Maize possesses exceptional diversity and undergoes rapid and extensive genetic changes during breeding. New genotypes impact soil microbiota, and respond differently to current climates compared with older genotypes in diverse environments, assessment of such interactions was a key novelty of the present study. Here, we investigated associations between genetic relationship, plant traits and soil bacterial and fungal composition based on six decades of maize breeding in China. Soil microbiome of six maize cultivars, each representing a popular variety developed each decade from the 1950s to 2000s, were collected from a long-term field experiment (established in 2012) and a pot experiment. Microbial community shifts were deduced from the taxonomic co-occurrence and co-exclusion network dynamics across maize growth stages. As expected, cultivar replacement influenced the soil bacterial and fungal composition (P < 0.001). At flowering, different maize genotype groups had distinctive bacterial community structure in the rhizosphere and root-zone soil. Aboveground dry matter, plant height and leaf area were plant traits that best explained the bacterial community variance (29.0 % in rhizosphere and 19.3 % in root-zone soil; P = 0.01) among maize cultivars. Specific root length showed a negative correlation with the gene copy numbers of alpha-Proteobacteria. The major maize cultivar from the 2000s (M-00s) had relatively more cultivar-enriched bacterial taxa, with a greater proportion of the genera Acidibacter and Variibacter in root-zone soil. Furthermore, the M-00s cluster contained the most phoD-genes related to phosphorus cycling at harvest, and had the highest bacteria/fungi ratio in the root zone at elongation and flowering. The predominant taxa in the biggest module changed with cultivar replacement, from Proteobacteria in the older maize cultivars to Acidobacteria in the M-00s cultivar. The contemporary M-00s cultivar may attract beneficial bacteria and fungi while reducing contact with other fungi, which improves soil nitrogen and phosphorus availability. If the plant-associated microbiome could serve as an extended phenotype, then specific gene locus in the maize genome could be targeted to optimize maize breeding for sustainable farming systems.

Maximizing the nitrogen (N) legacy effects of legumes is crucial for reducing N inputs in legume-based rotations to achieve high yield. Excessive N inputs have significantly negatively influenced the N legacy effects of peanut in the peanut-wheat rotation in the North China Plain (NCP). The optimization of N inputs to maximize N legacy effects of peanut and obtain high yields in peanut-wheat rotation has received considerable attention but remains uncertain. A field and pot experiment, comprising five treatments i.e., 0, 50, 100, 150 and 200 kg N ha-1 for peanut and 120 kg N ha-1 for wheat, were set up between 2019 and 2022. Our results showed that more N inputs in the peanut season resulted in higher wheat yields and N uptake. Additionally, higher N inputs of peanut caused larger N legacies from peanut residue to wheat. The N legacy from the peanut residue and soil N mineralization make a significant contribution to wheat. However, excessive N rates (N200) in the peanut season provided minimal improvement in the wheat yield but caused larger N surpluses at the rotational scale. The optimal N rate to achieve high wheat yields with a low N surplus was 270 kg N ha-1 in the peanut-wheat rotation, achieving wheat yield of 8249 kg ha-1 with an N legacy of 20.5 kg N ha-1. Our research should be beneficial for promoting sustainable wheat-peanut production in the NCP as well as in similar areas globally.

Context: The winter wheat-summer maize rotation in China's Huang-Huai-Hai (HHH) farming region has been plagued by the long-standing problem of excessive nitrogen (N) application, driven by ambiguous N fertilizer recommendations, due to insufficient understanding of inter-seasonal N turnover and long-term N accumulation effects in the crop-soil system. Objective: Our aims were (1) to calibrate the STICS model for the wheat-maize rotation in the HHH region, (2) to elucidate the annual N turnover characteristics affected by seasonal differences in N use, mineralization and leaching, and (3) to determine optimal N rates considering long-term cumulative effects of N fertilizer management. Methods: Data from an 11-year field experiment were used to calibrate and evaluate the STICS model. Scenario analysis contrasting different N rates for wheat and maize, as well as their pairwise combinations, was conducted to identify optimal N ranges for each season, aiming for high yields and nitrogen-use efficiency (NUE) in concert with low N surplus. Results: STICS well captured the dynamics of shoot biomass (rRMSE: 20-22 %), N uptake (rRMSE: 22-28 %) and soil water content (rRMSE: 19-24 %) under different N treatments, respectively. STICS relatively well simulated crop yields under various N rates, with rRMSE of 9-13 % in the short term, and 13-15 % in the long term. Simulated N mineralization was higher in maize seasons than in wheat seasons due to the higher temperature and soil moisture, leading to a greater N surplus and increased leaching under the current management. Our simulations revealed optimal N rates of 180 kg N ha-1 for wheat and 164 kg N ha-1 for maize, which were 12 % and 38 % lower than contemporary N use in the region, achieving a long-term stable annual yield of 18.2 Mg ha-1, along with an annual NUE of 78 % and an N surplus of 80 kg N ha-1 per year. Conclusions: High residual soil N from the wheat season and strong N mineralization during the maize season suggest that less N fertilizer can be applied to maize without influencing yield level. Implications: A systematic perspective and consideration of long-term N turnover within crop rotations provided by crop models and field observations are crucial for improving N management in the wheat-maize rotation in the HHH region of China.

Introduction: Leaching losses of applied N are an indirect source of nitrous oxide (N2O) emission, a major greenhouse gas emitted from fertilized soils. Mineral nitrogen (N) leaching research has largely concentrated on nitrate (NO3-), while ammonium (NH4+) leaching remains understudied. The cultivation conditions for rice and wheat are distinctly different, impacting the leaching losses of both NH4+ and NO3-. Methods: This study investigated the influence of different N treatments, i.e., no-N control, neem coated urea (NCU-N 100%; 120 kgN ha(-1)), 60 kgN ha(-1) Neem coated urea +30 kgN ha(-1) compost (75% N); 90 kgN ha(-1) Neem coated urea +30 kgN ha(-1) compost (100% N) and 120 kgN ha(-1) Neem coated urea +30 kgN ha(-1) compost (125% N) in comparison with prilled urea (PU, 120 kgN ha(-1)). Compost was applied @ 2.6 tonnes ha(-1) to all integrated treatments to provide 30 kgN ha(-1). Results and discussion: The peak concentration of soil NH4+ and NO3- was delayed by two-three days in NCU and integrated NCU + compost compared to PU in both rice and wheat, due to the slow-release effect of neem oil coating in NCU. In rice, the percolation rate of water was almost half than in wheat soil. The mineral N leaching loss in rice ranged from 0.4 to 4.6 kg NH4+-N ha(-1) and 0.46-5.12 kg NO3-N ha(-1) during the 2 years. In an annual rice-wheat cycle, the total N leaching loss was 6.2%-7.0% of the applied N fertilizer. The total mineral N loss was higher in PU than NCU by 7.8% and 10% in rice and wheat, respectively. Substitution of 25% of mineral N with compost decreased the total N leaching by 14.8% and 10.3% in rice and wheat, respectively, compared to NCU (100%). The crop N uptake increased significantly (p < 0.05) with NCU and integrated NCU + compost (100%) over PU. Application of 125%-N significantly increased the total mineral N leaching. The total mineral-N leaching loss was 15.9% higher in rice than wheat across the different treatments. The integrated N application, combining 75% NCU and 25% compost, can reduce mineral-N leaching, improve nitrogen uptake and maintain economic yields in rice-wheat cropping system.

Context: Maize plays a crucial role in global food security, while extensive use of nitrogen (N) fertilizers in maize production has posed severe environmental risks. The challenge of optimizing N fertilizer applications to obtain high maize yield, high NUE and low N losses has received considerable attention but lacks evidence from longterm field experiments. Objective: This study aims to quantify the influences of long-term continuous N applications on soil mineral N (SMN) and their subsequent effects on root growth, aboveground biomass accumulation, yield formation, and environmental benefits of maize, and determine the optimal N rate that ensures sustained high maize yield and environmental sustainability over the long-term. Methods: A winter wheat-summer maize double cropping system was established in the North China Plain (NCP) in 2010. This included five continuous N fertilizer treatments during the maize season, comprising 0, 75, 150, 225 and 300 kg N ha-1, which were denoted as N0, N75, N150, N225 and N300 in the study. Results: Increasing N rates resulted in higher N surpluses and SMN, leading to much higher aboveground biomass and maize yield, but also caused reduced NUE over the 12-year period. Specifically, the mean maize yield was 6.7, 8.8, 9.9, 10.4 and 10.1 Mg ha-1 for the N0-N300 treatments during 2011-2022, respectively. The low yield in the N0 treatment was mainly because long-term zero N inputs led to low SMN thus restricting roots growth, aboveground biomass accumulation and yield formation. In contrast, high SMN inhibited roots distribution, which subsequently negatively influenced post-silking dry matter remobilization and yield and thus caused a much lower harvest index (HI) in the N300 treatment. Effects of N fertilizer on maize yield intensified along with increasing experimental duration, thus requiring more N to achieve high yields in the latter years. The optimal N rates showed a strong positive correlation with the annual maximum yields over the experimental period, averaging 153 kg N ha-1 in achieving high yield, high NUE and low surplus. Conclusions: Our findings demonstrated that the prolonged low N input could result in soil depletion, limiting maize growth and thereby compromising yield sustainability. Conversely, excessive N application led to SMN accumulation and higher N loss risks. The optimal N rate is 153 kg N ha-1 that can obtain long-term high maize yield stability while minimizing environmental costs in the NCP. Implications: Our long-term experimental results provide robust evidence for optimizing N fertilizer applications in achieving high yield and high NUE with low N surplus in maize production in the wheat-maize double cropping in the NCP and similar cropping systems worldwide.

The future of reactive nitrogen (N) for subtropical lowland rice to be characterised under diverse N -management to develop adequate sustainable practices. It is a challenge to increase the efficiency of N use in lowland rice, as N can be lost in various ways, e.g., through nitrous oxide (N2O) or dinitrogen (N2) emissions, ammonia (NH3) volatilization and nitrate (NO3-) leaching. A field study was carried out in the subsequent wet (2021) and dry (2022) seasons to assess the impacts of different N management strategies on yield, N use efficiency and different N losses in a double -cropped rice system. Seven different N -management practices including application of chemical fertilisers, liquid organic fertiliser, nitrification inhibitors, organic nutrient management and integrated nutrient management (INM) were studied. The application of soil test -based neem-coated urea (NCU) during the wet season resulted in the highest economic yield, while integrated nutrient management showed the highest economic yield during the dry season. Total N losses by volatilization of NH3, N2O loss and leaching were 0.06-4.73, 0.32-2.14 and 0.25-1.93 kg ha - 1, corresponding to 0.06-5.84%, 0.11-2.20% and 0.09-1.81% of total applied N, respectively. The total N -uptake in grain and straw was highest in INM (87-89% over control) followed by the soil test -based NCU (77-82% over control). In comparison, recovery efficiency of N was maximum from application of NCU + dicyandiamide during both the seasons. The N footprint of paddy rice ranged 0.46-2.01 kg N-eq. t-1 during both seasons under various N management. Ammonia volatilization was the process responsible for the largest N loss, followed by N2O emissions, and NO3- leaching in these subtropical lowland rice fields. After ranking the different N management practices on a scale of 1-7, soil test -based NCU was considered the best N management approach in the wet year 2021, while INM scored the best in the dry year 2022.

The primary driver of increasing atmospheric concentrations of nitrous oxide (N2O) is the use of organic and synthetic fertilizer to increase agricultural crop production. Current global estimates are based on IPCC N2O emission factor (EF) calculations, although there are shortcomings as many of the N2O EFs are derived from measurements during the cropping season. These neglect the fallow season, and do not adequately account for double or even triple cropping systems or legacy effects on soil N2O emissions in the following year. In this study, we assessed the legacy effect of fertilization on soil N2O fluxes using data from a long-term double-cropping field experiment with summer maize and winter wheat in rotation, in which no nitrogen (N; NN) and balanced manure with synthetic N (MN) fertilized treatments were switched to allow an assessment of legacy effects. Based on high-frequency measurements of N2O and previous data, we calculated that the historical N fertilization, or legacy effect, explained 23 % of the annual flux of 0.81 kg N ha−1 yr−1 in the first season of observation. In the following three seasons, the legacy effect of the previous N fertilization regime decreased to a negligible level, with N2O emissions mainly driven by in-season fertilization. Our data show that, on average, the seasonal EF for N2O was about 0.11 % higher in response to the previous N fertilization. Our study indicates that the current N2O EF may severely underestimate emissions because studies ignore legacy effects on N2O emissions from zero N plots and only compare zero N with N fertilization treatments for a given season or year to derive seasonal or annual N2O EF.

Labile carbon (C) continuously delivered from the rhizosphere profoundly affects terrestrial nitrogen (N) cycling. However, nitrous oxide (N2O) and dinitrogen (N2) production in agricultural soils in the presence of continuous root C exudation with applied N remains poorly understood. We conducted an incubation experiment using artificial roots to continuously deliver small-dose labile C combined with 15N tracers to investigate N2O and N2 emissions in agricultural soils with pH and organic C (SOC) gradients. A significantly negative exponential relationship existed between N2O and N2 emissions under continuous C exudation. Increasing soil pH significantly promoted N2 emissions while reducing N2O emissions. Higher SOC further promoted N2 emissions in alkaline soils. Native soil-N (versus fertilizer-N) was the main source of N2O (average 67%) and N2 (average 80%) emissions across all tested soils. Our study revealed the overlooked high N2 emissions, mainly derived from native soil-N and strengthened by increasing soil pH, under relatively real-world conditions with continuous root C exudation. This highlights the important role of N2O and N2 production from native soil-N in terrestrial N cycling when there is a continuous C supply (e.g., plant-root exudate) and helps mitigate emissions and constrain global budgets of the two concerned nitrogenous gases.

Carbon within mineral associated organic matter (MAOM) is an important persistent form of soil organic carbon (SOC). However, processes driving the retention of new labile C in MAOM are not fully understood. We investigated the effects of glucose and ammonium nitrate (AN) addition on the short-term (72 h) retention of applied 13C-glucose within MAOM. We found an interactive effect of AN addition with the glucose addition rate. Higher rates of glucose addition resulted in proportionally less glucose-C retained, indicating lower MAOM-C formation efficiency. Addition of AN only altered the proportional retention of glucose where glucose was applied at the lowest rate. In this instance glucose-13C recovery increased with AN addition. However, after 72 h there was no treatment difference in total MAOM-C, indicating that any changes in formation efficiency as a result of AN and glucose additions, did not result in differences in total MAOM-C in the short-term. Whether and how this affects the medium and longer-term dynamics of MAOM-C requires further investigation.

While wheat domestication is reported to influence the soil microbial community, few studies have evaluated the influence of cultivar replacement in modern breeding on both bacterial and fungal communities. Especially, few studies reported the bacterial-fungal interkingdom association by analysis of taxa co-occurrence or co-exclusion between different wheat growth stages. In this study, we selected major wheat cultivars from different decades to investigate their genetic relatedness, plant traits, soil bacterial and fungal communities in the rhizosphere and proximal root zone, and the relationships between them. Our results indicated that host selection had the greatest impact on bacterial and fungal communities compared to growth stage and sampling location (P<0.001). At flowering, the soil microbial community in the genotype group consisting of the 1950 s (W-50 s) and 1960 s (W-60 s) cultivars could be clearly distinguished from those in later genotype groups. Plant traits explained the largest source of variation in microbial beta-diversity (12.8-20.6%) (P=0.01), with plant height, aboveground dry matter, leaf area per plant and specific root length being associated with the divergence in microbial composition or quantity among cultivars. The cultivar from the 1970 s (W-70 s) enriched a greater number of microbial taxa with the highest relative abundance, suggesting that old cultivar could be considered as a source of cultivar-microbe interaction. The cultivar from the 2000 s (W-00 s) enriched taxa from the bacterial genus Nocardioides and increased the fungal phylum Glomeromycota in the rhizosphere. At three growth stages, W-00 s root-zone exhibited the highest bacteria/fungi ratio (B/F) and contained more phosphorus cycle-related bacterial phoD-genes than W-50 s and W-60 s. The co-occurrence network revealed more operational taxonomic units (OTUs) from the bacterial order Rhizobiales in the largest module of W-00 s. The increased B/F ratio and the aforementioned taxa are reported to be involved in soil nitrogen and phosphorus availability, suggesting that contemporary cultivar may recruit beneficial bacteria and fungi while weaken the association with other fungi. These findings contribute to the development of microbiome-based breeding strategies for sustainable wheat farming.

Nitrogen (N) losses from agriculture through leaching and volatilization have significant environmental and economic impacts. To find better options for reducing N losses, different N management approaches were compared to determine leaching losses of Nr (NH4+-N and NO3−-N) and ammonia (NH3) volatilization from wetland rice. The experiment comprised seven treatments, viz., zero N (control), recommended dose of N (RDN), 125

Soil is a valuable natural resource and medium for plant growth. Modern approaches to agricultural production can have negative impacts on soil health through interventions such as injudicious fertilizer application, tillage operations, and pesticide applications. The aims of this study were to explore whether nitrogen (N) fertilizer management could contribute to improved soil health in degraded calcareous dark gray soils in the northern part of Bangladesh. We investigated the effect of applying N as different fertilizer options (1) Zero N, (2) recommended dose (180 kg ha-1) prilled urea (PU) N, (3) recommended dose plus 25% extra prilled urea (PU) N, (4) 25% minus of recommended dose prilled urea (PU) N, (5) recommended dose in 2 metric ton ha-1 (MT ha-1) cow dung with prilled urea (PU) N, (6) Urea super granule (USG) deep placement and (7) 4 MT ha-1 biochar with recommended prilled urea (PU) N. In our experiment, we observed that fertilizer management options using biochar (4 MT ha-1) with the recommended rate of PU N and cow dung N (2 MT ha-1) supplemented with PU N contributed to the maintenance of good such as physical and chemical properties of soil. After three years of experimentation, the proportion of sand particles in the experimental soil was reduced slightly. On the other hand, the proportion of silt and clay particles increased due to the application of cow dung N 2 MT ha-1 supplemented with PU N and biochar 4 MT ha-1 with recommended PU N. The combined application of cow dung and biochar with fertilizer N significantly increased soil organic matter (1.79 and 1.38% where the initial value was 1.20%) and total N content (0.07-0.09%). The addition of biochar in the soil increased the soil pH (7.62-8.60). The available phosphorus and exchangeable potassium were improved in the soil due to application of cow dung and biochar. Likewise, the zinc content of the post-harvest soil also increased. Therefore, the application of biochar 4 MT ha-1 with recommended prilled urea N and cow dung N 2 MTha-1 with supplemented prilled urea N are the two good options for restoration or improvement of soil physical and chemical properties.

CONTEXT: The UK Climate Change Committee has recommended a 64% reduction in greenhouse gas emissions from the agriculture and land -use sector to meet the 2050 Net Zero target in the UK. However, it is unclear how this reduction can be achieved at a farm level. OBJECTIVE: Using detailed real farm data and novel modelling approaches, we investigated the management interventions and afforestation that would be required to deliver Net Zero within the farm boundary. METHODS: Baseline carbon footprints were calculated for twenty Welsh beef and sheep farms using the Agrecalc carbon calculator, whilst carbon sequestration was estimated using Bangor University's Carbon Footprinting Tool. Scenarios were created to determine the emissions reductions achievable on each farm through implementation of cost-effective mitigation measures. Mitigation measures and their abatement potentials were sourced from the most recent UK Marginal Abatement Cost Curve, which allow emissions to be reduced mostly through improvements in efficiency thus maintaining the production of the system. Area footprints were calculated for production, with and without offset (afforested) areas needed to achieve Net Zero. RESULTS AND CONCLUSION: Emission reductions following the implementation of cost-effective mitigation measures averaged 28% across all farms, ranging from 19 to 35%. The woodland needed to offset the remaining emissions to achieve Net Zero ranged from 8 to 85% of the farm area, with an average 38%. This offset area was equivalent to on average 17.4 m2.yr kg -1 deadweight (carcass weight). Apparent area efficiency decreased when the offset area was accounted for, however, the ranking of farms in terms of efficiency was largely unaffected. Mitigation scenarios rely on several assumptions and these need to be refined to accurately inform Net Zero pathways. SIGNIFICANCE: Based on the results for these study farms, our modelling indicates that even after implementation of ambitious mitigation across beef and sheep farms, large-scale land use change will be required to achieve Net Zero at an individual farm -level. However, this reform could lead to the unintended consequence of displacing production to less efficient systems and increase overall emissions. Instead, we advocate a combined approach of carbon and land footprints that could help to identify farms on which either food production or carbon removals should be prioritised to move the industry towards achieving Net Zero at a sectoral, regional or national level.

Soybean-based rotations have long proven beneficial for increasing subsequent crop productivity and nitrogen (N) use efficiency (NUE) under low chemical N inputs. Despite this, importance of soil microbial community and enzymes in N cycling processes has not been well investigated. As well, optimal fertilizer-N that achieve high yield and NUE with low GHG emissions remain uncertain, as perceived “optimal” fertilization varies widely across agroclimatic regions, seasons and production systems. Here, our systematic review indicated that soybean-based rotations mitigate soil-borne diseases, such as cyst nematodes, and thus contribute to increased soybean yield. We show that soybean roots produce large amounts of root exudates, which are conducive to formation of soil macroaggregates and carbon accumulation, enhancing soil health and productivity of gramineous crops. Biological N fixation (BNF) and rhizosphere N deposition of soybean crops together evoke high soil N content and low C:N ratio. We found that soybean-based rotations significantly alleviated acidification and positively influenced soil microbial activities and enzyme activities, reducing N2O and CO2 emissions. Our study demonstrates that reduced fertilizer N inputs catalyse greater BNF and pre-crop effects of soybean in rotations. We provide compelling dialogue that underlines the biological, environmental and economic implications of soybean crops for long term sustainability in farming systems.

Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2 O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2 O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2 O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N2 O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2 O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2 O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N2 O emissions.

The consumption of meat and dairy products raise enormous environmental concerns. Circa 80% of global greenhouse gas emissions (GHG) from the livestock industry originate from beef, milk and pork production. Changing the production and consumption of meat and dairy products is considered to offer an important contribution to achieving the Paris Agreement climate targets (UNFCCC, 2015), and could reduce the import of soybean meal to Europe from countries where it is linked with deforestation. However, individual diet substitutions may have indirect and unintended environmental consequences across interlinked livestock systems - hence a wider assessment of impacts of consumption changes is required using consequential life cycle assessment (LCA). In this study, we investigated the environmental consequences of two independent yet interconnected diet choices in a German context: (i) replacing dairy milk with soy milk, and; (ii) replacing beef meatballs with pea protein balls. We related commodity demand to detailed agricultural rotations and land use changes via farm scale economic modelling coupled with consequential LCA. The substitution of beef meatballs with pea-derived protein balls can result in GHG savings of 2.4 kg CO2e per 100 g serving, and up to 7.3 kg CO2e per 100 g serving if spared land is afforested. Environmental problems related to nutrient leakage such as acidification and eutrophication are also mitigated. Meanwhile, unless accompanied by dramatic reductions in beef consumption, the substitution of cow milk with soy-based milk does not lead to significant GHG mitigation owing to the displacement of dairy-beef production to less efficient suckler-beef systems. Nonetheless, land sparing by cow milk substitution could support overall GHG mitigation if combined with afforestation. This study confirms that legumes can play an important role in diet transitions towards climate neutrality, especially via substitution of meat (as opposed to dairy) products.

Nitrous oxide (N2O) emissions occur as a consequence of the turnover of soil nitrogen (N), but gross N transformations and N2O production are often not studied in combination, so the relationships are poorly understood. Here, we quantified gross N transformations and the N2O production pathway of alkaline fluvo-aquic soils under different fertilization regimes collected from a long-term field experiment in the North China Plain and compared them with six acidic UK soils (one was alkaline for reference) with high soil organic carbon (SOC). We found that nitrification was the dominant N2O production pathway in the alkaline Chinese soil with a contribution of nitrification to N2O emissions (N2Onit) of 81%. By contrast, denitrification was the main N2O production pathway for the acidic UK soils with the contribution of denitrification to N2O emissions (N2Oden) of 66%. Long-term manure applications significantly increased N2Oden, compared to the synthetic N and no N treatments (25% vs. 18%). The N2Onit was positively correlated with gross autotrophic nitrification rates and pH but negatively correlated with gross N mineralization, SOC, soil total N content, and C:N ratios. Our findings highlight the importance of soil pH in controlling the N2O production in cropland soils, and suggest that the increased contribution of denitrification to N2O emissions should be considered, when increasing SOC through long-term manure and straw management for carbon sequestration and soil fertility improvement.

The optimization of nitrogen (N) fertilization has become an ever more important global challenge with the aim of achieving high crop yields and high N use efficiency (NUE) with low environmental risks. The North China Plain (NCP) is China's most important wheat (Triticum aestivum Linn.) production region, and a global hotspot for N fertilizer use. How much nitrogen can be saved compared to the farmers' level that would not influence wheat yield, and lead to high NUE with low N surplus? It is still challenging as there are not enough evidences from the long-term experiments. Thus, continuous detailed observations from an ongoing long-term experiment in the NCP since 2010 with five N rates, namely 0 (N0), 60 (N60), 120 (N120), 180 (N180) and 240 (N240) kg N ha-1, were included in the study. Our results indicated that stable high wheat yield cannot be achieved without enough N inputs from the long-term, because of severely depleted N pool in the N0 and N60 treatments seriously influenced root growth and wheat development thus damaged wheat yield. Though highest wheat yield was obtained in the N240 treatment, the high N rate caused lowest NUE and largest N surplus with high soil mineral N (SMN) with the mean value of 143 kg N ha-1 at the 0-60 cm layer at harvest. Besides, both root weight density (RWD) and root length density (RLD) were much lower in the N240 treatment compared to that in the N180 treatment. Our integrative analyses clearly indicate that the optimal N application for achieving high yield, high NUE and low environmental risks in wheat production was 180 kg N ha-1 based on long-term observations. Our results should be beneficial for promoting sustainable wheat production in the NCP and similar regions with wheat-based double cropping over the world.