Nitrogen, Volume 5, Issue 1 (March 2024) – 16 articles

Nitrogen (N) is abundant in the atmosphere as N_2, which is converted into reactive forms (Nr) for plant assimilation. In pre-industrial times, atmospheric N₂ conversion to Nr balanced Nr reconversion to N₂, but 20th-century human activity intensified this conversion via synthetic fertilizers, biological N₂ fixation, and fossil fuel burning. The surplus of Nr detrimentally impacts ecosystems and human well-being. This study aimed to assess the N use efficiency in the soil–plant system of the soybean-corn succession (${\mathrm{S}\mathrm{P}\mathrm{S}}_{S,C}$) in Mato Grosso and Mato Grosso do Sul, Brazil’s midwest. We estimated N macrofluxes in ${\mathrm{S}\mathrm{P}\mathrm{S}}_{S,C}$ and identified key agro-environmental indicators. Between 2008 and 2020, the yearly sowed area for the ${\mathrm{S}\mathrm{P}\mathrm{S}}_{S,C}$ increased by 3.3-fold (currently 7.3 million ha). The average annual input of net anthropogenic Nr, average annual N balance, and N loss in ${\mathrm{S}\mathrm{P}\mathrm{S}}_{S,C}$ was estimated to be ~204 kg [N] ha⁻¹_, 57 kg [N] ha⁻¹, and 30 kg [N] ha⁻¹, respectively, indicating persistent N accumulation and loss. The average results of the agronomic efficiency and N retention indicator in the ${\mathrm{S}\mathrm{P}\mathrm{S}}_{S,C}$ was 0.71 and 0.90, respectively. Modest N use efficiency results reflect N loss effects. Despite these limitations, there are opportunities in ${\mathrm{S}\mathrm{P}\mathrm{S}}_{S,C}$ for management strategies to reduce N loss and enhance efficiency. Full article

The low efficiency of nitrogen (N) fertilizers is a frequent problem in agriculture that impacts the environment. Omeprazole (OMP) has been reported to promote N uptake and assimilation in tomato, basil, and corn. However, information about the effect of omeprazole on N assimilation, recovery, and N use efficiency parameters for bean plants is limited. Therefore, the objective of the present study was to determine the effect of foliar applications of OMP at 0, 1, 10, and 100 µM on nitrogen assimilation, growth, yield, nitrogen use efficiency parameters, and recovery percentage in green bean plants. Green bean plants cv. Strike grown in pots were used. Biomass, yield, nitrate reductase activity, photosynthetic pigments concentration, soluble amino acids and protein concentrations, total nitrogen concentration, nitrogen use efficiency parameters, and nitrogen recovery were analyzed. The results obtained indicate that the application of OMP at 1 µM increased yield and biomass, promoted N assimilation through higher NR enzyme activity, higher amino acid concentration, higher N use efficiency coefficient, and allowed a more efficient nitrogen recovery percentage. Full article

This study aimed to clarify the differences in the decomposition rates, soil carbon and nitrogen contents, soil enzyme activities, and the structure of the soil bacterial community between the four Asteraceae invasive plants (AIPs), Bidens pilosa L., Conyza canadensis (L.) Cronq., Solidago canadensis L., and Symphyotrichum subulatum (Michx.) G.L. Nesom, and the native plant Pterocypsela laciniata (Houtt.) Shih under the artificially modeled nitrogen with four forms (including nitrate, ammonium, urea, and the mixed nitrogen forms with an equal mixture of three individual nitrogen forms). The mixed nitrogen forms significantly increased the decomposition rate of the four AIPs and P. laciniata. The positive effects of the mixed nitrogen forms on the decomposition rate of the four AIPs and P. laciniata were obviously greater than those of individual nitrogen forms. Nitrogen with four forms visibly up- or down-regulated the dominant role of predominant soil bacterial biomarkers, and significantly increased the species number, richness, and phylogenetic diversity of the soil bacterial community, as well as the number of most of the functional gene pathways of the soil bacterial communities involved in the decomposition process. The decomposition rate of the four AIPs was similar to that of P. laciniata. The leaves of C. canadensis decomposed more easily than those of S. subulatum. The decomposition process of the four AIPs caused remarkable changes in the relative abundance of several taxa of the soil bacterial community and soil bacterial beta diversity, and caused apparent up- or down-regulation in the dominant role of predominant soil bacterial biomarkers and the number of several functional gene pathways of the soil bacterial communities involved in the decomposition process. Full article

Selenium (Se) and nitrate have the potential to modify rice root architecture, but it is unclear how Se is linked to changes in the rice seedlings nitrate status. Thus, rice seedlings were grown in nutrient solutions containing either 0- or 10-µM Se that were supplemented with 0.05 (low nitrate condition) or 5.0 mM nitrate (high nitrate condition). Se application to seedlings treated with low nitrate led to sugar accumulation in shoot and root and increased cytokinin concentrations in root, while decreasing cytokinin concentrations in shoot compared with seedlings in 0.05 mM nitrate alone. This, in turn, resulted in decreased shoot growth, while downregulation of OsXTH and OsEXP negatively affected root expansion. On the other hand, Se combined with 5.0 mM nitrate did not affect sugar concentration in tissues compared with seedlings in 5.0 mM nitrate. Moreover, Se negatively regulated the cytokinin biosynthesis in shoot and root of seedlings grown under 5.0 mM nitrate. The reduction in cytokinin concentrations by Se under high nitrate condition decreased shoot growth, but increased root growth through induction of OsXTH and OsEXP. Thus, many of the effects of Se in shoot and root growth are due to a shift in nitrate status of the seedlings. Full article

Recovery efforts for the endangered Serianthes nelsonii have been deficient. To learn more about leaf development costs, the content of biomass and essential elements were determined in the supportive and laminae tissue of leaves that were constructed under different levels of incident light. The biomass required to construct a leaf in 22% light transmission was 65% of that in full sun, and light treatment did not influence the balance between supportive and laminae tissues. Concentrations of carbon, phosphorus, iron, manganese, and boron were greatest for in full-sun laminae, but those of nitrogen, potassium, calcium, magnesium, and zinc were greatest in shaded laminae. The same patterns with regard to light were exhibited in supportive tissues for carbon, nitrogen, potassium, calcium, magnesium, and zinc. In contrast, the supportive tissue phosphorus content was greatest in shaded leaves, and the light level did not influence the supportive tissue concentrations of the remaining elements. The leaf laminae consistently exhibited greater concentrations of elements with the exception of potassium and nickel, which were greater in the supportive tissues. These results indicate that the construction of full-sun S. nelsonii leaves is more costly than that of shaded leaves, and the transfer of biomass and essential elements between the supportive and laminae tissues is not substantially influenced by the developmental light level. Identifying the drivers of S. nelsonii leaf element concentrations is crucial for understanding the role of this charismatic tree in community-level processes. Full article

The complex ramifications of global climate change, which is caused by heightened concentrations of greenhouse gases in the Earth’s atmosphere, are deeply concerning. Addressing this crisis necessitates the immediate implementation of adaptive mitigation strategies, especially within the agricultural sector. In this context, this study aimed to assess how the supply of nitrogen (N) (0, 70, 140, and 210 kg N ha⁻¹) in the forms of ammonium nitrate and urea affects the agronomic performance, food quality, greenhouse gas emissions (GHG), and carbon footprint of potato plants. The examined hypothesis was that by precisely calibrating N doses alongside appropriate sourcing, over-fertilization in potato cultivation can be mitigated. A decline in stomatal conductance and net photosynthetic rate disturbs physiological mechanisms, reflecting in biomass production. Application of 136 kg N ha⁻¹ as urea showed a remarkable yield increase compared to other doses and sources. The highest nitrate content in potato tubers was achieved at 210 kg N ha⁻¹ for both sources, not exceeding the limit (200 mg kg⁻¹ of fresh mass) recommended for human consumption. The lowest carbon footprint was obtained when 70 kg N ha⁻¹ was applied, around 41% and 26% lower than when 210 kg N ha⁻¹ and 140 kg N ha⁻¹ were applied, respectively. The results demonstrated that over-fertilization not only worsened the yield and tuber quality of potato plants, but also increased greenhouse gas emissions. This information is valuable for establishing an effective fertilization program for the potato crop and reducing carbon footprint. Full article

The risk of nitrate contamination became a reality for Fairmont in Minnesota, when water rich in NO₃-N exceeded the drinking water standard of 10 mg/L. This was unexpected because this city draws its municipal water from a chain of lakes that are fed primarily by shallow groundwater under row-crop land use. Spring soil thaw drives cold water into a subsurface pipe where almost no NO₃-N reduction occurs. This paper focuses on NO₃-N reduction before the water enters the lakes and no other nitrogen management practices in the watershed. A novel denitrifying bioreactor was constructed behind a sediment forebay, which then flowed into a chamber covered by a greenhouse before entering a woodchip bioreactor. In 2022 and 2023, water depth, dissolved oxygen, and temperature were measured at several locations in the bioreactor, and continuous NO₃-N was measured at the entry and exit of the bioreactor. The results showed better performance at a low water depth with lower dissolved oxygen and higher water temperature. The greenhouse raised the inlet temperature in 2022 but did not in 2023. The forebay and the greenhouse may have impeded the denitrification process due to the high dissolved oxygen concentrations in the influent and the stratification of dissolved oxygen caused by algae in the bioreactor. Full article

Heterocyst-forming cyanobacteria that colonize the drylands contribute to carbon and nitrogen supplies in nutrient-poor soils. As one of the representative cyanobacteria, Nostoc flagelliforme adapts well to the arid environment in the form of filamentous colonies (or filaments). To date, the adaptive changes, either genetic or micromorphological, that occur within single colonies of dryland cyanobacteria remain largely unclear. In this study, unusual long chains or trichomes of vegetative cells (not containing heterocysts) were observed within N. flagelliforme filaments. And the overall heterocyst frequency in the trichomes was counted to be 1.3–2.7%, different from the usually observed 5–10% heterocyst frequency in model Nostoc strains when grown in nitrogen-deprived medium. Thus, these phenomena seem contradictory to our usual recognition of Nostoc strains. Related transcriptional and heterocyst frequency analyses suggested no genetically significant alteration in heterocyst formation and nitrogen fixation in this strain. Also, the amounts of nitrogen sources in the extracellular polysaccharide (EPS) matrix released by N. flagelliforme cells that may cause the low heterocyst frequency were assessed to be equivalent to 0.28–1.10 mM NaNO₃. When combining these findings with the habitat characters, it can be envisaged that the released nitrogen sources from cells are confined, accumulated, and re-utilized in the EPS matrix, thereby leading to the formation of reduced heterocyst frequency and long-chained vegetative cells. This study will contribute to our understanding of the distinctive adaptation properties of colonial cyanobacteria in dryland areas. Full article

Nitrogen (N) is the most limiting nutrient for the production of vegetable crops, but anthropogenic sources pose risks due to its transformation into several reactive forms and movement throughout the environment. The bulk of the N research to date to improve Nitrogen Use Efficiency (NUE) has followed a reductionist factorial approach focused on synthetic N application rates and crop growth response, under monocultures. The increased adoption of diversified cropping systems, organic N sources, and alternative management practices makes it more challenging to unravel N form transformation, movement, and crop uptake dynamics, in time and space. Here, based on a selected review of the recent literature, we propose a holistic approach of nutrient management to highlight key management and production variables as well as multilevel cropping system, genetic, environmental, ecological, and socioeconomic interactions to improve the N cycle and NUE. The best management strategies to improve NUE include both organic and inorganic N rate calibration studies, germplasm selection, crop rotations, identification of nutrient x nutrient interactions, and pest and water management. Agroecological practices that may improve NUE include vegetational diversification in time and space, integrated crop–livestock systems, conservation tillage, organic amendment inputs, legume-based cropping systems, as well as a landscape approach to nutrient management. Full article

The availability of nitrogen in the soil is influenced by several factors associated with the forms and characteristics of organic nitrogen present in it, as well as by any property that impacts its microbiological and biochemical activity. The objective of the present work was to evaluate the combined effect of manure fertilization, soil type, and incubation time on soil N forms and availability. The experiment was conducted in a factorial scheme (2 soils × with (20 Mg ha⁻¹) or without manure × 4 incubation times (15, 45, 90, and 180 days)). The levels of organic matter and fractions of organic N and mineral N were evaluated. Fertilization increased the organic matter and mineral N content in both soils, but the effect of fertilization on the organic N fractions was different depending on the type of soil. In the clayey soil, there was an accumulation of nitrogen in the unidentified hydrolysable fraction, whereas, in the sandy soil, the greatest increase occurred in the hydrolysable ammonium fraction. The application of manure generated different effects on the dynamics of N forms, depending on the type of soil. It is important to understand the impacts of different soil properties on the forms of nitrogen. Full article

Common bean (Phaseolus vulgaris L.) ranks among the most produced and consumed legume crops and contains essential macro- and micronutrients. Grain yield of the food crop is markedly decreased by poor management, especially a lack of additional essential nutrient elements through the application of fertilizers. In addition to the application of fertilizers, scholarly research and crop farmers have shown that the use of biofertilizer inoculants improves the yield of legume crops. The objective of this research study was to assess the effectiveness of peat-based Rhizobium tropici sp. UD5 on the growth, yield, and nitrogen concentration of common bean. The peat inoculant contained 6.5 × 10⁹ viable cells/g. The experiment was conducted in two climatic zones, as described by the Koppen–Gieger climatic classification system. Treatments involved the peat-based inoculant Rhizobium tropici (T0 = 0 g without inoculation, T1 = 250 g of peat inoculant of strain UD5 for 50 kg seeds, T2 = 500 g of inoculant of strain UD5, and T3 = 200 g of comparative peat inoculant). The results indicated that common-bean-inoculated formulation of R. tropici sp. strain UD5 increased the following parameters compared to the controls: plant height (T1 = 18.22%, T2 = 20.41%, and T3 = 19.93% for bioclimatic zone 1; T1 = 16.78%, T2 = 20.71%, and T3 = 19.93% for bioclimatic zone 2), root length (T1 = 13.26%, T2 = 21.28%, and T3 = 19.38% for zone 1; T1 = 15.06%, T2 = 23.70%, and T3 = 19.20% for zone 2), number of nodules (T1 = 1162.57%, T2 = 1166.36%, and T3 = 1180.30% for zone 1; T1 = 1575%, T2 = 1616.5%, and T3 = 1608.25% for zone 2), size of nodules (T1 = 224.07%, T2 = 224.07%, and T3 = 208.33% for zone 1; T1 = 166.4%, T2 = 180%, and T3 = 140% for zone 2), and yield (T1 = 40.49%, T2 = 47.10%, and T3 = 45.45% for zone 1; T1 = 62.16%, T2 = 54.05%, and T3 = 58.55% for zone 2). R. tropici sp. UD5 peat inoculant formulation also increased the nitrogen concentration in leaves compared to the control (T1 = 3.75%, T2 = 1.12%, and T3 = 8.72%) in both bioclimatic zones. The findings of this study provide significant information on the positive effect of R. tropic UD5 strain peat inoculant application in the improvement of plant growth, development, and yield through the formation of nodules. Full article

Sugarcane crops typically have a high fertiliser nitrogen (N) input, with low N recovery efficiencies. Nitrogen is essential to crop productivity, but excess application can have negative environmental consequences. Despite the importance of coordinating N fertiliser input with crop N requirements, certain components of the sugarcane plant are typically not considered when evaluating N nutrition. The objective of this study was to establish which sugarcane crop components should be included in these evaluations given their impact on N mass accumulation and on fertiliser N recovery efficiencies. The respective biomass, N mass, and fertiliser N recovery efficiency were evaluated for sugarcane shoots, tillers, strawfall, root, and stool components over two experimental years, for fertilised (urea) and unfertilised treatments. The root component comprised, respectively, 57–65% of the aboveground N mass of fertilised sugarcane, and 74–104% of the unfertilised sugarcane. The sugarcane N requirements and uptake were shown to be more progressive over the growth-cycle when considering the strawfall and tiller components. This study emphasises the importance of evaluating belowground biomass in sugarcane N studies, and suggests that the tiller and strawfall components should also be considered when evaluating the evolution of N mass and fertiliser N recovery efficiency. Full article

Organic vegetable producers in Georgia, USA, utilize a range of amendments to supply nitrogen (N) for crop production. However, differences in soil type, fertilizers and environmental conditions can result in variability in N mineralization rates among commonly utilized organic fertilizers in the region. In this study, the effects of temperature on N mineralization from three commercial organic fertilizers [feather meal (FM), pelleted poultry litter (PPL) and a mixed organic fertilizer (MIX)] in two soil types from Georgia, USA (Cecil sandy clay loam and Tifton loamy sand) were evaluated for 120 d. Net N mineralization (Net N_min) varied with soil type, fertilizer and temperature. After 120 d, Net N_min from the FM fertilizer ranged between 41% and 77% of total organic N applied, the MIX fertilizer ranged between 26% and 59% and the PPL fertilizer ranged between 0% and 22% across all soil types and temperatures. Incubation at higher temperatures (20 °C and 30 °C) impacted Net N_min of FM fertilizer in the Tifton series soil. Temperature and soil type had a relatively minor impact on the potentially mineralizable N of the PPL and MIX fertilizers after 120 d of incubation; however, both factors impacted the rate of fertilizer release shortly after application, which could impact the synchronicity of N availability and plant uptake. Temperature-related differences in the mineralization of organic fertilizers may not be large enough to influence a grower’s decisions regarding N fertilizer inputs for vegetable crop production in the two soils. However, organic fertilizer source will likely play a significant role in N availability during the cropping season. Full article

In Northwestern Pakistan’s rice-based cropping systems, the prevalent reliance on inorganic nitrogen fertilizers (INF) has led to insufficient nitrogen (N) contributions from soil organic manures (OM). This study aims to evaluate the impact of organic sources (OS), including animal manures (AM) and crop residues (CR), on crop growth rates (CGR) in a rice-wheat rotation. A two-year field experiment involving hybrid rice (Oryza sativa L., Pukhraj) was conducted in Batkhela, Khyber Pakhtunkhwa. Various OS and inorganic-N (urea) combinations were applied, emphasizing their influence on CGR. The findings highlight poultry manure (PM) application as the most impactful on CGR, while wheat straw (WS) application resulted in the lowest CGR among the six OS investigated. Additionally, the use of AM showcased superior CGR compared to CR. In the initial year, the highest CGR occurred, with 75% of N sourced from urea and 25% from OS. In the second year, a balanced 50% N application from each source yielded the highest CGR. Urea and PM demonstrated the most robust CGR among OS combinations, while urea and WS yielded the lowest. Notably, onion leaves, a cost-effective option, delivered promising results comparable to berseem residues, indicating their potential as organic manure, especially in sulfur-deficient soils. These findings underscore the viability of onion residue management as a cost-effective alternative to ammonium sulfate fertilizers with global applicability. The abstract recommends promoting organic sources, particularly poultry manure and onion leaves, alongside inorganic-N fertilizers to enhance CGR and reduce dependence on costly alternatives. However, further research and field trials are necessary to explore the long-term impacts of these organic sources on soil health, nutrient cycling, and the sustainability of rice-based cropping systems in Northwestern Pakistan and beyond. In conclusion, this study investigates the influence of organic sources on CGR in rice-wheat rotations, emphasizing the superiority of poultry manure and onion leaves. The findings highlight cost-effective alternatives to conventional fertilizers, emphasizing the need for further research to validate long-term sustainability and applicability beyond the study area. Full article

Poor soil fertility, imbalanced fertilization, and limited use of organic fertilizer by farmers are significant limitations contributing to lower crop productivity in Nepal. Biochar-based organic fertilizers have been identified as efficient soil amendments to improve soil fertility and boost crop yields. In this study, we investigated the effects of biochar-based organic fertilizers on soil properties, fertilizing efficiency, and maize yields in low-productivity Nepalese soil. A field trial was conducted using a randomized complete block design comprising four treatments with three replications: (1) control without biochar (CK), (2) biochar (BC), (3) biochar + manure (BC+M), and (4) urine-enriched biochar + manure (BU+M). Recommended NPK fertilizers were applied to all plots, including the control. Urine-enriched biochar (BU+M) significantly improved soil pH, organic carbon, and soil nutrient levels (N, P, and K) compared to the control (CK). Total N, available P, and K were significantly higher (p < 0.05) in BU+M treatments compared to the other two biochar amendments (BC and BC+M). A similar trend was observed in the NPK uptake by plants, with BU+M outperforming CK, BC, and BC+M. Moreover, BU+M increased (p < 0.05) the partial factor of productivity of N (PFPN) and P (PFPP) compared to CK. The application of urine-enriched biochar resulted in a 62% increase in maize yield compared to the CK. These findings suggest that farmers can improve soil fertility and increase grain production with the use of urine-enriched biochar, which can be easily produced by farmers themselves using locally available feedstocks and cattle urine. Full article

Nitrate (NO₃⁻) and ammonium (NH₄⁺) are the primary forms of nitrogen (N) taken up by plants and can exhibit different effects on plant nutrition, photosynthesis, and growth. The objective was to investigate the influence of nitrate/ammonium proportions (%) on the nutritional status, photosynthetic parameters, and the development of Cedrela odorata seedlings after 150 days of cultivation. We tested six nitrate/ammonium ratios (100/0; 80/20; 60/40; 40/60; 20/80; and 0/100 of NO₃⁻ and NH₄⁺, respectively), plus a control treatment (without N supply). Based on the results, the species responds to the supply of N; however, the NO₃⁻ and NH₄⁺ proportions did not show any significant effect on plant growth. The deficiency of nitrogen (N) in Cedrela odorata decreases the photosynthetic rate, nutrient absorption, and initial growth of this species. Increasing the proportion of N in the form of nitrate inhibited the absorption of S (sulfur) but did not interfere with the accumulation of N, Ca (calcium), Mg (magnesium), Mn (manganese), Zn (zinc), B (boron), and Cu (copper). Cedrela odorata apparently does not distinguish between nitrate and ammonium in the N absorption process, since the proportions between these forms of N did not affect its photosynthetic rate, nutrient accumulation, or growth. Full article