Perspectives for Biochar as a vehicle for inoculation of phosphate solubilizing bacteria: a review

Phosphorus (P) plays a vital role in many aspects of plant growth and development. The low amount of available P in agricultural soils reduces crop productivity and phosphate fertilizers are often applied. However, due to the high affinity of P for the soil constituents, the availability of this element becomes limited to plants. Thus, alternative, ecological, and low-cost techniques have been studied to improve P acquisition by crops. Microorganisms able to solubilize P, mainly phosphate-solubilizing bacteria (PSB) have stood out, since they offer an approach to overcome P scarcity by their introduction in agricultural systems via inoculants. In this paper, we showed the potential of P-solubilizing microorganisms and their mechanisms of action, the potential of different inoculation vehicles, also highlighting the biochar as a viable biological product for production of inoculants. The combined effects of these factors (PSB and biochar) add several benefits to the soil-plant system. Results from this review demonstrate that biochar amendments have great potential as a vehicle for inoculation of PSB. However, studies of biochar combined with PSB is still incipient. Future research should focus efforts on exploring highly efficient strains, optimizing conditions, and assessing several sources of waste for production of biochar and their efficiency in field experiments.

The Fate of Glyphosate in Soil and Water: A Review

The fate of glyphosate in soil and water is dependent on the properties of glyphosate and its envoronement. Behaviour of glyphosate in soil, sediment and water is strongly influenced the way by which it can be adsorbed by soils, sediments, and suspended material in water. The role of soil organic matter, clay mineral, and amorphous minerals on the adsorption of glyphosate depends primarily on the nature and properties of the soil itself and the properties of glyphosate. Environmental factors have some influence on sorption and degradation of glyphosate. Glyphosate is rapidly inactivated in soil, is in part due to adsorption. Some soil properties have been identified strongly influence adsorption of glyphosate, such as clay minerals, composition of cations in exchangeable site of clay and organic matter, unoccupied phosphate adsorption site, degree of humification, and soil pH. Adsorption limits the availability of glyposate for microbial degradation. The sorbed glyphosate is not directly available to microorganisms in soil. Evidence also suggests that not only a strongly sorbed compound such as paraquat but also weakly sorbed compounds such as flumetsulam and picloram can persist for long periods when they are sorbed by soil constituents. This suggests that the interaction between sorption and biodegradation should be considered in predicting the fate of pesticides in soils and sediments.

Physical Attributes of Ferralsol in Fertigated Sugarcane Production Environments for Bioethanol in the Midwest of Brazil

Brazil is the world leader in the production and export of sugarcane derivatives, and its center-south region is the main producer. Fertigation with byproducts from bioethanol production can be adopted as a strategy to mitigate the soil physical deterioration resulting from the intensification of mechanized farming practices. The objective of this study was to evaluate the behavior of soil physical attributes under sugarcane cultivation in different crop cycles in fertigated areas in the midwest region of Brazil. The samples were collected in different Ferralsol layers (0.0–0.1, 0.1–0.2, 0.2–0.3, and 0.4–0.5 m) and fertigated crop cycles (first, third, fifth, seventh, and twelfth sugarcane cycles), as well as from native Cerrado vegetation (reference area), and the weight and volume relationships of the soil constituents and total soil were evaluated. Soil physical attributes are affected by sugarcane cultivation cycles and fertigation with vinasse. In the short term (third cycle), the results indicate deterioration of the physical attributes of the soil. However, throughout the cycles of sugarcane culture via fertigation (twelve cycles), the addition of vinasse leads to improvements in physical attributes and soil aggregation, promoting an increase in the longevity of the sugarcane crop. Therefore, the evaluation of the physical attributes of the soil in areas with vinasse application in different sugarcane cultivation cycles should be analyzed in areas of different regions, as this management practice indicates a high potential to increase the longevity of cultivation sugarcane, reducing production costs in the bioenergy sector.

Comparable Discrimination of Soil Constituents Using Spectral Reflectance Data (400–1000 nm) Acquired with Hyperspectral Radiometry

Currently, a gap exists in inventorying and monitoring the impact of land use and management on soil resources. Reducing the number of samples required to determine the impact of land management on soil carbon (C) and mineral constituents via proximal sensing techniques such as hyper-spectral radiometry can reduce the cost and personnel required to monitor changes in our natural resource base. Previously, we used an expensive, high signal-to-noise ratio (SNR) field spectrometer to correlate soil constituents to hyperspectral diffuse reflectance (HDR), over the 350–2500 nm (VIS-SWIR) wavelength range. This research is an extension of preceding research but focuses solely on the 400–1000 nm (VIS-NIR) region of the electromagnetic spectrum. This region can be measured using less expensive (albeit with lower SNR), miniaturized, field spectrometers that allow minimal sample preparation. Our objectives are to: (1) further evaluate the use of soil HDR in the visible and near-infrared (VIS-NIR) region acquired using an expensive field hyperspectral spectroradiometer for prediction of soil C and selected fractions and nitrogen (N) constituents, (2) repeat the above measurements using HDR data from samples examined in objective (1) using lower SNR hyperspectral radiometers, and (3) add to the limited literature that addresses determinations of selected soil properties using proximal sensing in the VIS-NIR region. Data analyzed in this study confirms that good to satisfactory prediction equations for soil constituents can be developed from spectral reflectance data within the 400–1000 nm wavelength region obtained using relatively inexpensive field radiometers. This application could reduce the time and resources required to monitor gains or losses in carbon constituents, information that can be used in programing such as Conservation Technical Assistance (CTA), the Conservation Reserve Program (CRP) and Climate-smart agriculture (CSA).

Inventory and Statistical Characterization of Inorganic Soil Constituents in Illinois: Appendices

This report presents detailed histograms of data from the Regulated Substances Library (RSL) developed by the Illinois Department of Transportation (IDOT). RSL data are provided for state and IDOT region, IDOT district, and county spatial subsets to examine the spatial variability and its relationship to thresholds defining natural background concentrations. The RSL is comprised of surficial soil chemistry data obtained from rights-of-way (ROW) subsurface soil sampling conducted for routine preliminary site investigations. A selection of 22 inorganic soil analytes are examined in this report: Al, Sb, As, Ba, Be, Cd, Ca, Cr, Co, Cu, Fe, Pb, Mg, Mn, Hg, Ni, K, Se, Na, Tl, V, and Zn. RSL database summary statistics, mean, median, minimum, maximum, 5th percentile, and 95th percentile, are determined for Illinois counties and for recognized environmental concern, non-recognized environmental concern, and de minimis site contamination classifications.

Inventory and Statistical Characterization of Inorganic Soil Constituents in Illinois

This report presents a statistical analysis of the Regulated Substances Library (RSL) developed by the Illinois Department of Transportation. The RSL is comprised of surficial soil chemistry data obtained from rights-of-way subsurface soil sampling conducted for routine preliminary site investigations. The 3.7-million-record RSL database is compared with four independent studies of inorganic soil constituents of naturally occurring soils in Illinois. A selection of 22 inorganic soil analytes are examined in this study: Al, Sb, As, Ba, Be, Cd, Ca, Cr, Co, Cu, Fe, Pb, Mg, Mn, Hg, Ni, K, Se, Na, Tl, V, and Zn. RSL database summary statistics, mean, median, minimum, maximum, 5th percentile, and 95th percentile, are determined for Illinois counties and for recognized environmental concern, non-recognized environmental concern, and de minimis site contamination classifications. The RSL database at a 95% confidence level is compared with current and proposed thresholds for defining naturally occurring soil concentrations for the selected analytes. The revised thresholds proposed by Cahill in 2017 are predominantly larger than the current standards found in the Tiered Approach to Corrective Action Objectives rules and are in better agreement with observed distributions of soil concentrations for both naturally occurring and RSL soils. A notable exception is antimony (Sb), for which Cahill proposed a reduced threshold similar in magnitude to the median for many Illinois Department of Transportation districts.

New Insight into Mechanism of Cr(VI) Migration and Transformation in Typical Soils of Chromite ore Processing Residue (COPR) Contaminated Sites

Chromite ore processing residue (COPR) storage sites are widely distributed all over the world, causing serious soil and groundwater pollution. However, the differences in soil constituents and properties between different regions are significant, and the dynamic migration and transformation of Cr(VI) in different types of soil under alkaline condition of the COPR site is still unclear. In this study, the typical black soil, red soil and loess in different regions of China were chosen to investigate the adsorption kinetics and thermodynamics of Cr(VI) under the original pH conditions of the soil, and then the alkaline Cr(VI) solution was introduced into the soil column to simulate the dynamic migration and transformation process of Cr(VI) at COPR sites. According to the results, the Cr(VI) breakthrough curve predicted by the solid-liquid distribution coefficient Kd based on the static isotherm adsorption experiments significantly underestimated and overestimated the retention effect of black soil and red soil on Cr(VI) dynamic migration, respectively. For the black soil, the retention of Cr(VI) was dominated by Cr(VI) reduction, which is a slow reaction compared with Cr(VI) adsorption. Therefore, the reduction kinetics process during the column experiment cannot be neglected. In respect to the red soil, the outlet Cr(VI) concentration turned to be higher than the inlet concentration with the soil alkalization, which indicated that the adsorbed Cr(VI) desorbed again, and this is the main reason for the overestimation of Cr(VI) retention effect by the red soil. This study shows that the environmental risks of Cr in different types of soil are quite different, mainly related to the valence and occurrence form of Cr that governed by the soil constituents and properties. In addition, the stable form of Cr in the black soil column after the reaction indicates that the soil organic matter can be used as a potential environmentally friendly remediation material for Cr(VI) contaminated soils at COPR sites.

Clay Minerals Affect the Solubility of Zn and Other Bivalent Cations in the Digestive Tract of Ruminants In Vitro

Ruminants ingest large quantities of clay minerals along with inorganic soil constituents in roughages. The layered structure of clay minerals, however, may adsorb cations and may, thus, interfere with the ruminants’ supply of essential trace metals, such as Zn, Mn, Cu, and Fe. As quantitative knowledge about interactions between clay ingestion and essential trace metal metabolism are largely lacking, this in vitro study focussed on the effect of clay on the solubility of dietary Zn and other bivalent trace metals in the digestive tract of ruminants. Therefore, buffered rumen fluid was used for the simulation of ruminal conditions (RC), acidified rumen fluid (pH 2) was used for abomasal conditions (AC), and duodenal chyme was used for duodenal conditions (DC). These media were added with gradient levels of zinc and incubated at 39 °C for 24 h in the absence or presence of clay minerals. Soluble Zn, Cu, Mn, and Fe were derived by centrifugation (10,000× g) of incubated media, and the supernatants were analysed. Clay depressed the solubility of added Zn in ruminal (65.3% vs. 16.5%), abomasal (97.7% vs. 33.7%), and duodenal conditions (41.3% vs. 21.1%), the results of which were statistically significant (p < 0.001). Moreover, clay reduced dissolved Cu (µg/mL) (RC: 0.13 vs. 0.10; AC: 0.16 vs. 0.13; DC: 0.10 vs. 0.08) and Mn (µg/mL) (RC: 3.00 vs. 1.80; AC: 5.53 vs. 4.80; DC: 3.18 vs. 1.77) (p < 0.05 in all cases). The presence of clay minerals increased the concentrations of solubilised Fe (µg/mL) in abomasal (1.80 vs. 2.86, p < 0.05) and duodenal conditions (1.76 vs. 2.67; p < 0.05). In total, the present in vitro study demonstrates the potential of clay minerals ingested with ruminant feeds for depressing the solubility of dietary Zn, as well as the depression of dietary Cu and Mn along the passage of the digesta from the rumen until the duodenum. Additionally, clay minerals may release Fe into the digesta.

The Organization of Soil Fragments

Kubiëna (1938) was the first to introduce the concept of fabric in soil micromorphology, so this term has been used in soil micromorphology for a long time. The term “fabric” was initially applied to rocks by geologists and petrologists. This type of fabric is defined as the “factor of the texture of a crystalline rock which depends on the relative sizes, the shapes, and the arrangement of the component crystals” (Matthews and Boyer 1976). This definition has been adapted for soil micromorphology and its latest definition has been given by Bullock et al. (1985) as: “soil fabric deals with the total organization of a soil, expressed by the spatial arrangement of the soil constituents (solid, liquid, and gaseous), their shape, size, and frequency, considered from a configurational, functional and genetic view-point”. In conclusion, the soil micromorphologist should consider the fabric as an arrangement and∕or organization of soil constituents.