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This review article explores the impact of nitrogen fertilizers on the symbiotic relationship between Rhizobium bacteria and legume plants. Nitrogen fixation has the potential to address the global protein shortage by increasing nitrogen supply in agriculture. However, the excessive use of synthetic fertilizers has led to environmental consequences and high energy consumption. To promote sustainable agriculture, alternative approaches such as biofertilizers that utilize biological nitrogen fixation have been introduced to minimize ecological impact. Understanding the process of biological nitrogen fixation, where certain bacteria convert atmospheric nitrogen into ammonia, is crucial for sustainable agriculture. This knowledge helps reduce reliance on synthetic fertilizers and maintain soil fertility. The symbiotic relationship between Rhizobium bacteria and leguminous plants plays a vital role in sustainable agriculture by facilitating access to atmospheric nitrogen, improving soil fertility, and reducing the need for chemical fertilizers. To achieve optimal nitrogen fixation and plant growth, it is important to effectively manage nitrogen availability, soil conditions, and environmental stressors. Excessive nitrogen fertilization can negatively affect the symbiotic association between plants and rhizobia, resulting in reduced soil health, altered mutualistic relationships, and environmental concerns. Various techniques can be employed to enhance symbiotic efficiency by manipulating chemotaxis, which is the ability of rhizobia to move towards plant roots. Plant-specific metabolites called (iso)flavonoids play a crucial role in signaling and communication between legume plants and rhizobia bacteria, initiating the symbiotic relationship and enhancing nitrogen fixation and plant growth. Excessive nitrogen fertilizer application can disrupt the communication between rhizobia and legumes, impacting chemotaxis, root exudation patterns, nodulation, and the symbiotic relationship. High levels of nitrogen fertilizers can inhibit nitrogenase, a critical enzyme for plant growth, leading to reduced nitrogenase activity. Additionally, excessive nitrogen can compromise the energy demands of nitrogen fixation, resulting in decreased nitrogenase activity. This review discusses the disadvantages of using nitrogenous fertilizers and the role of symbiotic biological nitrogen fixation in reducing the need for these fertilizers. By using effective rhizobial strains with compatible legume cultivars, not only can the amounts of nitrogenous fertilizers be reduced, but also the energy inputs and greenhouse gas emissions associated with their manufacturing and application. This approach offers benefits in terms of reducing greenhouse gas emissions and saving energy. In conclusion, this paper provides a comprehensive overview of the current understanding of the impact of nitrogen fertilizers on the symbiotic relationship between Rhizobium and legume plants. It also discusses potential strategies for sustainable agricultural practices. By managing nitrogen fertilizers carefully and improving our understanding of the symbiotic relationship, we can contribute to sustainable agriculture and minimize environmental impact.

More diverse crop rotations have been promoted for their potential to remediate the range of ecosystem services compromised by biologically simplified grain-based agroecosystems, including increasing soil organic carbon (SOC). We hypothesized that functional diversity offers a more predictive means of characterizing the impact of crop rotations on SOC concentrations than species diversity per se. Furthermore, we hypothesized that functional diversity can either increase or decrease SOC depending on its associated carbon (C) input to soil. We compiled a database of 27 cropping system sites and 169 cropping systems, recorded the species and functional diversity of crop rotations, SOC concentrations (g C kg/soil), nitrogen (N) fertilizer applications (kg N·ha−1·yr−1), and estimated C input to soil (Mg C·ha−1·yr−1). We categorized crop rotations into three broad categories: grain-only rotations, grain rotations with cover crops, and grain rotations with perennial crops. We divided the grain-only rotations into two sub-categories: cereal-only rotations and those that included both cereals and a legume grain. We compared changes in SOC and C input using mean effect sizes and 95% bootstrapped confidence intervals. Cover cropped and perennial cropped rotations, relative to grain-only rotations, increased C input by 42% and 23% and SOC concentrations by 6.3% and 12.5%, respectively. Within grain-only rotations, cereal + legume grain rotations decreased total C input (−16%), root C input (−12%), and SOC (−5.3%) relative to cereal-only rotations. We found no effect of species diversity on SOC within grain-only rotations. N fertilizer rates mediated the effect of functional diversity on SOC within grain-only crop rotations: at low N fertilizer rates (≤75 kg N·ha−1·yr−1), the decrease in SOC with cereal + legume grain rotations was less than at high N fertilizer rates. Our results show that increasing the functional diversity of crop rotations is more likely to increase SOC concentrations if it is accompanied by an increase in C input. Functionally diverse perennial and cover cropped rotations increased both C input and SOC concentrations, potentially by exploiting niches in time that would otherwise be unproductive, that is, increasing the “perenniality” of crop rotations.

Background and aims Nitrogen (N), commonly applied to increase rice yield, can influence grain quality by its effect on grain zinc (Zn) concentration. This study evaluated the effects of N fertilizer as applied to the soil and as foliar N on the yield and grain Zn and N concentrations. Methods Two rice varieties with low grain Zn and high yield potential (CNT1 and RD21), one variety with medium grain Zn and moderate yield potential (KDML105), and two with high grain Zn and low yield potential (KPK and NR) varieties were used in this study. Soil N fertilizer was applied at 50–300 kg ha −1 , and foliar N was applied at 0–2.5% N. Results Soil N fertilizer increased grain Zn concentration in all five rice varieties, but with different effects on grain yield. Increased grain Zn was associated with increases in grain yield in the high yield varieties with low Zn, while there were positive to no effects on grain yield in the varieties with moderate yield potential and moderate Zn. The largest increases in grain Zn from application of soil N were associated with yield depression in the high grain Zn and low yield potential varieties, while foliar N had little effect on grain yield. Positive associations between grain N and Zn were observed in both concentration and contents. Conclusions This study suggests that N and Zn act synergistically in their effects on the accumulation of grain Zn in rice, irrespective of initial grain Zn and yield potential of rice varieties.

The impact of chemical to organic fertilizer substitution on soil labile organic and stabilized N pools under intensive farming systems is unclear. Therefore, we analyzed the distribution of soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), dissolved organic N (DON), and mineral N (NO3

Nitrogen is a vital ingredient for plant development and growth. It is one of the most crucial indicators of soil fertility and crop growth conditions. For the monitoring of nitrogen loss patterns and the development of crop nitrogen fertilizer application strategies, an accurate determination of soil nitrogen concentration can be a valuable source of information. For the advancement of precision agriculture and the preservation of the natural ecological environment, an accurate, quick, and low-cost determination of soil nitrogen content and its variations is essential. This paper systematically analyzes and summarizes soil nitrogen detection methods by compiling and analyzing the relevant literature, comparing the advantages and disadvantages of various methods, and concluding with a discussion of the most significant challenges and future research trends in this field. This study provides a helpful resource for understanding the current status, application constraints, and future developments of nitrogen-sensing technologies in precision agriculture.

The nitrogen fertilizer replacement value (NFRV) quantifies the value of organic amendments as a nitrogen (N) fertilizer, and is commonly defined as the extent to which organic fertilizer N can replace mineral fertilizer N. NFRVs can be calculated by comparing the crop N uptake from equal N application rates of mineral and organic fertilizer, or by comparing the N rates of both fertilizers needed to obtain equal crop N uptake. Currently, NFRVs are mainly known for animal manure, whereas other organic waste products may become available as fertilizer products in the future. In this study, a pot experiment with spring wheat was performed to (1) assess NFRVs of a range of organic amendments; (2) compare NFRVs based on equal N application with NFRVs based on equal N uptake; and (3) assess which product characteristics explain observed variation. Observed NFRVs varied between 6.2 and 78.8%, with the lowest value for raw food waste and the highest for fishmeal. NFRVs were overestimated when calculated based on equal N application rate (with on average 6.9% point), and more so at high N application rate (9.0% point). NFRVs should therefore be calculated based on equal N uptake from organic and mineral fertilizers. Nitrogen concentration of the organic fertilizer provided the best explanation of variation observed in NFRVs (R 2  = 0.86). These findings give valuable insights into the large variation in value of organic waste streams as organic fertilizer and can support decisions on sustainable N application rates, to increase crop N uptake and reduce N losses to the environment.

Conversion of coastal mudflats into paddy soils is an effective measure to alleviate the pressures on land resources. However, few studies have evaluated the effects of nitrogen (N) fertilizers on bacterial communities in newly reclaimed mudflat paddy soils. We performed a field plot experiment with six N fertilizer rates (0, 210, 255, 300, 345, and 390 kg N ha −1 ) in a newly reclaimed mudflat paddy for 2 consecutive years and used Illumina sequencing and qPCR to investigate the effects of N fertilizers on bacterial communities and N-cycling genes. Results showed that high N fertilization (above 300 kg N ha −1 ) increased the contents of organic matter (OM), total N (TN), ammonium (NH 4 + ), and nitrate (NO 3 − ) and significantly decreased the diversity and richness of bacteria. Furthermore, high N fertilization had a stronger effect on bacterial communities than low N fertilization, probably due to high concentrations of NH 4 + , OM, and NO 3 − . Additionally, in paddy soils with high N fertilizer application, the relative abundances of Bacteroidetes, γ-proteobacteria, and Actinobacteria increased significantly, but the reverse was true for those of Chloroflexi, Firmicutes, δ-proteobacteria, α-proteobacteria, Acidobacteria, and β-proteobacteria. The results of qPCR indicated that high N fertilization significantly increased the relative abundance of nif H genes involved in N fixation and decreased that of amo A-archaea involved in ammonia oxidation, nir S genes involved in nitrite reduction, and nos Z genes involved in nitrous oxide reduction, which suggested that high N fertilization increased the potential of available N retention and reduced the potential of nitrous oxide emission. Overall, N fertilizers with an N fertilizer rate of above 300 kg N ha −1 significantly altered the bacterial communities and N-cycle of mudflat paddy soils.

Aims Rhizosphere metabolomics can potentially help us to better understand belowground root-environment interactions that are mediated by root exudation in the rhizosphere. The main goals of the present work were to characterize the pattern of maize root exudation in response to straw-derived biochar (BC) addition and chemical nitrogen (N) fertilizer reduction and to explore the underlying mechanisms. Methods Two sets of pot experiments were performed independently that involved planting maize in aquic brown soil to which BC was added at dosages of 0 or 5% (w/w, equivalent to 112.5 t ha−1) combined with urea N application at rates of 150 kg ha−1 (100%) or 105 kg ha−1 (70%) for a total of four treatments. Samples containing root exudates were analyzed using nuclear magnetic resonance, and quantitative real-time reverse transcription-PCR (qRT-PCR) was performed to analyze gene expression in maize roots. Results The 5% BC addition significantly influenced the global rhizosphere metabolome of the maize seedlings regardless of the N application level, but without BC addition, the rhizosphere metabolome was not significantly affected by a 30% reduction in N. The effects of N reduction on the metabolite profiling of the native root exudates were stronger than those of BC addition and an obvious interaction was observed between BC addition and N reduction. BC addition combined with N reduction significantly changed the levels of some amino acids (e.g., causing a 1.75-fold increase in isoleucine) and organic acids (e.g., causing a 2.16-fold increase in malonate and a 2.15-fold increase in acetate) in the root exudates. Soil environmental factors, including the size of NH4+-N pool and total P content, had a strong positive correlation with rhizosphere metabolome. The decrease in root biomass caused by N reduction was partially mitigated by BC addition, and the expression of ZmMATE1 (for multi-drug and toxic compound extrusion transporter) in root was significantly upregulated (P < 0.05) by BC addition and N reduction. Conclusions Maize roots can reshape their rhizosphere metabolome under BC addition combined with N reduction and its underlying mechanism may involve the synergistic effects of soil environmental factors, root growth, and the expression of transport-associated genes.

BackgroundRice is a key global food crop. Rice lodging causes a reduction in plant height and crop yield, and rice is prone to lodging in the late growth stage because of panicle initiation. We used two water irrigation modes and four fertilizer application intervals to investigate the relationship between lodging and various cultivation conditions over 2 years.ResultsPlant height data were collected and combined with aerial images, revealing that rice lodging was closely related to the nitrogen fertilizer content. The aerial images demonstrated that lodging mainly occurred in the fields treated with a high-nitrogen fertilizer, and analysis of variance revealed that plant height was signifi-cantly affected by nitrogen fertilizer. These results demonstrated that rice plant height in the booting stage was significantly positively correlated with the lodging results (r = 0.67) and nega-tively correlated with yield (r = − 0.46). If the rice plant height in the booting stage exceeded 70.7 cm and nitrogen fertilizer was continuously applied, according to the predicted growing curve of plant height, the plant would be at risk of lodging. Results showed more rainfall accumulated in the later stage of rice growth accompanied by strong instantaneous gusts, the risk of lodging in-creased.ConclusionThe results provide predictions that can be applied in intelligent production and lodging risk management, and they form the basis of cultivation management and response policies for each growth period.

A comprehensive understanding of the transformation, migration and loss pathways of nitrogen (N) fertilizer was pivotal for optimum nutrient management. Three different cultivation practices (conventional cultivation, plastic film mulching and straw retention) and N rates (0, 144 and 180 kg N ha −1 ) were assigned as the main plots and split plots separately in a split-plot design during 2017–2020. Moreover 15 N-labeled urea was used in each microplot to trace the fertilizer N fate. The results showed that the N recovery efficiencies with plastic film mulching, straw retention and conventional cultivation were 44–46%, 34–37% and 43–44% in the first season. However, it sharply decreased in the next two seasons. The N residual rates in straw retention and plastic film mulching were 21–26% and 20–27% after three wheat seasons, which were higher than that in conventional cultivation. Furthermore, residual nitrate nitrogen was detected in the deep profiles in plastic film mulching and straw retention at the third season. The ammonia volatilization sourced from fertilizer was 3–5 kg ha −1 in the first season and accounted for 2–3% of the total applied N. Overall, plastic film mulching treatment increased fertilizer N utilization by plants and residual fertilizer N in soil, and reduced unidentified fertilizer N. Although, straw retention depressed fertilizer N uptake by plants, it improved the N budget and had the potential to reduce N input. Accordingly, plastic film mulching and straw retention are recommended in dryland wheat cropping systems. However, we should pay attention to the residual plastic pollution in the practice.