Nitrated Residues Research Articles

Metagenomic insights into microbial metabolic mechanisms of a combined solid-phase denitrification and anammox process for nitrogen removal in mainstream wastewater treatment

To overcome the significant challenges associated with nitrite supply and nitrate residues in mainstream anaerobic ammonium oxidation (anammox)-based processes, this study developed a combined solid-phase denitrification (SPD) and anammox process for low-strength nitrogen removal without the addition of nitrite. The SPD step was performed in a packed-bed reactor containing poly-3-hydroxybutyrate-co-3-hyroxyvelate (PHBV) prior to employing the anammox granular sludge reactor in the continuous-flow mode. The removal efficiency of total inorganic nitrogen reached 95.7 ± 1.2% under a nitrogen loading rate of 0.18 ± 0.01 kg N·m3·d−1, and it required 1.02 mol of nitrate to remove 1 mol of ammonium nitrogen. The PHBV particles not only served as biofilm carriers for the symbiosis of hydrolytic bacteria (HB) and denitrifying bacteria (DB), but also carbon sources that facilitated the coupling of partial denitrification and anammox in the granules. Metagenomic sequencing analysis indicated that Burkholderiales was the most abundant HB genus in SPD. The metabolic correlations between DB (Betaproteobacteria, Rhodocyclaceae, and Anaerolineae) and anammox bacteria (Candidatus Brocadiac and Kuenenia) in the granules were confirmed through microbial co-occurrence networks analysis and functional gene annotations. Additionally, the genes encoding nitrate reductase (Nap) and nitrite reductase (Nir) in DB primarily facilitated nitrate reduction, thereby supplying nitric oxide to anammox bacteria for subsequent nitrogen removal with hydrazine synthase (Hzs) and hydrazine dehydrogenase (Hdh). The findings provide insights into microbial metabolism within combined SPD and anammox processes, thus advancing the development of mainstream anammox-based processes in engineering applications.

Changing Drip Fertigation Strategy to Decrease Greenhouse Agroecosystem Soil Nitrate Residue and Improve Tomato Production in Northwest of China

Changing Drip Fertigation Strategy to Decrease Greenhouse Agroecosystem Soil Nitrate Residue and Improve Tomato Production in Northwest of China

Effects of feeding whole-cracked rapeseeds, nitrate, and 3-nitrooxypropanol on protein composition, minerals, and vitamin B in milk from Danish Holstein cows

The present study was conducted to assess the individual or combined effects of feeding dietary fat (whole-cracked rapeseed), nitrate, and 3-nitrooxypropanol (3-NOP) on protein profile, mineral composition, B vitamins, and nitrate residues in milk from dairy cows. Forty-eight Danish Holstein cows used in an 8 × 8 incomplete Latin square design were fed 8 factorially arranged diets ((30 or 63 g crude fat/kg DM) × (0 or 10 g nitrate/kg DM) × (0 or 80 mg 3-NOP/kg DM)) over 6 periods of 21 d each. In each period, milk samples were collected from individual cows during the third week by pooling milk obtained from 4 consecutive milkings, and analyzed for protein profile including protein modifications, mineral composition, riboflavin, cobalamin, and presence of nitrate residues. Fat supplementation led to an increase in the phosphorylation degree of αS1-CN by 8.5% due to a decreased relative proportion of αS1-CN 8P and an increased relative proportion of αS1-CN 9P and further to a decrease in the relative proportion of αS2-CN by 2.4%. Additionally, fat supplementation decreased the relative proportions of glycosylated and unglycosylated forms of κ-CN, consequently leading to a 3.6% decrease in total κ-CN. In skim milk, K, Ca, P, and Mg concentrations were altered by individual use of fat, nitrate, and 3-NOP. Feeding nitrate resulted in a 5.4% increase in riboflavin concentration in milk while supplementing 3-NOP increased cobalamin concentration in milk by 21.1%. The nitrate concentration in milk was increased upon feeding nitrate however, this increased concentration was well below the maximum permissible limit of nitrate in milk (<50 mg/L). In conclusion, no major changes were observed in milk protein, and mineral compositions by feeding fat, nitrate, and 3-NOP to dairy cows while the increased riboflavin and cobalamin by nitrate and 3-NOP, respectively, could be of beneficial nutritional value for milk consumers.

Optimizing irrigation and nitrogen management improves soil soluble nitrogen pools and reduces nitrate residues in a drip-fertigated apple orchard on the Loess Plateau

Appropriate water and nitrogen fertilizer management is crucial for achieving sustainable development in the apple industry. However, the soil nitrogen supply capacity and residual nitrate characteristics under drip fertigation remain poorly understood. Therefore, this study aims to (1) investigate the coupling effects of irrigation and nitrogen levels on the concentrations and distribution characteristics of soil soluble nitrogen fractions and residual soil nitrate; (2) explore the relationships between Christiansen uniformity coefficient (CU) of soil nitrate and apple yield, water productivity (WPc) and nitrogen use efficiency (nitrogen agronomic efficiency, AEn). The field experiment was conducted in a drip-fertigated apple orchard starting in 2017, which included two irrigation levels, 85% (W1) and 100% (W2) of field capacity (FC), and four nitrogen rates, 0 (N1), 120 (N2), 240 (N3) and 360 (N4) kg ha–1. The results showed that nitrogen inputs significantly increased soil soluble inorganic nitrogen and soluble organic nitrogen (SON) contents. However, the SON content significantly decreased when 360 kg N ha–1 was applied, particularly at W1. The maximum nitrate accumulation in the 0–3 m soil layer at N4 reached 2540.97 kg ha–1 in 2021, but the maximum value decreased to 1251.62 kg ha–1 in 2022 due to extreme rainfall. The average CU of residual nitrate across irrigation levels in the 0–3 m soil layer was highest at N3, with values of 0.68 and 0.57 in 2021 and 2022, respectively. High irrigation level increased the diffusion distances of nitrate both vertically and horizontally, resulting in a significant effect on CU. Apple yield and WPc first increased and then decreased with increasing nitrogen rates, while AEn consistently decreased, but they were all greater with a higher CU. The recommended combination of irrigation and nitrogen application was 85% FC and 240 kg N ha–1, which can achieve the dual goals of enhancing soil nitrogen supply capacity and minimizing environmental risks while improving orchard productivity.

Potential to reduce the nitrate residue after harvest in maize fields without sacrificing yield through precision nitrogen management

Potential to reduce the nitrate residue after harvest in maize fields without sacrificing yield through precision nitrogen management

Optimization of fertilization scheme based on sustainable wheat productivity and minor nitrate residue in organic dry farming: An empirical study

The substitution of chemical nitrogen fertilizer with manure holds the potential for a synergistic rise in wheat grain yield and protein concentration, while minimizing residual nitrate in soil. We conducted a 6-year field fertilization experiment including two manure treatments (with or without) and five nitrogen applications rates (0, 60, 120, 180 and 240 kg ha−1). The study investigated the impact of single chemical nitrogen (CN) and manure substitution for nitrogen fertilizer (MN) on the grain yield (GY), grain protein concentration (GPC), plant nitrogen uptake (PNupt) and plant nitrogen requirement (PNR) of wheat, and the dynamic change of soil nitrate-N. The findings revealed that: (1) the MN demonstrated a greater advantage over CN, as evidenced by a 13.4–16.0 % increase in GY, a 2.6–3.8 % increase in GPC, a 7.2–15.7 % increase in PNupt and a 1.5–4.7 % reduction in PNR. (2) Soil nitrate accumulation (SNA) significantly increased when fertilizer rates ≥180 kg ha−1 and the peak annually shifted to deeper layer. The MN increased the SNA0–100 by 20.9–21.8 %, but significantly reduced SNA0–200 by 11.8–13.5 % compared with the CN. Topsoil nitrate content (SNC0–20) can be adopted as a substitute for SNA0–100 to make the fertilization schedule convenient. (3) Regression analysis revealed (taking the MN for example) that the optimum N rates for the maximum GY (5417 kg ha−1) and GPC (15.3 %) were 164 and 211 kg N ha−1, respectively. The nitrate-N safety threshold was 62 kg ha−1 at the fertilizer rate of 89 kg N ha−1. Based on this, nitrogen fertilizer input reduced by 44.8–57.2 % and SNA0–200 by 17.9–33.6 %, with achieving 91.8–95.0 % of maximum GY and 89.7–92.9 % of maximum GPC. Substituting manure for nitrogen fertilizer achieved the potential of maintaining the grain yield and protein concentration while the minimization in soil nitrate residue. This study offers a feasible way for fertilization recommendation and nitrate residue controlling in dry farming.

Integration of double nitrite autotrophic shunt enhances anammox-based wastewater treatment for sustainable nitrogen removal and energy efficiency

Anammox holds significant promise as a next-generation technology for achieving energy-positive wastewater treatment. However, its application remains challenging due to unstable nitrite supply and excessive nitrate residue. To address this, a groundbreaking Anammox bioprocess incorporating a double nitrite autotrophic shunt was developed within single system to realize energy-efficient nitrogen removal from wastewater. Partial nitrification/Anammox converted a portion of ammonia in leachate to nitrogen gas in oxic stage. Significantly, sulfur-driven partial denitrification utilizing sulfide as electron donor, efficiently reduced generated nitrate to nitrite in subsequent anoxic stage, facilitating nitrite reutilization via Anammox and removing residual ammonia. Over 200-day monitoring, bioprocess demonstrated desirable effluent quality with 9.0 mg/L NH4+-N, 0.6 mg/L NO2−-N, and 6.2 mg/L NO3−-N. Delightedly, efficient nitrogen removal efficiency of 97.8 % was achieved even under fluctuation conditions. Priority position held by Anammox consortium (Candidatus Kuenenia 11.2 %) mainly derives from similar growth rate of autotrophic bacteria within their shared ecological niche and stable nitrite supply, enabling Anammox to contribute impressive 72.4 % of nitrogen removal. By combing electron flow preference kinetic, stability toward fluctuation, core microbial community, the ecological niche of Candidatus Kuenenia and self consistent logic governing functional microorganisms were revealed. The cost-effective system exhibited significant advantages over conventional bioprocess, reducing organic matter demand by 100 %, aeration energy consumption by 61.7 %, and biomass production by 82.9 %.

The response of celeriac yield, quality and soil nitrate residue to nitrogen fertilization and supply

The response of celeriac yield, quality and soil nitrate residue to nitrogen fertilization and supply

Efficacy of Agricultural and Food Wastes as the Growing Media for Sunflower and Water Spinach Microgreens Production

The growing media is one of the significant elements affecting microgreens’ yield and quality. This experiment investigated the possibility of waste utilization instead of employing peat moss to produce sunflower and water-spinach microgreens. The treatments consisted of peat moss (Control), coconut coir dust (CD), leaf compost (LC), food waste compost (FC), CD:LC = 1:1 v/v, CD:FC = 1:1 v/v, LC:FC = 1:1 v/v, and CD:LC:FC = 1:1:1 v/v. The results proved that the highest yield of sunflower microgreens was observed when cultivated in 1:1 v/v of CD:LC media (10,114.81 g m−2), whereas the highest yield of water spinach microgreens was recorded under the treatments of CD, Control, 1:1 v/v of CD:LC, and 1:1:1 v/v of CD:LC:FC media (10,966.67–9800.00 g m−2). The biochemical composition of the microgreens varied within the types. Our findings demonstrated that a tendency of an increase in chlorophyll and carotenoid contents depended on the growth of both microgreens under different growing media. All growing media did not cause excess nitrate residue or pathogenic contamination in both microgreens, namely Clostridium perfringens, Salmonella spp., and Staphylococcus aureus. In contrast, almost all the growing media resulted in a higher population of Bacillus cereus contamination in both microgreens than the standard set limit, except for sunflower microgreens grown in the control and CD growing media. These findings could suggest that the 1:1 v/v of CD:LC and CD media were the most effective growing media for sunflower and water spinach microgreens, respectively, but further cleaning before consumption is recommended to avoid or reduce the foodborne incidences caused by B. cereus in microgreens.

Poly-γ-glutamic acid improved biological nitrogen fixation, water-nitrogen productivity, and nitrate residue in cotton/soybean intercropping.

Poly-γ-glutamic acid (γ-PGA) can efficiently promote crop growth and improve soil properties. However, the optimal application rate of γ-PGA is still unclear in the legume/non-legume intercropping system. A potted experiment was conducted to investigate the effects of five γ-PGA rates (0%, 0.1%, 0.2%, 0.3%, and 0.4%, represented by CK, P1, P2, P3, and P4, respectively) on biological nitrogen (N) fixation (BNF), water-N productivity, and nitrate (NO- 3-N) distribution in cotton/soybean intercropping system. The results showed that the growth indicators (plant height, stem diameter, leaf area index, root dry weight, root length) of cotton and soybean increased first and then decreased with increasing γ-PGA rates, and all growth indicators of cotton and soybean showed peaks in P3 and P2 treatments respectively. The stable 15 N isotope method indicated that γ-PGA promoted the BNF capacity of soybean and soil, especially the percentage of N derived from the atmosphere (Ndfa) in soybean reached 61.94% in P2 treatment. The γ-PGA improved water-N productivity, and the total N partial factor productivity (NPFP) and water productivity (WP) in P3 treatment increased by 23.80% and 43.86% compared with the CK. In addition, the γ-PGA mitigation of potential NO- 3-N residue was decreased first and then increased with increasing γ-PGA rates. Multivariate regression analysis showed that 0.22% of the optimal γ-PGA application rate could simultaneously obtain a higher yield and water-N productivity in cotton/soybean intercropping system. This article is protected by copyright. All rights reserved.

Regulation of soil water and nitrate by optimizing nitrogen fertilization and the addition of manure based on precipitation: An 8-year field record

Optimizing fertilization strategies to improve water utilization efficiency and obtain higher crop yields and low nitrate leaching is essential for balancing food security and environmental risks in the rain-fed area of the Loess Plateau. The eight consecutive years (2014–2022) field experiment followed a split-plot design, and the experimental factors were nitrogen application rate (N0, N75, N150, N225, and N300) and manure application rate (M0 and M1). In general, (1) the relationships between nitrogen application rate and grain yield (GY), crop N uptake and water utilization efficiency (WUE) followed a quadratic curve. Compared with chemical fertilizer alone (NPK), chemical fertilizer plus manure (MNPK) significantly increased the annual average grain yield by 28.5%, 18.3%, 8.9%, 6.9% and 4.2% at the N application rate of N0, N75, N150, N225 and N300. (2) The nitrate accumulation (SNA) in the same soil layer increased with the nitrogen application rate. The residue nitrate will increase dramatically when the N application rate exceeds 150 kg ha-1. The peaks of SNA gradually moved to the deeper layer with increasing years of fertilization. The total soil nitrate accumulation (TSNA) of NPK was significantly higher than that of MNPK in dry and normal years, but the opposite was true in wet years. The total soil water storage (TSWS) decreased and then increased with the N application rate, and the annual average TSWS of the MNPK treatments was 3.9% less than that of the NPK treatments. (3) The addition of manure significantly increased the annual average moisture storage rate (MSR) during the fallow season by 4.6%. The GY in dry and normal years was more dependent on MSR than that in wet years. In terms of the long-term effects, the MSR contributes more to GY than growing season precipitation (GSP), and the high MSR caused by manure application reduced TSNA and TSWS by promoting crop growth. The results showed that M1N150 could obtain a high grain yield while maintaining low nitrate residue. Taken together, this study emphasized the importance of optimizing nitrogen fertilizer management and cattle manure application in combination with precipitation types to ensure food production and reduce negative environmental effects in the rain-fed area of the Loess Plateau in China.

Effects of Sodium Nitrate and Coated Methionine on Lactation Performance, Rumen Fermentation Characteristics, Amino Acid Metabolism, and Microbial Communities in Lactating Buffaloes.

Sodium nitrate is used as a non-protein nitrogen supplement while methionine is considered as a common methionine additive for ruminants. This study investigated the effects of sodium nitrate and coated methionine supplementation on milk yield, milk composition, rumen fermentation parameters, amino acid composition, and rumen microbial communities in lactating buffaloes. Forty mid-lactation multiparous Murrah buffaloes within the initial days in milk (DIM) = 180.83 ± 56.78 d, milk yield = 7.63 ± 0.19 kg, body weight = 645 ± 25 kg were selected and randomly allocated into four groups (N = 10). All of animals received the same total mixed ratio (TMR) diet. Furthermore, the groups were divided into the control group (CON), 70 g/d sodium nitrate group (SN), 15 g/d palmitate coated L-methionine group (MET), and 70 g/d sodium nitrate +15 g/d palmitate coated L-methionine group (SN+MET). The experiment lasted for six weeks, including two weeks of adaption. The results showed that most rumen-free amino acids, total essential amino acids, and total amino acids in Group SN increased (p < 0.05), while the dry matter intake (DMI) and rumen acetate, propionate, valerate, and total volatile fatty acids (TVFA) in Group MET decreased (p < 0.05). However, there was no significant difference in milk yield, milk protein, milk fat, lactose, total solid content, and sodium nitrate residue in milk among groups (p > 0.05). Group SN+MET had a decreased rumen propionate and valerate (p < 0.05), while increasing the Ace, Chao, and Simpson indices of alpha diversity of rumen bacteria. Proteobacteria and Actinobacteriota were significantly increased (p < 0.05) in Group SN+MET, but Bacteroidota, and Spirochaetota were decreased (p < 0.05). In addition, Group SN+MET also increased the relative abundance of Acinetobacter, Lactococcus, Microbacterium, Chryseobacterium, and Klebsiella, which were positively correlated with cysteine and negatively correlated with rumen acetate, propionate, valerate, and TVFA. Rikenellaceae_RC9_gut_group was identified as a biomarker in Group SN. Norank_f__UCG-011 was identified as a biomarker in Group MET. Acinetobacter, Kurthia, Bacillus, and Corynebacterium were identified as biomarkers in Group SN+MET. In conclusion, sodium nitrate increased rumen free amino acids, while methionine decreased dry matter intake (DMI) and rumen volatile fatty acids. The combined use of sodium nitrate and methionine enriched the species abundance of microorganisms in the rumen and affected the composition of microorganisms in the rumen. However, sodium nitrate, methionine, and their combination had no significant effect on the milk yield and milk composition. It was suggested that the combined use of sodium nitrate and methionine in buffalo production was more beneficial.

Long-term maize and pea intercropping improved subsoil carbon storage while reduced greenhouse gas emissions

Intercropping cereals with legumes is considered a promising option for improving productivity and sustaining soil health. However, the long-term effects of cereal and legume intercropping on soil carbon (C) storage and the physicochemical properties of soil profiles remain elusive. In the present study, an 11-year long-term field experiment was carried out on maize monoculture with zero (control) and conventional 375 kg ha−1 nitrogen (N) application rates (N375), as well as on pea and maize intercropping with zero N (Ps) and a 20% reduction in conventional N (PsN300). The crop yield was obtained each year. The cumulative changes in organic C, bulk density, and other physicochemical properties of the top 20 cm of soil at the beginning and end of the experiment, as well as their spatial changes along the 1 m soil profile at the end, were closely investigated. Greenhouse gas emissions were estimated based on reported emission factors. Pea and maize intercropping under reduced fertilizer N application maintained maize growth and grain yield and increased land use efficiency (land equivalent ratio 1.1) relative to monoculture with farmers’ N inputs. After an 11-year intercropping, soil organic C concentrations increased by 6.7–12.4% in the top 0–20 cm layer and organic C stocks increased by 8.3–17.9%, and bulk density decreased by 6.4–14.2%. Intercropped soils with optimal N application (PsN300) sequestrated 14.8% more organic C in the 0–100 cm soil profile, particularly at depths of 40 cm and below, and the bulk density decreased by 7.0% on average compared with the monoculture with farmers’ N practices. Such intercropping benefits for soil organic C storage and physical properties in the 1-m profile were associated with greater soil microbial biomass C and N and dissolved organic C and N in the profile. Meanwhile, compared to farmers’ N and monoculture, intercropping under reduced N fertilizer application substantially decreased nitrate residues by 30.8% and GHG emissions by 17.8% per hectare or by 15.4% per ton grain yield, which was attributed to less N input, and downregulated enzyme activities involved in soil denitrification. Overall, this study showed that intercropping peas and maize with reduced N inputs is an environmentally sound strategy that improves soil physical quality and enhances deep C storage while reducing greenhouse gas emissions.

Risk of Nitrate Residues in Food Products and Drinking Water

Although nitrate is the essential nutrient of our body, the excess amount of it as residues strongly causes disease. Nitrate comes from plant and animal foods that are vital to our metabolism. The nitrate is absorbed through the soil by plants and becomes an herbal protein that is placed in the food chain. If the nitrate is absorbed more than the plant requirement, it will be accumulated into the plant’s organs. Since nitrogen fertilizers increase the weight and yield of the plants, farmers consume large amounts of which. Hence, we investigate the consumption of nitrogen fertilizers in the world and the standard allowable residual nitrate in food and water considering the accumulation of nitrate in water and food. Excess amount of nitrate in the soil enters the drinking water after leaching or directly transported from groundwater to surface water and drinking water. The entry of the excess amount of nitrate from food products and drinking water into our bodies causes dangerous diseases such as different types of cancers, methemoglobinemia, osteoporosis, kidney stones, and some other diseases. The present article, besides indicating the benefits of nitrate for Treatment purposes and demonstrating the state of nitrate accumulation in food and water as well as its standards, deals with diseases caused by it and presents some remedies to reduce the risks.

Nitrite and Nitrate Residue in Non-Heat Treated Meat Products Marketed in East Azerbaijan Province

Background: Nitrite and nitrate salts are used as preservatives in meat products to prevent the growth of pathogen organisms such as Clostridium botulinum. Nitrogen salts additives create the desired color in meat products. However, the use of these salts accelerates nitrosamine production and increases the risk of carcinogenesis. Hence, nitrate and nitrite consumption rate should be according to the approved standards. This analytical study is designed to determine nitrate and nitrite residue of non-heat-treated meat products including hamburger and kebab in East Azerbaijan Province, Iran during 2015-2020. Methods: 120 samples of non-heat-treated meat products from different brands were randomly collected. They consisted of 60 products manufactured in East Azerbaijan province and 60 products imported from other provinces. Nitrate and Nitrite residues in non-heat-treated meat products including hamburger and kebab were determined by spectrophotometric method. Results: Results showed that the residue levels of nitrate and nitrite content regarding non-heat- treated meat products were less than maximum residual limits (MRLs) of national standards. The study also indicated that frozen non-heated meat products did not have any nitrogenous additive. Conclusion: The results of this research revealed that the frozen non-heat treated meat products including hamburger and kebab, produced or consumed in East Azerbaijan province during 2015-2020 did not have nitrate and nitrite additives. Continuous monitoring to ensure the compliance of meat products with the standards is necessary.

Managing straw and nitrogen fertilizer based on nitrate threshold for balancing nitrogen requirement of maize and nitrate residue

Optimized straw and nitrogen (N) fertilizer management instrumental in realizing synchronized soil N supply and crop N requirement (Nr), reducing nitrate-N leaching and achieving efficient and cleaner agricultural production systems, especially in the areas with poor soil fertility retention. A three-year field trial during 2019–2021 was conducted in northwest China with different straw incorporation methods (SM) (without straw or biochar (NI), straw incorporation (SI) and straw-derived biochar incorporation (BI)) combined with four N application rates (NR) (0, 225, 300, and 375 kg ha−1). The grain yield, Nr and the critical nitrate threshold in the root zone (0–100 cm soil layer; NAc) after maize harvest were determined to optimize straw and N inputs for maize yield enhancement and nitrate residue control. Then the prediction methods of optimal N rate determined with NAc (TONR) and soil testing were modified for straw or straw-derived biochar incorporated spring maize production in the future. The results showed that grain yield and nitrate residue in the deep soil (100–200 cm soil; NA100-200) after maize harvest increased by N application, grain yield further increased but NA100-200 decreased when combined with SI and BI (P < 0.05). In particular, a significant increase in grain yield, Nr and N recovery efficiency (NRE) under BI was attributed to an increase in soil N supply and N assimilation after the tassel stage (VT) of maize as compared with SI (P < 0.05). The NAc values were determined as 49, 104 and 67 kg ha−1 under NI, SI and BI, respectively for maintaining N supply and preventing leaching into 100–200 cm soil. Compared with the economically optimal N rate (EONR), BI combined with TONR (268 kg N ha−1) reduced the N rate by 22 kg ha−1 per year and NA100-200 by 5.3% and increased NRE by 5.7% to achieve 99.7% maximum yield (14.448 Mg ha−1), which was a sustainable management method of straw and N rate for enhancing spring maize production and controlling soil nitrate leaching.

Supplemental Effects of Self-extracted Organic Nutrient Solution on the Growth and Yied of Water Spinach (Ipomoea Aquatic F.) in an Aquaponic System

Aquaponics combines two technologies, recirculating aquaculture systems and hydroponics in a closed system. The nutrients recycled from fish tanks supply nutrients for vegetables grown in hydroponics, however in some cases, the nutrient levels may not be sufficient for the optimal growth and yield of plants. In this study, two experiments were conducted to understand the effects of supplemental organic nutrient solutions on plant growth and yield in climbing perch-water spinach aquaponics. Experiment 1 (Exp.1) was conducted to evaluate the effects of three types of leaf-based organic fertilizers on the growth and yield of water spinach, namely self-extracted organic nutrient solution (OE), and two popular commercial foliar organic fertilizers, Hydro Fulvic (OF1) and TCN HUME (OF2), with the dose of 1%. Exp.1 showed that supplementation with the self-extracted solution significantly increased the growth and yield of water spinach but did not change the quality of water spinach in terms of the Brix values and nitrate residue content compared to the control. However, the self-extracted solution showed less effectiveness than the two commercial fertilizers in this experiment. Therefore, we conducted experiment 2 (Exp.2) to determine the suitable concentration and potential use of this extract for water spinach in aquaponics. The results of Exp.2 indicated that the concentration of 2% was the most economical and effective to provide supplemental nutrients for water spinach in the climbing perch-water spinach system. The study suggests that self-extracted organic nutrient solutions can be effectively used for growing water spinach in aquaponic systems.

Feeding Calcium-Ammonium Nitrate to Lactating Dairy Goats: Milk Quality and Ruminal Fermentation Responses.

Simple SummaryCalcium-ammonium nitrate (CAN) has been extensively used as a potential methane inhibitor for ruminants; however, there is still a need for studies focused on investigating its effects on the fatty acid profile and antioxidant capacity of milk, especially from dairy goats. Therefore, we evaluated the effects of CAN on nutrient digestibility, ruminal fermentation, and milk quality of lactating Saanen goats. Treatments consisted of a control diet (without CAN), 10 g of CAN per kg of dry matter, and 20 g of CAN per kg of dry matter. Supplemental CAN did not affect feed intake, digestibility of nutrients, and most ruminal fermentation parameters. Yields and composition of milk were not affected, and minor treatment effects were observed on the milk fatty acid profile. Milk antioxidant capacity was altered by increased conjugated dienes and reduced thiobarbituric acid reactive substances, along with greater concentrations of nitrate and nitrite residues in milk. Calcium-ammonium nitrate can be fed to lactating dairy goats up to 20 g per kg of dry matter without negative effects on nutrient digestibility and milk composition; however, it increased the concentration of conjugated dienes in milk, which may induce its faster lipid oxidation.We aimed to investigate the effects of calcium-ammonium nitrate (CAN) fed to lactating dairy goats on dry matter (DM) intake, digestibility of nutrients, milk properties (composition, antioxidant capacity, fatty acid profile, and nitrate residues), and ruminal fermentation parameters. Twelve lactating Saanen goats averaging 98.5 ± 13.1 days in milk, 53.5 ± 3.3 kg of body weight, and 2.53 ± 0.34 kg of milk/day were randomly assigned in four 3 × 3 Latin squares to receive the following diets: a control group (without CAN) with 7.3 g/kg DM of urea (URE), 10 g/kg DM of CAN (CAN10), and 20 g/kg DM of CAN (CAN20). Each period lasted 21 days, with 14 days for diet adaptation and seven days for data and sample collection. The DM intake, digestibility of nutrients, yields of milk, 3.5% fat-corrected milk, and energy-corrected milk were not affected by treatments. Similarly, there were no treatment effects on the yields and concentrations of milk fat, true protein, and lactose, along with minor effects on milk fatty acid profile. Total antioxidant capacity in milk was unaffected by treatments; however, concentration of conjugated dienes increased, while thiobarbituric acid reactive substances in milk decreased linearly. Nitrate and nitrite residues in milk were elevated by treatments, while the total of volatile fatty acids and ammonia-N concentration in the rumen were unaffected. Collectively, feeding CAN (up to 20 g/kg of DM) to lactating dairy goats did not affect feed intake, nutrient digestibility, and milk composition; however, it may increase milk lipid oxidation, as evidenced by increased conjugated diene concentration.

Multiple roles of complex organics in polishing THP-AD filtrate with double-line anammox: Inhibitory relief and bacterial selection

Anammox process has been widely regarded as an energy-efficient method for sludge digestion filtrate treatment. However, the complex high-strength organics in the filtrate, especially of Anaerobic Digestion after Thermal Hydrolysis Pretreatment (THP-AD), brings serious threat to anammox bacteria, and the high nitrate residue in effluent remains another significant barrier in operation. In this study, a novel double-line anammox-mediated system, integrating the Partial Nitrification/Anammox (PNA) with Partial Denitrification/Anammox (PDA) processes in separately sequencing batch reactors (SBRs), was developed to polish the THP-AD filtrate. When the real THP-AD filtrate (1946.5 mg NH4+-N/L, 2076.0 mg COD/L) was fed to the front PNA reactor (SBRPNA) with 5-fold dilution, effluent total nitrogen (TN) remained at 93.0 mg/L. Notably, the final effluent TN was effectively polished to as low as 8.8 mg/L by the following PDA reactor (SBRPDA), which was fed with the SBRPNA effluent and real domestic wastewater (71.0 mg NH4+-N/L, 209.1 mg COD/L). More severe inhibition on anammox activity was observed in SBRPNA rather than SBRPDA by refractory organics in filtrate. Fortunately, it could be alleviated with the enhanced degradability of particulate organics and aromatic protein-like compounds, attributed to the enrichment of class Anaerolineae in both SBRPNA and SBRPDA. This further stimulated the electron donor supply for PDA process with much lower external carbon source demand. 16S rRNA sequencing analysis revealed that Candidatus Brocadia as dominant anammox bacteria were efficiently enriched in both SBRPNA and SBRPDA, indicating its unexpected toughness and adaptability to the complex organic compounds in THP-AD filtrate. Overall, this study suggested that the novel double-line anammox would be a promising alternative for cost-efficient nitrogen removal from high-strength wastewater containing complex organic matter.

Can deep fertilizer application enhance maize productivity by delaying leaf senescence and decreasing nitrate residue levels?

Deep fertilizer application is an effective strategy for minimizing gaseous losses and improving the nutrient use efficiency and grain yield. However, it is unclear whether deep fertilizer application can improve the antioxidant defense system in maize ( Zea mays L.) leaves and the photosynthetic capacity after silking to delay senescence, and then contribute to improvements in the yield and resource utilization efficiency. The effects on the NO 3 – -N residue levels also require elucidation. Therefore, we tested different fertilization application depths in the field during 2019–2020, where all of the N-P fertilizer was applied underground at 5 cm (D5), 15 cm (D15), 25 cm (D25), and 35 cm (D35) before sowing spring maize in the Loess Plateau region of China. The results showed that the antioxidant and photosynthetic performance of the leaves followed the order of: D25 > D15 > D5 > D35. The H 2 O 2 and O 2 – contents decreased by 2 1.5% and 14.0% under D25 compared with D5, respectively, and the net photosynthetic rate (Pn) and mean grain filling rate (G mean ) increased by 32.9% and 5.0%. The translocation and assimilation of nitrogen under D25 increased by 20.1% and 18.6% compared with D5, respectively, the translocation and assimilation of phosphorus increased by 43.6% and 54.3%, and the biomass and maize yield increased by 12.7% and 13.8%. The water use efficiency (23.5 kg·ha –1 ·mm –1 ), water productivity (45.7 kg ha –1 mm –1 ), nitrogen use efficiency (43.6%), and phosphorus use efficiency (20.3%) were significantly higher under D25 than the other treatments. The accumulated residual nitrate contents in the 0–100 cm soil layer were 6.0% and 8.0% lower under D15 and D25 than D5, respectively ( P < 0.05). However, D35 significantly increased the accumulated residual nitrate content in the 0–200 cm soil depth to increase the risk of leaching. A fertilization depth of 25 cm can delay maize leaf senescence and enhance the grain-filling capability by improving the antioxidant defense system and photosynthetic capacity of the leaves after silking, thereby increasing the maize yield and resource utilization efficiency. • Fertilization depth influenced spatial and temporal distribution of soil NO 3 – -N. • Leaf antioxidant defense system improved with appropriate fertilization depth. • Fertilization depth of 25 cm enhanced maize productivity and resource utilization. • Fertilization depth of 35 cm increased NO 3 – -N residue contents in 0–200 soil layer.