Factors affecting ammonium capture by some Victorian lignites.

HighlightsVictorian lignites were assessed for their NH4+ retention capacity using adsorption isotherms and 15N tracing.NH4+ adsorption capacity of lignites increased (up to 3-fold) with pH, especially from pH 5 to 7.Biological immobilisation did not play a substantial role in the NH4+ retention capacity of the lignites.pH-dependent NH4+ adsorption was the dominant means by which lignite retained NH4+.

Next-generation enhanced-efficiency fertilizers for sustained food security.

Nitrogen losses in agricultural systems can be reduced through enhanced-efficiency fertilizers (EEFs), which control the physicochemical release from fertilizers and biological nitrogen transformations in soils. The adoption of EEFs by farmers requires evidence of consistent performance across soils, crops and climates, paired with information on the economic advantages. Here we show that the benefits of EEFs due to avoided social costs of nitrogen pollution considerably outweigh their costs-and must be incorporated in fertilizer policies. We outline new approaches to the design of EEFs using enzyme inhibitors with modifiable chemical structures and engineered, biodegradable coatings that respond to plant rhizosphere signalling molecules.

Opportunities to improve nitrogen use efficiency in an intensive vegetable system without compromising yield.

Intensive vegetable cropping systems rely heavily on nitrogen (N) inputs from multiple synthetic and organic fertilizer applications. The majority of applied N is lost to the environment through numerous pathways, including as nitrous oxide (N2 O). A field trial was conducted to examine the opportunities to reduce N input in an intensive vegetable system without compromising yield. Treatments applied were control (no N), manure (M, 408 kg N ha-1 from chicken manure), grower practice (GP, 408 kg N ha-1 from chicken manure + 195 kg N ha-1 from fertilizer), and 2/3 GP (two-thirds of the total N input in GP), all with and without 3,4-dimethylpyrazole phosphate (DMPP). Nitrogen recovery in the GP treatment was determined using 15 N-labeled fertilizer. Using only manure significantly lowered celery (Apium graveolens L.) yield and apparent N use efficiency (ANUE) compared with GP. Reducing N input by one-third did not affect yield or ANUE. Use of DMPP increased ANUE despite no yield improvement. More than 50% of the applied N in the GP treatment was lost to the environment, with almost 10 kg N ha-1 emitted as N2 O over the season, which was 67 times more than from the control. Reducing the N input by one-third or using manure only reduced N2 O emissions by more than 70% relative to GP. This study shows that there is a clear opportunity to reduce N input and N2 O emissions in high-fertilizer-input vegetable systems without compromising vegetable yield.

Different responses of soil bacterial and fungal communities to nitrogen deposition in a subtropical forest.

China has experienced a widespread increase in N deposition due to intensive anthropogenic activities, particularly in the subtropical regions. However, the effects of long-term N deposition on soil bacterial and fungal abundance, diversity, and community composition remain largely unclear. We assessed the effects of N deposition on soil microbial communities in summer and winter, using quantitative polymerase chain reaction and Illumina Miseq sequencing of bacterial 16S rRNA and fungal ITS genes from subtropical natural forest soils. The abundance of both soil bacteria and fungi exhibited a decreasing pattern with increasing N deposition rates. Nitrogen deposition increased bacterial diversity in both summer and winter, whereas fungal diversity was significantly decreased in summer, but greatly increased under the highest level of N deposition (150 kg N ha-1 yr-1) in winter. Nitrogen deposition significantly increased the relative abundance of bacterial phyla Actinobacteria, Chloroflexi, and WPS-2, but decreased that of Acidobacteria and Verrucomicrobia. In addition, N deposition significantly decreased the relative abundance of Ascomycetes, but did not exert any significant effect on Basidiomycetes. The bacterial and fungal community compositions were greatly influenced by N deposition, with soil N availability and soil pH identified as the two most influential soil properties. This study demonstrates that the fungal community was more sensitive than the bacterial community to N deposition, and further emphasizes the importance of simultaneously evaluating soil bacterial and fungal communities in response to global environmental changes.

Enhanced efficiency fertilisers reduce nitrous oxide emissions and improve fertiliser 15N recovery in a Southern Australian pasture.

The effects of reducing nitrogen (N) rates or using enhanced efficiency fertilisers (EEFs) (i.e. urease and nitrification inhibitors, and controlled release fertilisers) on nitrous oxide (N2O) emissions and nitrogen use efficiency (NUE) are not well understood in temperate, rainfed pastures. A field experiment on rainfed ryegrass pasture in southern Australia examined the effect of granular urea N rate (0, 250 and 420 kg N ha-1 over 6 months) and EEF use (at 250 kg N ha-1 with NBPT, DMPP, or polymer coating (PCU)) on N2O emissions, NUE and fertiliser N recovery (using 15N techniques). Cumulative net-N2O emissions increased with N rate from 308 g N2O-N ha-1 (250 kg N ha-1) to 514 g N2O-N ha-1 (420 kg N ha-1). Using EEFs reduced N2O emissions by 22% (NBPT), 44% (DMPP) and 56% (PCU) compared to urea. The emission factor (EF) (kg net N2O-N per kg N applied) was 0.12 for both N rates (250 and 420 kg N ha-1) but reduced with the EEFs to 0.10 (NBPT) and 0.07 (DMPP and PCU) compared to urea. EEF use had no significant impact on biomass or apparent NUE but led to a greater recovery of N in the soil after one month (44.8% (DMPP) and 45.9% (NBPT) compared to urea (33.7%)). Within one month 42% of the N applied as urea (U50) was lost from the plant-soil system, which was reduced with DMPP (32% loss) and NBPT (33% loss). After six months, 52% (U50) to 59% (U84) of the urea N applied was lost. The positive effect of the EEFs on N2O emissions, and the increased recovery of N in the soil-plant system with the EEFs over one month indicates they could provide longer term benefits though soil N storage, and could be applied at lower N rates to achieve NUE benefit.

Effects of nitrification inhibitors on gross N nitrification rate, ammonia oxidizers, and N2O production under different temperatures in two pasture soils.

Australian pasture soil for cattle and sheep industries constitutes the principal land use with considerable N fertilizer consumption, which is one of the causes of local environmental problems. Nitrification plays a key role in regulating soil inorganic N concentration and its environmental diffusion. The effects of different nitrification inhibitors (NIs) on gross N nitrification (ngross) rate and N2O production under different temperatures in pasture soils remain unclear. A laboratory incubation experiment was conducted to determine the effect of NIs (dicyandiamide [DCD], 3,4-dimethylpyrazole phosphate [DMPP], and 3-methylpyrazol and 1H-1,2,4-triazol [3MP + TZ]) on N2O emissions, ngross and net N nitrification (nnet) rates, and the abundance of ammonia oxidizers, namely, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), in two Australian pasture soils incubated at temperatures of 15, 25, and 35 °C. All NIs reduced both ngross and nnet rates and N2O production rate from the two pasture soils but to different extents. The inhibitory rates of NIs on ngross and nnet reached 6.80-63.8 and 5.91-62.3%, respectively, whereas that on N2O production rate totaled 4.5-41.4% in the tested soils. NIs reduced nitrification and N2O production by inhibiting the growth of AOB rather than AOA. The inhibitory effects of NIs were temperature-dependent, that is, decreasing with increasing temperature from 15 to 35 °C. In general, DMPP performed better than DCD and 3MP + TZ at 15 and 35 °C, whereas DCD performed more effectively than the other two NIs at 25 °C. Our results suggest that the utilization of NIs will depend on the conditions present, especially soil temperature. Additionally, AOB is the target of inhibition when mitigating nitrification and N2O emission by applying NIs in pasture soils.

Nitrogen Addition Decreases Dissimilatory Nitrate Reduction to Ammonium in Rice Paddies.

Dissimilatory nitrate reduction to ammonium (DNRA), denitrification, anaerobic ammonium oxidation (anammox), and biological N2 fixation (BNF) can influence the nitrogen (N) use efficiency of rice production. While the effect of N application on BNF is known, little is known about its effect on NO3- partitioning between DNRA, denitrification, and anammox. Here, we investigated the effect of N application on DNRA, denitrification, anammox, and BNF and on the abundance of relevant genes in three paddy soils in Australia. Rice was grown in a glasshouse with N fertilizer (150 kg N ha-1) and without N fertilizer for 75 days, and the rhizosphere and bulk soils were collected separately for laboratory incubation and quantitative PCR analysis. Nitrogen application reduced DNRA rates by >16% in all the soils regardless of the rhizospheric zone, but it did not affect the nrfA gene abundance. Without N, the amount and proportion of NO3- reduced by DNRA (0.42 to 0.52 µg g-1 soil day-1 and 45 to 55%, respectively) were similar to or higher than the amount and proportion reduced by denitrification. However, with N the amount of NO3- reduced by DNRA (0.32 to 0.40 µg g-1 soil day-1) was 40 to 50% lower than the amount of NO3- reduced by denitrification. Denitrification loss increased by >20% with N addition and was affected by the rhizospheric zones. Nitrogen loss was minimal through anammox, while BNF added 0.02 to 0.25 µg N g-1 soil day-1 We found that DNRA plays a significant positive role in paddy soil N retention, as it accounts for up to 55% of the total NO3- reduction, but this is reduced by N application.IMPORTANCE This study provides evidence that nitrogen addition reduces nitrogen retention through DNRA and increases nitrogen loss via denitrification in a paddy soil ecosystem. DNRA is one of the major NO3- reduction processes, and it can outcompete denitrification in NO3- consumption when rice paddies are low in nitrogen. A significant level of DNRA activity in paddy soils indicates that DNRA plays an important role in retaining nitrogen by reducing NO3- availability for denitrification and leaching. Our study shows that by reducing N addition to rice paddies, there is a positive effect from reduced nitrogen loss but, more importantly, from the conversion of NO3- to NH4+, which is the favored form of mineral nitrogen for plant uptake.

Using urease and nitrification inhibitors to decrease ammonia and nitrous oxide emissions and improve productivity in a subtropical pasture.

Urease and nitrification inhibitors are designed to mitigate ammonia (NH3) volatilization and nitrous oxide (N2O) emission, but uncertainties on the agronomic and economic benefits of these inhibitors prevent their widespread adoption in pasture systems, particularly in subtropical regions where no such information is available. Here we report a field experiment that was conducted in a subtropical pasture in Queensland, Australia to examine whether the use of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT, applied as Green UreaNV®) and the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP, applied as Urea with ENTEC®) is environmentally, agronomically and economically viable. We found that Green UreaNV® and Urea with ENTEC® decreased NH3 volatilization and N2O emission by 44 and 15%, respectively, compared to granular urea. Pasture biomass and nitrogen (N) uptake were increased by 22-36% and 23-32%, respectively, with application of the inhibitors compared to granular urea. A simple economic assessment indicates that the fertilizer cost for pasture production was 5.4, 4.4 and 6.0 Australian cents per kg dry matter for urea, Green UreaNV® and Urea with ENTEC®, respectively, during the experimental period. The mitigation of N loss using the inhibitors can reduce the environmental cost associated with pasture production. These results suggest that the use of these inhibitors can provide environmental, agronomic and economic benefits to a subtropical pasture.

Nitrifier-induced denitrification is an important source of soil nitrous oxide and can be inhibited by a nitrification inhibitor 3,4-dimethylpyrazole phosphate.

Soil ecosystem represents the largest contributor to global nitrous oxide (N2 O) production, which is regulated by a wide variety of microbial communities in multiple biological pathways. A mechanistic understanding of these N2 O production biological pathways in complex soil environment is essential for improving model performance and developing innovative mitigation strategies. Here, combined approaches of the 15 N-18 O labelling technique, transcriptome analysis, and Illumina MiSeq sequencing were used to identify the relative contributions of four N2 O pathways including nitrification, nitrifier-induced denitrification (nitrifier denitrification and nitrification-coupled denitrification) and heterotrophic denitrification in six soils (alkaline vs. acid soils). In alkaline soils, nitrification and nitrifier-induced denitrification were the dominant pathways of N2 O production, and application of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) significantly reduced the N2 O production from these pathways; this is probably due to the observed reduction in the expression of the amoA gene in ammonia-oxidizing bacteria (AOB) in the DMPP-amended treatments. In acid soils, however, heterotrophic denitrification was the main source for N2 O production, and was not impacted by the application of DMPP. Our results provide robust evidence that the nitrification inhibitor DMPP can inhibit the N2 O production from nitrifier-induced denitrification, a potential significant source of N2 O production in agricultural soils.

Using nitrification inhibitors to mitigate agricultural N2 O emission: a double-edged sword?

Nitrification inhibitors show promise in decreasing nitrous oxide (N2 O) emission from agricultural systems worldwide, but they may be much less effective than previously thought when both direct and indirect emissions are taken into account. Whilst nitrification inhibitors are effective at decreasing direct N2 O emission and nitrate (NO3- ) leaching, limited studies suggest that they may increase ammonia (NH3 ) volatilization and, subsequently, indirect N2 O emission. These dual effects are typically not considered when evaluating the inhibitors as a climate change mitigation tool. Here, we collate results from the literature that simultaneously examined the effects of nitrification inhibitors on N2 O and NH3 emissions. We found that nitrification inhibitors decreased direct N2 O emission by 0.2-4.5 kg N2 O-N ha-1 (8-57%), but generally increased NH3 emission by 0.2-18.7 kg NH3 -N ha-1 (3-65%). Taking into account the estimated indirect N2 O emission from deposited NH3 , the overall impact of nitrification inhibitors ranged from -4.5 (reduction) to +0.5 (increase) kg N2 O-N ha-1 . Our results suggest that the beneficial effect of nitrification inhibitors in decreasing direct N2 O emission can be undermined or even outweighed by an increase in NH3 volatilization.

Nitrification Is a Primary Driver of Nitrous Oxide Production in Laboratory Microcosms from Different Land-Use Soils.

Most studies on soil N2O emissions have focused either on the quantifying of agricultural N2O fluxes or on the effect of environmental factors on N2O emissions. However, very limited information is available on how land-use will affect N2O production, and nitrifiers involved in N2O emissions in agricultural soil ecosystems. Therefore, this study aimed at evaluating the relative importance of nitrification and denitrification to N2O emissions from different land-use soils and identifying the potential underlying microbial mechanisms. A (15)N-tracing experiment was conducted under controlled laboratory conditions on four agricultural soils collected from different land-use. We measured N2O fluxes, nitrate ([Formula: see text]), and ammonium ([Formula: see text]) concentration and (15)N2O, (15)[Formula: see text], and (15)[Formula: see text] enrichment during the incubation. Quantitative PCR was used to quantify ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Our results showed that nitrification was the main contributor to N2O production in soils from sugarcane, dairy pasture and cereal cropping systems, while denitrification played a major role in N2O production in the vegetable soil under the experimental conditions. Nitrification contributed to 96.7% of the N2O emissions in sugarcane soil followed by 71.3% in the cereal cropping soil and 70.9% in the dairy pasture soil, while only around 20.0% of N2O was produced from nitrification in vegetable soil. The proportion of nitrified nitrogen as N2O (PN2O-value) varied across different soils, with the highest PN2O-value (0.26‰) found in the cereal cropping soil, which was around 10 times higher than that in other three systems. AOA were the abundant ammonia oxidizers, and were significantly correlated to N2O emitted from nitrification in the sugarcane soil, while AOB were significantly correlated with N2O emitted from nitrification in the cereal cropping soil. Our findings suggested that soil type and land-use might have strongly affected the relative contribution of nitrification and denitrification to N2O production from agricultural soils.

Effects of the Nitrification Inhibitor 3,4-Dimethylpyrazole Phosphate on Nitrification and Nitrifiers in Two Contrasting Agricultural Soils.

UNLABELLED: The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is a powerful tool that can be used to promote nitrogen (N) use efficiency and reduce N losses from agricultural systems by slowing nitrification. Mounting evidence has confirmed the functional importance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in nitrification and N2O production; however, their responses to DMPP amendment and the microbial mechanisms underlying the variable efficiencies of DMPP across different soils remain largely unknown. Here we compared the impacts of DMPP on nitrification and the dynamics of ammonia oxidizers between an acidic pasture soil and an alkaline vegetable soil using a (15)N tracing and (13)CO2-DNA-stable-isotope probing (SIP) technique. The results showed that DMPP significantly inhibited nitrification and N2O production in the vegetable soil only, and the transient inhibition was coupled with a significant decrease in AOB abundance. No significant effects on the community structure of ammonia oxidizers or the abundances of total bacteria and denitrifiers were observed in either soil. The (15)N tracing experiment revealed that autotrophic nitrification was the predominant form of nitrification in both soils. The (13)CO2-DNA-SIP results indicated the involvement of AOB in active nitrification in both soils, but DMPP inhibited the assimilation of (13)CO2 into AOB only in the vegetable soil. Our findings provide evidence that DMPP could effectively inhibit nitrification through impeding the abundance and metabolic activity of AOB in the alkaline vegetable soil but not in the acidic pasture soil, possibly due to the low AOB abundance or the adsorption of DMPP by organic matter. IMPORTANCE: The combination of the (15)N tracing model and (13)CO2-DNA-SIP technique provides important evidence that the nitrification inhibitor DMPP could effectively inhibit nitrification and nitrous oxide emission in an alkaline soil through influencing the abundance and metabolic activity of AOB. In contrast, DMPP amendment has no significant effect on nitrification or nitrifiers in an acidic soil, potentially owing to the low abundance of AOB and the possible adsorption of DMPP by organic matter. Our findings have direct implications for improved agricultural practices through utilizing the nitrification inhibitor DMPP in appropriate situations, and they emphasize the importance of microbial communities to the efficacy of DMPP.

Measurement and mitigation of nitrous oxide emissions from a high nitrogen input vegetable system.

The emission and mitigation of nitrous oxide (N2O) from high nitrogen (N) vegetable systems is not well understood. Nitrification inhibitors are widely used to decrease N2O emissions in many cropping systems. However, most N2O flux measurements and inhibitor impacts have been made with small chambers and have not been investigated at a paddock-scale using micrometeorological techniques. We quantified N2O fluxes over a four ha celery paddock using open-path Fourier Transform Infrared spectroscopy in conjunction with a backward Lagrangian stochastic model, in addition to using a closed chamber technique. The celery crop was grown on a sandy soil in southern Victoria, Australia. The emission of N2O was measured following the application of chicken manure and N fertilizer with and without the application of a nitrification inhibitor 3, 4-dimethyl pyrazole phosphate (DMPP). The two techniques consistently demonstrated that DMPP application reduced N2O emission by 37-44%, even though the N2O fluxes measured by a micrometeorological technique were more than 10 times higher than the small chamber measurements. The results suggest that nitrification inhibitors have the potential to mitigate N2O emission from intensive vegetable production systems, and that the national soil N2O emission inventory assessments and modelling predictions may vary with gas measurement techniques.

Long-term effects of municipal sewage on soils and pastures.

Land application of municipal wastewater is widely practised worldwide as a means of treating wastes and obtaining a benefit from the water and nutrients by growing pastures, trees, and sometimes edible crops such as vegetables, fruit and fibre, etc. Irrigation of pastures by treated and untreated sewage near Melbourne, Australia, for more than a century has increased heavy metals concentrations in the soil, but appears not to have increased their concentrations in the herbage and in animal tissues of animals grazed on these pastures. There seem to be sound reasons why this practice may be sustainable.