Nitrogen Use Efficiency In Crops Research Articles

Transcription factor ZmEREB97 regulates nitrate uptake in maize (Zea mays) roots.

Maize (Zea mays L.) has very strong requirements for nitrogen. However, the molecular mechanisms underlying the regulations of nitrogen uptake and translocation in this species are not fully understood. Here, we report that an APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) transcription factor ZmEREB97 functions as an important regulator in the N-signaling network in maize. Predominantly expressed and accumulated in main root and lateral root primordia, ZmEREB97 rapidly responded to nitrate treatment. By overlapping the analyses of differentially expressed genes and conducting a DAP-seq assay, we identified 1446 potential target genes of ZmEREB97. Among these, 764 genes were co-regulated in two lines of zmereb97 mutants. Loss of function of ZmEREB97 substantially weakened plant growth under both hydroponic and soil conditions. Physiological characterization of zmereb97 mutant plants demonstrated that reduced biomass and grain yield were both associated with reduced nitrate influx, decreased nitrate content and less N accumulation. We further demonstrated that ZmEREB97 directly targets and regulates the expression of six ZmNRT genes by binding to the GCC box-related sequences in gene promoters. Collectively, these data suggest that ZmEREB97 is a major positive regulator of the nitrate response and that it plays an important role in optimizing nitrate uptake, offering a target for improvement of nitrogen use efficiency in crops.

Methods for Measuring Nutrient Uptake in Maize Using Nitrogen Stable Isotopes.

Nitrogen is a key nutrient for plant growth and development, and understanding nutrient uptake is central to improving nitrogen use efficiency in crops, including maize. Reducing the need for fertilizer without reducing yield is extremely important, as nitrogen fertilizers come with a high environmental cost, in terms of both emissions from manufacturing and losses to waterways or volatilization off fields. Maize develops multiple different root types, including primary, seminal, crown, and brace roots. Part of improving efficiency in maize involves understanding the differences in nutrient uptake via each distinct root type, but these differences have been largely ignored to date. Here, we describe a protocol that uses stable isotopes for determining nitrogen uptake rates by maize root types. We describe the steps both for intact roots, for which we use rhizoboxes with openable front windows that allow access to the roots without disturbing the rest of the plant, and for field-grown plants, for which intact analysis is not feasible and requires excising the roots. The methods described here can also be modified to measure uptake kinetics and for monitoring nutrient translocation between roots and shoots. Advancing our understanding of root physiology and nutrient dynamics will improve breeding opportunities for efficient nutrient uptake varieties, reducing the need for fertilizer additions.

Linkages of soil and microbial stoichiometry to crop nitrogen use efficiency: Evidence from a long-term nitrogen addition experiment

Increasing crop nitrogen use efficiency (NUE) has important implications for food security and agricultural sustainability. Changes in nutrient availability due to stoichiometric imbalances in soil under long-term application of nitrogen (N) can limit crop NUE and yield. However, little is known about the linkages across stoichiometric balance, N fertilizer application, and N uptake. We investigated the changes in soil stoichiometry, microbial community, and crop NUE relative to N fertilizer application in a 16-year field experiment in which five levels (0, 70, 140, 210 and 280 kg N ha−1) of mineral N fertilizer treatment were applied to wheat and maize cropland. The results showed that the P storage decreased from 4.3 Mg P ha–1 under the fertilizer dose of 0 kg N ha−1 to 3.5 Mg P ha–1 under the fertilizer dose of 280 kg N ha−1. Thus, long-term N application increased soil C/P and N/P ratios, in a marked decrease in the content of soil available P. The microbial community based on phospholipid fatty acids (PLFAs) increased with increasing N addition rates, from 0 to 140 kg N ha−1, but significantly decreased at application rates above 210 kg N ha−1. Thus, applying N at a rate of 140 kg ha−1 resulted in the N threshold rate for microorganism survival being reached or exceeded. The crop NUE peak occurred at the urea application rate of 140 kg N ha−1 (60.4 %), after which NUE declined. The soil elementary and enzymatic stoichiometric ratios under long-term N addition directly affected crop NUE in the topsoil. Soil elementary stoichiometric ratios affected crop NUE by indirectly altering microbial biomass of the subsoil. Overall, soil stoichiometric imbalances under long-term N addition were the key factors driving NUE across N gradients.

Strategies to utilize genome editing for increasing nitrogen use efficiency in crops

Strategies to utilize genome editing for increasing nitrogen use efficiency in crops

Meta-Analysis Assessing Potential of Drone Remote Sensing in Estimating Plant Traits Related to Nitrogen Use Efficiency

Unmanned Aerial Systems (UASs) are increasingly vital in precision agriculture, offering detailed, real-time insights into plant health across multiple spectral domains. However, this technology’s precision in estimating plant traits associated with Nitrogen Use Efficiency (NUE), and the factors affecting this precision, are not well-documented. This review examines the capabilities of UASs in assessing NUE in crops. Our analysis specifically highlights how different growth stages critically influence NUE and biomass assessments in crops and reveals a significant impact of specific signal processing techniques and sensor types on the accuracy of remote sensing data. Optimized flight parameters and precise sensor calibration are underscored as key for ensuring the reliability and validity of collected data. Additionally, the review delves into how different canopy structures, like planophile and erect leaf orientations, uniquely influence spectral data interpretation. The study also recognizes the untapped potential of image texture features in UAV-based remote sensing for detailed analysis of canopy micro-architecture. Overall, this research not only underscores the transformative impact of UAS technology on agricultural productivity and sustainability but also demonstrates its potential in providing more accurate and comprehensive insights for effective crop health and nutrient management strategies.

Nitrogen sensing and regulatory networks: it's about time and space.

A plant's response to external and internal nitrogen signals/status relies on sensing and signaling mechanisms that operate across spatial and temporal dimensions. From a comprehensive systems biology perspective, this involves integrating nitrogen responses in different cell types and over long distances to ensure organ coordination in real time and yield practical applications. In this prospective review, we focus on novel aspects of nitrogen (N) sensing/signaling uncovered using temporal and spatial systems biology approaches, largely in the model Arabidopsis. The temporal aspects span: transcriptional responses to N-dose mediated by Michaelis-Menten kinetics, the role of the master NLP7 transcription factor as a nitrate sensor, its nitrate-dependent TF nuclear retention, its "hit-and-run" mode of target gene regulation, and temporal transcriptional cascade identified by "network walking." Spatial aspects of N-sensing/signaling have been uncovered in cell type-specific studies in roots and in root-to-shoot communication. We explore new approaches using single-cell sequencing data, trajectory inference, and pseudotime analysis as well as machine learning and artificial intelligence approaches. Finally, unveiling the mechanisms underlying the spatial dynamics of nitrogen sensing/signaling networks across species from model to crop could pave the way for translational studies to improve nitrogen-use efficiency in crops. Such outcomes could potentially reduce the detrimental effects of excessive fertilizer usage on groundwater pollution and greenhouse gas emissions.

NRG2 family members of Arabidopsis and maize regulate nitrate signalling and promote nitrogen use efficiency.

Nitrogen (N) is an essential nutrient for plant growth, and most plants absorb it as nitrate. AtNRG2 has been reported to play an important role in nitrate regulation. In this study, we investigated the functions of AtNRG2 family members of Arabidopsis thaliana and maize in nitrate signalling and metabolism. Our results showed that both AtNRG2.10 and AtNRG2.15 regulated nitrate signalling and metabolism. Overexpression of AtNRG2.11 (AtNRG2) could promote plant growth and improve nitrogen use efficiency (NUE). In addition, the maize genome harbors 23 ZmNRG2 members. We detected the expression of these genes treated with nitrate and the expression of four genes was strongly induced with ZmNRG2.7 having the highest levels. Overexpression of ZmNRG2.7 in the atnrg2 mutant could restore the defects of atnrg2, suggesting that ZmNRG2.7 is involved in nitrate signalling and metabolism. Moreover, the overexpression lines of ZmNRG2.7 showed increased biomass and NUE. These findings demonstrate that at least a part of NRG2 family genes in Arabidopsis and maize regulate nitrate signalling and provide a molecular basis for improving the NUE of crops.

Global meta-analysis and three-year field experiment shows that deep placement of fertilizer can enhance crop productivity and decrease gaseous nitrogen losses

Context or problemThere is an urgent need to address the contradiction between food security and climate change, and achieve the highest crop productivity at the lowest environmental cost. Scientific fertilization is the key to solving this problem. Objective or research questionDeep placement of fertilizer (DPF) is an effective fertilization strategy for improving crop productivity and reducing gaseous N losses, but its effectiveness varies among agricultural systems and appropriate fertilization depths have not yet been determined. MethodsIn this study, we synthesized 99 global studies (120 locations) and conducted a three-year field experiment to evaluate the effects of DPF on the crop yield, nitrogen use efficiency (NUE), and nitrous oxide (N2O), and ammonia (NH3) emissions, and explored their responses to different climates, field management practices, and environmental factors. ResultsDPF could increase the grain yield by 13.5%, and NUE by 33.8%, and reduce N2O emission by 16.2%, and NH3 emissions by 86.6%, respectively. Random forest analysis showed that the fertilization depth and nitrogen application rate were the most important factors that determined the impacts of DPF on the crop yield, NUE, and N2O and NH3 emissions, but their effects also depended on the climate conditions, field management practices, and soil environmental factors. Meta-regression modeling showed that the effects of DPF on the crop yield and NUE increased but then decreased as the fertilizer application depth and nitrogen application rate increased, and the effects on N2O and NH3 emissions tended to increase gradually. The meta-analysis also demonstrated that under DPF, the emission factors for N2O and NH3 decreased by 35.8% and 84.5%, respectively. According to the meta-analysis, the global N2O and NH3 emissions under DPF can be reduced by 0.23 and 5.46 Tg N·year–1 respectively. ConclusionsThe results obtained based on global meta-analysis and a three-year experiment demonstrated that DPF obtained higher grain production with lower environmental costs, and the most suitable fertilization depth was identified as 15–25 cm. Implications or significanceThe results obtained in this study provide valuable insights into food security and environmental costs under effective fertilization management.

Effect of Zn Applied with or Without Palm Stearin Coated Urea on The Growth and Mineral Element Concentration of Maize (Zea mays L.)

Inhibition of ammonia (NH3) volatilization by deaccelerating urea hydrolysis rate in Central Anatolian lands is the indispensable approach for eco-friendly fertilization and nitrogen use efficiency (NUE). Nitrogen (N) and zinc (Zn) are critically limited here in alkaline soils. An experiment was conducted under controlled conditions to determine the availability of Zn applied as a solution and bound with polymer palm stearin (PS) coating material as a urease inhibitor. The treatments consisted of urea as a commercial commodity, urea with PS only, urea impregnated with PS and Zn, Zn-coated urea, and Zn in solution (SOL) form. During winter, 2019-20, the experiment was conducted in the glasshouse of the department of Soil Science and Plant Nutrition at Ankara University, Türkiye. Data indicated that Zn with PS and in SOL form produced more growth traits i.e., plant height (130 cm), stem girth (13.2 mm), shoot dry matter (4.63 g plant-1), root dry matter yield (0.61 g plant-1), and chlorophyll (42.16 mg g-1) content (p<0.01). Similarly, we had higher concentration of N (3.19%) and Zn (50.46 mg kg-1) content in maize plants (p<0.01) as compared to control. In conclusion, Zn at the rate of 10 mg kg-1 either in solution or coated with urea seems highly effective to sustain better crop productivity and NUE. While concerning N and Zn content, coated urea with Zn markedly responded as compared to Zn in SOL. Synergism between N and Zn can lead to better fertilizer management

Genome‐wide identification of nitrate transporter 1/peptide transporter family (NPF) in cassava (Manihot esculenta) and functional analysis of MeNPF5.4 and MeNPF6.2 in response to nitrogen and salinity stresses in rice

AbstractNitrogen is a major driving force for the improvement of crop yield worldwide but brings detrimental effects on ecosystems. Therefore, enhancing nitrogen use efficiency (NUE) is vital for sustainable agriculture. The nitrate transporter (NRT1/NPF) family associated with nitrogen uptake and utilization is indispensable to the improvement of NUE in crops. As an important food security crop, cassava (Manihot esculenta) produces an acceptable yield in nutrient‐deficient soil. Here, we identified and systematically analyzed the NPF gene family in cassava, including phylogenetic relationship, chromosome location, gene duplication, and gene expression in response to different nitrogen supplies. The stem is involved in nitrogen transportation and remobilization. Gene expression analysis revealed that MeNPF5.4 and MeNPF6.2 were specifically expressed in the stem, and have diverse expression in different nitrogen conditions. To facilitate the functional analysis of MeNPF5.4 and MeNPF6.2, we constructed their overexpression (OE) lines in rice. A NO3− flux assay showed that MeNPF5.4 and MeNPF6.2 OE lines exhibited a marked decrease in NO3− efflux and significant NO3− influx compared with WT, which suggests that they might have contributed to the NUE improvement of rice. Notably, overexpressing MeNPF5.4 showed increased grain size, grain number, and grain weight per panicle. More importantly, the MeNPF5.4 OE line contributed to salt tolerance. Nevertheless, an obvious reduction in grain number and grain weight per panicle was detected in the MeNPF6.2 OE line compared with WT. Strikingly, the MeNPF6.2 OE line showed higher salt stress tolerance than WT in LN conditions. Taken together, our results demonstrated that MeNPF5.4 can potentially improve the NUE and salt stress tolerance of rice, which reveals valuable breeding targets to improve crop yield and stress tolerance.

Effect of replacing synthetic nitrogen fertilizer with animal manure on grain yield and nitrogen use efficiency in China: a meta-analysis.

To reduce reliance on synthetic nitrogen (N) fertilizer and sustain food production, replacing synthetic N fertilizer with animal manure as an effective method is widely used. However, the effects of replacing synthetic N fertilizer with animal manure on crop yield and nitrogen use efficiency (NUE) remain uncertain under varying fertilization management practices, climate conditions, and soil properties. Here, we performed a meta-analysis of wheat (Triticum aestivum L.), maize (Zea mays L.), and rice (Oryza sativa L.) based on 118 published studies conducted in China. Overall, the results indicated that substituting synthetic N fertilizer with manure increased yield by 3.3%-3.9% for the three grain crops and increased NUE by 6.3%-10.0%. Crop yields and NUE did not significantly increase at a low N application rate (≤120 kg ha-1) or high substitution rate (>60%). Yields and NUE values had higher increases for upland crops (wheat and maize) in temperate monsoon climate/temperate continental climate regions with less average annual rainfall (AAR) and lower mean annual temperature (MAT), while rice had higher increases in subtropical monsoon climate regions with more AAR and higher MAT. The effect of manure substitution was better in soil with low organic matter and available phosphorus. Our study shows that the optimal substitution rate was 44% and the total N fertilizer input cannot be less than 161kg ha-1 when substituting synthetic N fertilizer with manure. Moreover, site-specific conditions should also be considered.

Crop responses to application of optimum nitrogen fertilizers on soils of various fertilities formed from long-term fertilization regimes

How crops uptake synthetic nitrogen (N) applied to soils of differing fertilities formed from long-term fertilization regimes is a noteworthy scientific question that remains unclear. This is important for understanding nitrogen use efficiency (NUE) and N losses of synthetic N input to soils of different quality. Here, we investigated crop biomass, N uptake, root growth, and NUE in response to three synthetic N rates (including no N fertilizer, No-N; optimum N, Opt.-N; original N, Ori.-N) in long-term plots (since 2006), with various background fertilities induced by long-term fertilization regimes (nil N, optimum synthetic N, conventional synthetic N, and balanced synthetic N and manure) in a cropping system of winter wheat–summer maize rotation. When Opt.-N was applied, no significant differences in crop biomass between soils. However, N uptake by the crops on nil N soils was lower than that on N-fertilized soils. Crop biomass and N uptake in the nil N soils were significantly lower than those in the N-fertilized soils under No-N and Ori.-N supply, and no significant differences were observed between the N-fertilized soils. When Opt.-N was supplied to the nil N soils, grain yield and N uptake increased by 126–191% and 138–148%, respectively, compared with No-N. This change was associated with a large increase in root mass and root length density in the soils. In optimum synthetic N soils, the crop maintained a high yield (7.0–8.2 Mg ha−1) and N uptake (136–228 kg N ha−1) when they received continuous Opt.-N rate. Crop yield and N uptake significantly decreased when N fertilizer supply was ceased, indicating a low legacy effect; however, the long-term straw return alleviated the above decline. Conventional synthetic N soils with long-term excessive N application continued to maintain a comparable high yield (6.1–7.0 Mg ha−1) and N uptake (128–206 kg N ha−1) even after N fertilizer supply was stopped, indicating a high legacy effect. This effect could be applied with less N fertilizer to reduce N losses. Balanced synthetic N and manure could provide resistance to N fertilizer reduction and maintain high yield and soil fertility even after N fertilizer supply is ceased. Our results highlight the strong resilience of soils to crop productivity when resupplying N fertilizer to long-term nil N soils and the different legacy effects from historic fertilization regimes, while emphasizing that balanced synthetic N and manure is an ideal measure for sustainable N management.

Nitrogen use efficiency-a key to enhance crop productivity under a changing climate.

Nitrogen (N) is an essential element required for the growth and development of all plants. On a global scale, N is agriculture's most widely used fertilizer nutrient. Studies have shown that crops use only 50% of the applied N effectively, while the rest is lost through various pathways to the surrounding environment. Furthermore, lost N negatively impacts the farmer's return on investment and pollutes the water, soil, and air. Therefore, enhancing nitrogen use efficiency (NUE) is critical in crop improvement programs and agronomic management systems. The major processes responsible for low N use are the volatilization, surface runoff, leaching, and denitrification of N. Improving NUE through agronomic management practices and high-throughput technologies would reduce the need for intensive N application and minimize the negative impact of N on the environment. The harmonization of agronomic, genetic, and biotechnological tools will improve the efficiency of N assimilation in crops and align agricultural systems with global needs to protect environmental functions and resources. Therefore, this review summarizes the literature on nitrogen loss, factors affecting NUE, and agronomic and genetic approaches for improving NUE in various crops and proposes a pathway to bring together agronomic and environmental needs.

Genetic regulation of nitrogen use efficiency in Gossypium spp.

Cotton (Gossypium spp.) is the most important fibre crop, with desirable characteristics preferred for textile production. Cotton fibre output relies heavily on nitrate as the most important source of inorganic nitrogen (N). However, nitrogen dynamics in extreme environments limit plant growth and lead to yield loss and pollution. Therefore, nitrogen use efficiency (NUE), which involves the utilisation of the 'right rate', 'right source', 'right time', and 'right place' (4Rs), is key for efficient N management. Recent omics techniques have genetically improved NUE in crops. We herein highlight the mechanisms of N uptake and assimilation in the vegetative and reproductive branches of the cotton plant while considering the known and unknown regulatory factors. The phylogenetic relationships among N transporters in four Gossypium spp. have been reviewed. Further, the N regulatory genes that participate in xylem transport and phloem loading are also discussed. In addition, the functions of microRNAs and transcription factors in modulating the expression of target N regulatory genes are highlighted. Overall, this review provides a detailed perspective on the complex N regulatory mechanism in cotton, which would accelerate the research toward improving NUE in crops.

Combined Effects of Biochar and Inhibitors on Greenhouse Gas Emissions, Global Warming Potential, and Nitrogen Use Efficiency in the Tobacco Field

Biochar (BC), nitrification inhibitors (methyl 3-(4-hydroxyphenyl) propionate, MHPP), and urease inhibitors (n-butyl phosphorothioate triamine, NBPT) have emerged as effective soil greenhouse gas (GHG) mitigation strategies in agroecosystems. However, the combined use of BC and inhibitors in karst areas has no available data. Therefore, the combined effects of BC, MHPP, and NBPT on GHG emissions, global warming potential (GWP) and nitrogen use efficiency (NUE) in roasted tobacco cropping systems were studied to improve the understanding in climate mitigation. CO2, CH4, and N2O emissions from soils were measured using static chamber-gas chromatography. Results showed that the combined use of BC and inhibitors significantly increased soil total nitrogen, available potassium, electric conductivity, pH, and soil organic matter compared to the control. The combined use of BC and MHPP or NBPT significantly increased cumulative soil CO2 emissions by 33.95% and 34.25%, respectively. The exponential–exponential function of soil CO2 fluxes with soil moisture and temperature demonstrated good fit (R2: 0.506–0.836). The combination of BC and NBPT increased the cumulative soil CH4 emissions by 14.28% but not significantly compared to the fertiliser treatment. However, the combination of BC and MHPP resulted in a significant reduction in cumulative soil CH4 emissions by 80.26%. In addition, the combined use of BC and MHPP or NBPT significantly reduced the cumulative soil N2O emissions by 26.55% and 40.67%, respectively. The inhibition effect of NBPT was better than MHPP. Overall, the combined use of BC and inhibitors significantly reduced the yield-scaled GWP, markedly increased crop yield and NUE, and mitigated climate change in the southwest karst region.

Unlocking the potentials of nitrate transporters at improving plant nitrogen use efficiency.

Nitrate ( ) transporters have been identified as the primary targets involved in plant nitrogen (N) uptake, transport, assimilation, and remobilization, all of which are key determinants of nitrogen use efficiency (NUE). However, less attention has been directed toward the influence of plant nutrients and environmental cues on the expression and activities of transporters. To better understand how these transporters function in improving plant NUE, this review critically examined the roles of transporters in N uptake, transport, and distribution processes. It also described their influence on crop productivity and NUE, especially when co-expressed with other transcription factors, and discussed these transporters' functional roles in helping plants cope with adverse environmental conditions. We equally established the possible impacts of transporters on the uptake and utilization efficiency of other plant nutrients while suggesting possible strategic approaches to improving NUE in plants. Understanding the specificity of these determinants is crucial to achieving better N utilization efficiency in crops within a given environment.

Overexpression of MYB-like transcription factor SiMYB30 from foxtail millet (Setaria italica L.) confers tolerance to low nitrogen stress in transgenic rice

Nitrogen fertilizers significantly increase crop yield; however, the negative impact of excessive nitrogen use on the environment and soil requires urgent attention. Improving crop nitrogen use efficiency (NUE) is crucial to increase yields and protect the environment. Foxtail millet (Setaria italica L.), a gramineous crop with significant tolerance to barren croplands, is an ideal model crop for studying abiotic stress resistance in gramineous crops. However, knowledge of the regulatory network for NUE in foxtail millet is fragmentary. Herein, we identified an R2R3-like MYB transcription factor in foxtail millet, SiMYB30, which belongs to MYB subfamily 17. The expression of SiMYB30 is responsive to low nitrogen (LN) concentration. Compared with wildtype Kitaake, seedlings of rice lines overexpressing SiMYB30 showed significantly increased shoot fresh and dry weights, plant height, and root area under LN treatment indoors. Consistently, overexpression of SiMYB30 in field experiments significantly increased grain and stem nitrogen contents, grain yield per plant, and stem weight in rice. Furthermore, qRT-PCR revealed that SiMYB30 effectively activated the expression of nitrogen uptake-related genes—OsNRT1, OsNRT1.1B, and OsNPF2.4—and nitrogen assimilation-related genes—OsGOGAT1, OsGOGAT2, and OsNIA2. Notably, SiMYB30 directly bound to the promoter of OsGOGAT2 and regulated its expression. These results highlight the novel and pivotal role of SiMYB30 in improving crop NUE.

Optimum Rate and Deep Placement of Nitrogen Fertilizer Improves Nitrogen Use Efficiency and Tomato Yield in Nepal

In Nepal, blanket fertilizer recommendations without considering diverse soil types, nutrient status, climate and crop management practices along with imbalanced fertilization practices by farmers, mainly “urea fertilizer,” have resulted in reduced nitrogen use efficiency (NUE) and productivity in tomato production. Optimizing the rate of nitrogen (N) fertilizer, application time and improved application methods could increase crop yields and NUE and reduce environmental costs. This study was conducted to identify the optimum N rate and application method for increased tomato yield and NUE. Multilocation trials (n = 28) conducted in a randomized complete block design with nine treatments across five districts included the omission of N, P and K (N0, P0, K0), variable N rates of 100, 150, 200 and 250 kg ha−1 (N-100, N-150, N-200 and N-250), use of urea briquettes (UB) with deep placement (UBN-150) and a control (CK). N input in UB was reduced by 25% from the recommended N rate of 200 kg ha−1 considering its expected higher NUE. Yield responses from an NPK omission plot revealed N as the most limiting plant nutrient. Applications of fertilizer at N-100, N-150, N-200 and N-250 increased tomato yield by 27%, 35%, 43% and 27%, respectively, over N0. Tomato yields responded quadratically to the added N fertilizers with optimum rates ranging from 150 to 200 kg ha−1 across districts. UBN-150 significantly increased tomato yield by 12% over N-150 and produced a similar yield to N-200 (the recommended rate). The highest partial factor productivity of nitrogen (PFPN) was observed at N-100 and the highest agronomic efficiency of N (AEN) was at N-200. Deep placement of UB at-150 increased PFPN by 8% and 21% and AEN by 27% and 21% compared with N-150 and N-200, respectively. These results have positive implications for developing efficient N fertilization strategies to increase tomato yields and reduce environmental impacts in Nepal.

Responses of Tobacco Growth and Development, Nitrogen Use Efficiency, Crop Yield and Economic Benefits to Smash Ridge Tillage and Nitrogen Reduction

Long-term rotary tillage leads to thinning of the soil layer and low nitrogen use efficiency of crops, resulting in a decrease in crop yield and quality. Therefore, a new alternative method to improve nitrogen use efficiency of crops needs to be found urgently. Here, we analyzed the effects of a new smash ridge tillage method combined with reduced nitrogen application on tobacco growth and development, and nitrogen use efficiency and its economic benefits. The results showed that, compared with conventional tillage and nitrogen application of 180 kg N ha−1, smash ridge tillage and a 30% reduction in nitrogen rate resulted in greater root length density, more primary lateral roots and greater rooting depth in the subsoil. It is also beneficial to maintain a high level of biomass and nitrogen accumulation in the later growth period, increasing the output value of tobacco by CNY 1588.35 ha−1 and reducing the cost by CNY 974.1 ha−1 on average in two years. In conclusion, our study highlights the economic benefits of smash ridge tillage and nitrogen reduction for tobacco growth and development, and considers them an effective method for improving agricultural productivity and nitrogen use efficiency.

Advances in Barley Breeding for Improving Nitrogen Use Efficiency

Crop breeding for high nitrogen use efficiency (NUE) or tolerance to low nitrogen fertilization is thought to be an ideal solution to reduce the cost, carbon footprint, and other environmental problems caused by the excess use of nitrogen fertilizers. As a model plant for cereal crops, barley has many advantages, including good adaptability, a short growth period, and high natural stress resistance or tolerance. Therefore, research on improving NUE in barley is not only beneficial for nitrogen-efficient barley breeding but will also inform NUE improvement in other cereal crops. In this review, recent progress in understanding barley’s response to nitrogen nutrition, evaluation of NUE or low-nitrogen tolerance, quantitative trait loci (QTL) mapping and gene cloning associated with improving NUE, and breeding of nitrogen-efficient barley is summarized. Furthermore, several biotechnological tools that could be used for revealing the molecular mechanisms of NUE or breeding for improving NUE in barley are introduced, including GWAS, omics, and gene editing. The latest research ideas in unraveling the molecular mechanisms of improving NUE in other crops are also discussed. Thus, this review provides a better understanding of improving the NUE of barley and some directions for future research in this area.