Manure replacing synthetic fertilizer improves crop yield sustainability and reduces carbon footprint under winter wheat-summer maize cropping system.

Manure replacing synthetic fertilizer is a viable practice to ensure crop yield and increase soil organic carbon (SOC), but its impact on greenhouse gas (GHG) emissions is inconsistent, thus remains its effect on CF unclear. In this study, a 7-year field experiment was conducted to assess the impact of replacing synthetic fertilizer with manure on crop productivity, SOC sequestration, GHG emissions and crop CF under winter wheat-summer maize cropping system. Five treatments were involved: synthetic nitrogen, phosphorus, and potassium fertilizer (NPK) and 25%, 50%, 75%, and 100% of manure replacing synthetic N (25%M, 50%M, 75%M, and 100%M). Compared with NPK treatment, 25%M and 50%M treatments maintained annual yield (winter wheat plus summer maize) and sustainable yield index (SYI), but 75%M and 100%M treatments significantly decreased annual yield, and 100%M treatment also significantly reduced annual SYI. The SOC content exhibited a significant increasing trend over years in all treatments. After 7 years, SOC storage in manure treatments increased by 3.06-11.82 Mg ha-1 relative to NPK treatment. Manure treatments reduced annual GHG emissions by 14%-60% over NPK treatment. The CF of the cropping system ranged from 0.16 to 0.39 kg CO2 eq kg-1 of grain without considering SOC sequestration, in which the CF of manure treatments lowered by 18%-58% relative to NPK treatment. When SOC sequestration was involved in, the CF varied from -0.39 to 0.37 kg CO2 eq kg-1 of grain, manure treatments significantly reduced the CF by 22%-208% over NPK treatment. It was concluded that replacing 50% of synthetic fertilizer with manure was a sound option for achieving high crop yield and SYI but low CF under the tested cropping system.

Physically separated soil organic matter pools as indicators of carbon and nitrogen change under long-term fertilization in a Chinese Mollisol.

Isolation and quantification of soil organic matter (SOM) pools under the influence of management practices is needed for assessing the changes in soil fertility. However, the knowledge on how the active, slow and passive pools of SOM respond to long-term fertilization is scarce. Therefore, the present study was designed to isolate the active, slow, and passive pools of soil organic matter through physical fractionation under long-term fertilization. The treatments included; inorganic fertilization (NPK) either alone or combined with a normal dose of manure (MNPK) or a high dose of manure (1.5MNPK) with an unfertilized control (CK) for comparison. The isolated pools were analyzed and compared for their sizes, SOC and TN storage and their contribution to total SOC and TN sequestration. The results revealed that the fertilization enhanced the active, slow and passive pools of SOC and TN and their storage under applied treatments was patterned as 1.5MNK > MNPK > NPK > CK. The highest SOC and TN storage was observed in the active pool, while, greater response to fertilization (in terms of response ratio) was associated with the slow pool. Results show that fertilization enhanced the proportion of SOC and TN stocks to bulk SOC and TN stocks in active and slow pools, while a diminishing trend was found for passive pools. Moreover, the highest response ratio was found for TN sequestration in each pool as compared to SOC, suggesting preferential accumulation of TN over SOC in the studied soil. Nevertheless, the highest SOC and TN storage took place in the active pool. The slow pool showed greater response to applied fertilizer, with the highest values being observed under 1.5MNPK. This study concluded that long-term manure + inorganic fertilization is crucial for enhancing C and N sequestration by altering the size and response of SOM pools.

Biochar application for remediation of organic toxic pollutants in contaminated soils; An update.

Bioremediation of organic contaminants has become a major environmental concern in the last few years, due to its bio-resistance and potential to accumulate in the environment. The use of diverse technologies, involving chemical and physical principles, and passive uptake utilizing sorption using ecofriendly substrates have drawn a lot of interest. Biochar has got attention mainly due to its simplicity of manufacturing, treatment, and disposal, as it is a less expensive and more efficient material, and has a lot of potential for the remediation of organic contaminants. This review highlighted the adverse impact of persistent organic pollutants on the environment and soil biota. The utilization of biochar to remediate soil and contaminated compounds i.e., pesticides, polycyclic aromatic hydrocarbons, antibiotics, and organic dyes has also been discussed. The soil application of biochar has a significant impact on the biodegradation, leaching, and sorption/desorption of organic contaminants. The sorption/desorption of organic contaminants is influenced by chemical composition and structure, porosity, surface area, pH, and elemental ratios, and surface functional groups of biochar. All the above biochar characteristics depend on the type of feedstock and pyrolysis conditions. However, the concentration and nature of organic pollutants significantly alters the sorption capability of biochar. Therefore, the physicochemical properties of biochar and soils/wastewater, and the nature of organic contaminants, should be evaluated before biochar application to soil and wastewater. Future initiatives, however, are needed to develop biochars with better adsorption capacity, and long-term sustainability for use in the xenobiotic/organic contaminant remediation strategy.

Rhizosphere Bacteria in Plant Growth Promotion, Biocontrol, and Bioremediation of Contaminated Sites: A Comprehensive Review of Effects and Mechanisms.

Agriculture in the 21st century is facing multiple challenges, such as those related to soil fertility, climatic fluctuations, environmental degradation, urbanization, and the increase in food demand for the increasing world population. In the meanwhile, the scientific community is facing key challenges in increasing crop production from the existing land base. In this regard, traditional farming has witnessed enhanced per acre crop yields due to irregular and injudicious use of agrochemicals, including pesticides and synthetic fertilizers, but at a substantial environmental cost. Another major concern in modern agriculture is that crop pests are developing pesticide resistance. Therefore, the future of sustainable crop production requires the use of alternative strategies that can enhance crop yields in an environmentally sound manner. The application of rhizobacteria, specifically, plant growth-promoting rhizobacteria (PGPR), as an alternative to chemical pesticides has gained much attention from the scientific community. These rhizobacteria harbor a number of mechanisms through which they promote plant growth, control plant pests, and induce resistance to various abiotic stresses. This review presents a comprehensive overview of the mechanisms of rhizobacteria involved in plant growth promotion, biocontrol of pests, and bioremediation of contaminated soils. It also focuses on the effects of PGPR inoculation on plant growth survival under environmental stress. Furthermore, the pros and cons of rhizobacterial application along with future directions for the sustainable use of rhizobacteria in agriculture are discussed in depth.

Soil aggregation and soil aggregate stability regulate organic carbon and nitrogen storage in a red soil of southern China.

Soil aggregation plays a critical role in the maintenance of soil structure, as well as in its productivity. Fertilization influences soil aggregation, especially by regulating soil organic carbon (SOC) and total nitrogen (TN) contents in aggregate fractions. The present study evaluated the influence of three contrasting fertilizer regimes (unfertilized control -CK-, mineral fertilization -NPK- and manure combined with NPK -NPKM) on soil aggregate stability, aggregate-associated organic carbon and total nitrogen sequestration and mineralization of SOC. Soil samples from (20 cm) depth were collected from a long-term fertilization experiment and analysed for size distribution ranging (>250 µm, 250-53 µm and <53 µm sizes), SOC and TN contents, as well as for mineralization of bulk and aggregate associated-SOC. Both NPK and NPKM fertilizations significantly enhanced SOC and TN contents in bulk soil and its constituent aggregates of >250 µm, 250-53 µm and <53 µm sizes, as compared to CK. Long-term NPK and NPKM increased SOC and TN stock in bulk soil by 45 and 98%, and by 70 and 144%, respectively, as compared to CK. Similarly, higher values of SOC and TN stock in all aggregate fractions was observed with the application of NPKM. Application of NPK and NPKM for 26 years significantly increased aggregate stability, which was positively correlated with total SOC contents in terms of mean weight diameter (MWD) (Adj. R2 = 0.689, p < 0.03) and geometric mean diameter (GMD) (Adj. R2 = 0.471, p < 0.24). Moreover, higher scores regarding cumulative mineralization for bulk soil and aggregate associated OC were observed with the application of NPK and NPKM. Irrespective of treatments, higher cumulative C-mineralization was observed for macro-aggregates (>250 µm size) followed by 250-53 µm and <53 µm size aggregates. Interestingly, a highly positive correlation was observed between aggregate stability and the cumulative amount of mineralization for bulk soil and aggregate fractions, with R2 ranging from 0.84 to 0.99. This study evidenced that long-term fertilization of NPK and NPKM can improve soil aggregation, stability and associated OC and TN stock in aggregates, as well as aggregate-associated OC mineralization, which was further governed by aggregate size.

Cadmium mediated phytotoxic impacts in Brassica napus: Managing growth, physiological and oxidative disturbances through combined use of biochar and Enterobacter sp. MN17.

Cadmium (Cd) is a toxic heavy metal with unknown biological role. Interactive effect of Enterobacter sp. MN17 and biochar was studied on the growth, physiology and antioxidant defense system of Brassica napus under Cd contaminated soil. A multi-metal tolerant endophytic bacterium, Enterobacter sp. MN17, was able to grow in tryptic soy agar (TSA) medium with up to 160, 200, 300, 700, 160 and 400 µg mL-1 of Cd, Cu, Cr, Pb, Ni and Zn, respectively. Paper and pulp waste biochar was prepared at 450 °C and applied to pots (7 kg soil) at a rate of 1% (w/w), while Cd was spiked at 80 mg kg-1 soil. Application of Enterobacter sp. MN17 and biochar, alone or combined, was found effective in the amelioration of Cd stress. Combined application of Enterobacter sp. MN17 and biochar caused the maximum appraisal in shoot and root length (52.5 and 76.5%), fresh and dry weights of shoot (77.1 and 70.7%) and root (81.2 and 57.9%), photosynthetic and transpiration rate (120.2 and 106.6%), stomatal and sub-stomatal conductance (81.3 and 75.5%), chlorophyll content and relative water content (RWC) (78.4 and 102.9%) than control. Their combined use showed a significant decrease in electrolyte leakage (EL), proline, malondialdehyde (MDA), catalase (CAT), glutathione peroxidase (GPX), glutathione S transferase (GST) and superoxide dismutase (SOD) by 39.3, 39.4, 39.5, 37.0, 39.0 42.1 and 30.8%, respectively, relative to control. Likewise, the combined application of bacterial strain MN17 and biochar reduced Cd in soil by 45.6%, thereby decreasing its uptake in root and shoot by 40.1 and 38.2%, respectively in Cd contaminated soil. The application of biochar supported the maximum colonization of strain MN17 in the rhizosphere soil, root and shoot tissues. These results reflected that inoculation with Enterobacter sp. MN17 could be an effective approach to accelerate biochar-mediated remediation of Cd contaminated soil for sustainable production of crops.

Wood ash application for crop production, amelioration of soil acidity and contaminated environments.

Agriculture is vital to human life and economic development even though it may have a detrimental influence on soil quality. Agricultural activities can deteriorate the soil quality, endangers the ecosystem health and functioning, food safety, and human health. To resolve the problem of soil degradation, alternative soil conditioners such as wood ash are being explored for their potential to improve soil-plant systems. This study provides an overview of the production, properties, and effects of wood ash on soil properties, crop productivity, and environmental remediation. A comprehensive search of relevant databases was conducted in order to locate and assess original research publications on the use of wood ash in agricultural and environmental management. According to the findings, wood ash, a byproduct of burning wood, may improve the structure, water-holding capacity, nutrient availability, and buffering capacity of soil as well as other physico-chemical, and biological attributes of soil. Wood ash has also been shown to increase agricultural crop yields and help with the remediation of polluted regions. Wood ash treatment, however, has been linked to several adverse effects, such as increased trace element concentrations and altered microbial activity. The examination found that wood ash could be a promising material to be used as soil conditioner and an alternative supply of nutrients for agricultural soils, while, wood ash contributes to soil improvement and environmental remediation, highlighting its potential as a sustainable solution for addressing soil degradation and promoting environmental sustainability in agricultural systems.

Nickel (Ni) phytotoxicity and detoxification mechanisms: A review.

Scientists studying the environment, physiology, and biology have been particularly interested in nickel (Ni) because of its dual effects (essentiality and toxicity) on terrestrial biota. It has been reported in some studies that without an adequate supply of Ni, plants are unable to finish their life cycle. The safest Ni limit for plants is 1.5 µg g-1, while the limit for soil is between 75 and 150 µg g-1. Ni at lethal levels harms plants by interfering with a variety of physiological functions, including enzyme activity, root development, photosynthesis, and mineral uptake. This review focuses on the occurrence and phytotoxicity of Ni with respect to growth, physiological and biochemical aspects. It also delves into advanced Ni detoxification mechanisms such as cellular modifications, organic acids, and chelation of Ni by plant roots, and emphasizes the role of genes involved in Ni detoxification. The discussion has been carried out on the current state of using soil amendments and plant-microbe interactions to successfully remediate Ni from contaminated sites. This review has identified potential drawbacks and difficulties of various strategies for Ni remediation, discussed the importance of these findings for environmental authorities and decision-makers, and concluded by noting the sustainability concerns and future research needs regarding Ni remediation.

Co-Application of Biochar and Arbuscular mycorrhizal Fungi Improves Salinity Tolerance, Growth and Lipid Metabolism of Maize (Zea mays L.) in an Alkaline Soil.

This study reports the mitigating strategy against salinity by exploring the potential effects of biochar (5%), Arbuscular mycorrhizal fungi (20 g/pot, AMF), and biochar + AMF on maize (Zea mays L.) plants grown under saline stress in a greenhouse. The maize was grown on alkaline soil and subjected to four different saline levels; 0, 50, 100, and 150 mM NaCl. After 90 d for 100 mM NaCl treatment, the plant's height and fresh weight were reduced by 17.84% and 39.28%, respectively, compared to the control. When the saline-treated soil (100 mM NaCl) was amended with AMF, biochar, and biochar + AMF, the growth parameters were increased by 22.04%, 26.97%, 30.92% (height) and 24.79%, 62.36%, and 107.7% (fresh weight), respectively. Compared to the control and single AMF/biochar treatments, the combined application of biochar and AMF showed the most significant effect in improving maize growth under saline stress. The superior mitigating effect of biochar + AMF was attributed to its effective ability in (i) improving soil nutrient content, (ii) enhancing plant nutrient uptake, (iii) increasing the activities of antioxidant enzymes, and (iv improving the contents of palmitoleic acid (C16:1), oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3). Thus, our study shows that amending alkaline and saline soils with a combination of biochar-AMF can effectively mitigate abiotic stress and improve plant growth. Therefore, it can serve as a reference for managing salinity stress in agricultural soils.

Co-composted Biochar Enhances Growth, Physiological, and Phytostabilization Efficiency of Brassica napus and Reduces Associated Health Risks Under Chromium Stress.

Among heavy metals, chromium (Cr) contamination is increasing gradually due to the use of untreated industrial effluents for irrigation purposes, thereby posing a severe threat to crop production. This study aimed to evaluate the potential of compost, biochar (BC), and co-composted BC on the growth, physiological, biochemical attributes, and health risks associated with the consumption of Brassica grown on Cr-contaminated soil. Results revealed that Cr stress (Cr-25) significantly reduced the growth and physiological attributes and increased antioxidant enzyme activities in Brassica, but the applied amendments considerably retrieved the negative effects of Cr toxicity through improving the growth and physiology of plants. The maximum increase in plant height (75.3%), root length (151.0%), shoot dry weight (139.4%), root dry weight (158.5%), and photosynthetic rate (151.0%) was noted with the application of co-composted BC under Cr stress (Cr-25) in comparison to the control. The application of co-composted BC significantly reduced antioxidant enzyme activities, such as APX (42.5%), GP (45.1%), CAT (45.4%), GST (47.8%), GR (47.1%), and RG (48.2%), as compared to the control under Cr stress. The same treatment reduced the accumulation of Cr in grain, shoot, and roots of Brassica by 4.12, 2.27, and 2.17 times and enhanced the accumulation in soil by 1.52 times as compared to the control. Moreover, the application of co-composted BC significantly enhanced phytostabilization efficiency and reduced associated health risks with the consumption of Brassica. It is concluded that the application of co-composted BC in Cr-contaminated soil can significantly enhance the growth, physiological, and biochemical attributes of Brassica by reducing its uptake in plants and enhanced phytostabilization efficiency. The tested product may also help in restoring the soils contaminated with Cr.

Enhancing Cadmium Tolerance and Pea Plant Health through Enterobacter sp. MN17 Inoculation Together with Biochar and Gravel Sand.

Contamination of soils with heavy metals, particularly cadmium (Cd), is an increasingly alarming environmental issue around the world. Application of organic and inorganic immobilizing amendments such as biochar and gravel sand in combination with metal-tolerant microbes has the potential to minimize the bioavailability of Cd to plants. The present study was designed to identify the possible additive effects of the application of Enterobacter sp. MN17 as well as biochar and gravel sand on the reduction of Cd stress in plants and improvement of growth and nutritional quality of pea (Pisum sativum) plants through the reduction of Cd uptake. Pea seeds were surface sterilized then non-inoculated seeds and seeds inoculated with Enterobacter sp. MN17 were planted in artificially Cd-polluted soil, amended with the immobilizing agents biochar and gravel sand. Application of biochar and gravel sand alone and in combination not only improved the growth and nutritional quality of pea plants by in situ immobilization but also reduced the uptake of Cd by plant roots and its transport to shoots. However, microbial inoculation further enhanced the overall plant health as well as alleviated the toxic effects of Cd on the pea plants. These soil treatments also improved rates of photosynthesis and transpiration. The combined use of biochar and gravel sand with bacterial inoculation resulted in an increase in plant height (47%), shoot dry weight (42%), root dry weight (57%), and 100 seeds weight (49%) as compared to control plants in Cd contaminated soil. Likewise, biochemical constituents of pea seeds (protein, fat, fiber, and ash) were significantly increased up to 41%, 74%, 32%, and 72%, respectively, with the combined use of these immobilizing agents and bacterium. Overall, this study demonstrated that the combined application of biochar and gravel sand, particularly in combination with Enterobacter sp. MN17, could be an efficient strategy for the remediation of Cd contaminated soil. It could support better growth and nutritional quality of pea plants.