Luvisol Soil Research Articles

Gray Luvisols are polygenetic

With respect to the pedosphere, human activities in the last 100 years have been the major driver of soil change. Despite human activities being one of the main soil forming factors recognized by soil scientists (in addition to climate, organisms, parent material, relief, groundwater, and time), the Canadian System of Soil Classification (CSSC) emphasizes soil as a natural body. We argue human agricultural activities are direct and indirect drivers of significant changes to the carbon balance and cycling in A horizons of Gray Luvisolic soils in western Canada, resulting in changes to A horizon carbon stocks, structure, and micromorphology. Evidence from scientific literature, in-field soil profile observations, and the National Pedon Database are presented in support of our argument. We propose a polygenetic, two-stage model of Gray Luvisol soil formation. The first stage is dominated by the climate forcing of the Holocene, resulting in a relatively stable boreal forest ecosystem including perturbations from natural and human-induced wildfire and other disturbances. The second stage is dominated by direct, human-driven disturbances such as cultivation, release of exotic fauna (earthworms), and indirect human-driven disturbances associated with anthropogenic climate change. Further, we propose modest amendments to the CSSC to reflect a polygenetic model of soil genesis in Gray Luvisolic soils that preserve the balance between observation and interpretation inherent in the system.

Effects of soil bund spacing on runoff, soil loss, and soil water content in the Lake Tana Basin of Ethiopia

Land degradation is primarily caused by accelerated soil erosion rate, which results in a loss in soil fertility and agricultural production. An improved understanding of the effect of soil bund spacing is a precondition for sustainable land management practices on sloping highlands. We examined the effects of bund spacing on soil loss, runoff, and soil water content on teff (Eragrostis tef [Zucc.] Trotter) cropland in an area of 9 % slope on Luvisol soil in the Aba Gerima (micro) watershed of the Lake Tana Basin, Ethiopia. We measured these parameters during 2018 and 2019 on five adjoining runoff plots (each 30 m long × 3 m wide) separated by metal sheets 0.35 m high. We used a plot with no bunds as a control. In the other four plots, we installed bunds at spacings of 27.2, 12.7, 7.87, and 5.45 m. Both runoff and soil loss were considerably higher in the control plot than in the plots with bunds. Narrower bund spacings resulted in substantial reductions of runoff and soil loss. The two-year average runoff depths in the control, 27.2, 12.7, 8.97, and 5.45 m bund spacing plots were 517, 454, 365, 306, and 243 mm, respectively. Average soil loss for the control plot was 25.7 ton ha−1, whereas it was 17.9, 11.8, 6.5, and 4 ton ha−1 for the 27.2, 12.7, 8.97, and 5.45 m bund spacing plots, respectively. The efficiency of soil bunds in enhancing soil water content increased with reduced soil bund spacing. Over the course of the measurement period, average soil water levels for soil bund spacings of 27.2, 12.7, 8.78, and 5.45 m were 0.30 kg kg−1, 0.31 kg kg−1, 0.32 kg kg−1, and 0.32 kg kg−1, respectively. Further cost–benefit analyses and statistical tests are needed to determine optimum bund spacings in the Ethiopian highlands.

Soil, climate, and variety impact on quantity and quality of maize root mucilage exudation

AimsThis study investigated the influence of climate and soil on the exudation rate and polysaccharide composition of aerial nodal root mucilage from drought-resistant and drought-susceptible maize varieties.MethodsTwo maize varieties were grown in two different soils (sandy-clay loam Acrisol and loam Luvisol) under simulated climatic conditions of their agroecological zones of origin in Kenya and Germany. The exudation rate of mucilage from the aerial nodal roots was quantified as dry weight per root tip per day and the mucilage was characterized for its polysaccharide composition.ResultsOn average, the mucilage exudation rate was 35.8% higher under the Kenyan semi-arid tropical than under the German humid temperate climatic conditions. However, cultivation in the loam Luvisol soil from Germany led to 73.7% higher mucilage exudation rate than cultivation in the sandy-clay loam Acrisol soil from Kenya, plausibly due to its higher microbial biomass and nutrient availability. The drought-resistant Kenyan maize variety exuded 58.2% more mucilage than the drought-susceptible German variety. On average, mucilage polysaccharides were composed of 40.6% galactose, 26.2% fucose, 13.1% mannose, 11% arabinose, 3.5% glucose, 3.2% xylose, 1.3% glucuronic acid, and 1% an unknown uronic acid. Overall, significantly higher proportions of the uronic acids were found in the mucilage of the plants grown in the Kenyan sandy-clay loam soil and under the Kenyan semi-arid tropical climatic conditions.ConclusionsMaize is able to enhance its mucilage exudation rate under warm climatic conditions and in soils of high microbial activity to mitigate water stress and support the rhizosphere microbiome, respectively.Graphical abstract

Integration of perennial forage seed crops for cropping systems resiliency in the Peace River region of western Canada

The Peace River region is one of the northern agricultural frontiers in Canada, undergoing farmland expansion as well as intensification with input-intensive industrial agriculture. The cropping systems evolved with the rotations between annual grain and perennial forage crops as a prudent adaptation to fragile, crust-forming, runoff-prone, poorly developed, platy-structured acidic Luvisolic soils. In recent years, there is a decline in the acreage of perennial forage seed crops leading to simplified low-diversity cropping systems with heavy reliance on external inputs. The production systems have been prone to the rapid evolution of herbicide-resistant weeds, and outbreaks of crop diseases and insect pests in the face of global warming. A number of studies conducted in the Peace River region and other parts of North America have shown multiple benefits of integrating perennial forage crops in the cropping systems. By virtue of high root-to-shoot ratio and perennial growth, forage seed crops can provide multiple ecological services in the fragile Luvisolic soil through increased soil organic matter, carbon sequestration, soil biological diversity, soil structural improvement, nutrient mobilization, crop protection and environmental health, thereby creating conducive effects to the resilient performance of the cropping systems. This review discusses the merits of crop rotations in general and those of perennial forage seed crops in particular in the face of changing climate, with special reference to studies conducted in the Prairies and Peace region of western Canada. Research opportunities are highlighted to elucidate multidimensional ecosystem services from diversified cropping sequences integrating perennial forage seed crops.

Monitoring the concentrations of Cd, Cu, Pb, Ni, Cr, Zn, Mn and Fe in cultivated Haplic Luvisol soils using near-infrared reflectance spectroscopy and chemometrics

This study illustrates the successful application of near-infrared reflectance spectroscopy extended with chemometric modeling to profile Cd, Cu, Pb, Ni, Cr, Zn, Mn, and Fe in cultivated and fertilized Haplic Luvisol soils. The partial least-squares regression (PLSR) models were built to predict the elements present in the soil samples at very low contents. A total of 234 soil samples were investigated, and their reflectance spectra were recorded in the spectral range of 1100–2500 nm. The optimal spectral preprocessing was selected among 56 different scenarios considering the root mean squared error of prediction (RMSEP). The partial robust M-regression method (PRM) was used to handle the outlying samples. The most promising models were obtained for estimating the amount of Cu (using PRM) and Pb (using the classic PLS), leading to RMSEP expressed as a percentage of the response range, equal to 9.63% and 11.5%, respectively. The respective coefficients of determination for validation samples were equal to 0.86 and 0.58, respectively. Assuming similar variability of model residuals for the model and test set samples, coefficients of determination for validation samples were 0.94 and 0.89, respectively. Moreover, the favorable PLS models were also built for Zn, Mn, and Fe with coefficients of determinations equal to 0.87, 0.87, and 0.79.

EFFECT OF THREE GREEN MANURES ON THE AGRONOMIC CHARACTERISTICS OF NATIVE X’MEJEN NAAL MAIZE IN CAMPECHE, MEXICO

In the agronomic management of maize (Zea mays L.), chemical fertilizers can be substituted for fertilizing techniques that reduce the pollutant effect of the excessive use of commercial fertilizers. The hypothesis was the green manure of legumes with or without the inoculation of microorganisms are capable of promoting agronomic characteristics of X’mejen Naal maize, comparable to conventional fertilization. In order to measure the effect in the agronomic characteristics of X´mejen Naal maize, an experiment was designed in complete randomized blocks in a bifactorial arrangement with four repetitions, in which three green manures were tested, with or without the inoculation of Fosfonat (endomycorrhizas, EM, plus nitrogen fixating bacteria, NFB). Treatments were Mucuna (Mucuna pruriens, T1=MUC), Xpelón (Vigna unguiculata, T2=PEL), Ibes (Phaseolus lunatus, T3=IBE), inoculated Mucuna (T4=MUCEM), inoculated Xpelón (T5=PELEM), inoculated Ibes (T6= IBEEM) and the control with the incorporated biomass of weeds plus the addition of 200 kg ha-1 of diammonium phosphate (T7=ARDAP). Results showed that there were only differences caused by the types of green manure and their interaction with the inoculated symbionts in the fresh weight or biomass in X´mejen Naal maize. IBE and ARDAP stood out in fresh weight (1162 and 1251 g), dry weight (168.6 and 163.6 g), 7.3 Mg ha-1 (Megagrams per hectare) in the dry aerial biomass in the maize plants, respectively. Despite the grain yield of maize was similar among treatments, it was noticeable that the higher average yields were also observed in IBE and ARDAP with 3.5 and 3.3 Mg ha-1 respectively. All yields (fodder and grain) managed to express the potential of the X´mejen Naal, which is relevant to recommend the use of green manures as an agro-environmental alternative to conventional fertilization in the Luvisol soils of Campeche.

Effect of Nitrogen Fertilizer and Soil Moisture Levels on the Performance of Drought-Tolerant Maize on Ferric Luvisol and Rhodic Ferralsol Soils

Globally, water and nitrogen have been known as the most important resources that significantly impact crop productivity. This study assessed the response of Water Efficient Maize for Africa, WEMA3127 variety to different soil moisture levels, and nitrogen fertilizer rates on Ferric Luvisol and Rhodic Ferralsol soils. A greenhouse experiment was conducted to investigate the effect of different N fertilizer and soil moisture levels on the growth, yields and water-use efficiency of the water-efficient maize for Africa (WEMA) variety on two distinct soils. The experiment was designed as a completely randomized design with three replicates and used a factorial design with a 5 x 2 x 2 design. Treatments comprised five N fertilizer rates (0, 60, 120, 180 and 240 kg N/ha), two soil moisture levels (45 and 100% field capacity), and two soil types (Ferric Luvisol and Rhodic Ferralsol). Plant height, chlorophyll content and total dry matter weight as growth attributes, grain yield, total biological yield and water-use efficiency parameters were determined. The tallest plant height (283.33 cm) was recorded in Ferric Luvisol supplied with 240 kg N/ha at 100% field capacity. The highest grain yield (136.8 g /pot) and water-use efficiency (1.94%) were obtained in Rhodic Ferralsol treated with 180 kg N/ha at 100% and 45% field capacity (FC), respectively. A linear relationship was obtained between N fertilizer rates and the grain yield (R2 = 0.91) and between total dry matter and grain yield (R2 = 0.51). The results showed that the growth and water-use efficiency of WE3127 maize variety was better on Rhodic Ferralsol than in Ferric Luvisol.

The Seed Yield of Soybean Cultivars and Their Quantity Depending on Sowing Term

The successful production of soybean seeds is dependent on the sowing date, because every sowing outside of the optimal time contributes to losses of yield. The aim of the study was to identify the response to sowing date of the chosen soybean cultivars by the evaluation of the length of the soybean vegetation period, yield level, its parameters and seed chemical composition. A field experiment was conducted in the years 2016–2019 at the Agricultural Experimental Station in Grabów (Masovian Voivodeship, Poland) belonging to the Institute of Soil Science and Plant Cultivation—State Research Institute in Puławy. Soybean cultivars (four in 2016–2017 and six in 2018–2019) listed in the EU Common Catalogue with various earliness were included in the experiment. Three different sowing dates were used: I—early, II—medium and III—delayed. The two-factor experiment was carried out using a split-plot design on Luvisol soil with sandy loam texture classes, in four replications. Soybean seeds were inoculated with a bacterial culture Nitragina containing strains Bradyrhizobium japonicum. After reaching full maturity, the most important morphological traits of 10 plants and yield components: the number of pods per plant and the number of seeds per pod were provided. After harvest, the seeds yield (kg per hectare at the 14% moisture), and 1000-seed weight were determined. The study showed that in the years with favourable weather conditions during the growing season the best yields were obtained for soybean sown on the second date, while in the year with unfavourable weather conditions, the sowing date had no significant effect on the yields. Seeds of the soybean cultivars grown under conditions of limited rainfall contained about 9% more protein than those grown under more favourable agroecological conditions. The delay of sowing date by about 20 days positively influenced the accumulation of protein in seeds.

Complex impacts of hydraulic fracturing return fluids on soil microbial community respiration, structure and functional potentials.

The consequences of soils exposed to hydraulic fracturing (HF) return fluid, often collectively termed flowback and produced water (FPW), are poorly understood, even though soils are a common receptor of FPW spills. Here, we investigate the impacts on soil microbiota exposed to FPW collected from the Montney Formation of western Canada. We measured soil respiration, microbial community structure and functional potentials under FPW exposure across a range of concentrations, exposure time and soil types (luvisol and chernozem). We find that soil type governs microbial community response upon FPW exposure. Within each soil, FPW exposure led to reduced biotic soil respiration, and shifted microbial community structure and functional potentials. We detect substantially higher species richness and more unique functional genes in FPW-exposed soils than in FPW-unexposed soils, with metagenome-assembled genomes (e.g. Marinobacter persicus) from luvisol soil exposed to concentrated FPW being most similar to genomes from HF/FPW sites. Our data demonstrate the complex impacts of microbial communities following FPW exposure and highlight the site-specific effects in evaluation of spills and agricultural reuse of FPW on the normal soil functions.

Digital Technologies Determination Effectiveness for the Productivity of Organic Winter Wheat Production in Low Soil Performance Indicator

The most important aspect of precision farming is the prediction of crop yield and quality. Digital technologies (soil maps and combine harvester with telemetry functions) were used to determinate the yield of organically grown winter wheat (variety Skagen) in two fields of 18.8 and 4.5 ha in Lithuanian regional conditions, in an area classified as low-performance for farming. The objective of the research was to determine the effectiveness of digital technologies (soil maps and combine harvester with telemetry functions) in assessment of the dynamics of soil pH, P2O5, and K2O, humus and organic winter wheat (variety Skagen) productivity, and grain crude-protein dependence in low-performance soils. Haplic Luvisol soils predominated, while Eutric Gleysols, Haplic Arenosols, and Eutric Planosols soils intervened in smaller areas, and the granulometric composition of the soil in the arable layer and the subsoil varied from sand to sandy loam, loam, and silt loam. In the sandy areas of Haplic Arenosols and in the lower parts of the field, where Eutric Gleysols, intervened in predominant Haplic Luvisols soils, winter wheat crude protein content and grain yield were lower. The biggest grain yield of 6.95 t ha−1 was obtained in Haplic Luvisols soils. Crude protein of winter wheat grains varied from 9.70 to 13.34%. Although both technologies reflected the non-uniform yields of the fields and correlation between them well, the information on the soil cover of the field better explained the reasons for lower yields. In the case of this research, sand inclusions and lower areas in winter wheat fields, causing plants to soak during winter, were identified. The combination of two digital technologies (soil maps and combine harvester with telemetry functions) made it possible to determine yields accurately, and quickly. Moreover, there is a need, in the future, to evaluate the reasons for yield variation and address changes in yields due to the improvement of certain low-performance soil areas. The complex use of these technologies can be beneficial in terms of labour and economy. However, the accurate benefit of labour time and economic should be investigated.

Effects of mechanochemically activated phosphate rock on maize growth and phosphorus use

It is well known that mechanochemically activated phosphate rock (MAPR) could improve extractable phosphorus (P) (extracted in 2% citric acid) greatly in an ecological way. To evaluate the agronomic effectiveness of MAPR, we conducted a field experiment using spring maize in Luvisol (pH 6.47) soil in Northeast China for three consecutive years. Treatments consist of variation of P levels for substitution of triple superphosphate (TSP) (100% TSP, 10% MAPR, 20% MAPR, 50% MAPR, 100% MAPR). Compared with 100% TSP, all the combined applications of MAPR and TSP were as effective on straw yield. Treatments of 10% MAPR and 20% MAPR had similar effect on grain yield and P uptake, while 50% MAPR and 100% MAPR were significantly lower. For P partial nutrient productivity and apparent P recovery with the treatment of 20% MAPR had equal effectivity, likewise. For soil P<sub>Olsen</sub>, treatment of 10% MAPR was equally operative, while 20% MAPR had the similar performance only in the last year (i.e. 2016). It is concluded that 10–20% of TSP can be effectively replaced by MAPR without affecting spring maize yield in soil with neutral pH.

Young and century-old biochars strongly affect nutrient cycling in a temperate agroecosystem

Biochar as a soil amendment is often described as a promising agricultural practice for climate change mitigation and adaptation. However, while recent research showed limited effects of biochar in temperate regions, its long-term impacts on nutrient management in-situ have been overlooked. Here we studied charcoal residues from pre-industrial kiln sites as a proxy to determine the effects of century-old biochar (~200 years old) on nutrient cycles of 3 land covers in a conventionally cropped field. We compared nutrient cycles of soil containing either century-old biochar (CoBC), recently pyrolyzed biochar (YBC) produced from similar feedstock (oak) and amended in similar amounts and a reference charcoal free soil (REF). For these three modalities, we characterized soil chemical properties, the pore water nutrient concentration evolution with time and depth using suction cups, and the crop nutrient uptakes. Our results revealed soil pore water nutrient concentrations strongly depended on biochar age. Indeed, YBC resulted in lower N-NO3- and K+ leaching but higher P-PO4– pore water concentrations in the topsoil Ap (0–30 cm) horizon. In CoBC higher K+ and Mg2+ concentrations occurred in the pore water than in REF for subsoil horizon E (30–60 cm) and Bt (60–100 cm). Beyond soil pore water, CoBC also strongly increased soil total N, available K+ and Ca2+ but decreased available P contents compared to REF and YBC. Finally, although no change in crop productivity occurred, lower N, K, Ca and higher Mg plant uptakes were observed for modalities with biochar. This resulted in no difference in terms of nutrient exports from the field in chicory but it significantly decreased N, K, Ca exports from biochar rich soil under winter wheat in straw. This study delivers the first field-based evidence that the effects of hardwood biochar on nutrient cycles change over its lifetime in a temperate Luvisol soil, whereby young biochar impacts mainly pore water nutrient concentrations and aged biochar mainly plant available contents. In such a strongly managed environment, no differences are noted in productivity despite strong changes in the nutrient cycle. Our study provides insights for addressing long-term effects of biochar in cultivated lands not only in terms of agronomic perspectives but through a biogeochemistry lens.

Quantifying the Effects of Induced Topsoil and Historical Subsoil Compaction Under Luvisol Soil in Belgium

Quantifying the Effects of Induced Topsoil and Historical Subsoil Compaction Under Luvisol Soil in Belgium

Monitoring the Concentrations of Cd, Cu, Pb, Ni, Cr, Zn, Mn and Fe in Cultivated Haplic Luvisol Soils Using Near-Infrared Reflectance Spectroscopy

Monitoring the Concentrations of Cd, Cu, Pb, Ni, Cr, Zn, Mn and Fe in Cultivated Haplic Luvisol Soils Using Near-Infrared Reflectance Spectroscopy

Evaluation of Soil S Pools under 23 Years of Maize Monoculture

Sulfur nutrition is a critical part of proper crop growth and development. In our study, biomass yields (BY) and S uptake were investigated on long-term maize monoculture on haplic luvisol soil during the 23 years of this trial, as well as changes in water extractable (Sw), adsorbed (Sads), mineral (Sav), and pseudo-total S (St) fractions. Treatments used in this study are: (1) Control (Cont); (2) ammonium sulfate (AS); (3) urea and ammonium nitrate (UAN); (4) UAN + phosphorus and potassium (UAN + PK); (5) UAN + phosphorus, magnesium, sulfur (UAN + PMgS); and (6) Fallow. Recently, the Mehlich 3 method started to be used in the Czech Republic to determine content of plant available S. Using this method, it was found that the content of S extracted by Mehlich 3 (SM3) closely correlates to Sav in both topsoil and subsoil (r = 0.958 in 1997 and 0.990 in 2019, both at p < 0.001). We also found that, on average, during the entire experiment, all treatments had increased yields over Cont (135–147%) and increased S uptake (291, 192, 180, and 246% of Cont for AS, UAN, UAN + PK, and UAN + PMgS, respectively). Examining the changes from 1997 to 2019 in topsoil (0–30 cm depth), we discovered a decrease of S content in Sw, Sads, Sav, and St fractions on all treatments to an average of 34.6%, 65.8%, 42.2%, and 78.6% of their initial values. The exception was AS treatment, which doubled its initial content in mineral fractions and maintained the same levels of St, and which we attribute to the very high dose of S on this treatment (142 kg ha−1 year−1). Using the simple balance method, AS and UAN + PMgS treatments lost 142.2 and 95.3 kg S ha−1 year−1 to other sinks, except plant uptake, from the entire soil profile (0–60 cm) during 23 years of experiment. Other treatments also show significant losses with the exception of Fallow. Given these results, it is clear that content of sulfur in soil is generally decreasing and attention should be paid mainly towards minimizing of its losses.

Soil freezing-thawing induces immediate shifts in microbial and resource stoichiometry in Luvisol soils along a postmining agricultural chronosequence in Western Germany

Freeze-thaw (FT) events exert a great physiological stress on soil microorganisms and hence impact biogeochemical processes in soils. As numerous environmental factors affect microbial and chemical responses to FT, a better understanding of the leverage factors that regulate the responses to FT events is required. To date, FT-induced shifts and transformations in microbial and resource stoichiometry have received particularly little attention. We exposed fifteen Luvisol soils with different time after restoration and corresponding differences in soil organic C contents from a postmining agricultural chronosequence to a single FT event and analysed changes in soil chemistry and microbial stoichiometry one hour and eighteen hours after thawing. FT considerably altered soil biochemical attributes within the first hours of thawing. Microbial biomass C declined substantially after FT, and its relative losses were positively correlated with enhanced dissolved organic C contents. Thus, microbial cell lysis likely led to the significant increase of dissolved organic C. Moreover, microbial biomass C losses were disproportionally higher in C-rich soils, suggesting that soil microorganisms in high-C soils might be particularly prone to FT stress. Microbial biomass N marginally decreased one hour after thawing, yet returned to initial levels eighteen hours after thawing. The alternating responses of microbial biomass C and N caused a strong stoichiometric reduction of the microbial C:N ratio. The resulting microbial oversaturation with N relative to C is likely the first step in the chain of processes that generally lead to the high N losses commonly recorded in agricultural soils in the aftermath of FT events. Metabolic activity of the soil microbial community increased with the relative decline of the microbial biomass C:N ratio eighteen hours after thawing, suggesting increased levels of microbial metabolic expenditure due to stoichiometric shifts. The strength of the FT-driven biochemical responses was strongly dependent on soil organic C content, indicating that high-C soils might be especially vulnerable to initial C and N losses due to shifts in microbial stoichiometry.

Shotgun metagenomics evaluation of soil fertilization effect on the rhizosphere viral community of maize plants.

The need for sustainability in food supply has led to progressive increase in soil nutrient enrichment. Fertilizer application effects both biological and abiotic processes in the soil, of which the bacterial community that support viral multiplication are equally influenced. Nevertheless, little is known on the effect of soil fertilization on the Soil viral community composition and dynamics. In this study, we evaluated the influence of soil fertilization on the maize rhizosphere viral community growing in Luvisolic soil. The highest abundance of bacteriophages were detected in soil treated with 8 tons/ha compost manure (Cp8), 60kg/ha inorganic fertilizer (N1), 4 tons/ha compost manure (Cp4) and the unfertilized control (Cn0). Our result showed higher relative abundance of Myoviridae, Podoviridae and Siphoviridae in 8 tons/ha organic manure (Cp8) fertilized compared to others. While Inoviridae and Microviridae were the most relative abundant phage families in 4 tons/ha organic manure (Cp4) fertilized soil. This demonstrate that soil fertilization with organic manure increases the abundance and diversity of viruses in the soil due to its soil conditioning effects.

Aging shapes Cr(VI) speciation in five different soils

To make sound decisions regarding management of heavy metal contamination in soils, it is necessary to understand contaminant transformations over extended periods. In this study, sequential extraction methods were applied to quantify the changes of Cr fractions [available Cr(VI), immobile Cr(VI) and immobile Cr(III)] in five contrasting soils spiked with Cr(VI) over a 240-day incubation. Results showed that available Cr(VI) in soils continually decreased during aging, with a sharp decline occurring in the first 30 days. The best fit of available Cr(VI) data was obtained using an Elovich model for Brunisol and Anthrosol-1, a fractional power model for Anthrosol-2, and a pseudo first-order kinetic model for Luvisol-1 and Luvisol-2. After aging for 240 days, immobile Cr(VI) increased by 4.5–31% and immobile Cr(III) increased by 68–95% of total spiked Cr(VI) in Brunisol, Anthrosol-1 and Anthrosol-2. The two Luvisol soils had relatively high reduction rates with no Cr(VI) immobilized. A multireaction model was developed in MATLAB Simulink toolbox to describe transformation flow rates among soluble Cr(VI), adsorbed Cr(VI), immobilized Cr(VI) and immobilized Cr(III) in soils with aging. We conclude that (i) Cr(VI) reduction and immobilization were occurring concurrently in soils and competing for available Cr(VI) species; (ii) Cr(VI) reduction is favored by low soil pH and high organic carbon, while Cr(VI) immobilization occurs with cations (such as Ca2+) and Fe oxides.

Effects of biochar application patterns on soil nutrients and nitrogen- and phosphorus-related enzyme activities in Phaeozem and Luvisol

We investigated the effects of different biochar application patterns on soil nutrient contents and element transformation, with soil samples being collected from two five-year field experiments in Phaeozem and Luvisol amended with biochar at annual low-rate (AL, 22.5 t·hm-2·a-1) and intervalic high-rate (IH, 112.5 t·hm-2·5 a-1). Changes of soil total carbon (C), nitrogen (N) and phosphorus (P) contents as well as the related enzyme activities were measured under different biochar application patterns to provide fundamental information for the straw utilization and soil fertility improvement in agroecosystem. Results showed that total C and organic N contents in AL treatment were significantly higher than those in IH treatment in Phaeozem soil. Compared with the control, the decreases of dehydrogenase activity in AL treatment was more pronounced than that in IH treatment in Phaeozem soil, and the increases of protease activity in IH treatment was pronounced than that in AL treatment in Luvisol. Compared with Luvisol soil, the application of biochar had stronger effect on total soil C and organic N contents in Phaeozem soil. Application of biochar significantly increased the activities of soil dehydrogenase and protease in Luvisol soil, but decreased the activity of soil dehydrogenase. Soil types and biochar application patterns interacted to affect soil C and N contents, microbial metabolic activity, N- and P-related enzyme activities. In summary, soil types and biochar addition affected soil properties and microbial characteristics, which would provide important information for straw application and soil management.

Interactions between soil properties, agricultural management and cultivar type drive structural and functional adaptations of the wheat rhizosphere microbiome to drought.

Rhizosphere microbial communities adapt their structural and functional compositions to water scarcity and have the potential to substantially mitigate drought stress of crops. To unlock this potential, it is crucial to understand community responses to drought in the complex interplay between soil properties, agricultural management and crop species. Two winter wheat cultivars, demanding and non-demanding, were exposed to drought stress in loamy Chernozem and sandy Luvisol soils under conventional or organic farming management. Structural and functional adaptations of the rhizosphere bacteria were assessed by 16S amplicon sequencing, the predicted abundance of drought-related functional genes in the bacterial community based on 16S amplicon sequences (Tax4Fun) and the activity potentials of extracellular enzymes involved in the carbon cycle. Bacterial community composition was strongly driven by drought and soil type. Under drought conditions, Gram-positive phyla became relatively more abundant, but either less or more diverse in Luvisol and Chernozem soil respectively. Enzyme activities and functional gene abundances related to carbon degradation were increased under drought in the rhizosphere of the demanding wheat cultivar in organic farming. We demonstrate that soil type, farming system and wheat cultivar each constitute important factors during the structural and/or functional adaptation of rhizobacterial communities in response to drought.