobalt (Co) contamination, including a site that had been previously limed. All sites responded similarly to simulated drought: pore water pH declined significantly following the 30 day drought and the decline was greater following the 60 day drought treatment. The decline in pore water pH was due to increasing sulphate concentrations, whereas nitrate increased more in the 60 day drought treatment. Decreases in pH were accompanied by large increases in Ni and Co that greatly exceeded provincial water quality guidelines. In contrast, dissolved organic carbon (DOC) concentrations decreased significantly following drought, along with concentrations of Cu and Al, which are strongly complexed by organic acids.