Reduce Nitrate Concentrations Research Articles

Assessment of Nitrate Reduction by Microbes in Artificial Groundwater Medium

There are significant reasons for nitrate contamination in groundwater (Delhi, India): sewage, runoff from landfill sites, nitrogenous chemical fertilisers, and pesticides from agricultural lands. The highest recorded concentration of nitrate in Delhi’s groundwater is reported to be 1500 mg/l. Consumption of high nitrate through water may pose serious health problems in humans, especially children (below five years). The study’s primary objective was to isolate and identify nitrate-remediating microbes from the nitrate-contaminated site Okhla Barrage, located on the Yamuna River in Delhi, India. A total of 11 different strains were isolated from this site. Among these four strains exhibited 40%–50% remediation efficiency at a nitrate concentration of 1000 mg/l. Molecular characterisation revealed that these four strains, Enterobacter aerogenes, E. coli K12, <i>Klebsiella oxytoca</i> and <i>Lelliottia amnigena</i>, belong to the Enterobacteriaceae family. This study assessed the nitrate remediation potential of isolated microbes in groundwater with 1000 and 1500 mg/l nitrate concentrations. By using a 2% inoculum, the microbes were incubated anaerobically at room temperature for ten days. Nitrate concentrations were monitored every 48 hours. <i>Lelliottia</i>, <i>E. coli</i>, and <i>Enterobacter</i> reduced nitrate (1500 mg/l) by approximately 42%, 24%, and 29%, respectively, while <i>K. oxytoca</i> showed minimal reduction. <i>L. amnigena</i> exhibited superior nitrate removal efficiency compared to other strains. According to the reported data, these strains are known to reduce nitrate concentrations of 620 mg/l. However, our findings demonstrate a remarkable nitrate remediation capacity of 1500 mg/l, showcasing a novel contribution to this study. Further detailed analysis for condition optimisation and association of microbe-microbe could be more helpful.

Removal of sulfamethoxazole in an algal-bacterial membrane aerated biofilm reactor: Microbial responses and antibiotic resistance genes

Antibiotics are frequently detected in wastewater, but often are poorly removed in conventional wastewater treatment processes. Combining microalgal and nitrifying bacterial processes may provide synergistic removal of antibiotics and ammonium. In this research, we studied the removal of the antibiotic sulfamethoxazole (SMX) in two different reactors: a conventional nitrifying bacterial membrane aerated biofilm reactor (bMABR) and algal-bacterial membrane aerated biofilm reactor (abMABR) systems. We investigated the synergistic removal of antibiotics and ammonium, antioxidant activity, microbial communities, antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and their potential hosts. Our findings show that the abMABR maintained a high sulfamethoxazole (SMX) removal efficiency, with a minimum of 44.6 % and a maximum of 75.8 %, despite SMX inhibition, it maintained a consistent 25.0 % ammonium removal efficiency compared to the bMABR. Through a production of extracellular polymeric substances (EPS) with increased proteins/polysaccharides (PN/PS), the abMABR possibly allowed the microalgae-bacteria consortium to protect the bacteria from SMX inactivation. The activity of antioxidant enzymes caused by SMX was reduced by 62.1–98.5 % in the abMABR compared to the bMABR. Metagenomic analysis revealed that the relative abundance of Methylophilus, Pseudoxanthomonas, and Acidovorax in the abMABR exhibited a significant positive correlation with SMX exposure and reduced nitrate concentrations and SMX removal. Sulfonamide ARGs (sul1 and sul2) appeared to be primarily responsible for defense against SMX stress, and Hyphomicrobium and Nitrosomonas were the key carriers of ARGs. This study demonstrated that the abMABR system has great potential for removing SMX and reducing the environmental risks of ARGs.

Advantages of compost tea: Promotion of nitrogen influx into the fruit and improvement of fruit nitrogen metabolism in tomato

The use of compost tea is important to improve food safety. However, the effect of compost tea on N uptake and partitioning in tomato is unclear. In this study, we measured temporal and spatial changes in nitrogen content, enzyme activities, and expression levels of nitrogen transporters genes in different organs of tomato treated with five nutrient solutions. The results showed that the expression levels of ammonium transporter protein genes (AMT1s) increased and that of a nitrogen transporters gene (NRT2.1) decreased under treatment with compost tea, which promoted NH4+ transport to the fruit and reduced nutrient wastage compared with the response to chemical fertilizers. In addition, the lowermost leaves on the stem showed reduced nitrate content, faster metabolism, and decreased chlorophyll a content, but fruit yield was not increased, in compost tea-treated plants. These changes were dependent on the expression level of the glutamine synthetase gene (GS1.1), which was increased in leaves and decreased in fruit. Compost tea influenced the expression of critical genes in the fruits and leaves, and improved the competitiveness of sexual reproductive growth as a sink for nitrogen. However, the benefits of compost tea were reduced when it was mixed chemical fertilizers. This research establishes a theoretical framework for optimization of organic vegetable cultivation and promoting the widespread production of organic crops.

The role of zeolite and mineral fertilizers in enhancing Table Beet (Beta vulgaris L.) productivity in dark chestnut soils of Southeast Kazakhstan

This study evaluated the effectiveness of zeolite, both alone and in combination with mineral fertilizers, in improving the yield and quality of table beets (Beta vulgaris L.) grown in dark chestnut soils of southeast Kazakhstan. The research was conducted at the Kazakh Research Institute of Horticulture during the 2022-2023 growing seasons using a randomized complete block design with six treatments: control (no fertilizers), zeolite 2 t/ha, N45P45K45 (single dose of mineral fertilizers), N90P90K90 (double dose of mineral fertilizers), zeolite 2 t/ha + N45P45K45, and zeolite 2 t/ha + N90P90K90, replicated three times. The application of zeolite significantly improved soil physical properties, such as water permeability and soil density, enhancing root development and water retention. Nutrient availability, particularly nitrate nitrogen and mobile phosphorus, increased significantly in zeolite-treated plots. The combination of zeolite and mineral fertilizers resulted in the highest improvements, with nitrate nitrogen content reaching 40.5 mg/kg and mobile phosphorus 89.2 mg/kg. Moreover, zeolite reduced heavy metal concentrations, particularly cadmium, by 50% compared to the control. Table beet yield significantly increased with zeolite application, with the highest yield of 62.7 t/ha achieved with 2 t/ha zeolite combined with double dose N90P90K90 fertilizers, compared to 42.8 t/ha in the control. Marketable yield also improved, indicating better crop quality. Nutrient composition of the beets improved, with increased dry matter content (21.9%) and reduced nitrate content (240 mg/kg) in zeolite-treated variants. In conclusion, zeolite, especially when combined with mineral fertilizers, effectively enhances soil health, nutrient availability, and table beet yield and quality.

Enhancing drought-salinity stress tolerance in lettuce: Synergistic effects of salicylic acid and melatonin

Salicylic acid (SA) and melatonin (MEL) are affordable and effective phytohormones that help mitigate environmental stress. However, the combined benefits of SA and MEL in managing salt and drought stress in lettuce have not been evaluated. Therefore, this study was designed to evaluate the effectiveness of foliar spraying with 1.0 mM SA and 100 µM MEL, either alone or in combination, to enhance lettuce yield, growth, photosynthetic pigments, mineral status, quality, and antioxidant response under four different irrigation regimes. The irrigation practices used were: full irrigation (FI, irrigated with 0.18 dS m−1 at 100 % field capacity [FC]), deficit irrigation (DI, irrigated with 0.18 dS m−1 at 75 % FC), saline irrigation (SW, irrigated with 2.5 dS m−1 at 100 % FC), and deficit saline irrigation (DSW, irrigated with 2.5 dS m−1 at 75 % FC). Additionally, a control treatment (CK) was carried out with foliar application of distilled water and irrigation at 0.18 dS m−1. Compared to the CK, the application of SA, MEL, and SA+MEL increased evapotranspiration by 4.3 %, 8.6 %, and 15.1 %, and yield by 10.2 %, 16.4 %, and 23.8 %, respectively, under FI conditions. Furthermore, the joint application of SA and MEL at FI showed 25.3 % and 20.2 % higher K+/Na+ and Ca2+/Na+ ratios, respectively, compared to the CK. Additionally, the co-application of SA+MEL improved chlorophyll a, b, and carotenoid levels by 19.2 %, 17.2 %, and 20.4 %, respectively, under FI conditions, compared to the CK. Exogenous application of SA, MEL, and SA+MEL also improved total soluble solids by 17.3 %, 18.5 %, and 11.1 % and reduced nitrate content by 9.7 %, 10.4 %, and 13.5 % in lettuce under FI conditions, compared to the CK. The application of SA+MEL together resulted in a more pronounced increase in vitamin C content compared to supplying SA and MEL individually. Moreover, under DSW conditions, exogenous application of SA, MEL, and SA+MEL decreased the membrane stability index by 13.7 %, 9.4 %, and 6.3 %, increased malondialdehyde by 65.4 %, 40.8 %, and 36.6 %, and increased proline content by 68.4 %, 65.4 %, and 96.4 %, respectively, compared to the CK. Moreover, exogenous SA+MEL significantly increased the activities of superoxide dismutase, catalase, peroxidase enzymes under both SW and DSW conditions compared to the SA or MEL. Conversely, the activity of ascorbate peroxidase enzyme showed a gradual decrease in DI, SW, and DSW conditions, relative to the FI conditions. In conclusion, the integrated application of SA+MEL is an optimal strategy to enhance yield, morpho-physiological traits, nutrient homeostasis, antioxidant capacity, and quality in lettuce and mitigate the adverse effects of drought, salinity, and drought-salinity stress.

Assessment of Nutrient Removal Efficiency of Marine Microalgae Dunaliella salina in Saline Food Industry Wastewater

Industrial wastewater release into the environment is a critical global challenge leading to severe water pollution, adversely impacting terrestrial and aquatic ecosystems requiring effective solutions. The treatment, disposal, and recirculation of saline wastewater from food containing nitrate and phosphate poses significant health and environmental risks. This research aims to address the challenge by investigating the potential of using the marine microalgae Dunaliella salina for treating saline food industry wastewater, both in laboratory and pilot-scale settings using raceway tanks. In the laboratory study, a mixture of wastewater and F/2 medium was inoculated with Dunaliella salina to assess its potential for growth in saline wastewater, rich in nitrate and phosphate. The study observed a cell density of 5.5 x 105 cells/ml. Subsequently, a pilot-scale study was conducted, where the maximum cell density of 6.2 x 105 cells/ml was achieved. The efficacy of Dunaliella salina in removing nitrate and phosphorus from the culture was evaluated by measuring the levels of these compounds. A significant reduction in nitrate concentration from 146 to 22.16 mg/l was observed, with a removal efficiency of 84.82%; similarly, the phosphate concentration decreased from 55.3 to 10.79 mg/l, with a removal efficiency of 80.49 %. The reductions in nitrate and phosphate concentrations, along with the demonstrated growth of Dunaliella salina in saline industrial wastewater, confirmed the feasibility of employing these microalgae for bioremediation treatment in a sustainable way.

Predicting nature recovery for river restoration planning and ecological assessment: A case study from England, 1991–2042

AbstractThe Global Biodiversity Framework established ambitious goals for nature recovery which governments must now incorporate into national legislation. In England, legally binding targets require authorities to halt the decline in species abundance by 2030 and reverse the decline by 2042. Riverine invertebrates represent a substantial proportion of the species contributing towards the targets. Thus, understanding the response of these species to potential river restoration actions is key to target delivery. We model counts for 188 riverine invertebrate taxa using zero‐inflated generalized Poisson models, applying the models to both inform river restoration planning and set expected values for use in ecological assessment. We identify catchment‐specific restoration strategies that combine one or more actions involving the removal of channel modifications, reductions in nitrate concentrations and reductions in total dissolved phosphorus concentrations as the most likely to deliver species abundance targets across three joint climate–socioeconomic scenarios. By hindcasting species abundances under alternative target frameworks, we also demonstrate a new approach to setting expected values in ecological assessment, accounting for changes in water temperature and hydrology that confound historical reference models presently used by regulators. Our findings represent the first systematic attempt to prioritise major actions to deliver species abundance targets in England, providing valuable insights for policymakers, river restoration practitioners and authorities responsible for monitoring river ecosystems.

Innovative Cultivation Practices for Reducing Nitrate Content in Baby Leaf Lettuce Grown in a Vertical Farm

The aim of this research is to introduce innovative cultivation practices that result in reduced nitrate levels in baby leaf lettuce grown under vertical farming conditions while maintaining high productivity. For this reason, three experiments were conducted. The first experiment focused on the impact of two “white” light spectra with a blue:green:red:far-red ratio of 14:32:43:10 (BlowRhigh) and 21:34:36:7 (BhighRlow). The second experiment assessed the effects of two nitrogen supply conditions: sufficient total nitrogen (N15) and limited total nitrogen (N5), and foliar biostimulant application. In the third experiment, the impact of replacing the nutrient solution in the N15 treatment with tap water for an additional 24 h (TW24) on leaf nitrate content was examined. Results from the lighting experiment revealed no significant effects on agronomical parameters or nitrate content between the two light spectra. Reducing nitrogen content in the nutrient solution reduced leaf nitrate content but negatively influenced agronomical characteristics. Biostimulant application and replacing the nutrient solution with water reduced leaf nitrate content compared to the control and positively affected growth. The most favorable outcomes were observed in plants supplied with sufficient nitrogen and foliar biostimulant but also cultivated for an additional 24 h with tap water (Sp-N15-TW24).

Assessing nitrate groundwater hotspots in Europe reveals an inadequate designation of Nitrate Vulnerable Zones

Monitoring networks show that the European Union Nitrates Directive (ND) has had mixed success in reducing nitrate concentrations in groundwater. By combining machine learning and monitored nitrate concentrations (1992–2019), we estimate the total area of nitrate hotspots in Europe to be 401,000 km2, with 47% occurring outside of Nitrate Vulnerable Zones (NVZs). We also found contrasting increasing or decreasing trends, varying per country and time periods. We estimate that only 5% of the 122,000 km2 of hotspots in 2019 will meet nitrate quality standards by 2040 and that these may be offset by the appearance of new hotspots. Our results reveal that the effectiveness of the ND is limited by both time-lags between the implementation of good practices and pollution reduction and an inadequate designation of NVZs. Substantial improvements in the designation and regulation of NVZs are necessary, as well as in the quality of monitoring stations in terms of spatial density and information available concerning sampling depth, if the objectives of EU legislation to protect groundwater are to be achieved.

Biochar's role in improving pakchoi quality and microbial community structure in rhizosphere soil.

Biochar amendments enhance crop productivity and improve agricultural quality. To date, studies on the correlation between different amounts of biochar in pakchoi (Brassica campestris L.) quality and rhizosphere soil microorganisms are limited, especially in weakly alkaline soils. The experiment was set up to explore the effect of different concentrations of biochar on vegetable quality and the correlation between the index of quality and soil bacterial community structure changes. The soil was treated in the following ways via pot culture: the blank control (CK) without biochar added and with biochar at different concentrations of 1% (T1), 3% (T2), 5% (T3), and 7% (T4). Here, we investigatedthe synergistic effect of biochar on the growth and quality of pakchoi, soil enzymatic activities, and soil nutrients. Microbial communities from pakchoi rhizosphere soil were analyzed by Illumina MiSeq. The results revealed that adding 3% biochar significantly increased plant height, root length, and dry weight of pakchoi and increased the contents of soluble sugars, soluble proteins, Vitamin C (VC), cellulose, and reduced nitrate content in pakchoi leaves. Meanwhile, soil enzyme activities and available nutrient content in rhizosphere soil increased. This study demonstrated that the the microbial community structure of bacteria in pakchoi rhizosphere soil was changed by applying more than 3% biochar. Among the relatively abundant dominant phyla, Gemmatimonadetes, Anaerolineae, Deltaproteobacteria and Verrucomicrobiae were reduced, and Alphaproteobacteria, Gammaproteobacteria, Bacteroidia, and Acidimicrobiia relative abundance increased. Furthermore, adding 3% biochar reduced the relative abundance of Gemmatimonas and increased the relative abundances of Ilumatobacter, Luteolibacter, Lysobacter, Arthrobacter, and Mesorhizobium. The nitrate content was positively correlated with the abundance of Gemmatimonadetes, and the nitrate content was significantly negatively correlated with the relative abundance of Ilumatobacter. Carbohydrate transport and metabolism in the rhizosphere soil of pakchoi decreased, and lipid transport and metabolism increased after biochar application. Overall, our results indicated that applying biochar improved soil physicochemical states and plant nutrient absorption, and affected the abundance of dominant bacterial groups (e.g., Gemmatimonadetes and Ilumatobacter), these were the main factors to increase pakchoi growth and promote quality of pakchoi. Therefore, considering the growth, quality of pakchoi, and soil environment, the effect of using 3% biochar is better.

Enhancing nitrogen removal from wastewater in a low C/N ratio using an air-lift bio-electrochemical reactor (ALBER)

This study focuses on the development of an air-lift bio-electrochemical reactor (ALBER) with a continuous feeding regime. The objective is to enhance nitrogen removal from synthetic wastewater with a low carbon-to-nitrogen (C/N) ratio. The chemical oxygen demand (COD) and total nitrogen (TN) of the influent wastewater were 500 and 200 mg/L, respectively. The effect of four independent variables, i.e., temperature, hydraulic retention time (HRT), N−NH4+/TN ratio and current density in the range of 16–32 °C, 6–12 h, 25–75%, and 2–10 A/m2, respectively, at three levels on the bio–electrochemical reactor performance were investigated during the bio–electrochemical reactor operation. The Face Center Cube (FCC) of response surface methodology (RSM) was used for design of experiments and model of obtained data. The ALBER achieved the maximum TN removal of 73% (146 mg/l) using external voltage and zeolite/plastic medium at temperature of 16 °C, HRT of 6 h, current density of 2 A/m2 and N−NH4+/TN ratio of 75%. The results indicated that shortening the HRT from 12 to 6 h, reducing the temperature from 32 °C to 24 °C, increasing the current density from 2 to 6 A/m2 and the reduction of nitrate concentration caused an increase in the TN removal. The results indicated that the performance of air-lift bio-electrochemical for nitrogen removal could be attributed to autotrophic denitrification (AD) and simultaneous nitrification/denitrification (SND). The research findings suggest that the ALBER should be further studied for potential use in treating industrial wastewater at low temperatures.

Examining the Optimal Amount of Moringa Leaf Extract to Improve the Morphological and Inner Quality of Cabbage (Brassica oleracea var. capitata)

Moringa leaves contain a proper amount of antioxidants, amino acids, vitamins, hormones, macronutrients, and micronutrients. Therefore, it is applied as a natural, inexpensive, and simple-to-make biostimulant to boost nutritional value and growth parameters in a variety of plants. The main purpose of this study is to determine the optimal concentration of Moringa oleifera L. leaf extract (MLE) as an effective biostimulant to improve nutritional and physical quality in cabbage (Brassica oleracea var. capitata). To do this, three concentrations of MLE (6, 8, and 10%) were foliar sprayed to the plant leaves at a rate of 25 mL plant−1 for every two weeks from transplantation till harvest, while control plants (Ø) were sprayed with distilled water only. Our results show that MLE greatly increased cabbage growth, nutrient content, pigment content, and nutrient absorption, while a high concentration of 10% MLE could also significantly reduce nitrate content in cabbage leaves. In comparison to the control plants, sprays of 6%, 8%, and 10% MLE reduced nitrate content by 23%, 14%, and 12%, respectively. However, the lowest nitrate content was found for the plants sprayed with 6% MLE. Except for the dry matter, all the growth parameters, mineral content, and pigment content were significantly higher after spraying with 10% MLE, while better vitamin C and lower nitrate were found in the plants treated with 6% MLE. A Pearson correlation reveals that head weight has a positive correlation with head diameter, head height, chlorophyll a, and carotenoids at p levels of 0.01 and a positive correlation with chlorophyll b and vitamin C at p levels of 0.05. Vitamin C and dry matter, on the other hand, had a negative connection with nitrate content.

Effects of biochar combined with MgO desulfurization waste residue on nitrogen conversion and odor emission in chicken manure composting

ABSTRACT Aim: Chicken manure is known to produce strong odors during aerobic composting, which not only pollutes the surrounding environment but also leads to the loss of valuable nutrients like nitrogen and sulfur, thus reducing the quality of the fertilizer. Methods: In this study, we explored the use of biochar combined with MgO desulfurization waste residue (MDWR) as a novel composting additive. Our approach involved conducting composting tests, characterizing the compost samples, conducting pot experiments, and examining the impact of the additives on nitrogen retention, deodorization, and compost quality. Results: Our findings revealed that the addition of biochar and MDWR significantly reduced ammonia volatilization in chicken manure compost, demonstrating a reduction rate of up to 60.12%. Additionally, the emission of volatile organic compounds (VOCs) from chicken manure compost treated with biochar and MDWR decreased by 44.63% compared to the control group. Conclusions: The composting product treated with both biochar and MDWR (CMB) exhibited a 67.7% increase in total nitrogen (TN) compared to the blank control group, surpassing the other treatment groups and showcasing the synergistic effect of these two additives on nitrogen retention. Moreover, the CMB treatment facilitated the formation of struvite crystals. Furthermore, our pot experiment results demonstrated that the CMB treatment enhanced vegetable yield and quality while reducing nitrate content. These findings highlight the significant impact of MDWR on nitrogen retention, deodorization, and compost quality enhancement, thereby indicating its promising application prospects.

Moringa leaf extract increases tolerance to salt stress, promotes growth, increases yield, and reduces nitrate concentration in lettuce plants

The use of large amounts of synthetic chemicals in plant cultivation harms the environment and reduces food quality. Therefore, natural alternatives should be used to protect the environment, increase food quality, and decrease food contamination. This study investigated the effect of moringa leaf extract (MLE) as a plant stimulator to enhance growth, yield, and quality of lettuce grown in a saline environment. To examine the effect of application method and extract concentration, this experiment included three levels of seed priming (0, 5 %, and 10 % MLE) and three levels of foliar spray (0, 5 %, and 10 % MLE). MLE application, either by seed priming or foliar spraying, reduced the adverse effects of salt stress and increased lettuce growth, yield, and quality. However, the combined treatment of 5 % seed soaking and 10 % foliar spray showed the best results in increasing antioxidant levels (catalase (CAT), ascorbate peroxidase (APX), and ascorbic acid), relative water content (RWC %), nutrient concentration (N, P, and K), and chlorophyll content, and maintaining membrane integrity by reducing electrolyte leakage (EL %) and sodium accumulation, leading to improved yield parameters (head diameter, head weight, and total yield), and increasing lettuce head quality by reducing nitrate concentration. The results suggest that MLE (5 % seed soaking and 10 % foliar spray) is a practical, effective, and inexpensive approach to alleviate salt stress and improve lettuce yield and quality under saline conditions. However, despite the observed positive effects, further studies are needed to understand the factors determining the response of plants to MLE application.

Quantification of soil N2O and CH4 fluxes using the flux gradient method on a drainage water managed farm on the eastern shore of Maryland

Drainage water management (DWM) is an effective best management practice (BMP) to reduce hydrological nitrate export from croplands to surface and ground water by controlling the timing and the amount of ditch discharge and retaining water within ditches and adjacent fields using drainage control structures (DCS). While the intended consequences of maintaining higher water table levels are to increase denitrification and thereby decrease nitrate leaching, an unintended consequence is possible increased production of nitrous oxide (N2O) from denitrification and methane (CH4) from methanogenesis, both potent greenhouse gasses (GHGs). Hence, application of DWM may lead to a "pollution swapping" concern – i.e., does DWM trade reduction of nitrate concentrations in ditch water for increases in soil emissions of N2O and CH4 to the atmosphere?Here we employed the micrometeorological flux gradient (FG) technique to a corn-soybean rotation on an operational farm with DCS in eastern Maryland on the Delmarva Peninsula to answer this question. Soil N2O and CH4 fluxes were quantified under DWM and non-DWM management of a soybean crop without N fertilization (2018) and a corn crop with synthetic N fertilization (2019). To our knowledge, this is the first study employing a micrometeorological method to evaluate the effects of agricultural DWM on GHG emissions. No consistent or statistically significant differences in N2O and CH4 fluxes were observed between DWM and non-DWM fields, suggesting that DWM did not trade reduced nitrate leaching for increased soil GHG emissions. The FG measurements were also compared with chamber measurements, which revealed similar patterns, but chamber measurements had large spatial variability and overall higher daily mean flux estimates, while the tower measurements revealed more frequent, short-lived N2O pulses following fertilization and precipitation events. This research adds to the existing understanding of benefits and risks of DWM as a BMP.

Effect of Amorphous Silicon Dioxide on Productivity and Quality of Tomato

Tomatoes are one of the most popular vegetables, improving their taste and biochemical quality is possible as a result of reducing the content of nitrates and increasing the sugar content. The effect of amorphous fine silica on the productivity and quality of tomatoes was studied in vegetation experiments. Silica was introduced into a mixture of gray forest soil and washed sand in doses of 0.1, 0.2 and 0.3 g/vessel, which corresponded to 100, 200 and 300 kg/ha, against the background of complex mineral fertilizers. It was shown that the improvement of silicon nutrition of tomatoes significantly increased their yield by 52–70%. There was also an improvement in fruit quality as a result of a 20–40% reduction in nitrate content and an increase in sugar content by 12.9–50.9%. Statistical analysis of the obtained data revealed that the concentration of monosilicon acid in soils treated with silicon dioxide was closely positively correlated with the yield of tomatoes, as well as the sugar content in fruits and negatively correlated with the content of nitrates.

Combined Application of Organic Fertilizer with Microbial Inoculum Improved Aggregate Formation and Salt Leaching in a Secondary Salinized Soil.

Greenhouse vegetable production provides significant quantities of vegetables throughout the year and improves farmers' income. However, over-fertilization with mineral fertilizer causes soil secondary salinization and decreases the stability of the soil structure. To improve aggregate formation and decrease salt accumulation in the soil profile, bio-organic fertilizers (Protaetia brevitarsis larvae frass with Bacillus amyloliticus and/or Trichoderma harziensis) were applied to partially substitute mineral fertilizer in a salinized vegetable soil. Soil nutrient condition, aggregate stability, and salt movement in the soil profile were measured in a greenhouse double-cucumber system. The results showed that soil organic matter (SOM), total nitrogen (TN), and available phosphorus (AP) increased significantly under bio-organic fertilizer treatments compared with control. Soil electrical conductivity (EC) and total salt content (TSC) decreased by 15.74-24.20% and 19.15-29.05%, respectively, with bio-organic fertilizers (p < 0.05). Cl-, NO3-, and SO42- content under double inoculation with B. amyloliticus and T. harziensis reduced by 31.19%, 26.30%, and 53.11%, respectively, compared to CK (p < 0.05). In addition, double inoculation was more efficient in reducing nitrate content in the soil profile than single inoculation. Soil microaggregates of 0.25-0.053 mm increased by 75.87-78.51% with bio-fertilizers compared with control, and double inoculation was the best for aggregate formation. In conclusion, the inoculation of plant-growth-promoting and salt-tolerant microorganisms with high humic acid larvae frass can alleviate salinization in vegetable soil, enhance soil nutrient content, and improve the soil structure.

Investigating pulsed LED effectiveness as an alternative to continuous LED through morpho-physiological evaluation of baby leaf lettuce (Lactuca sativa L. var. Acephala)

Photoperiod, light intensity, and spectral quantum distribution (SPD) affect plant development and physiology. Light determines morphological signals, influences plant behavior and regulates metabolism in addition to providing energy for photosynthesis. In this experiment, lettuce (Lactuca sativa) was grown in an indoor LED-equipped chamber, operated in a pulsed and continuous mode, with an average photosynthetic photon flux density (PPFD) at a seedling level of 150 µmole s¯¹ m¯², photoperiod of 16 h for growing cycle of 30 days. The primary aim of this study was to observe the effects of varying LED on the growth and quality of the produce. Regardless of the treatments, in both continuous and pulsed LED, an increment in the yield, leaf length and leaf width of lettuce was recorded in comparison to the control, which was managed in a glasshouse under controlled environmental conditions using a winter cropping cycle. In-vitro physiological analysis of lettuce revealed the outperformance of the continuous LED treatment over the pulsed LED as well as the control in terms of total sugars, chlorophyll concentration, carotenoids, phenolic index, and sucrose accumulation. Continuous LED treatment has also resulted in a significant reduction in nitrate content, a commercially vital parameter, making it the most advantageous and effective of all the treatments performed. However, the production of anthocyanins, an antioxidant released during stress, was enhanced under pulsed LED which requires further investigation and improvements to achieve an improved metabolite profile of lettuce with a minimal energy usage and cost.

Humate-Coated Urea as a Tool to Decrease Nitrogen Losses in Soil

Processes of N transformation in soil as affected by application of the three kinds of urea fertilizers, conventional urea (U), humate-coated urea (U_HA), and urea treated with the urease inhibitor NBPT (U_UI), are examined in a model laboratory experiment. Effects of urea fertilizers on soil chemical (content of water-extractable N-NH4 and N-NO3), and microbiological properties (rate of actual and potential N2O emission, basal and substrate-induced respiration, microbial biomass C, emission of ethylene) are focused to answer the following questions: (i) whether humate-coated urea has the ability to decrease N losses in soil; and (ii) how it affects soil biological activity comparable to synthetic urease inhibitor. The results showed that U_HA demonstrated advantages comparable to U in its ability to decrease N losses in soil: it increased N-NH4 content by 35%, reduced nitrate content by 9%, and decreased N2O emissions by 50%. U_HA promoted basal soil respiration by 10% and the specific activity of the soil microbial community by 7%, providing the highest metabolic quotient qCO2. Comparably to NBPT-treated U, U_HA mainly shows intermediate results between U-UI and conventional U. Considering the low cost of raw humates, U-HA can be regarded as a promising tool to decrease N losses in soils.

Water and nitrogen management scheme of melon based on yield−quality−efficiency matching perspective under CO2 enrichment

Rising CO2 concentration in the atmosphere may modulate the response of plants to water and nitrogen, and the existing research is not sufficient to support the fine management of water and nitrogen under CO2 rise. To determine the optimal water and nitrogen strategy for melon production under CO2 enrichment in the future, we conducted an experiment with 12 treatments over three growing seasons. The effects of water nitrogen coupling on the yield, quality, and water−nitrogen use efficiency of oriental melon (Cucumis melo L. Qianyu No. 6) under CO2 enrichment were investigated and evaluated comprehensively. The treatments included two CO2 concentrations, C1 (400 ppm) and C2 (800 ppm), three irrigation levels, I1 (80% evaporation (Ep)), I2 (100% Ep), and I3 (120% Ep); two nitrogen levels, N1 (S: 184.77 kg ha–1, F: 147.21 kg ha–1) and N2 (S: 369.54 kg ha–1, F: 294.42 kg ha–1). The result showed that the yield increased with increasing levels of irrigation and nitrogen, and enriched CO2 significantly increased the yield by 10.3 − 22.9%. N2 showed a significant promoting effect on the ratio of marketable fruit in the two spring seasons. Enriched CO2 significantly increased free amino acid of I1. C2 coupled with I1 significantly reduced nitrate content by 30.9%, 14.9% in 2020 F and 2021 S, respectively. The interaction of C*I was significant in irrigation water−use efficiency (IWUE) and nitrogen−use efficiency (NUE). In particular, C2 coupled with I2 increased IWUE by 40.5%, 18.7% and NUE by 43.9%, 13.9% in the two spring seasons, respectively. Ten indicators from three categories of yield, quality, and efficiency were used to establish the evaluation system of melon and were comprehensively evaluated based on Fuzzy−Borda model combined three single models. Based on the combined evaluation model, intermediate irrigation combined with higher nitrogen input was best for melon production under CO2 enrichment. This finding suggested that melon sustainable production should control irrigation and adequately increase nitrogen fertilizer to trade−off fruit, quality, and efficiency for the expected future higher CO2 concentrations.