Chlorophyll Meter Research Articles

Deep Learning for Non-Invasive Diagnosis of Nutrient Deficiencies in Sugar Beet Using RGB Images.

In order to enable timely actions to prevent major losses of crops caused by lack of nutrients and, hence, increase the potential yield throughout the growing season while at the same time prevent excess fertilization with detrimental environmental consequences, early, non-invasive, and on-site detection of nutrient deficiency is required. Current non-invasive methods for assessing the nutrient status of crops deal in most cases with nitrogen (N) deficiency only and optical sensors to diagnose N deficiency, such as chlorophyll meters or canopy reflectance sensors, do not monitor N, but instead measure changes in leaf spectral properties that may or may not be caused by N deficiency. In this work, we study how well nutrient deficiency symptoms can be recognized in RGB images of sugar beets. To this end, we collected the Deep Nutrient Deficiency for Sugar Beet (DND-SB) dataset, which contains 5648 images of sugar beets growing on a long-term fertilizer experiment with nutrient deficiency plots comprising N, phosphorous (P), and potassium (K) deficiency, as well as the omission of liming (Ca), full fertilization, and no fertilization at all. We use the dataset to analyse the performance of five convolutional neural networks for recognizing nutrient deficiency symptoms and discuss their limitations.

Nitrogen management practices for improving yield and nitrogen use efficiency in rice (Oryza sativa)

A field experiment was conducted on rice (Oryza sativa L.) during kharif season of 2017 at Crop Research Centre of Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut (U P) to assess the nitrogen (N) use efficiency and performance of rice under different nitrogen management practice. Management practices included N levels with modified application through leaf colour chart (LCC) and chlorophyll meter (SPAD). The study shows that treatment T6 (LCC (50 kg N/ha) with basal N @50 kg/ha)gave highest yield and N-use efficiency which were comparable to T9 (SPAD (67 kg N/ha) with basal N @33 kg/ha). The total biological yield (grain + straw) of rice was significantly higher in T6 (114.4 q/ha) as compared to control (66.9 q/ha). The SPAD and LCC-treated plot showed higher N-use efficiency in rice over fixed-scheduling N treatments. Highest N content(1.88% (grain) and 0.76% (straw)) and uptake (128.14 kg/ha) was recorded in T6 treatmentin all stages (tillering, PI and harvest) which was comparable with T8 and T9 treatment.

English

Increased production of sugar beet under rainfed conditions on saline–sodic soils in the Iranian areas highlights the importance of salt tolerant varieties. Screening of genotypes for salinity tolerance is difficult in field due to heterogeneity of physical and chemical properties of soil. In order to evaluate the salinity tolerance of 21 sugar beet monogerm O-types lines, a pot experiment was conducted using a split plot design. The evaluation of plants was performed using 11 morphological and physiological traits at vegetative growth stage under severe salt stress (∼16 dS m-1) and control (0.3 dS m-1) for 8 weeks. Salinity stress significantly reduced weight related traits. The response of genotypes for total weights and stem weights was very similar under both conditions. But, ranking of O-type lines for root weights under normal and stress condition was different. Indeed, there was high significant genotype × treat interaction for two these traits. Cluster analysis by using STI index of all traits allowed the identification of tolerant, moderate tolerant and sensitive genotypes toward salinity. The four salt-tolerant genotypes, O-type 9669, O-type 1609, O-type 463-2, and O-type 463-5 identified in this study, could be used in the development of salt-tolerant sugar beet varieties. In the second part of this study in order to assess a simple, rapid, and nondestructive method to estimate chlorophyll content, the chlorophyll meter (SPAD 502) readings were recorded and the relation was determined. Regression analysis indicated that there was a significant linear regression between chlorophyll content and chlorophyll meter and about 74% of changes in chlorophyll meter based on chlorophyll content were predicted.   Key words: Sugar beet (beta vulgaris L.), salt tolerant index, screening, hybrid.

Use of Non-Destructive Measurements to Identify Cucurbit Species (Cucurbita maxima and Cucurbita moschata) Tolerant to Waterlogged Conditions.

Limited information is available regarding the physiology of squash plants grown under waterlogging stress. The objectives of this study were to investigate the growth and physiological performances of three cucurbit species, Cucurbita maxima cultivar (cv.) OK-101 (OK) and Cucurbita moschata cv. Early Price (EP) and Strong Man (SM), in response to waterlogging conditions, and to develop a precise, integrated, and quantitative non-destructive measurement of squash genotypes under stress. All tested plants were grown in a growth chamber under optimal irrigation and growth conditions for a month, and the pot plants were then subjected to non-waterlogging (control) and waterlogging treatments for periods of 1, 3, 7, and 13 days (d), followed by a 3-d post-waterlogging recovery period after water drainage. Plants with phenotypes, such as fresh weight (FW), dry weight (DW), and dry matter (DM) of shoots and roots, and various physiological systems, including relative water content (RWC), soil and plant analysis development (SPAD) chlorophyll meter, ratio of variable/maximal fluorescence (Fv/Fm), quantum photosynthetic yield (YII), normalized difference vegetation index (NDVI), and photochemical reflectance index (PRI) values, responded differently to waterlogging stress in accordance with the duration of the stress period and subsequent recovery period. When plants were treated with stress for 13 d, all plants exhibited harmful effects to their leaves compared with the control, but EP squash grew better than SM and OK squashes and exhibited stronger tolerance to waterlogging and showed less injury. Changes in the fresh weight, dry weight, and dry matter of shoots and roots indicated that OK plants suffered more severely than EP plants at the 3-d drainage period. The values of RWC, SPAD, Fv/Fm, YII, NDVI, and PRI in both SM and OK plants remarkably decreased at waterlogging at the 13-d time point compared with controls under identical time periods. However, the increased levels of SPAD, Fv/Fm, YII, NDVI, and PRI observed on 7 d or 13 d of waterlogging afforded the EP plant leaf with improved waterlogged tolerance. Significant and positive correlations were observed among NDVI and PRI with SPAD, Fv/Fm, and YII, indicating that these photosynthetic indices can be useful for developing non-destructive estimations of chlorophyll content in squashes when screening for waterlogging-tolerant plants, for establishing development practices for their cultivation in fields, and for enhanced cultivation during waterlogging in frequently flooded areas.

Influence of nutrient management and moisture conservation practices on Growth and development of organic baby corn (Zea mays L.) in Assam

Background: Baby corn is the small (6-7 cm long) and young unfertilized corn ear harvested at the stage of silk emergence (i.e. within 2 - 3 days of silk emergence). In the present scenario, the use of chemical fertilizers may help in achieving maximum yield of baby corn but they pose serious health hazards and it is a big threat to the sustainability of agriculture. Assam has tremendous potential to grow crops organically and emerge as the main supplier of organic products in the world’s organic market. In Assam, baby corn is rather a new introduction, so efforts are required to standardize the its cultivation. Therefore, the need was felt to standardize organic production technology for baby corn through supplementation of the nutrient requirement through organic manures and biofertilizers. Moisture conservation in agriculture is also very essential in this dynamic climate change. Methods: A field experiment was conducted at Assam Agricultural University, Jorhat during the year 2016-17. The experiment consisted of two different factors i.e. nutrient management viz., control, enriched compost 2.5 t ha-1, vermicompost 2 t ha-1 incubated with bio-fertilizers, poultry manure 2 t ha-1 incubated with bio-fertilizers, FYM 2.5 t ha-1 incubated with bio-fertilizers and FYM 2.5 t ha-1+lime+ash (1000:10:1) and moisture conservation i.e. no mulch and mulch with paddy straw @ 2 t ha-1). Plant height at harvest, number of leaves plant-1 at harvest and dry matter production (g plant-1), LAI, LAD at 30 day days interval was recorded. Reading on chlorophyll content was taken by SPAD- 502 chlorophyll meter at 45 DAS and 90 DAS. Cob yield was recorded from the net plot area and expressed in t ha-1. Result: Application of enriched compost 2.5 t ha-1 in baby corn produced highest growth characters like plant height, number of leaves plant-1, dry matter production, leaf area index, leaf area duration, chlorophyll content, cob yield with husk (8.165 t ha-1) followed by FYM 2.5 t ha-1+lime+ash (6.495 t ha-1). Mulching with paddy straw 2 t ha-1 recorded the higher cob yield (6.172 t ha-1) over no mulch condition (5.431 t ha-1).

Nondestructive estimation of bok choy nitrogen status with an active canopy sensor in comparison to a chlorophyll meter

Precise estimation of vegetable nitrogen (N) status is critical in optimizing N fertilization management. However, nondestructive and accurate N diagnostic methods for vegetables are relatively scarce. In our two-year field experiment, we evaluated whether an active canopy sensor (GreenSeeker) could be used to nondestructively predict N status of bok choy (Brassica rapa subsp. chinensis) compared with a chlorophyll meter. Results showed that the normalized difference vegetation index (NDVI) and ratio vegetation index (RVI) generated by the active canopy sensor were well correlated with the aboveground biomass (AGB) (r = 0.698–0.967), plant N uptake (PNU) (r = 0.642–0.951), and root to shoot ratio (RTS) (r = −0.426 to −0.845). Compared with the chlorophyll meter, the active canopy sensor displayed much higher accuracy (5.0%–177.4% higher) in predicting AGB and PNU and equal or slightly worse (0.54–1.82 times that of the chlorophyll meter) for RTS. The sensor-based NDVI model performed equally well in estimating AGB (R2 = 0.63) and PNU (R2 = 0.61), but the meter-based model predicted RTS better (R2 = 0.50). Inclusion of the days after transplanting (DAT) significantly improved the accuracy of sensor-based AGB (19.0%–56.7% higher) and PNU (24.6%–84.6% higher) estimation models. These findings suggest that the active canopy sensor has a great potential for nondestructively estimating N status of bok choy accurately and thus for better N recommendations, especially with inclusion of DAT, and could be applied to more vegetables with some verification.

A Search for Suitable Growing Environment for Sesame Production in Nigeria

The economic relevance of farm management practices to the production of sesame crops in Nigeria includes preventing and combatting food crises, actualization and realization of national food security as well as enhancing gross domestic product. This research seeks to examine the edaphology of some soil types in relation to the productivity of sesame crops in Nigeria. The experiment was conducted in statistical farm of Hussaini Adamu Federal Polytechnic, Kazaure, Jigawa State, Nigeria during 2019 growing season. The experimental design was Completely Randomized Design with one hundred replications. There were three types of soils investigated; Clay, Sandy, and Loamy were compared with one another. The soils were made free of any nuisance factors effects. The chlorophyll content of the plants was read using Konica Minolta chlorophyll meter SPAD-502 plus, and the data analyzed using one-way ANOVA and the Statistical Package for Social Sciences (SPSS) version 20. The result of the analysis indicates a higher significant effect of Sandy soil (M = 11.20, SD = 2.37) on the yield of sesame crops in this region as compared to the effects of the Clay (M = 3.60, SD = 0.89), and Loamy (M = 6.86, SD = 3.39) soils. The overall ANOVA test indicates that growing environment does have effect on sesame production, F (2, 27) = 6.70, p = 0.00. However, the result indicates insignificant chlorophyll mean difference between Clay and Loamy soils. It is therefore evident from these results and the reviewed literatures that the suitable growing environment for sesame production in Nigeria is fertile Sandy soil that is deep, light textured, well-drained and that is exposed to an average temperature of 25oC to 37oC. The crop is also tolerant to draught, but not at the germination and seedling stages, water logging, and excessive rain fall while it requires 90–120 frost-free days to achieve optimal yields in cold regions. The challenges which stand in the way of increasing the productivity and quality of sesame crops need to be overcome. As with other crops, which is a major export crop in many countries, these crops should be given more research attention.

Leaf morpho-anatomical diversity analysis in mandarin (Citrus reticulata Blanco) genotypes using scanning electron microscopy

The leaf morpho-anatomical studies were performed to assess the genetic divergence in mandarin (Citrus reticulata Blanco) germplasm and for obtaining a strong descriptor (s) to help in easy identification among closely related genotypes during the year 2017–18. Morphological traits of mature leaves of mandarin accessions were observed on basis of citrus descriptors. Leaf chlorophyll content was determined with a SPAD-502 chlorophyll meter under field conditions. Morpho-anatomical attributes were analysed by optical and scanning electron microscopes.In our study, mandarin genotypes exhibited variation with respect to leaf anatomy and photosynthetic traits despite having same pedigree. PAU Kinnow-1, a mutant of Kinnow was clustered away from its parent probably due to multiple variations arising in the parent as PAU Kinnow-1 was developed through gamma irradiation treatment. Therefore, it is suggested from our findings that leaf characters may vary among apparently close genotype such as Kinnow and PAU Kinnow-1. Likewise, genotypes Kara and King exhibited disparate leaf morpho-anatomy characters though King is a parent of Kara. Similarly, the genotypes like Kara, King, Wilking, and Willow Leaf could be differentiated based on their leaf traits. Genotypes namely Fair Child and Sunburst formed clear distinct clusters on basis of the diverse morpho-anatomical attributes. The dendrogram clearly differentiated the genotypes irrespective of their pedigree and geographical area of origin. In FCA plot, mandarin genotypic differentiation was the main structural component defining the first axis (57.11% of total diversity) whereas the inertia for the second axis was 17.54 per cent. The higher genotypic and phenotypic coefficient of variations were associated with higher heritability for petiole wing width, the number of open stomata and palisade parenchyma tissue length traits that may be more effective during selection.

Spectral response of chlorophyll content during leaf senescence in European beech trees

Leaf chlorophyll content declines in response to environmental stressors and during natural senescence periods. Assessments of forest health and vulnerability to stressors require repeated measurements of forest health to quantify declines in chlorophyll content and identify shifts in the timing of key phenological events. Although remote sensing is ideal for making reliable and repeated forest health measurements to assess forest response to environmental change over large areas, reliable warning systems for monitoring plant health are lacking. To facilitate the estimation of chlorophyll content from remotely sensed data, we define the relationships between leaf chlorophyll content and spectral indices in European beech trees (Fagus sylvatica). We show that hand-held chlorophyll meters can be calibrated to leaf chlorophyll content providing a non-destructive method for rapid assessment of leaf chlorophyll content in the field. Spectral indices based on the red edge spectral region have the strongest relationship with leaf chlorophyll content (mND705 R2 = 0.95, RMSE = 4.70; mSR705 R2 = 0.95, RMSE = 4.71) but are unable to discriminate between photosynthetically active leaves and inactive leaves. Alternative spectral indices can discriminate effectively between photosynthetically active and inactive leaves but are less well suited to defining declines in chlorophyll content. These findings reveal key research needs for improving the use of remote sensing data for forest health assessments.

Evaluation of SPAD meter values for estimating rice nitrogen status

A field experiment with six rice genotypes were conducted to relate SPAD chlorophyll meter readings to variables reflecting nitrogen (N) status at different developmental stages. These indices can be used to predict foliar N concentration in rice without significant interferences of rice genotypes and growth stages. Dependence of nitrogen content from mineral element in the soil was established at the same time. Investigations were guided on six fertilization variants (N1: 0; N2: 40; N3: 60; N4: 80; N5: 100; N6:150 kg N ha-1). The results indicated that nitrogen content influenced from presence and ratio mineral elements in the soil. SPAD value increased with increase in N level and growth stages upto FL stage. However no clear trend is observed among cultivars, since ratio of SPAD readings to predict rice N status is not influenced by rice genotypes and is based on the principle of N translocation from old to young leaves when the plant is nitrogen deficient.

Evaluation of a SPAD-502 Plus Chlorophyll Meter to Estimate Chlorophyll Content in Leaves with Interveinal Chlorosis

The portable chlorophyll (Chl) meter SPAD-502 Plus (Konica Minolta Optics, Japan) is one of the most commonly used diagnostic tools for rapid and nondestructive estimation of Chl content in leaves of crops and tree species. The aim of this work was to evaluate the performance of a SPAD-502 Plus to estimate the content of Chl a, Chl b, and Chl (a + b) in Solanum lycopersicum L. leaves with mottled, interveinal chlorosis induced by continuous lighting. The results have shown positive correlation between the Chl content index (CCI) and contents per unit leaf area (mg/cm2) of Chl a (R2 = 0.89), Chl b (R2 = 0.79), Chl (a + b) (R2 = 0.90) and between CCI and content per unit leaf mass (mg/g) of Chl a (R2 = 0.88), Chl b (R2 = 0.78), Chl (a + b) (R2 = 0.89), suggesting that the portable Chl meter SPAD-502 Plus can be an effective tool for nondestructive estimation of Chl content in leaves with mottled, interveinal chlorosis. The accuracy of SPAD-502 Plus Chl meter tends to be higher for estimating Chl content per unit leaf area. Non-linear regressions were successfully used for estimating Chl content from SPAD measurements.

Stress Distribution Analysis on Hyperspectral Corn Leaf Images for Improved Phenotyping Quality.

High-throughput imaging technologies have been developing rapidly for agricultural plant phenotyping purposes. With most of the current crop plant image processing algorithms, the plant canopy pixels are segmented from the images, and the averaged spectrum across the whole canopy is calculated in order to predict the plant’s physiological features. However, the nutrients and stress levels vary significantly across the canopy. For example, it is common to have several times of difference among Soil Plant Analysis Development (SPAD) chlorophyll meter readings of chlorophyll content at different positions on the same leaf. The current plant image processing algorithms cannot provide satisfactory plant measurement quality, as the averaged color cannot characterize the different leaf parts. Meanwhile, the nutrients and stress distribution patterns contain unique features which might provide valuable signals for phenotyping. There is great potential to develop a finer level of image processing algorithm which analyzes the nutrients and stress distributions across the leaf for improved quality of phenotyping measurements. In this paper, a new leaf image processing algorithm based on Random Forest and leaf region rescaling was developed in order to analyze the distribution patterns on the corn leaf. The normalized difference vegetation index (NDVI) was used as an example to demonstrate the improvements of the new algorithm in differentiating between different nitrogen stress levels. With the Random Forest method integrated into the algorithm, the distribution patterns along the corn leaf’s mid-rib direction were successfully modeled and utilized for improved phenotyping quality. The algorithm was tested in a field corn plant phenotyping assay with different genotypes and nitrogen treatments. Compared with the traditional image processing algorithms which average the NDVI (for example) throughout the whole leaf, the new algorithm more clearly differentiates the leaves from different nitrogen treatments and genotypes. We expect that, besides NDVI, the new distribution analysis algorithm could improve the quality of other plant feature measurements in similar ways.

Investigation of Salt Stress in Rosemary (Rosmarinus officinalis L.) with the Remote Sensing Technique

Abstract: In the present work, the effect of different salt concentrations on growth and quality of rosemary (Rosmarinus officinalis L.) was investigated using ground-based remote sensing techniques under greenhouse conditions in 2018. The experiment was carried out in a randomized complete block design with three replications and lasted 8 weeks in total. Spectroradiometer measurements were performed on the leaves of rosemary plants to monitor changes in spectral signatures due to salt stress. Spectrophotometer and chlorophyll meter measurements were also taken from the leaves of the plants to investigate the reactions to salt stress at the end of 4th and 8th weeks simultaneously with all other measurements. According to the obtained data, there was a significant difference in the chlorophyll, brightness and colour values of the leaves in response to salt stress, and a difference was observed in the reflective values of the plants in the spectral measurements taken at 4th and 8th weeks. The region with the biggest difference between reflectance values was near-infrared among different salt concentrations applied plants. In the 4th week, the most vivid color (intense green) was obtained in the S3 and S4 applications, (19.80 and 19.40, respectively). However, as the stress application time and the applied salt rate increased, small changes in plant color occurred. Besides, it was concluded that salt treatment increased the NDVI (Normalized Difference Vegetation Index) values of the plants.

Optical Sensing and Arbuscular Mycorrhizal Fungi for Improving Fertilizer Nitrogen and Phosphorus Use Efficiencies in Maize

Application of fertilizer nitrogen (N) and phosphorus (P) in excess of crop requirement causes nutritional imbalances in soil along with economic and ecological losses. The optical sensors (leaf color chart, chlorophyll meter, and GreenSeeker) help guide real-time N topdressing decisions and arbuscular mycorrhizal fungi (AMF) further improve nutrient uptake from soil. A four-year field study was conducted to improve N- and P-use efficiencies in maize using different optical sensing tools and coating seeds with AMF. The AMF seed coating improved mycorrhizal colonization in soil. Higher mycorrhization was observed in no-P treatment; however, P fertilization and mycorrhiza inoculation diminish the effect as growth progressed from 30 to 60 days after sowing. The mycorrhizal inoculation increased grain yield by 17.1% in no-N treatment; however, the response diminishes with N fertilization. The optical sensing–based N management sustained grain yield, total N uptake, and root and plant dry weight equivalent to the soil test–based fertilizer N recommendation with the less use of 30 kg N ha−1. The respective improvement in agronomic and recovery efficiencies of applied fertilizer N up to 38.6 and 34.9% highlights the potential of optical sensing tools and the inability of soil test–based N recommendation for precision N management. Mitigated greenhouse and nitrous oxide emissions respectively by 30.7% and 29.7% further underline the prominence of replacing soil test N recommendations with optical sensing–guided N top-dressings. Sufficient inherent soil P restricts the AMF benefits in improving P-use efficiencies in maize.

ADAPTATION POSSIBILITIES OF INTRODUCED PLANTS OF VARIOUS ORIGIN IN CONDITIONS OF BOTANICAL GARDEN AT SURGUT STATE UNIVERSITY

The botanical garden in Surgut is the northernmost in Western Siberia and one of the northernmost botanical gardens in Russia. It is the major point for promoting new agricultural and biological technologies to the Far North. Currently, the collection of ornamental plants of the Surgut botanical garden comprises about 200 species and varieties of herbaceous plants belonging to 60 genera and 32 families, and about 210 species, forms and cultivars of woody plants. The research objective is to study the adaptation mechanisms of some ornamental plants from the collection of the botanical garden using the up-to-date portable flavonoid and chlorophyll meter DUALEX. The research objects are five species of herbaceous plants of genus Iris L. - Iris hungarica Waldst. &Kit., Iris variegata L., Iris sibirica L., Iris glaucescens Bunge, Iris sulfurea C. Koch. and eight species of woody plants of genus Acer L. - Acer pseudoplatanus L., Acer rubrum L., Acer trautvetteri Medw., Acer tataricum L., Acer ukurunduense Trautv. & C.A. Mey., Acer spicatum Lam., Acer mandshuricum Maxim., Acer ginnala Maxim. The range of nitrogen balance (Nbi) in herbaceous plants varied from 32.2 to 39.7, and the chlorophyll content was from 48.1 to 58.6 mg/cm2. In woody plants, the content of chlorophyll (Chl) ranged from 23.9 mg/cm2 ( Acer spicatum ) to 31.3 mg/cm2 ( Acer rubrum ), i.e. only 1.3 times within the group species growing on one flank. The content of flavanols in woody plants ranged from 1.3 mg/cm2 in Acer mandshuricum to 1.9 mg/cm2 in Acer ukurunduense . The maximum values of Nbi, Chl indices for Iris hungarica and Acer pseudoplatanus are an adaptive reaction to growing conditions and indicate the formation of plantprotective functions. The pigment content of leaves in ornamental plants indicates their satisfactory physiological state, as evidenced by a slight variation in biochemical parameters among the tested groups of ornamental plants.

Performance evaluation of low-cost IoT based chlorophyll meter

Nutrient deficiencies in plants can be identified using a chlorophyll meter. However, current chlorophyll meters are still expensive and have many disadvantages. In this paper, a low-cost IoT-based chlorophyll meter has been developed. The performance of a low-cost IoT-based chlorophyll meter has been compared with the performance of a spectrophotometer (SP-3000nano) and a commercial chlorophyll meter (SPAD-502). A low-cost IoT-based chlorophyll meter has been functioning properly which is able to measure the chlorophyll content of plants in the field, get positions based on GPS satellites, store data in a memory module, and send data to the service system platform. The test results showed the coefficient of determination (R2) between SPAD-502 values and low-cost IoT-based chlorophyll meter values is 0.9705, this shows a significant correlation. An IoT-based chlorophyll meter can be used as a cheap alternative to the SPAD-502 chlorophyll meter.

Precision nitrogen management improves grain yield, nitrogen use efficiency and reduces nitrous oxide emission from soil in spring maize

Precision nitrogen (N) management sustains high grain yield with low N optimum dose and thus may help reduce the escape of reactive nitrogen from soils to the atmosphere. Two-year field studies were conducted at two locations in sub-tropical and sub-humid climate in Indo-Gangetic plains of South Asia with the objectives to establish precision N management technology for fertilizer N topdressings in spring maize while quantifying nitrous oxide emission from soil. A significant positive correlation of 0.64 to 0.90 between LCC (Leaf color chart) scores and leaf N concentrations at different growth stages indicated that LCC scores can successfully be used as an index of leaf N content for precision N management in spring maize. A close linear relationship (R2 = 0.75) between chlorophyll meter (SPAD) readings and LCC score showed that like SPAD meter, LCC score can reliably consider leaf greenness as an indicator of leaf N concentration. Cate-Nelson plot of LCC scores verses relative grain yield expressed LCC score 5 as the threshold for sustaining potential yield. Fertilizer N topdressings based on threshold leaf greenness of LCC 5 produced 6 to 10 percent higher grain yield with improved recovery and agronomic efficiencies in comparison to soil-test based N recommendations. Nitrous oxide emission estimated using Cool Farm Tool (CFT); an empirical model specified that application of 120 kg N ha−1 at LCC 5 down turned nitrous oxide emission by 8.0 percent compared to soil test-based N management.

Spectral Reflectance Characteristics and Chlorophyll Content Estimation Model of Quercus aquifolioides Leaves at Different Altitudes in Sejila Mountain

Quercus aquifolioides is one of the most representative broad-leaved plants in Qinghai-Tibet Plateau with important ecological status. So far, understanding how to quickly estimate the chlorophyll content of plants in plateau areas is still an urgent problem. Field Spec 3 spectrometer was used to measure hyperspectral reflectance data of Quercus aquifolioides leaves at different altitudes, and CCI (chlorophyll relative content) of corresponding leaves was measured by a chlorophyll meter. The correlation and univariate linear fitting analysis techniques were used to establish their relationship models. The results showed that: (1) Chlorophyll relative content of Quercus aquifolioides, under different altitude gradients, were significantly different. From 2905 m to 3500 m, chlorophyll relative content increased first and then decreased. Altitude 3300 m was the most suitable growth area. (2) In 350~550 nm, the spectral reflectance was 3500 m > 3300 m > 2905 m. In 750~1100 nm, the spectral reflectivity was 2905 m > 3500 m > 3300 m. (3) There were 4 main reflection peaks and 5 main absorption valleys in the leaf surface spectral reflection curve. While, 750~1400 nm was the sensitive range of leaf spectral response of Quercus aquifolioides. (4) The red edge position and red valley position moved to short wave direction with the increase of altitude, while the yellow edge position and green peak position moved to long wave direction first and then to short wave direction. (5) The correlation curve between the original spectrum and the CCI value was the best between the wavelengths 509~650 nm. The correlation between the first derivative spectrum and CCI value was the best and most stable at 450~500 nm. The green peak reflectance was most sensitive to the relative chlorophyll content of Quercus aquifolioides. The estimation model R2 of green peak reflectance was the highest (y = 206.98e−10.85x, R2 = 0.8523), and the prediction accuracy was 95.85%. The research results can provide some technical and theoretical support for the protection of natural Quercus aquifolioides forests in Tibet.

SPAD-502 and atLEAF CHL PLUS values provide good estimation of the chlorophyll content for Hevea brasiliensis Müll. Arg. Leaves

Measurement of chlorophyll content using destructive methods is not efficient due to a large number of samples, cost, and time needed. Estimationof chlorophyll content by nondestructive methods using handheld chlorophyll meter may be considered to improve efficiency. This research aimed to determine the formula to convert SPAD-502 and atLEAF CHL PLUS values (relative indicator of chlorophyll content) to estimated (absolute) rubber leaves chlorophyll content. Twenty leaves of rubber plant were measured using SPAD-502 and atLEAF CHL PLUS at the same time to determine SPAD-502 and atLEAF CHL PLUS values. The measured leaves were then collected to determine the chlorophyll content using a standard laboratory procedure. Regression and correlation analyses (among 3 methods) were conducted using SAS v.9 software. The results showed that between SPAD-502 and atLEAF CHL PLUS values were closely correlated, hence both of the devices can substitute each other to estimate rubber leaf chlorophyll content. In addition, the relationship between atLEAF CHL PLUS and SPAD-502 values with actual chlorophyll content of rubber clone SP 217, PB 260, GT1, and all clones (general) were significant with high coefficient of determination (R2) as well as low Root Mean Square Error (RMSE) and Coefficient of Variation (CV). Therefore, by using formula determined in this study, both atLEAF CHL PLUS and SPAD-502 can be suggested for accurate, fast, and non-destructive estimation of chlorophyll content of rubber plant leaf.

Site-specific fertilizer nitrogen management in Bt cotton using chlorophyll meter

AbstractField experiments were conducted to standardize protocols for site-specific fertilizer nitrogen (N) management in Bt cotton using Soil Plant Analysis Development (SPAD) chlorophyll meter. Performance of different SPAD-based site-specific N management scenarios was evaluated vis-à-vis blanket fertilizer N recommendation. The N treatments comprised a no-N (control), four fixed-time and fixed N doses (60, 90, 120, and 150 kg N ha-1) including the recommended dose (150 kg ha-1), and eight fixed-time and adjustable N doses based on critical SPAD readings of 45 and 41 at first flowering and boll formation stages, respectively. The results revealed that by applying 45 or 60 kg N ha-1 at thinning stage of the crop and critical SPAD value-guided dose of 45 or 30 kg N ha-1 at first flowering stage resulted in yields similar to that recorded by applying the recommended dose of 150 kg N ha-1. However, significantly higher N use efficiency as well as 30–40% less total fertilizer N use was recorded with site-specific N management. Applying 30 kg N ha-1 at thinning and SPAD meter-guided 45 kg N ha-1 at first flowering were not enough and required additional SPAD meter-guided 45 kg N ha-1 at boll formation for sustaining yield levels equivalent to those observed by following blanket recommendation but resulted in 20% less fertilizer N application. Our data revealed that SPAD meter-based site-specific N management in Bt cotton results in optimum yield with dynamic adjustment of fertilizer N doses at first flowering and boll formation stages. The total amount of N fertilizer following site-specific management strategies was substantially less than the blanket recommendation of 150 kg N ha-1, but the extent may vary in different fields.