Search

Increasing biological nitrogen (N) fixation (BNF) in maize production could reduce the environmental impacts of N fertilizer use, but reactive N in the rhizosphere of maize limits the BNF process. Using non-transgenic methods, we developed gene-edited strains of Klebsiella variicola (Kv137-2253) and Kosakonia sacchari (Ks6-5687) bacteria optimized for root-associated BNF and ammonium excretion in N-rich conditions. The aim of this research was to elucidate the mechanism of action of these strains. We present evidence from in vitro, in planta and field experiments that confirms that our genetic remodeling strategy derepresses BNF activity in N-rich systems and increases ammonium excretion by orders of magnitude above the respective wildtype strains. BNF is demonstrated in controlled environments by the transfer of labeled 15N2 gas from the rhizosphere to the chlorophyll of inoculated maize plants. This was corroborated in several 15N isotope tracer field experiments where inoculation with the formulated, commercial-grade product derived from the gene-edited strains (PIVOT BIO PROVEN® 40) provided on average 21 kg N ha-1 to the plant by the VT-R1 growth stages. Data from small-plot and on-farm trials suggest that this technology can improve crop N status pre-flowering and has potential to mitigate the risk of yield loss associated with a reduction in synthetic N fertilizer inputs. [ABSTRACT FROM AUTHOR]

Replacing chemical nitrogen (N) fertilizer with monosodium glutamate waste liquid residue (MSGWLR) is beneficial for achieving clean production in both the monosodium glutamate (MSG) industry and agriculture. However, the impact of this method on rice production and environment has not yet been clear. This study adopted field experiments to clarify the rice yield, quality and carbon emissions applying conventional application of chemical N fertilizer (CF), reduction of N fertilizer by 20% (N80%), based on reduction of chemical N fertilizer by 20% and replacing 50% chemical N fertilizer with MSGWLR (MSGWLR50%), and replacing 100% chemical N fertilizer (MSGWLR100%). The results showed that compared with CF treatment, MSGWLR100% showed no significant changes in rice yield, milling quality, fatty acid value, and taste quality. The chalkiness rate of rice significantly decreased, and the protein content significantly increased. On the other hand, the carbon emissions from rice production treated with MSGWLR100% were the lowest, with a 58.5% decrease in global warming potential (GWP) compared to CF treatment. This was mainly because MSGWLR100% treatment could provide rich and balanced nutrients for rice growth, and it did not promote greenhouse gas (GHG) emissions from paddy field. At the same time, it effectively reduced the indirect carbon emissions in chemical fertilizer production by reducing chemical N fertilizer. Therefore, the MSGWLR100% fertilization treatment is beneficial for cleaner production in the MSG industry and rice cultivation. Highlights: • MSGWLR could effectively replace chemical N fertilizer while maintaining rice yield. • Both MSGWLR50% and MSGWLR100% treatments successfully maintained rice quality. • Replacing chemical N fertilizer with MSGWLR significantly reduced carbon emissions from rice production. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is one of the most important climate-forcing gases, and a large portion of global anthropogenic N2O emissions come from agricultural soils. Yet, how contrasting global change factors and agricultural management can interact to drive N2O emissions remains poorly understood. Here, conducted within a rice–wheat cropping system, we combined a two-year field experiment with two pot experiments to investigate the influences of elevated atmospheric carbon dioxide (eCO2) and crop straw addition to soil in altering N2O emissions under wheat cropping. Our analyses identified consistent and significant interactions between eCO2 and straw addition, whereby eCO2 increased N2O emissions (+ 19.9%) only when straw was added, and independent of different N fertilizer gradients and wheat varieties. Compared with the control (i.e., ambient CO2 without straw addition), eCO2 + straw addition increased N2O emission by 44.7% and dissolved organic carbon to total dissolved nitrogen (DOC/TDN) ratio by 115.3%. Similarly, eCO2 and straw addition significantly impacted soil N2O-related microbial activity. For instance, the ratio of the abundance of N2O production genes (i.e., nirK and nirS) to the abundance of the N2O reduction gene (i.e., nosZ) with straw addition was 26.0% higher than that without straw under eCO2. This indicates an increased denitrification potential and suggests a change in the stoichiometry of denitrification products, affecting the balance between N2O production and reduction, leading to an increase in N2O emissions. Taken together, our results emphasize the critical role of the interaction between the specific agronomic practice of straw addition and eCO2 in shaping greenhouse gas emissions in the wheat production system studied, and underline the need to test the efficacy of greenhouse gas mitigation measures under various management practices and global change scenarios. [ABSTRACT FROM AUTHOR]

Organic carbon based amendments can improve soil structure and fertility, as well as increase composition and diversity of soil microbial community. One of the major functions of improving soil fertility is to achieve effective nitrogen (N) management and mineralization. In this study, 746 paired observations were pooled from 20 long-term field experiments to verify the hypothesis that compared to synthetic only fertilization, long-term application of organic fertilization alone or in combination with synthetic fertilization could strengthen multiple internal pathways for soil N supply under various climatic conditions. We found that long-term application of synthetic N fertilizers alone or in combination with phosphorus (P) and potassium (K) led to an increase only in the recalcitrant organic N mineralization rate (MNrec) by 210% and 263%, respectively. However, long-term application of organic fertilizers alone or in combination with synthetic N fertilizers increased MNrec, labile organic N mineralization rate (MNlab) and release of adsorbed ammonium from cation exchange sites (RNH4a) by 160% and 200%, 153% and 353%, and 1025% and 541%, respectively. This indicates that organic fertilization can strengthen multiple internal pathways for mineral N production. The long-term co-application of organic and synthetic fertilizers stimulated MNlab (197%), MNrec (151%) and RNH4a (563%) in subtropical regions, but it had no effect on heterotrophic nitrification (ONrec). In contrast, it stimulated MNrec (505%), RNH4a (633%) and ONrec (184%) in temperate regions, with no observed effect on MNlab. These data confirm that if one N supply source is shut-off under specific climatic conditions the other pathways continue to provide N. The meta-analysis advances our understanding of agroecosystems and as such help to improve frameworks for enhancing soil health. [ABSTRACT FROM AUTHOR]

Intensified atmospheric nitrogen (N) deposition, coupled with increased application of N fertilizers in forest plantations, has resulted in N and phosphorus (P) imbalance in the forest soil system. However, it is seldom investigated whether an addition of N counteracts the effects of low P stress on N and P nutrient absorption and utilization efficiencies. Thus, we conducted a greenhouse experiment on three clones of Chinese fir (clones 061, 020 and 2 C) with four levels of N addition (2, 5, 10, and 15 mmol·L− 1 sodium nitrate) under normal P supply (1.0 mmol·L− 1 KH2PO4), moderately P deficiency (0.5 mmol·L− 1 KH2PO4) and severely P deficiency (0.1 mmol·L− 1 KH2PO4) conditions. The results showed that addition of moderate concentration of N (10 mmol·L− 1 N) significantly promoted root elongation, root dry mass accumulation, root surface area and root APase activity of Chinese fir seedlings under P-deficient conditions, with distinct clonal variation. Seedlings of clone 061 showed the most root APase activity in response to addition of moderate concentration of N under P deficient condition while clones 061 and 020 had the longest roots and the largest root dry mass accumulation. Under severe P deficiency, the N and P absorption efficiencies (NAE and PAE) of Chinese fir seedlings increased with increasing N concentration, while the N and P utilization efficiencies (NUE and PUE) decreased. The findings demonstrate that addition of moderate level of N modulates the adaptive responses of Chinese fir to P deficiency and enhances the absorption efficiency of P. The variation among clones suggests that the responses are genetically controlled and there exists great potential for breeding highly phosphorus efficient genotypes under coupled conditions of P deficiency and increased atmospheric nitrogen deposition. [ABSTRACT FROM AUTHOR]

The article presents the results of a three-year field study that was conducted in Poland to evaluate the yield and quality of seeds and oil from traditional (SAM) and canola-quality white mustard (SAC) in response to different N fertilizer rates (0, 40, 80, 120, and 160 kg ha–1). Seed yields were 25% higher in SAM than SAC. The seeds of SAC contained more crude fat (by 3%) and crude fiber (by 6%) than the seeds of SAM. In turn, the seeds of SAM were a richer source of total protein (by 7%). The content of glucosinolates (GSLs) was 8–10 times lower in the seeds of SAC than SAM. The seeds of both mustard cultivars were most abundant in γ-tocopherol (γ-T) (90–94%). The seeds of SAC were characterized by a higher content of γ-T and a lower α-T/γ-T ratio than SAM seeds. White mustard oil contained mostly MUFAs (69–75%). However, C22:1 accounted for more than 50% of MUFAs in the oil SAM. In the oil SAC, the proportion of C22:1 did not exceed 6%, whereas C18:1 accounted for nearly 85% of total MUFAs. Nitrogen fertilization induced a significant increase in seed yields (by 33%), a decrease in crude fat content (by 3–4%), and an increase in total protein content (by 4%), and crude fiber content (by 7%). Nitrogen decreased GSL levels by 31% in SAM seeds. In SAC, N fertilization induced differences in the qualitative composition of GSLs, but did not affect the total GSL content of seeds. Higher N rates increased the content of α-T and γ-T, the α-T/γ-T ratio, and total T content. Nitrogen fertilization decreased the content of C18:3 in the seeds of the SAM. In SAC, the application of N decreased the content of C18, C18:1, and C18:3, and increased the biosynthesis of C18:2, C20:1, and C22:1. [ABSTRACT FROM AUTHOR]

Fertilizers are an essential input in agriculture as they can enhance crop yields. However, their use also poses significant environmental risks. To thoroughly explore the intensity of fertilizer use and its potential threats to the ecological environment, this study analyzed the environmental risks of fertilizer use from a temporal and spatial perspective based on fertilizer application data in China from 1978 to 2022. Additionally, the contribution of fertilizer application in Chinese farmland to greenhouse gas N2O emissions was quantified using IPCC emission factor methodology. The results indicated that fertilizer application intensity and N2O emissions in China initially increased and then decreased from 1978 to 2022. Despite the implementation of various fertilizer control measures at the policy level, such as the Zero Growth of Fertilizer Action in 2015 and the Efficiency-Increasing Action for Reducing Fertilizer Use in 2022, the intensity of fertilizer application in China still exceeded international safety standards by 1.33-fold in 2022, reaching 298.79 kg/hm2. Furthermore, N2O emissions amounted to 50.17 × 104t, accounting for 16% of China's total agricultural greenhouse gas emissions that year. Correlation and regression analyses demonstrated that with increasing fertilizer application, crop production exhibits an inverted U-shaped growth trend, indicating limited effectiveness of high-intensity fertilizer use in increasing crop yields. These findings highlight the profound greenhouse effect resulting from the use of agricultural nitrogen fertilizer. Therefore, this study proposed technical and policy-level mitigation measures to address the issues caused by excessive fertilizer application, aiming to provide insights for controlling agricultural non-point source pollution and preserving the agroecological environment. [ABSTRACT FROM AUTHOR]

Urban rivers worldwide have been increasingly threatened by nitrate (NO3−) pollution. The Xianyang-Xi'an segment of the Weihe River, located in the loess plateau with serious soil erosion, has been highly urbanized and with intensive agricultural activities. Tracing the sources and transformations of NO3− is particularly challenging for this watershed which has multiple N sources and variable environmental factors. In this study, integrating antecedent studies with multiple stable isotopes and MixSIAR models, these river basins can be categorized into three classes: (1) urban areas, sewage, and manure were the predominant sources of NO3− in the Weihe River's mainstream, accounting for 73.4 ± 12.8%; (2) suburban areas, sewage and manure (Fenghe River, 58.0 ± 14.0%; Bahe River, 53.9 ± 15.0%) were recognized as the main sources of NO3−; (3) and the rural areas, ammonium nitrogen fertilizers were identified as the primary source of NO3− in the Heihe and Laohe Rivers. In addition, nitrification dominated the mainstream of the Weihe, Fenghe, and Bahe Rivers, while neither denitrification nor nitrification was evident in the Heihe and Laohe Rivers. In conclusion, this study is important for the improvement of surface water quality of rivers with different land use types and the development of targeted water environment management. [ABSTRACT FROM AUTHOR]

Symbiotic nitrogen fixation (SNF) in legume-rhizobia serves as a sustainable source of nitrogen (N) in agriculture. However, the addition of inorganic N fertilizers significantly inhibits SNF, and the underlying mechanisms remain not-well understood. Here, we report that inorganic N disrupts iron (Fe) homeostasis in soybean nodules, leading to a decrease in SNF efficiency. This disruption is attributed to the inhibition of the Fe transporter genes Natural Resistance-Associated Macrophage Protein 2a and 2b (GmNRAMP2a&2b) by inorganic N. GmNRAMP2a&2b are predominantly localized at the tonoplast of uninfected nodule tissues, affecting Fe transfer to infected cells and consequently, modulating SNF efficiency. In addition, we identified a pair of N-signal regulators, nitrogen-regulated GARP-type transcription factors 1a and 1b (GmNIGT1a&1b), that negatively regulate the expression of GmNRAMP2a&2b, which establishes a link between N signaling and Fe homeostasis in nodules. Our findings reveal a plausible mechanism by which soybean adjusts SNF efficiency through Fe allocation in response to fluctuating inorganic N conditions, offering valuable insights for optimizing N and Fe management in legume-based agricultural systems. Symbiotic nitrogen fixation is a tightly regulated process serving as a sustainable source of nitrogen (N) in agriculture. Here it is shown that external N sources precisely regulate N fixation efficiency by modulating iron transport in nodules of legumes. [ABSTRACT FROM AUTHOR]

The root system plays a crucial role in water and nutrient absorption, making it a significant factor affected by nitrogen (N) availability in the soil. However, the intricate dynamics and distribution patterns of cotton (Gossypium hirsutum L.) root density and N nutrient under varying N supplies in Southern Xinjiang, China, have not been thoroughly understood. A two-year experiment (2021 and 2022) was conducted to determine the effects of five N rates (0, 150, 225, 300, and 450 kg N ha−1) on the root system, shoot growth, N uptake and distribution, and cotton yield. Compared to the N0 treatment (0 kg N ha−1), the application of N fertilizer at a rate of 300 kg N ha−1 resulted in consistent and higher seed cotton yields of 5875 kg ha−1 and 6815 kg ha−1 in 2021 and 2022, respectively. This N fertilization also led to a significant improvement in dry matter weight and N uptake by 32.4% and 53.7%, respectively. Furthermore, applying N fertilizer at a rate of 225 kg N ha−1 significantly increased root length density (RLD), root surface density (RSD), and root volume density (RVD) by 49.6–113.3%, 29.1–95.1%, and 42.2–64.4%, respectively, compared to the treatment without N fertilization (0 kg N ha−1). Notably, the roots in the 0–20 cm soil layers exhibited a stronger response to N fertilization compared to the roots distributed in the 20–40 cm soil layers. The root morphology parameters (RLD, RSD, and RVD) at specific soil depths (0–10 cm in the seedling stage, 10–25 cm in the bud stage, and 20–40 cm in the peak boll stage) were significantly associated with N uptake and seed cotton yield. Optimizing nitrogen fertilizer supply within the range of 225–300 kg N ha−1 can enhance root foraging, thereby promoting the interaction between roots and shoots and ultimately improving cotton production in arid areas. [ABSTRACT FROM AUTHOR]

Background and aims: The halophile Halomonas maura and biological N-fixing Rhizobium may increase salinity tolerance of alfalfa (Medicago sativa L.), especially for alfalfa populations with improved salt tolerance. The objectives of this study were to 1) evaluate whether salt-tolerant bacteria or a 60 kg/ha nitrogen amendment could increase the salinity tolerance of alfalfa; 2) assess whether recurrent selections for salt tolerance in alfalfa populations would differentially interact with soil bacteria. Methods: Three alfalfa generations sequentially selected for improved salt tolerance were inoculated with either highly salt-tolerant (H. maura), moderately-tolerant (Ensifer meliloti) bacteria, or a 60 kg/ha nitrogen amendment in either non- (0 dS/m), moderate-(8 dS/m), or highly (16 dS/m) saline soil in the greenhouse. Results: Recurrent selection of alfalfa in salinity stress causes increased chlorophyll content, stem count, and plant height; however, yield loss occurred under 120 d of moderate salinity stress. Improved alfalfa generations in combination with nitrogen amendments were able to produce the highest biomass yields in moderate salinity stress. E. meliloti had a positive effect during regrowth, and it increased proline content in both shoot and root tissue. In comparison, H. maura provided no discernible benefits to alfalfa under salt stress. Conclusion: Recurrent plant selection combined with N-fixing rhizobium could increase alfalfa growth under a multi-harvest system. As alfalfa positively responded to N fertilizer and N fixing rhizobium, improvement of alfalfa traits related to nitrogen utilization and biological N fixation may be vital to alfalfa salt tolerance. [ABSTRACT FROM AUTHOR]

Cropping systems depend on external nitrogen (N) to produce food. However, we lack metrics to account for society's fertilizer dependency, although excessive increases in N application damage human and environmental health. The objective of this study is to propose a novel indicator, N fertilizer dependency, calculated as the ratio between human-controllable external inputs and total N inputs. Nitrogen fertilizer dependency has a solid mathematical base being derived from closing the nitrogen use efficiency (NUE) equation. This study also tests the value of the N fertilizer dependency concept at the cropping system (plant-soil) scale and at different spatial scales, from field to country, as a complementary indicator to promote sustainable production. The field experiments conducted with grain cereals as a main crop showed that when replacing the barley precedent crop with a legume, N fertilizer dependency accounted for soil legacy and was reduced by 15% in fertilized treatments. In a farm population, N fertilizer dependency ranged from 47 to 95% and accounted for the relevance of biological fixation and irrigation water N inputs, adding pertinent information to performance indicators (i.e., NUE). At the country scale, N fertilizer dependency showed different temporal patterns, depending mainly on the relevance of biological atmospheric N fixation. Nitrogen fertilizer dependency of global cropping systems has risen to ≈83% in the last five decades, even though the N exchange among regions has increased. Nitrogen fertilizer dependency has great potential to monitor the achievements of efforts aiming to boost system autonomy, and within similar agricultural systems, it can be used to identify practices that lead to a reduction of fertilizer needs. In summary, N fertilizer dependency is a new indicator to evaluate the agroenvironmental sustainability of cropping systems across the scales and provides a complementary dimension to the traditional indicators such as NUE, N output, and N surplus. [ABSTRACT FROM AUTHOR]

Nitrogen plays a crucial role in plant metabolism, growth, and development of plants, and its deficiency leads to severe growth retardation and reduced grain yield. The efficient utilization of nitrogenous fertilizers is needed to enhance crop yield and also to fetch the food demand of the world population. The accumulated nitrogen in the ecosystem leads to severe environmental pollution and health hazards to inhabited animals. However, nitrogen inside plants is regulated by a set of nitrogen metabolism genes, promoters, and transcription factors. Further, the identification and characterization of nitrogen metabolism genes in crop plants is a prerequisite for developing tailored crop plants for increased nitrogen use efficiency (NUE), grain yield, biomass, and other economic traits. Moreover, NUE is a complex trait, and breeding crops for improving NUE is still in the infancy stage. Therefore, a targeted and holistic approach is required for enhanced nitrogen uptake and its utilization. The precise modulation of key genes of nitrogen metabolism, amino acid biosynthesis, and carbon metabolism could result in enhancement of NUE, and the engineered crop plants for NUE traits were reported to be superior in terms of NUE and also incurred higher grain yield, biomass, and improved agronomical parameters as that of cultivated crop cultivars. In this review, we described the basics of nitrogen metabolism, genomics, and recently targeted genetic engineering strategies employed in crop plants for improving NUE. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is a long-lived greenhouse gas that mainly originates from agricultural soils. More and more studies have explored the sources, influencing factors and effective mitigation measures of N2O in recent decades. However, the hierarchy of factors influencing N2O emissions from agricultural soils at the global scale remains unclear. In this study, we carry out correlation and structural equation modeling analysis on a global N2O emission dataset to explore the hierarchy of influencing factors affecting N2O emissions from the nitrogen (N) and non-N fertilized upland farming systems, in terms of climatic factors, soil properties, and agricultural practices. Our results show that the average N2O emission intensity in the N fertilized soils (17.83 g N ha−1 d−1) was significantly greater than that in the non-N fertilized soils (5.34 g N ha−1 d−1) (p< 0.001). Climate factors and agricultural practices are the most important influencing factors on N2O emission in non-N and N fertilized upland soils, respectively. For different climatic zones, without fertilizer, the primary influence factors on soil N2O emissions are soil physical properties in subtropical monsoon zone, whereas climatic factors are key in the temperate zones. With fertilizer, the primary influence factors for subtropical monsoon and temperate continental zones are soil physical properties, while agricultural measures are the main factors in the temperate monsoon zone. Deploying enhanced agricultural practices, such as reduced N fertilizer rate combined with the addition of nitrification and urease inhibitors can potentially mitigate N2O emissions by more than 60% in upland farming systems. [ABSTRACT FROM AUTHOR]

Understanding the changes in nitrate nitrogen (NO3−-N) content in the rooting zone is crucial for reducing nitrate leaching and improving nitrogen (N) use efficiency. The main objective of this study was to investigate the effects of N management strategies on NO3−-N dynamics in the main root zone (0–60 cm) at critical growth stages of drip-irrigated potatoes and to quantify the retention capacity of NO3−-N at harvest in an intensive potato cropping system. Three field experiments with no N application (CK), optimized management (OM) based on a realistic yield goal and soil mineral N content (Nmin) and farmer practice (FP) for three potato cultivars were conducted in Inner Mongolia of Northwest China from 2014 to 2016. A total of 52 farmers with over 3000 ha of potato fields were also investigated at harvest. The results showed that OM treatment improved N use efficiency and reduced the environmental risk of N loss while ensuring potato yields compared with FP treatment. Overusing N fertilizer in farmer fields was common, but these N fertilizers only caused a temporary accumulation of NO3−-N during the growing season, then it was reduced to the same level as the optimal treatment at harvest. The NO3−-N retention was about 70 kg ha−1 at harvest in the drip-irrigated potatoes with higher yield, and the data from farmers' fields confirmed the universality of the NO3−-N retention content. Although retentional NO3−-N content in the main root zone at harvest was similar between FP and OM, obvious accumulation of NO3−-N content was observed during the growing season in FP treatments increasing N loss risk to the environment. The characteristics of soil NO3−-N accumulation in the root zone of drip-irrigated potatoes help to improve management strategies to maximize potato yield while minimizing environmental risks due to N fertilization. [ABSTRACT FROM AUTHOR]

The effect of long-term use of mineral fertilizers on changes in the content of total phosphorus and its organic, mineral, and mobile compounds in soddy-podzolic heavy loamy soil (Albiс Retisol (Abruptic, Aric, Loamic)) was analyzed. The studies were performed in a long-term stationary experiment initiated in Perm krai in 1978. The variants were: 0 (without fertilizers), N90, P90, K90, N90P90, N90K90, P90K90, N90P90K90, N30P30K30, N60P60K60, N120P120K120, and N150P150K150. Ammonium nitrate or urea, double or simple superphosphate, and potassium chloride were used in the experiment. It was established that long-term use of superphosphate during five eight-field crop rotations (P90, P90K90, N90P90, and N90P90K90) resulted in a significant increase in the contents of the total phosphorus, mineral phosphorus (by 1.3–1.8 times), and mobile phosphorus (by 1.9–2.7 times) compounds in the plow layer (0–20 cm). The use of nitrogen fertilizers (N90, N90K90, N90Р90, and N90Р90K90) affected the accumulation of organic phosphorus compounds in the soil. The increase in the content and reserves of both mineral and organic phosphorus compounds was significant only in the case of using complete mineral fertilizer N90P90K90. Different combinations of superphosphate with nitrogen fertilizers and potassium chloride, as well as the rate of fertilizer application, affected the accumulation intensity of mobile phosphorus compounds in the soil during rotations and the changes in their contents in the soil profile. The application of low fertilizer rates ((NPK)30–60) resulted in an increase in the content of mobile phosphorus compounds mainly in the plow layer, whereas higher rates ((NPK)90–150) caused changes in the 80-cm-thick soil layer. Long-term use of nitrogen and potassium fertilizers resulted in an increase in the content of mobile phosphorus compounds in the plow layer over time. [ABSTRACT FROM AUTHOR]

Purpose: Nitrogen (N) fertilizer is a critical factor in achieving high rice yields, but it can also contribute to increased CH4 emissions from rice paddies. Determining how to utilize N fertilizer to effectively balance the contradiction between methane (CH4) emissions and rice yield remains an urgent need in the face of unstoppable climate change. Materials and methods: In this study, the response of CH4 fluxes in rice paddies to elevated carbon dioxide (CO2) concentration (e[CO2]) and reduced N application were investigated. The rice biomass and yield, CH4 fluxes, soil properties, and methanogenic characteristics were observed in control (CK) (ambient CO2 concentration + application of 250 kg N ha−1 urea), C+ (e[CO2] by 200 ppm + 250 kg N ha−1 urea), N− (ambient CO2 concentration + 150 kg N ha−1 urea), and C+N− (e[CO2] by 200 ppm + 150 kg N ha−1 urea) treatments. Results and discussion: The results revealed that the C+ and C+N− treatments significantly increased the CH4 emissions/yield by 20.0% and 18.8%, respectively, while the N− treatment significantly suppressed the CH4 emissions/yield by 13.3% compared to CK. The N− treatment weakened the promotion effect of C+ on the rice total biomass, the soil dissolved organic carbon (DOC) concentration and invertase activity, and the CH4 emissions/yield. Moreover, the C+N− treatment significantly reduced the soil DOC concentration and the abundance of the mcrA gene in the grain-filling stage compared to C+. Conclusions: Overall, under climate change conditions, N reduction can mitigate CH4 fluxes from rice paddies by affecting rice growth, soil methanogenic characteristics, and the C substrate. [ABSTRACT FROM AUTHOR]

The traceability of groundwater nitrate pollution is crucial for controlling and managing polluted groundwater. This study integrates hydrochemistry, nitrate isotope (δ15N-NO3− and δ18O-NO3−), and self-organizing map (SOM) and end-member mixing (EMMTE) models to identify the sources and quantify the contributions of nitrate pollution to groundwater in an intensive agricultural region in the Sha River Basin in southwestern Henan Province. The results indicate that the NO3−-N concentration in 74% (n = 39) of the groundwater samples exceeded the WHO standard of 10 mg/L. According to the results of EMMTE modeling, soil nitrogen (68.4%) was the main source of nitrate in Cluster-1, followed by manure and sewage (16.5%), chemical fertilizer (11.9%) and atmospheric deposition (3.3%). In Cluster-2, soil nitrogen (60.1%) was the main source of nitrate, with a significant increase in the contribution of manure and sewage (35.5%). The considerable contributions of soil nitrogen may be attributed to the high nitrogen fertilizer usage that accumulated in the soil in this traditional agricultural area. Moreover, it is apparent that most Cluster-2 sampling sites with high contributions of manure and sewage are located around residential land. Therefore, the arbitrary discharge and leaching of domestic sewage may be responsible for these results. Therefore, this study provides useful assistance for the continuous management and pollution control of groundwater in the Sha River Basin. [ABSTRACT FROM AUTHOR]

Limited water resources and successive droughts in Iran have limited crop production. Therefore, modern irrigation methods to increase water use efficiency can become more necessary. A 2-year (2020, 2021) field experiment was carried out to determine the effect of irrigation method and nitrogen fertilizer on maize physiological traits, grain yield, water use efficiency, and soil temperature and moisture. The experimental design was factorial in the randomized complete block with three replicates. The studied irrigation and fertilizer treatments were the four levels of irrigation (wick irrigation, surface irrigation with 50, 70, and 100% of plant water requirement) and the two levels of nitrogen fertilizer (50 and 100% of the recommended urea fertilizer). Totally, wick irrigation with 100% fertilizer increased SPAD, leaf relative water content, leaf porometer, total dry weight, ear dry weight, ear diameter, number of rows per ear, number of grains per ear, and 100-grain weight compared to other treatments. Wick irrigation significantly increased soil moisture and decreased soil temperature compared to surface irrigation with 50, 70, and 100% plant water requirement at a depth of 10 cm. Although there was no significant difference between wick irrigation and 100% surface irrigation regarding grain yield, on average, for both years, wick irrigation reduced water consumption by 57.88% compared to 100% surface irrigation. Furthermore, wick irrigation with 100% fertilizer had the highest water use efficiency. Therefore, wick irrigation with 50% fertilizer application is the best treatment, because water and fertilizer are saved. [ABSTRACT FROM AUTHOR]

In order to the yield maintenance along with environmental protection, the replacement or combination of chemical fertilizers with organic ones has received increasing attention recently. However, the yield and quality of production in aromatic plants differ from other plants. The present experiment was conducted for 2 years with the aim of evaluating the potential of vermicompost instead of nitrogen fertilizer for the production of geraniums without reducing its perfume quality. Regarded to the macronutrients, essential oil, and shoot yield, geranium treated with 20 ton ha−1 vermicompost and 16 ton ha−1 vermicompost + 40 kg ha−1 nitrogen had the best condition compared to other fertilizer regimes. Geranium is a perennial plant; hence the traits related to plant growth and yield were higher in the second harvest. Besides that, compared to treatments with a high amount of chemical nitrogen, the effects of vermicompost on the quality and quantity of geranium in the second yield were more effective and sustainable. Moreover, these findings suggested that an appropriate proportion of organic substitution not only provides uptake nutrients but also improves the essential oil yield and chemical composition. In fact, increasing the level of vermicompost resulted in improved oxygenated monoterpene content in geranium essential oil. According to the results of this study, cow manure-derived vermicompost could be a suited and sustained replacement for nitrogen inorganic fertilizer without any significant reduction in the quality and quantity of geranium products. Thus, it can be a practical step to reduce production costs, and environmental issues own to chemical fertilizers, particularly in aromatic plant cultivation. [ABSTRACT FROM AUTHOR]

Plasma nitrogen fixation technology is of great significance in solving the problem of nitrogen fertilizer resource shortage, saving energy and reducing carbon emission, promoting sustainable development of agriculture and promoting resource recycling. To enhance the efficiency and treatment capacity of the two-dimensional, blade-type gliding arc nitrogen fixation reaction, a dielectric-boosted gliding arc discharge reactor with a 50-mm-diameter quartz dielectric (DBGADΦ50) was used to conduct N2 fixation into NOx. The impact of reactor parameters and gas parameters on the nitrogen fixation reaction was systematically investigated in this study. The findings revealed that the DBGADΦ50 significantly improved the nitrogen fixation effect. At a specific input energy of 2.7 kJ/L, the concentration of NOx generated by the dielectric-boosted gliding arc air discharge was 1.12 times that of the conventional gliding arc discharge (GAD). By utilizing the DBGADΦ50 reactor, the energy efficiency of 6.83 g/kW h was achieved at a gas flow rate of 5.6 L/min. Appropriately increasing O2 concentration favors the production of NOx. In the DBGADΦ50, the NOx concentration was 1.33 times higher than that in the air atmosphere when the added O2 volume fraction reached 30%. Performance can be further enhanced by adding TiO2 catalyst particles to the surface of the quartz dielectric to form a catalyst layer approximately 5 mm thick. At an O2 concentration of 30%, the DBGADΦ50 reactor loaded with TiO2 increased NOx concentration by 26% and energy efficiency by 49%, respectively, resulting in an efficiency of 14.9 g/kW h compared to the case without catalyst. [ABSTRACT FROM AUTHOR]

To maximize the efficiency of biomass waste utilization and waste management, a novel acid-modified magnetic biomass spent coffee grounds (NiFe2O4/SCG) was obtained by pyrolysis at 473 K and co-precipitation methods and employed to eliminate bivalent mercury (Hg(II)) in water bodies. The prepared NiFe2O4/SCG adsorbent exhibits remarkable magnetism with a strength of 45.78 emu/g and can easily be separated from water via a magnetic force. The adsorption of Hg(II) over the NiFe2O4/SCG has an optimal conditions of pH = 8, T = 39 ℃, and dosage of 0.055 g/L, and the maximal adsorption capacity for Hg(II) is 167.44 mg/g via Response Surface Methodology optimization. The removal of Hg(II) over NiFe2O4/SCG primarily involves ion exchange, electrostatic attraction, and chelation; conforms to the pseudo-second-order kinetic and Langmuir models; and is an endothermic reaction. Additionally, the magnetic biomass NiFe2O4/SCG has good regeneration capability and stability. The application research reveal that inorganic salt ions, nitrogen fertilizer urea, humus, and other contaminants in different actual water bodies (river water, lake water, and the effluent of sewage treatment plant) have little effect on the adsorption of Hg(II) over the NiFe2O4/SCG. The prepared adsorbent NiFe2O4/SCG has practical application value for removing Hg(II) from water bodies. [ABSTRACT FROM AUTHOR]

Hot pepper (Capsicum annum L.) is one of the most important vegetable crops produced in Ethiopia. However, production and productivity of the crop is far below the world average, which is mostly associated with soil fertility depletions as a result of inappropriate application of fertilizer. Therefore, this field experiment was conducted to evaluate the effects of organic eco-green and inorganic nitrogen fertilizer on the growth and green pod yield of hot pepper during the growing season of 2019/2020. The experiment was designed in factorial combinations of four levels of N (0, 59, 82 and 105 kg ha−1) and four levels of eco-green (0, 75, 125 and 175 L ha−1) which were laid down in Randomized Complete Block Design (RCBD) with three replications. Results revealed that application of N and eco-green (EG) fertilizers very highly significantly (P < 0.001) influenced plant height, numbers of different levels of branches, days to 50% flowering, days to 50% pod setting, days to first harvest, marketable, unmarketable and total green pod yields. Generally, the combination of high levels of nitrogen and EG increased the growth parameters of hot pepper including plant height and number of branches. The highest marketable (17.98 t ha−1) and total green pod yield (18.19 t ha−1) of hot pepper were recorded from the treatment combinations of 59 kg N ha−1 and 125 litter EG ha−1. The same treatment combination had also recorded the highest net benefit (318,516.91 ETB ha−1) with acceptable marginal rate of return (1706%) which can be recommended for economical production of green hot pepper in the study area and areas with similar agro-ecology. [ABSTRACT FROM AUTHOR]

High-quality japonica rice, distinguished by its unique flavor and enriched nutritional value, has attracted significant attention across Asia. The over-application of nitrogen (N) fertilizers, however, is a growing concern, threatening both the rice quality and the environmental sustainability of its production. This situation calls for a reevaluation and modification of traditional agricultural practices. Our study investigates the effects of reduced N fertilizer use, complemented by foliar fertilizer application, on the physiological attributes and yield of high-quality japonica rice. The aim is to achieve efficient N use and enhanced crop productivity. The experiment employed 'Sujing 1180', a high-quality japonica rice cultivar, utilizing urea as the N source and a comprehensive macronutrient-rich water-soluble fertilizer for foliar application. Five treatments were established: conventional N application (270 kg ha− 1, N100), 10% N reduction (N90), 10% N reduction with foliar application (N90 + FF), 20% N reduction (N80), and 20% N reduction with foliar application (N80 + FF). These treatments were meticulously examined throughout various growth stages. Photosynthetic parameter analysis indicated that N90 + FF significantly boosted the net photosynthetic rate during the heading stage. N80 + FF maintained higher stomatal conductance at the maturity stage, suggesting that foliar fertilizer is effective in enhancing photosynthetic efficiency and stomatal conductance. In terms of N metabolism, N90 + FF notably increased the accumulation of nitrate N during the jointing stage, surpassing other treatments. While N90 and N80 showed reductions in both nitrate and ammonium N levels compared to N100, N90 + FF was particularly effective in elevating nitrate and ammonium N as well as free amino acid concentrations. Regarding N fertilizer efficiency, N90 + FF surpassed N100 across several critical parameters, specifically total N absorption, N recovery efficiency, N agronomic efficiency, and N physiological efficiency. Significantly, N90 + FF showed marked improvements in both N agronomic efficiency and N partial factor productivity. In examining yield and its components, the N90 + FF treatment achieved a higher yield of 9872.48 kg ha− 1, surpassing the 9383.75 kg ha− 1 of N100. N90 + FF had better results in seed-setting rate and average grain number per panicle, with its 1000-grain weight similar to that of N100. The N90 and N80 treatments, however, were less effective in terms of yield and its components. The integrated study findings demonstrate that a strategy incorporating moderate N reduction and foliar fertilizer application markedly optimizes rice photosynthesis, augments N metabolism, and enhances utilization efficiency, leading to increased yields. These insights are valuable for advancing precision agriculture, enhancing japonica rice production efficiency, and promoting sustainable farming. [ABSTRACT FROM AUTHOR]

Regular application of synthetic chemicals in rice ecosystem led to loss of nitrogen (N) and affected the native microbial communities. Controlled release fertilizers (CRFs), a solution to poor nitrogen use efficiency (NUE) of urea and associated environmental implications while diminished economic advantages by high CRF use, is major obstacle that still exists. Reviving the diazotrophic native bacteria from rice cultivated locations should be the alternate for bounciness of potential bioinoculants for better performance and yield enhancement. In the present investigation, two potential nitrogen fixing bacteria, Pseudomonas lini GHM32 and Brevundimonas nasdae GHM62 isolated from rice rhizosphere on Rennie medium. These two bacteria were evaluated for yield and NUE in field studies in a randomized block design with treatments, T1- 100% recommended dose of nitrogen through neem coated urea (RDN), T2- 50% RDN, T3- 50% RDN + P. lini GHM32, T4- 50% RDN + B. nasdae GHM62 and T5- co-application of both bacterial isolates during Rabi-2020-21 (dry season) and Kharif-2021 (wet season). Experimental results for plant height, chlorophyll, nitrogen content and yield in T3 were on par T1. Nitrogen use efficiency indices, such as partial factor productivity (PFP), nitrogen use efficiency (NUE) and nitrogen requirement (NR) of T3 were at par T1 throughout the experimental period. This is the first report with field trials on P. lini and B. nasdae as potential diazotrophic bacterial application by reduction in application of inorganic N fertilizer through neem coated urea with a focus on NUE indices and yield improvement of rice. [ABSTRACT FROM AUTHOR]

Agricultural pollutants are commonly detected in Wisconsin groundwater around potato production on coarse-textured, low organic matter soils and practical nitrate reduction strategies are needed to address groundwater quality. Soil column studies with loamy sand soil common to the potato production region were conducted to explore the ability of organic soil additives incorporated below the simulated potato root zone to capture nitrogen in leachate water. Soil additives included two biochar types (biochar 400 and biochar 700, both at 5% wt wt− 1 concentrations) and two papermill residual lignocellulose products (papermill source 1 and papermill source 2, evaluated at 60,525 and 49,320 kg ha− 1, respectively) injected in the soil amendment zone below the simulated potato root zone. Additionally, one humic acid treatment with 500 kg ha− 1 dry lignite humic acid incorporated into the simulated potato root zone and 374 L ha− 1 liquid humic acid incorporated below the simulated potato root zone was included. Nitrogen fertilizer was added at study initiation and midway through the study. Distilled water was added every 14 days during the 14-week study period to simulate high precipitation events and leachate volume was quantified and analyzed for nitrate-nitrite nitrogen content. Leachate volume varied slightly and inconsistently among treatments and compared to soil with no additives. Biochar and papermill lignocellulose products reduced the season flow-weighted nitrate-nitrite nitrogen concentration by up to 7.6 and 34%, respectively, but humic acid was ineffective. Treatment efficacy diminished over time. Further research is needed to investigate soil treatment longevity and response to plant biotic interactions, but the papermill residual products were particularly effective at reducing nitrate-nitrite nitrogen content in leachate in this study. [ABSTRACT FROM AUTHOR]

Aims: Nitrogen (N) fertilizer application greatly enhances grain yield by improving dry matter accumulation and grain filling in winter wheat. However, the regulation mechanism of N rates on dry matter accumulation, transportation, and grain filling in winter wheat under dry farming could be more precise. Methods: Five N treatments viz. 0, 75, 150, 225, and 300 kg·N·ha−1, designated as N0, N75, N150, N225, and N300, were tested in two growing seasons of 2017–18 and 2018–19. Results: Fertilization significantly increased dry matter accumulation and intensity and assimilated accumulation after anthesis and its contribution to grain yield. N fertilizer significantly improved the superior and inferior grain weights, with the highest at N225, and increased by 22.29% and 24.41% in 2017–18 and 22.06% and 12.68% in 2018–19, respectively, compared to N0 (P < 0.05). Moreover, N fertilization increased the initial grain-filling potential and mean filling rate, shortened the days achieving the maximal grain-filling rate. N fertilizer increased the filling rate in the three periods, shortening the duration of the first-middle period, prolonging the late period, and increasing the contribution of the mid-late filling period to grain weight. However, excessive N application led to a reduction in the filling rate for each period. It prolonged the duration in the mid-late periods, which was not conducive to further increases in grain weight. Conclusions: The N225 can be a more suitable N fertilizer for improving the accumulation and transfer of dry matter, promoting grain-filling, and increasing wheat yield in dry farming in the Loess Plateau. [ABSTRACT FROM AUTHOR]

Aims: The application of biochar amendments or organic manure substitutions can alleviate the harmful environmental effects of inorganic fertilizers on agroecosystems, whereas they can also affect soil microenvironments which have not been fully explored on the Loess Plateau. Methods: Our field experiments consisted of no fertilizer (N0), N application (150 kg N hm−2, N150), 30% organic manure replacing N fertilizer (NO30), no fertilizer plus 10 t hm−2 biochar (N0 + C), N application plus 10 t hm−2 biochar (N150 + C), and 30% organic manure replacing N fertilizer plus 10 t hm−2 biochar (NO30 + C). The nutrient levels, bacterial community structure, ecological network, assembly process of bulk soil and rhizosphere at jointing and flowering stages, and crop yield in broomcorn millet field were investigated. Results: Fertilizer regimes and biochar amendments increased the bulk soil and rhizosphere nutrient contents than no fertilizer and no biochar. NO30 significantly improved the rhizosphere observed OTUs at jointing and flowering stages. Biochar amendments increased the observed OTUs of bulk soil and rhizosphere than no biochar. N150 and NO30 had a lower network complexity than N0 treatment, whereas N150 + C had the most complex network. Biochar amendments had more deterministic process than fertilization regimes. Meanwhile NH4+-N content was the major factor shaping the bacterial diversity, structure, and assembly process. NO30 + C has the highest yield of broomcorn millet. Conclusions: Compared with fertilizer regimes, biochar amendment had higher nutrient contents and observed OTUs of bulk soil and rhizosphere, and it also had a more substantial influence on the bacterial community structure and network stability. [ABSTRACT FROM AUTHOR]

Background and aims: Staged water shortages and excessive nitrogen application lead to a decline in crop yield, and nitrogen loss, waste of resources and environmental pollution. In order to explore the appropriate water management in humid areas and to determine an efficient nitrogen rates for maize, we conducted the two years' field experiment. Methods: We conducted a field experiment (2020–2021), with five nitrogen rates N0, N150, N200, N250, N300 (0, 150, 200, 250, 300 kg ha−1) under different water conditions (rainfed conditions and irrigated conditions). Results: Consequently, under the irrigated conditions, the soil organic matter (SOM), microbial biomass carbon (MBC), dry matter accumulation and grain yield were significantly (P < 0.05) increased by 8.06%, 15.50%, 11.43% and 13.86%, respectively, compared with the rainfed conditions. And the total nitrogen (TN), nitrate nitrogen (NO3−-N), ammonia nitrogen (NH4+-N) decreased significantly by 4.38%, 8.28%, 13.21%, respectively. Furthermore, compared with other nitrogen rates, N250 and N300 combined with irrigated conditions significantly (P < 0.05) increased soil carbon and nitrogen content, dry matter accumulation and grain yield. However, N250 and N300 displayed no significant difference (P > 0.05) in TN, NO3−-N, NH4+-N, SOM, MBC, dry matter accumulation and grain yield. Moreover, under the irrigated conditions, when the nitrogen rates increased more than 250 kg ha−1, the nitrogen use efficiency decreased. Conclusion: Application of nitrogen rates of 250 kg ha−1 under irrigated conditions is the best choice to increase grain yield, improve nitrogen use efficiency, and ensure safe and efficient production in maize. [ABSTRACT FROM AUTHOR]

Psyllids feed exclusively on plant sap, which is an unbalanced diet for herbivores due to its low nitrogen content. Therefore, the plant-psyllid-natural enemy interactions can be strongly shaped by the bottom-up forces of N fertilization. Pear psylla Cacopsylla chinensis is a notorious pest in East Asian countries, inflicting devastating damage to pear trees and fruits. However, the bottom-up effects of nitrogen fertilizer on C. chinensis and the mechanisms remain unexplored. Here, we evaluated the performance of C. chinensis larvae over the N application range of 0–1500 mg/kg. The feeding activity and body weight of C. chinensis increased and the developmental duration of C. chinensis decreased significantly when N application increased. Our results indicated that nitrogen application enhanced psyllid fitness on host plant. By analyzing pear leaf metabolites, we found that only ferulic acid increased with the increase of nitrogen fertilizer concentration among phenolics assessed. Exogenously application of ferulic acid accelerated the development of psyllid nymphs. We also found that the concentration of both essential and non-essential amino acids increased significantly when N supply increased, which provided C. chinensis with increased nutrients for their development. The expression levels of several C. chinensis genes in the amino acids synthesis pathway decreased significantly after nitrogen application, indicating that C. chinensis can adjust its amino acid synthesis levels based on its diet. We demonstrated that the enhanced fitness of psyllids under nitrogen supply stems from altered host chemical traits and nutritional quality. The manipulation of nitrogen fertilization has a high potential for use in psyllid IPM programs by reducing psyllid performance. [ABSTRACT FROM AUTHOR]

During the 2015–2016 growing season, a field experiment was conducted to investigate the impact of different irrigation regimes (low and severe water stress treatments) and nitrogen levels on the biochemical responses of sorghum and maize. Moisture environments were determined based on the maximum allowable depletion of available soil water (ASW), with depletion levels of 55–60% and 85–90% of ASW selected as the low and severe water stress levels, respectively. Nitrogen fertilizer was applied via drip fertigation at three stages (28, 43, and 55 days after sowing) in the form of Urea (N: 45%), at a rate of 37.5 kg ha−1 N for each stage. Under severe water stress, both crops showed a decrease in chlorophyll and carotenoid content, relative water content (RWC), and maximum quantum efficiency of photosystem II (Fv/Fm). Additionally, severe water stress led to an increase in antioxidant enzyme activity, proline, malondialdehyde (MDA), other aldehydes (Alds), and hydrogen peroxide, ultimately resulting in a 42% reduction in crop yield. Light intensity also increased under severe water stress, particularly in the middle and bottom of the plant canopy, indicating a decrease in the available leaf area for receiving light. Nitrogen application effectively reduced the production of oxygen free radicals, mitigated cell membrane damage, decreased the activity of antioxidant enzymes and osmolytes, and increased the activity of photosynthetic pigments, Fv/Fm, and RWC, resulting in an increase in crop yield of up to 18%. Compared to sorghum, maize exhibited lower antioxidant activity, proline content, chlorophyll, carotenoid, RWC, Fv/Fm, stress tolerance index, and higher concentrations of MDA, Alds, and H2O2, indicating its higher sensitivity to water deficit stress. Additionally, even under low water stress treatment, maize failed to produce an acceptable dry matter yield. [ABSTRACT FROM AUTHOR]

Purpose: Excessive application of nitrogen fertilizers on farmland widely occurs in China, which has been recognized as one of the main sources of non-point pollution. To reduce the nitrogen loss in agricultural soils, some specific biochar can be introduced to increase the water-holding capacity of soils and to reserve soil nutrition. The effects and mechanisms of biochar application on decreasing nutrient losses after fertilization were systematically evaluated and understood through both pot and field experiments. Materials and methods: This study was objected to investigate the effects of neutral biochar (NBC, pH 6.6–7.1) and its combination with urease inhibitor (UI) on nitrogen mitigation and reservation in farmland soil, and the interactions among the mixed soils (biochar, nitrogen fertilizer, and soil) under both pot and field experiments. Results and discussion: The application of straw biochar could reduce the amount of ammonia volatilization in soil. The maximum inhibition of ammonia volatilization loss accounted for 27.67% of fertilizer applications. In field experiments, neutral biochar could reduce the leaching of soil NH4+-N and NO3—-N, and this effect was more evident for NO3—-N (68 mg/kg) compared to no fertilization in the soil layer 20–40 cm. With the addition of neutral biochar and urease inhibitors, the content of soil total nitrogen increased greatly with 1.70 g/kg. Conclusion: Neutral biochar from waste agricultural straw and commercial urease inhibitors were applied for nitrogen reservation in pot and field experiments. The application of neutral biochar played a positive role in lower volatile ammonia loss and higher nitrate content compared to urease inhibitor application only. These findings reveal the potential of neutral biochar for the improvement of agricultural soil. [ABSTRACT FROM AUTHOR]

Active soil organic carbon (SOC) fractions are major driving factors of soil fertility. Understanding the effects of water and fertilizer management on changes in active SOC fractions helps improve soil quality and maintain high agricultural productivity. We conducted a 3-year field experiment in Northeast China. In this experiment, natural soil (CKT) was used as a blank, and two irrigation regimes were established: conventional flooded irrigation (FI) and controlled irrigation (CI). Four nitrogen application levels were set for both irrigation regimes under deep placement of basal fertilizer N: Nd0 (0 kg ha–1), Nd (110 kg ha–1), Nd1 (99 kg ha–1), and Nd2 (88 kg ha–1). After 3 years, at similar N fertilizer application rate, the rice yield, total organic carbon (TOC), and active SOC fraction content of CI were higher under CI than FI. The growth rate of rice yield was 3.8% − 8.63% under CI than FI. Under CI, the rice yield, active SOC fractions contents and carbon pool management index (CPMI) did not decrease with decreasing N application rate but instead reached the highest level in the CNd1 treatment. Overall, CI with Nd1 treatment appears to be the best practice for improving soil fertility and crop productivity in Northeast China. [ABSTRACT FROM AUTHOR]

Aims: The objective of this study was to determine the effects of different levels of irrigation water depth, nitrogen fertilizer, and Conocarpus biochar on the quantitative and qualitative characteristics of Roselle plants and their irrigation water use efficiency (IWUE) and soil nutrition. Methods: The experimental treatments included three levels of nitrogen fertilizer (N1: 100, N2: 150, N3: 200 t ha−1), three levels of irrigation water depth (I1: 50, I2: 75, I3: 100% of plant water requirement), and three levels of biochar (B1: 0, B2: 10, B3: 20 t ha−1). Results: The research findings indicated that the effects of irrigation water depth, nitrogen fertilizer, and biochar were significant on all measured parameters at a 1% and 5% probability level. The highest yield (710.58 kg ha −1) was achieved under the B3N2 treatment. The highest IWUE was observed under the I2N3 treatment (0.125 kg m−3). Applying biochar at all levels increased the total nitrogen content, organic matter, and microbial carbon biomass while reducing nitrate leaching in the soil. The total nitrogen, organic matter, and microbial carbon biomass increased by 82.92%, 47.31%, and 61.75%, respectively. Conclusions: Considering the region's water scarcity, applying 75% of the water requirement (I3) can help conserve water. Additionally, using 75% of the nitrogen content (N2) and applying 20 t ha−1 of biochar (B3) can improve Roselle's quality and mitigate drought stress's negative impacts. Furthermore, using Conocarpus waste and other agricultural residues as biochar can increase organic matter levels in dry soil areas while preventing environmental pollution. [ABSTRACT FROM AUTHOR]

Background and aims: Drought is one of the main causes of global crop decline. Plant growth-promoting rhizobacteria enhance plant tolerance to adverse environmental conditions. This study aimed to determine whether the rhizobacteria Microvirga vignae (BR 3296 and BR 3299) and Bradyrhizobium sp. (BR 3301) can maintain cowpea growth under drought stress. Methods: We analyzed biomass, nodulation, nitrogen accumulation, and physiological traits of the inoculated plants. Rhizobacterial strains were assessed for exopolysaccharide (EPS) and indole acetic acid (IAA) production, growth, and biofilm formation in a water-stress medium induced by polyethylene glycol (PEG)-6000. The expression of genes associated with abscisic acid (ABA) biosynthesis in root nodules was also investigated. Results: All evaluated strains were grown in a culture medium supplemented with PEG. M. vignae strains exhibited increased biofilm formation and EPS production, while Bradyrhizobium showed high IAA production. Cowpea plants inoculated with Bradyrhizobium exhibit higher levels of nodulation, biomass, and nitrogen accumulation. Conversely, M. vignae strains were more efficient at alleviating drought stress and maintaining nodulation, biomass, nitrogen accumulation, and stomatal conductance similar to well-watered plants. Drought-inducible genes were more strongly upregulated in the nodules of plants inoculated with Bradyrhizobium than in those inoculated with M. vignae. Conclusion: Our results suggest that M. vignae strains, isolated from a semi-arid region, help plants withstand water-stress, whereas the strain of Bradyrhizobium sp. isolated from a wet region did not effectively alleviate drought stress. However, Bradyrhizobium sp. conferred growth and nitrogen accumulation to cowpea superior to M. vignae and like plants supplied with nitrogen fertilizer. [ABSTRACT FROM AUTHOR]

Purpose: Reductive soil disinfestation (RSD) has been widely applied to improve soil degradation, enhancing vegetable N uptake and productivity. However, its effects on interactions between vegetable N uptake and soil gross N transformation remain unclear. Methods: Two degraded vegetable soils were treated with RSD and 15N tracing pot experiments were conducted to quantify the effects of RSD on N cycling in vegetable-soil systems. Results: Vegetable NH4+ and NO3− uptake rates were 1.0–6.5 times higher following RSD than CK, while soil gross N mineralization rates (M) ranged from 0.83–13.00 mg N kg−1 d−1, and were significantly higher than the CK (0.21–8.71 mg N kg−1 d−1). Meanwhile, autotropic nitrification rate (ONH4) increased by 1.7–4.2 following RSD, while NH4+ immobilization rates (INH4) were significantly inhibited by RSD in the presence of planting. This induced a decrease in (ONH4 + INH4)/M, and increases in NH4+ retention times and production rates of soil NO3− following RSD. In addition, RSD improved the overall quality of the degraded soils (increasing the pH, and decreasing EC and NO3− contents as well as pathogen abundance), further promoting vegetable N uptake. Conclusion: RSD promoted vegetable N uptake by regulating soil gross N transformation rates and improving the quality of degraded vegetable soil. However, NO3− production rates were enhanced following RSD, increasing the risk of NO3− leaching and gaseous N losses. N fertilizer management under RSD therefore requires further attention. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO), as a short-lived climate forcer, has direct and indirect detrimental impacts on environmental quality and human health. The amount of nitrogen (N) fertilizer application to agricultural soils is considered a robust predictor of total NO emissions, but the estimates of cropland NO emissions have large uncertainties due to the widely used constant emission factors (EF) as e.g., default values recommended by Intergovernmental Panel on Climate Change (IPCC) methodologies. By compiling 223 field experiments with at least three N-input levels across various croplands, we performed a meta-analysis to determine how soil NO emissions respond to N inputs. Our results showed for the first time that the mean change in EF per unit of additional N input (∆EF) across all available data was significantly higher as compared to zero, indicating that the NO response to N additions increased significantly faster than the assumed linear. On average, upland grain crops showed significantly higher ∆EF than that of horticultural crops or lowland rice. A higher ∆EF was also appeared in sites with mean annual precipitation < 600 mm, mean annual temperature ≥ 15 °C, soil organic carbon ≥ 14 g C kg− 1 or total N ≥ 1.4 g N kg− 1, and where synthetic N fertilizers were usually applied. By assuming various N application rates, the IPCC default (0.7% or 1.1%) EF model would have overestimated or underestimated NO emissions compared to our ∆EF model. Overall, our meta-analysis results exert high potential to improve estimates of cropland NO inventories, and help address disparities in global NO budgets and develop more targeted mitigation efforts. [ABSTRACT FROM AUTHOR]

The CERES-Maize model performance was investigated in simulating maize phenology, grain yield, soil–water, evapotranspiration, and water productivity under different irrigation and nitrogen (N) levels under a variable rate lateral (linear)-move sprinkler irrigation system. The irrigation levels were rainfed, full irrigation treatment (FIT) and 75% FIT. The N levels were 0, 84, 140, 196, and 252 kg/ha. The field experiment was conducted in the form of split plots with the irrigation levels as the main treatment and N levels as a sub-main treatment. The root mean squared error (RMSE), normalized RMSE (RMSEn), R2, T test, and model prediction error (Pe) statistics were used to evaluate the performance and accuracy of the model. Calibration of the model was done using the data of 2011 and 2012 and validation of the model was conducted for 2013 and 2014 by considering days after planting to flowering (DAPF), days after planting to maturity (DAPM), grain yield, crop evapotranspiration (ETc), water productivity (WP), and soil water content (SWC). The DAPF simulations based on the average values of Pe (0%), RMSE (2 days), and RMSEn (3%) and the DAPM simulation results based on the average values of Pe (2%), RMSE (4 days), and RMSEn (3%) showed that the model had an acceptable accuracy. In calibration years, RMSE, RMSEn, and R2, respectively, were 0.57 ton/ha, 5%, and 0.91; and in validation years, the same statistics, respectively, were 0.86 ton/ha, 10% and 0.94, indicating good performance of the model in estimating the grain yield. Good accuracy was observed in the estimation of ETc and WP. In most cases, the model accuracy was greatest for 75% FIT and FIT treatments than the stressed conditions in the rainfed treatment. The model accuracy can be enhanced by improving the model coefficients in response to low levels of water and N supply. R2 values obtained in rainfed (0.83), 75% FIT (0.81) and FIT (0.67) treatments in calibration years and R2 values in rainfed (0.75), 75% FIT (0.77) and FIT (0.86) treatments in validation years showed that the model predicted the SWC relatively well. The comparison of ETc values with respect to N levels showed that there was no considerable difference between levels of N applications impact(s) on the ETc magnitude in the rainfed treatment. Comparison of different levels of N in rainfed and FIT showed that the application of 252 kg/ha of N resulted in 2.37 kg/m3 and 2.56 kg/m3 of WP, respectively, which was significantly different from other levels of N fertilizer applications. In general, CERES-Maize model can be a useful tool for predicting plant phenology, grain yield, ETc, WP, and SWC for the conditions similar to those presented in this research. The CERES-Maize model can provide valuable data and information for sustainable maize production by examining the long-term grain yield and WP, which can be beneficial to growers, advisors, and stakeholders to enhance the maize production efficiency by accounting for irrigation and N management strategies. [ABSTRACT FROM AUTHOR]

Soil elemental stoichiometry can characterize soil nutrient storage, supply capacity, and limitation. C:N:P stoichiometry is considered an important indicator of soil nutrient status during soil development. Drylands are critical terrestrial environments and are considered to be the largest biome on Earth. Our study aimed to investigate the C:N:P stoichiometric characteristics and drivers of surface soil in the drylands of China. Our study was conducted based on soil nutrient data derived from the National Tibetan Plateau Data Center and environmental data. We used structural equation modeling, variation partitioning analysis, redundancy analysis, and other methods to investigate whether there are spatial patterns and interrelationships among soil C, N, P, and C:N:P in the drylands of China and to analyze the drivers influencing the changes in C, N, P, and C:N:P. Similarly, C, N, and P density of the surface soil in the drylands of China were low (3.44, 0.14 and 0.10 kg/m2, respectively). Highly significant non-linear relationships were observed between all the nutrients and their corresponding stoichiometric ratios, except for C and P, which exhibited significant linear relationships. Aridity and plant (vegetation) were the main drivers of soil C and N density in drylands, while the main driver of P density was aridity; the soil environment contributed most to the relative changes in C, N, P, and C:N:P. In conclusion, the soil C, N, and P densities in the drylands of China were low. Plant, climate, and soil together explained 47.5–81.3% of the total variation in C, N, P, and C:N:P. Our results indicated that the soil surface nutrient density is low in drylands; changes in C, N, P, and C:N:P are not influenced by a single factor but are driven by a combination of environmental factors. The results of this research provide a specific reference for a comprehensive understanding of changes in soil nutrient densities in drylands under global environmental change. For example, when plowing dryland farmland, the stability of the soil can be protected against land erosion and degradation by increasing soil organic matter; additionally, when applying fertilizers to dryland farmland, the amount of N fertilizer can increase, and the amount of P fertilizer can decrease in the future. [ABSTRACT FROM AUTHOR]

This study integrated bacterial community and soil chemicals to characterize the soil ecosystem in an open upland field managed by six controlled fertilizer programs using the minimum amount of pesticides. Amplicon sequencing the 16S rRNA gene revealed that inorganic nitrogen fertilizer and compost altered the diversity and structure of the soil bacterial community throughout buckwheat (Fagopyrum esculentum Moench 'Hitachiakisoba') cultivation. The bacterial community comprised three clusters that contained bacteria that are prevalent in soils fertilized with nitrogen (cluster 1, 340 taxa), without nitrogen and compost (cluster 2, 234 taxa), and with compost-fertilized (cluster 3, 296 taxa). Cluster 2 contained more taxa in Actinobacteriota and less in Acidobacteriota, and cluster 3 contained more taxa in Gemmatimonadota compared with the other clusters. The most frequent taxa in cluster 1 were within the Chloroflexi phylum. The bacterial community structure correlated with soil chemical properties including pH, total organic carbon, SO42−, soluble Ca2+. A co-occurrence network of bacterial taxa and chemicals identified key bacterial groups comprising the center of a community network that determined topology and dynamics of the network. Temporal dynamics of the bacterial community structure indicated that Burkholderiales were associated with buckwheat ripening, indicating plant-bacteria interaction in the ecosystem. [ABSTRACT FROM AUTHOR]

Interactions between microorganisms and plants can stimulate plant growth and promote nitrogen cycling. Nitrogen fertilizers are routinely used in agriculture to improve crop growth and yield; however, poor use efficiency impairs the optimal utilization of such fertilizers. Differences in the microbial diversity and plant growth of rice soil under different nitrogen application conditions and the expression of nitrogen-use efficiency-related genes have not been previously investigated. Therefore, this study investigates how nitrogen application and nitrogen-use efficiency-related gene NRT1.1B expression affect the soil microbial diversity and growth indices of two rice varieties, Huaidao 5 and Xinhuai 5. In total, 103,463 and 98,427 operational taxonomic units were detected in the soils of the Huaidao 5 and Xinhuai 5 rice varieties, respectively. The Shannon and Simpson indices initially increased and then decreased, whereas the Chao and abundance-based coverage estimator indices decreased after the application of nitrogen fertilizer. Nitrogen fertilization also reduced soil bacterial diversity and richness, as indicated by the reduced abundances of Azotobacter recorded in the soils of both rice varieties. Nitrogen application initially increased and then decreased the grain number per panicle, yield per plant, root, stem, and leaf nitrogen, total nitrogen content, glutamine synthetase, nitrate reductase, urease, and root activities of both varieties. Plant height showed positive linear trends in response to nitrogen application, whereas thousand-grain weights showed a negative trend. Our findings may be used to optimize nitrogen fertilizer use for rice cultivation and develop crop-variety-specific strategies for nitrogen fertilizer application. [ABSTRACT FROM AUTHOR]

Antibiotics in agricultural soil can be accumulated in crops and might pose a potential risk to human health. Nevertheless, there is a lack of knowledge about the impact of nitrogen fertilizers on the dissipation and uptake of antibiotics in soils. Therefore, our aim in this study is to investigate the effects of urea fertilizer on the residues of ciprofloxacin and its uptake by Chinese flowering cabbage (Brassica parachinensis L.) as affected by the associated changes on the soil microbial community. A pot experiment has been conducted using spiked soil with 20 mg ciprofloxacin /kg soil and fertilized with urea at dosages equal to 0, 0.2, 0.4, 0.8 t/ha. Application urea especially at 0.4 t/ha decreased the residue of ciprofloxacin in the soil and its uptake by the roots and its translocation to the shoots of Chinese flowering cabbage. The translocation factors (TFs) for ciprofloxacin were significantly decreased (P < 0.05) only at the treatment of 0.4 t/ha, while no significant difference of bio-concentration factors (BCFs). The average well color development (AWCD) values, Shannon diversity, and richness index were higher in the fertilized than the un-fertilized soils, and all such indicators were greater at the treatment of 0.4 t/ha than at 0.2 and 0.8 t/ha. The carbon substrate utilization of phenolic acids at the treatments of 0.4 t/ha were greater than with other levels of urea fertilizer. In conclusion, moderate urea addition significantly increased soil microbial activity and abundance, which in turn promoted the ciprofloxacin dissipation in soil and plant tissue. The present study provides an economical and operational strategy for the remediation of ciprofloxacin contaminated soils. [ABSTRACT FROM AUTHOR]

Cover cropping is a promising strategy to improve soil health, but it may also trigger greenhouse gas emissions, especially nitrous oxide (N2O). Beyond nitrogen (N) availability, cover crop residue decomposition may accelerate heterotrophic respiration to limit soil O2 availability, hence promote N2O emissions from denitrification under sub-optimal water-filled pore space (WFPS) conditions that are typically not conducive to large N2O production. We conducted a 21-day incubation experiment to examine the effects of contrasting cover crop residue (grass vs legume) decomposition on soil O2 and biogeochemical changes to influence N2O and CO2 emissions from 15N labeled fertilized soils under 50% and 80% WFPS levels. Irrespective of cover crop type, mixing cover crop residue with N fertilizer resulted in high cumulative N2O emissions under both WFPS conditions. In the absence of cover crop residues, the N fertilizer effect of N2O was only realized under 80% WFPS, whereas it was comparable to the control under 50% WFPS. The N2O peaks under 50% WFPS coincided with soil O2 depletion and concomitant high CO2 emissions when cover crop residues were mixed with N fertilizer. While N fertilizer largely contributed to the total N2O emissions from the cover crop treatments, soil organic matter and/or cover crop residue derived N2O had a greater contribution under 50% than 80% WFPS. Our results underscore the importance of N2O emissions from cover crop-based fertilized systems under relatively lower WFPS via a mechanism of respiration-induced anoxia and highlight potential risks of underestimating N2O emissions under sole reliance on WFPS. [ABSTRACT FROM AUTHOR]

Site-specific nitrogen management has been proposed as a tool to increase crop yield while decreasing nutrient losses to the environment. Many reports can be found on sensing technologies to quantify the variability within a field and the definition of management zones based on the observed variability. However, fewer studies have been dedicated to the selection of the most suitable N fertilizer management scenario: should more or less nutrients be applied in the zones with a lower crop productivity potential? To address this knowledge gap, nine Flemish maize fields were selected as potential candidates for precision fertilization based on the soil maps and historical vegetation index patterns. Within each field, two management zones were identified based on historical vegetation index patterns and electrical conductivity maps, and different fertilization strategies were tested in each zone. The field trial results in terms of yield and soil residual nitrate showed that site-specific N management outperforms the conventional practice only in the fields with temporally stable management zones. In the fields having differences in the physical soil properties (e.g. presence of stones or clay particles), affecting water availability, lower fertilization in zones with a poor soil productivity potential could be recommended. In the fields where the performance of the management zones changes from year to year mainly due to annual variation in precipitation, a risk of incorrect implementation of the precision fertilization concept was identified. Historical NDVI time series serve a good basis to delineate the temporally stable management zones. [ABSTRACT FROM AUTHOR]

Despite the documented increase in greenhouse gas (GHG) emissions from Southeast Asian peat swamp forest degradation and conversion to oil palm over recent decades, reliable estimates of emissions of nitrous oxide (N2O) and methane (CH4) are lacking. We measured soil fluxes of N2O and CH4 and their environmental controls along a peatland transition from primary forest (PF) to degraded drained forest (DF) to oil palm plantation (OP) over 18 months in Jambi, Sumatra, Indonesia. Sampling was conducted monthly at all sites and more intensively following two fertilization events in the OP. Mean annual emissions of N2O (kg N ha−1 yr−1) were 1.7 ± 0.2 for the PF, 2.3 ± 0.2 for the DF and for the OP 8.1 ± 0.8 without drainage canals (DC) and 7.7 ± 0.7 including DC. High N2O emissions in the OP were driven by peat decomposition, not by N fertilizer addition. Mean CH4 annual fluxes (kg C ha−1 yr−1) were 8.2 ± 1.9 for the PF, 1.9 ± 0.4 for the DF, and 1.6 ± 0.3 for the OP with DC and 1.1 ± 0.2 without. Considering their 20-year global warming potentials (GWP), the combined non-CO2 GHG emission (Mg CO2-equivalent ha−1 yr−1) was 3.3 ± 0.6 for the PF and 1.6 ± 0.2 for the DF. The emission in the OP (3.8 ± 0.3 with or without DC) was similar to the PF because reductions in CH4 emissions offset N2O increases. However, considering 100-year GWP, the combined non-CO2 GHG emission was larger in the OP (3.4 ± 0.3 with DC and 3.5 ± 0.3 without) compared to both the PF and the DF (1.5 ± 0.2 and 1.2 ± 0.1, respectively). The increase in peat N2O emissions associated with the land-use change transition from primary forest to oil palm plantation at our sites provides further evidence of the urgent need to protect tropical peat swamp forests from drainage and conversion. [ABSTRACT FROM AUTHOR]

The discord between the nitrogen (N) fertilizer use and the actual N requirement in Indian agriculture is of enormous concern. When N is overused, it emerges as a threat to the environment, and crop yields are affected when it is underused. Nutrient budgeting is a useful tool in assessing the inflows and outflows of nutrients to the agricultural system and formulating future strategies. We constructed a nitrogen budget for Indian agriculture for 1961–2017. The N input to Indian croplands increased from 4.87 million tons (Mt) to 24.08 Mt during this period. Among the different components of N use in 2017, the contribution of fertilizer is the highest (70%), followed by biological N fixation (16%), manure (9%), and atmospheric deposition (4%). The analysis portrayed Indian agriculture's transformation from the N deficit value of − 0.61 Mt in 1961 to a surplus-value of 1.21 Mt as of 2017. The crop N use efficiency during the period decreased from 72 to 55%. Since the policies and socio-economic factors are the commonly studied drivers of N fertilizer use, crop production factors have not received due attention. We dissect the contribution of these factors to N fertilizer use. The fertilizer application rate (FAR) is the most important among the major crop production factors that drive N fertilizer use. Our findings propose that the surplus N in Indian agriculture, hastened by higher FAR, may pose serious sustainability issues if not addressed. [ABSTRACT FROM AUTHOR]

The research was aimed at developing a conceptual model of digital nitrogen management in crops. Cognitive analysis of the knowledge structure in this subject area and conceptual modeling of digital nitrogen management in agrophytocenoses using an object-oriented approach and Unified Modeling Language (UML) were used. A detailed system of diagrams was created, encompassing class, process, and interaction diagrams. The model is anchored on three abstract objects: class (seven in total), attribute (32), and interclass relationships (18), which distribute the main concepts, emphasizing the complexity and multifaceted approaches to digital nitrogen management. The central class is "Agrophytocenosis", which directly interacts with five classes and indirectly with one class. Attributes are integral to the classes and reflect their specific characteristics. To depict the interaction between the classes and their attributes, four types of relationships are employed in the model: "dependency," "association," "aggregation," and "inner class." In the process diagram of the digital nitrogen management system, two primary subsystems are highlighted: the analysis and planning subsystem and the adjustment subsystem, as well as tools and sources for data acquisition and processing. A distinctive feature of the developed conceptual model is the application of the temporality principle, integrating static and dynamic processes in the digital nitrogen management system within the agrophytocenosis. Subsystems for analysis, planning, and adjustment of emerging conditions in the management areas allow ensuring more efficient use of nitrogen fertilizers in crops. The conceptual model is aimed at developing a hardware-software complex for diagnostics of nitrogen nutrition of cultivated plants and management of fertilizer application based on modern digital monitoring and data-processing tools. [ABSTRACT FROM AUTHOR]

Litter decomposition and livestock excreta are two important sources for replenishing nutrients in the soil of the pastures, and their decomposition rates are affected by their quality, management practices, forage productivity, and biotic and abiotic factors. The objective of this research was to assess the effects of escalating levels of N fertilization (0, 100, 200, and 400 kg N ha−1 yr−1) on litter and fecal decomposition in an agroforestry system comprising palisadegrass [Urochloa brizantha (Hochst. Ex A. Rich.) Stapf. cv. Marandu] intercropped with hybrid eucalyptus trees [Eucalyptus urophylla × Eucalyptus tereticornis], in a two-year field trial. The experiment was set in a randomized complete block design with four treatments and three repetitions. Litter (0, 4, 8, 16, 32, 64, 128, and 256 days) and cattle excrement samples (0, 4, 8, 16, 32, 64, and 128 days) were incubated on the ground. For forage litter samples, the interaction between N fertilization × year was observed for the decomposition rate (k) of DM (P = 0.0014) and OM (P = 0.0094). The greatest litter OM disappearance was observed at 400 kg N fertilization ha−1 year−1 (651 g kg−1 DM at 256 days). The interaction between nitrogen fertilizer rate × incubation time, or the isolated effect of the treatment was not observed on fecal decomposition (P > 0.05). Higher levels of N fertilization associated with the rainy period resulted in faster decomposition of palisadegrass litter, however, it did not show to have a strong influence on the excreta decomposition in this agroforestry system. [ABSTRACT FROM AUTHOR]

In the restoration of degraded wetlands, fertilization can improve the vegetation-soil-microorganisms complex, thereby affecting the organic carbon content. However, it is currently unclear whether these effects are sustainable. This study employed Biolog-Eco surveys to investigate the changes in vegetation characteristics, soil physicochemical properties, and soil microbial functional diversity in degraded alpine wetlands of the source region of the Yellow River at 3 and 15 months after the application of nitrogen, phosphorus, and organic mixed fertilizer. The following results were obtained: The addition of nitrogen fertilizer and organic compost significantly affects the soil organic carbon content in degraded wetlands. Three months after fertilization, nitrogen addition increases soil organic carbon in both lightly and severely degraded wetlands, whereas after 15 months, organic compost enhanced the soil organic carbon level in severely degraded wetlands. Structural equation modeling indicates that fertilization decreases the soil pH and directly or indirectly influences the soil organic carbon levels through variations in the soil water content and the aboveground biomass of vegetation. Three months after fertilization, nitrogen fertilizer showed a direct positive effect on soil organic carbon. However, organic mixed fertilizer indirectly reduced soil organic carbon by increasing biomass and decreasing soil moisture. After 15 months, none of the fertilizers significantly affected the soil organic carbon level. In summary, it can be inferred that the addition of nitrogen fertilizer lacks sustainability in positively influencing the organic carbon content. [ABSTRACT FROM AUTHOR]

Global warming is one of the eco-environmental problems of most concern to scientists. N2O, an atmospheric greenhouse gas, has been widely studied because of its high warming potential. As an excellent soil conditioner, biochar has a very broad research value and application path in the farmland. This work examined the impact of biochar application on N2O emissions reduction potential of farmland soils in northern China by meta analysis and path analysis. The results were as follows: the N2O emissions reduction potential changes corresponded with different biochar preparation materials, preparation temperature, C/N ratio and pH. Biochar is more suitable for application in soil with a bulk density < 1.3 g cm−3, sandy loam texture, neutral pH, organic matter content 20–30 g kg−1, soil C/N ratio 10–20, and total nitrogen < 2 g kg−1. At the same time, the maximum reduction of N2O emissions can be achieved in a scenario where the biochar is applied at 20 t ha−1- 40 t ha−1 and the application of nitrogen fertilizer is 100–200 kg N ha−1. Under the above ideal conditions, this study selected the data of soil mineralized nitrogen (X1), soil organic matter content (X2), soil water content (X3), average temperature (X4), total nitrogen (X5), and N2O emissions (Y) for correlation analysis and path analysis, and finally obtained the multiple stepwise regression equation between N2O emissions and various impact factors as follows: Y = -45.9102 + 0.6874X1 + 0.4634X2 + 0.3249X3 + 0.2698X4 + 0.2218X5 (R2 = 0.826, p < 0.01, n = 87). The direct relationships between N2O and soil mineralized nitrogen and soil organic matter content were very significant (P < 0.01). The second is soil water content, average temperature and total nitrogen. Indirect relationships between N2O and average temperature, total nitrogen and mineralized nitrogen were significant (P < 0.05). [ABSTRACT FROM AUTHOR]