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Nitrogen (N) is an important macronutrient needed for grain yield, grain N and grain protein content in rice. Grain yield and quality are significantly determined by N availability. In this study, to understand the mechanisms associated with reproductive stage N remobilization and N partitioning to grain 2 years of field experiments were conducted with 30 diverse rice genotypes during 2019-Kharif and 2020-Kharif seasons. The experiments were conducted with two different N treatments; N deficient (N0-no external N application, available soil N; 2019-234.15 kgha-1, 2020-225.79 kgha-1) and N sufficient (N120-120 kgha-1 external N application, available soil N; 2019-363.77 kgha-1, 2020-367.95 kgha-1). N application increased the NDVI value, biomass accumulation, grain yield, harvest index and grain N accumulation. Post-anthesis N uptake and N remobilization from vegetative tissues to grain are critical for grain yield and N harvest index. Rice genotypes, Kalinga-1, BAM-4234, IR-8384-B-B102-3, Sahbhagi Dhan, BVD-109 and Nerica-L-42 showed a higher rate of N remobilization under N sufficient conditions. But, under N deficiency, rice genotypes-83929-B-B-291-3-1-1, BVD-109, IR-8384-B-B102-3 and BAM-4234 performed well showing higher N remobilization efficiency. The total amount of N remobilization was recorded to be high in the N120 treatment. The harvest index was higher in N120 during both the cropping seasons. RANBIR BASMATI, BAM-832, APO, BAM-247, IR-64, Vandana, and Nerica-L-44 were more efficient in N grain production efficiency under N deficient conditions. From this study, it is evident that higher grain N accumulation is not always associated with higher yield. IR-83929-B-B-291-3-1-1, Kalinga-1, APO, Pusa Basmati-1, and Nerica-L-44 performed well for different N use efficiency component traits under both N deficient (N0) and N sufficient (N120) conditions. Identifying genotypes/donors for N use efficiency-component traits is crucial in improving the fertilizer N recovery rate and site specific N management.

Understanding the physiological processes that regulate nitrogen uptake efficiency (NUpE), nitrogen utilization efficiency (NUtE), and nitrogen use efficiency (NUE) in crops is essential for developing nitrogen-efficient varieties. We conducted a two−year field study (2021–2022, Shixing, southern China) comparing three flue−cured tobacco genotypes (Yunyan 87, Yueyan 97, K326) under two nitrogen application rates: traditional (150 kg ha -1 ) and reduced (105 kg ha -1 , −30%). Across both rates, the high−NUpE genotypes (Yueyan 97, K326) showed substantially greater root biomass, length, surface area, volume, vigor, bleeding sap and nitrate flow rates, and higher activities of key N−metabolism enzymes than low−NUpE Yunyan 87. These root and physiological traits were positively correlated with nitrogen uptake efficiency, indicating that they are major correlates of NUpE and may contribute to its variation. Compared with Yunyan 87 and K326 (both low−NUtE genotypes), Yueyan 97 (a high−NUtE genotype) exhibited a significantly lower respiratory rate despite a lower net photosynthetic rate. This pattern is consistent with higher NUtE being associated with a balance between net photosynthesis and respiration that favors reduced respiratory consumption. Path analysis indicated strong conditional associations of both NUpE and NUtE with NUE across genotypes. While path coefficients do not imply causality, the results suggest that jointly improving NUpE and NUtE may be a promising avenue for achieving high yield and improved NUE in flue-cured tobacco. In conclusion, this study identifies physiological traits that are strongly associated with NUpE and NUtE in flue-cured tobacco and provides insights to guide future efforts aimed at enhancing NUE in this crop.

The genetic architecture of nitrogen use efficiency (NUE) and its two component traits i.e. NUpE (N uptake efficiency) and NUtE (N utilization efficiency) was studied using a bi-parental RIL mapping population derived from a cross HUW468 (high NUE)/C306 (low NUE). The mapping population, two parental genotypes and three check genotypes were evaluated under four different N levels (0, 60, 120, and 180 kg/ha) over three years. A genetic map containing 456 SNP markers (2571.38 cM length) was used for QTL analysis. Thirty six main effect QTLs (17 QTLs for NUE, 13 NUpE and 6 QTLs for NUtE) distributed on 12 chromosomes (1B, 1D, 2A, 2B, 3A, 4B, 5A, 5B, 5D, 6A, 6D, and 7A) were identified at 2.52–9.27 LOD scores. Individual QTLs explained 6.65–22.89% phenotypic variation. Multi-traits QTLs (Mt-QTLs) and epistatic QTLs involving first-order epistatic (QTL × QTL) interactions were also discovered. Candidate genes (CGs, as many as 737) were mined from QTL regions which were mainly involved in metabolic process, cellular process and catalytic activity, etc.; differential expression was observed for 49 CGs in roots and 34 in shoots. The CGs encoded important transcription factors, transporters, etc. having a role in NUE. QTLs and CGs reported in this study enriched the available knowledge. Seven QTLs (including three Mt-QTLs) and QTLs involved in six epistatic interactions are recommended for MAS for improvement of NUE in wheat.

Enhancing the nitrogen (N) efficiency of maize hybrids is a common goal of researchers, but involves repeated field and laboratory measurements that are laborious and costly. Hyperspectral remote sensing has recently been investigated for measuring and predicting biomass, N content, and grain yield in maize. We hypothesized that vegetation indices (HSI) obtained mid-season through hyperspectral remote sensing could predict whole-plant biomass per unit of N taken up by plants (i.e., N conversion efficiency: NCE) and grain yield per unit of plant N (i.e., N internal efficiency: NIE). Our objectives were to identify the best mid-season HSI for predicting end-of-season NCE and NIE, rank hybrids by the selected HSI, and evaluate the effect of decreased spatial resolution on the HSI values and hybrid rankings. Analysis of 20 hyperspectral indices from imaging at V16/18 and R1/R2 by manned aircraft and UAVs over three site-years using mixed models showed that two indices, HBSI1 and HBS2, were predictive of NCE, and two indices, HBCI8 and HBCI9, were predictive of NIE for actual data collected from five to nine hybrids at maturity. Statistical differentiation of hybrids in their NCE or NIE performance was possible based on the models with the greatest accuracy obtained for NIE. Lastly, decreasing the spatial resolution changed the HSI values, but an effect on hybrid differentiation was not evident.

Overuse of nitrogen (N), an essential nutrient in food production systems, can lead to health issues and environmental degradation. Two parameters related to N efficiency, N Conversion Efficiency (NCE) and N Internal Efficiency (NIE), measure the amount of total biomass or grain produced, respectively, per unit of N in the plant. Utilizing remote sensing to improve these efficiency measures may positively impact the stewardship of agricultural N use in maize (Zea mays L.) production. We investigated in-season hyperspectral imaging for prediction of end-season whole-plant N concentration (pN), NCE, and NIE, using partial least squares regression (PLSR) models. Image data were collected at two mid-season growth stages (V16/V18 and R1/R2) from manned aircraft and unmanned aerial vehicles for three site years of 5 to 9 maize hybrids grown under 3 N treatments and 2 planting densities. PLSR models resulted in accurate predictions for pN at R6 (R2 = 0.73; R2 = 0.68) and NCE at R6 (R2 = 0.71; R2 = 0.73) from both imaging times. Additionally, the PLSR models based on the R1 images, the second imaging, accurately distinguished the highest and lowest ranked hybrids for pN and NCE across N rates. Neither timepoint resulted in accurate predictions for NIE. Genotype selection efficiency for end-season pN and NCE was increased through the use of the in-season PLSR imaging models, potentially benefiting early breeding screening methods.

mutagenesis via isolated microspore culture provides an efficient way to produce numerous double haploid (DH) lines with mutation introduction and homozygosity stabilization, which can be used for screening directly. In this study, 356 DH lines were produced from the malt barley ( L.) cultivar Hua-30 via microspore mutagenic treatment with ethyl methane sulfonate or pingyangmycin during culture. The lines were subjected to field screening under high nitrogen (HN) and low nitrogen (LN) conditions, and the number of productive tillers was used as the main screening index. Five mutant lines (A1-28, A1-84, A1-226, A16-11, and A9-29) with high numbers of productive tillers were obtained over three consecutive years of screening. In the fifth year, components related to N-use efficiency (NUE), including N accumulation, utilization, and translocation, were characterized for these lines based on N uptake efficiency (NUpE), N utilization efficiency (NUtE), and N translocation efficiency (NTE). The results show that the NUpE of four mutant lines (A1-84, A1-226, A9-29, and A16-11) improved significantly under HN, whereas that of two lines (A1-84 and A9-29) improved under LN. As a result, their NUE improved greatly. No improvement in NUtE was observed in any of the five mutant lines. A1-84 and A9-29 were selected as an enhanced genotype in N uptake, and A1-28 showed improved NTE at the grain-filling stage. Our results imply that high-NUpE mutants can be produced through microspore mutagenesis and field screening, and that improvement of NUE in barley depends on enhancement of N uptake.

Farming of barley and chickpea is nitrogen (N) fertilizer dependent. Using strategies that increase the nitrogen use efficiency (NUE) and its components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE) would reduce the N fertilizer application in the soil and its adverse environmental effects. We evaluated the effects of three different strains of diazotroph Klebsiella (K.p. SSN1, K.q. SGM81, and K.o. M5a1) to understand the role of biological nitrogen fixation (BNF) and bacterial indole-3-acetic acid (IAA) on NUE of the plants. A field study revealed that K.p. SSN1 results in profound increment of root surface area by eightfold and threefold compared to uninoculated (control) in barley and chickpea, respectively. We measured significant increase in the plant tissue nitrogen, chlorophyll content, protein content, nitrate reductase activity, and nitrate concentration in the inoculated plants (p ≤ 0.05). Treated barley and chickpea exhibited higher NUE and the components compared to the control plants (K.p. SSN1 ≥ K.q. SGM81> K.o. M5a1). Specifically, K.q. SGM81 treatment in barley increased NUpE by 72%, while in chickpea, K.p. SSN1 increased it by 187%. The substantial improvement in the NUpE and NUE by the auxin producers K.p. SSN1 and K.q. SGM81 compared with non-auxin producer K.o. M5a1 was accompanied by an augmented root architecture suggesting larger contribution of IAA over marginal contribution of BNF in nitrogen acquisition from the soil.

Black soldier fly frass fertilizer (BSFFF) is increasingly gaining momentum worldwide as organic fertilizer. However, research on its performance on crop production remains largely unknown. Here, we evaluate the comparative performance of BSFFF and commercial organic fertilizer (SAFI) on maize (H513) production. Both fertilizers were applied at the rates of 0, 2.5, 5, and 7.5 t ha-1, and 0, 30, 60, and 100 kg nitrogen (N) ha-1. Mineral fertilizer (urea) was also applied at 0, 30, 60 and 100 kg N ha-1 to establish the N fertilizer equivalence (NFE) of the organic fertilizers. Maize grown in plots treated with BSFFF had the tallest plants and highest chlorophyll concentrations. Plots treated with 7.5 t ha-1 of BSFFF had 14% higher grain yields than plots treated with a similar rate of SAFI. There was a 27% and 7% increase in grain yields in plots treated with 100 kg N ha-1 of BSFFF compared to those treated with equivalent rates of SAFI and urea fertilizers, respectively. Application of BSFFF at 7.5 t ha-1 significantly increased N uptake by up to 23% compared to the equivalent rate of SAFI. Likewise, application of BSFFF at 100 kg N ha-1 increased maize N uptake by 76% and 29% compared to SAFI and urea, respectively. Maize treated with BSFFF at 2.5 t ha-1 and 30 kg N ha-1 had higher nitrogen recovery efficiencies compared to equivalent rates of SAFI. The agronomic N use efficiency (AEN) of maize treated with 2.5 t ha-1 of BSFFF was 2.4 times higher than the value achieved using an equivalent rate of SAFI. Also, the AEN of maize grown using 30 kg N ha-1 was 27% and 116% higher than the values obtained using equivalent rates of SAFI and urea fertilizers, respectively. The NFE of BSFFF (108%) was 2.5 times higher than that of SAFI. Application rates of 2.5 t ha-1 and 30 kg N ha-1 of BSFFF were found to be effective in improving maize yield, while double rates of SAFI were required. Our findings demonstrate that BSFFF is a promising and sustainable alternative to commercial fertilizers for increased maize production.

Oilseed rape, a crop requiring a high level of nitogen (N) fertilizers, is characterized by low N use efficiency. To identify the limiting factors involved in the N use efficiency of winter oilseed rape, the response to low N supply was investigated at the vegetative stage in 10 genotypes by using long-term pulse–chase 15N labelling and studying the physiological processes of leaf N remobilization. Analysis of growth and components of N use efficiency allowed four profiles to be defined. Group 1 was characterized by an efficient N remobilization under low and high N conditions but by a decrease of leaf growth under N limitation. Group 2 showed a decrease in leaf growth under low N supply that was associated with a low N remobilization efficiency under both N supplies despite a high remobilization of soluble proteins. In response to N limitation, Group 3 is characterized by an increase in N use efficiency and leaf N remobilization compared with high N that is not sufficient to sustain the leaf biomass production at a similar level to non-limited plants. Genotypes of Group 4 subjected to low nitrate were able to maintain leaf growth to the same level as under high N. The profiling approach indicated that enhancement of amino acid export and soluble protein degradation was crucial for N remobilization improvement. At the whole-plant level, N fluxes revealed that Group 4 showed a high N remobilization in source leaves combined with a better N utilization in young leaves. Consequently, an enhanced N remobilization limits N loss in fallen leaves, but this remobilized N needs to be efficiently utilized in young leaves to improve N use efficiency.

The nitrogen use efficiency (NUE) and parameters contributing to it, of four sugarcane varieties (NCo376, N36, N12 and N19) were determined in vitro at 4 and 20 mM nitrogen (N), supplied as NO3−-N or NH4+-N. Significant differences amongst varieties were apparent at the lower N supply (4 mM) in the sub-components of NUE (N uptake efficiency and N utilisation efficiency) and overall NUE. All tested varieties had a higher NUE on medium with NO3−-N than NH4+-N. A concentration of 20 mM N was deemed too high to resolve differences amongst genotypes. Evidence for different mechanisms of NUE amongst varieties was provided under 4 mM NO3−-N supply where NCo376 and N12 displayed the highest NUE but this was attributed to superior NUpE in the former and NUtE in the latter. The NUE response of NCo376, N12 and N19 were similar in vitro, while N36 behaved differently. To our knowledge, this is the first report on the contribution of NUpE and NUtE to NUE in sugarcane in vitro. In terms of biomass production, in all cases but one, in vitro plants accumulated more biomass on medium with NO3−-N than NH4+-N. Furthermore, there was an indication that the distribution of NO3−-N between shoots and roots might affect NUE since varieties with a high in vitro NUE stored less NO3−-N in roots (compared with shoots) or exhibited better translocation of NO3−-N from roots to shoots than those with low NUE. In addition, evidence of luxury N uptake even at 4 mM N was obtained.