NC Curves Research Articles

Development of a novel critical nitrogen concentration–cumulative transpiration curve for optimizing nitrogen management under varying irrigation conditions in winter wheat

Accurate nitrogen (N) nutrition diagnosis is essential for improving N use efficiency in crop production. The widely used critical N (Nc) dilution curve traditionally depends solely on agronomic variables, neglecting crop water status. With three-year field experiments with winter wheat, encompassing two irrigation levels (rainfed and irrigation at jointing and anthesis) and three N levels (0, 180, and 270 kg ha−1), this study aims to establish a novel approach for determining the Nc dilution curve based on crop cumulative transpiration (T), providing a comprehensive analysis of the interaction between N and water availability. The Nc curves derived from both crop dry matter (DM) and T demonstrated N concentration dilution under different conditions with different parameters. The equation Nc = 6.43T−0.24 established a consistent relationship across varying irrigation regimes. Independent test results indicated that the nitrogen nutrition index (NNI), calculated from this curve, effectively identifies and quantifies the two sources of N deficiency: insufficient N supply in the soil and insufficient soil water concentration leading to decreased N availability for root absorption. Additionally, the NNI calculated from the Nc-DM and Nc-T curves exhibited a strong negative correlation with accumulated N deficit (Nand) and a positive correlation with relative grain yield (RGY). The NNI derived from the Nc-T curve outperformed the NNI derived from the Nc-DM curve concerning its relationship with Nand and RGY, as indicated by larger R2 values and smaller AIC. The novel Nc curve based on T serves as an effective diagnostic tool for assessing winter wheat N status, predicting grain yield, and optimizing N fertilizer management across varying irrigation conditions. These findings would provide new insights and methods to improve the simulations of water-N interaction relationship in crop growth models.

Revisiting the critical nitrogen dilution curve for tall fescue: A quantitative synthesis

Assessing the plant nitrogen (N) status is one of the major challenges for improving N fertilization management and reducing its environmental footprint on forage-based agricultural systems. We re-analyzed a dataset of biomass (W) and plant N concentration (%N) of tall fescue (Festuca arundinacea Schreb.) using a Bayesian statistical model for estimating the coefficients of the critical N (%Nc) dilution curve (Nc = A1 W −A2) with two objectives in mind: i) to revise the reference %Nc dilution curve established for tall fescue by Lemaire and Salette (1984), and ii) to analyze how the determination of %Nc curves is affected by the structure of the dataset (number of sampling dates and N rates) along with the range of shoot %N and W achieved. Our analysis suggests that the original tall fescue %Nc curve of Lemaire and Salette (1984) was overestimated. A critical %N curve for tall fescue was obtained using the Bayesian method across 14 unique genotype × environment × management (G × E × M) conditions (Nc = 3.93 W -0.42). We show that the high uncertainty associated with the %Nc curve could be reduced by increasing the number of experiments. When a single dataset was used, 95 % credibility intervals (95 % CI) were [2.52, 5.66] for A1 and [0.06, 0.63] for A2. However, 95 % CI were reduced up to a 73 % when the critical N dilution curve was based on 14 studies. We also show that a minimum of five studies (+100 data points for our study) are needed to avoid large biases and uncertainty levels in coefficient estimations with the Bayesian method. However, these studies must be carefully designed. The reliability of critical %N curves is greatly reduced when they are estimated with datasets comprising only a few data under non-limiting N conditions or data covering only very low or high W values. Our results suggest that more reliable critical N dilution curves for species can be developed by grouping numerous datasets covering a broad range of G × E × M conditions.

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.

An update to ANSI/ASA S12.2-2019: Criteria For evaluating room noise—Where to go next?

The S12.2 standard provides methods for evaluating room noise such as NC curves or overall dBA levels. It has been around, in a rather similar form, for more than 25 years. While some concepts have moved from the main section to the annex (e.g., NCB), other concepts remain unchanged. A survey was taken in 2019 to evaluate the use and functionality of the various elements of the standard (e.g., the degree of usage of NC versus dBA vs NCB versus PNC vs RNC versus RCMkII). Additional items for consideration into the a revision of the standard were polled (e.g., 1/3 Octaves, minimum background levels, etc.) This session will give a brief overview of the standard and significant time will be spent on the next steps and ideas for changes to the standard. Feedback will be welcome and additional time will be given for group discussion.

Growth, Critical N Concentration and Crop N Demand in Butterhead and Crisphead Lettuce Grown under Mediterranean Conditions

Excessive nitrogen (N) fertilizers are applied in lettuce causing both environmental issues and N crop luxury consumption. In order to improve the N use efficiency (NUE) by defining optimal crop growth and N requirements of butterhead and crisphead lettuce, two field experiments were conducted using 0, 50, and 100 kg ha−1 of N fertilizer to study (i) the growth and productivity, (ii) the NUE, (iii) the critical N dilution curve, and (iv) the N demand. Nitrogen supply enhanced dry weight (DW) accumulation in the butterhead (from 295 to 410 g m−2), but not in the crisphead type (251 g m−2). The NUE indices underlined the poor ability of the crisphead type in absorbing soil N and also in the utilization of the absorbed N for producing DW. The critical N dilution curves %Nc = 3.96 DW−0.205 and %Nc = 3.65 DW−0.115 were determined for crisphead and butterhead lettuce, respectively. Based on these type-specific %Nc curves, the estimated N demand was 125 kg ha−1 in the butterhead and 80 kg ha−1 in the crisphead lettuce for producing 4.3 and 2.5 Mg ha−1 of DW, respectively, under Mediterranean climate. Neither N fertilization nor genotype affected crop productivity.

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.

Sound data for a new format of short-profile fan coil units

In recent years, a new format of short-profile fan coil units as offered by several manufacturers has become increasingly popular. The sound data for such units are generally plotted in octave bands on NC curves, and have the appearance of great data. However, any scrutiny raises a variety of concerns. Fundamental methods were used to approximate power levels from the provided pressure levels for use in HVAC system noise calculations on various projects. In July 2015, test lab power level data were serendipitously provided for two fan coil units that had been included in the design for a new project. In due course, test lab data for six units, based on AHRI Standard 260, were obtained. This paper will discuss the approximation methods, ranges of differences between pressure level and power level data, effects on results of calculations, referenced measurement standards, and an issue related to pure tones.

Using leaf dry matter to quantify the critical nitrogen dilution curve for winter wheat cultivated in eastern China

Accurate measurement of the nitrogen (N) required for plant growth helps optimize grain yield, farm profits, and N-use efficiency. Critical nitrogen (Nc) curves have been developed to describe N dilution in plant tissues during crop growth and to estimate the N status of whole plants; however, Nc curves for leaves have yet to be constructed. We constructed and validated a leaf Nc curve for winter wheat based on leaf dry matter (LDM) and compared it with published whole-plant Nc curves to explore the potential for estimating leaf N status of winter wheat in eastern China. Four field experiments were conducted using a range of N fertilization levels (0–375kgha−1) applied to six wheat cultivars in eastern China. For our growth analyses, we determined LDM and leaf N concentration (LNC) in the developmental phases from spring regrowth to heading. The leaf Nc curve fit the following relationship: Nc=3.05LDM−0.15 when LDM ranged from 0.52 to 2.64tha−1. However, when LDM was <0.52tha−1, we applied a constant leaf critical value of 3.37%. The curve we constructed was lower than the reference whole-plant Nc curve. The N nutrition index (NNI) ranged from 0.34 to 1.31 during the vegetative stage across the 2009–2011 seasons. There was a significant positive relationship between the difference values of NNI (ΔNNI) and N (ΔN) applications over the four wheat developmental stages. We obtained a root-mean-squared-error (RMSE) of 24.53kgha−1 between the predicted and observed ΔN values when testing the models with independent data. The leaf Nc dilution curve correctly identified N-limiting and non-N-limiting statuses and may be used as a reliable indicator of N stress during the growing season of winter wheat in eastern China.

Noise control policy in Brazil and South America

There are noise policies and regulations in Brazil for occupational, community, and product noise. (1)Noise in the workplace, MTE 3214-1978, is a regulation of the Minister of Labor which specifies 85 dBA – 8 hours sift with 5 dBA rate (this should be changes to 3 dB). (2)Community Noise: There are two regulations of the Minister of the Environment covering noise which affects industrial, commercial, social, recreation, and political activities. A- Silence regulation NBR10151: SPL= 35-45 dBA between 10 PM to 6 AM. B- Comfort regulation NBR10152: Table of SPL (35 to 60 dBA) or NC curves for each place (hospital, hotel, residence, offices, school, etc.) range from C= 30 to 55. (3)Brazil also has Standard NBR 13910-1, 2, and 3:1999 which recommends noise labeling using the sound power level. Since 2001 the working party has been in power in Brazil, and since then industrial noise regulations have been enforced. If industrial noise cannot be reduced at the source, hearing protectors are required. All hearing protection devices must go through attenuation measurements in Brazil (ANSI S12.9-2008(B) subject fit method. Most of South America countries have similar regulations as those in Brazil. The Ibro-American Federation of Acoustics (FIA)in the last years has played an important role in noise control engineering education through its congresses in 1998 (Brazil), 2000 (Spain), 2002 (Cancun with ASA), 2004 (Portugal), and 2006 (Chile).

Sound, Noise and Speech at the 9000-Seat Holy Trinity Church in Fatima, Portugal

Abstract This paper presents the interior acoustical characterization of the 9,000-seat church of the Holy Trinity in the Sanctuary of Fátima, Portugal, inaugurated in 2007. In situ measurements were held regarding interior sound pressure levels (with and without the HVAC equipment working), NC curves, RASTI (with and without the installed sound system) and reverberation time. The results are presented and commented according to the design values. A comparison is made with other churches in the world, also with a very large volume (for instance the Basilica Mariacka in Gdańsk). The measured data are also used to calculate a global index of this church acoustic quality using Engel's and Kosała's Index Method.

Sulcal set optimization for cortical surface registration

Flat mapping based cortical surface registration constrained by manually traced sulcal curves has been widely used for inter subject comparisons of neuroanatomical data. Even for an experienced neuroanatomist, manual sulcal tracing can be quite time consuming, with the cost increasing with the number of sulcal curves used for registration. We present a method for estimation of an optimal subset of size NC from N possible candidate sulcal curves that minimizes a mean squared error metric over all combinations of NC curves. The resulting procedure allows us to estimate a subset with a reduced number of curves to be traced as part of the registration procedure leading to optimal use of manual labeling effort for registration. To minimize the error metric we analyze the correlation structure of the errors in the sulcal curves by modeling them as a multivariate Gaussian distribution. For a given subset of sulci used as constraints in surface registration, the proposed model estimates registration error based on the correlation structure of the sulcal errors. The optimal subset of constraint curves consists of the NC sulci that jointly minimize the estimated error variance for the subset of unconstrained curves conditioned on the NC constraint curves. The optimal subsets of sulci are presented and the estimated and actual registration errors for these subsets are computed.

EFFECTS ON PERFORMANCE AND WORK QUALITY DUE TO LOW FREQUENCY VENTILATION NOISE

A pilot study was carried out to assess method evaluating effects of low frequency noise on performance. Of special interest was to study objective and subjective effects over time. Two ventilation noises were used, one of a predominantly mid frequency character and the other of a predominantly low frequency character. Both had an NC value of 35. For the study, 50 students were recruited and 30 selected on the basis of subjective reports of pressure on the eardrum after exposure to a low frequency noise. Of these, 14 randomly selected subjects aged 21 and 34 took part. The subjects performed three computerized cognitive tests in the mid frequency or the low frequency noise condition alternatively. Tests I and II were performed together with a secondary task.Questionnaires were used to evaluate subjective symptoms, effects on mood and estimated interference with the test results due to temperature, light and noise. The results showed that the subjective estimations of noise interference with performance were higher for the low frequency noise (p<0·05). The exposure to low frequency noise resulted in lower social orientation (p<0·05) (more disagreeable, less co-operative, helpful) and a tendency to lower pleasantness (p=0·07) (more bothered, less content) as compared to the mid frequency noise exposure. Data from test III may indicate that the response time during the last part of the test was longer in the low frequency noise exposure. The effects seemed to appear over time. The hypothesis that cognitive demands are less well coped with under the low frequency noise condition, needs to be further studied. The results further indicate that the NC curves do not fully assess the negative effects of low frequency noise on work performance.

Room noise criteria—A consultant’s experience

There has been much controversy in recent years regarding the various room noise criteria that have been proposed and are in use today. Included in these criteria are the NC curves, the PNC curves, the RC curves, and most recently, the NCB curves. The NR curves, which are commonly used in Europe, must also be mentioned. The recent adoption of ANSI S12.2 has not resolved the controversy—in fact, it has actually heightened the debate because it acknowledges two room noise criteria (RC and NCB) that are clearly at odds with each other in the low-frequency region. This paper examines the limitations of each method (RC and NCB) and provides possible suggestions for modifications that might create a path for eventual resolution of this controversy. This paper also emphasizes the important characteristics of any room criteria method: it must be as simple as possible without sacrificing effectiveness, relatively easy to measure, and credible from the standpoint of human perception. In any event, it is the opinion of the author that any resolution will have to await the completion of the ASHRAE research project which is currently in progress in Australia. [See NOISE-CON Proceedings for full paper.]

Practical considerations in methods of rating room noise

Since 1955, the NC curves have been used with considerable success to specify and rate room sound quality. Although newer rating schemes have appeared, and in several areas supplanted the NC curves, many practitioners still use and prefer the old scheme. The newer RC and NC-B rating techniques exhibit one aspect which makes them both problematic in practical use. They both attempt to include in one rating number a further ‘‘quality’’ factor of the sound. While it is simple to establish the goal that room noise should meet a specific RC (or NC or NC-B) value, with a specific curve shape (neither ‘‘rumbly’’ or ‘‘hissy’’), it may be more difficult to evaluate whether a space meets the criteria. If the goal is to provide a background sound level of RC-40, or NC-B 40, does a room which is RC-35R meet the criteria, or fail it? Is an NC-B 30R better or worse than an NC-B 40? These questions are faced by the practitioner on a regular basis, and is one of the factors which makes the NC scheme more acceptable. When the room noise is ‘‘rumbly’’ or ‘‘hissy,’’ or when it is modulated or cyclic, or contains pure tones, a statement can be made to indicate this. The practitioner must first be able to specify the measurable physical quantities without ambiguity. Where there are sound quality factors present, they may indicate that an otherwise acceptable spectrum is unacceptable. Detailed background material is included along with examples, including those from the literature. [See NOISE-CON Proceedings for full paper.]

Suggested infrasound criteria for building spaces

Work by Leo L. Beranek [“Application of NCB Noise Criterion Curves,” Noise Control Eng. J. (Sept.–Oct. 1989)] presents and discusses a set of “balanced noise criterion curves.” These are cited as an improvement in the widely used NC curves and extends them down to the 16‐ and 31.5‐Hz octave bands. These curves are steeply sloped in the very low‐frequency range and are intended to be based wholly on audibility. The author draws upon his experience and a paper by H. Dawson [“Practical Aspects of the Low Frequency Noise Problem,” J. Low Freq. Noise Vib. 1 (1) (1982)] to arrive at a modified set of NC curves extending down to 16 Hz that combine audibility and feelability affects. Examples of the application of these suggested criteria curves will be discussed.

Accuracy of measured local strain and local strain approach to fatigue life prediction of welded structures.

The local strain approach is a very useful method to evaluate fatigue strength of complicated welded structures. In the local strain approach, the accuracy of measured local strain is very cirtical. The effects of the radius of toe grinding and the strain gage length on the accuracy of measured local strain and Δσ(= E·Δε) - Nc curves were examined in this study. An accuracy of 90% could be obtained for the measured local strain when the length of the strain gage was less than half the toe radius. For the measured local strain, a Δσ(= E·Δε) - Nc curves for welded structures agreed with that of the small round specimen. However toe grinding caused a decrease in the local strain, and as a result, Δσ decreased with a derease in strain concentration factor. The Δσ(= E·Δε) - Nc curves modified with toe grinding radius were proposed, and the results agreed with the test data for welded structures.

Revised noise criteria for design and rating of HVAC systems

This paper reviews current methods of rating the noise produced by HVAC systems and explains why these ratings fail to be correlated with subjective opinion in many cases. An entirely new method of assigning noise ratings is proposed which is expected to provide a significantly better correlation between objective measurements and subjective response. The proposed new rating method makes use of a revised set of noise criterion curves (RC curves) which appeared for the first time in Chap. 35 of the 1980 Systems Volume of the ASHRAE Handbook. This paper also discusses the technical considerations leading to the development of the RC curves as a replacement for the NC curves which have been used in the past.

A new charted system for the specification of structure-borne noise control

The practice of specifying noise levels in the various types of accommodation in buildings is increasing with the passing of each year. The architect employs various methods, the most commonly used being either NC or NR curves. Increasing, too, is the amount of mechanical equipment being installed, much of which requires protection against structure-borne noise. Most engineers specify this protection in terms of percentage isolation of vibration—a method totally unrelated to the architect's requirements. This note provides, by the use of a set of simple charts, a method whereby vibration data may, in many instances, be directly related to sound pressure levels and, thus, to NC or NR curves.

Single-Number Criteria for Room Noise

Subjective noise ratings by executive office personnel, reported at the time that the NC curves were introduced [L. L. Beranek, J. Acoust. Soc. Am. 28, 833–852 (1956)], have been correlated with various physical measures derived from the 17 noise spectra originally published. The rank-order correlation coefficients (in parentheses) for the respective physical measures are: A-sound level (0.96), B-sound level (0.96), NC level (0.95), NCA level (0.95), N level per ISO proposal (0.96), speech-interference level (0.86), speech-interference level based on the three octave-band levels from 300 to 2400 cps (0.91), calculated loudness level (0.96), perceived-noise level (0.96), 40-noy-weighted sound level (0.95). With only one exception each, loudness level and perceived-noise level for the 17 airbase office noises are 13±1 dB greater than the A-sound level. Some type noise spectra of various shapes are provided, along with an auxiliary table, to facilitate estimation of the several physical measures simply by curve-matching. Since subjective ratings of office noise appear to be correlated with the A-sound level as well or better than with other commonly known noise ratings, and since the A-sound level can be measured readily with widely available meters, it is recommended as a replacement for the NC level in single-number specifications for office noise.

Physical and Psychophysical Descriptions of Sixteen Equally Speech-Interfering Noises

Physical and psychophysical measurements and/or calculations were made on 16 equally speech-interfering noises. Speech-interference levels (SIL) based on octaves with center frequencies of 500, 1000, and 2000 cps or at 425, 850, and 1700 cps predicted very well that the noises were equally speech-interfering. These SIL's predicted better than the more conventional SIL based on octaves between 600 and 4800 cps. Articulation-index (AI) scores based on 5 or 6 weighted octaves were equivalent to the 20-band AI methods and were not necessarily better than SIL methods. Fitting the peaks of plotted spectra to noise-criteria (NC or NCA) curves was not adequate, although averaging that part of the spectra centered on octaves from 500 through 2000 cps through NC or NCA curves gave good prediction. Equally speech-interfering noises were not equal in loudness as calculated by Stevens' method, or in PNdB. There was evidence to show that the frequency that divided noise-masked speech into two equally intelligible frequency regions was 850 or 1000 cps, and was not 1700 and 1900 cps, which is the dividing frequency when the speech in quiet is progressively restricted in bandwidth by high- or low-passed filtering.