Greenhouse Cultivation of Cucumber (Cucumis sativus L.) in Standard Soilless Media Amended with Biochar and Compost

Peat is one of the most commonly used substrates in soilless cultivation. However, peat mining produces a negative carbon footprint, which raises the need for alternative sustainable substrate media. To address this, we studied the impact of peat replacement with a combination of various biochars and cotton burr compost on the growth and yield of cucumber (Cucumis sativus L.), and nutrient concentration of media, plant leaf, and fruit in greenhouse conditions. Two experiments were conducted from Nov 2020 through Jan 2021 (Trial 1) and from Feb to Apr 2021 (Trial 2). The treatments were control (peat, vermiculite, and perlite at 2:1:1) and in the control peat was either fully replaced (hardwood biochar+compost, softwood biochar+compost, and hemp biochar+compost) or partially replaced up to 50% (v/v) (hardwood biochar+compost, softwood biochar+compost, and hemp biochar+compost). The control media was more acidic with lowest electrical conductivity than the other treatments. The leaf chlorophyll content and the photosynthetic assimilation rate varied among the treatments in both trials. The final dry shoot biomass was lowest in peat-dominated control treatment suggesting biochar-compost in the substrate media contributed in increased dry biomass of the cucumber plant. The total number of fruits per plant and total yield per plant was significantly increased in all the treatments with the highest in hardwood biochar+compost, compared with the control. The nutrient concentration of media, leaf, and fruit indicates that biochar-compost enhances the nutritional status of the media, which supplies essential nutrients to the plant leaf and fruit while growing in different substrate compositions. Our results suggest that the replacement of peat with full or partial proportions of biochar-compost can produce similar and, in some cases, even better growth, yield, and physiology in potted cucumber than in the unamended control treatment

Natural speciation of nickel at the micrometer scale in serpentine (ultramafic) topsoils using microfocused X-ray fluorescence, diffraction, and absorption

Abstract Serpentine soils and ultramafic laterites develop over ultramafic bedrock and are important geological materials from environmental, geochemical, and industrial standpoints. They have naturally elevated concentrations of trace metals, such as Ni, Cr, and Co, and also high levels of Fe and Mg. Minerals host these trace metals and influence metal mobility. Ni in particular is an important trace metal in these soils, and the objective of this research was to use microscale (µ) techniques to identify naturally occurring minerals that contain Ni and Ni correlations with other trace metals, such as Fe, Mn, and Cr. Synchrotron based µ-XRF, µ-XRD, and µ-XAS were used. Ni was often located in the octahedral layer of serpentine minerals, such as lizardite, and in other layered phyllosilicate minerals with similar octahedral structure, such as chlorite group minerals including clinochlore and chamosite. Ni was also present in goethite, hematite, magnetite, and ferrihydrite. Goethite was present with lizardite and antigorite on the micrometer scale. Lizardite integrated both Ni and Mn simultaneously in its octahedral layer. Enstatite, pargasite, chamosite, phlogopite, and forsterite incorporated various amounts of Ni and Fe over the micrometer spatial scale. Ni content increased six to seven times within the same 500 µm µ-XRD transect on chamosite and phlogopite. Data are shown down to an 8 µm spatial scale. Ni was not associated with chromite or zincochromite particles. Ni often correlated with Fe and Mn, and generally did not correlate with Cr, Zn, Ca, or K in µ-XRF maps. A split shoulder feature in the µ-XAS data at 8400 eV (3.7 Å−1 in k-space) is highly correlated (94% of averaged LCF results) to Ni located in the octahedral sheet of layered phyllosilicate minerals, such as serpentine and chlorite-group minerals. A comparison of bulk-XAS LCF to averaged µ-XAS LCF results showed good representation of the bulk soil via the µ-XAS technique for two of the three soils. In the locations analyzed by µ-XAS, average Ni speciation was dominated by layered phyllosilicate and serpentine minerals (76%), iron oxides (18%), and manganese oxides (9%). In the locations analyzed by µ-XRD, average Ni speciation was dominated by layered phyllosilicate, serpentine, and ultramafic-related minerals (71%) and iron oxides (17%), illustrating the complementary nature of these two methods

Competitive sorption of Ni and Zn at the aluminum oxide/water interface: an XAFS study

Abstract Trace metals (e.g. Ni, Zn) leached from industrial and agricultural processes are often simultaneously present in contaminated soils and sediments. Their mobility, bioavailability, and ecotoxicity are affected by sorption and cosorption at mineral/solution interfaces. Cosorption of trace metals has been investigated at the macroscopic level, but there is not a clear understanding of the molecular-scale cosorption processes due to lack of spectroscopic information. In this study, Ni and Zn cosorption to aluminum oxides (γ-Al2O3) in binary-sorbate systems were compared to their sorption in single-sorbate systems as a function of pH using both macroscopic batch experiments and synchrotron-based X-ray absorption fine structure spectroscopy. At pH 6.0, Ni and Zn were sorbed as inner-sphere surface complexes and competed for the limited number of reactive sites on γ-Al2O3. In binary-sorbate systems, Ni had no effect on Zn sorption, owning to its lower affinity for the metal oxide surface. In contrast, Zn had a higher affinity for the metal oxide surface and reduced Ni sorption. At pH 7.5, Ni and Zn were sorbed as mixed-metal surface precipitates, including Ni–Al layered double hydroxides (LDHs), Zn–Al LDHs, and likely Ni–Zn–Al layered triple/ternary hydroxides. Additionally, at pH 7.5, Ni and Zn do not exhibit competitive sorption effects in the binary system. Taken together, these results indicated that pH critically influenced the reaction products, and provides a crucial scientific basis to understand the potential mobility, bioavailability, and ecotoxicity of Ni and Zn in natural and contaminated geochemical environments

Structural Differentiation between Layered Single (Ni) and Double Metal Hydroxides (Ni–Al LDHs) Using Wavelet Transformation

Layered double hydroxides (LDHs) are anionic clays important in disciplines such as environmental chemistry, geochemistry, and materials science. Developments in signal processing of extended X-ray absorption fine structure (EXAFS) data, such as wavelet transformation (WT), have been used to identify transition metals and Al present in the hydroxide sheets of LDHs. The WT plots of LDHs should be distinct from those of isostructural single metal hydroxides. However, no direct comparison of these minerals appears in the literature using WT. This work systematically analyzes a suite of Ni-rich mineral standards, including Ni–Al LDHs, single metal Ni hydroxides, and Ni-rich silicates using WT. The results illustrate that the WT plots for α-Ni­(OH)₂ and Ni–Al LDHs are often indistinguishable from each other, with similar two-component plots for the different mineral types. This demonstrates that the WT of the first metal shell often cannot be used to differentiate an LDH from a single metal hydroxide. Interlayer anions adsorbed to the hydroxide sheet of α-Ni­(OH)₂ affect the EXAFS spectra and are not visible in the FT but are clearly resolved and discrete in the WT

Systematic Study of Legacy Phosphorus (P) Desorption Mechanisms in High-P Agricultural Soils

Repeated manure additions containing phosphorus (P) in excess of crop needs have led to many agricultural soils with high levels of soil P (i.e., legacy P), particularly in the Delmarva region (USA). Due to the potential for P release, it is important to gain a better understanding of the mechanisms of P desorption and solubilization. Agricultural soils with high legacy P were collected from the Delmarva Peninsula, and soil P pools were determined using a suite of wet chemical and spectroscopic techniques, including a modified Hedley sequential extraction and X-ray absorption near-edge structure (XANES) spectroscopy. Five different desorption solutions were used to investigate P removal efficiency to assess release mechanisms. The results indicate that sulfate can have a stronger competition for P desorption than silicate, especially in the ditch sample with 21% labile P and 44% P adsorbed to iron and aluminum (via Hedley extraction). Additionally, linear combination fitting results of the ditch sample indicate 10.5% organic P and 73.9% P associated with iron and aluminum. This is an important finding because sulfate is a prevalent ion in sea water, and many agricultural soils with high legacy P in the Delmarva coastal area are threatened by sea level rise and inundation

The role of Fe(III) in soil organic matter stabilization in two size fractions having opposite features

Peer reviewe

Variation in cadmium accumulation and speciation within the same population of the hyperaccumulator Noccaea caerulescens grown in a moderately contaminated soil

Background and aims: Phytoextraction is an eco-friendly approach for remediation of heavy metal contaminated soil. The aim is to screen Noccaea caerulescens lines with higher cadmium (Cd) phytoextraction efficiency and investigate differences in Cd species and distribution in the leaves of high and low Cd accumulating lines. Methods: Biomass production and Cd bioaccumulation capacities of 29 Noccaea caerulescens lines, generated through single-seed-descent from a Cd hyperaccumulating calamine population, were assessed in a pot experiment with a moderately Cd contaminated soil (2.1 mg Cd kg− 1). Synchrotron-based techniques were employed to identify and characterize Cd speciation and distribution in Noccaea caerulescens leaves. Results: The largest biomass of Noccaea caerulescens reached 5.0 ± 3.3 g (D. W. pot− 1) after 6 months growth. The Cd concentrations in shoots varied from 85 to 203 mg kg− 1. The most efficient line removed 0.64 mg Cd pot− 1 and lowered the total Cd in soil by 30%. Synchrotron-based X-ray absorption spectroscopy showed that the dominant Cd species was Cd-thiol complexes. Cadmium-carboxyl and Cd-phytate/phosphate were present in the leaves of high and low Cd accumulating lines, respectively. Micro X-ray fluorescence microscopy showed cadmium was concentrated in leaf veins. Conclusions: There are wide variations including both biomass production and Cd accumulation capacity among different lines within the same calamine ecotype of Noccaea caerulescens. Cadmium-thiol complexes play the most important role in Cd detoxification in leaves of Noccaea caerulescens grown in moderately Cd contaminated paddy soil. These findings provide a physiological basis for breeding high Cd accumulation varieties of Noccaea caerulescens

The role of Fe(III) in soil organic matter stabilization in two size fractions having opposite features

Soil organic matter (SOM) protection, stability and long-term accumulation are controlled by several factors, including sorption onto mineral surfaces. Iron (Fe) has been suggested as a key regulator of SOM stability, both in acidic conditions, where Fe(III) is soluble, and in near-neutral pH environments, where it precipitates as Fe(III) (hydr)oxides. The present study aimed to probe, by sorption/desorption experiments in which Fe was added to the system, the mechanisms controlling Fe(III)-mediated organic carbon (C) stabilization; fine silt and clay (FSi + Cl) and fine sand (FSa) SOM fractions of three soils under different land uses were tested. Fe(III) addition caused a decrease in the organic C remaining in solution after reaction, indicating an Fe-mediated organic C stabilization effect. This effect was two times larger for FSa than for FSi + Cl, the former fraction being characterized by both low specific surface area and high organic C content. The organic C retained in the solid phase after Fe-mediated stabilization has relatively low sensitivity to desorption. Moreover, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy indicated that Fe-mediated organic C stabilization can be mainly ascribed to the formation of complexes between carbohydrate OH functional groups and Fe oxides. These results demonstrate that the binding of labile SOM compounds to Fe(III) contributes to its preservation, and that the mechanisms involved (flocculation vs. coating) depend on the size fractions

Iron(III) fate after complexation with soil organic matter in fine silt and clay fractions: An EXAFS spectroscopic approach

Iron (Fe) speciation in soils is highly dependent on environmental conditions, mineralogy, and chemical interactions with soil organic matter (SOM). The fine silt and clay (FSi + Cl) particle size fraction of soils constitutes a primary organo-mineral fraction and contains SOM with long turnover time. In this study, the FSi + Cl particle size fractions isolated from a coniferous forest, a grassland, a technosol, and an agricultural soil were reacted with Fe(III) at pH 7. Unreacted and reacted samples were then investigated by means of extended X-ray absorption fine structure (EXAFS) spectroscopy. Statistical methods were used to determine goodness-of-fit parameters for linear combination fitting (LCF) and wavelet transformation (WT) of the Fe K-edge EXAFS data. WT separated spectral contributions from different backscattering atoms in higher coordination shells located at similar interatomic distances from the central absorbing Fe atom. LCF results paired with WT showed that the FSi + Cl particle size fractions consisted of a mixture of Fe phyllosilicates, Fe (hydr)oxides, and organically complexed Fe in different proportions. Our research revealed that after sorption experiments, in which Fe(III) was added to the system, increasing amounts of Fe(III)-SOM complexes were found in the solid phase of grassland and agricultural soils, whereas the precipitation of Fe(III) led to the preferential formation of ferrihydrite in the coniferous forest soil and in the technosol. Although the quantitative Fe-mediated organic carbon stabilization effect after Fe(III) addition is shown in this work, Fe speciation is not clearly related to SOM amount or quality (i.e., carbon-to-nitrogen ratio). The variation of Fe chemical speciation among the soil fractions likely translates into differences in their environmental fate