Biological Nitrification Inhibition Research Articles

Benefits of biological nitrification inhibition of Leymus chinensis under alkaline stress: the regulatory function of ammonium-N exceeds its nutritional function.

The production of root exudates with biological nitrification inhibition (BNI) effects is a strategy adopted by ammonium-N () tolerant plant species that occur in N-limited environments. Most knowledge on BNI comes from plant species that occur in acidic soils. Here, combining field sampling and laboratory culture, we assessed the BNI-capacity of Leymus chinensis, a dominant grass species in alkaline grasslands in eastern Asia, and explored why L. chinensis has BNI ability. The results showed that L. chinensis has strong BNI-capacity. At a concentration of 1 mg mL-1, L. chinensis' root exudates inhibited nitrification in soils influenced by Puccinellia tenuiflora by 72.44%, while DCD only inhibited it by 68.29%. The nitrification potential of the soil of L. chinensis community was only 53% of the P. tenuiflora or 41% of the Suaeda salsa community. We also showed that the supply of driven by L. chinensis' BNI can meet its requirements . In addition, can enhance plant adaptation to alkaline stress by regulating pH, and in turn, the uptake of nitrate-N (). We further demonstrated that the regulatory function of is greater than its nutritional function in alkaline environment. The results offer novel insights into how L. chinensis adapts to high pH and nutrient deficiency stress by secreting BNIs, and reveal, for the first time, differences in the functional roles of and in growth and adaptation under alkaline conditions in a grass species.

Does subjecting plants to water stress enhance biological nitrification inhibition potential of rice?

Biological nitrification inhibition (BNI) is a trait that could improve nitrogen-use efficiency of a crop. We studied varietal differences in BNI potential of rice at the vegetative phase when plants were subjected to water stress. We obtained water-soluble root exudates (RE) and water-extracts of crushed root tissues (RT) from two-week-old seedlings of five rice cultivars grown continuously under adequate water or under water stress and assessed their ability to suppress the activity of Nitrosomonas europaea and the growth of lettuce seedlings. We also investigated how growing rice under continuously saturated (TC) and unsaturated (TU) soil moisture conditions affected potential nitrification rate (PNR) and community structure of ammonia-oxidizing bacteria (AOB) in the rhizosphere compared with bulk soil. We observed that only RT at ≥ 0.50 mg ml−1 suppressed the activity of N. europaea with significant (p < 0.05) differences among rice cultivars. Subjecting rice cultivars PI312777 and PI338046 to water stress significantly (p < 0.05) increased BNI of RT. Inhibition of lettuce root growth by RT was strongly correlated with its BNI (r = 0.83, p < 0.05). In T-RFLP profiles of AOB, the relative abundance of T-RF R205 was lower in TU than in TC in all cultivars except Rexmont. The rice cultivars studied produced compounds that could inhibit ammonia oxidizers, but the degree of BNI differed based on the moisture stress experienced by the crop. Lineages of rice cultivars with known allelopathic potential would be promising candidates to consider for BNI potential.

Intercropping with BNI-sorghum benefits neighbouring maize productivity and mitigates soil nitrification and N2O emission

Sorghum (Sorghum bicolor) roots are well-known for the release of Biological Nitrification Inhibitors (BNIs), such as sorgoleone (SGLN) and methyl 3–4-hydroxyphenyl propionate (MHPP). However, the deployment of sorghums with BNIs in agriculture practices has not been widely investigated and evaluated. In this study, sorghum and maize were intercropped in field and pot cultivation to investigate the Biological Nitrification Inhibition (BNI) effect of sorghum on the productivity of both crops and soil nitrification. Inorganic N content (NO3– and NH4+), N2O emission, and the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in soil were analyzed. The results showed intercropping with sorghum have the potential to improve crop productivity, as indicated by the Land Equivalent Ratio greater than 1.0. Intercropping with sorghum reduced the transformation rate of NH4+ to NO3– in soils and the emission of N2O, as compared to monoculture of maize. Additionally, the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) under intercropping mode were reduced by 41% and 28% in field trials, and reduced by 59% and 23% in pot experiments, respectively. Incubation of the same soils with SGLN and/or MHPP showed that the combined treatment of both BNIs strongly inhibited nitrification and N2O emission, along with lower AOB and AOA abundances, as compared with those under the sole treatment of SGLN or MHPP. Our results indicated that the root exudates of sorghum play a significant role in inhibiting soil nitrification due to the overlapping or amplified effect of various BNIs, which contribute to the nitrogen nutrition of the neighbouring crops under intercropping mode. Therefore, intercropping with BNI crops provides an eco-friendly strategy to improve crop production with reduced N2O emission.

Exploiting crop genotype-specific root-soil interactions to enhance agronomic efficiency

Challenges of soil degradation and changing climate pose major threats to food security in many parts of the world, and new approaches are required to close yield and nutrition gaps through enhanced agronomic efficiency. Combined use of mineral fertilizers, organic inputs, improved germplasm and adaptation of these practices to local contexts through improved agronomy can promote efficiency whilst building stocks of soil organic matter (SOM). Within this framework, recent attention has turned to the nature of plant-soil interactions to increase response to mineral fertilizer inputs through utilisation of nutrients from SOM that are replenished through management. This utilisation has been shown in barley and maize to vary with genotype and to be related to root physiological traits associated with rhizodeposition. The identification of candidate genes associated with rhizodeposition takes this a step closer towards the possibility of breeding for sustainability. Here we discuss this potential and feasibility in the context of maize cropping systems, and explore the potential for a combined approach that optimises utilisation of SOM nutrients together with enhanced biological nitrification inhibition to further improve agronomic efficiency.

Seed treatment with plant-defense elicitors decreases the abundance of ammonia oxidizers associated with winter wheat roots

Priming with elicitors, including phytohormones, is known to induce physiological changes in plants that affect resource allocation and nutrient uptake strategies. However, effects of these changes on belowground microbial communities, particularly those involved in nitrogen (N) transformations, remain poorly characterized. Here, we tested the hypothesis that treating seeds with elicitors would affect N-transforming communities associated to roots and rhizosphere, influencing soil N availability and thus plant performance. We measured the effects of treating winter wheat seeds with cis-jasmone, methyl jasmonate or methyl salicylate on plant traits and on the genetic potential for ammonia oxidation by ammonia-oxidizing bacteria (AOB) and archaea (AOA), the initial inorganic N transformation process resulting in N loss. Elicitors reduced the genetic potential for ammonia oxidation by AOB in root-associated microbial communities and increased traits reflecting N uptake in winter wheat. Proposed mechanisms include increased exploitative competition for ammonium, limiting substrate availability for microorganisms, and induced biological nitrification inhibition capacity actively suppressing ammonia oxidizers. There were minor effects on the composition of the AOB and AOA communities, but an indicator species analysis showed that several AOB and a few AOA genotypes were indicative of elicitor treatments. Seed treatment with elicitors may represent an overlooked strategy to minimize nitrification to mitigate N losses from arable soils.

Non-native Brachiaria humidicola with biological nitrification inhibition capacity stimulates in situ grassland N2O emissions.

Brachiaria humidicola, a tropical grass, could release root exudates with biological nitrification inhibition (BNI) capacity and reduce soil nitrous oxide (N2O) emissions from grasslands. However, evidence of the reduction effect in situ in tropical grasslands in China is lacking. To evaluate the potential effects of B. humidicola on soil N2O emissions, a 2-year (2015-2017) field experiment was established in a Latosol and included eight treatments, consisting of two pastures, non-native B. humidicola and a native grass, Eremochloa ophiuroide, with four nitrogen (N) application rates. The annual urea application rates were 0, 150, 300, and 450 kg N ha-1. The average 2-year E. ophiuroides biomass with and without N fertilization were 9.07-11.45 and 7.34 t ha-1, respectively, and corresponding values for B. humidicola increased to 31.97-39.07 and 29.54 t ha-1, respectively. The N-use efficiencies under E. ophiuroide and B. humidicola cultivation were 9.3-12.0 and 35.5-39.4%, respectively. Annual N2O emissions in the E. ophiuroides and B. humidicola fields were 1.37 and 2.83 kg N2O-N ha-1, respectively, under no N fertilization, and 1.54-3.46 and 4.30-7.19 kg N2O-N ha-1, respectively, under N fertilization. According to the results, B. humidicola cultivation increased soil N2O emissions, especially under N fertilization. This is because B. humidicola exhibited the more effective stimulation effect on N2O production via denitrification primarily due to increased soil organic carbon and exudates than the inhibition effect on N2O production via autotrophic nitrification. Annual yield-scaled N2O emissions in the B. humidicola treatment were 93.02-183.12 mg N2O-N kg-1 biomass, which were significantly lower than those in the E. ophiuroides treatment. Overall, our results suggest that cultivation of the non-native grass, B. humidicola with BNI capacity, increased soil N2O emissions, while decreasing yield-scaled N2O emissions, when compared with native grass cultivation.

An optimized hydroponic pipeline for large-scale identification of wheat genotypes with resilient biological nitrification inhibition activity.

Several plant species have been reported to inhibit nitrification via their root exudates, the so-called biological nitrification inhibition (BNI). Given the potential of BNI-producing plants to sustainably mitigate N losses in agrosystems, identification of BNI activity in existing germplasms is of paramount importance. A hydroponic system was combined with an optimized Nitrosomonas europaea-based bioassay to determine the BNI activity of root exudates. The pipeline allows collecting and processing hundreds of root exudates simultaneously. An additional assay was established to assess the potential bactericide effect of the root exudates. The pipeline was used to unravel the impact of developmental stage, temperature and osmotic stress on the BNI trait in selected wheat genotypes. Biological nitrification inhibition activity appeared consistently higher in wheat at the pretillering stage as compared to the tillering stage. While low-temperatures did not alter BNI activities in root exudates, osmotic stress appeared to change the BNI activity in a genotype-dependent manner. Further analysis of Nitrosomonas culture after pre-exposure to root exudates suggested that BNI activity has no or limited bactericide effects. The present pipeline will be instrumental to further investigating the dynamics of BNI activity and to uncover the diversity of the BNI trait in plant species.

Soil moisture modulates biological nitrification inhibitors release in sorghum plants

Background and aimsSorghum (Sorghum bicolor) is able to exude allelochemicals with biological nitrification inhibition (BNI) capacity. Therefore, sorghum might be an option as cover crop since its BNI ability may reduce N pollution in the following crop due to a decreased nitrification. However, BNI exudation is related to the physiological state and development of the plant, so abiotic stresses such as drought might modify the rate of BNI exudation. Hence, the objective was to determine the effect of drought stress on sorghum plants’ BNI release.MethodsThe residual effects of sorghum crops over ammonia-oxidizing bacteria (AOB) were monitored in a 3-year field experiment. In a controlled-conditions experiment, sorghum plants were grown under Watered (60% WFPS) or Moderate drought (30% WFPS) conditions, and fertilized with ammonium sulphate (A), ammonium sulphate + DMPP (A+D), or potassium nitrate (KNO3−). Soil mineral N was determined, and AOB populations were quantified. Additionally, plant biomass, isotopic discrimination of N and C, and photosynthetic parameters were measured in sorghum plants.ResultsIn the driest year, sorghum was able to reduce the AOB relative abundance by 50% at field conditions. In the plant-soil microcosm, drought stress reduced leaf photosynthetic parameters, which had an impact on plant biomass. Under these conditions, sorghum plants exposed to Moderate drought reduced the AOB abundance of A treatment by 25% compared to Watered treatment.ConclusionThe release of BNI by sorghum under limited water conditions might ensure high soil NH4+-N pool for crop uptake due to a reduction of nitrifying microorganisms.

PANOMICS at the interface of root-soil microbiome and BNI.

Nitrification and denitrification are soil biological processes responsible for large nitrogen losses from agricultural soils and generation of the greenhouse gas (GHG) N2O. Increased use of nitrogen fertilizer and the resulting decline in nitrogen use efficiency (NUE) are a major concern in agroecosystems. This nitrogen cycle in the rhizosphere is influenced by an intimate soil microbiome-root exudate interaction and biological nitrification inhibition (BNI). A PANOMICS approach can dissect these processes. We review breakthroughs in this area, including identification and characterization of root exudates by metabolomics and proteomics, which facilitate better understanding of belowground chemical communications and help identify new biological nitrification inhibitors (BNIs). We also address challenges for advancing the understanding of the role root exudates play in biotic and abiotic stresses.

Brachiaria humidicola Cultivation Enhances Soil Nitrous Oxide Emissions from Tropical Grassland by Promoting the Denitrification Potential: A 15N Tracing Study

Biological nitrification inhibition (BNI) in the tropical grass Brachiaria humidicola could reduce net nitrification rates and nitrous oxide (N2O) emissions in soil. To determine the effect on gross nitrogen (N) transformation processes and N2O emissions, an incubation experiment was carried out using 15N tracing of soil samples collected following 2 years of cultivation with high-BNI Brachiaria and native non-BNI grass Eremochloa ophiuroide. Brachiaria enhanced the soil ammonium (NH4+) supply by increasing gross mineralization of recalcitrant organic N and the net release of soil-adsorbed NH4+, while reducing the NH4+ immobilization rate. Compared with Eremochloa, Brachiaria decreased soil gross nitrification by 37.5% and N2O production via autotrophic nitrification by 14.7%. In contrast, Brachiaria cultivation significantly increased soil N2O emissions from 90.42 μg N2O-N kg−1 under Eremochloa cultivation to 144.31 μg N2O-N kg−1 during the 16-day incubation (p &lt; 0.05). This was primarily due to a 59.6% increase in N2O production during denitrification via enhanced soil organic C, notably labile organic C, which exceeded the mitigated N2O production rate during nitrification. The contribution of denitrification to emitted N2O also increased from 9.7% under Eremochloa cultivation to 47.1% in the Brachiaria soil. These findings confirmed that Brachiaria reduces soil gross nitrification and N2O production via autotrophic nitrification while efficiently stimulating denitrification, thereby increasing soil N2O emissions.

Biological nitrification inhibitor-trait enhances nitrogen uptake by suppressing nitrifier activity and improves ammonium assimilation in two elite wheat varieties.

Synthetic nitrification inhibitors (SNI) and biological nitrification inhibitors (BNI) are promising tools to limit nitrogen (N) pollution derived from agriculture. Modern wheat cultivars lack sufficient capacity to exude BNIs, but, fortunately, the chromosome region (Lr#n-SA) controlling BNI production in Leymus racemosus, a wild relative of wheat, was introduced into two elite wheat cultivars, ROELFS and MUNAL. Using BNI-isogenic-lines could become a cost-effective, farmer-friendly, and globally scalable technology that incentivizes more sustainable and environmentally friendly agronomic practices. We studied how BNI-trait improves N-uptake, and N-use, both with ammonium and nitrate fertilization, analysing representative indicators of soil nitrification inhibition, and plant metabolism. Synthesizing BNI molecules did not mean a metabolic cost since Control and BNI-isogenic-lines from ROELFS and MUNAL presented similar agronomic performance and plant development. In the soil, ROELFS-BNI and MUNAL-BNI plants decreased ammonia-oxidizing bacteria (AOB) abundance by 60% and 45% respectively, delaying ammonium oxidation without reducing the total abundance of bacteria or archaea. Interestingly, BNI-trait presented a synergistic effect with SNIs since made it also possible to decrease the AOA abundance. ROELFS-BNI and MUNAL-BNI plants showed a reduced leaf nitrate reductase (NR) activity as a consequence of lower soil formation and a higher amino acid content compared to BNI-trait lacking lines, indicating that the transfer of Lr#-SA was able to induce a higher capacity to assimilate ammonium. Moreover, the impact of the BNI-trait in wheat cultivars was also noticeable for nitrate fertilization, with improved N absorption, and therefore, reducing soil nitrate content.

Two newly-identified biological nitrification inhibitors in Suaeda salsa: Synthetic pathways and influencing mechanisms

Our research aimed at finding potential BNI resources and exploring the action mechanisms by multiomics. Here, we presented that the Suaeda salsa leaf extracts of both red and green phenotypes from the Yellow River Delta of China showed strong nitrification inhibition ability and selected oxalic acid (OA, molecular weight: 90) and protocatechuic aldehyde (PA, molecular weight: 138) as novel BNIs, then constructed the synthetic pathways and selected some key genes that may influence the synthesis of these two BNIs; and the inhibition mechanisms of these two BNIs on Nitrosomonas europaea were also revealed by performing transcriptomics and metabolomics; and we also found that PA had a nitrification inhibition effect among saline-alkali soil, cinnamon soil and red soil, and the inhibition effect in saline-alkali soil was the most effective, while OA only showed nitrification inhibition effect in red soil. Our findings pointed out a novel plant species as potential BNI resource, and provided opportunities for the design of novel fertilizers, which could improve the crop N utilization efficiency and reduce N loss in agricultural systems.

Phenotyping of Urochloa humidicola grass hybrids for agronomic and environmental performance in the Piedmont region of the Orinoquian savannas of Colombia

AbstractIn the low fertility acid soils of the Orinoquian savannas of Colombia, Urochloa humidicola cv. Tully or Humidicola is one of the most widely planted tropical forage grasses for improving livestock productivity. Low nutritional quality of this grass limits sustainable livestock production in this region. In this study, we conducted a phenotypic evaluation under field and greenhouse conditions of one of the first hybrid populations of U. humidicola generated from the forage breeding program of CIAT. Our objective was to identify a set of new hybrids of U. humidicola that combine improved productivity and nutritional quality plus the biological nitrification inhibition (BNI) trait/ability to reduce nitrogen (N) losses via leaching and nitrous oxide (N2O) emissions. To this end, we tested 118 hybrids (planted in pots) in the greenhouse for over 6 months and measured potential nitrification rates (NR) using soil microcosm incubation. NR values observed ranged from 0.27 to 5.75 mg N‐NO3− kg soil−1 day−1. Later, 12 hybrids with different levels of NR were selected and field‐tested in the Orinoquia region over a 4 years period (2013–2017) for dry matter production, nutrition quality (crude protein, in vitro digestibility and fibres content) and NR in each year. In the rainy season of 2018, two hybrids with superior agronomic performance and contrasting field level NR (Uh08/1149 and 0450) were subjected to analysis of soil‐borne N2O emissions after fertilization during 13 days. The NR values recorded were not directly correlated with the forage quality parameters evaluated, however, the two grasses with the lowest NR values were among those with the highest biomass production, crude protein content, and N uptake. The grass hybrid Uh08/1149 and the germplasm accession CIAT 16888 were found as materials with superior forage value, with production of 14.1 and 14.6 tons dry matter ha−1 year−1 (up to 8% higher than the cv. Tully), crude protein of 11.5 and 9.1% per cut (up to 20% higher than the cv. Tully), and N uptake of 31.6 and 25.7 kg N ha−1 cut−1 (up to 30% higher than the cv. Tully). Additionally, these two grasses are likely to exhibit high‐BNI ability, with potential to improve N use efficiency in managed pastures.

Arbuscular Mycorrhiza and Nitrification: Disentangling Processes and Players by Using Synthetic Nitrification Inhibitors.

ABSTRACTBoth plants and their associated arbuscular mycorrhizal (AM) fungi require nitrogen (N) for their metabolism and growth. This can result in both positive and negative effects of AM symbiosis on plant N nutrition. Either way, the demand for and efficiency of uptake of mineral N from the soil by mycorrhizal plants are often higher than those of nonmycorrhizal plants. In consequence, the symbiosis of plants with AM fungi exerts important feedbacks on soil processes in general and N cycling in particular. Here, we investigated the role of the AM symbiosis in N uptake by Andropogon gerardii from an organic source (15N-labeled plant litter) that was provided beyond the direct reach of roots. In addition, we tested if pathways of 15N uptake from litter by mycorrhizal hyphae were affected by amendment with different synthetic nitrification inhibitors (dicyandiamide [DCD], nitrapyrin, or 3,4-dimethylpyrazole phosphate [DMPP]). We observed efficient acquisition of 15N by mycorrhizal plants through the mycorrhizal pathway, independent of nitrification inhibitors. These results were in stark contrast to 15N uptake by nonmycorrhizal plants, which generally took up much less 15N, and the uptake was further suppressed by nitrapyrin or DMPP amendments. Quantitative real-time PCR analyses showed that bacteria involved in the rate-limiting step of nitrification, ammonia oxidation, were suppressed similarly by the presence of AM fungi and by nitrapyrin or DMPP (but not DCD) amendments. On the other hand, abundances of ammonia-oxidizing archaea were not strongly affected by either the AM fungi or the nitrification inhibitors.IMPORTANCE Nitrogen is one of the most important elements for all life on Earth. In soil, N is present in various chemical forms and is fiercely competed for by various microorganisms as well as plants. Here, we address competition for reduced N (ammonia) between ammonia-oxidizing prokaryotes and arbuscular mycorrhizal fungi. These two functionally important groups of soil microorganisms, participating in nitrification and plant mineral nutrient acquisition, respectively, have often been studied in separation in the past. Here, we showed, using various biochemical and molecular approaches, that the fungi systematically suppress ammonia-oxidizing bacteria to an extent similar to that of some widely used synthetic nitrification inhibitors, whereas they have only a limited impact on abundance of ammonia-oxidizing archaea. Competition for free ammonium is a plausible explanation here, but it is also possible that the fungi produce some compounds acting as so-called biological nitrification inhibitors.

Seasonal effects reveal potential mitigation strategies to reduce N2O emission and N leaching from grassland swards of differing composition (grass monoculture, grass/clover and multispecies)

Multispecies pastures containing grasses, N-fixing legumes and forage herbs can maintain high herbage dry matter (DM) yield, while reducing the need for fertiliser N inputs thus potentially reducing harmful N losses such as nitrous oxide (N2O) emission and nitrate (NO3−) leaching to the wider environment. However, our understanding of these processes in grassland swards of contrasting composition is still very limited. A lysimeter experiment was carried out over 12 months to test the hypotheses that (1) cumulative and (2) seasonal N2O emission and N leaching would be highest from the Perennial Ryegrass only (PRG, 250 kg N ha-1 yr-1) treatment compared to three other treatments; Perennial Ryegrass and Low White Clover (PRG+LWC, 90 kg N ha-1 yr-1), Perennial Ryegrass and High White Clover (PRG+HWC, 0 kg N ha-1 yr-1) and Perennial Ryegrass, White Clover and Ribwort Plantain (PRG+WC+P, 45 kg N ha-1 yr-1) and (3) that the soil N cycling pathways (nitrification/denitrification) linked to these N losses would be different between treatments. Cumulative N2O emissions (2.74–3.25 kg N2O-N ha-1), leached N (10.91–13.70 kg N ha-1), DM yields (5083–5493 kg DM ha-1 yr-1) and N uptake (122–169 kg N ha-1 yr-1) were not significantly different between treatments. Nitrogen yield scaled N2O emissions were significantly lower from all other treatments compared to the high fertiliser N input PRG monoculture. A significant interaction between treatment and season showed that in Spring, N2O emission was significantly higher from PRG (1.39 kg N2O-N ha-1) and PRG+LWC (1.19 kg N2O-N ha-1) than PRG+HWC (0.81 kg N2O-N ha-1) and PRG+WC+P (0.85 kg N2O-N ha-1). This result was linked to a numerically lower fraction of nitrification (FN) for PRG+WC+P potentially indicating that biological nitrification inhibition associated with ribwort plantain could lessen N2O emissions. This study demonstrates some of the environmental benefits of grassland management systems that require less intensive chemical fertiliser N input.

Soil carbon stocks and nitrous oxide emissions of pasture systems in Orinoquía region of Colombia: Potential for developing land-based greenhouse gas removal projects

Improving grassland conditions under grazing has the potential not only to accumulate carbon in soils, but also to reduce nitrous oxide (N2O) emissions from animal urine deposition. However, measurements in developing countries are still scarce. In the Orinoquia region, permanent grasslands (PG; this unimproved, native pasture is considered as at some state of degradation) based on unimproved grasses are found due to extensive, inefficient grazing combined with annual burning of pastures. We hypothesized that, compared to PG, improved grasslands (IG) managed through rotational grazing of introduced, productive and deep-rooted pasture grass species promote soil organic carbon (SOC) accumulation and reduce N2O emission from urine deposited by grazing cattle. We determined SOC and N2O emissions from urine deposited on soils in an area of PG and in a 6.5 year-old IG area of Urochloa (Syn. Brachiaria) humidicola grass pasture in a beef cattle ranch in Orinoquía region (Colombia). In both areas, we sampled soil for chemical/physical analysis, and measured N2O emissions by simulating urine deposition over 21 days. We applied two-way analysis of variance considering pasture type and soil depth as fixed factors. Estimated SOC stocks (0–100 cm) were in the range of 224.8 Mg C ha−1 for the PG and 259.0 Mg C ha−1 for the IG, with a significant (p &amp;lt; 0.05) average accumulation of 2.0 Mg C ha−1 y−1 (0–20 cm) in the IG area. N2O emissions were 10 times lower in the IG compared to the PG. The introduction of U. humidicola grass influenced SOC accumulation probably through its more abundant root system and greater turnover together with higher (14%) forage dry matter production compared to PG. The reduced N2O emissions observed from urine patches in IG were attributed to biological nitrification inhibition ability and greater nitrogen uptake of U. humidicola grass. Compared to the reference default value of IPCC for, the SOC stock found in PG was almost 40% higher, whereas the N2O emission factor (5%) was within the uncertainty range (0.7–6%). The Orinoquía region shows significant potential for SOC storage and reduced N2O emissions in improved pastures with deep root systems. Thus, scaling the implementation of land-based SOC storage practices/projects could significantly contribute to reducing net emissions from beef production from this region.

Effects of biological nitrification inhibitor in regulating NH3 volatilization and fertilizer nitrogen recovery efficiency in soils under rice cropping.

Biological nitrification inhibitors are exudates from plant roots that can inhibit nitrification, and have advantages over traditional synthetic nitrification inhibitors. However, our understanding of the effects of biological nitrification inhibitors on nitrogen (N) loss and fertilizer N recovery efficiency in staple food crops is limited. In this study, acidic and calcareous soils were selected, and rice growth pot experiments were conducted to investigate the effects of the biological nitrification inhibitor, methyl 3-(4-hydroxyphenyl) propionate (MHPP) and/or a urease inhibitor (N-[n-butyl], thiophosphoric triamide [NBPT]) on NH3 volatilization, N leaching, fertilizer N recovery efficiency under a 20% reduction of the conventional N application rate. Our results show that rice yield and fertilizer N recovery efficiency were more sensitive to reduced N application in the calcareous soil than in the acidic soil. MHPP stimulated NH3 volatilization by 13.2% in acidic soil and 9.06% in calcareous soil but these results were not significant. In the calcareous soil, fertilizer N recovery efficiency significantly increased by 19.3% and 44.4% in the MHPP and NBPT+MHPP groups, respectively, relative to the reduced N treatment, and the rice yield increased by 16.7% in the NBPT+MHPP treatment (P < 0.05). However, such effects were not significant in the acidic soil. MHPP exerted a significant effect on soil ammonia oxidizers, and the response of abundance and community structure of ammonia-oxidizing archaea, ammonia-oxidizing bacteria, and total bacteria to MHPP depended on the soil type. MHPP+NBPT reduced NH3 volatilization, N leaching, and maintaining rice yield for a 20% reduction in conventional N fertilizer application rate. This could represent a viable strategy for more sustainable rice production, despite the inevitable increase in cost for famers.

Current Scenario and Perspectives for Nitrogen Fertilization Strategies on Tropical Perennial Grass Pastures: A Review

Traditional Nitrogen (N) fertilization practices for tropical perennial grass are still based on annual amounts, following flat N rates instalments. This strategy does not consider variations in climatic conditions along the growing season, their impacts on the plant’s demand and the soil N availability. At regrowth cycles where the amount of soil N released from mineralization or through animal excreta surpass the plant’s demand, most of the N may be lost (as ammonia, nitrate, and nitrous oxide), increasing production costs and environmental pollution. This paper examines current N fertilization and discusses possible gaps in knowledge for the definition of more precise fertilization guidelines in pasture-based livestock systems based on tropical perennial grasses. More precise fertilization practices, based upon site and seasonal-specific recommendations, will substantially contribute to the establishment of best fertilization guidelines. Sustainable approaches can be defined by combining the identification of regrowth cycles where high N rates are required, with enhanced efficiency fertilizers, and/or using grass species with the potential for biological nitrification inhibition. The lack of information on tropical grasses requirements, and soil and climatic factors driving the N fate into the mineralization and immobilization processes and how these factors affect plant’s N demand, still prevents opportunities for tactical applications and the establishment of best management guidelines.

Sugarcane root exudate impact on the potential nitrification rate and N dynamics in the rhizosphere

Soil nitrification is a key process in regulating nitrogen transformation of various inorganic N forms for plant uptake and reducing N loss (N2O and NO3−). Nitrification inhibition by plant-released root exudates is referred to as biological nitrification inhibition (BNI). This study aimed to detect the BNI capacity of sugarcane (Saccharum spp.) root exudates and determine the influence of BNI compounds (BNIs) on the net nitrification rate in rhizosphere soil during sugarcane growth. Three sugarcane varieties were considered in this study, i.e., wild cane, UT13 and KK3. This study included 3 experiments, namely, Experiment I, determination of the potential nitrification rate (PNR) via a soil bioassay and assessment of the effect of dicyandiamide (DCD) on the PNR via a microcosm incubation study; Experiment II, assessment of the effect of sugarcane cultivation on soil N dynamics and the net nitrification rate in rhizosphere soil (in situ); and Experiment III, assessment of the PNR and immobilization in soil via microcosm incubation (ex situ). Sugarcane root exudates were collected under hydroponics, and the BNI capacity was obtained through a soil bioassay. Pot experiments were conducted to determine the influence of sugarcane growth on the net nitrification rate relative to unplanted soil. The results of Experiment I indicated that sugarcane root exudates significantly inhibited the nitrification rate via a soil bioassay (p < 0.05), with a high variation in the BNI capacity according to the sequence of Spone (84.29% inhibition) > UT13 (80.94% inhibition) > KK3 (45.4% inhibition). In addition, Experiment II confirmed a reduced net nitrification rate (p < 0.05) among all three sugarcane varieties. However, net nitrification rate reduction was more notably the result of heterotrophic N immobilization and plant N uptake than the result of BNIs. Evidence of BNI-induced reduction in gross nitrification among all sugarcane varieties was confirmed via soil incubation (Experiment III), and a notable difference in the BNI capacity was found among all sugarcane varieties. Based on the difference in plant mechanisms controlling the net nitrification rate, our study demonstrates that the dominant mechanisms are determined by the soil N availability.

Improving Nitrogen Use Efficiency in Aerobic Rice Based on Insights Into the Ecophysiology of Archaeal and Bacterial Ammonia Oxidizers.

The abundance and structural composition of nitrogen (N) transformation-related microbial communities under certain environmental conditions provide sufficient information about N cycle under different soil conditions. This study aims to explore the major challenge of low N use efficiency (NUE) and N dynamics in aerobic rice systems and reveal the agronomic-adjustive measures to increase NUE through insights into the ecophysiology of ammonia oxidizers. Water-saving practices, like alternate wetting and drying (AWD), dry direct seeded rice (DDSR), wet direct seeding, and saturated soil culture (SSC), have been evaluated in lowland rice; however, only few studies have been conducted on N dynamics in aerobic rice systems. Biological ammonia oxidation is majorly conducted by two types of microorganisms, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). This review focuses on how diversified are ammonia oxidizers (AOA and AOB), whose factors affect their activities and abundance under different soil conditions. It summarizes findings on pathways of N cycle, rationalize recent research on ammonia oxidizers in N-cycle, and thereby suggests adjustive agronomic measures to reduce N losses. This review also suggests that variations in soil properties significantly impact the structural composition and abundance of ammonia oxidizers. Nitrification inhibitors (NIs) especially nitrapyrin, reduce the nitrification rate and inhibit the abundance of bacterial amoA without impacting archaeal amoA. In contrast, some NIs confine the hydrolysis of synthetic N and, therefore, keep low NH4+-N concentrations that exhibit no or very slight impact on ammonia oxidizers. Variations in soil properties are more influential in the community structure and abundance of ammonia oxidizers than application of synthetic N fertilizers and NIs. Biological nitrification inhibitors (BNIs) are natural bioactive compounds released from roots of certain plant species, such as sorghum, and could be commercialized to suppress the capacity of nitrifying soil microbes. Mixed application of synthetic and organic N fertilizers enhances NUE and plant N-uptake by reducing ammonia N losses. High salt concentration promotes community abundance while limiting the diversity of AOB and vice versa for AOA, whereas AOA have lower rate for potential nitrification than AOB, and denitrification accounts for higher N2 production. Archaeal abundance, diversity, and structural composition change along an elevation gradient and mainly depend on various soil factors, such as soil saturation, availability of NH4+, and organic matter contents. Microbial abundance and structural analyses revealed that the structural composition of AOA was not highly responsive to changes in soil conditions or N amendment. Further studies are suggested to cultivate AOA and AOB in controlled-environment experiments to understand the mechanisms of AOA and AOB under different conditions. Together, this evaluation will better facilitate the projections and interpretations of ammonia oxidizer community structural composition with provision of a strong basis to establish robust testable hypotheses on the competitiveness between AOB and AOA. Moreover, after this evaluation, managing soils agronomically for potential utilization of metabolic functions of ammonia oxidizers would be easier.