Critical Nitrogen Concentration Research Articles

Nitrogen nutritional status in perennial grasses under defoliation: Do stubble height and mixed cultivation matter?

AbstractBackground and aims: The concepts of critical nitrogen (N) concentration and nitrogen nutrition index (NNI) provide effective tools for assessing the N nutritional status of pastoral systems. However, no conclusive data exist concerning the effects of stubble height at harvest on the N dilution curve [N concentration (N%) = a(biomass)−b] and mixed species cultivation on N nutritional status of forage plants with contrasting growth strategies. To evaluate these effects, three cool‐season perennial grasses (exploitative, Arrhenatherum elatius L.; moderately exploitative, Dactylis glomerata L.; conservative, Festuca arundinacea Scherb.) were grown under different cultivation methods either as pure stands or as a mixture and conducted two experiments.Methods: In experiment I, canopies of different grass species pure stands and mixtures were subjected to defoliation managements aimed to not exceed the critical LAI at harvest. Forage samples were collected from October 2015 to August 2016 to determine the N nutritional status throughout the seasons. In experiment II, half of each pure stand was mowed to 10 cm in height, and the other half to ground level. Thereafter, herbage samples were taken during regrowth to determine N dilution curves in both scenarios (from ground level and from stubble height of 10 cm).Results: We verified an NNI above 0.8 during autumn and winter for A. elatius, D. glomerata, and the mixture but only in winter for F. arundinacea. Dactylis glomerata grown in the mixture had a lower N% than its pure stand during autumn and winter, whereas A. elatius and F. arundinacea showed no differences irrespective of cultivation method throughout the year. The three forage species presented classical dilution curves when regrowth was initiated from ground level, but quadratic trends were observed when regrowth was initiated from stubble heights of 10 cm.Conclusions: Overall the N nutritional status of cool‐season perennial grasses was not affected by cultivation method when pastures were managed in conditions of non‐limiting N supply and with pre‐cut/grazing height targets derived from critical LAI measured at the full vegetative growth stage. Moreover, the N nutrition status in pastures managed under moderate/lenient defoliation should not be evaluated during periods of less intense canopy renewal and/or right after the cut/grazing events.

Does the Organ-Based N Dilution Curve Improve the Predictions of N Status in Winter Wheat?

Accurately summarizing Nitrogen (N) content as a prelude to optimal N fertilizer application is complicated during the vegetative growth period of all the crop species studied. The critical nitrogen (N) concentration (Nc) dilution curve is a stable diagnostic indicator, which performs plant critical N concentration trends as crop grows. This study developed efficient technologies for different organ-based (plant dry matters (PDM), leaf DM (LDM), stem DM (SDM), and leaf area index (LAI)) estimation of Nc curves to enrich the practical applications of precision N management strategies. Four winter wheat cultivars were planted with 10 different N treatments in Jiangsu province of eastern China. Results showed the SDM-based curve had a better performance than the PDM-based curve in N nutrition index (NNI) estimation, accumulated N deficit (AND) calculation, and N requirement (NR) determination. The regression coefficients ‘a’ and ‘b’ varied among the four critical N dilution models: Nc = 3.61 × LDM–0.19, R2 = 0.77; Nc = 2.50 × SDM–0.44, R2 = 0.89; Nc = 4.16 × PDM–0.41, R2 = 0.87; and Nc = 3.82 × LAI–0.36, R2 = 0.81. In later growth periods, the SDM-based curve was found to be a feasible indicator for calculating NNI, AND, and NR, relative to curves based on the other indicators. Meanwhile, the lower LAI-based curve coefficient variation values stated that leaf-related indicators were also a good choice for developing the N curve with high efficiency as compared to other biomass-based approaches. The SDM-based curve was the more reliable predictor of relative yield because of its low relative root mean square error in most of the growth stages. The curves developed in this study will provide diverse choices of indicators for establishing an integrated procedure of diagnosing wheat N status, and improving the accuracy and efficiency of wheat N fertilizer management.

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.

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.

Analyzing uncertainty in critical nitrogen dilution curves

Abstract Nitrogen critical curves are frequently used to diagnose the N status of crops and grasslands. They play an important role in plant modelling and are frequently used in fertilizer management tools. During the last 20 years, a number of studies have been conducted for comparing critical curves obtained in various conditions (e.g., different cultivars) and understanding the origin of their differences. However, uncertainty in the determination of these curves is generally poorly analyzed in these studies, which increase the risk of false conclusions, in particular on the existence of differences between species, cultivars and cropping systems. Here, we present a Bayesian statistical model for estimating parameters of critical nitrogen dilution curve from experimental data. Contrary to standard methods commonly used for fitting critical nitrogen dilution curves, the proposed approach allows one to fit these curves in only one step, i.e., directly from the original biomass and nitrogen content measurements. Specifically, this method does not require the classification of nitrogen-limited data against non-nitrogen-limited data and does not necessitate the preliminary identification of critical nitrogen concentrations. Another advantage of the proposed method is that it can be easily implemented using freely-available software. We illustrate its practical interest using experimental data collected for winter wheat in France, and for maize and rice in China. We show that this method is useful for analyzing uncertainty in the fitted critical nitrogen curves and for comparing several curves obtained for different crop species and cultivars. The proposed method is based on the specification of prior probability distributions defining plausible ranges of values for the critical curve parameters, and we show here that it is preferable to use prior distributions that are not very informative if we want to limit their influence on the final result.

Critical nitrogen dilution curves and nitrogen nutrition diagnosis of spring maize under different precipitation patterns in Weibei dryland

<p indent=0mm>The excessive nitrogen (N) applications, large rainfall variations and poor water-nitrogen couplings are main problems to efficient nitrogen fertilizer uses in spring maize production of Weibei dryland. Critical nitrogen dilution curves under different rainfall scenarios in Weibei dryland were constructed in this study to analyze the feasibilities of diagnosing and evaluating nitrogen nutritional conditions in terms of nitrogen nutrition index (NNI), which would provide a theoretical basis for reasonable nitrogen fertilizations application of dryland maize in response to different rainfalls. The experiment design using Zhengdan 958 (ZD958) and Shaandan 8806 (SD8806) as tested materials was five treatments level, N applied at 0(N0), 75(N1), 150(N2), 270(N3), and 360(N4) kg hm^–2 in 2016 and 2017, and at 0(N0), 90(N0), 180(N2), 270(N3), and 360(N4) kg hm^–2 in 2018 and 2019, respectively. It was rainy at the ear stage and dry at the grain stage in 2016 and 2018, whereas dry at the ear stage and rainy at the grain stage in 2017 and 2019. Critical nitrogen dilution curve models for spring maize with two precipitation patterns were constructed and verified using the data collected in the four-year position nitrogen fertilization experiment. The results showed that: (1) increased nitrogen fertilizer application significantly increased aboveground biomass and plant N concentrations, and there were significantly different among different treatments. Both critical nitrogen concentrations (<italic>N</italic>_c) and aboveground biomass conformed the exponential relations with the two precipitation patterns, but there were differences between the parameters of the models for these relations (a. Rainy at the ear stage: <italic>N</italic>_c = 35.98DM^–0.35; b. Dry at the ear stage: <italic>N</italic>_c = 35.04DM^–0.23). The relatively stable model had a linear correlation between the fitted and actual plant N concentrations, which shown that the RMSE and <italic>n</italic>–RMSE were 1.03 and 5.75% at the ear stage over the rainy years and 1.53 and 6.78% at the ear stage in the dry years, respectively. (2) at the different growth stages, NNI were increased with the increased application, and there were differences in the optimal nitrogen application under different precipitation conditions. The optimum N rate in the form of basal fertilizers was <sc>150–180 kg</sc> hm^–2, and in the form of top dressing fertilizers was <sc>45–75 kg</sc> hm^–2 at the ear stage in the rainy years. The nitrogen nutrition index (NNI) was significantly correlated with relative nitrogen uptake (RN_upt), as were relative aboveground biomass (RDW) and relative yield (RY). When the NNI was 1.02 at the ear stage in the rainy years, the maximum RY was 0.95; and when the NNI was 1.08 at the ear stage in the dry years, the maximum RY was 0.92. The critical nitrogen dilution curve model and nitrogen nutrition index model constructed in this study were able to accurately predict nitrogen nutrition conditions from jointing stage to maturity stage under the two precipitation patterns of spring maize. They would provide an important guidance for nitrogen diagnosis and fertilization application in maize growing stage.

Establishment of Critical Nitrogen Concentration Models in Winter Wheat under Different Irrigation Levels

The aim of this study was to verify the applicability of the critical nitrogen concentration dilution curve (Nc) of wheat grown under different irrigation conditions in the field, and discuss the feasibility of using the N nutrition index (NNI) to optimize N fertilizer application. The high-yield, medium-protein wheat varieties Zhoumai 27 and Zhoumai 22 were used in field experiments in two different locations (Zhengzhou and Shangshui) in Huang-Huai, China. Plants were grown under rainfed and irrigation conditions, with five N application rates. Nc models of the leaves, stems, and whole plant were constructed, followed by establishment of an NNI model and accumulative N deficit model (Nand). As previous research reported, our results also showed that the critical N concentration and biomass formed a power function relationship (N = aDW−b). When the biomass was the same, the critical N concentration was higher under irrigation than rainfed treatment. Meanwhile, the fitting accuracy (R2) of the Nc model was also higher under irrigation than rainfed treatment in both sites, and was higher in the stems and whole plant. The NNI calculated using the Nc model increased with increasing N application, reflecting N deficiency. Moreover, there was a significant negative linear correlation between NNI and Nand, and both indices could be uniformly modeled between locations and water treatments. The accuracy of the Nand model was highest in the whole plant, followed by the leaves and stems. The models constructed in this paper provide a theoretical basis for accurate management of N fertilizer application in wheat production.

Critical nitrogen dilution curves and productivity assessments for plant cane

ABSTRACT Nitrogen is the most limiting nutrient for the development of sugarcane and particularly the use of more productive and demanding varieties, for which the doses of nitrogen fertilization necessary during the plant cane cycle may be underestimated and the critical levels of nitrogen in the leaf may be modified. The objective of this study was to determine the critical nitrogen dilution curve (CNDC) for leaves, evaluate the aboveground dry mass production (DM) and productivity of two varieties fertilized with N in the plant cane cycle. The study was conducted under field conditions, evaluating two sugarcane varieties RB92579 and RB867515, fertilized with seven doses of N (0, 30, 60, 90, 120, 150 and 200 kg ha-1). The varieties and doses were arranged in randomized blocks and analyzed in the 2 × 7 factorial scheme. It was found that the nitrogen concentration in the leaf decreased with four repetitions increase in DM yield and adjusted an exponential model, which enabled to estimate the critical levels of 13.03 and 12.46 g N kg-1 dry matter in the varieties RB92579 and RB867515, respectively. The plant cane cycle were observed to respond positively to nitrogen fertilization, with increase of 18.66% in tons of stalk per hectare (TSH) in response to the application addition of up to 129.45 kg N ha-1. The variety RB92579 showed the lowest dilution of the critical nitrogen concentration, the highest production of DM and higher stalk yield, and accordingly is considered to be the more efficient of the two varieties with respect to nitrogen fertilizer utilization.

Establishment and Application of Critical Nitrogen Dilution Curve for Rice Based on Leaf Dry Matter

In order to investigate the feasibility of using rice leaf critical nitrogen concentration as a nitrogen nutrition diagnosis index, a three-year positioning experiment with large-spike rice cultivar (Wuyoudao4) and multiple-spike rice cultivar (Songjing9) under five nitrogen levels (0, 60, 120, 180, and 240 kg·ha−1) was conducted. A critical nitrogen dilution curve and a nitrogen nutrition index (NNI) of rice leaf dry matter were constructed for Wuyoudao4 (Nc = 1.96LDM−0.56, R2 = 0.87, NNI was between 0.6–1.26, and Normalized Root Mean Square Error (n-RMSE) = 13.07%) and Songjing9 (Nc = 1.99LDM−0.44, R2 = 0.94, NNI was between 0.64–1.29, and n-RMSE = 15.89%). The relationship between dry matter and nitrogen concentration of rice leaves was a negative power function, and the model had good stability over the three years. The developed critical nitrogen concentration dilution curve, based on leaf dry matter, was able to diagnose nitrogen nutrition in rice efficiently. The model established in this study could be used to directly regulate and control the nitrogen nutrition of rice leaves.

Development of critical nitrogen dilution curve based on leaf dry matter for maize under drip irrigation

To provide a theoretical reference to nitrogen fertilizer management for maize and eco-enviromental protection in the irrigated area of Ningxia, we established the critical nitrogen concentration (Nc) dilution curve of maize under drip-irrigated condition. The nitrogen nutrition index (NNI) was deduced from the established Nc curve model, to diagnose feasibility of nitrogen nutrition. Six levels of nitrogen application rates including 0, 90, 180, 270, 360 and 450 kg·hm-2 were conducted in field with maize variety 'Tianci 19'. During two-year field study, the Nc dilution curve and NNI model of maize were established based on leaf dry matter (LDM). The results showed that: 1) There was a negative power function relationship between LDM and Nc, which presented as two parts, if LDM<1.15 t·hm-2, Nc=3.2%, while if LDM≥1.15 t·hm-2, Nc=3.29LDM-0.29. 2) The root mean square error (RMSE) and standardized root mean square error (n-RMSE) of the model were 0.203 and 8.0%, respectively, with fine stability among years. 3) The NNI ranged from 0.47 to 1.44 with different nitrogen application rates. In addition, NNI was positively correlated with yield and negatively correlated with agronomic utilization efficiency of nitrogen fertilizer at different growth stages of maize. Therefore, NNI could be used to explain maize yield changes with and without nitrogen limit under drip-irrigated system. In conclusion, the critical nitrogen dilution curve established from leaf dry matter could be applied to accurately estimate nitrogen nutrition status throughout the whole growing stages from the jointing stage to silking stage of maize under drip irrigated system.

Effect of slow‐release nitrogen on the nitrogen availability in an andisol and the critical nitrogen concentration in wheat

AbstractThe use of coated fertilizers and the concept of the critical N dilution curve are alternatives capable of improving the production efficiency of wheat (Triticum aestivum L.) crops in agro‐ecosystems. The objectives of this work were to evaluate the effect of a slow release urea‐coated fertilizer on (i) the production of wheat's shoot biomass at the anthesis stage, (ii) the concentration of N in the shoot biomass, and (iii) the N availability in the Andisol. Two fertilizers: urea and urea‐coated were evaluated using four increasing N rates and a control treatment (without fertilization), in three application strategies, during two growing seasons (late sowing [S1] and early sowing [S2]). Samples of shoot biomass and soil (0–20‐cm depths) were collected at five wheat growth stages (Z21, Z31, Z39, Z45, Z69 on the Zadoks scale). The average production of shoot biomass was 10.3 t dry matter (DM) ha–1 for S2 and 7.9 t DM ha–1 for S1 and N concentrations was between 1.0–3.0%. When using a coated urea fertilizer in this Valdivian agro‐ecosystem, no statistical differences (P &lt; .05) in shoot biomass or wheat N concentrations were found at anthesis (Z69). Differences were principally between seasons. We therefore proposed a new adjustment to the dilution N curve, with a value concentration critical, Nc start of 3.80%, and 4.15%, for S1 and S2, respectively. Use demand parameters such as Nc adjusted to the agro‐ecosystem for wheat crop, allows to rationalize the fertilization according to inorganic N available from the soil.

Development of a Critical Nitrogen Dilution Curve for Basil (Ocimum basilicum L.) Under Greenhouse Conditions

Nitrogen (N) is the most limiting nutrient for crops growth and development. The optimal application of N significantly enhances crop metabolic process. On the other hand, overuse of nitrogenous fertilizer leads to excess N accumulation in crop tissues that increases the risk of health-related problems. Therefore, it is mandatory to develop a quantitative approach for monitoring the crop N status during growth period. The main objective of this study was to establish the critical nitrogen dilution curve as an effective method to diagnose nitrogen status of sweet basil (Ocimum basilicum L.) grown under controlled greenhouse conditions. Two experiments were carried out with seven N application rates in the research greenhouse of University of Tehran, Iran. Values of crop shoot biomass (t ha−1) and N concentration (%) were measured in each sampling date to develop the critical nitrogen concentration (Nc) equation. The relationship between Nc and shoot dry matter (DM) was described by a power function (Nc = 4.80DM-0.38, R2 = 0.98). The validation results showed that the developed equation effectively distinguishes N-limiting from non-N-limiting treatments. The N nutrition index (NNI) ranged from 0.52 to 1.18 and 0.53 to 1.26 for the first and second experiment, respectively. It was concluded that the developed N dilution curve could provide useful insight into determination of basil N nutrition status and proper fertilizer management.

NITROGEN STEELS AND HIGH NITROGEN STEELS. INDUSTRIAL TECHNOLOGIES AND PROPERTIES

Nitrogen pressure can be a basis for the most general classification of steel, alloyed by nitrogen. Nitrogen steels are made under normal pressure, high nitrogen steels are made under pressure that is higher than atmospheric in special units. Nitrogen, as well as carbon, also strengthens austenite, but increases thermal stability of austenite, has the smaller sizes of ions and high solubility in γ- and α-phases. The result is smaller size of nitrides, smaller superficial energy, their higher strengthening effect and possibility of simultaneous increase in durability and corrosion resistance of austenite. The article considers the mechanisms of nitrogen influence on properties of steel, thermodynamics and kinetics of steels alloying with nitrogen, critical concentration of nitrogen and influence of nitrogen on properties of steel. There is no uniform balanced database and thermodynamic model now. Therefore any choice of values of equilibrium constant and parameters of interaction according to tabular data reduces the accuracy of calculations of nitrogen solubility in steel. In the circumstances it is better to use experimental data for concrete alloy from original works. At the choice of data it is necessary to be guided by the following control values: KN = 0,044, A ≥ 600. The nitrogen solubility in liquid metal, in α- and γ-phases is significantly various. Critical nitrogen concentration Nk, which excess leads to formation of bubbles and interstices at steel solidification, depends on composition of steel. Now the acceptable results when determining critical nitrogen concentration, can be received from the following condition: during the whole time of solidification the nitrogen content in residual liquid has to be less its equilibrium with the general pressure in the system of content in liquid metal at the same temperature T. Examples of nitrogen and high nitrogen steels, including steels with special properties, such as corrosion-resistant in bioactive environments, bactericidal steel, alloyed according on the scheme C + N steels, are given.

Tailoring Nitrogen‐Doped Carbons as Hosts for Single‐Atom Catalysts

AbstractThe application of nitrogen‐doped carbons (NDCs) as host materials for single‐atom catalysts (SACs) is increasing because of the strong binding affinity of the heteroatom with transition metals. Establishment of the relation between the properties of NDCs, their interaction with metals, and the performance of the resulting catalysts is crucial to guide the design of more effective SACs but has not been critically addressed. Here, a series of NDCs is prepared and studied as hosts for palladium atoms. The amount of nitrogen incorporated primarily depends on the choice of carbon followed by the doping temperature and nitrogen source. Pyridinic and pyrrolic species predominate in all cases, especially at lower doping temperatures. The stabilization of palladium atoms is successful above a critical nitrogen content that depends on the carbon type. Evaluation in the catalytic semi‐hydrogenation of 2‐methyl‐3‐butyn‐2‐ol readily distinguishes the reactivity of single atoms and nanoparticles, which correlates with the electronic properties of palladium described by the average oxidation state. Comparison with SACs based on compositionally‐related carbon nitride hosts shows that similarly high stability and tunability of the metal is achievable over NDCs, despite their lower nitrogen contents and greater heterogeneity of coordination sites.

Determination of critical nitrogen concentration and dilution curve based on leaf area index for summer maize

Injudicious nitrogen (N) fertilizer application has increased the risk of environmental pollution and decreased grain yields, farm profits, and N use efficiency. The plant based N diagnostic tools can be used to optimize N management of summer maize production. This study was designed to develop and validate a leaf area index (LAI) based critical N (Nc) dilution curve and to establish a theoretical framework to link the relationship of LAI and plant dry matter (DM) based curves, as well as to compare the differences between LAI, plant DM and growth stage-based Nc curves. Six field experiments were set with a range of N application rates (0–320 kg N ha−1) and plant densities (6 to 8 × 104 plants ha-1) using four summer maize cultivars (Zhengdan958, Denghai605, Xundan20, and Denghai661) in Henan province of China. LAI and plant N concentration (PNC) were determined from V6 to R1 stages in each experiment for the development of the Nc curve. LAI and PNC ranged from 1.28 to 6.12 and 1.34% to 3.31% under different N levels, respectively. Allometric relationships between LAI, plant DM, and critical N uptake (Nuc) were developed under non-N-limiting treatments. The relationship between Nc and LAI during vegetative growth period was described by a power function (Nc = 3.84LAI−0.45). N nutrition index (NNI) increased with the increasing N application rate and ranged from 0.56 and 1.23 across different N treatments. Our results validated that plant N uptake was proportional with LAI, and the allometric parameter between LAI and plant DM of summer maize was close to the theoretical value 2/3. The newly developed LAI-based Nc curve could identify plant N status (N-limiting and non-N-limiting) during key N requirement period of summer maize and can be used for precision N management for summer maize grown in China.

Key variables for simulating leaf area and N status: Biomass based relations versus phenology driven approaches

Abstract Phenological development can be seen as the biological clock of crops and crop model developers used this timeline for describing various processes associated with leaf area dynamics. The critical shoot nitrogen concentration (cNcrit; a reference to quantify crop nitrogen status), leaf-stem partitioning and specific leaf area (SLA) are often simulated as a function of developmental stages or thermal time driven functions. However, the impact of environmental variability might be better incorporated by considering process formulations related to biomass. Using published and novel data, this paper compares the simulation of processes associated with leaf area dynamics of winter wheat and maize using (a) BBCH (decimal code similar to the scale of Zadoks), xsatge or thermal time scale and (b) alternative formulations based on shoot dry mass (DM) or leaf area index (LAI). For both cNcrit and leaf-stem partitioning, the model based on DM was superior to the developmental approaches, as reflected in lower RMSE. Owing to the allometric link between LAI and DM, leaf-stem partitioning and SLA are not independent. Consequently, LAI explained canopy SLA better than developmental traits. Developmental stages are necessary to determine certain events like the switch from vegetative to reproductive development, but our results indicate that phenology cannot capture the allometric relationship between LAI and DM.

Water Stress Scatters Nitrogen Dilution Curves in Wheat.

Nitrogen dilution curves relate a crop’s critical nitrogen concentration (%Nc) to biomass (W) according to the allometric model %Nc = a W-b. This model has a strong theoretical foundation, and parameters a and b show little variation for well-watered crops. Here we explore the robustness of this model for water stressed crops. We established experiments to examine the combined effects of water stress, phenology, partitioning of biomass, and water-soluble carbohydrates (WSC), as driven by environment and variety, on the %Nc of wheat crops. We compared models where %Nc was plotted against biomass, growth stage and thermal time. The models were similarly scattered. Residuals of the %Nc - biomass model at anthesis were positively related to biomass, stem:biomass ratio, Δ13C and water supply, and negatively related to ear:biomass ratio and concentration of WSC. These are physiologically meaningful associations explaining the scatter of biomass-based dilution curves. Residuals of the thermal time model showed less consistent associations with these variables. The biomass dilution model developed for well-watered crops overestimates nitrogen deficiency of water-stressed crops, and a biomass-based model is conceptually more justified than developmental models. This has implications for diagnostic and modeling. As theory is lagging, a greater degree of empiricism might be useful to capture environmental, chiefly water, and genotype-dependent traits in the determination of critical nitrogen for diagnostic purposes. Sensitivity analysis would help to decide if scaling nitrogen dilution curves for crop water status, and genotype-dependent parameters are needed.

Relation between nitrogen nutrition index and production of spring malting barley

Although the nitrogen nutrition index (NNI) is a widely used indicator of plant nitrogenstatus, no model of NNI calculation for spring barley (Hordeum vulgare) reflecting also specificmalting requirements on grain has been published. The aim of this study was to determinean optimal range of the nitrogen nutrition index (ratio of nitrogen concentration in shootbiomass to critical nitrogen concentration) with respect to optimal grain protein content(N × 6.25 = 9.0 – 11.5 %), plump grain (grain > 2.5 mm) yield and lodging of spring maltingbarley during 7-year (2007 – 2013) strict field experiments realized under the conditions of threeexperimental sites in the Czech Republic. A dose of 80 kg N/ha and 130 kg N/ha, respectively,was applied in mineral fertilizers. The nitrogen nutrition index was determined at the BBCH 30(beginning of stem elongation) and BBCH 45 (late boot stage) growth stages. The most suitableindicators for evaluation of the nitrogen concentration in shoot biomass of the spring maltingbarley in our experiments proved to be Justes et al.´s model Nc = 5.35 DM(-0.442) designated forwinter wheat and Zhao´s model Nc = 4.76 DM(-0.39) designated for winter barley, where DM isshoot dry matter in t/ha. The nitrogen nutrition index for spring malting barley should notexceed a value of NNI = 0.80 and NNI = 0.90 using the Justes et al.´s model and the Zhao´s oneduring the BBCH 30 – 45 growth stages.

Development of a Critical Nitrogen Dilution Curve of Double Cropping Rice in South China.

The concept of critical nitrogen (Nc) concentration can be implemented to diagnose in-season plant nitrogen (N) status for optimizing N fertilizer management. The Nc dilution curves have been established for rice (Oryza sativa L.) grown in different climatic regions, yet no attempt has been made to develop the Nc dilution curve for double cropping rice regions. This study was undertaken to develop the Nc dilution curves for double cropping rice in south China for assessment of in-season N status and to establish the relationships N nutrition index (NNI) and relative yield (RY) for in-season prediction of rice grain yield. Three different N application rate field experiments using six Indica rice varieties, including two early rice hybrids and four late rice hybrids were carried out in east China. The Nc dilution curves based on whole plant N concentration were determined and described as, Nc = 3.37 W−0.44 for early rice and Nc = 3.69 W−0.34 for late rice. The constant N concentration at early growth stage was 3.31 and 3.15% DM for early and late rice, respectively. Late rice showed a higher capacity of N accumulation and a lower rate of N decline per unit shoot biomass as compared to early rice. The curves for present study were different from the existing reference curves for Indica and Japonica rice grown in different rice growing regions. Integrated N nutrition index (NNIint) based on Nc was used to estimate RY at different growth periods using linear regression functions. The results showed that the critical curves and relationship between NNIint and RY could be used as a reliable indicator of N status diagnosis, grain yield prediction as well as to provide technical support in N management for double cropping rice in south China.

Increases in leaf nitrogen concentration and leaf area did not enhance spur survival and return bloom in almonds (Prunus dulcis [Mill.] DA Webb)

Mature almond trees bear fruit mainly on short shoots called spurs, with only a small percentage of fruit produced laterally on long 1-year-old shoots. As a result, maintenance of large numbers of healthy spurs per tree is critical for fruit production. However, spurs that bear fruit have lower leaf area, leaf nitrogen content, and CO2 assimilation rate than non-fruiting spurs. This has been correlated with reduced percentages of spur survival and return bloom the following season. Thus, we hypothesized that spur leaf area, and ultimately spur health could be enhanced through application of foliar sprays and soil nitrogen treatments that would enhance leaf nitrogen content and spur leaf area. To test our hypothesis, we selected almond trees exhibiting significant yield differences as a consequence of differential soil rates of nitrogen fertilization (N rate) for three prior years (140, 224, and 392 kg/ha). In each tree, three spur types [non-fruiting spurs (F0); spurs with one fruit (F1); spurs with two fruit (F2)] were selected on the east side of the canopy and tracked for one complete season (2011–2012). Four foliar treatments (nutrient replacement, nutrient replacement with biostimulant, nitrogen, and non-spray) were directly applied to individual spurs in each N rate in the spring of 2011 and characteristic such as leaf nitrogen, and fruit quality were recorded throughout the season. In winter of 2012, spur survival and return bloom were addressed through individual visual inspection of the tagged spurs. In this experiment, soil and foliar N treatments effectively increased spur leaf area, fruit, and leaf nitrogen concentration. In the high N treatment, the leaf nitrogen values exceeded the critical nitrogen concentration established for almond trees and the critical leaf area for spur survival and blooming thresholds established by past research in this area. However, none of these positive changes in leaf N or leaf area improved spur survival and/or return boom of any spur type. Indeed, survival and hull + shell weight tended to be lower in the population of fruiting spurs with the highest leaf area and leaf nitrogen concentration and the return bloom probabilities were always lower in fruiting spurs than in non-fruiting spurs, independent of the nitrogen rate. These results and the relationship between nitrogen rate and spur survival are discussed.