Residue Amendment Research Articles

Selection of Suitable Organic Amendments to Balance Agricultural Economic Benefits and Carbon Sequestration.

Long-term excessive use of fertilizers and intensive cultivation not only decreases soil organic carbon (SOC) and productivity, but also increases greenhouse gas emissions, which is detrimental to sustainable agricultural development. The purpose of this paper is to identify organic amendments suitable for winter wheat growth in the North China Plain by studying the effects of organic amendments on the economic benefits, carbon emissions, and carbon sequestration for winter wheat fields and to provide a theoretical basis for the wide application of organic amendments in agricultural fields. The two nitrogen rates were N0 (0 kg ha-1) and N240 (240 kg ha-1), and the four organic amendments were straw, manure, mushroom residue (M R), and biochar. The results showed that, compared to N0, N240 significantly increased the yield by 244.1-318.4% and the organic carbon storage by 16.7-30.5%, respectively, but increased the carbon emissions by 29.3-45.5%. In addition, soil carbon stocks increased with all three types of organic amendments compared to the straw amendment, with the biochar treatment being the largest, increasing carbon storage by 13.3-33.6%. In terms of yield and economic benefits, compared to the straw amendment, the manure and biochar amendments increased winter wheat yields by 0.0-1.5% and 4.0-13.3%, respectively, and M R slightly decreased wheat yield; only the economic benefit of the M R amendment was greater than that of the straw amendment, with an increase in economic benefit of 1.3% and 8.2% in the 2021-2022 and 2022-2023 seasons, respectively. Furthermore, according to the net ecosystem productivity (NEP), N0 was the source of CO2, while N240 was a sink of CO2. The TOPSIS results showed that N240 with a mushroom residue amendment could be recommended for increasing soil carbon stocks and economic benefits for winter wheat in the NCP and similar regions. Low-cost M R can increase farmer motivation and improve soil organic carbon, making a big step forward in the spread of organic materials on farmland.

Characteristics and modification mechanism of recycled waste silty clay slurry as the shield slag conditioner

The construction process of earth pressure balance shield (EPBS) generates a large amount of shield slag. In China, the conventional methods for treating shield slag involve crude landfill and stockpiling, resulting in increased cost and significant environmental issues. To expand the recycling of shield slag, this study proposes to use waste silty clay to completely replace bentonite as a conditioner in coarse-grained strata. Firstly, the physical properties of silty clay slurries are investigated with four additives. There are six modified silty clay slurries with good improved performance. Then, analyzing the rheological properties of six modified silty clay slurries, and verifying the feasibility of replacing bentonite slurry with modified silty clay slurry. Next, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Zeta potential were used to analyse the micromechanisms, molecular structures and molecular forces of 14 % bentonite slurry, silty clay slurry with a soil-water ratio of 1:1, sodium carbonate 3 % and sodium silicate 0.1 % in a silty clay slurry with a soil-water ratio of 1:1. Finally, the slump test was carried out to verify the improvement effect of the modified silty clay slurry on the shield slag. The results show that sodium carbonate modified silty clay slurry has a higher interlayer water content and greater ion exchange capacity. When the soil-water ratio is 1:1 and the concentration of sodium carbonate is 3 %, the apparent viscosity and shear force of the modified silty clay slurries are between those of bentonite slurries with a concentration of 10 % and 14 %. Additionally, the modified silty clay slurry showed a stable microstructure and good residue amendment effect, making it suitable as a soil conditioner during EPBS construction in coarse-grained strata. This study offers a viable approach for recycling EPBS slurry.

Cereal-Legume Mixed Residue Addition Increases Yield and Reduces Soil Greenhouse Gas Emissions from Fertilized Winter Wheat in the North China Plain

Incorporating crop residues into the soil is an effective method for improving soil carbon sequestration, fertility, and crop productivity. Such potential benefits, however, may be offset if residue addition leads to a substantial increase in soil greenhouse gas (GHG) emissions. This study aimed to quantify the effect of different crop residues with varying C/N ratios and different nitrogen (N) fertilizers on GHG emissions, yield, and yield-scaled emissions (GHGI) in winter wheat. The field experiment was conducted during the 2018–2019 winter wheat season, comprising of four residue treatments (no residue, maize residue, soybean residue, and maize-soybean mixed residue) and four fertilizer treatments (control, urea, manure, and manure + urea). The experiment followed a randomized split-plot design, with N treatments as the main plot factor and crop residue treatments as the sub-plot factor. Except for the control, all N treatments received 150 kg N ha−1 season−1. The results showed that soils from all treatments acted as a net source of N2O and CO2 fluxes but as a net sink of CH4 fluxes. Soybean residue significantly increased soil N2O emissions, while mixed residue had the lowest N2O emissions among the three residues. However, all residue amendments significantly increased soil CO2 emissions. Furthermore, soybean and mixed residues significantly increased grain yield by 24% and 21%, respectively, compared to no residue amendment. Both soybean and mixed residues reduced GHGI by 25% compared to maize residue. Additionally, the urea and manure + urea treatments exhibited higher N2O emissions among the N treatments, but they contributed to significantly higher grain yields and resulted in lower GHGI. Moreover, crop residue incorporation significantly altered soil N dynamics. In soybean residue-amended soil, both NH4+ and NO3− concentrations were significantly higher (p < 0.05). Conversely, soil NO3− content was notably lower in the maize-soybean mixed residue amendment. Overall, our findings contribute to a comprehensive understanding of how different residue additions from different cropping systems influence soil N dynamics and GHG emissions, offering valuable insights into effective agroecosystems management for long-term food security and soil sustainability while mitigating GHG emissions.

Effects of Straw Amendment in Combination with Synthetic N Fertilizer Addition on N2O, N2, and Their Stoichiometric Ratios in Three Different Agro-Ecosystems

Nitrogen (N) fertilizer and crop residue amendments are important agricultural practices that could increase soil health, fertility, and crop yield. Such practices may also change soil denitrification processes where contradictory observations have been reported on soil N2O emissions with fewer studies on N2 emissions due to its large atmospheric background concentrations limiting its soil-borne measurement. This study aims to investigate N2O production and reduction of N2 emissions under a conducive denitrifying environment (like anaerobic microsites, 80% WFPS, available N and C) after rice straw amendment and KNO3 application to three different soil types (fluvo-aquic, black, and paddy soils). In this regard, three treatments for three different soil types were set consisting of (a) a non-amended treatment (control), (b) a KNO3 treatment (KNO3, 20 mM KNO3), and (c) a straw plus KNO3 treatment (2.5 g rice straw kg−1 dry soil and 20 mM KNO3), which were incubated under 80% WFPS. Moreover, direct N2O and N2 fluxes were measured over 17 days in the current incubation experiment with a robotized incubation system using a helium atmosphere. Results showed that rice straw amendment combined with N fertilizer increased both N2O and N2 fluxes compared with control or KNO3 treatments in all three soil types. Overall, compared with the black and paddy soils, the N2O and N2 fluxes were higher in the fluvo-aquic soil, with a maximum of 234.2 ± 6.3 and 590.1 ± 27.3 g N ha−1 from F_SK treatment, respectively, during the incubation period. The general trends in three soil types of both N2O and N2 emissions were control < KNO3 < rice straw plus KNO3 treatments. Straw amendment in combination with KNO3 can stimulate a high denitrification rate (less N2O and higher N2), whereas their effect on stoichiometric ratios of N2O/(N2O + N2) highly depends on soil nitrate concentration, oxygen level, soil moisture content, and labile C. The current study underscores that the rice straw amendment in combination with N fertilizer can trigger denitrification with less increment on soil N2O but higher N2 emissions under conditions favoring denitrification.

Mix-method toolbox for monitoring greenhouse gas production and microbiome responses to soil amendments

In this study, we adopt an interdisciplinary approach, integrating agronomic field experiments with soil chemistry, molecular biology techniques, and statistics to investigate the impact of organic residue amendments, such as vinasse (a by-product of sugarcane ethanol production), on soil microbiome and greenhouse gas (GHG) production. The research investigates the effects of distinct disturbances, including organic residue application alone or combined with inorganic N fertilizer on the environment. The methods assess soil microbiome dynamics (composition and function), GHG emissions, and plant productivity. Detailed steps for field experimental setup, soil sampling, soil chemical analyses, determination of bacterial and fungal community diversity, quantification of genes related to nitrification and denitrification pathways, measurement and analysis of gas fluxes (N2O, CH4, and CO2), and determination of plant productivity are provided. The outcomes of the methods are detailed in our publications (Lourenço et al., 2018a; Lourenço et al., 2018b; Lourenço et al., 2019; Lourenço et al., 2020). Additionally, the statistical methods and scripts used for analyzing large datasets are outlined. The aim is to assist researchers by addressing common challenges in large-scale field experiments, offering practical recommendations to avoid common pitfalls, and proposing potential analyses, thereby encouraging collaboration among diverse research groups.•Interdisciplinary methods and scientific questions allow for exploring broader interconnected environmental problems.•The proposed method can serve as a model and protocol for evaluating the impact of soil amendments on soil microbiome, GHG emissions, and plant productivity, promoting more sustainable management practices.•Time-series data can offer detailed insights into specific ecosystems, particularly concerning soil microbiota (taxonomy and functions).

Sorghum and cowpea intercropping response to woody residue amendments in Sahelian agro-ecosystems of Burkina Faso

In West African agro-ecosystems, soils are inherently low in soil organic carbon decreasing the capacity of soils to sustain crop productivity. Woody Residues instead of being burnt or exported out of the cropping systems, can be managed to optimize soil organic carbon build-up, nutrient cycling and crop productivity. The aim of this study was to determine the effect of woody residue amendments from Piliostigma reticulatum (D.C.) Hochst associated with sorghum-cowpea intercropping on the soil residual property and crop productivity. The investigation was carried out in two experimental sites in the Sudano-Sahelian (Gampela and Kulungu) area of Burkina Faso (West Africa). The experimental design was organized into four replicates consisting of two treatments of woody residue amendments: amended (WR+) and unamended (WR-) soils. The results for both sites showed an overall significant increase in numbers (+ 35%) and biomass (+ 64%) of cowpea nodules. The root and aerial biomasses at the flowering stage of cowpeas were significantly improved in amended soils (WR+) by 26% and 44%, respectively compared to unamended soils (WR-). In addition, the WR+ treatment increase significantly cowpea and sorghum yields by 41% and 25%, respectively, as well as water use efficiency (+ 40% and + 26%, respectively) compared to the WR- treatment. Moreover, our results exhibited a strong correlation (r = 0,95) between cowpea nodular biomass and sorghum grain yields, reflecting more contribution of cowpea ecosystem services (facilitation and complementarity) for associated sorghum productivity. However, despite favorable soil conditions (soil water and organic carbon content) that occurred by WR input, it was not sufficient to improve soil residual total nitrogen and available phosphorus. The woody residue management associated with cereal-legume intercropping is a promising option to sustain crop productivity in Sahelian agro-ecosystems.

Awakening soil microbial utilization of nitrate by carbon regulation to lower nitrogen pollution

Soil microbial immobilization of nitrate (NO3−-N, INO3) and its role in mitigating NO3−-N pollution in agricultural ecosystems globally is often neglected because of the tenet that microbes preferentially use ammonium over NO3−-N. Soil INO3 driven by heterotrophic microorganisms is often carbon (C)-limited, and may therefore be stimulated by C sources with high C/nitrogen (N) ratios. Here, using 15NO3−-N labelling coupled with acetylene inhibition, quantitative PCR and Illumina high-throughput sequencing approaches, we demonstrated that INO3 was stimulated from zero to a substantial level by crop residue amendment without any environmental risk; the degree of stimulation depending on residue quality and soil type. The stimulation was predicted well by C mineralization of the added residue. Soil with a lower initial nutrient status had reduced INO3 efficiency due to stronger C constraint and lower return on energy investment. Fast-growing bacterial r-strategists were identified as the key driver of INO3. We estimate that, globally, residue amendment could cause a total NO3−-N loss reduction of about 33.6 Tg N yr−1 through INO3 stimulation. We suggest that soil INO3 driven by addition of exogenous C is an overlooked process that can help curb NO3−-N accumulation in soil and its subsequent release to the environment, the “nitrate time bomb”.

Relative contribution of ammonia-oxidizing bacteria and denitrifying fungi to N2O production during rice straw composting with biochar and biogas residue amendments

Nitrous oxide (N2O) production is associated with ammonia-oxidizing bacteria (amoA-AOB) and denitrifying fungi (nirK-fungi) during the incorporation of biochar and biogas residue composting. This research examined the relative contribution of alterations in the abundance, diversity and structure of amoA-AOB and nirK-fungi communities on N2O emission by real-time PCR and sequence processing. Results showed that N2O emissions showed an extreme relation with the abundance of amoA-AOB (rs = 0.584) while giving credit to nirK-fungi (rs = 0.500). Nitrosomonas and Nitrosospira emerged as the dominant genera driving ammoxidation process. Biogas residue changed the community structure of AOB by altering Nitrosomonadaceae proportion and physiological capacity. The denitrification process, primarily governed by nirK-fungi, served as a crucial pathway for N2O production, unveiling the pivotal mechanism of biochar to suppress N2O emissions. C/N and NH4+-N were identified as significant parameters influencing the distribution of nirK-fungi, especially Micromonospora, Halomonas and Mesorhizobium.

Impact of Chemically Diverse Organic Residue Amendment on Soil Enzymatic Activities in a Sandy Loam Soil

To monitor soil biological quality, it is of paramount importance to assess how chemically diverse organic residue amendments reciprocate to organic matter. The present incubation study aimed to evaluate the effect of organic residue amendments varying widely in their biochemical composition on the dynamics of soil enzymatic activity. The changes in the pattern of soil enzymatic activity have been monitored over a period of 63 days using a total of eleven different crop residues. The enzyme activity (dehydrogenase, fluorescein diacetate hydrolysis, acid phosphatase, alkaline phosphatase and phytase) in soils amended with chemically diverse organic residues were significantly higher as compared to the control. It was further observed that the enzymatic activities in Azadirachta indica, Avena sativa and Lens culinaris continued to be higher up to 28 days after their incorporation (DAI). Our study showed that plant residues varying in different cellulose and hemicellulose contents influenced the enzymatic activities as well as functional diversity of soil microbial communities.

Rhizosphere-induced shift in the composition of bacterial community favors mineralization of crop residue nitrogen

In agricultural systems, residue amendment is an important practice for nutrient management, but the role of microbes in mineralization of crop residue nitrogen (N) is not well known. Therefore, this study aimed to examine how the residue N mineralization was associated with changes of the microbial community composition in crop rhizosphere. A rhizobox system was deployed to separate the rhizosphere zone into the root-growth (central), and 2 mm (proximal) and 4 mm (transitional) zones away from the central zone, and the gradient change of the residue-N mineralization along the zones was assessed. Soybean plants were grown in a Mollisol without or with amendment of 15N-labelled soybean and maize residues. Furthermore, amplicon sequencing was performed to detect the shift of microbial community composition associated with the residue-N mineralization. The residue-N was mineralized faster in the rhizosphere than the bulk soil, and from soybean residue than maize residue. Greater enrichment of taxa against the unit of residue-N mineralization in the soybean than maize residue treatment was correspondent with the enriched ammonification genes, likely contributing to the enhanced mineralization of soybean residue-N in the rhizosphere. A gradual increase in dissolved organic C and a decrease in available N concentration from the central root zone to the bulk soil, might shift bacterial community favoring the residue-N mineralization in the rhizosphere. The spatial changes in chemical properties across the rhizosphere lead to the recruitment of microbiome taxa to enhance the mineralization of N derived from crop residues.

Microbial gene activity in straw residue amendments reveals carbon sequestration mechanisms in agricultural soils

Land-use practices and their intensity along with climatic conditions alter amounts of soil organic carbon content and consequently influence soil microorganisms. However, land-use management, such as crop residue incorporation to soils has a potential to mitigate losses of soil organic carbon and thereafter promote the diversity of soil microorganisms. To gain insight of microbial functional diversity and activity under organic soil amendments, a glasshouse experiment with arable and grassland soils was performed. Straw was added as a crop residue and microbial activity in the soils was monitored using a captured metatranscriptomics technique. The overall expression of genes related to soil organic matter degradation differed between the two land-use systems. Straw addition enhanced the expression of genes involved in the degradation of organic material, particularly in arable soils. After a month of the amendment, the overall gene expression in arable soils had a similar pattern to that of the grasslands. The straw addition triggered the upregulation of a set of enzyme families catalysing the organic matter degradation in both land-uses but downregulated a higher number of enzyme families in grasslands. However, in the grasslands, the gene families involved in the biosynthesis of carbohydrates were upregulated at straw addition. These findings indicate that arable soils with a low organic carbon content have a potential to get a higher and more active microbial diversity with amendments. In soils such as grasslands the amendments trigger a carbon sequestration process from the added organic material to the soil and can significantly contribute to enhanced soil carbon sequestration.

Management of Reniform Nematode in Cotton Using Winter Crop Residue Amendments Under Greenhouse Conditions.

Rotylenchulus reniformis (reniform nematode, RN) is among the most important nematodes affecting cotton. Cultural practices, such as rotation and soil amendment, are established methods for managing RN. Management may be enhanced if crop residue has biofumigant properties against RN. The objective was to evaluate the efficacy of winter crop amendments for managing RN in the greenhouse. Reniform nematode-infested soil was amended with dry or fresh organic matter (OM, 2% w/w) from winter crops - canola, carinata, hairy vetch, oat, or no crop. Cotton was subsequently grown in this soil. Independent of the crop, dry OM amendments were more effective than no amendment at managing RN, while fresh OM amendments were not. Soil and root RN abundances and reproduction factors were generally lower in Trials 1 and 3 for dry OM than fresh OM amendments or control without OM. In Trial 2, none of the OM treatments reduced RN parameters compared with no OM control. In general, when compared to plants without RN or OM, RN did not produce significant changes in growth parameters but did affect physiology (Soil Plant Analysis Development, or SPAD, values). In conclusion, dry OM amendments can help manage RN, crop growth does not always relate to RN abundances, and SPAD values could help indicate RN presence.

Suppression of Banana Fusarium Wilt Disease with Soil Microbial Mechanisms via Pineapple Rotation and Residue Amendment

The large outbreak of banana Fusarium wilt has become a bottleneck limiting the industry’s development, and crop rotation is a cost-effective and essential measure to overcome the obstacles of banana crop monoculture. The present work was carried out to explore the mechanisms of how changes in soil chemical properties and the reestablishment of soil microorganisms in high-incidence soils are affected by crop rotation and plant residue. In this study, pineapple–banana crop rotation and pineapple residue amendment were carried out to alleviate banana Fusarium wilt, and their effects on bacterial and fungal communities were analyzed using the MiSeq Illumina sequencing platform. Both pineapple–banana rotation and residue addition significantly reduced disease incidence. Moreover, pineapple rotation and residue amendment altered the bacterial and fungal community composition. The taxonomic and phylogenetic alpha diversity of bacteria and fungi significantly increased against disease suppression and nutrition competition. The relative abundances of the Burkholderia, Pseudomonas, Elaphocordyceps, Penicillium, and Talaromyces genera were higher, and the number of Fusarium was significantly lower in rotational soil than in banana monoculture soil. Finally, linear models (LM) showed that the Burkholderia and Talaromyces in crop rotation, and Aspergillus in residue amendment had a significantly negative relationship to disease incidence, which plays a key role in Fusarium reduction. To consider the economic benefits and protect the vitality of the soil, this study suggested that pineapple–banana rotation and pineapple residue amendment both could be considered for the sustainable management of banana wilt.

Response characteristics of antibiotic resistance genes and bacterial communities during agricultural waste composting: Focusing on biogas residue combined with biochar amendments

This research investigated biogas residue and biochar addition on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and changes in bacterial community during agricultural waste composting. Sequencing technique investigated bacterial community structure and ARGs, MGEs changes. Correlations among physicochemical factors, ARGs, MGEs, and bacterial community structure were determined using redundancy analysis. Results confirmed that biochar and biogas residue amendments effectively lowered the contents of ARGs and MGEs. The main ARGs detected was sul1. Proteobacteria and Firmicutes were the main host bacteria strongly associated with the dissemination of ARGs. The dynamic characteristics of the bacterial community were strongly correlated with pile temperature and pH (P < 0.05). Redundancy and network analysis revealed that nitrate, intI1, and Firmicutes mainly affected the in ARGs changes. Therefore, regulating these key variables would effectively suppress the ARGs spread and risk of compost use.

The influence of plant residues on soil aggregation and carbon content: A meta‐analysis

AbstractBackgroundSoil aggregation and organic carbon (OC) content are important indicators of soil quality that can be improved with plant residue amendments. The extent of the effects of plant residue amendments on soil aggregation and OC content across different plant residue and soil types is not fully understood.AimIn this meta‐analysis, we evaluated the effects of plant residue amendments on soil aggregation and OC content for different plant residues (fresh, charred) and soil types varying in clay content, initial OC content, and pH.MethodsOur meta‐analysis included 50 published studies (total of 299 paired observations). We estimated the response ratios of mean weight diameter (MWD) and separate aggregate size classes, total soil OC (TSC), and aggregate‐associated OC. We also considered the effect of experimental factors (study duration, residue type, residue amount, initial soil OC, clay content, and pH).ResultsThe benefit of plant residue amendment on soil aggregation was larger in soils with initially low OC content and neutral pH. Initial soil OC content and pH were more important than soil clay content for OC storage in soil aggregates. Both fresh and charred plant residue amendments were effective in forming aggregates, whereas charred residues were more effective in increasing TSC. We found only a weak positive relationship between the response ratio of TSC and MWD indicating that other factors besides soil aggregation contributed to the increase in soil C storage.ConclusionsWhile plant residue amendments can enhance soil aggregation and TSC, these effects are likely governed by the type of plant residue and soil properties such as the initial soil pH and OC content.

Characteristics of carbon, nitrogen, phosphorus and sulfur cycling genes, microbial community metabolism and key influencing factors during composting process supplemented with biochar and biogas residue

Carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling functional genes and bacterial and fungal communities during composting with biochar and biogas residue amendments were studied. Correlations between microbial community structure, functional genes and physicochemical properties were investigated by network analysis and redundancy analysis. It was shown that the gene of acsA abundance accounted for about 50% of the C-related genes. Biogas residue significantly decreased the abundance of denitrification gene nirK. Biogas residues can better promote the diversity of bacteria and fungi during composting. Biochar significantly increased the abundance of Humicola. Redundancy analysis indicated that pile temperature, pH, EC were the main physicochemical factors affecting the microbial community. WSC and NO3−-N have significant correlation with C, N, P, S functional genes. The research provides a theoretical basis for clarifying the metabolic characteristics of microbial communities during composting and for the application of biochar and biogas residues in composting.

Modeling nitrous oxide emissions from agricultural soil incubation experiments using CoupModel

Abstract. Efforts to develop effective climate mitigation strategies for agriculture require methods to estimate nitrous oxide (N2O) emissions from soil. Process-based biogeochemical models have been often used for field- and large-scale estimates, while the sensitivity and uncertainty of model applications to incubation experiments are less investigated. In this study, a process-oriented model (CoupModel) was used to simulate N2O and CO2 fluxes and soil mineral nitrogen (N) contents in a short-term (43 d) factorial incubation experiment (16 treatments). A global sensitivity analysis (GSA) approach, “Morris screening”, was applied to quantify parameter sensitivity. The GSA suggested that a higher number of sensitive parameters was associated with N2O flux estimates and that inter-treatment variations in parameter sensitivities were distinguished by soil moisture levels or NO3- content and residue types. Important parameters regarding N2O flux estimates were linked to the decomposability of soil organic matter (e.g., organic C pool sizes) and the denitrification process (e.g., Michaelis constant and denitrifier respiratory rates). After calibration, the model better captured temporal variations and magnitude of gas fluxes and mineral N in unamended soils than in residue-amended soils. Low-magnitude daily and cumulative N2O fluxes were well simulated with mean errors (MEs) close to zero, but the model tended to underestimate N2O fluxes, as observed daily values increased by over 0.1 g N m−2 d−1, in which the major mismatch was due to limited success of the model to describe the high emissions during the first few days after crop residue addition. A larger uncertainty was also seen in the magnitude of pulse emissions by the posterior simulations. We also evaluated ancillary variables regarding N cycling, which indicated that more frequent measurements and additional types of observed data such as soil oxygen content and the microbial sources of emitted N2O are required to further evaluate model performance and biases. The major challenges for calibration were associated with high sensitivities of denitrification parameters to initial soil abiotic conditions and the instantaneous residue amendment. Model structure uncertainties and improved modeling practices in the context of incubation experiments were discussed.

Priming of soil organic carbon mineralization and its temperature sensitivity in response to vegetation restoration in a karst area of Southwest China

Plant residue input alters native soil organic carbon (SOC) mineralization through the priming effect, which strongly controls C sequestration during vegetation restoration. However, the effects of different vegetation types on SOC priming and the underlying microbial mechanisms due to global warming are poorly understood. To elucidate these unknowns, the current study quantified soil priming effects using 13C-labeled maize residue amendments and analyzed the community structure and abundances in the soils of a vegetation succession gradient (maize field (MF), grassland (GL), and secondary forest (SF)) from a karst region under two incubation temperatures (15 °C and 25 °C). Results revealed that after 120 d of incubation, vegetation restoration increased the soil priming effects. Compared to MF, the priming effects of SF at 15 °C and 25 °C increased by 142.36 % and 161.09 %, respectively. This may be attributed to a high C/N ratio and low-N availability (NO3−), which supports the “microbial nitrogen mining” theory. Variations in soil priming were linked to changes in microbial properties. Moreover, with vegetation restoration, the relative abundance of Actinobacteria (copiotrophs) increased, while Ascomycota (oligotrophs) decreased, which accelerated native SOC decomposition. Co-occurrence network analysis indicated that the cooperative interactions of co-existing keystone taxa may facilitate SOC priming. Furthermore, structural equation modeling (SEM) indicated that changes in the priming effects were directly related to the fungal Shannon index and microbial biomass C (MBC), which were affected by soil C/N and NO3−. Warming significantly decreased soil priming, which may be attributed to the increase in microbial respiration (qCO2) and decreased MBC. The temperature sensitivity (Q10) of SOC mineralization was higher after residue amendment, but significant differences were not detected among the vegetation types. Collectively, our results indicated that the intensity of priming effects was dependent on vegetation type and temperature. Microbial community alterations and physicochemical interactions played important roles in SOC decomposition and sequestration.

Comparison of Phytoremediation Potential of Nerium indicum with Inorganic Modifier Calcium Carbonate and Organic Modifier Mushroom Residue to Lead-Zinc Tailings.

At present, the application of phytoremediation technology in the ecological remediation of heavy metal tailings is receiving more and more attention. In this study, the physiological and biochemical response and tolerance mechanism of woody plant Nerium indicum to Pb and Zn under different proportions of inorganic modifier calcium carbonate (C1: 5%, C2: 10%, C3: 15%) and organic modifier mushroom residue (M1: 10%, M2: 20%, M3: 30%) was compared. The results showed that the pH value has a trend of C group > M group > CK group and organic matter has a trend of M group > CK group > C group. Phosphatase activity and catalase activity has a trend of M group > C group > CK group, but catalase was more vulnerable to the calcium carbonate concentration. Both modifiers can promote the transformation of Pb, Zn, Cu, and Cd in tailings to more stable organic bound and residual states. However, the stabilization effect of mushroom residue is better, and its stability is Pb, Zn > Cd, Cu. Both modifiers can increase the biomass of Nerium indicum and the modification effect of mushroom residue is better than calcium carbonate. Pb/Zn content and accumulation in Nerium indicum organs showed root > stem > leaf in all groups. Compared with the CK group, the enrichment coefficient of Pb/Zn in C1 and M1 groups decreased, while the translocation factor of Pb/Zn in C1 and M1 groups increased. With the increase in modifier concentration, the enrichment coefficient increases about 1.75~52.94%, but the translocation factor decreases rapidly (20.01~64.46%). Clearly, both the calcium carbonate and mushroom residue amendment could promote the growth ability of Nerium indicum in lead–zinc tailings and strengthen the phytoremediation potential.

​​Marigold (Tagetes spp.): A Diverse Crop with Multipurpose Value for Health and Environment: A Review

Marigold (Tagetes spp.) is one of the most popular flower crop commercially exploited for multipurpose use. Apart from great demand of marigold flowers, the plants use in phytoremediation and allelopathic effect has been greatly exploited. Marigolds can be used against plant parasitic nematodes as a cover crop in rotation, as an intercrop, or as a crop residue amendment. Successful use of marigold as trap crop is well on record whereas its use as potential natural herbicide needs to be explored. Essential oils obtained from marigold possess antibacterial and antifungal properties and are widely used in perfumery industries, as insect repellent and as flavor component. Its extracts can be explored as alternative natural insecticides towards the stored products. Use of marigold for its medicinal value for curing various diseases has been well documented. Carotenoids extracted from flowers are being used commercially in pharmaceuticals. Marigold extract also finds application in coloring foods and various dairy products. Marigold petals are used as additives for poultry feed, as they provide bright colors in egg yolks, skin and fatty tissues and also as emulsifying gum. Silver and gold nanoparticles have been synthesized from marigold for antimicrobial activity. This review paper discusses the research undertaken for various uses of marigold plant worldwide.