Nitrogen, Volume 3, Issue 3 (September 2022) – 10 articles

The nitrogen applied (N-input) to cropping systems supports a high yield but generates major environmental pollution in the form of greenhouse gas (GHG) emissions and losses to land and water (N-surplus). This paper examines the scope to meet both GHG emission targets and zero N-surplus in high-intensity, mainly cereal, cropping in a region of the Atlantic zone in Europe. A regional survey provides background to crops grown at an experimental farm platform over a run of 5 years. For three main cereal crops under standard management (mean N-input 154 kg ha⁻¹), N-surplus remained well above zero (single year maximum 55% of N-input, five-year mean 27%), but was reduced to near zero by crop diversification (three cereals, one oilseed and one grain legume) and converted to a net nitrogen gain (+39 kg ha⁻¹, 25 crop-years) by implementing low nitrification management in all fields. Up-scaling N-input to the agricultural region indicated the government GHG emissions target of 70% of the 1990 mean could only be met with a combination of low nitrification management and raising the proportion of grain legumes from the current 1–2% to at least 10% at the expense of high-input cereals. Major strategic change in the agri-food system of the region is therefore needed to meet GHG emissions targets. Full article

In this study, a lab-scale fixed-film bio-media process was developed and operated to evaluate nitrogen removal from domestic sewage treatment plants. For nitrogen removal, the fixed-film bio-media process was applied in series with anaerobic, anoxic, and aerobic units in three separate reactors that were operated continuously at the same loading rates and hydraulic retention time. A biofilm separation bioreactor was developed for on-site domestic wastewater treatment and the bioreactor employed synthetic fiber modules so that the biomass could be completely attached to the media. In this paper, the performance of the fixed-film bio-media process with an average flow rate was evaluated before and after stabilization of the treatment system for nitrogen removal. The results show that the fixed-film bio-media process was successful for improved nitrogen removal from secondary and tertiary treated wastewater, with a 77% decrease in the total nitrogen discharge. Rapid nitrification could be achieved, and denitrification was performed in the anoxic filter with external carbon supplements during tertiary treated sewage wastewater. However, aeration was supplied after the stabilization process to achieve the nitrification and denitrification reaction for nitrogen removal. However, stable aeration supply could enhance nitrification at moderate temperature with benefits from complete retention of nitrifying bacteria within the system due to bio-media separation. Full article

An online calculator is available to determine economic optimum nitrogen rate (EONR) for maize (Zea mays L.) production in the USA Corn Belt. For Minnesota, this calculator considers nitrogen (N) fertilizer cost, maize grain price and crop history, and produces a statewide N rate based on maximum economic return to N (MRTN). However, a clear precipitation and temperature gradient, and soil heterogeneity across the state, and recent changes in fertilizer cost and maize grain price require the comparison of EONR from this calculator with results from field study. The objectives of this research were to determine the agronomic and economic benefits of basal and split application of N fertilizer on maize grain yield and yield components and compare EONR from field study with N recommendation from the online calculator. The nitrogen fertilizer rate for the field study ranged from 0 to 224 kg N ha⁻¹, either split or all applied at planting. The results showed that there were no interaction effects of N rate by time or N rate by year on maize grain yield. Maize grain yield had a quadratic response to N rate, and agronomic maximum grain yield peaked at 205 kg N ha⁻¹. The EONR from the field study was 168 kg N ha⁻¹ and it remained stable under a wide range of economic analysis scenarios with net benefit reaching up to 2474 USD ha⁻¹. The N rate from the online calculator at MRTN was 151 kg N ha⁻¹ and this rate may cause N deficiency in maize resulting in a yield penalty compared with the field study results. The field study was performed under specific soil and climatic conditions. Therefore, extensive research under various soil types, agronomic management practices and climatic conditions is warranted to evaluate the online calculator performance and its reliability as a precision tool for N fertilizer management in maize production. Full article

Understanding the stoichiometry of nitrogen (N) and phosphorus (P) plays a pivotal role in the ecological restoration of degraded landscapes. Here, the N and P limitation and stoichiometry of dominant tree species in mine-disturbed ultramafic areas in the Southern Philippines are reported. Field surveys revealed that out of a total of 1491 trees/shrubs recorded from all quadrats, comprising 22 native and 9 non-native species, there were six tree species (native: Alstonia macrophylla Wallich., Buchanania arborescens Blume., Syzygium sp., and non-native: Casuarina equisetifolia L., Terminalia catappa L. and Acacia mangium Wild.) that were found dominant, having >10% relative abundance. Significant differences (p < 0.01) in the leaf N and leaf P content among these species were observed, where C.equisetifolia (due to N fixation ability) and T. catappa had the highest values, respectively. These did not, however, translate to statistical differences in the leaf N:P ratios either in individual species or when grouped by origin (native or non-native). Interestingly, all dominant tree species revealed very low leaf N:P ratios (<4), suggesting that N rather than P limits the productivity in mine-disturbed ultramafic areas, which is also confirmed by low levels of leaf N (<2.0%). Results further revealed a poor correlation between leaf N and leaf N:P ratios (r = 0.13; p = 0.60), while leaf P (r = 0.49; p < 0.05) revealed otherwise, reinforcing that P is not a limiting factor as also shown in high levels of leaf P (>0.20%). Despite the N-limitation, B. arborescens, C. equisetifolia, and T. catappa had the highest leaf N and P content, suggesting their higher suitability for revegetation of the sites. These findings warrant further verification taking into account the plant physiology, phenology, and soil nutrient availability in natural, degraded, and rehabilitated ultramafic environments. Full article

Permafrost-affected tundra soils are large carbon (C) and nitrogen (N) reservoirs. However, N is largely bound in soil organic matter (SOM), and ecosystems generally have low N availability. Therefore, microbial induced N-cycling processes and N losses were considered negligible. Recent studies show that microbial N processing rates, inorganic N availability, and lateral N losses from thawing permafrost increase when vegetation cover is disturbed, resulting in reduced N uptake or increased N input from thawing permafrost. In this review, we describe currently known N hotspots, particularly bare patches in permafrost peatland or permafrost soils affected by thermokarst, and their microbiogeochemical characteristics, and present evidence for previously unrecorded N hotspots in the tundra. We summarize the current understanding of microbial N cycling processes that promote the release of the potent greenhouse gas (GHG) nitrous oxide (N₂O) and the translocation of inorganic N from terrestrial into aquatic ecosystems. We suggest that certain soil characteristics and microbial traits can be used as indicators of N availability and N losses. Identifying N hotspots in permafrost soils is key to assessing the potential for N release from permafrost-affected soils under global warming, as well as the impact of increased N availability on emissions of carbon-containing GHGs. Full article

Optimizing root system architecture is a strategy for coping with soil fertility, such as low nitrogen input. An ample number of Arabidopsis thaliana natural accessions have set the foundation for studies on mechanisms that regulate root morphology. This report compares the Columbia-0 (Col-0) reference and Pyla-1 (Pyl-1) from a coastal zone in France, known for having the tallest sand dune in Europe. Seedlings were grown on vertical agar plates with different nitrate concentrations. The lateral root outgrowth of Col-0 was stimulated under mild depletion and repressed under nitrate enrichment. The Pyl-1 produced a long primary root and any or very few visible lateral roots across the nitrate supplies. This could reflect an adaptation to sandy soil conditions, where the primary root grows downwards to the lower strata to take up water and mobile soil resources without elongating the lateral roots. Microscopic observations revealed similar densities of lateral root primordia in both accessions. The Pyl-1 maintained the ability to initiate lateral root primordia. However, the post-initiation events seemed to be critical in modulating the lateral-root-less phenotype. In Pyl-1, the emergence of primordia through the primary root tissues was slowed, and newly formed lateral roots stayed stunted. In brief, Pyl-1 is a fascinating genotype for studying the nutritional influences on lateral root development. Full article

Drained cultivated peatlands have been an essential agricultural resource for many years. To slow and reduce the degradation of these soils, which increases with drainage, the use of plant-based amendments (straw, wood chips, and biochar) has been proposed. Literature on the effects of such amendments in cultivated peatlands is scarce, and questions have been raised regarding the impact of this practice on nutrient cycling, particularly nitrogen (N) dynamics. By means of a six-month incubation experiment, this study assessed the effects of four plant-based amendments (biochar, a forest mix, willow, and miscanthus) on the release kinetics of water-soluble N pools (mineral and organic) in two histosols of differing degrees of decomposition (Haplosaprist and Haplohemist). The amendment rate was set at 15 Mg ha⁻¹ on a dry weight basis. The N release kinetics were significantly impacted by soil type and amendment. Miscanthus and willow were the amendments that most reduced the release of soluble organic N (SON) and mineral N (minN). The addition of plant-based amendments reduced the total amount of released N pools during the incubation (cumulative N pools) by 50.3 to 355.2 mg kg⁻¹, depending on the soil type, the N pool, and the type of amendment. A significant relationship was found between microbial biomass N, urease activity, and the cumulative N at the end of the incubation. The results showed that the input of plant-based amendments in cultivated peatland decreases N release, which could have a beneficial impact by decreasing N leaching; however, it could also restrict crop growth. Further research is needed to fully assess the impact of such amendments used in cultivated peatlands on N and on C fluxes at the soil–plant and soil–atmosphere interfaces to determine if they constitute a long-term solution for more sustainable agriculture. Full article

Inherent low soil fertility status limits productivity of rice in the lowland ecologies in Northern Ghana. Combining organic and inorganic nitrogen fertilizers could help to maintain the fertility of lowland soils for rice production. A screen house pot experiment was carried out to investigate the combined effect of biochar compost and inorganic nitrogen fertilizer on the nitrogen uptake and agronomic performance of rice plants grown on an eutric gleysol lowland soil. Inorganic nitrogen fertilizer alone and its combinations with different types of biochar compost (based on the proportions of biochar and compost) were used as treatment. A control (unamended soil) was also included. The incorporation of biochar compost and inorganic nitrogen fertilizer improved the growth parameters and yield components of rice plants. The combination of biochar compost and inorganic nitrogen fertilizer was also found to improve nitrogen uptake in rice plants. This practice could be the most likely viable option for alleviating lowland soil fertility issues and increasing rice productivity in Northern Ghana. Full article

The reaction of molecular nitrogen with molecular hydrogen was simulated using ab initio molecular dynamics. The reaction was catalyzed by the addition of bulk lithium and oxygen. As is known from the experiment, the limiting step is the breaking of the nitrogen–nitrogen triple bond. We observed a mechanism that has not been discussed before: one of the nitrogen atoms of a nitrogen molecule is absorbed by the lithium bulk, whereas the other nitrogen atom reacts with hydrogen. Adding oxygen leads to a dominating reaction of oxygen with the lithium surface. The oxygen molecules break easily into single atoms and are, in part, absorbed by the lithium structure. Part of them remains on the surface and reacts with hydrogen. In this way, hydrogen is activated and can, in turn, react easily with molecular nitrogen. The overall reactivity as observed in the ab initio simulations reflects the extremely low density of lithium. Interstitial sites are readily occupied, leading to oxide and nitride structures. Full article