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The impact of dairy farm effluent and manure applications upon gas emissions from soil is of concern for agronomic, ecological, and environmental reasons. Yet it remains unclear how the optimized manure and effluent additions may affect gas (nitrous oxide (N2O), nitric oxide (NO), and ammonia (NH3)) emissions during wheat cultivation. We conducted a field experiment in Zhuzhen (Jiangsu), China, from November 2018 to May 2019 to examine the effects of effluent and manure on gas emissions from the wheat fields that had seven treatments (4 replicates, 28 plots): no fertilizer (control); inorganic fertilizer at a conventional application rate of 200 kg N ha−1 (NPK); 100 kg N ha−1 inorganic fertilizer plus 100 (DE1), 150 (DE2), and 250 (DE3) kg N ha−1 farm dairy effluent; 100 kg N ha−1 inorganic fertilizer plus 100 kg N ha−1 farm dairy manure (SM1); and 150 kg N ha−1 inorganic fertilizer plus 50 kg N ha−1 farm dairy manure (SM2). Applying dairy effluent during the wheat season significantly (P < 0.05) increased NH3 emissions from 1.83 (NPK) to 3.81 kg N ha−1 (DE1) and 11.4 kg N ha−1 (DE3), probably due to elevated levels of soil NH4+ and pH, with no discernable impact on N2O emissions compared with NPK. The greater application of effluent in the DE3 treatment increased NO emissions significantly by 33.3% relative to NPK. The combined application of manure and urea significantly reduced N2O and NO emissions by 25.2–27.6% and 8.3–45.8%, respectively, but increased NH3 emissions in the SM1 treatment by 73.8%, when compared with NPK. Overall, our results suggest that replacing 25% of the current conventional chemical N application rate with dairy manure could considerably mitigate gas emissions in the wheat season.

A 15N tracing incubation study was carried out using a sandy loam soil without (control) and with field-aged biochar (biochar) to investigate the mechanisms underlying the effects of field-aged biochar on nitrous oxide (N2O) emissions. During the incubation, carried out at 40%, 60%, and 80% water-filled pore space (WFPS), cumulative N2O emission decreased from 24.13–26.40 μg N kg−1 in the control soil to 18.27–23.94 μg N kg−1 in the biochar soil, with a reduction of 9.3–24.3%. The contribution of autotrophic nitrification to total N2O production was 81.8–87.6% in the control soil under 40–80% WFPS, which was significantly reduced by field-aged biochar to 67.1–78.6%. Under 60% WFPS, the gross rates of autotrophic nitrification and gross mineralization were reduced from 11.95 and 4.43 μg N g−1 d−1, respectively, in the control soil to 7.32 and 0.60 μg N g−1 d−1, respectively, in the biochar soil. The field-aged biochar increased the NH4+ immobilization rate by 440%, primarily by immobilizing NH4+ into the recalcitrant organic N pool. Both the turnover rate of NH4+ mineralization-immobilization and the ratio of nitrification to NH4+ immobilization were reduced under biochar amendment, consequently lowering the supply of NH4+ for nitrifiers. In addition, compared with the control soil, the gross rate of NH4+ adsorption was significantly higher in the biochar soil. Taken together, our results suggest that field-aged biochar contributes to mitigating N2O emissions, primarily by decreasing the autotrophic nitrification rate through a reduced NH4+ supply due to increased mineral N immobilization and adsorption and lowered organic N mineralization.

Positive and negative effects coexist in applying nitrification inhibitors (NIs) in China, making it difficult to accurately evaluate the risks and benefits brought by applying NIs. Thus, this study comprehensively investigated the benefits and risks for the environment and crops when applying three commonly used NIs: 3,4-dimethypyrazole phosphate (DMPP), dicyandiamide (DCD), and 2-chloro-6-trichloromethyl pyridine (nitrapyrin) in China. A meta-analysis including 617 observations from 172 studies in China was conducted in this study. DMPP, DCD, and nitrapyrin averagely reduced nitrous (N2O) emissions by 60.1%, 30.4%, and 36.1%, nitrate (NO3−) leaching by 49.5%, 51.9%, and 49.4%, respectively. Methane (CH4) and carbon dioxide (CO2) emissions were also inhibited by NIs. However, the application of DMPP, DCD, and nitrapyrin aggravated ammonia (NH3) volatilization by 43.2%, 27.4%, and 28.5%, respectively, and ammonium (NH4+) leaching by an average of 28.2%, 80.1%, and 30.9%, respectively. NIs increased crop yields and the magnitudes of the effects were in the following order: nitrapyrin (8.6–12%) > DCD (6.9–10.3%) > DMPP (5.8–8%). Furthermore, plant NO3− content was reduced by NIs and crop growth characteristics and qualities (e.g., plant height and sugar content) all exhibited positive responses to NI application. NI application provided benefits by decreasing N2O, CH4, and CO2 emissions and NO3−-N leaching and by enhancing crop yields and quality. The risks of NI application were caused by increasing NH3 volatilization and NH4+-N leaching. Considering all the environmental and crop factors together, the benefits in applying NIs were greater than the risks.

Paddy fields are an important source of nitrous oxide (N2O) emission. The application of biochar or the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) to paddy soils have been proposed as technologies to mitigate N2O emissions, but their mechanisms remain poorly understood. An experiment was undertaken to study the combined and individual effects of biochar and DMPP on N2O emission from a paddy field. Changes in soil microbial community composition were investigated. Four fertilized treatments were established as follows: fertilizer only, biochar, DMPP, and biochar combined with DMPP; along with an unfertilized control. The application of biochar and/or DMPP decreased N2O emission by 18.9–39.6% compared with fertilizer only. The combination of biochar and DMPP exhibited higher efficiency at suppressing N2O emission than biochar alone but not as effective as DMPP alone. Biochar promoted the growth of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), while DMPP suppressed AOB and increased AOA. Applying biochar with DMPP reduced the impact of DMPP on AOB. The nirS-/nirK- denitrifiers were decreased and nosZ-N2O reducers were increased by DMPP and the combination of DMPP and biochar. The abundance of the nirK gene was increased by biochar at the elongation and heading stages of rice development. Compared with fertilizer only, the application of biochar and/or DMPP promoted the abundance of nosZ genes. These results suggest that applying biochar and/or DMPP to rice paddy fields is a promising strategy to reduce N2O emissions by regulating the dynamics of ammonia oxidizers and N2O reducers.

BACKGROUND 3,4-Dimethylpyrazole phosphate (DMPP) is a nitrification inhibitor which can restrict nitrate (NO3- ) production. Boric acid is a substance which inhibits urease activity. However, few studies have focused on the inhibitory effect of boric acid on urea hydrolysis and the possible synergistic effect with DMPP. Thus, an incubation trial was conducted to determine the impact of boric acid and DMPP addition on urea-N transformation, and their synergistic effects, in chernozem soil (Che) and red soil (RS). Four treatments were set up in each soil: urea only (U); urea combined with DMPP (UD); urea combined with boric acid (UB); and urea combined with both DMPP and boric acid (UDB). RESULTS Compared to U, adding DMPP (UD) increased NH3 emissions by 11% and 13% and decreased soil NO3- -N concentration by 38% and 13% in Che and RS, respectively. Boric acid addition (UB) effectively prolonged the half-life time of urea by 0.8 and 0.4 days, reduced NH3 volatilizations by 11% and 16% and delayed the occurrence of NH3 emission peaks for 3 and 4 days in contrast to U treatment in Che and RS, respectively. UDB treatment mitigated the NH3 volatilizations caused by the addition of DMPP (UD) by 16% and 29% in Che and RS, respectively. Additionally, a better nitrification inhibition rate was found in the UDB treatment compared to other treatments in both soils. CONCLUSIONS There is potential to develop a new N transformation inhibition strategy with the use of a combination of boric acid and DMPP. © 2020 Society of Chemical Industry.

A field micro-plot experiment with nitrogen isotope (15 N) labelling was performed to study the impacts of the timing of aside-dressed Napplication on urea-15 N in amaize-soil system. The treatment...

The large amount of ammonia released during agricultural application of urea fertilizer can result in a partial loss of applied nitrogen, having a detrimental effect on air quality. Although Chamomile recutita has nitrogen transformation inhibitory properties, providing potential agricultural and environmental benefits, the full extent of the effects of the major constituents of this plant on urease activity and NH3 volatilization in soils is currently unknown. Soil incubation experiments were established using 2-Cyclopenten-1-one and Eugenol, two major constituents of C. recutita, to evaluate their effects on inorganic soil nitrogen pools, urease activity, and NH3 volatilization in grey desert soil and red soil. An application rate of 0.25 g N kg−1 soil fertilizer was applied as urea with and without additives. An unfertilized treatment was also included as a control. In order to compare results, N(butyl) thiophosphoric triamide (NBPT), a common synthetic urease inhibitor, was also used. NBPT, 2-Cyclopenten-1-one and Eugenol were applied at a rate of 0.00125 g kg−1 soil (equivalent to 0.5% N). The results indicated that the rate of urea hydrolysis was higher in grey desert soil compared to red soil. Soil in the urea-only treatments recorded urea hydrolysis to be almost complete within seven days of application. The rate of hydrolysis was inhibited by the two natural compounds, and higher concentrations of urea were maintained for more than two weeks. Soil amended with the two materials exhibited strong soil urease inhibition in both soil treatments (75.1% in the alkaline grey desert soil and 72.8% in the acidic red soil). The strongest inhibitory effect occurred one to three days after incubation in the Eugenol treatment. Moreover, the inhibitory effects of Cyclopenten-1-one and Eugenol were superior to that of NBPT in the two soils. Cyclopenten-1-one and Eugenol also significantly reduced soil NH3 emissions by 14.2 to 45.3%, especially in the acidic red soil. Molecular docking studies confirmed inhibition mechanisms, highlighting that natural compounds interacted with the amino acid residues of the urease active center. This action resulted in the urease active pocket being blocked, thereby inhibiting enzyme activity. Overall, our findings suggest that 2-Cyclopenten-1-one and Eugenol are both capable of hindering urease activity and reducing the risk of N loss in the two tested soils. Results highlight their applicability as urease inhibitors and their effect in delaying the release of ammonia nitrogen, thereby increasing fertilizer N use efficiency. However, in order to fully assess N use efficiency and the N balance due to the presence of Chamomile extract in soil-crop systems, further field scale investigations are required.

Organic fertilizers increase soil organic matter (SOM) stocks, but the underlying processes depend on the fertilizer type and remain largely unknown. To evaluate the predominant C stabilization mechanisms, upland Ultisols subjected to 27 years of mineral and organic fertilization were analyzed for SOM content, aggregate size classes, and amino sugar composition. The long-term field experiment had seven treatments: no fertilization (Control), mineral NPK fertilizers (NPK), NPK plus lime (NPK + Lime), NPK plus peanut straw (NPK + PeanutStraw), NPK plus rice straw (NPK + RiceStraw), NPK plus radish residue (NPK + RadishResidue), and NPK plus pig manure (NPK + PigManure). The 27-year application of mineral fertilizers (NPK and NPK + Lime), NPK + crop residues, and NPK + PigManure increased SOM content by 11.0–13.2%, 16.3–25.3%, and 44.3%, respectively, compared with the Control. The aliphaticity and recalcitrance indices based on 13C nuclear magnetic resonance spectra of organic fertilizers were higher for pig manure than for crop residues. Both indices were closely correlated with SOM content after 27 years, so higher proportions of recalcitrant C in manure facilitated SOM accumulation. NPK + PigManure increased the mass proportion of large macroaggregates 2.9-fold compared with the Control, and reduced the effective diffusion coefficient of oxygen in the soil. Consequently, NPK + PigManure limited the activity and abundance of aerobes and the accessibility of SOM to microorganisms, in turn facilitating SOM accumulation. The application of mineral fertilizers, NPK + crop residues, and NPK + PigManure increased microbial necromass to 2.85–3.03, 3.21–3.45, and 3.62 g C kg−1, respectively, from 2.63 g C kg−1 in the Control. Compared with crop residues, pig manure did not affect bacterial necromass but increased fungal necromass from 2.19 to 2.39 g C kg−1 to 2.58 g C kg−1, which might associate with increased SOM stability. However, the relative contribution of microbial necromass to SOM was lower under NPK + PigManure than under NPK + crop residues, since more added C was protected in the NPK + PigManure soil. Our results suggest that manure may contribute to SOM accumulation and stabilization in three ways: directly through the input of recalcitrant organic C, indirectly through the stabilization of aggregates and physical protection of C, and to a lesser extent through increasing fungal necromass.

Calculated N2O emission factors (EFs) of applied nitrogen (N) fertilizer are currently based upon a single, universal value advocated by the IPCC (Inter-governmental Panel on Climate Change) even though EFs are thought to vary with climate and soil types. Here, we compiled and analyzed 151 N2O EF values from agricultural fields across China. The EF of synthetic N applied to these croplands was 0.60%, on average, but differed significantly among six climatic zones across the country, with the highest EF found in the north subtropical zone for upland fields (0.93%) and the lowest in the middle subtropical zone for paddy fields (0.20%). Precipitation and soil pH, which showed non-linear relationships with EF, are among the factors governing it, explaining 7.0% and 8.0% of the regional variation in EFs, respectively. Annual precipitation was the key factor regulating N2O emissions from synthetic N fertilizers. Among crop types, legume crops had the highest EFs, which were significantly (P

Residue return in combination with synthetic nitrogen (N) fertilizer is increasingly being considered to be beneficial to soil fertility and crop yield. In most studies, however, attention has mainly been paid to the way that significant changes in the soil N mineralization process affect the soil N cycle, while the effect of different residue return amounts on ammonia (NH3) volatilization and nitrous oxide (N2O) emissions, potentially the most important components of N losses and environmental effects has, to a certain extent, been neglected, notably in north-eastern China. Therefore, a trial was set up in an Alfisol/arable soil during 2015–2016 to monitor annual NH3 volatilization and N2O emission dynamics from a fertilized maize field with residue return at different rates. Treatments included N fertilizer alone and N fertilizer in combination with either half or the full yield of the maize residue (5.8 × 103 or 11.6 × 103 kg ha−1, respectively) returned to the soil surface after harvest. Over a growing season of maize, the NH3 volatilization loss rate from the full residue return treatment was 4.6%, which was significantly lower than that in the N fertilizer application only and half residue return plots (6.1%). Meanwhile, residue return rates showed a significant effect on annual N2O emissions from the maize system. Half residue return increased N2O emission (921.1 g N·ha−1), while full residue return marginally decreased N2O emissions (862.6 g N·ha−1) during the maize growing season, compared to the fertilizer-only treatment (881.2 g N·ha−1) (P

The effects of combined biochar and double inhibitor application on gaseous nitrogen (N; nitrous oxide [N

A field experiment was conducted to evaluate the influence of the continuous application of organic and mineral N fertilizer on N2O and NO emissions under maize and wheat rotation on the North China Plain. This study included eight treatments: no fertilizer (control), mineral N fertilizer (Nmin) at a rate of 200 kg N ha&minus, 1 per season, 50% mineral fertilizer N plus 50% cattle manure N (50% CM), 50% chicken manure N (50% FC) or 50% pig manure N (50% FP), 75% mineral fertilizer N plus 25% cattle manure N (25% CM), 25% chicken manure N (25% FC) or 25% pig manure N (25% FP). The annual N2O and NO emissions were 2.71 and 0.39 kg N ha&minus, 1, respectively, under the Nmin treatment, with an emission factor of 0.50% for N2O and 0.07% for NO. Compared with the Nmin treatment, N2O emissions did not differ when 50% of the mineral N was replaced with manure N (50% CM, 50% FC and 50% FP), while annual NO emissions were significantly reduced by 49.0% and 27.8% under 50% FC and 50% FP, respectively. In contrast, annual N2O emissions decreased by 21&ndash, 38% compared to the Nmin treatment when 25% of the mineral N was replaced with manure N (25% CM, 25% FC and 25% FP). Most of the reduction occurred during the maize season. The 25% CM, 25% FC and 25% FP treatments had no effect on NO emissions compared to the Nmin treatment. There was no obvious difference in annual N2O and NO emissions among the organic manures at the same application rate, probably due to their similar C/N ratio. Replacing a portion of the mineral fertilizer N with organic fertilizer N did not significantly affect crop grain yield, except for the 50% FC treatment in the wheat season. Overall, the results suggest that the combined application of 25% organic manure N plus 75% mineral fertilizer N had the most potential to mitigate N2O emissions while not affecting crop yield in the maize and wheat rotation system in this area of China.

The conversion of natural grassland to semi-natural or artificial ecosystems is a large-scale land-use change (LUC) commonly occurring to saline–alkaline land. Conversion of natural to artificial ecosystems, with addition of anthropogenic nitrogen (N) fertilizer, influences N availability in the soil that may result in higher N2O emission along with depletion of 15N, while converting from natural to semi-natural the influence may be small. So, this study assesses the impact of LUC on N2O emission and 15N in N2O emitted from naturally occurring saline–alkaline soil when changing from natural grassland (Phragmites australis) to semi-natural [Tamarix chinensis (Tamarix)] and to cropland (Gossypium spp.). The grassland and Tamarix ecosystems were not subject to any management practice, while the cropland received fertilizer and irrigation. Overall, median N2O flux was significantly different among the ecosystems with the highest from the cropland (25.3 N2O-N µg m−2 h−1), intermediate (8.2 N2O-N µg m−2 h−1) from the Tamarix and the lowest (4.0 N2O-N µg m−2 h−1) from the grassland ecosystem. The 15N isotopic signatures in N2O emitted from the soil were also significantly affected by the LUC with more depleted from cropland (− 25.3 ‰) and less depleted from grassland (− 0.18 ‰). Our results suggested that the conversion of native saline–alkaline grassland with low N to Tamarix or cropland is likely to result in increased soil N2O emission and also contributes significantly to the depletion of the 15N in atmospheric N2O, and the contribution of anthropogenic N addition was found more significant than any other processes.

Dairy farms produce considerable quantities of nutrient-rich effluent, which is generally stored before use as a soil amendment. Unfortunately, a portion of the dairy effluent N can be lost through volatilization during open pond storage to the atmosphere. Adding of covering materials to effluent during storage could increase contact with NH4+ and modify effluent pH, thereby reducing NH3 volatilization and retaining the effluent N as fertilizer for crop application. Here the mitigation effect of cover materials on ammonia (NH3) volatilization from open stored effluents was measured. A pilot-scale study was conducted using effluent collected at the Youran Dairy Farm Company Limited, Luhe County, Jiangsu, China, from 15 June to 15 August 2019. The study included seven treatments: control without amendment (Control), 30-mm × 25-mm corn cob pieces (CC), light expanded clay aggregate - LECA (CP), lactic acid (LA) and lactic acid plus CC (CCL), CP (CPL) or 20-mm plastic balls (PBL). The NH3 emission from the Control treatment was 120.1 g N m−2, which was increased by 38.1% in the CP treatment, possibly due to increased effluent pH. The application of CC reduced NH3 loss by 69.2%, compared with the Control, possibly due to high physical resistance, adsorption of NH4+ and effluent pH reduction. The lactic acid amendment alone and in combination with other materials also reduced NH3 volatilization by 27.4% and 31.0–46.7%, respectively. After 62 days of storage, effluent N conserved in the CC and CCL treatments were 21.0% and 22.0% higher than that in the Control (P

Biochar and inhibitors applications have been proposed for mitigating soil greenhouse gas emissions. However, how biochar, inhibitors and the combination of biochar and inhibitors affect CH

It is widely acknowledged that dams affect sediment transport and water quality. To support water management of reservoirs, it is useful to explore how the fractions of phosphorus (P) in sediments were changed after the dam was built. The aim of this study was to assess the spatial and temporal trends of the P fractions in sediments from the Miyun Reservoir, a pivotal drinking water supply for Beijing City, the capital of China. Nine surface sediment samples, together with a sediment core, were collected. The concentrations of total P (TP) and their fractions were then determined by using a sequential extraction method. The results showed that the reservoir was classified into three areas spatially based on the TP concentrations, i.e., high (Baihe area), medium (transitional area), and low (Chaohe area) concentrations. The concentrations of iron-bound P (BD-P) and metal oxide-bound P (NaOH-P) were higher in the Baihe and Chaohe regions than those in the transitional area and tended to increase with water depth. Dam construction can lead to the concentrations of P increased in sediments and further increase the potential of internal P loadings. This study revealed the effect of dam construction on sedimentary P accumulation. The results will be helpful in better understanding the mobility and bioavailability of P in the aquatic ecosystem, which aim to achieve a more highly targeted environmental management for this important region.

Nitrous oxide (N2O) emissions from dairy-grazing pastures can be dominated by large emissions from small areas (‘hotspots’) frequently used by grazing dairy cattle (i.e., water troughs and gateways). N2O emissions from these hotspots are quantified by investigating whether N2O emissions and emission factors (% of applied N emitted as N2O, EF3) from potential hotspots are different from non-hotspots. To better characterise N2O emissions from hotspots and non-hotspots of farms to understand their contributions to national agricultural greenhouse gas inventory calculations, a series of measurements were conducted during winter and spring on two NZ typical dairy farms with contrasting soil drainage (poorly versus well drained). Before measurements were taken, the soils either received a cow urine application or remained untreated. The results showed that changes in water-filled pore space (WFPS) and mineral N around water troughs and gateways, due to additional stock movements and disproportionate excreta-N deposition during previous grazing events, affected both background and total N2O emissions. But there was little impact on EF3 values (calculated using IPCC guidelines) from deposited urine between hotspot and pasture areas. These results suggest the same EF3 values can be used for both to calculate emissions from urine deposited on grazed pastures. However, these results raise concerns about higher background emission in hotspots subtracted from measured emissions from urine-N deposition in calculating EF3 values and discounting the effects of disproportionate N inputs in intensive agriculture on increased background emissions (legacy effect). This IPCC inventory method does not account for the legacy effect of N loading prior to the measurements which may underestimate the emissions. Thus, an allowance for higher hotspot background emissions could be included in the Inventory to accurately estimate total emissions from agriculture.

Soil temperature is a key parameter affecting changes in the balance among energy flow, water flow, nutrient cycling, and ecological stability. In previous research on soil temperature estimation, field measurement has been valuable. However its value is uncertain for regional scale research. A regression equation algorithm approach introduces the environmental factors into consideration. The correlations between soil temperature and environmental covariates may not be linear, and most of them conform to a parabolic relationship. Therefore, based on 53 years' data (1958-2010) from 140 meteorological stations in Australia, this study applied a 3-parameter cosine wave model to fit the monthly air and soil temperature. Further, this study identified the correlations between the parameters and landscape factors using stepwise regression. The root mean square error (RMSE) and Nash-Sutcliffe efficiency coefficient (NS) were used to evaluate the accuracy of the model. The results showed that: (1) The cosine-wave function can effectively identify the monthly air/soil temperature fluctuation and the prediction accuracy increases gradually from north to south in Australia. (2) The precipitation, horizontal irradiation and elevation are predominant factors that affecting soil temperature fluctuation given a defined air temperature fluctuation. (3) Landscape factors regulate the hysteresis of air/soil temperature fluctuation. The hysteresis of soil temperature response to air temperature in Australia is in order of duration: central > south > north. Therefore, the application of the cosine function is a useful and novel technique for estimation of soil temperature, which could provide better understanding of how soil temperature fluctuation responds to the global warming.

The effects of combined biochar and double inhibitor application on gaseous nitrogen (N; nitrous oxide [N2O] and ammonia [NH3]) emissions and N leaching in paddy soils remain unclear. We investigated the effects of biochar application at different rates and double inhibitor application (hydroquinone [HQ] and dicyandiamide [DCD]) on NH3 and N2O emissions, N leaching, as well as rice yield in a paddy field, with eight treatments, including conventional urea N application at 280 kg N ha−1 (CN); reduced N application at 240 kg N ha−1 (RN); RN + 7.5 t ha−1 biochar (RNB1); RN + 15 t ha−1 biochar (RNB2); RN + HQ + DCD (RNI); RNB1 + HQ + DCD (RNIB1); RNB2 + HQ + DCD (RNIB2); and a control without N fertilizer. When compared with N leaching under RN, biochar application reduced total N leaching by 26.9–34.8% but stimulated NH3 emissions by 13.2–27.1%, mainly because of enhanced floodwater and soil NH4+-N concentrations and pH, and increased N2O emission by 7.7–21.2%, potentially due to increased soil NO3−-N concentrations. Urease and nitrification inhibitor addition decreased NH3 and N2O emissions, and total N leaching by 20.1%, 21.5%, and 22.1%, respectively. Compared with RN, combined biochar (7.5 t ha−1) and double inhibitor application decreased NH3 and N2O emissions, with reductions of 24.3% and 14.6%, respectively, and reduced total N leaching by up to 45.4%. Biochar application alone or combined with double inhibitors enhanced N use efficiency from 26.2% (RN) to 44.7% (RNIB2). Conversely, double inhibitor application alone or combined with biochar enhanced rice yield and reduced yield-scaled N2O emissions. Our results suggest that double inhibitor application alone or combined with 7.5 t ha−1 biochar is an effective practice to mitigate NH3 and N2O emission and N leaching in paddy fields.

Nitrification and denitrification in the N cycle are affected by various ammonia oxidizers and denitrifying microbes in intensive vegetable cultivation soils, but our current understanding of the effect these microbes have on N2O emissions is limited. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), acts by slowing nitrification and is used to improve fertilizer use efficiency and reduce N losses from agricultural systems; however, its effects on nitrifier and denitrifier activities in intensive vegetable cultivation soils are unknown. In this study, we measured the impacts of DMPP on N2O emissions, ammonia oxidizers, and denitrifying microbes in two intensive vegetable cultivation soils: one that had been cultivated for a short term (1 year) and one that had been cultivated over a longer term (29 years). The quantitative PCR technique was used in this study. Three treatments, including control (no fertilizer), urea alone, and urea with DMPP, were included for each soil. The application rates of urea and DMPP were 1800 kg ha−1 and 0.5% of the urea-N application rate. The application of N significantly increased N2O emissions in both soils. The abundance of ammonia-oxidizing bacteria (AOB) increased significantly with high rate of N fertilizer application in both soils. Conversely, there was no change in the growth rate of ammonia-oxidizing archaea (AOA) in response to the applied urea despite the presence of larger numbers of AOA in these soils. This suggests AOB may play a greater role than AOA in the nitrification process, and N2O emission in intensive vegetable cultivation soils. The application of DMPP significantly reduced soil NO3−-N content and N2O emission, and delayed ammonia oxidation. It greatly reduced AOB abundance, but not AOA abundance. Moreover, the presence of DMPP was correlated with a significant decrease in the abundance of nitrite reductase (nirS and nirK) genes. Long-term intensive vegetable cultivation with heavy N fertilization altered AOB and nirS abundance. In vegetable cultivation soils with high N levels, DMPP can be effective in mitigating N2O emissions by directly inhibiting both ammonia oxidizing and denitrifying microbes.

Increasing nitrogen (N) application to croplands in order to support growing food demand is a major cause of environmental degradation. However, evaluations of suitable N application rates based on environmental benefit have rarely been carried out for paddy-rice at a national scale in China. To address this challenge, we investigated the current status of N management in 1531 counties, covering the primary agro-ecological regions of Chinese rice production in 2008, and conducted 12 field experiments with six N level practices for 3 years (2011–2013). Results showed that the highest yields for rice were 5.8–8.6 Mg ha−1 with N rates of 209.4–289.8 kg N ha−1. Compared with the N rate for the highest yield (YHN), the environmentally optimal N rate (EnON) was lower by 20–39% and the corresponding N loss was reduced by 21–45%, while ensuring 95–99% of the highest crop yield. In China, the N inputs to paddy fields exceeded the YHN and EnON rates by 10% and 45%, respectively. After adjusting the N rate to paddy fields to the EnON rate, the N amount used in China and the corresponding N lost would be reduced by 0.9 and 0.5 Tg N yr−1, respectively, which enable highly efficient production of food with the lowest N loss possible. Thus, we suggest that N use rates for 45% of rice paddy fields in China, for which N application rates exceed the EnON rate, need to be reduced to mitigate environmental damage, and this can be done while still meeting China’s food demand.

China is the world’s largest emitter of gaseous ammonia (NH3), a compound that poses severe risks to human and ecosystem health. Adding biochar and inhibitors to soils has been suggested as a method to increase carbon sequestration and reduce nitrous oxide emissions, however, the effects of the amendments on NH3 emissions are poorly understood. We conducted a field experiment to evaluate the effect of applying biochar combined with a urease inhibitor (hydroquinone, HQ) and a nitrification inhibitor (dicyandiamide, DCD) on NH3 emissions, rice yields, and N use efficiency (NUE) during two growth seasons. Four replicates of seven treatments comprising no urea fertilizer (control), urea (N), biochar (B), urea + biochar (NB), NB + urease inhibitor (NBUI), NB + nitrification inhibitor (NBNI), and NB + urease and nitrification inhibitors (double inhibitor) (NBDI), were arranged in a randomized complete block design. Wheat straw biochar was applied once, in June 2014. Biochar in the NB treatment increased NH3 losses by 14.1% in the first rice season (P

The effects of biochar combined with the urease inhibitor, hydroquinone, and nitrification inhibitor, dicyandiamide, on gaseous nitrogen (N2O, NO and NH3) emissions and wheat yield were examined in a wheat crop cultivated in a rice-wheat rotation system in the Taihu Lake region of China. Eight treatments comprised N fertilizer at a conventional application rate of 150kgNha-1 (CN); N fertilizer at an optimal application rate of 125kgNha-1 (ON); ON+wheat-derived biochar at rates of 7.5 (ONB1) and 15tha-1 (ONB2); ON+nitrification and urease inhibitors (ONI); ONI+wheat-derived biochar at rates of 7.5 (ONIB1) and 15tha-1 (ONIB2); and, a control. The reduced N fertilizer application rate in the ON treatment decreased N2O, NO, and NH3 emissions by 45.7%, 17.1%, and 12.3%, respectively, compared with the CN treatment. Biochar application increased soil organic carbon, total N, and pH, and also increased NH3 and N2O emissions by 32.4-68.2% and 9.4-35.2%, respectively, compared with the ON treatment. In contrast, addition of urease and nitrification inhibitors decreased N2O, NO, and NH3 emissions by 11.3%, 37.9%, and 38.5%, respectively. The combined application of biochar and inhibitors more effectively reduced N2O and NO emissions by 49.1-49.7% and 51.7-55.2%, respectively, compared with ON and decreased NH3 emission by 33.4-35.2% compared with the ONB1 and ONB2 treatments. Compared with the ON treatment, biochar amendment, either alone or in combination with inhibitors, increased wheat yield and N use efficiency (NUE), while addition of inhibitors alone increased NUE but not wheat yield. We suggest that an optimal N fertilizer rate and combined application of inhibitors+biochar at a low application rate, instead of biochar application alone, could increase soil fertility and wheat yields, and mitigate gaseous N emissions.

A field experiment was conducted to evaluate the combined or individual effects of biochar and nitrapyrin (a nitrification inhibitor) on N2O and NO emissions from a sandy loam soil cropped to maize. The study included nine treatments: addition of urea alone or combined with nitrapyrin to soils that had been amended with biochar at 0, 3, 6, and 12 t ha−1 in the preceding year, and a control without the addition of N fertilizer. Peaks in N2O and NO flux occurred simultaneously following fertilizer application and intense rainfall events, and the peak of NO flux was much higher than that of N2O following application of basal fertilizer. Mean emission ratios of NO/N2O ranged from 1.11 to 1.72, suggesting that N2O was primarily derived from nitrification. Cumulative N2O and NO emissions were 1.00 kg N2O-N ha−1 and 1.39 kg NO-N ha−1 in the N treatment, respectively, decreasing to 0.81–0.85 kg N2O-N ha−1 and 1.31–1.35 kg NO-N ha−1 in the biochar amended soils, respectively, while there was no significant difference among the treatments. NO emissions were significantly lower in the nitrapyrin treatments than in the N fertilization-alone treatments (P

Optimizing the nitrogen (N) application rate can increase crop yield while reducing the environmental risks. However, the optimal N rates vary substantially when different targets such as maximum yield or maximum economic benefit are considered. Taking the wheat-maize rotation cropping system on the North China Plain as a case study, we quantified the variation of N application rates when targeting constraints on yield, economic performance, N uptake and N utilization, by conducting field experiments between 2011 and 2013. Results showed that the optimal N application rate was highest when targeting N uptake (240 kg ha− 1 for maize, and 326 kg ha− 1 for wheat), followed by crop yield (208 kg ha− 1 for maize, and 277 kg ha− 1 for wheat) and economic income (191 kg ha− 1 for maize, and 253 kg ha− 1 for wheat). If environmental costs were considered, the optimal N application rates were further reduced by 20–30% compared to those when targeting maximum economic income. However, the optimal N rate, with environmental cost included, may result in soil nutrient mining under maize, and an extra input of 43 kg N ha− 1 was needed to make the soil N balanced and maintain soil fertility in the long term. To obtain a win-win situation for both yield and environment, the optimal N rate should be controlled at 179 kg ha− 1 for maize, which could achieve above 99.5% of maximum yield and have a favorable N balance, and at 202 kg ha− 1 for wheat to achieve 97.4% of maximum yield, which was about 20 kg N ha− 1 higher than that when N surplus was nil. Although these optimal N rates vary on spatial and temporal scales, they are still effective for the North China Plain where 32% of China's total maize and 45% of China's total wheat are produced. More experiments are still needed to determine the optimal N application rates in other regions. Use of these different optimal N rates would contribute to improving the sustainability of agricultural development in China.

The soil nitrogen (N) cycle is crucial to biogeochemical cycling, plant nutrient absorption, and greenhouse gas emissions and is primarily mediated by microorganisms. Although organic fertilization regulating aggregation has been well studied in various soils, how organic fertilization mediates microbial groups involved in soil N cycle in aggregates remained largely unclear. Therefore, the objective was to investigate the effect of 27 years of application of mineral and organic fertilizers (peanut straw, rice straw, radish, and pig manure) on the abundance of major microbial groups involved in the soil N cycle in four soil aggregate size classes. The results showed that organic fertilizers exerted significant impacts on the communities of microbes possessing N-cycling-related genes, with pig manure having a more important effect than plant residues. However, aggregate size classes contributed more to the variation (20%) than organic fertilizers (12%). Organic fertilizer types did not impact the abundance of ammonia-oxidizing archaea (AOA) or ammonia-oxidizing bacteria (AOB). However, aggregate size strongly altered the abundance of AOA, but not AOB, with AOA being particularly abundant in

The conversion of natural grassland to semi-natural or artificial ecosystems is a large-scale land-use change (LUC) commonly occurring to saline–alkaline land. Conversion of natural to artificial ecosystems, with addition of anthropogenic nitrogen (N) fertilizer, influences N availability in the soil that may result in higher N2O emission along with depletion of 15N, while converting from natural to semi-natural the influence may be small. So, this study assesses the impact of LUC on N2O emission and 15N in N2O emitted from naturally occurring saline–alkaline soil when changing from natural grassland (Phragmites australis) to semi-natural [Tamarix chinensis (Tamarix)] and to cropland (Gossypium spp.). The grassland and Tamarix ecosystems were not subject to any management practice, while the cropland received fertilizer and irrigation. Overall, median N2O flux was significantly different among the ecosystems with the highest from the cropland (25.3 N2O-N µg m−2 h−1), intermediate (8.2 N2O-N µg m−2 h−1) from the Tamarix and the lowest (4.0 N2O-N µg m−2 h−1) from the grassland ecosystem. The 15N isotopic signatures in N2O emitted from the soil were also significantly affected by the LUC with more depleted from cropland (− 25.3 ‰) and less depleted from grassland (− 0.18 ‰). Our results suggested that the conversion of native saline–alkaline grassland with low N to Tamarix or cropland is likely to result in increased soil N2O emission and also contributes significantly to the depletion of the 15N in atmospheric N2O, and the contribution of anthropogenic N addition was found more significant than any other processes.

Nitrous oxide (N2O) emissions (EN2O) from drained peat soils used for pastoral agriculture have not been measured throughout the year in New Zealand. In response to this research gap, EN2O was measured fortnightly for 1 year in the Waikato region in a plot that was not grazed or nitrogen (N) fertilised. The time series was variable, the frequency distribution skewed and the fortnightly means correlated. To account for these factors, the data were loge transformed and an order 2 autoregressive model used to estimate a mean EN2O of 4.3 g N ha−1 d−1 and 95% confidence limits of 0.6–29.1 g N ha−1 d−1. There was a statistically significant, inverse relationship between EN2O and the depth to groundwater. In winter, when rainfall totalled 393 mm, EN2O and soil N content were significantly greater under a rain shelter designed to minimise N loss by leaching, than in an uncovered plot.

There is increasing scrutiny of the impact of grazing systems on the wider environment. Urine deposition during grazing has a dominant influence on inorganic nitrogen (N) loss to air and water, and in particular on emissions of nitrous oxide (N2O), a potent greenhouse gas. A series of three field trials were conducted to determine N2O emission factors of urine (EF3: N2O-N emitted as % of urine N applied) from animals on two different forage diets: forage rape (Brassica napus L.) and a conventional ryegrass/white clover (Lolium perenne L./Trifolium repens). Emission factors were measured over two winter trials and one summer trial, using both sheep and cattle urine. All three trials were conducted on a poorly drained soil. It was found that there was a tendency for a higher EF3 for urine from animals on a forage rape diet, both when applied to the forage rape soil and when applied to the pasture soil, although differences were not significant on an individual trial basis. When the data for all three trials was combined in a meta-analysis, urine from forage rape-fed animals had a significantly higher EF3 than urine from pasture-fed animals (1.54 vs. 1.20%). This was despite background emissions from the soil under forage rape being higher than from the soil under pasture. Our results suggest that there may be scope to influence N2O emissions via forage type on offer.

Biochar and inhibitors applications have been proposed for mitigating soil greenhouse gas emissions. However, how biochar, inhibitors and the combination of biochar and inhibitors affect CH4 emissions remains unclear in paddy soils. The objective of this study was to explore the effects of biochar application alone, and in combination with urease (hydroquinone) and nitrification inhibitors (dicyandiamide) on CH4 emissions and yield-scaled CH4 emissions during three rice growing seasons in the Taihu Lake region (Suzhou and Jurong), China. In Suzhou, N fertilization rates of 120–280 kg N ha−1 increased CH4 emissions compared to no N fertilization (Control) (P

Biochar application has been reported to effectively mitigate N2O emissions and increase crop yield; however, its long-term residual effects remain largely unknown. A four-year field experiment was designed in the North China Plain (NCP) to evaluate the residual effect of biochar on N2O and NO emissions and crop yield under maize-wheat rotation. The study included five treatments: no N fertilization (Control), N fertilizer application (CN), and N fertilizer plus maize-straw biochar application at 3 (NB3), 6 (NB6) and 12 t ha−1 (NB12). Biochar amendment had no effect on maize yield during the four-year rotation, but increased maize grain N uptake by 12.9 − 14.1 % and fertilizer N use efficiency by 13.8 % in the fourth year. Meanwhile, NB12 treatment decreased wheat yield by 11.7 − 15.5 % in each year, except the second, while decreased average wheat yield. Biochar application significantly reduced N2O emissions by 31.5 − 42.4 % during the first maize season, and by 6.9 − 21.3 % in the third and fourth years primarily due to reduction in NH4+ availability for nitrification. Furthermore, this mitigation effect was positively related to soil moisture content and decreased with time after biochar application. Cumulative N2O emissions during the four wheat seasons were 0.25 − 0.85 kg N2O-N ha−1, and only decreased by 8.9 − 9.9 % under biochar amendment in the third and fourth years probably because low soil temperature suppressed N2O production. Biochar addition in the third and fourth years significantly reduced NO emissions by 9.0 − 20.1 % during the maize growing seasons and 10.5 − 19.1 % during the wheat growing seasons, especially under NB6 treatment. The average yield-scaled N2O and NO emissions were lowest in the NB6 treatment during the maize and wheat season. Overall, these findings suggest that 6 t ha−1 is the optimal biochar application rate for reducing N2O/NO emissions and yield-scaled N2O/NO emission under four-year maize-wheat rotation in the NCP.

While it is recognized that the accumulation and turnover of soil organic carbon (SOC) is driven by plant inputs and their subsequent microbial-mediated transformations, the roles of plant residue chemistry and microbial processes in controlling SOC dynamics under different fertilizer application regimes have not been well explored. In the present study, amino sugars and lignin phenols were used as biomarkers to investigate the changes in microbial necromass and plant-derived components in a 30-year cultivated Mollisol (0–20 cm) in response to different fertilizer application treatments, including synthetic fertilizers (NPK, 165 kg N ha−1, 82.5 kg P2O5 ha−1, and 82.5 kg K2O ha−1 per year), pig manure at two application rates of 30 and 60 t ha−1 per year, and combinations of manure and synthetic fertilizers (30 or 60 t ha−1 manure per year plus 165 kg N ha−1, 82.5 kg P2O5 ha−1, and 82.5 kg K2O ha−1 per year). Compared with the unfertilized plot (Control), 30-year application of synthetic fertilizers increased microbial biomass (161%) and amino sugar production (19.7%), but did not alter lignin phenol and SOC concentrations despite the increased plant input. Comparatively, long term manure applications increased the concentration of SOC (30.8–70.9%), as well as that of amino sugars (82.9–107%) and lignin (96.8–212%) in soil. Nevertheless, despite the enhanced microbial biomass from low to high manure application rate, the proportion of amino sugars in the SOC decreased, reflecting a diluted contribution of microbial necromass in SOC pool buildup at high-rate manure application. On the contrary, the proportions of lignin phenols in the SOC in the manure treatments, as well as the ratios of lignin phenols and amino sugars (0.26–0.42), were larger than that in the NPK treatment (0.22) and increased with increasing manure application rate. Therefore, the manipulation of synthetic or organic fertilizer on SOC dynamics is associated with differential accumulation of microbial necromass and plant lignin in agro-ecosystems. The manure amendment enhanced the contribution of plant-derived components more than microbial necromass to long term SOC accumulation.

Nitrogen (N) and phosphorus (P) availability strongly affects carbon (C) cycling and storage in terrestrial ecosystems. Nutrient addition can increase C inputs into soil via increased above- and belowground plant productivity, but at the same time can accelerate organic matter decomposition in the soil. The mechanisms underlying these effects on soil organic C (SOC) dynamics remain unclear, especially in nutrient-limited alpine ecosystems that have been subjected to increasing N and P availability in recent decades. The aim of this study was to clarify the mechanisms underlying SOC decomposition and stabilization in an alpine grassland soil after four years of N and P additions. The soil aggregate size distribution, microbial community structure (lipid biomarkers), microbial C use efficiency (CUE) and microbial necromass composition (amino sugar biomarkers) were analyzed. Nutrient addition increased dominance of fast-growing bacteria (copiotrophs), while P addition alone intensified the competitive interactions between arbuscular mycorrhizal and saprotrophic fungi. These changes led to decreases in the microbial CUE of glucose by 1.6–3.5% and of vanillin by 8.5%, and therefore, reduced SOC content in the topsoil. The total microbial necromass remained unaffected by nutrient addition, but the contribution of fungal necromass to SOC increased. The increased abundance of arbuscular mycorrhizal fungi and fungal necromass under elevated N availability raised the mass proportion of soil macroaggregates (>250 μm) by 16.5–20.3%. Therefore, fungi were highly involved in macroaggregation following N addition, and so, moderated the SOC losses through enhanced physical protection. Overall, the complex interactions between microbial physiology (CUE), necromass composition (amino sugars) and physical protection (macroaggregation) in mediating SOC dynamics in response to nutrient enrichment were disentangled to better predict the capability of alpine grassland soils to act as a C sink or source under global change.

Urine patches represent hot-spots of nitrogen (N) loss in dairy-grazed soils. Targeted application of urease and nitrification inhibitors that slow down certain N transformations in the urine patches is a potential method to reduce N losses. However, for optimum effectiveness the inhibitors need to be in close physical contact with the urine in the soil under urine patches. In practice, there will always be some time delay between urine deposition and application of inhibitors. It is therefore important to understand how the urine is transported in the soil following deposition. In this study, we developed an empirical model of urine patch area from thermal images of urine patches applied on two different soil types, at two different initial moisture contents, and with three different applied urine volumes. Spatial measurements using Spikey®-R (a mobile device that measures soil surface layer electrical conductivity) were used to test the model. A linear regression model of the ratio (urine volume)/(patch area) against the soil air-filled pore space explained 45 % of the variation in the ratio and had a Nash-Sutcliffe efficiency of +0.74 in predicting the mean patch area. This regression model was then used to define the boundary conditions for HYDRUS2D/3D simulations of urine movement through the soil after application. These simulations reasonably predicted the amount of urine-N in the top 50 and 100 mm of the soil 4 h after application (model efficiencies +0.38 and +0.42, respectively), but the model efficiencies were only −0.18 and +0.14 after 24 h. The measurements also had a high degree of spatial variability. After 24 h 44–78 % of the urine-N measured in the profile was within 50 mm of the surface. This represents a limit on the proportion of urine-N that could be physically intercepted by a post-grazing inhibitor application.

Fungal communities play a critical role in regulating soil nutrient cycling and plant growth. However, the effects of long-term mineral and organic fertilization on fungal communities in Ultisols remain largely unknown. Soil samples from a 27-year fertilization experiment were used to investigate fungal communities through high-throughput sequencing along with literature data. The study involved seven treatments: no fertilization (Control), mineral NPK fertilizer (NPK), NPK fertilizer plus lime (NPK + Lime), NPK fertilizer plus peanut straw (NPK + PeanStraw), NPK fertilizer plus rice straw (NPK + RiceStraw), NPK fertilizer plus radish residue (NPK + RadResidue), and NPK fertilizer plus pig manure (NPK + PigManure). Long-term amendment of mineral and organic fertilizers did not alter fungal diversity in strong acidic Ultisols (original soil pH = 4.96). Meta-analysis of 60 global measurements in literature showed that fertilizer-induced decreases in fungal diversity (Hedge's d = −0.36; p 6 rather than