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The aim of the paper is to give an overview on the chemistry of soil organic carbon (SOC) affecting nutrient availability, the emission of greenhouse gases and detoxifying harmful substances in soil. Humic substances represent the stable part of SOC, accounting for between 50 and more than 80% of organically bound carbon in soil. Humic substances strongly affect the soil solution concentration of several plant nutrients and may increase P-, Fe-, and Cu- solubility, thereby increasing their plant availability. Soil organic carbon, mainly humic substances, can detoxify monomeric Al in acid soils, can strongly bind toxic heavy metals, making them unavailable to the plant roots, and may strongly bind a vast variety of harmful organic pollutants. Increasing SOC is an important goal in agriculture. The inclusion of mixtures of semi-perennial plant species and cultivars may strongly increase SOC and humic substance content in soils. To increase SOC, farmyard manure and its rotted or composted forms are superior compared to the separate application of straw and slurry to soil. The storage of carbon, mainly in organic form, in soils is very important in the context of the emission of greenhouse gases. Worldwide, soils release about 10 times more greenhouse gases compared to fossil fuel combustion. Small increments in SOC worldwide will strongly affect the concentration of atmospheric CO2. The public discussion on soil fertility and greenhouse gas emissionshas been politically controlled in a way that leaves the important and positive contribution of soil organic carbon and mainly humic substances partly misinterpreted and partly underestimated.

BACKGROUND: In 1994, a “Pan-European Programme for Intensive and Continuous Monitoring of Forest Ecosystems” started to contribute to a better understanding of the impact of air pollution, climate change and natural stress factors on forest ecosystems. The programme today counts approximately 760 permanent observation plots including near 500 plots with data on both air quality and forest ecosystem impacts. SCOPE: This paper first presents impacts of air pollution and climate on forests ecosystems as reported in the literature on the basis of laboratory and field research. Next, results from monitoring studies, both at a European wide scale and related national studies, are presented in terms of trends and geographic variations in nitrogen and sulphur deposition and ozone concentrations and the impacts of those changes in interaction with weather conditions on (i) water and element budgets and nutrient-acidity status, (ii) forest crown condition, (iii) forest growth and carbon sequestration and (iv) species diversity of the ground vegetation. The empirical, field based forest responses to the various drivers are evaluated in view of available knowledge. CONCLUSIONS: Analyses of large scale monitoring data sets show significant effects of atmospheric deposition on nutrient-acidity status in terms of elevated nitrogen and sulphur or sulphate concentrations in forest foliage and soil solution and related soil acidification in terms of elevated aluminium and/or base cation leaching from the forest ecosystem. Relationships of air pollution with crown condition, however, appear to be weak and limited in time and space, while climatic factors appear to be more important drivers. Regarding forest growth, monitoring results indicate a clear fertilization effect of N deposition on European forests but the field evidence for impacts of ambient ozone exposure on tree growth is less clear.

A novel method, ECWS, is proposed for measuring soil initial salinity content (b), based on the soil electrical conductivity EC and soil moisture content WS. This pioneering model rigorously establishes and incorporates the inherent potential correlation among soil bulk conductivity (ECa), soil solution conductivity (ECw), volume water content (θc), and soil salinity content (SSC). First of all, in order to delve the deeper relationship between ECa, ECw, θc and SSC, the soil salinity conductivity conversion coefficient ρa and soil leaching solution salinity conductivity conversion coefficient ρw were employed based on the formula of parallel conducting channels of the soil–water system, and a new measurement model of salinity content was constructed. After that, a mathematical analysis method was used to transform the coefficients of multiple sets of regression equations into matrices to solve ρa, ρw and b. Finally, to validate the accuracy of the proposed ECWS method, verification tests were conducted by utilizing TDR and PWMER sensors. The results with different salinity contents showed that the b size obtained by ECWS model were K2SO4 (1.84 g/kg), NaCl (1.91 g/kg), and KCl (1.92 g/kg). The maximum deviation was less than 0.08 g/kg (relative error less than 5%). The results showed that the influence of different anions and cations on the measurement of salinity content Cl− is greater than that of SO42−, and K+ is greater than that of Na+. This study revealed the relationship between soil electrical conductivity and soil salinity content to a certain extent, and realized the transformation between them, which provided a new method for the measurement of soil salinity content, and also provided a reference for related research on the measurement of soil salinization.

Arbuscular mycorrhizal (AM) fungi increase phosphate (P) uptake by plants. Organic phosphate comprises 30–80% of total P in most agricultural soils. Some plants can utilize organic phosphate by secreting acid phosphatase (ACP) from their roots, especially under low P conditions. Although secretion of ACP from extraradical hyphae of AM fungi has been reported, the specific factors that affect the secretion of ACP are unknown. The objective of the present study was to investigate whether secretion of ACP from extraradical hyphae is induced by low P conditions. First, specimens of Allium fistulosum were either inoculated with the AM fungus Rhizophagus clarus strain CK001 or remained uninoculated and were grown in soil with 0.5 g P2O5 kg−1 soil or without P fertilization using two-compartment pots. Soil solution was collected using mullite ceramic tubes 45 days after sowing. The soil solution was analyzed for ACP activity by using p-nitrophenylphosphate. Second, Ri T-DNA transformed roots (i.e., hairy roots) of Linum usitatissimum inoculated with R. clarus were grown on solid minimal media with two P levels applied (3 and 30 μM P) using two-compartment Petri dishes under in vitro conditions. Hyphal exudates, extraradical hyphae, and hairy roots were collected and analyzed for ACP activity. ACP activity in the soil solution of the hyphal compartment in the A. fistulosum inoculation treatment was higher without P fertilization than with P fertilization. AM colonization also was higher without P fertilization than with P fertilization. In the in vitro two-compartment culture, ACP activity of hyphal exudates and extraradical hyphae were higher under the 3-μM treatment than under the 30-μM treatment. These findings suggest that the secretion of ACP from the extraradical hyphae of R. clarus into the hyphosphere is promoted under low P conditions.

Currently, the concept of a double electric layer in soil colloids is often used to explain the effect of the ionic strength of soil solutions on soil properties. It is known that when the ionic strength increases, the double electric layer contracts. The aim of the work is to study the effect of increasing the ionic strength of a soil solution on the rheological properties and soil water retention curve. Loamy soils were studied: sod-podzolic, gray forest, and leached chernozem. The rheological characteristics of the soil pastes were determined on a vibrating viscometer, the soil water retention curve by the method of equilibrium centrifugation. The particle size distribution in the suspensions was determined using a laser diffractometer. In the course of experiments, it was found that an increase in the ionic strength of the dispersion medium in pastes leads to a sharp increase in the viscosity of pastes. From the perspective of double electric layer compression, the viscosity should decrease. In addition, it was found that in soil pastes prepared with 1 N potassium chloride, the amount of rheopexy decreases. At the same time, there is no influence of the ionic strength of solutions on the soil water retention curve, although from the standpoint of double electric layer, it was assumed that the soil water retention curves would shift to the left. The experiments conducted to study the swelling of soil pastes suggest that periodic colloidal structures of a local type exist in soils. Thus, the concept of a double electric layer does not allow us to explain changes in all soil properties.

World phosphorus (P) resources are limited and may be exhausted within 70–175 years. Therefore recycling of P from waste materials by chemical or thermal processes is important. This study evaluated the effectiveness of recycled P products from sewage sludge and animal wastes as P fertilizer. Four products were obtained from chemical processes, three magnesium-ammonium-phosphates (MAP) of different sewage treatment plants and a Ca phosphate precipitated from wastewater (Ca-P) and four from thermal processes, an alkali sinter phosphate (Sinter-P), a heavy metal depleted sewage sludge ash (Sl-ash), a cupola furnace slag made from sewage sludge (Cupola slag) and a meat-and-bone meal ash (MB meal ash). The effectiveness of these products as P fertilizers compared with triple superphosphate (TSP) and phosphate rock (PR) was determined in a 2-year pot experiment with maize ( Zea mays L., cv. Atletico) in two soils with contrasting pH (pH(CaCl 2 ) 4.7 and 6.6). The parameters used to evaluate the effectiveness were P uptake, P concentration in soil solution (C Li ) and isotopically exchangeable P (IEP). MAP products were as effective as TSP in both soils, while Ca-P was only effective in the acid soil. Sinter-P was as effective as TSP in the acid soil, while Cupola slag was in the neutral soil. The products Sl-ash and MB meal ash were of low effectiveness and were comparable to PR. The effect of the fertilizers on IEP, but not on C Li , described their effectiveness. Recycled P products obtained by chemical processes, especially MAP, could be directly applied as P fertilizers, while products such as Sl-ash and MB meal ash are potential raw materials for P fertilizer production.

The toxicity of aluminum (Al) to plants in acidic soils depends on the Al species in soil solution. The effects of crop straw biochars on Al species in the soil solution, and canola growth and yield were investigated in this study. In a long-term field experiment, there were four treatments, which were a control, rice straw biochar (RSB), canola straw biochar (CSB), and peanut straw biochar (PSB). The soil solution was collected in situ, the Al species were identified, and the relationships between the concentration of phytotoxic Al and canola growth and yield were evaluated. The results showed that applying the three biochars resulted in significant decreases in the concentrations of total Al, monomeric Al, and monomeric inorganic Al ( P  < 0.05). The Al 3+ , Al-OH, and Al-SO 4 proportions of the total Al also decreased. The abilities of the different biochars to reduce dissolved Al followed the order PSB > CSB > RSB, which was consistent with the alkalinity of these biochars. Application of the biochars significantly decreased the concentration of phytotoxic Al (Al 3+ + Al-OH), which improved canola growth and increased the canola seed and straw yields. Plant height, leaf number per plant, area per leaf, chlorophyll content, and canola yield were negatively correlated with the Al 3+ + Al-OH concentrations. Therefore, the results showed that crop straw biochars can be used to ameliorate soil acidity and alleviate Al toxicity in acidic soils, and that peanut straw biochar is the best amendment for acidic soils.

Potassium (K) fertilizer application in garlic (Allium sativum L) is commonly based on current cultivars that are normally infected with phytopathogenic viruses. Garlic are being developed using meristem culture, but methods for K diagnosis in this type of garlic need to be validated. The objective was to evaluate methods for diagnosing nutritional status of virus-free garlic as a result of K doses through use of a specific K+ meter in soil solution and foliar sap, and to determine foliar K content and its relationship with yield and quality of bulbs. Treatments consisted of K2O doses: 0, 50, 100, 250 or 500 kg ha-1 established in 5 separate locations. In all locations, K2O was applied in a single dose, before planting and incorporated in the 0-0.2 m layer. Response of garlic to K fertilization was low, with marketable yield being significant at a single location, with the highest marketable yield associated with 309 kg ha-1 of K2O. The K content of the soil solution and the K in the foliar sap increased with application of increasing K dose. Due to the low response of marketable yield of garlic to K fertilization, technologies of nutritional diagnosis of K was not efficient. Therefore, future studies should focus on different soil K concentrations to validate the sensibility of these technologies. Potassium (K) fertilizer application in garlic (Allium sativum L) is commonly based on current cultivars that are normally infected with phytopathogenic viruses. Garlic are being developed using meristem culture, but methods for K diagnosis in this type of garlic need to be validated. The objective was to evaluate methods for diagnosing nutritional status of virus-free garlic as a result of K doses through use of a specific K+ meter in soil solution and foliar sap, and to determine foliar K content and its relationship with yield and quality of bulbs. Treatments consisted of K2O doses: 0, 50, 100, 250 or 500 kg ha-1 established in 5 separate locations. In all locations, K2O was applied in a single dose, before planting and incorporated in the 0-0.2 m layer. Response of garlic to K fertilization was low, with marketable yield being significant at a single location, with the highest marketable yield associated with 309 kg ha-1 of K2O. The K content of the soil solution and the K in the foliar sap increased with application of increasing K dose. Due to the low response of marketable yield of garlic to K fertilization, technologies of nutritional diagnosis of K was not efficient. Therefore, future studies should focus on different soil K concentrations to validate the sensibility of these technologies.

Bamboo invasion into adjacent forests highlights the need to clarify its ecological impacts, particularly on soil solution chemistry, which influences forest nutrient availability and downstream water quality. This study examined how bamboo invasion alters base cations and anion concentrations, their vertical distribution, and the distinct ionic compositions maintaining charge balance in soil solution by comparing Moso bamboo (BF) and adjacent Japanese cedar (CF) forests. In surface soil solution (5 cm), most ion concentrations were significantly higher in CF than in BF, likely attributable to a greater interception of atmospheric nitrogen resulting from taller tree height in CF. In vertical distribution, CF showed generally higher ion concentrations in surface soil solution than at 50 cm, whereas in BF, this phenomenon was observed only for NO3−, NH4+, and K+, consistent with bamboo’s high demand for macronutrients. Significant correlations between the concentration of NO3− and those of Ca2+ and Mg2+ were absent only in BF soil leachate. Conversely, a deficit of strong anions showed a significant correlation with the concentration of Ca2+ and Mg2+ in BF soil leachate, with HCO3− identified as a potentially major component. Our findings provide insights into the concomitant-ion relationships between base cations and NO3− across forest types and soil depths.

Soils play a fundamental role in plant nutrition as primary sources of potassium (K) and magnesium (Mg), whose availability depends on soil properties and environmental conditions. The composition of major cations in the soil solution is governed by interacting factors, including soil texture, acidity, mineralogical composition, and seasonal variability during the growing cycle. This study examines the availability, mobility, and seasonal dynamics of K and Mg in the soil solution of seven naturally managed soils across four distinct periods of a complete growing season beginning in spring. An integrated field and laboratory approach was applied to assess the influence of clay mineralogy on K and Mg behavior and overall soil fertility. Seasonal soil samples were analyzed for mineral composition, total elemental chemistry, exchangeable cation pools, and soil solution chemistry. Total elemental concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS), and clay mineral assemblages were identified by X-ray diffraction (XRD), focusing on 2:1 clay minerals, mixed-layer phases, and hydroxy-interlayered minerals (HIMs). The soils were dominated by 2:1 and mixed-layer assemblages, including illite/smectite (Ill/Sm), mica/illite–vermiculite (M/Vm), and chlorite/smectite (Chl/Sm), as well as transitional HIMs such as hydroxy-interlayered smectite (HIS) and hydroxy-interlayered vermiculite (HIV). Exchangeable Mg (0.28–1.30 cmolc kg−1) and K (0.12–0.97 cmolc kg−1) occurred in relatively high amounts, with maximum base saturation values of 13.14% (Mg) and 4.55% (K). Soil solution concentrations ranged from 1.60 to 3.00 ppm for K+ and 0.90–1.70 ppm for Mg2+, indicating substantial mobility and enrichment from the solid phase. These findings demonstrate that 2:1 clay minerals and mixed-layer phases act as key reservoirs regulating K and Mg exchangeability and release under natural acidic conditions, thereby sustaining soil fertility and nutrient availability for plant uptake.