Soil Biochemical Properties Research Articles

Carbon nanomaterials are a superior soil amendment for sandy soils than biochar based on impacts on lettuce growth, physiology and soil biochemical quality

A significant bottleneck of current agricultural systems remains the very low agronomic efficiency of conventional agrochemicals, particularly in sandy soils. Carbon nanomaterials (CNMs) have been proposed to address this inefficiency in sandy soils, which could potentially improve soil fertility and enhance crop growth and physiological processes. However, the effects of different rates of CNMs on crop physiological and soil biochemical quality in sandy soils must be compared to other carbon sources (e.g., biochar) before CNMs can be broadly used. To address this, a 70-day pot experiment was set up, growing lettuce under ten treatments: a negative control with no CNMs, biochar or fertilizer; a fertilizer-only control; three CNMs-only unfertilized treatments (CNMs at 200, 400 and 800 mg kg−1 soil); two biochar treatments with fertilizer (biochar at 0.5% and 1% by soil mass + fertilizer); and three CNMs treatments with fertilizer (CNMs at 200, 400 and 800 mg kg−1 soil + fertilizer). A novel amorphous, water-dispersible, and carboxyl-functionalized CNMs with pH of 5.5, zeta potential of −40.6 mV and primary particle diameter of 30–60 nm was used for this experiment. Compared to the fertilizer-only control, CNMs applied at low to medium levels (200–400 mg kg−1) significantly increased lettuce shoot biomass (20–21%), total chlorophyll (23–27%), and fluorescence and photosynthetic activities (4–10%), which was associated with greater soil nutrient availability (N: 24–58%, K: 68–111%) and higher leaf tissue accumulation (N: 25–27%; K: 66%). Low to medium levels of CNMs also significantly increased soil biochemical properties, such as higher soil microbial biomass carbon (27–29%) and urease enzyme activity (34–44%) relative to fertilizer-only applications. In contrast, biochar (0.5%) increased lettuce biomass relative to fertilizer-only but had no significant effect on soil fertility and biological properties. These results suggest that CNMs at low to medium application rates are a superior carbon-based amendment relative to biochar in sandy soils.

Effect of Wheat Straw Addition on Organic Carbon Mineralisation and Bacterial Community in Orchard Soil

Crop straw returning can stimulate organic carbon mineralisation and C sequestration simultaneously, which affects soil fertility. However, the effects of crop straw on organic carbon mineralisation and soil bacterial community in orchards are not fully understood. A 90-day incubation experiment was performed to investigate the effects of wheat straw (0, 1, 4, 6, 8, and 10 t·ha−1) on organic carbon mineralisation and bacterial community in orchard soil. Wheat straw addition enhanced the CO2 efflux rate and cumulative organic carbon mineralisation (Cmin), especially high level. The trend of CO2 efflux rate was increased sharply, especially during the early incubation stage (the first 13 days), and then decreased in the later phase. Furthermore, soil bacterial community structure displayed distinct changes in response to straw addition. Available nitrogen, potassium, organic carbon, β-glucosidase, and pH were the key factors driving soil bacterial community changes. The bacterial taxa in networks were significantly related to Cmin. The Proteobacteria, Actinobacteria, and Chloroflexi were positively related to Cmin; while Planctomycetes, Patescibacteria, and Gemmatimonadetes showed a negative relationship with Cmin by correlation and redundancy analyses. Co-occurrence network analysis showed a discrete bacterial network in 10 t·ha−1 of straw, while cohesive networks in others. Straw addition promoted organic carbon mineralisation by improving the soil biochemical properties, including enzymes activities, and nutrient contents, and regulating bacterial community composition. On the whole, 4 t·ha−1 of straw could be considered an economical level for improving soil organic carbon and bacterial community stability in orchards.

Flying Laboratory of Imaging Systems: Fusion of Airborne Hyperspectral and Laser Scanning for Ecosystem Research

Synergies of optical, thermal and laser scanning remotely sensed data provide valuable information to study the structure and functioning of terrestrial ecosystems. One of the few fully operational airborne multi-sensor platforms for ecosystem research in Europe is the Flying Laboratory of Imaging Systems (FLIS), operated by the Global Change Research Institute of the Czech Academy of Sciences. The system consists of three commercial imaging spectroradiometers. One spectroradiometer covers the visible and near-infrared, and the other covers the shortwave infrared part of the electromagnetic spectrum. These two provide full spectral data between 380–2450 nm, mainly for the assessment of biochemical properties of vegetation, soil and water. The third spectroradiometer covers the thermal long-wave infrared part of the electromagnetic spectrum and allows for mapping of surface emissivity and temperature properties. The fourth instrument onboard is the full waveform laser scanning system, which provides data on landscape orography and 3D structure. Here, we describe the FLIS design, data acquisition plan and primary data pre-processing. The synchronous acquisition of multiple data sources provides a complex analytical and data framework for the assessment of vegetation ecosystems (such as plant species composition, plant functional traits, biomass and carbon stocks), as well as for studying the role of greenery or blue-green infrastructure on the thermal behaviour of urban systems. In addition, the FLIS airborne infrastructure supports calibration and validation activities for existing and upcoming satellite missions (e.g., FLEX, PRISMA).

Aggregate pore structure, stability characteristics, and biochemical properties induced by different cultivation durations in the Mollisol region of Northeast China

Long-term cultivation tends to cause thinning and even partial disappearance of Mollisols, which largely limits the sustainable development of agriculture. Cultivation duration greatly affects soil pore structure and biochemical properties of Mollisols. This study aims to elucidate the response of aggregate pore structure, stability, and biochemical properties of soil during degradation under long-term cultivation in Mollisols. The study involved four croplands with different cultivation durations (20, 40, 60, and 100 years; designated as AL20, AL40, AL60, and AL100, respectively) and one undisturbed forest land (FR). Samples were collected from three soil depths (0–20, 20–40, and 40–60 cm). Pore structure and biochemical properties were analyzed by X-ray Computed Tomography (CT) and standard method. As a result, the aggregate stability and biochemical properties of soil showed different degrees of degradation with the extension of cultivation duration. The mean weight diameter, soil organic carbon, total nitrogen, and microbial biomass carbon followed the order of AL20 > FR > AL40 > AL60 > AL100, while the soil bulk density exhibited an opposite trend. FR and AL20 showed significant differences from other sites (P < 0.05). The CT results revealed that total porosity and pore number approximately decreased with cultivation duration, with their maximum appearing in FR and minimum occurring in AL100. The pore shape and pore size of aggregates were dominated by elongated pores (> 65%) and porosity > 100 µm, respectively, both of which declined with increasing cultivation duration. Similarly, the fractal dimension and connectivity were the highest in FR. These results demonstrated that the pore structure of soil aggregates tended to be "simplified" with increasing cultivation duration. Soil structure index, which varied significantly with cultivation duration, was used to comprehensively evaluate the soil structure. The results provide important insights into soil structural degradation caused by long-term cultivation.

Biochemical Properties of Calcareous Soil Affected by the Source of Sulphur-Organo Fertilizers

Biochemical Properties of Calcareous Soil Affected by the Source of Sulphur-Organo Fertilizers

Influence of herbivores and trees on soil biochemical properties of a semi-arid savanna

Influence of herbivores and trees on soil biochemical properties of a semi-arid savanna

A short period of revegetation and fertilization increased the nutrients, enzyme activities, and bacterial community diversity in backfill soils

The ecosystem stability of abandoned mines can be restored using vegetation restoration methods. In the present study, we aimed to investigate the variations in the physicochemical and biochemical properties of backfill soils at a quarry mining slope platform with a 1-year period of revegetation and fertilization in Anhui Province, East China. We collected backfill and native soils in different periods and analyzed their nutrients, enzyme activities, and bacterial communities. Two fertilization cycles increased the nutrients in revegetation backfill soils significantly (p < 0.05), including the available nitrogen (AN) (47.35 ± 9.40 mg/kg vs 134.23 ± 42.37 mg/kg), total phosphorus (TP) (0.38 ± 0.06 g/kg vs 0.78 ± 0.04 g/kg), available phosphorus (AP) (3.99 ± 0.84 mg/kg vs 17.23 ± 7.86 mg/kg), total potassium (TK) (14.33 ± 1.16 g/kg vs 30.74 ± 3.50 g/kg), available potassium (AK) (56.77 ± 7.33 mg/kg vs 339.26 ± 95.67 mg/kg), and soil organic matter (SOM) (13.13 ± 6.12 g/kg vs 19.60 ± 1.06 g/kg); however, the TN and SOM in revegetation and fertilization backfill soils were still much lower than those in native soils. Compared to the initial backfill soils with no revegetation, the activities of sucrase (SUC) and urease (URE) in revegetation and fertilization backfill soils increased from 2.79 ± 0.55 mg/(g·d) to 6.17 ± 3.19 mg/(g·d) and 0.12 ± 0.02 mg/(g·d) to 0.16 ± 0.02 mg/(g·d), respectively; however, they were still much lower than those in native soils. The bacterial community in backfill soils was stable during revegetation and fertilization, similar to that in native soils, with the dominant phyla being Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria. The relative abundance of Proteobacteria in backfill soils decreased from 46.12 % to 22.94 % during revegetation and fertilization, whereas those of Actinobacteria, Chloroflexi, and Acidobacteria increased from 22.2 % to 45.14 %, from 6.24 % to 15.18 %, and from 4.76 % to 24.12 %, respectively. Revegetation and fertilization improved the evenness (Simpsoneven index) and diversity (Shannon index) of bacterial community in backfill soils. The bacterial community structure in backfill soils during revegetation and fertilization approached that of the native soils. The results of redundancy analysis indicated that the bacterial communities in revegetation and fertilization backfill soils were influenced by AK, AN, SOM, URE, and SUC, whereas those in native soils were influenced by TN, SOM, and SUC. Our study indicated that only a short period of revegetation and fertilization improved physicochemical properties and enzyme activities and stabilized the structure of the bacterial community in backfill soils.

Elevated CO2 altered the nano-ZnO-induced influence on bacterial and fungal composition in tomato (Solanum lycopersicum L.) rhizosphere soils.

To investigate whether elevated CO2 (eCO2) changes the influence of nanoparticles (NPs) on soil microbial communities and the mechanisms, various nano-ZnO (0, 100, 300, and 500mg·kg-1) and CO2 concentrations (400 and 800µmol·mol-1) were applied to tomato plants (Solanum lycopersicum L.) in growth chambers. Plant growth, soil biochemical properties, and rhizosphere soil microbial community composition were analyzed. In 500mg·kg-1 nano-ZnO-treated soils, root Zn content was 58% higher, while total dry weight (TDW) was 39.8% lower under eCO2 than under atmospheric CO2 (aCO2). Compared with the control, the interaction of eCO2 and 300mg·kg-1 nano-ZnO decreased and increased bacterial and fungal alpha diversities, respectively, which was caused by the direct effect of nano-ZnO (r = - 1.47, p < 0.01). Specifically, the bacterial OTUs decreased from 2691 to 2494, while fungal OTUs increased from 266 to 307, when 800-300 was compared with 400-0 treatment. eCO2 enhanced the influence of nano-ZnO on bacterial community structure, while only eCO2 significantly shaped fungal composition. In detail, nano-ZnO explained 32.4% of the bacterial variations, while the interaction of CO2 and nano-ZnO explained 47.9%. Betaproteobacteria, which are involved in C, N, and S cycling, and r-strategists, such as Alpha- and Gammaproteobacteria and Bacteroidetes, significantly decreased under 300mg·kg-1 nano-ZnO, confirming reduced root secretions. In contrast, Alpha- and Gammaproteobacteria, Bacteroidetes, Chloroflexi, and Acidobacteria were enriched in 300mg·kg-1 nano-ZnO under eCO2, suggesting greater adaptation to both nano-ZnO and eCO2. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUSt2) analysis demonstrated that bacterial functionality was unchanged under short-term nano-ZnO and eCO2 exposure. In conclusion, nano-ZnO significantly affected microbial diversities and the bacterial composition, and eCO2 intensified the damage of nano-ZnO, while the bacterial functionality was not changed in this study.

Effects of atrazine on microbial metabolic limitations in black soils: Evidence from enzyme stoichiometry

Long-term input of agricultural chemicals such as pesticides into the soil can increase soil pollution, thereby affecting the productivity and quality of black soil. Triazine herbicide atrazine has been shown to have long-lasting residual effects in black soil. The atrazine residues affected soil biochemical properties, further leading to microbial metabolism restriction. It is necessary to explore the strategies to mitigate the limitations on microbial metabolism in atrazine-contaminated soils. Here, we evaluated the effect of the atrazine on microbial nutrient acquisition strategies as indicated by extracellular enzyme stoichiometry (EES) in four black soils. Atrazine degradation in soil followed the first-order kinetics model across various concentrations ranging from 10 to 100 mg kg−1. We found that the atrazine was negatively correlated with the EES for C-, N-, and P-acquisition. Vector lengths and angles decreased and increased significantly with an increase of atrazine concentration in tested black soils except for Lishu soils. Moreover, the vector angles were >45° for tested four black soils, indicating that atrazine residue had the greatest P-limitation on soil microorganisms. Interestingly, microbial C- and P-limitations with different atrazine concentrations showed a strong linear relationship, especially in Qiqihar and Nongan soils. Atrazine treatment significantly negatively affected microbial metabolic limitation. Soil properties and EES interaction explained up to 88.2% for microbial C-/P-limitation. In conclusion, this study confirms the EES as a useful method in evaluating the effects of pesticides on microbial metabolic limitations.

Biochar alleviated the toxic effects of PVC microplastic in a soil-plant system by upregulating soil enzyme activities and microbial abundance

Plastics have become an emerging pollutant threatening the sustainability of agroecosystems and global food security. Biochar, a pro-ecosystem/negative carbon emission technology can be exploited as a circular approach for the conservation of plastics contaminated agricultural soils. However, relatively few studies have focused on the effects of biochar on plant growth and soil biochemical properties in a microplastic contaminated soil. This study investigated the effects of a cotton stalk (Gossypium hirsutum L.) biochar on plant growth, soil microbes, and enzyme activity in PVC microplastic (PVC-MPs) contaminated soil. Biochar amendment increased shoot dry matter production in PVC-MPs contaminated soil. However, PVC-MPs alone significantly reduced the soil urease and dehydrogenase activity, soil organic and microbial biomass carbon, bacterial/fungal community percentage, and their abundance (16S rRNA and 18S rRNA genes, respectively). Interestingly, biochar amendment with PVC-MPs significantly alleviated the hazardous effects. Principal component and redundancy analysis of the soil properties, bacterial 16S rRNA genes, and fungal ITS in the biochar-amended PVC-MPs treatments revealed that the observed traits formed an obvious cluster compared to non-biochar treatments. To sum up, this study indicated that PVC-MPs contamination was not benign, while biochar shielded the hazardous effects and sustained soil microbial functionality.

Effects of groundwater and seasonal streamflow on the symbiotic nitrogen fixation of deep-rooted legumes in a dryland floodplain

Biological nitrogen fixation of deep-rooted legumes is a major pathway of nitrogen (N) inputs to drylands. Water sources including groundwater and streamflow are vital to the growth of deep-rooted legumes in drylands, but it is unclear how their different availability and biochemical properties may influence plant N fixation. We established two sampling transects at the southern fringe of the Taklimakan Desert (Xinjiang province, north-west China) to study the effects of both the groundwater depth and distance to a seasonally active river on the N fixation rate of Alhagi sparsifolia, a dominant deep-rooted legume species. We quantified the N fixation rate of A. sparsifolia using the 15N natural abundance method, and related variation in N fixation to water source use and soil biochemical properties along the two transects. The N fixation rate of A. sparsifolia decreased with groundwater depth and increased with distance from the river channel. Instead of variation in the water source or nutrient concentrations, we found that the gradient in salinity formed by groundwater flow and streamflow was most responsible for the spatial pattern in N fixation of A. sparsifolia. In many dryland regions, water availability controls the spatial variability of symbiotic N fixation along hydrological gradients. Our study system provides a contrasting condition where salinity most strongly regulates N fixation. In addition to understanding the important role of variation in water source and nutrient availability, our study suggests that the impact of soil salinity in mediating N fixation in dryland ecosystems is deserving of attention.

From Waste to Resources: Sewage Sludges from the Citrus Processing Industry to Improve Soil Fertility and Performance of Lettuce (Lactuca sativa L.)

The citrus industry produces a large number of sludges as a consequence of citrus wastewater treatment. The correct disposal of citrus sewage sludges (CSSs) has been attempted using anaerobic digestion, aerobic digestion, and lime stabilization. However, since CSSs hold nitrogen, phosphorus, and other macronutrients required by crops, in line with the circular economy principles, they could be utilized for agricultural purposes, such as organic fertilizer. The aim of this study was to assess the effect of CSSs supplied at different doses on soil fertility and lettuce performance. To this end, a pot experiment was established. The soil was amended with CSSs at three different concentrations (2.5, 5, 10 t ha−1). After 46 days of lettuce growth, the experiment was stopped, and soils and plants were analyzed. Soil amended with CSSs showed an increase in total organic C ranging from 7% to 11%. Additionally, available P increased but only at the highest CSS dose. The addition of CSSs affected the biochemical properties of soil, but a univocal trend related to the number of CSSs applied was not found. Microbial biomass C increased only with the highest dose of CSS applied, while the metabolic quotient (qCO2) decreased. Such a positive effect on soil fertility and soil microorganisms, in turn, lead to an increase in lettuce biomass. Moreover, results indicated that following CSS addition, lettuce crops adsorbed more N in leaves than in roots, whereas P, Ca, Mg, K, and Na showed an opposite pattern and increased more consistently in roots. In conclusion, amendment with CSSs enhances soil fertility by increasing, regardless of CSS dose, total organic C, and, at the highest dose, P availability and microbial biomass C. Such improvement in soil fertility, in turn, increases lettuce biomass production without affecting its quality, i.e., alteration of the (K + Na)/(Ca + Mg) ratio.

Effects of α-Fe2O3 modified chicken manure biochar on the availability of multiple heavy metals and soil biochemical properties

The problem of increasingly severe soil heavy metals contamination is of great concern worldwide. Herein, chicken manure and potassium ferrocyanide were used as raw materials to prepare a α-Fe2O3 loaded biochar (Fe2O3/BC) composite material through a simple calcination method. We found Fe2O3/BC obtained at 350 ℃ (Fe2O3/BC-350) exhibited excellent immobilization efficiency on multiple heavy metals in soil. And then density functional theory (DFT) calculations explained the reason of Fe2O3/BC-350 exhibited better remediation performance than the Fe2O3/BC-250 and Fe2O3/BC-550. When cultured for 90 days, the passivation effect of the 1% Fe2O3/BC-350 dosage treatment achieved the highest with the immobilization rates for Cu(II), Cd(II) and Pb(II) reaching 62.5%, 45.56% and 42.56%, respectively. The composite material increased soil pH and cation exchange capacity (CEC), and promoted the transformation of Cu(II), Cd(II) and Pb(II) ions from acid-soluble to more stable forms through ion exchange, precipitation and complexation. The soybean pot experiment further verified that Fe2O3/BC-350 could reduce the phytoavailable fractions of heavy metal soil remediation material. In addition, Fe2O3/BC-350 increased the activity of soil urease and sucrase. Meanwhile, the diversity and richness of the soil microbial community were improved. These results demonstrated that Fe2O3/BC-350 not only had an excellent immobilization effect on heavy metals in the soil, but also Fe2O3/BC-350 exhibited environmentally friendly in soil. As a result, Fe2O3/BC can serve as a promising remediation agent for multiple heavy metal polluted soils.

Influence of spent mushroom compost on crop productivity

As development of mushroom industry in Russia is growing, and the amount of spent mushroom composts is increasing, they are actively used as organomineral fertilizers for agricultural crops. Therefore, from the rather large problem of storing waste composts, these fertilizers began to be in great demand in the agricultural industry. Organic fertilizers are characterized by a high percentage of nutrients. They are able to improve physical properties of soil by increasing aggregative stability and reducing soil density. Organic fertilizers improve biological and biochemical properties of soil, and positively affect the development of soil microbial community. In the experiments, the content of nutrients in fresh compost and compost after one year of storage averaged: ash content - 8.0 and 74.1 %; organic matter - 66.3 and 25.9 %; NPK (%) - 0.50, 0.63, 0.44 and 0.45, 0.51, 0.39, respectively, under a favorable soil acidity (pH 8.0-7.3). In studies carried out on dark grey forest soils of the Ryazan region, the maximum productivity of agricultural crops was noted in variants with application of half-ripened compost: the yield of spring wheat was 2.82 t/ha (+ 0.23 t/ha compared to the control); spring barley - 3.21 t/ha (+0.17); spring rapeseed - 1.77 t/ha (+0.24); potato cv. Vympel - 27.91 (+ 4.41); potato cv. Kolobok - 11.21 t/ha (+1.63); pea - 2.10 t/ha (+0.21). The high efficiency of spent mushroom composts as fertilizers for increasing yields of spring barley and wheat, spring rapeseed, potatoes and peas was confirmed.

Planting Suaeda salsa improved the soil properties and bacterial community diversity in a coastal mudflat

AbstractPlanting halophytes is an effective strategy to improve saline soils and prevent soil degradation. However, the effects of planting halophytes on saline soil biochemical properties and bacterial communities remain largely unexplored. In this study, soils were sampled from a field where Suaeda salsa was planted over a three‐year (TY) and one‐year (OY) period on a coastal saline mudflat to investigate the effects of S. salsa growth on soil chemical and biological properties. The results showed that OY and TY significantly reduced soil EC by 76.59% to 79.45% (0–10 cm soil layer) and 31.85% to 43.40% (10–20 cm soil layer) in comparison with the control without S. salsa planting (control). For the characteristics of soil enzyme activity, the alkaline phosphatase activity of TY was significantly reduced in the 0–10 cm soil layer (39.76%) and increased in the 10–20 cm layer (13.37%) relative to control. Alkaline phosphatase activity was the predominant factor affecting soil bacterial community composition. Moreover, the relative abundances of Proteobacteria and Chloroflexi were increased in both the OY and TY treatments compared to control, and were positively correlated with soil organic matter and available nitrogen. The complexity of the soil microbial network and the bacterial community diversity and richness were higher in OY and TY than in control. Our findings suggested that planting S. salsa benefited saline soil in coastal land by reducing soil salt stress, preventing salt soil degradation, and increasing soil bacterial community diversity.

Activation and tolerance of Siegesbeckia Orientalis L. rhizosphere to Cd stress.

This experiment investigated the changes of rhizosphere soil microenvironment for hyperaccumulation-soil system under Cd stress in order to reveal the mechanism of hyperaccumulation and tolerance. Thus, Cd fractions, chemical compositions, and biochemical characteristics in rhizosphere soil of Siegesbeckia orientalis L. under Cd stress conditions of 0, 5, 10, 25, 50, 100, and 150 mg kg-1 were investigated through a root bag experiment, respectively. As a result, Cd induced the acidification of S. orientalis rhizosphere soil, and promoted the accumulation of dissolved organic carbon (DOC) and readily oxidizable organic carbon (ROC), which increased by 28.39% and 6.98% at the maximum compared with control. The percentage of labile Cd (acid-soluble and reducible Cd) in soil solution increased significantly (P < 0.05) from 31.87% to 64.60% and from 26.00% to 34.49%, respectively. In addition, rhizosphere microenvironment can alleviate the inhibition of Cd on soil microorganisms and enzymes compare with bulk soils. Under medium and low concentrations of Cd, the rhizosphere soil microbial biomass carbon (MBC), basal respiration, ammonification and nitrification were significantly increased (P < 0.05), and the activities of key enzymes were not significantly inhibited. This suggests that pH reduction and organic carbon (DOC and ROC) accumulation increase the bioavailability of Cd and may have contributed to Cd accumulation in S. orientalis. Moreover, microorganisms and enzymes in rhizosphere soils can enhance S. orientalis tolerance to Cd, alleviating the nutrient imbalance and toxicity caused by Cd pollution. This study revealed the changes of physicochemical and biochemical properties of rhizosphere soil under Cd stress. Rhizosphere soil acidification and organic carbon accumulation are key factors promoting Cd activation, and microorganisms and enzymes are the responses of Cd tolerance.

Effect of pretreated and anaerobically digested microalgae on the chemical and biochemical properties of soil and wheat grown on fluvisol

ABSTRACT In this study, the effects of the potential application of digestate as an agricultural fertiliser obtained from anaerobically digested microalgae treated by three pretreatment methods, namely alkaline hydrogen peroxide (AHP), high temperature and pressure (HTP), and hydrodynamic cavitation (HC) on some properties of soil, and wheat growth and yield were investigated. For this purpose, pretreated and anaerobically digested microalgae digestates alone or together with diammonium phosphate (DAP) as a chemical fertiliser were applied to soil for wheat growth. The highest dosage of AHP pretreated digestate combined with a half dose of DAP applied to soil was rich in nutrients as 0.25%N and 7.19 mg kg−1 compared to all groups. The properties of the soils were enhanced by applying the highest dosage (0.06 g kg−1) of microalgae digestate combined with a half dose of DAP. 0.02 g kg−1 dosage of HC pretreated digestate combined with a half dose of DAP also greatly improved nitrogen use efficiency indices by up to 104%. The soils’ enzyme activities increased in wheat growth experiments by applying either raw or pretreated microalgae digestates. The soils’ β-glycosidase, alkaline phosphatase, and urease enzyme activities increased to 1.38 mg pNP g−1 soil, 4.91 mg pNP g−1 soil, and 2.27 mg NH4-N 100 g−1 soil respectively by the application of highest dosage of HC pretreated digestate. The digestates did not have a toxic effect on wheat growth, it was determined that applied pretreatment processes did not cause significant changes in wheat plant height or wet and dry weight.

Biochar application method influences root growth of tea (Camellia sinensis L.) by altering soil biochemical properties

Although the application of biochar increases crop productivity and soil fertility, the effects of different biochar application methods on tea plant growth and soil nutrient status remain unclear. In this study, we conducted a root chamber experiment to assess the effects of various biochar application methods on root growth in tea plants and edaphic factors. Four treatments were included: T1) No biochar, T2) Homogenized biochar, T3) Localized biochar, and T4) Strip biochar. Biochar application generally resulted in higher macronutrient contents in tea plants, with 114–371%, 196–1167%, and 327–960% increases in nitrogen (N), phosphorus (P), and potassium (K), respectively. Biochar application also increased the soil pH by 18.7–22.5% compared to the control. T2 treatment increased the leaf and root biomasses by 80.9% and 262.2%, respectively, compared to the control, and the total carbon and soil nutrient [i.e., total N, inorganic N, available P, and available K, calcium (Ca), and magnesium (Mg)] contents were significantly higher than in the control. Variation in root growth was significantly explained by soil properties, including microbial biomass carbon, Ca, Mg, and total N (P < 0.05), with contributions of 47.9%, 15.6%, 17.6%, and 4.7%, respectively. These results suggest that biochar application in acidic soils would increase tea plant productivity and soil nutrient contents. Overall, homogenized biochar application led to optimal tea plant growth and soil fertility.

Insights into the impacts of autotoxic allelochemicals from rhizosphere of Atractylodes lancea on soil microenvironments.

Atractylodes lancea suffers from continuous cropping obstacles that have become a major constraint in its cultivation, but there is still little information on the autotoxic allelochemicals and their interaction with soil microorganisms. In this study, we firstly identified the autotoxic allelochemicals from rhizosphere of A. lancea and determined their autotoxicity. Third-year continuous A. lancea cropping soils, i.e., rhizospheric soil and bulk soil, compared with control soil and one-year natural fallow soil were used to determine soil biochemical properties and microbial community. Eight allelochemicals from A. lancea roots were detected and exhibited significant autotoxicity effects on seed germination and seedling growth of A. lancea with the highest content of dibutyl phthalate in rhizospheric soil and lowest IC50 value of 2,4-di-tert-butylphenol inhibiting seed germination. The contents of soil nutrients and organic matter, pH value, and enzyme activity were altered between different soils, and the parameters of fallow soil were close to those of the unplanted soil. The PCoA analysis indicated that the community composition of both bacteria and fungi were differed significantly among the soil samples. Continuous cropping decreased OTUs numbers of bacterial and fungal communities, and natural fallow restored them. The relative abundance of Proteobacteria, Planctomycetes, and Actinobacteria decreased, and that of Acidobacteria and Ascomycota increased after three years cultivation. The LEfSe analysis identified 115 and 49 biomarkers for bacterial and fungal communities, respectively. The results suggested that natural fallow restored the structure of soil microbial community. Overall, our results revealed that autotoxic allelochemicals caused the variations of soil microenvironments and resulted in replantation problem of A. lancea, and natural fallow alleviated the soil deterioration by remodeling the rhizospheric microbial community and restoring soil biochemical properties. These findings provide important insights and clues for solving the continuous cropping problems and guiding the management of sustainable farmland.

The presence of soybean, but not soybean cropping frequency has influence on SOM priming in crop rotation systems

Legume crops are advocated for integration into crop rotation systems, and cereal-based rotations with the presence of legumes have a substantial effect on improving soil fertility and health. It is not yet clear whether the frequency of legume inclusion in crop rotation systems influences soil biochemical properties and soil organic matter (SOM) mineralization. An incubation experiment was conducted with 13C-glucose addition to evaluate the influences of soybean (Glycine max L.) cropping frequency on SOM mineralization under long-term wheat (Triticum aestivum L.)- and maize (Zea mays L.)-based rotation systems. Phospholipid fatty acids (PLFAs) and 13C-PLFAs were measured to explore microbial biomass, community structure and microbial utilization of glucose in wheat and maize systems. Glucose addition increased native SOM mineralization, i.e. positive priming effect. Compared with less soybean cropping frequency under long-term wheat- and maize-based rotation systems, wheat-soybean-soybean-soybean rotation and maize-soybean-soybean rotation increased the total biomass (PLFAs), fungal biomass and decreased the ratio of bacteria to fungi. Furthermore, the ratio of bacteria to fungi was negatively correlated with PE intensity, indicating that greater fungal biomass played a key role in stimulating SOM priming. That the proportion of 13C-glucose in G- and fungi had a positive relationship with PE intensity also supported this conclusion. The presence of soybean in wheat- and maize-based rotations increased SOM priming, while the soybean cropping frequency had no significant influence on SOM priming. However, in contrast to a maize-based rotation system, the same frequency of soybean in a wheat-based rotation system had lower soil C/N ratio and higher B/F ratio, and resulted in lower PE intensity. Our findings indicated that the presence of soybean in wheat- and maize-based rotation systems increased PE intensity because of higher soil C/N ratio and lower B/F ratio, while the soybean cropping frequency had no significant influence on SOM priming. Furthermore, the presence of soybean in maize system induced more SOM priming than that in wheat system with glucose addition.