•Chemical composition and decomposition dynamics of organic manures were studied.•Manure quality indicators were measured by 13C NMR, colorimetry and CuO oxidation.•N effect on C decomposition shifted from initial stimulation to inhibition.•Stimulation and inhibition were related to high and low C quality, respectively.•Organic manure combined with N fertilizer could effectively increase soil C storage.Understanding the interactions among organic manure chemical composition, decomposition and nitrogen (N) fertilization is critical for sustainable agriculture management. Six organic manures were incubated in a cultivated black soil with or without N addition for one year, and carbon dioxide (CO2) emissions from these organic manures were monitored. Chemical compositions of the organic manures were determined by elemental analysis, proximate chemical analysis, and carbon (C)-13 nuclear magnetic resonance spectroscopy, and evaluated after cupric-oxide oxidation for lignin biomarkers. During the experimental period, 19–44% of manure C was decomposed without N addition, which decreased to 17–35% with N addition, except for the composted furfural residue with rice dregs. However, during different decomposition stages, N effect changed from stimulation to inhibition, or behaved as increasing inhibition. During stage 1 (days 0–100) when N stimulation effect reached a maximum, CO2 emissions from manure had positive relationships with labile C fraction indicators, including total sugars, soluble polyphenols, and lignin cinnamyl/vanillyl ratio regardless of N addition. N effect on manure decomposition was related to the C/N ratio and labile organic C content. During stage 2 (days 101–267), N effect shifted to inhibition, with CO2 emissions from manure negatively related to lignin vanillyl-units content. The magnitude of N inhibition increased linearly with the aromaticity of dissolved organic C, and was strengthened by nitrate in manure. Finally, N inhibition effect reached a maximum during stage 3 (days 268–365), increasing with higher aromatic C in manure. Critical factors for manure decomposition shifted from total sugars, soluble polyphenols, and lignin cinnamyl-units to recalcitrant lignin vanillyl-units and aromatic C fraction, which mediated the type and magnitude of N effect on decomposition. Our results suggested that the potential for enhancing soil C sequestration with organic manures would magnify under combined application with N fertilizer in the long term.Download high-res image (244KB)Download full-size image

•Biochar significantly stimulated N2O emission from paddy soils.•Biochar increased soil pH and bacterial amoA gene abundance.•Increased N2O emission was mainly due to increased bacterial amoA gene abundance.•Biochar shifted the community structure of AOB from Nitrosospira toward Nitrosomonas.•Biochar reduced the abundance of the nosZ gene but did not alter nirK and nirS levels.Biochar amendment of upland soil has been generally accepted to mitigate nitrous oxide (N2O) emissions. However, this is not always the case in rice paddy soil, and the underlying mechanisms are not well understood. To evaluate how biochar amendment affects N2O production and emissions in paddy soil, an incubation experiment was designed including six treatments: wheat straw-derived biochar (slow pyrolyzed at 400 °C) amendment at rates of 0% (Control), 1% and 4% soil mass (w/w), inorganic nitrogen (N) fertilizer amendment (with urea), and N fertilizer plus 1% biochar and 4% biochar. The application of 4% biochar significantly increased N2O emissions from N-unfertilized and fertilized soils during the 45-day incubation, by 291% and 256%, respectively, while 1% biochar amendment significantly increased soil N2O emissions when accompanied by N fertilizer addition. On day 14, when the N2O emission peaks occurred, N2O flux was significantly correlated with soil pH in all treatments. Biochar addition also enhanced the abundance of ammonia-oxidizing bacteria (AOB) amoA genes, which was significantly related to soil pH. Among all detected N2O-forming and reducing microbial genes, the abundance of AOB amoA genes was most closely related to N2O flux. On biochar addition, the AOB community structure shifted from Nitrosospira-dominated toward Nitrosomonas, and the diversity of AOB was significantly increased. Compared with the control, biochar amendment decreased, albeit not significantly, the abundance of the nitrous oxide reductase encoding gene nosZ, but did not alter the abundance of nitrite reductase encoding genes nirK and nirS. Our study suggests that wheat straw-derived biochar amendment of paddy soils increased soil pH, which in turn increased the abundance and diversity of AOB and N2O emissions.

•Interaction existed between biochar, N fertilizer and N2O emissions.•Biochar plus N fertilizer reduced N2O emissions during maize growing season.•Yield-scaled N2O emissions during maize growing season were considerably reduced by biochar.•Biochar application without N fertilization significantly increased wheat yield.•Biochar at 3 t ha−1 is considered to be beneficial for yield and mitigating N2O emissions.It is increasingly recognized that the addition of biochar to soil has potential to mitigate climate change and increase soil fertility by enhancing carbon (C) storage. However, the effect of biochar on yield and nitrous oxide (N2O) emissions from upland fields remains unclear. In this study, a one-year field experiment was conducted in an area of calcareous fluvo-aquic soil to assess and quantify the effect of maize straw biochar in reducing N2O loss during 2014–2015 in the North China Plain. Eight treatments were designed as follows: no nitrogen (N) fertilizer (control, CK); biochar application at rates of 3 (B3), 6 (B6) and 12 (B12) t ha−1; chemical fertilizer (NPK) application at 200 kg N ha−1 (F); and fertilizer plus biochar application at rates of 3 (FB3), 6 (FB6) and 12 (FB12) t ha−1. Crop yield, N2O fluxes, soil mineral N concentrations, and soil auxiliary parameters were measured following the application of treatments during each season. During the maize growing season, N2O emission was 0.57 kg N2O-N ha−1 under CK treatment, and increased to 0.88, 0.93 and 1.10 kg N2O-N ha−1 under B3, B6 and B12, respectively. In contrast, N2O emissions were significantly reduced by 31.4–39.9% (P < 0.05) under FB treatments compared with F, and the N2O emission factor of the applied N was reduced from 1.36% under F to 0.71–0.85% under FB. There was also a significant interaction effect of fertilizer and biochar on N2O emissions (P < 0.01). During the wheat growing season, biochar had no effect on N2O emissions regardless of the fertilizer regime. Biochar application did not affect maize yield; however, a significant increase in wheat yield of 16.6–25.9% (P < 0.05) was observed without N fertilization. Nevertheless, a reduction in wheat yield was measured at a biochar rate of 12 t ha−1 with fertilization. Overall, under maize cropping, N2O emissions per unit yield of grain, biomass, grain N and biomass N (yield-scaled N2O emissions) were significantly reduced by 32.4–39.9% under FB compared with F treatment, regardless of the biochar application rate. Biochar did not affect yield-scaled N2O emissions in wheat. Decreased soil bulk density with biochar is suggested to reduce the denitrification potential and N2O emissions; while increased retention capacity of fertilizer N in biochar-added soil decreased wheat growth and yield. These findings suggest that N fertilization plus biochar application at 3 t ha−1 is a practical strategy for reducing yield-scaled N2O emissions from maize fields in the North China Plain.Download high-res image (333KB)Download full-size image

•Soil respiration (Rs) was divided into auto- (Ra) and heterotrophic (Rh) component.•Ra was more temperature-sensitive than Rh; Rh was more moisture-sensitive than Ra.•Increase in Rs by N fertilization was largely due to the response of Ra.•Type and application rate of organic fertilizer affected Rs and Ra, but not Rh.•Applying half inorganic N plus half organic N potentially enhanced C sequestration.Partitioning soil respiration (Rs) into its heterotrophic (Rh) and autotrophic (Ra) components is crucial to evaluate the effects of inorganic and organic nitrogen (N) fertilization on carbon (C) cycling in agricultural ecosystems. We carried out a field experiment in a maize cropland in Northeast China using the root exclusion method to separate Rh and Ra, and investigate their responses to different fertilization regimes. These included no N fertilization (CK), inorganic N fertilizer (NPK), 75% urea N plus 25% pig (PM1) or chicken (CM1) manure N, and 50% urea N plus 50% pig (PM2) or chicken (CM2) manure N. Annual Rs was significantly increased from 314 g C m−2 in CK to 389, 366, and 371 g C m−2 in NPK, CM1, and PM2, respectively, and further to 420 g C m−2 in PM1, whereas a similar value to CK was observed in CM2 (327 g C m−2). N-induced increases in Rs were largely attributable to the response of Ra (except CM2), which increased by 18–54% due to higher nitrate supply. Rh increased from 183 to 192–209 g C m−2 in plots receiving N fertilizer, with significant increases observed in PM1 and PM2, likely due to the high ammonium and labile organic C concentrations in these treatments. Manure type and application rate had significant effects on Rs and Ra, but not Rh. Compared with CM, PM was more effective in stimulating Ra due to its greater decomposability. Rs and Ra decreased in the order of PM1 > PM2 and CM1 ≥ CM2, presumably because of the lower inorganic N supply with increasing manure application rate. The estimated C sequestration rate shifted from negative in CK and NPK to positive in the manure treatments, especially in PM2 and CM2 that gained 0.44 and 0.49 Mg C ha−1 yr−1, respectively. These results suggested that combined application of half inorganic N plus half organic N might have potential to enhance soil C sequestration in cropland of Northeast China.

Nitrogen (N) and sulfur (S) deposition are important drivers of global climate change, but their effects on litter decomposition remain unclear in the subtropical regions. We investigated the influences of N, S, and their interactions on the decomposition of 13C-labeled Pinus massoniana leaf litter. An orthogonal experiment with three levels of N (0, 81, and 270 mg N kg−1 soil) and S (0, 121, and 405 mg S kg−1 soil) was conducted. We traced the incorporation of 13C-litter into carbon dioxide (CO2), dissolved organic C (DOC), and microbial phospholipids. Over the 420-day incubation, litter decomposition did not respond to low N and S additions but increased under high levels and combined amendments (NS). However, litter-derived CO2 emissions were enhanced during the first 56 days, with a positive interaction of N × S. N additions promoted fungal growth, while S stimulated growth of Gram-positive bacteria, fungi, and actinobacteria. Increased decomposition was related to higher litter-derived DOC and fungi/bacteria ratio. Inversely, N and/or S amendments inhibited decomposition (N > NS > S) from day 57 afterwards, possibly due to C limitation and decreased abundances of Gram-negative bacteria and actinobacteria. These results suggested that N deposition interacted with S to affect litter decomposition, and this effect depended on N and S deposition levels and litter decomposition stage.

Repeated compost or inorganic fertilization may increase soil organic C (SOC) but how SOC accumulation relates to changes in soil aggregation, microenvironment and microbial community structure is unclear. Arable soils (Aquic Inceptisol) following a 20-year (1989–2009) application of inorganic fertilizer nitrogen (N), phosphorus (P) and potassium (K) (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK), compost (CM), half compost N plus half fertilizer N (HCM), and non-fertilization (Control) were collected to evaluate the relationship between SOC accumulation rate, soil aggregation, microenvironment and microbial community composition using phospholipid fatty acid (PLFA) analysis. Compared to the starting year, SOC content after 20 years under CM, HCM and NPK was significantly (P < 0.05) increased by 172 %, 107 % and 56 %, respectively, and by less than 50 % under NP, NK and PK. The mass proportion of macroaggregates was increased by 101–250 % under CM, but was not significantly affected by inorganic fertilizations, except PK. Compost and NPK significantly (P < 0.05) reduced the effective diffusion coefficient of oxygen primarily by increasing the proportion of pores <4 μm, and in contrast, increased the abundance of branched PLFAs and Gram-positive (G+) bacteria, resulting in the reduction of the ratio of monounsaturated/branched PLFAs (M/B) compared with Control. The mass proportion of macroaggregates was significantly (P < 0.01) and negatively correlated with the effective diffusion coefficient of oxygen; the latter was positively associated with M/B ratio. The SOC accumulation rate (z) had a significant interaction with the mass proportion of macroaggregates (x) and M/B ratio (y) (z = 0.514 + 4.345ex-15–0.149ey). Our results suggested that SOC accumulation promoted the macroaggregation and reduced the effective diffusion coefficient of oxygen, causing changes in microhabitats and a shift in microbial community composition to more facultative and/or obligate anaerobes; such microbial community shifts favored accumulation of SOC in turn.

The aim of this study was to understand the effect of nitrogen fertilization on soil respiration and native soil organic carbon (SOC) decomposition and to identify the key factor affecting soil respiration in a cultivated black soil.A field experiment was conducted at the Harbin State Key Agroecological Experimental Station, China. The study consisted of four treatments: unplanted and N-unfertilized soil (U0), unplanted soil treated with 225 kg N ha−1 (UN), maize planted and N-unfertilized soil (P0), and planted soil fertilized with 225 kg N ha−1 (PN). Soil CO2 and N2O fluxes were measured using the static closed chamber method.Cumulative CO2 emissions during the maize growing season with the U0, UN, P0, and PN treatments were 1.29, 1.04, 2.30 and 2.27 Mg C ha−1, respectively, indicating that N fertilization significantly reduced the decomposition of native SOC. However, no marked effect on soil respiration in planted soil was observed because the increase of rhizosphere respiration caused by N addition was counteracted by the reduction of native SOC decomposition. Soil CO2 fluxes were significantly affected by soil temperature but not by soil moisture. The temperature sensitivity (Q10) of soil respiration was 2.16–2.47 for unplanted soil but increased to 3.16–3.44 in planted soil. N addition reduced the Q10 of native SOC decomposition possibly due to low labile organic C but increased the Q10 of soil respiration due to the stimulation of maize growth. The estimated annual CO2 emission in N-fertilized soil was 1.28 Mg C ha−1 and was replenished by the residual stubble, roots, and exudates. In contrast, the lost C (1.53 Mg C ha−1) in N-unfertilized soil was not completely supplemented by maize residues, resulting in a reduction of SOC. Although N fertilization significantly increased N2O emissions, the global warming potential of N2O and CO2 emissions in N-fertilized soil was significantly lower than in N-unfertilized soil.The stimulatory or inhibitory effect of N fertilization on soil respiration and basal respiration may depend on labile organic C concentration in soil. The inhibitory effect of N fertilization on native SOC decomposition was mainly associated with low labile organic C in tested black soil. N application could reduce the global warming potential of CO2 and N2O emissions in black soil.

Nitrous oxide emission (N2O) from applied fertilizer across the different agricultural landscapes especially those of rainfed area is extremely variable (both spatially and temporally), thus posing the greatest challenge to researchers, modelers, and policy makers to accurately predict N2O emissions. Nitrous oxide emissions from a rainfed, maize-planted, black soil (Udic Mollisols) were monitored in the Harbin State Key Agroecological Experimental Station (Harbin, Heilongjiang Province, China). The four treatments were: a bare soil amended with no N (C0) or with 225 kg N ha−1 (CN), and maize (Zea mays L.)-planted soils fertilized with no N (P0) or with 225 kg N ha−1 (PN). Nitrous oxide emissions significantly (P < 0.05) increased from 141 ± 5 g N2O-N ha−1 (C0) to 570 ± 33 g N2O-N ha−1 (CN) in unplanted soil, and from 209 ± 29 g N2O-N ha−1 (P0) to 884 ± 45 g N2O-N ha−1 (PN) in planted soil. Approximately 75 % of N2O emissions were from fertilizer N applied and the emission factor (EF) of applied fertilizer N as N2O in unplanted and planted soils was 0.19 and 0.30 %, respectively. The presence of maize crop significantly (P < 0.05) increased the N2O emission by 55 % in the N-fertilized soil but not in the N-unfertilized soil. There was a significant (P < 0.05) interaction effect of fertilization × maize on N2O emissions. Nitrous oxide fluxes were significantly affected by soil moisture and soil temperature (P < 0.05), with the temperature sensitivity of 1.73–2.24, which together explained 62–76 % of seasonal variation in N2O fluxes. Our results demonstrated that N2O emissions from rainfed arable black soils in Northeast China primarily depended on the application of fertilizer N; however, the EF of fertilizer N as N2O was low, probably due to low precipitation and soil moisture.

The study examined the influence of compost and mineral fertilizer application on the content and stability of soil organic carbon (SOC). Soil samples collected from a long-term field experiment were separated into macroaggregate, microaggregate, and silt + clay fractions by wet-sieving. The experiment involved seven treatments: compost, half-compost N plus half-fertilizer N, fertilizer NPK, fertilizer NP, fertilizer NK, fertilizer PK, and control. The 18-year application of compost increased SOC by 70.7–121.7%, and mineral fertilizer increased by 5.4–25.5%, with no significant difference between control soil and initial soil. The C mineralization rate (rate per unit dry mass) in microaggregates was 1.52–2.87 mg C kg−1 day−1, significantly lower than in macroaggregate and silt + clay fractions (P < 0.05). Specific C mineralization rate (rate per unit SOC) in silt + clay fraction amounted to 0.48–0.87 mg C g−1 SOC day−1 and was higher than in macroaggregates and microaggregates. Our data indicate that SOC in microaggregates is more stable than in macroaggregate and silt + clay fractions. Compost and mineral fertilizer application increased C mineralization rate in all aggregates compared with control. However, compost application significantly decreased specific C mineralization rate in microaggregate and silt + clay fractions by 2.6–28.2% and 21.9–25.0%, respectively (P < 0.05). By contrast, fertilizer NPK application did not affect specific C mineralization rate in microaggregates but significantly increased that in silt + clay fractions. Carbon sequestration in compost-amended soil was therefore due to improving SOC stability in microaggregate and silt + clay fractions. In contrast, fertilizer NPK application enhanced SOC with low stability in macroaggregate and silt + clay fractions.

Little information is available on the effects of urease inhibitor, N-(n-butyl)thiophosphoric triamide (NBPT), and nitrification inhibitor, dicyandiamide (DCD), on nitrous oxide (N2O) emissions from fluvo-aquic soil in the North China Plain. A field experiment was conducted at the Fengqiu State Key Agro-Ecological Experimental Station, Henan Province, China, to study the influence of urea added with NBPT, DCD, and combination of both NBPT and DCD on N2O emissions during the maize growing season in 2009. Two peaks of N2O fluxes occurred during the maize growing season: the small one following irrigation and the big one after nitrogen (N) fertilizer application. There was a significant positive relationship between ln [N2O flux] and soil moisture during the maize growing season excluding the 11-day datasets after N fertilizer application, indicating that N2O flux was affected by soil moisture. Mean N2O flux was the highest in the control with urea alone, while the application of urea together with NBPT, DCD, and NBPT + DCD significantly lowered the mean N2O flux. Total N2O emission in the NBPT + DCD, DCD, NBPT, and urea alone treatments during the experimental period was 0.41, 0.47, 0.48, and 0.77 kg N2O–N ha−1, respectively. Application of urea with NBPT, DCD, and NBPT + DCD reduced N2O emission by 37.7%, 39.0%, and 46.8%, respectively, over urea alone. Based on our findings, the combination of DCD and NBPT together with urea may reduce N2O emission and improve the maize yield from fluvo-aquic soil in the North China Plain.

Literature reports on N2O and NO emissions from organic and mineral agricultural soil amended with N-containing fertilizers have reached contradictory conclusions. To understand the influence of organic manure (OM) and chemical fertilizer application on N2O and NO emissions, we conducted laboratory incubation experiments on an agricultural sandy loam soil exposed to different long-term fertilization practices. The fertilizer treatments were initiated in 1989 at the Fengqiu State Key Agro-ecological Experimental Station and included a control without fertilizer (CK), OM, mineral NPK fertilizer (NPK), mineral NP fertilizer (NP), and mineral NK fertilizer (NK). The proportion of N emitted as NO and N2O varied considerably among fertilizer treatments, ranging from 0.83% to 2.50% as NO and from 0.08% to 0.36% as N2O. Cumulative NO emission was highest in the CK treatment after NH4+-N was added at a rate of 200 mg N kg−1 soil during the 612-h incubation period, whereas the long-term application of fertilizers significantly reduced NO emission by 54–67%. In contrast, the long-term application of NPK fertilizer and OM significantly enhanced N2O emission by 95.6% and 253%, respectively, compared to CK conditions. The addition of NP fertilizer (no K) significantly reduced N2O emission by 25.5%, whereas applications of NK fertilizer (no P) had no effect. The difference among the N-fertilized treatments was due probably to discrepancies in the N2O production potential of the dominant ammonia-oxidizing bacteria (AOB) species rather than AOB abundance. The ratio of NO/N2O was approximately 24 in the CK treatment, significantly higher than those in the N-fertilized treatments (3–11), and it decreased with increasing N2O production potential in N-fertilized treatments. Our data suggests that the shift in the dominant AOB species might produce reciprocal change in cumulative NO and N2O emissions.

•13C-glucose addition resulted in a positive priming effect in Control, NPK and CM treatments.•G+ bacteria make a greater contribution to priming effects in the first 15 days.•Fungi and actinobacteria play a more important role later in the incubation period.•Compost and NPK fertilizer application reduced the priming effect in soil compared with Control.The altered mineralization rate of soil organic carbon (SOC) in the presence of exogenous organic substrates occurs by stimulating microbial activity. In this study, 13C-glucose was applied at a rate of 1000 μg 13C g−1 soil to arable soils following a 20-year application of compost (CM), inorganic NPK fertilizer (NPK) and a no-fertilizer Control. It was incubated for 30 days to evaluate how the labile substrate affected the microbial abundance and native SOC decomposition. Phospholipid fatty acids (PLFAs) were used as biomarkers for bacteria (Gram-positive bacteria, Gram-negative bacteria and actinobacteria) and fungi. 13C-glucose application resulted in a significant increase in microbial abundance and positive priming effect for all treatments. The primed CO2 flux derived from native SOC peaked on day 11, then increased gradually again from day 15 onwards in all treatments. The increase of abundance peaked on days 7 and 15 for Gram-negative (G−) bacteria and Gram-positive (G+) bacteria, however, fungal and actinobacterial PLFAs increased steadily from day 3 onwards under all three fertilization regimes. The results suggest that G+ and G− bacteria make a greater contribution to priming effects during the first 15 days of incubation, while fungi and actinobacteria are more important at the latter stages. The difference between glucose-derived 13C remaining in soils and primed CO2 from native SOC was 480, 381 and 263 mg C kg−1 in CM, NPK and Control treatments, respectively. Our study demonstrates that the exogenous labile organic substrate addition can more effectively promote C sequestration in organic C-rich soil (CM) than in organic C-poor soil (NPK or Control).

To understand the effects of long-term amendment of organic manure and N fertilizer on N2O emission in the North China Plain, a laboratory incubation at different temperatures and soil moistures were carried out using soils treated with organic manure (OM), half organic manure plus half fertilizer N (HOM), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (NK) and control (CK) since 1989. Cumulative N2O emission in OM soil during the 17 d incubation period was slightly higher than in NPK soil under optimum nitrification conditions (25°C and 60% water-filled pore space, WFPS), but more than twice under the optimum denitrification conditions (35°C and 90% WFPS). N2O produced by denitrification was 2.1–2.3 times greater than that by nitrification in OM and HOM soils, but only 1.5 times greater in NPK and NP soils. These results-implied that the long-term amendment of organic manure could significantly increase the N2O emission via denitrification in OM soil as compared to NPK soil. This is quite different from field measurement between OM soil and NPK soil. Substantial inhibition of the formation of anaerobic environment for denitrification in field might result in no marked difference in N2O emission between OM and NPK soils. This is due in part to more rapid oxygen diffusion in coarse textured soils than consumption by aerobic microbes until WFPS was 75% and to low easily decomposed organic C of organic manure. This finding suggested that addition of organic manure in the tested sandy loam might be a good management option since it seldom caused a burst of N2O emission but sequestered atmospheric C and maintained efficiently applied N in soil.

•O-alkyl C regulated initial N and S stimulation of litter decomposition.•Later N and S inhibition of decomposition was due to increased residue recalcitrance.•Microbial composition and activity were highly related to litter chemical changes.•N and S treatments had similar litter decay rates but distinct chemical changes.•N and S deposition facilitate C storage in subtropical plantation forest soils.Understanding the links between litter chemical transformations and functional microbial communities is key to elucidating the mechanisms of litter decomposition processes under nitrogen (N) and sulfur (S) deposition. Carbon (C)-13-labelled Pinus massoniana needles were incubated in a subtropical plantation forest soil exposed to: no amendment (Control), N amendments of 81 (N1) and 270 (N2) mg kg− 1, S amendments of 121 (S1) and 405 (S2) mg kg− 1 and combined N and S amendments. Litter decomposition was measured as litter-derived carbon dioxide (CO2) emissions and the litter C pools were partitioned using a two-pool model. Relationships between litter residue chemistry (assessed by 13C nuclear magnetic resonance spectroscopy analysis) and microbial community composition (probed by phospholipid fatty acid analysis, PLFA) and activity (the metabolic quotient, qCO2) were investigated. Over the 420 days incubation period, N and S additions (except N and S addition alone at low rate) significantly increased litter decomposition by 7.2–18.9% compared to the Control. Decomposition was stimulated by 10.2–61.9% during the initial 56 days (stage 1) and in contrast, 8.3–42.1% inhibition was measured during 57–420 days (stage 2) across the addition treatments. Stimulation on litter-derived CO2 emissions under the N and S additions was largely dependent on the loss of O-alkyl C, a dominant component of the litter active C pool. During the initial 7 days, N and S additions increased the ratio of fungal to bacterial PLFAs compared to the Control, which was accompanied by the increases in methoxyl C. The activity of microbes, particularly gram-negative bacteria, was also increased by N and S additions at stage 1, which was related to di-O-alkyl C. In contrast, fungal activity decreased under N and S additions at stage 2, accompanied by lowered C availability and increased methoxyl C. Alkyl C and aromatic C in the litter had positive relationships with the half-life of the slow C pool. Accordingly, the residue recalcitrance was increased under N and S additions compared with Control at stage 2, and was largely responsible for the inhibition of litter decomposition. Thus, N and S deposition is likely to increase the persistence of litter-derived recalcitrant C in subtropical forest soils in the long term.

•Application of dairy farm manure and effluent or inorganic fertilizer raises concerns on groundwater quality.•NO3− contributed 34–92% of total N leaching loss, followed by DON (14–57%).•Annual N leaching from inorganic N fertilizer treatment was the highest among treatments.•Yield-scaled N leaching of composted manure was the lowest among the treatments.•Use of composted manure could reduce N leaching loss while ensuring high crop yield.Dairy farm manure and effluent are applied to cropland in China to provide a source of plant nutrients, but there are concerns over its effect on nitrogen (N) leaching loss and groundwater quality. To investigate the effects of land application of dairy manure and effluent on potential N leaching loss, two lysimeter trials were set up in clayey fluvo-aquic soil in a winter wheat-summer maize rotation cropping system on the North China Plain. The solid dairy manure trial included control without N fertilization (CK), inorganic N fertilizer (SNPK), and fresh (RAW) and composted (COM) dairy manure. The liquid dairy effluent trial consisted of control without N fertilization (CF), inorganic N fertilizer (ENPK), and fresh (FDE) and stored (SDE) dairy effluent. The N application rate was 225 kg N ha− 1 for inorganic N fertilizer, dairy manure, and effluent treatments in both seasons. Annual N leaching loss (ANLL) was highest in SNPK (53.02 and 16.21 kg N ha− 1 in 2013/2014 and 2014/2015, respectively), which were 1.65- and 2.04-fold that of COM, and 1.59- and 1.26-fold that of RAW. In the effluent trial (2014/2015), ANLL for ENPK and SDE (16.22 and 16.86 kg N ha− 1, respectively) were significantly higher than CF and FDE (6.3 and 13.21 kg N ha− 1, respectively). NO3− contributed the most (34–92%) to total N leaching loss among all treatments, followed by dissolved organic N (14–57%). COM showed the lowest N leaching loss due to a reduction in NO3− loss. Yield-scaled N leaching in COM (0.35 kg N Mg− 1 silage) was significantly (P < 0.05) lower than that in the other fertilization treatments. Therefore, the use of composted dairy manure should be increased and that of inorganic fertilizer decreased to reduce N leaching loss while ensuring high crop yield in the North China Plain.Download high-res image (219KB)Download full-size image