Plant Nitrogen Content Research Articles

Enhancing the Nitrogen Signals of Rice Canopies across Critical Growth Stages through the Integration of Textural and Spectral Information from Unmanned Aerial Vehicle (UAV) Multispectral Imagery

This paper evaluates the potential of integrating textural and spectral information from unmanned aerial vehicle (UAV)-based multispectral imagery for improving the quantification of nitrogen (N) status in rice crops. Vegetation indices (VIs), normalized difference texture indices (NDTIs), and their combination were used to estimate four N nutrition parameters leaf nitrogen concentration (LNC), leaf nitrogen accumulation (LNA), plant nitrogen concentration (PNC), and plant nitrogen accumulation (PNA). Results demonstrated that the normalized difference red-edge index (NDRE) performed best in estimating the N nutrition parameters among all the VI candidates. The optimal texture indices had comparable performance in N nutrition parameters estimation as compared to NDRE. Significant improvement for all N nutrition parameters could be obtained by integrating VIs with NDTIs using multiple linear regression. While tested across years and growth stages, the multivariate models also exhibited satisfactory estimation accuracy. For texture analysis, texture metrics calculated in the direction D3 (perpendicular to the row orientation) are recommended for monitoring row-planted crops. These findings indicate that the addition of textural information derived from UAV multispectral imagery could reduce the effects of background materials and saturation and enhance the N signals of rice canopies for the entire season.

Effect of organic nutrient sources on plant nitrogen, phosphorus and potassium content at different stages of wheat crop

The investigation entitled Effect of Organic Nutrient Sources on Soil Health and Productivity of Wheat under Rice-Wheat System was carried out at the Crop Research Centre of Sardar Vallabhbhai Patel University of Agriculture & Technology, Meerut, (U.P) during Rabi seasons of 2017-18. The experiment consisting seven treatments viz. T1- Control, T2- 10 t ha-1 FYM, T3-10 t ha-1 FYM +Cow urine + Azotobacter, T4- 10 t ha-1 Vermicompost, T5- 10 t ha-1 Vermicompost+ Cow urine + Azotobacter, T6- 7.5 t ha-1 FYM+ Cow urine + Azotobacter, T7- 80% of RDF of nitrogen through vermicompost + 10% through neem cake + Azotobacter was laid out in randomized block design with three replication. Result show that T7 (80% of RDF of nitrogen through vermicompost + 10% through neem cake + Azotobacter) significantly higher plant Nitrogen, Phosphorus and Potassium content at tillering, jointing and at harvesting stage (grains and straw) over the control plot.

Evaluating maize phenotypic variance, heritability, and yield relationships at multiple biological scales across agronomically relevant environments.

A challenge to improve an integrative phenotype, like yield, is the interaction between the broad range of possible molecular and physiological traits that contribute to yield and the multitude of potential environmental conditions in which they are expressed. This study collected data on 31 phenotypic traits, 83 annotated metabolites, and nearly 22,000 transcripts from a set of 57 diverse, commercially relevant maize hybrids across three years in central U.S. Corn Belt environments. Although variability in characteristics created a complex picture of how traits interact produce yield, phenotypic traits and gene expression were more consistent across environments, while metabolite levels showed low repeatability. Phenology traits, such as green leaf number and grain moisture and whole plant nitrogen content showed the most consistent correlation with yield. A machine learning predictive analysis of phenotypic traits revealed that ear traits, phenology, and root traits were most important to predicting yield. Analysis suggested little correlation between biomass traits and yield, suggesting there is more of a sink limitation to yield under the conditions studied here. This work suggests that continued improvement of maize yields requires a strong understanding of baseline variation of plant characteristics across commercially-relevant germplasm to drive strategies for consistently improving yield.

Effect of variety and growth period on NDVI estimation of nitrogen concentration in potato plants

The normalized difference vegetation index (NDVI) is an important parameter to reflect relative chlorophyll content and nitrogen level of crops, but NDVI’s ability to estimate nitrogen nutrition is affected by varieties and growth period. The field experiments using several varieties were conducted in the main potato producing areas at the north foot of Yinshan mountain, Inner Mongolia. From early July to mid-august in 2014 to 2016, the canopy spectral index NDVI was measured by using the pocket active crop sensor GreenSeeker during potato critical growth period. The effects of cultivars and growth stages on NDVI estimation of nitrogen concentration in potato plants were compared. The linear correlation between NDVI and plant nitrogen concentration (PNC) was poor in tuber initiation, but increased in process of growth period. The combination of tuber bulking period and starch accumulation period significantly improved the linear modeling effect of NDVI and PNC. Variety combination reduced the sensitivity of NDVI and increased the discreteness of data, which could be offset by NDVI time series normalization (TNDVI), especially the fitting coefficient of determination ( R 2) of TNDVI and PNC increased from 0.13 to 0.47 in the tuber bulking period. The R 2 of linear estimation model of TNDVI for the combination of tuber initiation, tuber bulking and starch accumulation period was 0.76, which was significantly higher than that of NDVI. Plant-expanded varieties had a more linear fitting trend during tuber bulking and starch accumulation. The growth period and potato varieties had significant effects on NDVI estimation of PNC, and growth period had a greater effect. The established TNDVI spectral index overcame the data differentiation and saturation phenomenon during tuber bulking and starch accumulation caused by variety difference, which provides a theoretical basis and method for the application of NDVI in the diagnosis of nitrogen concentration in potato plants.

Exploring the phytoremediation potential of Cynara cardunculus: a trial on an industrial soil highly contaminated by heavy metals.

Metal uptake capacity and growth patterns of three cardoon cultivars (Sardo, Siciliano, and Spagnolo) were investigated for phytoremediation in a metal-contaminated soil. Metal concentrations after one and two growth rounds were measured in soil and plants by ICP-MS. Potentially and promptly available metal fractions were estimated by EDTA and ammonium nitrate. Plant weight, water and nitrogen content, and life span were considered as growth parameters. After the first growth cycle, a significant accumulation of all elements was observed in roots, whereas only Cd, Cu, Fe, Pb, and Sb were significantly translocated to the shoots. After the second growth cycle, a further significant increase, especially in roots, was observed in all cultivars and for all elements considered. High percentages of the potentially available fraction were found for As, Cd, Cu, Pb, and Sb. Metal concentrations in plants were far higher than the promptly available fraction, indicating an increase of metal bioavailability during culture rounds. A severe decrease of weight and life span was observed in Sardo and Siciliano grown on polluted soil, along with an increase in N content. The cultivar Spagnolo, harmonizing a high ability of metal uptake and tolerance, proved the most efficient cultivar in metal phytoremediation.

Возможность определения содержания азота в растениях озимой пшеницы в фазе колошения с применением данных дистанционного зондирования

The study examined the possibility of using remote sensing Data (RED, NIR, NDVI) for monitoring winter wheat crops in production conditions for nitrogen content in plants. This work is divided into two stages: 1) analysis of the correlation between NDVI indicators and nitrogen content on production crops of the North-Caucasian FNAC; 2) comparative analysis of the correlation between nitrogen content and remote sensing data in the conditions of the “Rodina” agricultural enterprise in the Shpakovsky district of the Stavropol territory. Selection of plant samples (sheaf material) was carried out according to the generally accepted method. Repeatability — 4-fold. The chemical composition of plant organs was determined using the method of V.T. Kurkaev and co-authors, and the chlorophyll content was determined by Y.I. Milaeva and N.P. Primak. We used the earth remote sensing data provided by the Terra satellite and obtained by the Modis scanning Spectroradiometer. At the first stage, the relationships between the nitrogen content in winter wheat plants and the values of the normalized difference vegetation index (NDVI) were studied. At the early stages of growth and development of winter wheat plants, high correlation coefficients between these indicators were obtained. Thus, the correlation coefficient on average for the fields in 2012 was equal to -0.89, and in 2013 and 2014 — -0.82. In later phases of growth and development of winter wheat plants, this relationship was not observed. At the second stage, it was found that it is advisable to use the red reflection index to assess the nitrogen content at the local level (a separate agricultural enterprise) in the earing phase. In this case, there is a stable inverse correlation — the average for three years of research was -0.71. When other remote sensing indicators (NDVI and NIR) are used in the analysis, the links are either absent or less apparent.

Оптимізація мінерального живлення гібридів кукурудзи на основі рослинної діагностики

The article presents the results of research conducted during 2016-2019 on the impact of different rates of mineral fertilizers and by-products of the predecessor on the content of chemical nutrients in plants and the yield of maize hybrids in the Forest-Steppe. The aim of the research was to establish the peculiarities of nitrogen, phosphorus and potassium accumulation in maize plants in ontogenesis in relation to the yield of hybrids of early and middle-early maturity groups to optimize the mineral nutrition of the crop. The research was conducted on dark gray wooded soil using field, chemical, calculation-weight and mathematical-statistical methods. According to the stages of growth and development of BBCH, the peculiarities of the dynamics of nitrogen, phosphorus and potassium content in plants of hybrids with FAO 190 and 280 depending on the agrochemical load of growing technology are established. Varietal regularities of concentration of chemical elements in maize plants in connection with the accumulation of dry matter by crops in ontogenesis and yield were revealed. Hybrids with the corresponding genetically determined level of nitrogen, phosphorus and potassium content in plants have been identified and its influence on the realization of genotype productivity potential has been shown. The decisive role of potassium and nitrogen in the formation of the corn crop on dark gray wooded soil has been experimentally proved and confirmed on the basis of statistical and correlation analyzes. All hybrids were characterized by high tightness of correlations between yield and content in plants of nitrogen (r = 0.760–0.934) and potassium (r = 0.755–0.943) during the growing season as opposed to phosphorus, where these connections were of medium strength (r = 0.334–0.589) and only partially close (r = 0.702–0.806). According to the results of plant diagnostics of mineral nutrition of plants, the most effective growing technologies with different agrochemical loading are singled out, which ensure the yield of early and middle-early maize hybrids in agro-climatic conditions of the Forest-Steppe at 9.56–10.39 and 11.21–12.10 t/ha.

Rose Quality as Affected by Higher Air Temperatures Resulting from Poly-Tunnel Height in a Subtropical Region

Highlights Interior temperatures increased with decreasing poly-tunnel height. In subtropical regions, high interior temperatures of poly-tunnels could degrade quality of rose-cut flower. Stunted growth of rose plants because of higher temperatures could lead to mis-interpretations of nutrient deficiency. Abstract . High temperature is a major constraint to plant production in many regions of the world. Observations indicate that poly-tunnel structure design can influence interior temperature, and in turn determine the quality of cut flowers, including the length of the stems, the leaf biomass, and nutrient uptake. In this study, interior temperature and cut-flower quality of roses were assessed in five poly-tunnels with eave heights ranging from 2 to 4 m. Interior temperatures from 11:00-15:00 h in the hottest months of July and August were monitored. Rose (Rosa hybrida ‘Peach Avalanche’) was cultivated in these poly-tunnels with the same cultivation regimes. Higher interior temperatures were observed in poly-tunnels with lower eave heights. Leaf membrane thermal stability (MTS) values were negatively correlated with higher interior temperatures, indicating that the photosynthetic system of plant leaves was impaired. Stem length and mass were decreased with higher temperature by over 50%, while leaf biomass decreased by 25% in the poly-tunnel with eave height of 2 m in comparison with that of 4 m. Nitrogen concentration in plant leaves increased with higher temperature, whereas the patterns of other elements were not associated with different poly-tunnel eave heights. These results indicate that poly-tunnel interior high temperatures that were associated with lower eave heights are a major constraint for commercialized rose-cut flower production in this region, and improved design of poly-tunnels could increase production. Keywords: Cut flower, Membrane thermal stability, Stem length, Stem mass, Yunnan Province.

Consumption of Soil Nitrogen by Plants under the Application of a Mineral Fertilizer, Green Manure, and Biopreparation (the study involves 15N)

The use of soil nitrogen by spring wheat plants in sod-podzolic medium loamy soil enriched with a stable nitrogen isotope 15N was researched in a model experiment involving the application of ammonium nitrate and white mustard biomass and seed inoculation with associative nitrogen fixer Rhizoagrin. It is established that plants primarily consume nitrogen contained in the recently applied mineral fertilizer. After the application of white mustard biomass and seed inoculation with Rhizoagrin, spring wheat consumes soil nitrogen; after the combined application of the above components and ammonium nitrate, spring wheat consumes both soil nitrogen and nitrogen contained in the fertilizer. The plant biomass accumulation increases predominantly due to nitrogen contained in the recently applied mineral fertilizer, regardless of whether it was applied separately or in combination with green manure and seed inoculation with the biopreparation. The increase in the plant biomass accumulation reaches 14–28% in comparison with the control variant (no fertilizers). After the application of the nitrogen fertilizer, either separately or in combination with green manure and the biopreparation, the concentration of nitrogen in spring wheat increases by up to 1.5 times. A clear upward trend is observed in relation to the nitrogen concentration in plants after the application of white mustard biomass and seed inoculation with Rhizoagrin. As a result, the total nitrogen accumulation in plants increases twofold after the application of the nitrogen fertilizer and by 1.2 times after the application of white mustard biomass and seed inoculation with the biopreparation. This is due to the presence of nitrogen compounds available to plants in the growing medium. The accumulation of 15N in plants characterizes the consumption of soil nitrogen by them. This parameter decreases after the application of the nitrogen fertilizer and remains equal to that in the control variant (no fertilizers) after the application of white mustard biomass and Rhizoagrin. This indicates that plants consume large amounts of mineralized soil nitrogen after the application of the two latter components and that nitrogen fertilizer is not a factor in the mineralization of soil organic matter. The application of white mustard biomass prior to spring wheat sowing and inoculation of its seeds with Rhizoagrin ensure that plants consume soil nitrogen in the initial vegetation period.

Вплив добрив на вміст елементів мінерального живлення в рослинах пшениці озимої та ярої

The influence of systematic application of mineral fertilizers, on the background (BG) of the after-effect of 30 t on ha of manure, on the content of nutrients in spring wheat plants of “Myronivska Yara” regional variety and winter wheat plants of “Myronivska 61” variety, and on nutrients removal by plants, during cultivation on Meadow-Chernozemic Carbonate Soil, was studied. The results indicate a close relationship between external conditions and internal metabolic processes in winter and spring wheat plants. Thus, a balanced ratio of nitrogen, phosphorus and potassium provides a more intensive supply of these elements from the soil, what increases their content in plants. The highest content of total nitrogen, phosphorus and potassium in winter wheat plants was observed in the variant, where 1.5 rate of mineral fertilizers was applied with the background of 30 t on ha of manure, in the tillering phase and was 4.86; 2.17; 3.48 %, respectively, what is almost 2 times higher, than the control. During the growing season, the nutrients content in all variants decreased. The same pattern was observed in plants of spring wheat. The maximum nutrients content was recorded in all variants in the phase of spring tillering, and also was recorded significant reduction in their adsorption from the soil and using by plants during the growing season. The content of total nitrogen in spring wheat plants in the tillering phase fluctuated in fertilized variants in the range of 2.21-2.51 %, compared with the control – 2.10 %; phosphorus – in the range of 1.20-1.47 %, compared with the content on the control – 1.04 %; potassium – 1.88-3.08 %, in the control, respectively – 1.68 %. The results of research indicate, that long-term application of fertilizers in crop rotation affects, as a result, also on the removal of nutrients with the crop. Thus, the removal of basic nutrients by plants of winter and spring wheat was the highest in the variant “BG + N110P120K120”. Under winter wheat it was 210 kg on ha N, 122 P2O5, 157 kg on ha K2O, compared with the control variant – 86.3 N, 48.2 P2O5, 57.8 kg on ha K2O. Under the spring wheat it was 119 N, 66.4 P2O5, 85.4 kg on ha K2O, and in control variant, respectively, – 46.6 N, 26.5 P2O5, 32.8 kg on ha K2O.

Estimation and correlation of chlorophyll and nitrogen contents in Psidium guajava L. with destructive and non-destructive methods

Estimating photosynthetic pigments, such as chlorophylls, as well as the foliar nitrogen content is very important for the evaluation of the nutritional and physiological status of a plant. However, producers cannot easily carry out these estimations because they involve analyses in laboratories that are costly and time-consuming. The SPAD-502 total chlorophyll index meter is efficient at rapidly estimating total chlorophyll contents in situ, along with its relationship with the total nitrogen concentration in tissues. The objective of this research was to validate a non-destructive in situ method (SPAD) for use in place of destructive estimation methods for chlorophylls a, b and total, as well as the foliar nitrogen concentration in guava plants (Pisium guajaba L.), cv. Regional Roja, in three phenological stages under the conditions of the municipality of Vélez-Santander (Colombia). The data obtained with the SPAD-502 and the content of chlorophylls a, b and total were adjusted to a second-degree polynomial with correlation coefficients (r) greater than 0.91 for the three phenological stages, while the concentration of foliar nitrogen was adjusted to a linear type model with determination coefficients (R2) higher than 0.90, indicating a highly linear correlation between the non-destructive method and the destructive methods used in the present study.

Preparation and Properties of Immobilized Particles Containing Highly Efficient Nitrogen-Fixing Klebsiella variicola GN02 Cells Isolated from the Pennisetum giganteum z. x. lin Roots

The biological properties, structural characterization, and performance of Klebsiella variicola GN02 isolated from the roots of P. sinense and embedded in sodium alginate supplemented with 10% sterile skim milk were investigated. The results showed that the immobilized K. variicola GN02 particles were more stable and had a higher survival rate than free bacteria. Infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis showed that immobilized K. variicola GN02 particles had the peaks associated with sodium alginate and K. variicola GN02 cells, indicating that K. variicola GN02 cells were successfully embedded in the sodium alginate. Compared with free bacteria, the immobilized K. variicola GN02 cells revealed slower but a longer growth period during the 40 h culture period. The OD600 and ammonia secretion of immobilized K. variicola GN02 particles were 0.87 and 18.45 mg/L, respectively. A solution incubated with immobilized K. variicola GN02 exhibited a growth-promoting effect on corn than free K. variicola GN02. Root length, plant height, fresh weight, and total nitrogen content of plants subjected to immobilized K. variicola GN02 increased by 15.3, 16.3, 8.9, and 32.3%, respectively. The number of viable K. variicola GN02 in soil also increased significantly to 20.86 × 105 CFU/g. Therefore, immobilized K. variicola GN02 has promising application value, and this study provides a theoretical basis and reference for developing a biological fertilizer with new nitrogen-fixing bacteria.

水氮添加对内蒙古温带典型草原植被氮含量季节和年际动态的影响

水氮添加对内蒙古温带典型草原植被氮含量季节和年际动态的影响

Consumption of soil nitrogen by plants in the use of fertilizer, green manure and biopreparation (study with 15n)

In a model experiment on a sod-podzolic medium loamy soil enriched with a stable nitrogen isotope 15N, the use of soil nitrogen by spring wheat studied when ammonium nitrate was introduced, mustard biomass and seed inoculation with the associated nitrogen fixer Rhizoagrin were introduced. It has been established that plants consume nitrogen primarily from recently applied nitrogen of fertilizer. When making biomass of mustard and inoculating seeds with Rhizoagrin, spring wheat uses soil nitrogen, with the integrated use of these components and applying ammonium nitrate soil nitrogen and fertilizer. The accumulation of plant biomass predominantly increases from recently applied nitrogen of fertilizer, both separately and when combined with green manure and seed inoculation with a biopreparation and is 14-28% relative to the control without fertilizers. When applying nitrogen fertilizer, as well as when combined with green manure and biopreparation, the concentration of nitrogen in spring wheat increases up to 1.5 times. There is a clear upward trend in the concentration of nitrogen in plants with the addition of mustard biomass and it increases with inoculation of seeds with Rhizoagrin. As a result, the accumulation of total nitrogen in plants increases when nitrogen fertilizer is applied, and the use of mustard biomass and biopreparation increases this indicator by 1.2 times, which is due to the presence of nitrogen compounds available to plants in the nutrient medium. The accumulation in plants of 15N characterizes the consumption of soil nitrogen by plants, when introducing nitrogen fertilizer, this indicator is less, and using only biomass of mustard and Rhizoagrin is equivalent to control without fertilizers, indicating large amounts of mineralized nitrogen consumption from the soil when using the last two components, and that nitrogen fertilizer is not a factor in the mineralization of soil organic matter. The use of mustard biomass for spring wheat and seed inoculation with Rhizoagrin leads to the consumption of soil nitrogen by plants during the initial growing season.

Использование NDVI для определения содержания азота в растениях озимой пшеницы в условиях Ставропольского края

Abstract. Lack of nitrogen leads to a decrease in yield and grain quality in winter wheat plants. Therefore, it is necessary to monitor nitrogen nutrition throughout the period of growth and development of plants, which will quickly assess the need for fertilizing to obtain high yields of quality grain. Therefore, the aim of the study was to establish the possibility of using the normalized difference vegetation index (NDVI) to control the nitrogen content in winter wheat plants in the Stavropol territory. Methods. The work was performed in federal state budgetary scientific institution “North-Caucasian Federal Agricultural Research Centre” at the production of winter crops. Selection of plant samples (sheaf material) was carried out according to the generally accepted method. Repeated – 4x. Determination of the chemical composition of plant organs was carried out by the method of V. T. Kurkaev with co-authors, and the content of chlorophyll – Milaeva and Primak. Results. Since the quality of winter wheat grain directly depends on the nitrogen supply of plants, the relationships between the nitrogen content in winter wheat plants and the values of the vegetation index NDVI were studied. High correlation coefficients between these indicators are obtained. Thus, the average of Rcorr fields.in 2012 it was equal to –0.89, and in 2013 and 2014 –0.82. In addition, due to the dependence of nitrogen content on the amount of chlorophyll, it was possible to analyze the correlation between these indicators and NDVI fields, which showed that a stable relationship (inverse) is observed in the case of the amount of chlorophyll per unit biomass (mg/g), which is estimated on average at –0.79. The interrelation between grain quality and earth remote sensing data is revealed. It is most clearly seen in the case of the maximum and average NDVI for the period from the resumption of spring vegetation to full ripeness of winter wheat. Scientific novelty. For the first time in the conditions of unstable humidification of the Stavropol territory, a high inverse correlation between the vegetation index NDVI and the nitrogen content in winter wheat plants was determined, which on average is estimated by the correlation coefficient equal to –0.84.

Estimation of Nitrogen Nutrition Status in Winter Wheat From Unmanned Aerial Vehicle Based Multi-Angular Multispectral Imagery

Rapid, non-destructive and accurate detection of crop N status is beneficial for optimized fertilizer applications and grain quality prediction in the context of precision crop management. Previous research on the remote estimation of crop N nutrition status was mostly conducted with ground-based spectral data from nadir or oblique angles. Few studies investigated the performance of unmanned aerial vehicle (UAV) based multispectral imagery in regular nadir views for such a purpose, not to mention the feasibility of oblique or multi-angular images for improved estimation. This study employed a UAV-based five-band camera to acquire multispectral images at seven view zenith angles (VZAs) (0°, ± 20°, ± 40° and ±60°) for three critical growth stages of winter wheat. Four representative vegetation indices encompassing the Visible Atmospherically Resistant Index (VARI), Red edge Chlorophyll Index (CIred-edge), Green band Chlorophyll Index (CIgreen), Modified Normalized Difference Vegetation Index with a blue band (mNDblue) were derived from the multi-angular images. They were used to estimate the N nutrition status in leaf nitrogen concentration (LNC), plant nitrogen concentration (PNC), leaf nitrogen accumulation (LNA), and plant nitrogen accumulation (PNA) of wheat canopies for a combination of treatments in N rate, variety and planting density. The results demonstrated that the highest accuracy for single-angle images was obtained with CIgreen for LNC from a VZA of -60° (R2 = 0.71, RMSE = 0.34%) and PNC from a VZA of -40° (R2 = 0.36, RMSE = 0.29%). When combining an off-nadir image (-40°) and the 0° image, the accuracy of PNC estimation was substantially improved (CIred-edge: R2 = 0.52, RMSE = 0.28%). However, the use of dual-angle images did not significantly increase the estimation accuracy for LNA and PNA compared to the use of single-angle images. Our findings suggest that it is important and practical to use oblique images from a UAV-based multispectral camera for better estimation of nitrogen concentration in wheat leaves or plants. The oblique images acquired from additional flights could be used alone or combined with the nadir-view images for improved crop N status monitoring.

Predicting Canopy Nitrogen Content in Citrus-Trees Using Random Forest Algorithm Associated to Spectral Vegetation Indices from UAV-Imagery

The traditional method of measuring nitrogen content in plants is a time-consuming and labor-intensive task. Spectral vegetation indices extracted from unmanned aerial vehicle (UAV) images and machine learning algorithms have been proved effective in assisting nutritional analysis in plants. Still, this analysis has not considered the combination of spectral indices and machine learning algorithms to predict nitrogen in tree-canopy structures. This paper proposes a new framework to infer the nitrogen content in citrus-tree at a canopy-level using spectral vegetation indices processed with the random forest algorithm. A total of 33 spectral indices were estimated from multispectral images acquired with a UAV-based sensor. Leaf samples were gathered from different planting-fields and the leaf nitrogen content (LNC) was measured in the laboratory, and later converted into the canopy nitrogen content (CNC). To evaluate the robustness of the proposed framework, we compared it with other machine learning algorithms. We used 33,600 citrus trees to evaluate the performance of the machine learning models. The random forest algorithm had higher performance in predicting CNC than all models tested, reaching an R2 of 0.90, MAE of 0.341 g·kg−1 and MSE of 0.307 g·kg−1. We demonstrated that our approach is able to reduce the need for chemical analysis of the leaf tissue and optimizes citrus orchard CNC monitoring.

Vegetative and Physiological Responses of “Emerald” Blueberry to Ammoniacal Sources with a Nitrification Inhibitor

The nitrogen nutrition in blueberry has been studied by some authors; however, the effect of N-nitrate or N-ammoniacal fertilizers with nitrification inhibitors on plant growth and physiology has not been known. The aim of this investigation was to study the effectiveness and physiological implications of ammoniacal fertilizers, with or without nitrification inhibitors in blueberry. An experiment was conducted on 1-year “Emerald” blueberries grown in 20-L plastic pots. Our data indicate that ammonium-containing fertilizers promote vegetative growth and increase the leaf nitrogen concentration and gas exchange in plants, possibly due to higher nitrogen root absorption compared with nitrate. On the other hand, fertilization with ammonium with a nitrification inhibitor increases the leaf chlorophyll concentration compared with the addition of ammonium without a nitrification inhibitor and nitrate. However, the ammonium supply decreases the concentration of calcium and potassium in leaves. Our data suggest, for the first time, that fertilization with ammonium accompanied by a nitrification inhibitor is an effective strategy to improve the nitrogen status and promote plant development in “Emerald” blueberry.

Determination of Plant Nitrogen Content in Wheat Plants via Spectral Reflectance Measurements: Impact of Leaf Number and Leaf Position

The determination of plant nitrogen (N) content (%) in wheat via destructive lab analysis is expensive and inadequate for precision farming applications. Vegetation indices (VI) based on spectral reflectance can be used to predict plant N content indirectly. For these VI, reflectance from space-borne, airborne, or ground-borne sensors is captured. Measurements are often taken at the canopy level for practical reasons. Hence, translocation processes of nutrients that take place within the plant might be ignored or measurements might be less accurate if nutrient deficiency symptoms occur on the older leaves. This study investigated the impact of leaf number and measurement position on the leaf itself on the determination of plant N content (%) via reflectance measurements. Two hydroponic experiments were carried out. In the first experiment, the N fertilizer amount and growth stage for the determination of N content was varied, while the second experiment focused on a secondary induction of N deficiency due to drought stress. For each plant, reflectance measurements were taken from three leaves (L1, L2, L3) and at three positions on the leaf (P1, P2, P3). In addition, the N content (%) of the whole plant was determined by chemical lab analysis. Reflectance spectrometer measurements (400–1650 nm) were used to calculate 16 VI for each combination of leaf and position. N content (%) was predicted using each VI for each leaf and each position. Significant lower mean residual error variance (MREV) was found for leaves L1 and L3 and for measurement position on P3 in the N trial, but the difference of MREV between the leaves was very low and therefore considered as not relevant. The drought stress trial also led to no significant differences in MREV between leaves and positions. Neither the position on the leaf nor the leaf number had an impact on the accuracy of plant nitrogen determination via spectral reflectance measurements, wherefore measurements taken at the canopy level seem to be a valid approach.

Interactions of bacterial-feeding nematodes and indole-3-acetic acid (IAA)-producing bacteria promotes growth of Arabidopsis thaliana by regulating soil auxin status

To clarify the ‘auxin-driven’ effect of bacterial-feeding nematodes on plant growth, the influence of an indole-3-acetic acid (IAA)-producing bacteria, Bacillus amyloliquefaciens, non-IAA-producing bacteria Variovorax sp., and two bacterial-feeding nematodes (Cephalobus sp. and Mesorhabditis sp.) on the growth of Arabidopsis thaliana after various exposure durations was investigated using a gnotobiotic microcosm incubation system. The nematodes, responses of soil chemistry (IAA and mineral nitrogen), plant growth (root architecture, shoot dry weight, and plant nitrogen), and the expression of two IAA-responsive genes, IAA3 and IAA13, were measured. Bacterial-feeding nematodes stimulated the activity of IAA-producing bacteria by grazing, and promoted the mineralization of nitrogen in the soil, thus increasing the soil IAA and nitrogen content and promoting shoot dry weight and plant nitrogen content. The A. thaliana root architecture consisted of a highly branched root system, with bigger surface area. The IAA3 and IAA13 genes in A. thaliana roots significantly increased and there were significant correlations with the soil IAA content. This study further confirms the existence of an auxin-driven effect that promotes A. thaliana growth by bacterial-feeding nematodes through changes in the expression of root genes.