Circular economy fertilization: Phycoremediated algal biomass as biofertilizers for sustainable crop production.

There is an urgent need to meet the demand of water and nutrients by their reuse and recycling to gratify sustainable food production system and resource conservation. Chlorella minutissima was found to be very effective in the removal of electrical conductivity (EC), total dissolved solids, phosphorous (P), potassium (K), ammonium, nitrate, biological oxygen demand (BOD5) and chemical oxygen demand (COD) of sewage wastewater. We tested the effects of phycoremediated algal biomass addition to soil in field plots of baby corn and spinach, on plant growth, yield and soil chemical properties. The application of 100% nitrogen (N) fertilizer by algal biomass lead to higher economic yield of spinach and baby corn than recommended dose of mineral fertilizers. The available N and P content in experimental plots applied with algae biomass as biofertilizers were significantly higher than other treatments. The soil enzymes, such as urease, nitrate reductase, and dehydrogenase were analysed during the cropping season of baby corn and spinach. The soil supplied with 100% N by algae biomass (C. minutissima) significantly (P < 0.05) increased the dehydrogenase activity in spinach grown soil. While the nitrate reductase activity in soil supplied with algal manure was maximum (0.13 mg NO2-N produced g-1 soil 24 h-1) and significantly higher than other treatments in baby corn grown soil. This study revealed that phycoremediation coupled with biofertilizers production from algae biomass is a recycling and resource conservation exercise to reduce eutrophication, recycling of wastewater, recycling of plant nutrients and improvement of the soil quality in circular economy fertilization.

Hazardous heavy metals contamination of vegetables and food chain: Role of sustainable remediation approaches - A review.

This review emphasizes the role of toxic metal remediation approaches due to their broad sustainability and applicability. The rapid developmental processes can incorporate a large quantity of hazardous and unseen heavy metals in all the segments of the environment, including soil, water, air and plants. The released hazardous heavy metals (HHMs) entered into the food chain and biomagnified into living beings via food and vegetable consumption and originate potentially health-threatening effects. The physical and chemical remediation approaches are restricted and localized and, mainly applied to wastewater and soils and not the plant. The nanotechnological, biotechnological and genetical approaches required to more rectification and sustainability. A cellular, molecular and nano-level understanding of the pathways and reactions are responsible for potentially toxic metals (TMs) accumulation. These approaches can enable the development of crop varieties with highly reduced concentrations of TMs in their consumable foods and vegetables. As a critical analysis by authors observed that nanoparticles could provide very high adaptability for both in-situ and ex-situ remediation of hazardous heavy metals (HHMs) in the environment. These methods could be used for the improvement of the inbuilt genetic potential and phytoremediation ability of plants by developing transgenic. These biological processes involve the transfer of gene of interest, which plays a role in hazardous metal uptake, transport, stabilization, inactivation and accumulation to increased host tolerance. This review identified that use of nanoremediation and combined biotechnological and, transgenic could help to enhance phytoremediation efficiency in a sustainable way.

Zinc supplementation imparts tolerance to arsenite stress in Hydrilla verticillata (L.f.) Royle.

The present study was aimed to analyze the effects of external Zn supply on arsenic (As) toxicity in Hydrilla verticillata (L.f.) Royle. The plants were exposed to arsenite (AsIII; 10 µM) with or without 50 and 100 µM Zn. The level of As accumulation (µg g-1 dw) after 2 and 4 days was not significantly affected by Zn supply. The plants showed a significant stimulation of the thiol metabolism (nonprotein thiols, cysteine, glutathione-S-transferase activity) upon As(III) exposure in the presence of Zn as compared to As(III) alone treatment. Besides, they did not experience significant toxicity, measured in terms of hydrogen peroxide and malondialdehyde accumulation, which are the indicators of oxidative stress. The minus Zn plants suffered from oxidative stress probably due to insufficient increase in thiols to counteract the stress. Stress amelioration by Zn supply was also evident from antioxidant enzyme activities, which came close to control levels with increasing Zn supply as compared to the increase observed in As(III) alone treatment. Variable Zn supply also modulated the level of photosynthetic pigments and restored them to control levels. In conclusion, an improved supply of Zn to plants was found to augment their ability to withstand As toxicity through enhanced thiol metabolism.

Environmental applications of chitosan and its derivatives.

Chitosan originates from the seafood processing industry and is one of the most abundant of bio-waste materials. Chitosan is a by-product of the alkaline deacetylation process of chitin. Chemically, chitosan is a polysaccharide that is soluble in acidic solution and precipitates at higher pHs. It has great potential for certain environmental applications, such as remediation of organic and inorganic contaminants, including toxic metals and dyes in soil, sediment and water, and development of contaminant sensors. Traditionally, seafood waste has been the primary source of chitin. More recently, alternative sources have emerged such as fungal mycelium, mushroom and krill wastes, and these new sources of chitin and chitosan may overcome seasonal supply limitations that have existed. The production of chitosan from the above-mentioned waste streams not only reduces waste volume, but alleviates pressure on landfills to which the waste would otherwise go. Chitosan production involves four major steps, viz., deproteination, demineralization, bleaching and deacetylation. These four processes require excessive usage of strong alkali at different stages, and drives chitosan's production cost up, potentially making the application of high-grade chitosan for commercial remediation untenable. Alternate chitosan processing techniques, such as microbial or enzymatic processes, may become more cost-effective due to lower energy consumption and waste generation. Chitosan has proved to be versatile for so many environmental applications, because it possesses certain key functional groups, including - OH and -NH2 . However, the efficacy of chitosan is diminished at low pH because of its increased solubility and instability. These deficiencies can be overcome by modifying chitosan's structure via crosslinking. Such modification not only enhances the structural stability of chitosan under low pH conditions, but also improves its physicochemical characteristics, such as porosity, hydraulic conductivity, permeability, surface area and sorption capacity. Crosslinked chitosan is an excellent sorbent for trace metals especially because of the high flexibility of its structural stability. Sorption of trace metals by chitosan is selective and independent of the size and hardness of metal ions, or the physical form of chitosan (e.g., film, powder and solution). Both -OH and -NH2 groups in chitosan provide vital binding sites for complexing metal cations. At low pH, -NH3 + groups attract and coagulate negatively charged contaminants such as metal oxyanions, humic acids and dye molecules. Grafting certain functional molecules into the chitin structure improves sorption capacity and selectivity for remediating specific metal ions. For example, introducing sulfur and nitrogen donor ligands to chitosan alters the sorption preference for metals. Low molecular weight chitosan derivatives have been used to remediate metal contaminated soil and sediments. They have also been applied in permeable reactive barriers to remediate metals in soil and groundwater. Both chitosan and modified chitosan have been used to phytoremediate metals; however, the mechanisms by which they assist in mobilizing metals are not yet well understood. In addition, microbes have been used in combination with chitosan to remediate metals (e.g., Cu and Zn) in contaminated soils. Chitosan has also been used to remediate organic contaminants, such as oil-based wastewater, dyes, tannins, humic acids, phenols, bisphenoi-A, p-benzoquinone, organo-phosphorus insecticides, among others. Chitosan has also been utilized to develop optical and electrochemical sensors for in-situ detection of trace contaminants. In sensor technology, naturally-derived chitosan is used primarily as an immobilizing agent that results from its enzyme compatibility, and stabilizing effect on nanoparticles. Contaminant-sensing agents, such as enzymes, microbes and nanoparticles, have been homogeneously immobilized in chitosan gels by using coagulating (e.g., alginate, phosphate) or crosslinking agents (e.g., GA, ECH). Such immobilization maintains the stability of sensing elements in the chitosan gel phase, and prevents inactivation and loss of the sensing agent. In this review, we have shown that chitosan, an efficient by-product of a waste biomaterial, has great potential for many environmental applications. With certain limitations, chitosan and its derivatives can be used for remediating contaminated soil and wastewater. Notwithstanding, further research is needed to enhance the physicochemical properties of chitosan and mitigate its deficiencies.

Valorisation of phyto-biochars as slow release micronutrients and sulphur carrier for agriculture.

Slow release micronutrients and sulphur sources are required for higher use efficiency of fertilizers in agriculture. The present investigation was undertaken to examine the salt soluble, desorbed and specifically sorbed fractions of micronutrients and sulphur in nutrient enriched phyto-biochars incubated at 15, 25 and 35°C for 48 h after pyrolysis of Lantana sp., Pinus sp. needles and wheat straw at 300 and 450 °C. The highest salt soluble fractions of Zn, Cu, Fe, Mn and B were recorded with pine needle biochar pyrolyzed at 300 °C, whereas that of S with lantana biochar pyrolyzed at 300 °C. The highest desorbed contents of Zn, Cu and Mn were with pine needle biochar (300 °C) and that of B and S with wheat straw biochar (450 °C) and lantana biochar (300 °C), respectively. An increase in incubation temperature from 15 to 25 °C increased the salt soluble contents of Zn and specifically sorbed contents of Fe and B but decreased salt soluble contents of Fe and B and desorbed amount of S significantly. Further, increase in incubation temperature from 25 to 35 °C significantly decreased the salt soluble contents of all nutrients except Mn and desorbed amount of S but increased specifically sorbed amount of Fe, B and S. Considering the salt soluble and desorbed contents of nutrients in enriched phyto-biochars, especially pine needle biochar pyrolyzed at 300 °C and treated with marginal or deficient nutrients for 2 d at 15-25 °C appeared to be suitable as a slow release fertilizer.

Reducing options of ammonia volatilization and improving nitrogen use efficiency via organic and inorganic amendments in wheat (Triticum aestivum L.).

Background: This study investigates the effect of organic and inorganic supplements on the reduction of ammonia (NH3) volatilization, improvement in nitrogen use efficiency (NUE), and wheat yield. Methods: A field experiment was conducted following a randomized block design with 10 treatments i.e., T1-without nitrogen (control), T2-recommended dose of nitrogen (RDN), T3-(N-(n-butyl) thiophosphoric triamide) (NBPT @ 0.5% w/w of RDN), T4-hydroquinone (HQ @ 0.3% w/w of RDN), T5-calcium carbide (CaC2 @ 1% w/w of RDN), T6-vesicular arbuscular mycorrhiza (VAM @ 10 kg ha-1), T7-(azotobacter @ 50 g kg-1 seeds), T8-(garlic powder @ 0.8% w/w of RDN), T9-(linseed oil @ 0.06% w/w of RDN), T10-(pongamia oil @ 0.06% w/w of RDN). Results: The highest NH3 volatilization losses were observed in T2 at about 20.4 kg ha-1 per season. Significant reduction in NH3 volatilization losses were observed in T3 by 40%, T4 by 27%, and T8 by 17% when compared to the control treatment. Soil urease activity was found to be decreased in plots receiving amendments, T3, T4, and T5. The highest grain yield was observed in the T7 treated plot with 5.09 t ha-1, and straw yield of 9.44 t ha-1 in T4. Conclusion: The shifting towards organic amendments is a feasible option to reduce NH3 volatilization from wheat cultivation and improves NUE.

Utilization of molasses based distillery effluent for fertigation of sugarcane.

A field study was carried out to monitor the effect of application of molasses based distillery effluent on yields of sugarcane and soil properties. The treatments consisted of main plots: control (I0), first pre-sowing irrigation with undiluted effluent (I1), one irrigation with effluent: tube-well water (1:3) at tillering stage (I2), two irrigations with effluent: tube-well water (1:4) at tillering and 30 d after tillering stage (I3). The subplots either received no fertilizer application (F0) or had 50 % of recommended dose (50 kg N, 60 kg P(2)O(5) and 40 kg K(2)O ha(-1) as basal dose (F1) with top dressing of 50 kg N ha(-1) at tillering and in June before the onset of monsoon. Nitrogen to the ratoon crops was applied in three equal splits. Application of 50 % recommended fertilizer dose increased the cumulative cane yields under different effluent treatments. Use of distillery effluent irrespective of the method of application significantly increased the cumulative yields of sugarcane over no application of effluent significantly at p ≤ 0.05. After the harvest of second ratoon crop, no significant effect of different treatments was noted on soil pH, electrical conductance and exchangeable Na. Significantly higher build-up of organic C in surface soil was noted under I2 treatment in comparison to I0 treatment at p ≤ 0.05. With no fertilizer application, both I1 and I2 significantly increased accumulation of alkaline KMnO(4) hydrolysable N in 30-45 cm layer in comparison to I0F0 at p ≤ 0.05. In comparison to I0, use of I2 increased the content of Olsen's P significantly (p ≤ 0.05) in 30-45 and 45-60 cm layers while I3 increased it significantly at p ≤ 0.05 in 0-15 and 45-60 cm layers. Use of distillery effluent as pre-sowing or standing crop irrigation increased ammonium acetate extractable K in surface and sub-surface layers significantly in comparison to I0 at p ≤ 0.05. Thus, use of distillery effluent in sugarcane crop as pre-sown or standing crop irrigation had no adverse impact on soil reaction or electrical conductivity and could save at least fifty percent of basal NPK application with significantly higher cumulative millable cane yields of main crop and two subsequent ratoons.

Metal doped nitrogenous hydroxyapatite nanohybrids slowly release nitrogen to crops and mitigate ammonia volatilization: An impact assessment.

To supply adequate food, the ongoing and unrestrained administration of nitrogen fertilizer to agricultural fields is polluting the climate and living organisms. On the other hand, the agriculture sector urgently needs a technological upgrade to effectively confront hunger and poverty. Here, we report a rapid synthesis of zinc and magnesium-doped hydroxyapatite-urea nanohybrids for slow release and delivery of nitrogen to wheat and rice crops. Nanohybrids slowly release nitrogen for up to six weeks compared to the burst release of nitrogen from urea, and their use substantially reduces, by at least 3.8 times, ammonia emissions into the environment compared with that of urea fertilizer. A half­nitrogen dose applied as multi-nutrient complexed nanohybrids maintained crop growth, yield, and nutritional compositions in wheat and subsequent rice crops. Nanohybrids enhanced the wheat crop yield and nitrogen uptake by 22.13% and 58.30%, respectively. The synthesized nitrogen nanohybrids remained in the soil for two continuous crop cycles, reduced ammonia volatilization, and achieved nitrogen delivery to the crops. Additionally, soil dehydrogenase activity (534.55% above control) and urease activities (81.82% above control) suggest that nanohybrids exhibited no adverse impact on soil microorganisms. Our comprehensive study demonstrates the advantages of 'doping' as a method for tailoring hydroxyapatite nanoparticles properties for extended agricultural and environmental applications. The use of nanohybrids substantially reduced greenhouse gas emissions and enabled the reduction, by half, of nitrogen inputs into the agricultural fields. This study, therefore, reports a novel nano-enabled platform of engineered hydroxyapatite-urea nanohybrids as a nitrogen fertilizer for efficient nitrogen delivery that results in improved crop growth while minimizing environmental pollution.

Sorption-desorption of some transition metals, boron and sulphur in a multi-ionic system onto phyto-biochars prepared at two pyrolysis temperatures.

The sorption-desorption of transition metals, B and S onto phyto-biochars prepared from lantana, pine needles and wheat straw by pyrolysis at 300 °C and 450 °C were studied using the batch method. Their sorption-desorption onto phyto-biochars conformed to Freundlich isotherms. Phyto-biochars pyrolyzed at 450 °C had higher sorption capacity for transition metals (Zn, Cu, Fe, and Mn) but lower sorption capacity for S as compared to those pyrolyzed at 300 °C. The desorption capacity of phyto-biochars pyrolyzed at 450 °C for transition metals, B and S was also higher than that of phyto-biochars pyrolyzed at 300 °C except for S in pine needle biochar. Percent desorption of all transition metals, B and S was lower for phyto-biochars pyrolyzed at 450 °C compared to those pyrolyzed at 300 °C; however, an opposite trend was noted for Mn and S in the case of pine needle and wheat biochars, respectively. Simple correlation analysis of Freundlich model constants, desorption index and percent desorption values of transition metals, B and S with the properties of phyto-biochars and changes in Fourier transform infra-red spectra after sorption revealed that several conjunctive mechanisms such as cation exchange, complexation and co-precipitation for the sorption of transition metals, H-bonding/ligand exchange for B and H-bonding/cation bridging for S were operative in phyto-biochars. Phyto-biochars produced from plant biomass wastes by pyrolysis at 300 °C, which have been enriched with Zn, Cu, Fe, Mn, B and S may serve as a potential slow-release nutrient carrier in agriculture.

Appraisal of probabilistic levels of toxic metals and health risk in cultivated and marketed vegetables in urban and peri-urban areas of Delhi, India.

A total of six vegetables (S. tuberosum, D. carota, S. lycopersicum, A. esculentus, S. oleracea and B. juncea) were analysed for five heavy metals (As, Cd, Cr, Hg, and Pb) to evaluate the contamination load in vegetables collected from five cultivated and two market sites (n = 504) at Delhi, India. The irrigation water samples and soil samples (n = 180) were only collected from cultivated sites. The results showed that the concentration of heavy metals in soil and water samples were well below the permissible level except for Cd 0.001-0.013 µg g-1. Similarly, the concentration of Cd (>0.20 µg g-1) was detected higher in all investigated vegetables except for tomato. The evaluation index value was highest for spinach and lowest for tomato. The transfer factor values and metal pollution index was maximum in spinach and okra. Principal component analysis (PCA), Tukey's HSD (Honestly Significant Difference) test, and one-way and two-way ANOVA (Analysis of Variance) were also applied to statistically analyse the results.

Genome-wide association studies reveal putative QTLs for physiological traits under contrasting phosphorous conditions in wheat (Triticum aestivum L.).

A Genome-wide association (GWAS) study was conducted for phosphorous (P)-use responsive physiological traits in bread wheat at the seedling stage under contrasting P regimes. A panel of 158 diverse advanced breeding lines and released varieties, and a set of 10,800 filtered single nucleotide polymorphism (SNP) markers were used to study marker-trait associations over the eight shoot traits. Principle component analysis separated the two environments (P regimes) because of the differential response of the traits indicating the essentiality of the separate breeding programmes for each environment. Significant variations for genotypic, environmental, and genotype × environment (GEI) effects were observed for all the traits in the combined analysis of variance with moderately high broad sense heritability traits (0.50-0.73). With the different algorithms of association mapping viz., BLINK, FarmCPU, and MLM, 38 unique QTLs under non-limiting P (NLP) and 45 QTLs for limiting P (LP) conditions for various shoot traits were identified. Some of these QTLs were captured by all three algorithms. Interestingly, a Q.iari.dt.sdw.1 on chromosome 1D was found to explain the significant variations in three important physiological traits under non-limiting phosphorus (NLP) conditions. We identified the putative candidate genes for QTLs namely Q.iari.dt.chl.1, Q.iari.dt.sdw.16, Q.iari.dt.sdw.9 and Q.iari.dt.tpc.1 which are potentially involved in the mechanism regulating phosphorus use efficiency through improved P absorption due to improved root architectural traits and better mobilization such as sulfotransferase involved in postembryonic root development, WALLS ARE THIN1 (WAT1), a plant-specific protein that facilitates auxin export; lectin receptor-like kinase essentially involved in plant development, stress response during germination and lateral root development and F-box component of the SKP-Cullin-F box E3 ubiquitin ligase complex and strigolactone signal perception. Expression profiling of putative genes located in identified genomic regions against the wheat expression atlas revealed their significance based on the expression of these genes for stress response and growth development processes in wheat. Our results thus provide an important insight into understanding the genetic basis for improving PUE under phosphorus stress conditions and can shape the future breeding programme by developing and integrating molecular markers for these difficult-to-score important traits.

Conservation agricultural practices for minimizing ammonia volatilization and maximizing wheat productivity.

A large amount of ammonia volatilization from the agricultural system causes environmental problems and increases production costs. Conservation agriculture has emerged as an alternate and sustainable crop production system. Therefore, in the present study, ammonia losses from different agricultural practices were evaluated for the wheat crop under different tillage practices. The results of the present study showed that the cumulative emission of ammonia flux from the wheat field varied from 6.23 to 24.00 kg ha-1 (P ≤ 0.05) in conservation tillage (CA) and 7.03 to 26.58 kg ha-1 (P ≤ 0.05) in conventional tillage (CT) among different treatments. Application of basal 80% nitrogen resulted in the highest ammonia flux in conventional and conservation tillage practices. The ammonia volatilization followed the following trend: urea super granules with band placement > neem-coated urea with band placement > neem-coated urea with broadcast before irrigation > neem-coated urea with broadcast after irrigation > slow-release N fertilizer (urea stabilized with DCD and N(n-butyl)thiophosphoric triamide) with band placement. The conservation agricultural practices involving conservation tillage appear to be a sustainable approach for minimizing ammonia volatilization and improving wheat productivity.

Effect of ZnO Nanoparticles on Growth and Biochemical Responses of Wheat and Maize.

Zinc is an essential element that is also renowned for widespread contamination and toxicity at high concentrations. The present study was carried out to analyze the responses induced by lower, as well as higher, doses of zinc (0-200 mg/L), in the form of zinc oxide nanoparticles (ZnO NPs) in wheat and maize, for a period of 21 days. Accumulation of zinc increases with increasing Zn doses in both wheat and maize, with higher doses being in wheat (121 mg/kg in root and 66 mg/kg in shoot) than in maize (95 mg/kg in root and 48 mg/kg in shoot). The activity of alpha-amylase showed increase, while that of dehydrogenase decline, in response to ZnO NPs. The length and biomass of plants and photosynthetic pigments increased slightly upon ZnO NPs supply. Malondialdehyde content showed a progressive increase in root and shoot of both plants. However, in response, antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, and catalase) showed increase up to lower concentrations (100 mg/L) of ZnO NPs but decline variably at higher levels (150-200 mg/L) in wheat and maize. The results suggest that lower supply of ZnO NPs (100 mg/L) could be stimulatory to the growth of plants and can be recommended as a Zn fertilizer source for crop production.

Survival of phosphate-solubilizing bacteria against DNA damaging agents.

Phosphate-solubilizing bacteria (PSBs) were isolated from different plant rhizosphere soils of various agroecological regions of India. These isolates showed synthesis of pyrroloquinoline quinone (PQQ), production of gluconic acid, and release of phosphorus from insoluble tricalcium phosphate. The bacterial isolates synthesizing PQQ also showed higher tolerance to ultraviolet C radiation and mitomycin C as compared to Escherichia coli but were less tolerant than Deinococcus radiodurans. Unlike E. coli, PSB isolates showed higher tolerance to DNA damage when grown in the absence of inorganic phosphate. Higher tolerance to ultraviolet C radiation and oxidative stress in these PSBs grown under PQQ synthesis inducible conditions, namely phosphate starvation, might suggest the possible additional role of this redox cofactor in the survival of these isolates under extreme abiotic stress conditions.