Nitrogen Amendment Research Articles

Using inhibitors to trade greenhouse gas emission for ammonia losses in paddy soil: A zero-sum game

Nitrogen (N) amendment of soil ecosystems alters GHG fluxes to the atmosphere by increasing nitrous oxide (N 2 O) emission and affecting methane (CH 4 ) uptake in well-aerated soils. Although nitrification inhibitors (NIs) can decrease N 2 O emission, this may alter the rate of ammonia (NH 3 ) volatilization, crop yield, and soil CH 4 fluxes by directly or indirectly affecting methane-oxidizing bacteria, causing severe environmental and economic damages. Here, we measured the response of gaseous N loss (N 2 O + NH 3 ) and GHG fluxes (CH 4 + direct N 2 O + indirect N 2 O) to the intensive application of three different rates of DCD (15 to 45 kg ha −1 ) and DMPP (3 to 9 kg ha −1 ) in N fertilized soils imposed upon six different rice cultivars. N addition increased NH 3 volatilization by several orders of magnitude, N 2 O emission by 7- to 10-fold, and CH 4 emission by 2- to 4-fold. DCD and DMPP strongly inhibited the N 2 O emission and, to a lesser extent, CH 4 emission but promoted greater NH 3 losses in a dose-dependent manner. The soil receiving urea with inhibitors exhibited up to 62.7% additional NH 3 volatilization than untreated (inhibitor-free) soils over the rice growth cycle. Considering the estimated indirect N 2 O emission from deposited NH 3 , the overall inhibitory effect of nitrification inhibitors (at different application rates) ranged from 17.4% to 36.6% (reduction) for global warming potential and -6.7% to -45.9% (increase) for nitrogen losses. Collectively, our results suggest moderate inhibition of global warming potential but inadequate reduction of gaseous nitrogen losses by NIs, which were outweighed by increased NH 3 volatilization. Consequently, NIs appear to be a potentially double-edged sword when targeting to diminish gaseous nitrogen losses from N fertilized soils. • N fertilization significantly enhanced the emission of NH 3 , CH 4 and N 2 O. • Higher inhibitory effect of DCD and DMPP for N 2 O than CH 4 fluxes. • DMPP exhibited a similar inhibitory effect to DCD at five-fold low application rates. • NIs appear to be a double-edged sword in diminishing gaseous nitrogen losses.

Straw and nitrogen amendments improve soil, rice yield, and roots in a saline sodic soil

Straw return can improve the physical properties and nutrient status of the soil. However, there are few studies on straw return coupled with nitrogen (N) fertilizer for rice planting in saline sodic areas. Therefore, we conducted a two-year field experiment to evaluate the effects of straw management (retention or removal) with N fertilizer (0, 90, 180, 270 and 360 kg N ha−1) on soil properties, root characteristics, rice yield and N use efficiency in a saline sodic rice growing area. The results showed that straw return significantly reduced soil bulk density, pH, soil electrical conductivity of saturated paste extraction (ECe), exchangeable sodium (ENa+), exchangeable sodium percentage (ESP), and also significantly increased soil organic matter and cation exchange capacity (CEC). Compared with straw removal, straw return reduced soil pH, ECe, ENa+, and ESP by 2.97%, 10.90%, 8.95%, and 13.78%, respectively. At the same N level, straw retention reduced rice root morphology and root vigor at mid-tillering and panicle initiation, but N fertilizer was able to alleviate root inhibition by straw return. Straw return improved root morphology and root vigor in mid and late rice growth and promoted nutrient uptake. Compared with straw removal, the agronomic efficiency nitrogen and partial factor productivity were significantly increased by 13.97% and 4.59%, respectively, in the straw return treatment. With or without straw retention, rice yield increased and then decreased with increasing N fertilizer application rate, and was maximum at 270 kg N ha−1. Compared to straw removal, rice yield was significantly increased by 4.37% (2020) and 7.17% (2021) for straw return treatments, respectively. Meanwhile, straw return can reduce mineral N fertilizer inputs by about 36–43% without affecting rice yield. Under straw return conditions, soil characteristics, root characteristics, and rice yield were optimal at 270 kg N ha−1. Our results suggest that straw return combined with nitrogen fertilization may be a promising management practice to reduce mineral N application without loss of rice yield in saline sodic soils. Among them, straw return combined with 270 kg N ha−1 was most effective in the early stages of straw return in saline sodic rice growing areas.

Impact of different nitrogen amendments on the biodegradation of 14C-phenanthrene by endophytic fungal strains in liquid culture

In this study, the biodegradation of phenanthrene was investigated in newly isolated endophytic fungal strains, Fusarium sp. (KTS01), Trichoderma harzianum (LAN03), Fusarium oxysporum (KTS02), Fusarium oxysporum (LAN04), and Clonostachys rosea (KTS05). This was performed under different carbon:nitrogen ratios (10:1, 20:1, and 30:1) using different nitrogen sources (urea and malt extract and ammonium nitrate) over a 30 d incubation period in both static and agitated liquid media. The kinetics of polycyclic aromatic hydrocarbons (PAH) mineralisation to CO2 (lag phases, fastest rates, and overall extents) were measured for all of the fungal strains and nutrient conditions using 14C-phenanthrene. All fungal strains were able to biodegrade 14C-phenanthrene to 14CO2 under the different nutrient amendments. However, 14C-phenanthrene mineralisation varied for most of the fungal strains in static and agitated culture conditions. Greater extents of mineralisation were found in fungal cultures (strains KTS05 and KTS01) with C:N ratio of 10:1 in both static and agitated conditions, while the fungal strains (KTS05 and LAN03) showed the greatest phenanthrene mineralisation after N source amendments, particularly with malt extract. In addition, the phenanthrene mineralisation increased with higher C:N ratios for Clonostachys rosea (KTS05) only. Consequently, the results reported here provide a promising potential for the endophytic fungal strains and the importance of nutrients amendments for the enhanced degradation of PAHs contaminated environments.

Morphology and Nitrogen Uptake and Distribution of Wheat Plants as Influenced by Applying Remedial Urea Prior to or Post Low-Temperature Stress at Seedling Stage

Wheat production is dramatically influenced by temperature. Low-temperature stress that frequently occurs seriously hampers the growth and development of wheat seedlings. In order to alleviate the damage of low temperature to wheat plant growth, remedial nitrogen was applied prior to or post low-temperature stress at seedling stage using controlled-temperature incubators to explore the difference in wheat morphology and nitrogen absorption and utilization efficiency. Nitrogen amendment significantly increased the leaf area, seedling height, tiller number and dry matter weight of wheat plants as compared with the treatment without nitrogen amendment under temperature stress. Remedial nitrogen applied prior to low-temperature stress (N-LT) was more conducive to increase the above parameters than that applied post low-temperature stress (LT-N). In addition, N-LT enhanced the ability of roots to absorb remedial 15N urea, promoted the growth and development of wheat plants under low-temperature stress, resulting in higher leaf SPAD readings, more new tillers, as well as increased dry weight of roots and above-ground organs. This study suggested that remedial nitrogen should be applied prior to low-temperature stress because it is more effective in restoring the growth of wheat plants under low-temperature stress.

Amelioration of cadmium toxicity by enhancing nitrogen assimilation and photosynthetic activity by two different nitrogen supplements in rice (Oryza sativa L.) cv. Lalat

Rapid industrialization and over-use of agrochemicals may lead to cadmium (Cd) contamination in agricultural soil, posing serious threat to human health. In recent times, application of plant nutrients and other growth promoting substances, like, nanoparticles (nZVI), silicon, salicylic acid were reported to have ameliorated Cd toxicity, in this regard, nitrogen (N) amendment can be a promising technique to ameliorate Cd toxicity as, N is an essential macronutrient responsible for plant growth and development. In the present study, seven days old seedlings of Oryza sativa L. cv. Lalat were co-treated with 10 µM CdCl2 and two different nitrogen supplements (Calcium nitrate and Ammonium acetate) separately to evaluate its ameliorating potential. It was observed that, Cd stress impaired plant vigor, biomass, RWC, nitrogen-containing components and non-enzymatic antioxidants causing significant reduction in photosynthesis and N-assimilation, indicating sensitivity of the cultivar to Cd stress. Cd stress also enhanced lipid peroxidation, enzymatic-antioxidant activity, proline and non-protein thiol accumulation. N-supplementation to Cd stressed plants rescued plant growth, biomass, protein content and nitrogen containing compounds leading to the upregulation of photosynthesis and nitrogen assimilation. N amendment was found to downregulate lipid peroxidation, enzymatic antioxidant activity, proline and non-protein thiol content and upregulate non-enzymatic antioxidant. Agronomical parameters and yield also improved significantly by N supplementation as compared to Cd stressed plants. Supplementation with N salts also improved grain quality by enhancing grain nutrients and reduced grain Cd by decreasing bioavailable Cd in soil, thereby reducing daily Cd intake and cancer risk. Among the two N-supplements, ammonium acetate showed better ameliorating effect compared to calcium nitrate.

Salt and nitrogen amendment and optimization for cellulase and xylanase production using dilute acid hydrolysate of distillers' dried grains with solubles (DDGS) as the feedstock.

Distillers' dried grains with solubles (DDGS) is a by-product of dry-mill corn ethanol production comprising a high nutritional value due to residual fiber, protein, and lipid contents. The fiber content of DDGS is high enough to be considered a valuable source for the production of hydrolytic enzymes, such as cellulase and xylanases, which can be used for hydrolysis of lignocellulosic feedstock during ethanol production. The DDGS-based medium prepared after acid hydrolysis provides adequate sugars for enzyme production, while additional macronutrients, such as salts and nitrogen sources, can enhance the enzyme production. Therefore, this study was undertaken to evaluate the effect of salts (KH2PO4, CaCl2·2H2O, MgSO4·7H2O, FeSO4·7H2O, CoCl2·6H2O, and MnSO4·H2O), peptone, and yeast extract on enzyme secretion by four different Aspergillus niger strains and to optimize the nitrogen source for maximum enzyme production. Yeast extract improved the cellulase production (0.38IU/ml) for A. niger (NRRL 1956) as compared to peptone (0.29IU/ml). However, maximum cellulase productions of 0.42IU/ml and 0.45IU/ml were obtained by A. niger (NRRL 330) and A. niger (NRRL 567), respectively, in presence of ammonium sulfate. The optimized nitrogen amounts resulted in a significant increase in the cellulase production from 0.174 to 0.63IU/ml on day 9 of the fermentation with A. niger (NRRL 330). The composite model improved both cellulase and xylanase production. In conclusion, the optimization of all three nitrogen sources improved both cellulase and xylanase production in the DDGS-based media.

The combined effect of nitrogen and biochar amendments on the yield and glucosinolate contents of the Chinese cabbage

Nitrogen plays an important role in plant growth as an essential nutrient. When crops are grown on biochar applied soil, their growth be positive affected. Biochar has been announced as a soil amendment to improve nitrogen (N) use efficiency. The present study aimed to investigate the combined effect of nitrogen fertilizer and biochar amendment on the growth of Chinese cabbage including its glucosinolates (GSLs) functional compounds. Acidic (AB), neutral (NB) and basic (BB) biochars produced at 330 °C, 400 °C and at 600 °C, respectively were employed in the study with each of them applied to the soil at a rate of 1% (w/w). N fertilizer in form of urea was split applied to the soil at three different rates of 160, 320, 640 kg ha−1. The Chinese cabbage yield was highest in the 320 kg ha−1 nitrogen amendment and all the biochar amendments decreased yield in comparison to the 320 kg ha−1 nitrogen amendment. The Chinese cabbage yield in the biochar amended soils increased with increasing amount of nitrogen applied to the soil. The GSLs content was highest in the Chinese cabbage grown on the 320 kg ha−1 N amendment in all the treatments. Except, BB, biochar amendments generally produced Chinese cabbage with higher GSLs content than the urea only amendment.

Performance of a wheat–soybean cropping system as affected by applying phosphogypsum in combination with urea

High-intensity crop-production seeking for higher grain yields increases nutrient demand by plants. A field experiment was performed in Parana State, Brazil, on a clayey Haplic Cambisol to evaluate the effects of phosphogypsum and nitrogen (N) amendments on a wheat–soybean rotation. Phosphogypsum was surface-applied to plots at 0, 2, 4, and 6 Mg ha−1 before wheat sowing and two rates of urea at 40 and 80 kg N ha−1 were applied to subplots in top dressing at tillering of wheat. Phosphogypsum improved the yield performance of wheat–soybean rotation. Wheat grain yield increased by 20% due to phosphogypsum application only when a higher rate of urea at 80 kg N ha−1 was applied in top dressing, indicating an influence of the interaction between N and sulfur (S). Soybean grain yield increased by 16% with phosphogypsum application, regardless of the urea-N rates to the previous wheat crop. Higher grain yields of wheat and soybean were related to higher levels of Ca2+ and S in the soil profile (0–0.40 m). Although there was a slight involvement of phosphogypsum in reducing aluminum Al3+ toxicity in the subsoil due to a reduction in Al3+ saturation caused by increased Ca2+ concentration, the improvements imparted by the use of phosphogypsum resulted mainly from increased S concentration. The results showed that the critical levels of SO4–S by 0.01 mol L−1 Ca(H2PO4)2 were 14 and 27 mg dm−3 at 0–0.20 m and 0–0.40 m depths, respectively, for the wheat–soybean cropping system.

The response of coarse root biomass to long-term CO2 enrichment and nitrogen application in a maturing Pinus taeda stand with a large broadleaved component.

Elevated atmospheric CO2 (eCO2 ) typically increases aboveground growth in both growth chamber and free-air carbon enrichment (FACE) studies. Here we report on the impacts of eCO2 and nitrogen amendment on coarse root biomass and net primary productivity (NPP) at the Duke FACE study, where half of the eight plots in a 30-year-old loblolly pine (Pinus taeda, L.) plantation, including competing naturally regenerated broadleaved species, were subjected to eCO2 (ambient, aCO2 plus 200ppm) for 15-17years, combined with annual nitrogen amendments (11.2gNm-2 ) for 6years. Allometric equations were developed following harvest to estimate coarse root (>2mm diameter) biomass. Pine root biomass under eCO2 increased 32%, 1.80kgm-2 above the 5.66kgm-2 observed in aCO2 , largely accumulating in the top 30cm of soil. In contrast, eCO2 increased broadleaved root biomass more than twofold (aCO2 : 0.81, eCO2 : 2.07kgm-2 ), primarily accumulating in the 30-60cm soil depth. Combined, pine and broadleaved root biomass increased 3.08kgm-2 over aCO2 of 6.46kgm-2 , a 48% increase. Elevated CO2 did not increase pine root:shoot ratio (average 0.24) but increased the ratio from 0.57 to 1.12 in broadleaved species. Averaged over the study (1997-2010), eCO2 increased pine, broadleaved and total coarse root NPP by 49%, 373% and 86% respectively. Nitrogen amendment had smaller effects on any component, singly or interacting with eCO2 . A sustained increase in root NPP under eCO2 over the study period indicates that soil nutrients were sufficient to maintain root growth response to eCO2 . These responses must be considered in computing coarse root carbon sequestration of the extensive southern pine and similar forests, and in modelling the responses of coarse root biomass of pine-broadleaved forests to CO2 concentration over a range of soil N availability.

Lowered water table causes species substitution while nitrogen amendment causes species loss in alpine wetland microbial communities

Alpine wetlands are hotspots of carbon (C) storage and methane emission, and they could be key contributors to global warming. In recent years, rapid warming has lowered the water table in alpine wetlands on the Tibetan Plateau, concurrent with intensified nitrogen (N) deposition via anthropogenic activities. We carried out a field experiment to investigate the ecological impacts of these two factors on soil bacterial and functional communities, which are essential drivers of greenhouse gas emissions. Nitrogen amendment alone decreased the phylogenetic alpha-diversity of bacterial communities which could be offset by lowered water table. In contrast, microbial functional alpha-diversity, revealed by a high-throughput microarray, remained unchanged. Both bacterial and functional beta-diversity responded to lowered water table, but only bacterial community responded to N amendment. The alpha-Proteobacteria, beta-Proteobacteria, and Bacteroidetes were the major responsive bacterial lineages, and C degradation, methanogenesis, alkaline shock, and phosphorus oxidation were the major responsive functional processes. Partitioning analysis revealed that N amendment changed bacterial community structure mainly via species loss processes but did not affect bacterial functional communities, with soil pH and ammonium as the key factors influencing changes in bacterial community structure. Conversely, lowered water table altered bacterial and functional communities through species substitution processes linked to soil pH and soil moisture. According to our results, the response mechanisms of microbial communities to lowered water table and N amendment are fundamentally different in alpine wetlands.

Response of soybean (Glycine max) to Rhizobia inoculation, mineral nitrogen and inoculation amendment at the two agro ecological zones of northern Nigerian savannah

For sustainable agriculture nitrogen must be adequately supplied because it is the most limiting major nutrient required by all living plants. This experiment was conducted at the two ecological zones, Sudan savannah in Kano State and Guinea savannah in Bauchi state of Nigeria during the 2016 cropping season. The design of the experiment was Randomized Complete Block Design (RCBD) with seven treatments and four replications in each site. The treatments were; legume fix, alosca, 50 kg N ha-1, cattle manure, legume fix + cattle manure, alosca + cattle manure and control. The result showed that Legume fix had the highest grain N uptake (90.51 kg N ha-1) which differed significantly (P≤0.001) from the rest of the treatments. At Guinea savannah legume fix gave the highest N uptake value (95.53 kg N ha-1) which was significantly different from all treatments except legume fix + cattle manure. However, 50 kg N ha-1 gave the least (48.64 kg N ha-1) even lower than the control and differs significantly with the rest of treatments (P≤0.001). Legume fix gave the highest P uptake value (9.66 kg P ha-1) which significantly differed from all other treatments. At Sudan savannah, significant differences (P ≤ 0.001) occurred between some of the treatments. Alosca + cattle manure recorded the highest K uptake (49.99 kg K ha-1). Result for the fixed N in the Sudan and Guinea savannahs soybean field revealed a significant difference between the treatments and the control.

Effects of Different Nitrogen Sources and Ratios to Carbon on Larval Development and Bioconversion Efficiency in Food Waste Treatment by Black Soldier Fly Larvae (Hermetia illucens).

Simple SummaryBlack soldier fly larvae (BSFL) have received global research interest and industrial application due to their high performance on the organic waste treatment. However, the substrate C/N property, which may affect larvae development and the waste bioconversion process greatly, is significantly less studied. The current study focused on the food waste treatment by BSFL, compared the nitrogen supplying effects of 9 nitrogen species (i.e., NH4Cl, NaNO3, urea, uric acid, Gly, L-Glu, L-Glu:L-Asp (1:1, w/w), soybean flour, and fish meal), and further examined the C/N effects on the larval development and bioconversion process. We found that NH4Cl and NaNO3 led to poor larval growth and survival, while 7 organic nitrogen species exerted no harm to the larvae. Urea was further chosen to adjust the C/Ns. Results showed that lowering the C/N from the initial 21:1 to 18:1–14:1 improved the waste reduction and larvae production performance, and C/N of 18:1–16:1 was further beneficial for the larval protein and lipid bioconversion, whereas C/N of 12:1–10:1 resulted in a significant performance decline. Therefore, the C/N range of 18:1–16:1 is likely the optimal condition for food waste treatment by BSFL and adjusting food waste C/N with urea could be a practical method for the performance improvement.Biowaste treatment by black soldier fly larvae (BSFL, Hermetia illucens) has received global research interest and growing industrial application. Larvae farming conditions, such as temperature, pH, and moisture, have been critically examined. However, the substrate carbon to nitrogen ratio (C/N), one of the key parameters that may affect larval survival and bioconversion efficiency, is significantly less studied. The current study aimed to compare the nitrogen supplying effects of 9 nitrogen species (i.e., NH4Cl, NaNO3, urea, uric acid, Gly, L-Glu, L-Glu:L-Asp (1:1, w/w), soybean flour, and fish meal) during food waste larval treatment, and further examine the C/N effects on the larval development and bioconversion process, using the C/N adjustment with urea from the initial 21:1 to 18:1, 16:1, 14:1, 12:1, and 10:1, respectively. The food wastes were supplied with the same amount of nitrogen element (1 g N/100 g dry wt) in the nitrogen source trial and different amount of urea in the C/N adjustment trial following larvae treatment. The results showed that NH4Cl and NaNO3 caused significant harmful impacts on the larval survival and bioconversion process, while the 7 organic nitrogen species resulted in no significant negative effect. Further adjustment of C/N with urea showed that the C/N range between 18:1 and 14:1 was optimal for a high waste reduction performance (73.5–84.8%, p < 0.001) and a high larvae yield (25.3–26.6%, p = 0.015), while the C/N range of 18:1 to 16:1 was further optimal for an efficient larval protein yield (10.1–11.1%, p = 0.003) and lipid yield (7.6–8.1%, p = 0.002). The adjustment of C/N influenced the activity of antioxidant enzymes, such as superoxide dismutase (SOD, p = 0.015), whereas exerted no obvious impact on the larval amino acid composition. Altogether, organic nitrogen is more suitable than NH4Cl and NaNO3 as the nitrogen amendment during larval food waste treatment, addition of small amounts of urea, targeting C/N of 18:1–14:1, would improve the waste reduction performance, and application of C/N at 18:1–16:1 would facilitate the larval protein and lipid bioconversion process.

Management of Pea Leaf Weevil (Coleoptera: Curculionidae) and Development of a Nominal Threshold in Faba Beans.

Pea leaf weevil, Sitona lineatus (L.) (Coleoptera: Curculionidae), can reduce the yield of field pea [Pisum sativum (L.) (Fabales: Fabaceae)] and faba bean [Vicia faba (L.) (Fabales: Fabaceae)]. Adults feed on the foliage and larvae feed on root nodules and nodule-associated Rhizobium Frank (Rhizobiales: Rhizobiacea) bacteria. In this study, we developed a data-based nominal threshold for pea leaf weevil in faba bean. We further tested the efficacy of insecticidal seed treatment and foliar insecticide (thiamethoxam and lambda-cyhalothrin, respectively), and nitrogen amendment for pea leaf weevil control using a multi-year field plot study at two sites in Alberta, Canada. Pea leaf weevil feeding damage significantly reduced faba bean yields. Thiamethoxam reduced adult and larval damage, and protected faba bean yield, while neither lambda-cyhalothrin nor a nitrogen amendment was effective in protecting yield. The percentage of seedlings with feeding on the terminal leaf had a negative relationship with yield and was used to estimate a nominal threshold near 15% of seedlings with terminal leaf damage. Since lambda-cyhalothrin is not effective in managing pea leaf weevil on faba bean, there is a need to research additional integrated pest management strategies to reduce prophylactic insecticidal seed treatments.

Straw Incorporation with Nitrogen Amendment Shapes Bacterial Community Structure in an Iron-Rich Paddy Soil by Altering Nitrogen Reserves.

Incorporation of crop straw into the soil along with inorganic fertilization is a widespread agricultural practice and is essential in nutrient-scarce soils, such as iron-rich (ferruginous) paddy soils. The responses of soil bacterial communities to straw incorporation under different nitrogen inputs in iron-rich soils remain unclear. Therefore, 6000 kg ha−1 dry wheat (Triticum aestivum L. cv. Zhengmai 12) straw was applied to a rice paddy with and without nitrogen amendment (0, 80, 300, and 450 kg ha−1 N as urea), to investigate its effects on soil fertility and bacterial community structure. Organic matter, total nitrogen, and water contents tended to decrease in straw-incorporated soils with different nitrogen inputs. Proteobacteria was the dominant bacterial phylum across all treatments (26.3–32.5% of total sequences), followed by Chloroflexi, Acidobacteria, and Nitrospirae. Up to 18.0% of all the taxa in the bacterial communities were associated with iron cycling. Straw incorporation with nitrogen amendment increased the relative abundance of iron oxidizers, Gallionellaceae, while decreasing the relative abundance of iron reducers, Geobacteraceae. Bacterial community composition shifted in different treatments, with total nitrogen, water, and Fe(III) contents being the key drivers. Straw incorporation supplemented by 300 kg ha−1 N increased bacterial richness and enhanced all the predicted bacterial functions, so that it is recommended as the optimal nitrogen dosage in practice.

Irrigation and fertilizer treatments affecting rosmarinic acid accumulation, total phenolic content, antioxidant potential and correlation between them in peppermint (Mentha piperita L.)

One of the greatest challenges in recent years is providing enough food to feed the increasing world population, while available freshwater resources become limited. However, effective fertilizer management has also a fundamental role to improve yield quality and quantity. A field experiment was conducted over 2 years, using a split-plot arrangement in a randomized complete block design. The experiments had three water deficit severity treatments: 25% (control), 40% (mild stress), and 55% (severe stress) depletion from the available water. The subplot division consisted of six fertilizer treatments; FR1: unfertilized (control), FR2: 140 kg ha−1 urea; FR3: 105 kg ha−1 urea + 3.3 ton ha−1 vermicompost; FR4: 70 kg ha−1 urea + 6.6 ton ha−1 vermicompost; FR5: 35 kg ha−1 urea + 10 ton ha−1 vermicompost, and FR6: 13.5 ton ha−1 vermicompost. The maximum essential oil (0.97%) was observed under mild water deficit stress. The highest antioxidant activity (DPPH) and superoxide dismutase activity could be monitored under unfertilized and 140 kg ha−1 urea fertilized conditions, respectively. Vermicompost-treated soils reduced antioxidant features, total phenol, and rosmarinic acid content under water deficit. These results indicate that mild drought stress can increases the synthesis of medical compound and vermicomposting can alleviate the impact of drought by conserving soil moisture and improve nutrient uptake. Therefore, the results suggest that using vermicompost as a fast-acting nitrogen amendment can improve the leaf area index.

Soil microorganisms decrease barley biomass uniformly across contrasting nitrogen availability

AimsMicroorganisms play a dichotomous role in the soil nitrogen cycle through mineralization and immobilization. We aimed to understand how nitrogen availability modifies the effect of microorganisms on plant growth. We hypothesized that soil microorganisms would increase plant biomass following amendment with a substrate rich in organic nitrogen (net mineralization), be neutral when adding inorganic nitrogen, and decrease biomass when adding organic nitrogen-limited substrate (nitrogen competition). MethodBarley (Hordeum vulgare L., cv. Evergreen) was exposed to either i) limited, organically bound nitrogen, ii) organically bound nitrogen or iii) inorganic nitrogen. In these amendments, we assessed the differences in plant biomass and physiology between plants with or without soil microbiome addition. ResultsThe soil microbiome reduced shoot biomass equally (12%) across all nitrogen amendments. However, nitrogen availability did modulate the effect of the soil microbiome on plant physiological parameters associated with nitrogen deficiency. ConclusionsThe results indicate that the net negative effect of complex microbiomes on shoot biomass is independent of nitrogen availability. Thus, microbiome addition was deleterious to biomass even in a nutrient-stress-free environment. We suggest that strategies for improving plant growth through manipulation of microorganisms should not exclusively focus on beneficial and pathogenic microorganisms, but also include minimizing plant metabolic costs of microbiome interactions.

Viromes outperform total metagenomes in revealing the spatiotemporal patterns of agricultural soil viral communities

Viruses are abundant yet understudied members of soil environments that influence terrestrial biogeochemical cycles. Here, we characterized the dsDNA viral diversity in biochar-amended agricultural soils at the preplanting and harvesting stages of a tomato growing season via paired total metagenomes and viral size fraction metagenomes (viromes). Size fractionation prior to DNA extraction reduced sources of nonviral DNA in viromes, enabling the recovery of a vaster richness of viral populations (vOTUs), greater viral taxonomic diversity, broader range of predicted hosts, and better access to the rare virosphere, relative to total metagenomes, which tended to recover only the most persistent and abundant vOTUs. Of 2961 detected vOTUs, 2684 were recovered exclusively from viromes, while only three were recovered from total metagenomes alone. Both viral and microbial communities differed significantly over time, suggesting a coupled response to rhizosphere recruitment processes and/or nitrogen amendments. Viral communities alone were also structured along an 18 m spatial gradient. Overall, our results highlight the utility of soil viromics and reveal similarities between viral and microbial community dynamics throughout the tomato growing season yet suggest a partial decoupling of the processes driving their spatial distributions, potentially due to differences in dispersal, decay rates, and/or sensitivities to soil heterogeneity.

Evaluation of foliar and seed treatments for integrated management of root rot and pea leaf weevil in field pea and faba bean

Increased production of field pea (Pisum sativum L.) and faba bean (Vicia faba L.) in Canada has led to a greater incidence of disease and the range expansion of insect pests. Several soil-borne pathogens cause root rot in these crops, while the feeding activity of the pea leaf weevil (Sitona lineatus L.) significantly reduces nitrogen fixation. As pathogens and pea leaf weevil larva are associated with the roots of their mutual host, there is potential for synergistic interactions to occur that may ultimately reduce yield. Field trials at three locations in southern Alberta in 2016 and 2017 evaluated the use of insecticidal and fungicidal seed treatments, a foliar insecticide spray, alone and in combination, and nitrogen amendment as strategies to reduce impacts of both root rots and pea leaf weevil. The fungicides ethaboxam and fludioxonil did not reduce disease severity in pea or faba bean during the two-year field study. Quantitative PCR assays demonstrated that the pathogens Aphanomyces euteiches and Fusarium spp. co-infect pea roots under field conditions, but pathogen levels were not consistently reduced by any of the treatments. The insecticide thiamethoxam reduced nodule and foliar herbivory, whereas the foliar insecticide, lambda-cyhalothrin, and nitrogen fertilization at seeding had no consistent impact. No single or combined treatment protected yield or seed quality, therefore an effective method of managing these constraints to pea and faba bean production is still required.

Metagenomics analysis identifies nitrogen metabolic pathway in bioremediation of diesel contaminated soil

Nitrogen amendment is known to effectively enhance the bioremediation of hydrocarbon-contaminated soil, but the nitrogen metabolism in this process is not well understood. To unravel the nitrogen metabolic pathway(s) of diesel contaminated soil, six types of nitrogen sources were added to the diesel contaminated soil. Changes in microbial community and soil enzyme genes were investigated by metagenomics analysis and chemical analysis through a 30-day incubation study. The results showed that ammonium based nitrogen sources significantly accelerated the degradation of total petroleum hydrocarbon (TPH) (79–81%) compared to the control treatment (38%) and other non-ammonium based nitrogen amendments (43–57%). Different types of nitrogen sources could dramatically change the microbial community structure and soil enzyme gene abundance. Proteobacteria and Actinobacteria were identified as the two dominant phyla in the remediation of diesel contaminated soil. Metagenomics analysis revealed that the preferred metabolic pathway of nitrogen was from ammonium to glutamate via glutamine, and the enzymes governing this transformation were glutamine synthetase and glutamate synthetase; while in nitrate based amendment, the conversion from nitrite to ammonium was restrained by the low abundance of nitrite reductase enzyme and therefore retarded the TPH degradation rate. It is concluded that during the process of nitrogen enhanced bioremediation, the most efficient nitrogen cycling direction was from ammonium to glutamine, then to glutamate, and finally joined with carbon metabolism after transforming to 2-oxoglutarate.

Role of antioxidant pool in management of ozone stress through soil nitrogen amendments in two cultivars of a tropical legume.

The present experiment was done on two different cultivars of a tropical legume, Cymopsis tetragonoloba L. Taub. (cluster bean) cvv. Pusa-Naubahar (PUSA-N) and Selection-151 (S-151). The experiment was conducted under ambient ozone (O3) conditions with inputs of three different doses of inorganic nitrogen (N1, recommended; N2, 1.5-times recommended and N3, 2-times recommended) as well as control plants. The objective of this study was to evaluate the effectiveness of soil nitrogen amendments in management of ambient ozone stress in the two cultivars of C. tetragonoloba. Our experiment showed that nitrogen amendments can be an efficient measure to manage O3 injury in plants. Stimulation of antioxidant enzyme activities under nitrogen amendments is an important feature of plants that help plants cope with ambient O3 stress. Nitrogen amendments strengthened the antioxidant machinery in a more effective way in the tolerant cultivar PUSA-N, while in the sensitive cultivar S-151, avoidance strategy marked by more reduction in stomatal conductance was more prominent. Enzymes of the Halliwell-Asada pathway, especially ascorbate peroxidase and glutathione reductase, were more responsive and synchronised in PUSA-N than S-151, under similar nitrogen amendment regimes and were responsible for the differential sensitivities of the two cultivars of C. tetragonoloba. The present study shows that 1.5-times recommended dose of soil nitrogen amendments was sufficient in partial mitigation of O3 injury and the higher nitrogen dose (2-times recommended, in our case), did not provide any extra advantage to the plant's metabolism compared with plants treated with the lower nitrogen dose (1.5-times recommended).