Chlorophyll Meter Research Articles

Evaluation of the Use of SPAD-502 Chlorophyll meter for non-destructive estimation of nitrogen status of tea leaf (Camellia sinensis L. Kuntze)

Efficient nutrient management requires estimating factual fertilizer requirements. This study was aimed to test the use of chlorophyll meter SPAD-502 to estimate the nitrogen status of tea maintenance leaf. The test was carried out by correlating the SPAD readings with destructively measured leaf nitrogen content using samples oGbtained from nitrogen fertilizer dosage experiments. Observations were made at 15, 32, 45 and 62 days after the application of N fertilizer treatments. The results showed that the SPAD readings and total nitrogen leaf content correlated significantly with the time of observation. Estimation of leaf N content based on the SPAD readings follows linear line equation y = 0.0311x + 1.5856 with coefficient determinant (R²) = 0.62 significantly at P less than 0.01. It was concluded that SPAD-502 chlorophyll meter is reliable to assess the leaf nitrogen content of tea maintenance leaf and is adequate to predict future nitrogen fertilizer requirements.

Non-destructive analysis of photosynthetic pigments in Avena strigosa and Avena sativa

Chlorophylls and carotenoids are the main photosynthetic pigments in plants. The photosynthetic potential of crop plants is used to determine the correct rate of nitrogen fertilization. To date, no studies have been conducted to understand the relationship between different methods of measurement of photosynthetic pigments in oats. The objective of this study was to quantify and compare the levels of photosynthetic pigments in Avena strigosa and A. sativa using two different methods, the extraction method and portable chlorophyll meter, and to determine whether the results of these two methods showed a significant correlation. Photosynthetic pigments were measured using both methods in a greenhouse and the laboratory at four developmental stages: tillering [28 days after sowing (DAS)], vegetative stage I (55 DAS), vegetative stage II (75 DAS), and reproductive stage (120 DAS). The same leaves were used to measure the relative chlorophyll content using a portable chlorophyll meter and extractable chlorophyll using the laboratory extraction method. The readings of the chlorophyll index differed for each developmental stage of both A. sativa and A. strigosa. The contents of chlorophyll a, chlorophyll b, and carotenoids determined using the extraction method showed high coefficients of correlation with the total chlorophyll index determined using the portable chlorophyll meter. Thus, the measurement of chlorophyll using the portable chlorophyll meter can be used for the accurate evaluation of the photosynthetic potential of oats, thus saving time and reagents.

Phenotyping flag leaf nitrogen content in rice using a three-band spectral index

Accurate, rapid and non-destructive measurements of rice flag leaf nitrogen content (LNC) are crucial for geneticists and breeders. To help design a less expensive, non-destructive, real-time LNC sensor, we developed a Three-Band Difference Ratio (TBDR) spectral index, TBDR (R755, R513, R508). This spectral index could accurately and rapidly estimate rice LNC in a population of chromosome segment substitution lines with small variation in LNC. The model estimating LNC was validated using a leave-one-out cross-validation technique; the achieved root mean square error was 0.13% and the relative error was 4.74%. In comparison with SPAD-502plus chlorophyll meter readings and commonly used spectral indices, including GreenSeeker- and Crop Circle-based indices, TBDR (R755, R513, R508) produced higher accuracy in LNC estimation.

Plants Recovery Performance from Water Stress

Recovery of plants after water stress events represents their high suitability for the urban condition areas. Reaction to drought and recovery of woody plants Cornus mas L., Lonicera caerulea L. and perennials Alchemilla mollis (Buser) Rothm., Geranium maculatum L., Geranium x magnificum Hyl. ‘Rosemoor’ and Geranium ‘Philippe Vapelle’ were evaluate. Within a pot experiment the non‑destructive methods of monitoring: measurement of chlorophyll content using chlorophyll meter CL‑01, leaf stomatal conductance using Delta T Leaf porometer AP4 and modulated chlorophyll fluorescence using Hansatech FMS 1 were chosen. Based upon our results we may demonstrate different protective mechanisms of plants in water stress conditions. An increase in the chlorophyll concentration in stress‑exposed tissues and recovery of stomatal conductance in Cornus mas L. and in Alchemilla mollis (Buser) Rothm. were observed. In Cornus mas L. and Lonicera caerulea L. the early recovery of parameter ɸPSII (after 2 days of re‑watering) and the delayed recovery (after 6 days of re‑watering) in Geranium plants and Alchemilla mollis (Buser) Rothm.) were shown.

Genetic variability analyses for yield and physiological traits in groundnut (Arachis hypogaea L.) genotypes

Twenty different groundnut genotypes were evaluated in a randomized block design with three replications during kharif 2012 to study the variability parameters, heritability, genetic advance, correlation coefficient and path analysis for ten characters. Analysis of variance revealed highly significant differences among genotypes for all the traits except stability of soil plant analytical development (SPAD) and Chlorophyll Meter Reading 45 days after sowing indicating that adequate variability was found in the genotypes studied for most of the characters. The characters like 100 kernel weight, SPAD Chlorophyll Meter Reading 75 days after sowing, specific leaf area 75 days after sowing and rust resistance had high heritability with high genetic advance as per cent of mean and medium genotypic coefficient of variation indicating greater role of additive gene effects on these traits. While pod yield had moderate genotypic coefficient of variation and heritability along with high genetic advance as per cent of mean revealed that this character is also governed by additive gene effects and selection would be effective even in the early generation. Days to maturity, shelling outturn and specific leaf area 45 days after sowing had moderate heritability accompanied with low genotypic coefficient of variation and genetic advance indicating these traits are governed by non-additive gene effects. Selection may be practiced in later generations for improving these traits. The results on genotypic correlation coefficients revealed that pod yield had significant highly positive correlation with days to maturity, 100-kernel weight, and SPAD Chlorophyll Meter Reading 45 days after sowing while it was negative and significant for days to flower initiation and rust disease. SPAD Chlorophyll Meter Reading 45 days after sowing and SPAD Chlorophyll Meter Reading 75 days after sowing had highly significant negative correlation with specific leaf area 45 days after sowing and specific leaf area 75 days after sowing. Specific leaf area 45 days after sowing had highly significant negative correlation with rust. Therefore, SPAD Chlorophyll Meter Reading value could be used to identify genotypes with low specific leaf area and rust resistance. Path analysis indicated that 100-kernel weight had high positive direct effect with highly significant positive correlation with pod yield. Hence, this character may be effective for selection of high pod yield.

Association of Physiological Responses and Root Distribution Patterns of Ratooning Ability and Yield of the Second Ratoon Cane in Sugarcane Elite Clones

Poor ratooning ability for sugarcane can limit crop productivity and profitability of sugarcane growers. The objective of this study was to determine the association of physiological responses and root distribution patterns on the yield of the second ratoon cane, and the relationships between these traits. Seventeen sugarcane genotypes were planted in a randomized complete block design with four replications. The second ratoon crop was evaluated for germination percentage, cane yield, Soil Plant Analysis Development (SPAD) chlorophyll meter reading (SCMR), chlorophyll fluorescence, relative water content (RWC), specific leaf area (SLA), and stomatal conductance. Root length density (RLD) was evaluated through the auger method. The root samples were divided into upper and lower soil layers in order to study root distribution patterns. Sugarcane genotypes were significantly different for RLD, germination percentage, and cane yield. Root distribution patterns were classified into three groups based on the RLD. High RLD between plants in the upper soil layers at 90 days after harvest (DAH) was positively correlated with high germination, whereas high RLD between rows in the lower soil layers at 90 and 270 DAH was associated with high cane yield. RWC at 90 DAH and stomatal conductance at 180 DAH were closely related to germination percentage, whereas chlorophyll fluorescence and stomatal conductance at 180 DAH were closely related to cane yield.

Crescimento do milheto (Pennisetum glaucum) irrigado com água residuária no Seridó Paraibano

The use of wastewater can be an irrigation alternative for millet, especially in areas with low availability of water, such as the Seridó Paraibano Region. The objective of this work was to evaluate the growth and production of millet irrigated with wastewater under a consortium with lab-lab beans. The experiment was conducted at the Caboré site, in the municipality of Frei Martinho-PB. The experimental design was a randomized complete block design with five plots (40, 60, 80, 100 and 120% of available water) in a consortium with lab-lab bean in the subplot. The treated wastewater came from the Sewage Treatment Plant of the municipality. The variables measured were: height of the plant; leaf area; number of leaves; diameters and SPAD (chlorophyll meter). There was a significant difference in relation to plant growth, leaf area and number of leaves. The stem diameter and SPAD had no significant effect, an average of 11.197 mm / plant and an average of 60.952 units were observed. The millet plants presented high number of leaves and high leaf area when applied to the irrigation blade of 300 mm of wastewater. The consortium of millet X-lab-lab beans did not interfere interfere with the growth of millet.

Response of four potato cultivars to soil application with organic and amino acid compounds

A field experiment was implemented at Vegetable field, Department of Plant Production, Agricultural Technical College, Mosul, Iraq during spring season of 2018 to study the response of four potato cultivars (Actrice, Arizona, Riviera and Universa) to four organic and amino acid compounds (Azomine 4 ml/l, Tecamin Max 3 ml/l, Delfan plus 3 ml/l and Humibest 4 g/l) as soil application. These compounds were applied near the plant roots three times, the first after complete tubers emergency 45 days after planting, the second after 60 days and the third after 75 days of planting. The four potato cultivars were sown on 1st February in loamy soil, sprouted seed tubers were planted at 25 cm apart within the row. The treatments were arranged incomplete randomized block design with three replicates. The area of each plot was 6.75m2 (3linex3m long x 0.75 m wide). All experimental areas received the recommended dose of organic and mineral fertilizers. Samples of three plants from each treatment and each plot were randomly taken after 90days of planting and growth characters recorded were plant length, shoot number, leaf area, fresh and dry weights of shoots/plant. The total chlorophyll content in fully expanded leaves after 80 days of planting was measured as SPAD units using Minolta Chlorophyll Meter (model SPAD 502).

Possibility of using a SPAD chlorophyll meter to establish a normalized threshold index of nitrogen status in different potato cultivars

Leaf SPAD values are thought to be an indicator of potato nitrogen (N) status; however, when making plant N diagnosis, no single threshold leaf SPAD value can be used for all potato cultivars because of cultivar variation. We conducted field experiments over 3 years to test whether the difference in SPAD values between the upper and lower leaves was consistent among potato cultivars, and whether this value responded to N application levels. The results showed cultivar affects the SPAD values of the fourth and eighth leaves (SPADL4 and SPADL8), but not SPADL4-8, the difference between SPADL4 and SPADL8. Moreover, the SPADL4-8 values responded well to N application levels. Therefore the SPADL4-8 could be applied as a general index of N status across different potato cultivars, and establishing a threshold SPADL4-8 value might be more useful in guiding N fertilization recommendations for different potato cultivars.

Estimating chlorophyll content at leaf scale in viroid-inoculated oil palm seedlings (Elaeis guineensis Jacq.) using reflectance spectra (400 nm–1050 nm)

ABSTRACTOrange Spotting (OS) is an emerging disease in oil palm (Elaeis guineensis Jacq) that has been associated with Coconut cadang-cadang viroid (CCCVd; Cocadviroid, Pospiviroidae). This study was aimed at selecting efficient wavebands in the Visible/near infrared (VNIR) spectrum (400–1050 nm) for estimation of chlorophyll content in CCCVd-inoculated oil palm seedlings. The VNIR spectrum is most sensitive to chlorophyll stress and able to differentiate between healthy and diseased plants. Therefore, a greenhouse experiment was conducted to remotely sense the chlorophyll content using a hyperspectral hand-held spectroradiometer (Analytical Spectral Device (ASD) FieldSpec–II) and a portable chlorophyll meter (Minolta Soil-Plant Analysis Development (SPAD)−502). FieldSpec–II provides reflectance spectra with narrow and contiguous wavebands while SPAD-502 churns out SPAD readings corresponding to chlorophyll content. Interval Partial Least Squares (iPLS) model was used to assess the relationship between independent variable (spectra) and dependent variable (SPAD readings). Five different spectral datasets (i.e. raw spectra, first-order derivatives, Savitzky-Golay smoothing, Multiplicative Scatter Correction (MSC), and standard normal transformation) were investigated. Results showed that the MSC dataset yielded the most accurate estimation with a root mean square error of prediction of 3.70% and a correlation coefficient for prediction of 0.72. A total of thirty wavebands within a range between 601 nm and 630 nm was selected. This work showed that VNIR spectra has the potential to diagnose OS disease in oil palm using the iPLS regression method. This is completely a new application of hyperspectral remote sensing for the oil palm industry, particularly in the domain of plant protection.

Influence of time of day on measurement with chlorophyll meters and canopy reflectance sensors of different crop N status

Optical sensors are a promising approach for assessing nitrogen (N) status of vegetable crops. However, their potential may be undermined if time of day influences measurements. This study evaluated the effects of time of day and N addition on measurements, made with two chlorophyll meters, SPAD-502 and MC-100, and two active canopy reflectance sensors, GreenSeeker handheld and Crop Circle ACS-470. Three treatments (N1, deficient, N2, conventional, and N3, excessive N application) of N concentration in the nutrient solution were applied by fertigation throughout a sweet pepper crop grown in soil in a greenhouse. Time of day of 12:00 and 15:00 h had an effect on measurements made with the SPAD-502, but only in the N1 treatment, suggesting that the effects of time of day were related to crop N status. This effect was slight, being 1.7 ± 0.02 SPAD units lower at 12:00 and 15:00 h compared to at 9:00 h (relative decrease of 3.6%). For the MC-100, a slight increase in Chlorophyll Content Index (CCI) values of 3.3 ± 0.1 units (relative increase of 6.3%) was observed at 15:00 and 18:00 h, relative to CCI values at 9:00 h, regardless of N treatment. The time of day effect on chlorophyll meters appears to be negligible in relation to the wide range of values measured in greenhouse-grown sweet pepper. Normalized Difference Vegetation Index, measured both with the GreenSeeker and Crop Circle, and Green Normalized Difference Vegetation Index, measured with the Crop Circle, were not affected by time of day in any of the N treatments, showing that these sensors and indices can be used with confidence at any time of the day.

Early Visual Detection of Wheat Stripe Rust Using Visible/Near-Infrared Hyperspectral Imaging.

Wheat stripe rust is one of the most important and devastating diseases in wheat production. In order to detect wheat stripe rust at an early stage, a visual detection method based on hyperspectral imaging is proposed in this paper. Hyperspectral images of wheat leaves infected by stripe rust for 15 consecutive days were collected, and their corresponding chlorophyll content (SPAD value) were measured using a handheld SPAD-502 chlorophyll meter. The spectral reflectance of the samples were then extracted from the hyperspectral images, using image segmentation based on a leaf mask. The effective wavebands were selected by the loadings of principal component analysis (PCA-loadings) and the successive projections algorithm (SPA). Next, the regression model of the SPAD values in wheat leaves was established, based on the back propagation neural network (BPNN), using the full spectra and the selected effective wavelengths as inputs, respectively. The results showed that the PCA-loadings–BPNN model had the best performance, which modeling accuracy (RC2) and validation accuracy (RP2) were 0.921 and 0.918, respectively, and the RPD was 3.363. The number of effective wavelengths extracted by this model accounted for only 3.12% of the total number of wavelengths, thus simplifying the models and improving the rate of operation greatly. Finally, the optimal models were used to estimate the SPAD of each pixel within the wheat leaf images, to generate spatial distribution maps of chlorophyll content. The visualized distribution map showed that wheat leaves infected by stripe rust could be identified six days after inoculation, and at least three days before the appearance of visible symptoms, which provides a new method for the early detection of wheat stripe rust.

Preliminary Study of Variable Rate Application – Organic Liquid Fertilizer by Using SPAD Chlorophyll Meter on System of Rice Intensification (SRI) Cultivation

ABSTRACTKnowing actual nutrient requirements for rice plants is crucial in supplying the correct amount of fertilizer, especially nitrogen since nitrogen is one of the most key limiting nutrients in rice cultivation. A preliminary study of variable rate application (VRA) on System of Rice Intensification (SRI) planting by using organic foliar fertilizer was carried out to determine the effectiveness of precision fertilization. Foliar fertilizer was formulated based on actual nitrogen needed by rice plants using Soil-Plant Analyses Development (SPAD) chlorophyll meter measurements. The experiment was laid out in a randomized complete block design (RCBD) with four treatments (50% fixed rate, 100% fixed rate, 150% fixed rate and VRA) and four replications for each treatment. Plant growth performances (plant heights, number of tillers, number of panicle and flower) and yield performances (grain yield, number of grain, 1000-grain weight and number of spikelets) were recorded during the study. The results showed that foliar application of VRA resulted in significantly higher yield performances; grain yield (13.65 g), number of grain (807.50), 1000-grain weight (16.79 g), and number of spikelets (7.50) compared to uniform fertilizer applications. VRA treatments had the highest SPAD readings at every planting stage during the experiment; however, a high nitrogen supply was needed during the mid-tillering stages (35 DAT) compared to other fertilizer rates. Besides, VRA application shows the most savings in term of total nitrogen supply (415 µg) compared to uniform rates application; 50% fixed rate (400 µg), 100% fixed rate (810 µg), and 150% fixed rate (1210 µg).

Screening Corn Hybrids for Soil Waterlogging Tolerance at an Early Growth Stage

Identification of corn hybrids that can withstand wet soil conditions is one approach to prevent crop production losses from abiotic stress caused by excessive soil moisture during early spring season in the midwestern United States. A greenhouse pot experiment was conducted in 2013 to screen and identify corn hybrids tolerant or susceptible to soil waterlogging at the V2 growth stage. The main plots included waterlogging durations: no waterlogging; 14-day waterlogging and then allowing recovery from waterlogging stress for 7 days; and 21-day waterlogging. Subplots included eight commercial corn hybrids. The shoot and root biomass, plant height, stomatal conductance, and chlorophyll meter readings were decreased due to waterlogging for 14 days and 21 days. Hybrid #2 appeared to be more tolerant to waterlogging as evidenced by greater growth and higher stomatal conductance and chlorophyll meter readings on newer leaves under waterlogged conditions. Hybrid #5 and Hybrid #8 were more susceptible to waterlogging than other hybrids. Large variability occurred among corn hybrids in response to soil waterlogging durations. Beneficial effects of improved soil conditions after excess water removal from 14-day waterlogged pots were not seen in this experiment, probably due to the short recovery time period between the excess water removal and experiment termination.

Respon Beberapa Genotip Kacang Tunggak (Vigna unguiculata L.) terhadap Cekaman Salinitas

Salinity stress in plants still an important problem in agriculture throughout the world. Salinity makes plants unable to grow and produce well. Cowpea is one of the legume plants that is tolerant of drought and acidity so that it is prospectively developed on land such as dry land and acid soils. The purpose of this study was to determine cowpea genotypes that showed the most tolerant response to salinity and to know the interaction of genotypes and salinity. The tools used in the study were stationery,shovels,buckets,dipper,rulers,analytical scales,camera, pots, portable EC meters,chlorophyll meters. The materials used in the study were the seeds of ten cowpea genotypes (MLG 17013, MLG 17019,MLG17027,MLG17042,MLG17051,MLG17055,MLG17057,MLG17060,KT-4,KT-5),soil,water,fertilizer,urea,TSPfertilizer,KCL fertilizer, manure, NaCl and labels. This study using slit plot design with 3 replications. The mainplot is EC soil at 4 dS/m and 8 dS/m and nonstress. The subplot is 10 genotypes of cowpea. The study was carried out in a greenhouse of the Various Peanut and Tuberculosis Research Institute,Malang Regency,East Java. The research was conducted from March to June 2018. The results of the study were that salinity affected the decrease in germination percentage,plant height, number of branches, chlorophyll index,weight of pod/plant, number of pods/plants,length of pods/plants, weight of 100 seeds,weight of planting seeds,age of flowering and age of harvesting. The conclusions from the study were that the 3 most tolerant genotypes based on stress tolerance index (ITC) and based on scoring of cowpea plants showed tolerance from somewhat tolerant to sensitive.

Development of SPAD value-based linear models for non-destructive estimation of photosynthetic pigments in wheat (Triticum aestivum L.)

Chlorophyll content in leaf which can be measured and expressed as SPAD values, is a good indicator of plant health. The present study aimed to develop linear models for studying relationship between SPAD values and spectrophotometrically determined chlorophylls and carotenoid contents in leaves of 468 wheat genotypes. The SPAD values were taken in the flag leaves at heading stage. Chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (total Chl) and total carotenoids (total Car) contents were assessed using dimethyl sulfoxide (DMSO) extraction method. To estimate photosynthetic pigment content in leaves, SPAD value-based linear models were developed and Chla (Chlb = 0.0690 x SPAD Value - 1.082), Chla (Chlb = 0.021 x SPAD Value 0.396), total Chl (Total chlorophyll = 0.090 x SPAD Value - 1.477) and total carotenoids (Total Carotenoids = 0.013 x SPAD Value 0.074) were estimated. The present study reports development of linear model for quantification of the photosynthetic pigment content in wheat leaves using chlorophyll meter.

Assessment of salt tolerance and analysis of the salt tolerance gene Ncl in Indonesian soybean germplasm

AbstractSoybean [Glycine max (L.) Merr.] is one of the most important legume crops in the world. However, soybean grain yield is extensively affected by environmental stresses such as soil salinity. In this study, we evaluated the germplasm of 51 Indonesian soybean accessions for salt tolerance to identify salt-tolerant germplasms for possible use in breeding for soybean salt tolerance. Based on experiments under hydroponic conditions, adding 100 mM of NaCl to a 1/2 concentration of Hoagland and Arnon solution, several Indonesian soybean germplasms, such as Java 7, Seputih Raman, Tambora, Ringgit (JP 30217), Sinyonya (early) and Sinyonya (late) were identified as salt-tolerant in terms of salt tolerance rate (STR) and leaf chlorophyll content (SPAD value) taken with the Konica Minolta SPAD-502 chlorophyll meter. The selected salt-tolerant germplasms were further evaluated under soil medium cultivation in pots irrigated with 100 mM NaCl for around 5 weeks. The six selected soybean germplasms again showed higher salt tolerance in terms of SPAD, STR and shoot dry weight. Expression analysis of the salt tolerance gene Ncl revealed a significant positive correlation between Ncl expression and salt tolerance, suggesting that Ncl is essential for salt tolerance in the Indonesian soybean germplasms we tested. The salt-tolerant Indonesian soybean germplasms identified in this study could be used in local soybean breeding practices for the improvement of salt tolerance.

Establishing indicator leaf and its threshold values for need based nitrogen management using chlorophyll meter and leaf color chart in Bt cotton

Over application of fertilizer N to cotton is not only a potential threat to environment but also leads to increased costs of cultivation. The study aimed to establish the indicator leaf and its critical greenness for in-season management of fertilizer nitrogen (N) in Bt cotton using chlorophyll (SPAD) meter and leaf color chart (LCC). The response of three varieties and N treatments viz. 0, 30, 60, 90,120, 150 and 180 kg N ha−1 applied in two splits {(50% at thinning and 50% at first flowering) and three splits (50% at thinning, 25% at first flowering and 25% at boll formation)} was studied through split plot design. SPAD values and LCC scores of first, second, third and fourth fully opened leaves from the top of the main stem was recorded at first flowering and boll formation. The physiological efficiency and harvest index was highest for 90 Kg N ha−1 applied in two splits. Beyond 120 kg N ha−1, the N use efficiency parameters were higher for the N treatments applied in three split compared to the respective two split N treatments. The fourth leaf from the top in terms of SPAD values and LCC scores correlated best with N concentration compared to other leaves at all growth stages. The calculated critical SPAD values for the fourth leaf were 45 and 41 at first flowering and boll formation, respectively. Critical score of fourth leaf was 4.1 and 4, respectively at first flowering and boll formation, respectively. It is suggested that color of the fourth leaf from the top of Bt cotton can well indicate N supply from the soil and can help in need based N management.

Monitoring Wheat (Triticum aestivum L.) Leaf Nitrogen using Diagnostic Tools for Fertilizer Nitrogen Management

A field experiment was conducted to evaluate the leaf colour chart (LCC) and chlorophyll meter (SPAD and fieldscout chlorophyll meter (FSCM)) for developing site specific nitrogen (N) management strategy in wheat (Triticum aestivum L.). Four levels of fertilizer N (0, 70, 140 and 210 kg ha−1) were used to determine the growth stage specific optimum LCC, SPAD and FSCM chlorophyll meter values for achieving economic optimum grain yield. A positive and significant (R2 = 0.93–0.97, p<0.01) quadratic response between N application levels and wheat grain yield was observed. Economic optimum grain yield of 4.68 t ha−1 (first year) and 4.57 t ha−1 (second year) corresponding to economic optimum dose of 141 and 144 kg N ha−1, respectively were observed using quadratic response function. Nitrogen concentration in fully expanded youngest leaf correlated significantly (p<0.01) and positively with LCC score (r = 0.89), SPAD value (r = 0.94), FSCM value (r = 0.68) and total chlorophyll concentration (r = 0.91). Two chlorophyll meters used in the study were calibrated with a significant (p<0.01) linear response as ‘FSCM value = 11.3×SPAD value-221.5’ (R2 = 0.60). The LCC score, SPAD and FSCM values observed at maximum tillering, booting and flowering stages were highly and significantly correlated with wheat grain yield. The optimum LCC score, SPAD values, FSCM values, leaf chlorophyll and N concentration at maximum tillering (most important crop growth stage for N management) to fetch economic optimum grain yield were found to be 4.5, 45, 295, 2.47 mg g−1 and 2.74%, respectively. Growth stage specific optimum and critical values of the above mentioned leaf N indicators for achieving economic optimum and critical grain yield of wheat crop were developed in the present investigation.

Critical Sulfur Dilution Curve and Sulfur Nutrition Index in Maize

Core Ideas Critical S dilution curve was established for maize: S concentration = 2.13 × biomass−0.23. The S nutrition index successfully diagnosed S status at early crop stages (∼V6). Sulfur concentration and chlorophyll meter reading, both in the upper leaf, were good predictors of the S nutrition index. Sulfur (S) deficiency can severely limit maize (Zea mays L.) yield. This deficiency could be predicted by quantifying the S concentration (SC) in the shoot biomass (BM) and by calculating the S nutrition index (SNI = observed SC/critical SC). However, as shoot SC determination is laborious, alternative S diagnostic methods should be developed in maize. Thus, the objectives of our study were to: (i) determine and validate a critical S dilution curve, (ii) quantify the critical SNI, and (iii) explore the use of SC and chlorophyll meter reading (CMR), both determined in the uppermost developed leaf at vegetative growth stages, to predict SNI and for diagnosing S status in maize. Six field studies evaluating fertilizer S rates were executed, collecting maize shoot and uppermost developed leaf samples and determining Sc, CMR, yield, and SNI parameters. The main outcomes from our study were: (i) a maize critical S dilution curve was fitted (SC = 2.13BM−0.23) and validated with an independent dataset; (ii) a critical SNI threshold of 0.79 adequately diagnosed S status at ∼V6 stage; (iii) at V6, SNI was linearly related to SC (R2 = 0.65) and CMR (R2 = 0.85). As a result, a threshold value of 2.0 g S kg−1 for SC, 47.5 units for CMR, and 0.94 units for relative CMR can be used to successfully diagnose S deficiencies at early vegetative (∼V6) maize stages. Future studies testing S diagnostic tools for maize should be performed in environments with severe S deficiency and nutrient co‐limitations.