Nitrogen Dilution Research Articles

Uncertainty analysis of critical nitrogen dilution curves for wheat

Critical nitrogen (Nc) dilution curves have been widely used for the plant N status diagnosis, N management, crop modeling, and remote sensing. Wheat is a major crop worldwide whose Nc dilution curves developed under different conditions (genotype × environment × management) show large parameter variations. Herein, a dataset of 19 nitrogen fertilizer experiments (n = 656) from five wheat planting sites in China was used to evaluate the uncertainty in these curves and explain the sources of differences using the Bayesian theory method. The uncertainty of the fitted curve decreased with the increase in plant biomass. The parameter A2 of fitted curves of genotype × environment × management combinations showed a greater variation than A1, with slight parameter differences among different genotypes and planting sites. The variables related to genotype and growth environment, i.e., maximum N concentration, maximum biomass, and accumulated growing degree days during the vegetative growth period, were the sources of differences in curve parameters. Though the Nc curve differences between genotype × environment × management were statistically significant, the nitrogen nutrition index (NNI) differences remained relatively small. This study provides insights for developing a more diverse Nc dilution curve to aid in optimal nitrogen fertilization management in wheat.

Determining nitrogen status and quantifying nitrogen fertilizer requirement using a critical nitrogen dilution curve for hybrid indica rice under mechanical pot-seedling transplanting pattern

Field experiments of nitrogen (N) treatment at five different application rates (0, 75, 150, 225, and 300 kg ha−1) were conducted under pot-seedling mechanical transplanting (PMT) in 2018 and 2019. Two high-quality and high-yielding hybrids of indica rice, Huiliangyou 898 and Y Liangyou 900, were used in this study. The N nutrition index (NNI) and accumulated N deficit (Nand), used to assess the N nutrition status in real-time, were calculated for the indica cultivars under PMT with a critical nitrogen concentration (Nc) dilution model based on shoot dry matter (DM) during the whole rice growth stage. The relationships between NNI and Nand with relative yield (RY) were determined, and accurate N application schemes were developed for hybrids indica rice under PMT. The results indicated that high application rate of N-fertilizer significantly increased the concentrations of shoot DM and N in aboveground organs during the observed stages in the two cultivars for two years (P<0.05). The Nc dilution model of hybrid indica cultivars was Nc=4.02DM−0.42 (R2=0.97) combining the two cultivars under PMT. Root-mean-square error and normalized root-mean-square error of the curve verification were 0.23 and 10.61%, respectively. The NNI and Nand ranged from 0.58 to 1.31 and 109 to –55 kg ha−1, respectively, in the two cultivars for all N treatments. NNI showed a linear relationship with Nand during the entire growth stage (0.53<R2<0.99, P<0.01). In addition, NNI showed a linear-plateau relationship with RY (0.73<R2<0.92, P<0.01) throughout the observed stages. These results suggest that the models can accurately diagnose the N-nutrition status and support effective N-fertilizer management in real-time for hybrid indica rice under PMT.

The Effects of Modifying the Activity of Nitriding Media by Diluting Ammonia with Nitrogen.

This paper discusses the issue of the effects of modifying the activity of nitriding media by diluting ammonia with nitrogen and the concomitant variation in the degree of ammonia dissociation on the layer’s growth kinetics and their phase composition. To understand and quantify the effects of the variation in the main parameters that influence the layer growth kinetics, the experimental programming method was used and mathematical models of interactions between influence and kinetics parameters were obtained for two metallic materials: Fe-ARMCO and 34CrAlMo5 nitralloy steel. It was concluded that the nitriding operating temperature and the degree of nitrogen dilution of the ammonia have statistically significant influences on the kinetics of the nitrided layer. In the same context, it was analytically proved and experimentally confirmed that the ammonia degree dissociation from the gaseous ammonia-nitrogen mixture, along with the dilution degree of the medium with nitrogen, significantly influences the nitrogen potential of the gaseous mixture used for nitriding and thus the concentration of nitrogen in balance at the medium thermochemically processed metal product interface.

Effect of dilution gas composition on the evolution of graphite electrode characteristics in the spark gap switch

As the widely implemented electrode material, graphite has the characteristic of sublimation by the thermal shock of the switching arc, and the produced carbon vapor is easy to condense into carbon powders and deposit in the switch. The impact of the type of dilution gas in a mixture of 20% oxygen and 80% dilution gas on the sublimation and oxidation characteristics of the graphite electrode is investigated. It is found that when nitrogen dilution gas was replaced by argon, the heat flux to the electrodes decreased, which led to a 63% reduction of graphite sublimation. At the same time, the cooling rate of the arc was slower in argon, which promotes oxidation of the carbon vapor. The residual solid carbon can be reduced by 70%–85% by using argon as the dilution gas. Consequently, it is demonstrated that the stability and working life of the switch could be increased by appropriate selection of the dilution gas.

Diffraction of weakly unstable detonation through an obstacle with different sizes and shapes

Two-dimensional simulations considering detailed chemistry are conducted to investigate the weakly unstable detonation diffracting through an obstacle. Subcritical, critical, and supercritical regimes are identified and their distributions are significantly affected by the obstacle size and shape. In contrast, the mixtures with different nitrogen dilution have little influence on the regime distributions.

Effects of oxygen depletion on soot production, emission and radiative heat transfer in opposed-flow flame spreading over insulated wire in microgravity

The main objective of this article is to investigate experimentally and numerically the effects of reduced-oxygen contents on the soot production and emission from solid fuels in microgravity, which constitute an important issue in terms of fire safety for manned space missions. Due to its convenience for the implementation of soot-related optical diagnostics, the configuration of a flame spreading in an opposed flow over thin nickel chromium (NiCr) wires coated by low density PolyEthylene (LDPE) is considered. Experiments are conducted at a pressure of 101.3 kPa and an oxidizer velocity of 150 mm/s. The oxygen mole fraction in the oxidizer, XO2, is varied from 18% to 21% by nitrogen dilution of air. The modeling strategy lies on a surrogate fuel to mimic the combustion of LDPE by preserving its stoichiometry and the laminar smoke-point (LSP) flame height. The numerical model considers a detailed chemistry, a two-equation soot production model involving laminar smoke point (LSP)-based soot formation rates and oxidation by OH and O2, a radiation model coupling the Full-Spectrum correlated-k method with the finite volume method, and a simple degradation model for LDPE. Based on experimental evidence, the soot formation rate is scaled by the adiabatic flame temperature to account for thermal effects due to variation in XO2. The model reproduces quantitatively the increase in flame size, residence time, and soot volume fraction observed experimentally as XO2 is enhanced as well as the transition from a non-smoking to a smoking flame, which occurs for XO2 between 19% and 20%. The increase in soot volume fraction results of a combined enhancement in both residence time, owing to an increase in the fuel mass flow rate, and soot formation rate due to higher temperature in the soot formation region. The radiant fraction increases significantly with XO2 from about 17% for XO2=18% to about 36% for XO2= 21%. This increase in radiative losses is accompanied by a reduction of the temperature in the soot oxidation region. Therefore, for increasing XO2, the soot oxidation process is governed by a competition between oxygen-enhanced conditions that promote the formation of soot oxidizing species and the increase in radiative losses that dampens their formation. For the present flames, the first mechanism prevails as XO2 increases from 18% to 19% whereas the second dominates as XO2 is further increased, leading to smoking flames as actually observed for XO2=20 and 21%. The radiant fraction at the smoke-point transition and the soot oxidation freezing temperature are in line with those reported at normal gravity. Finally, model results show that, whatever XO2, the contribution of radiation to the heating process is negligible ahead of the pyrolysis front and is largely overcome by surface radiative losses along the pyrolysis region.

A new canopy chlorophyll index-based paddy rice critical nitrogen dilution curve in eastern China

Abstract Nitrogen (N) plays an essential role in the crop growing cycle. Canopy vegetation indexes and chlorophyll concentration were important tools in-crop N status diagnosis and provided a crucial guide for agricultural managers. This work focused on evaluating the performance of different chlorophyll-related indexes (canopy chlorophyll index, CCI) and Greenseeker RT 200 values (GS values, normalized difference vegetation index, NDVI & Ratio vegetation index, RVI) in crop N nutrient diagnosis. Four experiments were conducted with multiple N fertilizer rates (0 ∼ 390 kg N ha−1) and seven Japonica rice (Oryza sativa L.). Results suggested that the relationship between CCI value and tissue nitrogen accumulation [including leaf nitrogen accumulation (LNA) and plant N accumulation (PNA)] was more reliable than that of GS values. Compered GS values with CCI values-based N concentration dilution curves, CCI-based Nc curve showed better accuracy and lower bias than GS values-based curves. And this curve lower than the reference LAI basis Nc curve and higher than the dry matter-based curve. The N nutrition index (NNI), calculated by the CCI-based curve, ranged from 0.31 to 1.33 during the vegetative stage. A significant positive relationship between CCI values and accumulated N deficit (AND) applications over the rice developmental stages. This present study also proved that CCI could be used to predict grain yield in total growth periods. These developed canopy level vegetation indexes-based Nc curve as a novel tool to offer more choices for evaluating crop N nutrition status and precision N topdressing management in Japonica rice of China.

Plastic film mulching affects the critical nitrogen dilution curve of drip-irrigated maize

Critical nitrogen dilution curves (CNDC) can efficiently diagnose nitrogen (N) condition of crops. Unfortunately, no CNDC exits for mulched drip-irrigated crops. Here we determine the CNDCs of drip-irrigated maize (Zea mays L.) with and without plastic mulch and investigate effects of plastic mulch on soil NO3−-N concentration in root zone (Nsoil), maize morphology, and CNDC changes. Aboveground dry biomass (DM), crop N concentration, soil N concentration, and related morphological characteristics of maize were measured in Northwest China under five N application rates with and without plastic mulch to calculate critical N concentration (Nc) and develop CNDCs. Plastic film mulching decreased Nsoil by 16.5 % and increased DM by 25.9 %. Mulching increased DM more than root growth and resulted in a lower root to shoot ratio compared with that of no mulching. Plastic film mulching affected CNDC and grain yields by increasing DM, thus lowering root to shoot ratio. CNDCs were Nc = 3.58DM−0.36 [R2 = 0.98] for drip-irrigated maize and Nc = 4.17DM−0.35 [R2 = 0.94] for mulched drip-irrigated maize. Mulching lowered nitrogen nutrition index at silking stage and increased it at physiological maturity stage. These results indicate that CNDC can be used to correctly determine N application rates for mulched drip-irrigated maize production.

Experimental investigation on the propagation characteristics of detonations in a semi-confined straight channel

In a rotating detonation engine, detonation waves propagate in the combustor chamber with one side unconfined which will introduce lateral relief and, therefore, results in deficits of the propagation velocity and the peak pressure. To study the critical mixture height for detonation propagation, a simple combustor without considering the curvature has been used, which provides a planar semi-confined channel with different channel heights, e.g., 10 mm, 20 mm, and 30 mm. Effects of the nitrogen dilution ratio, the equivalence ratio, and the channel height on the propagation modes, the velocity deficit, and the cellular structure have been investigated when ethylene was utilized. The non-dimensional channel height (h/λa) was also adopted to evaluate the impacts of lateral relief. Experimental results indicated that three different propagation modes existed in the semi-confined channel. Velocity deficits resulted from the lateral relief mechanism were observed and the maximum velocity deficit is around 10–15%. Besides, the cell width increased and became more irregular when reducing the channel height. Successful detonation propagation can be obtained with a minimum normalized channel height of h/λa > 2, which will provide information for practical detonation operations.

Effects of the Gas Preheat Temperature and Nitrogen Dilution on Soot Formation in Co-flow Methane, Ethane, and Propane Diffusion Flames

This work investigates the effects of gas preheating and N2 dilution on soot formation in a series of laminar methane (CH4), ethane (C2H6), and propane (C3H8) co-flow diffusion flames. A modified S...

Nitrogen dilution effects on the local detachment of the oblique detonation wave in the 2H2–O2 mixture

The transition pattern and the initiation length are the core features of the oblique detonation wave. Two transition patterns have been widely studied. A new transition pattern is observed recently. However, the relationship between the new pattern and the former two patterns is not clear, which prevent the oblique detonation wave from the realistic application. Besides, what causes the new pattern is still unknown. In the current research, the new transition pattern is defined as ‘local detachment’ due to its unique features. Different nitrogen dilutions are utilized to obtain different detonation velocities. The effects of the nitrogen dilution on the Chapman-Jouguet velocity and the overdriven detonation velocity are discussed in detail. The features of different transition patterns are compared. The local detachment is featured by an upstream propagation of the wave front and a jump of the initiation location. Although the local detachment can bring forward the initiation location significantly, it is suggested to avoid it during designing the engine because the local high pressure can erode the combustor and leave the initiation location uncontrollable. The formation mechanism of the local detachment is discussed in detail. The local detachment is dominated by the ratio of detonation velocity to free stream velocity. When the ratio increases, the transition pattern changes as Smooth → Abrupt → Local detachment. This relationship is vital for predicting the local detachment of the oblique detonation wave.

Construction of critical nitrogen dilution curve based on dry matter in diffe rent organs of summer maize and estimation of grain yield

Construction of critical nitrogen dilution curve based on dry matter in diffe rent organs of summer maize and estimation of grain yield

Diagnosis of camelina seed yield and quality across an on-farm experimental network

Camelina [Camelina sativa (L.) Crantz] is an emerging oilseed crop combining both industrial and agronomic advantages. Camelina seed yield, oil and protein contents, and fatty-acid composition, vary across genotypes, environments, and agricultural practices. However, no studies have been conducted to identify and rank major limiting factors explaining yield and quality variations under on-farm conditions. Camelina performance was measured on 39 experimental strips corresponding to five camelina crop management routes (grown as an intercrop or sole crop), implemented in nine farmers’ fields across northern France in 2017 and 2018. The ranking of candidate limiting factors, defined a priori from scientific literature, was carried out using a model mixing method based on the Akaike Information Criterion. Main limiting factors of camelina yield (ranging from 62 to 2585 kg ha−1) were nitrogen crop status at flowering stage and downy mildew. Camelina yield was indeed positively correlated with the Nitrogen Nutrition Index at flowering stage (R2 = 0.44, p = 0.007). Oil content varied from 36.6 to 46.5 % and was negatively correlated with protein content. Main indicators explaining oil content variations were grain filling duration and downy mildew. Both poly-unsaturated and linolenic acid contents were positively correlated to grain filling duration, and negatively correlated to temperature during grain filling period. Camelina nitrogen status at flowering stage was mainly explained by N uptake of the intercropped species (pea or barley), and the amount of available inorganic nitrogen in the soil between sowing and flowering. Downy mildew was influenced by both weather conditions and the amount of weed biomass.This study showed a large variability in camelina seed yield and quality under on-farm conditions. The identification of the major limiting factors made it possible to pinpoint ways of improving camelina performance namely choosing genotypes with high resistance to mildew, better managing nitrogen fertilization or delaying camelina sowing date. Finally we also identified major research topics to be addressed to support the adoption of this new crop by farmers as the elaboration of the critical nitrogen dilution curve.

A Modified Critical Nitrogen Dilution Curve for Winter Wheat to Diagnose Nitrogen Status Under Different Nitrogen and Irrigation Rates.

The accuracy of nitrogen (N) diagnosis is essential to improve N use efficiency. The standard critical N concentration (standard Nc) dilution curves, an expression of the dynamics of N uptake and dry matter accumulation in plants, are widely used to diagnose the N status of crops. Several standard Nc dilution curves were proposed and validated for several crops, based on experiments involving different N fertilizer treatments. However, standard Nc dilution curves are affected by crop water status, e.g., resulting from differences in irrigation management. This paper aimed at developing a N diagnostic model under the coupling effect of irrigation and fertilizer managements. For this purpose, Nc dilution curves were developed under different irrigation rates. Additionally, plant water content (PWC), leaf water content (LWC), leaf area index (LAI), equivalent water thickness (EWT), and leaf area duration (LAD) were introduced into the model, to construct a modified Nc (mNc) dilution curve. The mNc dilution curves were designed using the principle of hierarchical linear model (HLM), introducing aboveground dry biomass (AGB) as the first layer of information, whereas the second layer of information included the different agronomic variables (PWC, LWC, LAI, EWT, and LAD). The results showed that parameters “a” and “b” of the standard Nc dilution curves ranged from 5.17 to 6.52 and −0.69 to −0.38 respectively. Parameter “a” was easily affected by different management conditions. The performance of standard Nc dilution models obtained by the cross-validation method was worse than that of mNc dilution models. The Nc dilution curve based on 4 years of data was described by the negative power equation Nc = 5.05 × AGB–0.47, with R2 and nRMSE of 0.63 and 0.21, respectively. The mNc dilution curve considers different treatments and was represented by the equation mNc = a×AGB−b, where a = 2.09 × PWC + 3.24, b = −0.02 × LAI + 0.51, with R2 and nRMSE of 0.79 and 0.13, respectively. For winter wheat, C3 crop, there would be a few problems in using standard Nc dilution methods to guide field management, however, this study provides a reliable method for constructing mNc dilution curves under different water and N fertilizer management. Due to the significant differences in hereditary, CO2 fixation efficiency and N metabolism pathways for C3 and C4 crops, the construction of mNc dilution curve suitable for different N response mechanisms will be conducive to the sustainable N management in crop plants.

New Insights on Protein Recovery from Olive Oil Mill Wastewater through Bioconversion with Edible Filamentous Fungi

Olive oil mills represent an important sector in the Mediterranean Sea Basin but also an environmental hazard due to untreated wastewater. Recovery of nutrients from olive oil mill wastewater (OMWW) as protein-rich microbial biomass can produce novel feed and reduce its chemical oxygen demand; however, low-protein containing products have been reported. New strategies leading to higher protein-containing fungal biomass could renew the research interest on bioconversion for pollution mitigation of OMWW. In this work, through cultivation of edible filamentous fungi (Aspergillus oryzae, Neurospora intermedia, and Rhizopus delemar), a link between the protein content in the originated fungal biomass, and the addition of nitrogen and medium dilution was established. Addition of nitrogen in the form of NaNO3 reduced the cultivation time from 96 h to 48 h while achieving a similar biomass mass concentration of 8.43 g/L and increased biomass protein content, from w = 15.9% to w = 29.5%. Nitrogen addition and dilution of OMWW, and consequent reduction of suspended solids, led to an increase in the protein content to up to w = 44.9%. To the best of our knowledge, the protein contents achieved are the highest reported to date and can open new research avenues towards bioconversion of OMWW using edible filamentous fungi.

Determination of Critical Nitrogen Dilution Curve Based on Canopy Cover Data for Summer Maize

ABSTRACT Estimation of canopy cover (CC) can be replaced with measurement of dry matter (DM) during the growing season, which leads to saving cost and time. A variety of software programs, such as Canopeo, have recently been launched for estimating CC by processing digital images. The main objective of the present study was to validate whether the CC estimated by Canopeo could be used to determine the critical nitrogen dilution curve (CNDC) of maize. DM and critical nitrogen concentration (%Nc) of summer maize were measured during the growing seasons in 2015 and 2016. On the same dates, CC was estimated by digital images and Canopeo. The CNDC based on DM (Nc, DM) was accurately described by the equation Nc, DM = 2.9DM−0.27. Furthermore, an exponential relationship was observed between CC and DM (R2 = 0.934) that resulted in the estimation of DM based on CC (DMcc). A new CNDC based on CC was determined (Nc,CC = 4e −1.17CC) by replacing DMcc in the Nc,DM which has an acceptable accuracy in estimating Nitrogen Nutrition Index. These results demonstrate that Canopeo can be applied as a useful tool to develop CNDC and Nitrogen management for different varieties of plants under various climatic conditions.

Quantification of PAH concentrations in premixed turbulent flames crossing the soot inception limit

Soot formation in combustors is a complex process comprising highly intermittent interactions between physical and chemical processes across a wide range of time-scales and the influence of turbulence on the soot inception process remains substantially conjectural. The current study quantifies the impact of flame temperature, equivalence ratio, and strain rate on PAH concentrations in premixed turbulent ethylene flames crossing the soot inception limit using a back–to–burnt opposed jet configuration that provides accurate control of flow parameters. The upper nozzle features fractal grid generated turbulence and provides premixed ethylene/air mixtures with equivalence ratios 1.7 ≤ ϕ ≤ 2.2 with flames stabilised against well-defined lower nozzle hot combustion products (HCP) from N2 diluted H2 flames. The flame structures are initially analysed using PAH/CH2O/PLIF and elastic light scattering with gas chromatography–mass spectrometry (GC–MS) subsequently used to quantify PAH samples from inside the turbulent flame brush. A combination of hot nitrogen dilution and a heated sampling line is used to minimise PAH and particle losses during sample extraction. The work quantifies the growth in PAH concentrations across the soot inception limit and shows that the rate of strain exerts a dominant influence. It is further shown, through centrifuging of samples, that soot particles contain large amounts of PAHs (e.g. benzo[a]pyrene) with EDX used to quantify the growth in carbon deposition.

Evaluating the effect of multiple flammable gases on the flammability limit of CH4: Experimental study and theoretical calculation

As the main component of natural gas and an important chemical raw material, methane easily forms a mixture of flammable gases during production and processing. Therefore, understanding the flammability limit and limiting oxygen concentration of methane is very important in predicting the possibility of fire and explosion in industrial production and designing the corresponding monitoring parameters. To solve this problem, the effects of the addition of a C2H6/C2H4/CO/H2 mixture on the flammability limit of methane and the limiting oxygen concentration under N2 dilution were systematically studied. In addition, the flammability limit was evaluated using the limiting burning velocity theory and detailed reaction kinetic model, and a sensitivity analysis was conducted to study the chemical kinetics near the limit. The experimental results show that when the volume fraction of mixed gas gradually increases, the upper and lower flammability limit of methane both decrease, and the decrease in the lower flammability limit is larger than that of the upper flammability limit. Under the condition of nitrogen dilution, the limiting oxygen concentration gradually decreases with an increase in mixed gas concentration. The explosion triangle expands and moves to the lower-left corner, the flammability limit range increases, and a greater danger of explosion exists. The calculated results based on the limit laminar burning velocity are in good agreement with the experimental data. The sensitivity analysis shows that elementary reactions involving the active free radicals of OH, H and O have higher sensitivity. With the addition of mixed gas, the chain-branching reaction R31 is promoted, the chain termination reactions R12 and R41 are inhibited, the competition between the chain-branching reaction and chain termination reaction changes, and the flammability limit range of methane expands.

Detonation propagation across a stratified layer with a diffuse interface

A study was conducted to examine detonation propagation in a stratified layer of hydrogen-oxygen-nitrogen above an inert gas in a horizontal narrow channel. The stratified layer was produced by a gravity current, generated by retracting a door initially separating a hydrogen-oxygen-nitrogen mixture in the predetonator and a heavier inert gas in the test-section. A steady detonation wave generated in the predetonator was transmitted into the stratified layer. The reactivity of the predetonator mixture was varied via the hydrogen-oxygen equivalence ratio and the amount of nitrogen dilution. Schlieren photography was used to visualize the detonation front in the test-section, and soot foils were used to obtain the cellular structure. Schlieren imaging showed a curved detonation front that decoupled at about mid channel height, into a shock wave and trailing contact surface. Both the hydrogen-oxygen-nitrogen reactivity and the type of inert gas initially in the test-section affected the distance travelled by the detonation wave in the stratified layer. The mixture composition distribution within the test-section before ignition was obtained via a three-dimensional CFD simulation. The lateral extent of the cellular structure captured on the soot foil, coincided with the calculated inert gas mole fraction contour that corresponds to a sharp increase in the ZND induction zone length, e.g., 70% argon dilution for a stoichiometric hydrogen-oxygen predetonator mixture.

Construction of a critical nitrogen dilution curve for maize in Southwest China

There is an urgent need for suitable nitrogen nutrition models for Southwest China, which take into account nutritional differences at the cultivar level, to provide scientific guidance for cultivar-specific fertilizer applications during maize production. In this study, the nitrogen-efficient maize cultivar Zhenghong 311 and the nitrogen-inefficient maize cultivar Xianyu 508 were used in a three-year field experiment and a 2-year field pot experiment with nitrogen application rates ranging from 0 to 450 kg·hm−2 to construct a critical nitrogen dilution curve model for each maize cultivar. The usefulness of this model to diagnose nitrogen status and evaluate maize fertilization needs was subsequently analyzed. We found that the critical nitrogen concentration in maize aboveground tissues was a power function of the biomass, described by the equations Nc = 26.126 W−0.292 and Nc = 25.826 W−0.302 for ZH 311 and XY 508 cultivars, respectively. The fitting degree of these equations was significant or highly significant, demonstrating the suitability of these models to diagnose N deficiency and fertilization needs in maize plants grown in the hilly areas of central Sichuan. A very significant linear positive correlation between the nitrogen nutrient index (NNI) and nitrogen concentration in the aboveground tissues was detected. Based on this, we calculated the nitrogen concentration (Nt) for an NNI equal to 1 at different maize growth stages in both cultivars and observed that the Nt value can be used as a reference index for nitrogen nutrition diagnosis. Additionally, we found a highly significant quadratic convex function relationship between the NNI (y) and the nitrogen fertilizer level (x). The following regression equations were derived for these maize cultivars with the data obtained from each growth period along five consecutive years (2011–2015): yZH 311 = − 0.000005x2 + 0.003074x + 0.553206 (R2 = 0.5432**) and yXY 508 = − 0.000004x2 + 0.002914x + 0.512555 (R2 = 0.6279**). For an NNI value equal to 1, the nitrogen application level required was 224.07 kg·hm−2 for ZH 311 and 283.01 kg·hm−2 for XY 508, indicating that the suitable application rate for the nitrogen-efficient cultivar is lower than that for the nitrogen-inefficient cultivar. Our experimental data reinforce the concept that selecting nitrogen-efficient maize cultivars is an effective technical measure to reduce nitrogen input needs and increase nitrogen use efficiency during maize production.