Nitrogen Fertilization Regimes Research Articles

Comprehensive analysis of fresh tea (Camellia sinensis cv. Lingtou Dancong) leaf quality under different nitrogen fertilization regimes

Our study investigated the impact of nitrogen fertilization at 0, 150, 300, and 450 kg/ha on the non-volatile and volatile substances, as well as gene expression in fresh leaves from Lingtou tea plants. We found that applying nitrogen at 450 kg/ha notably increased total polyphenols (TPs) and free amino acids (AAs) while decreasing the TP to AA ratio (TP/AA) and total catechins (TC) contents. Chlorophyll, caffeine (CAF) and theanine accumulated to a greater extent with nitrogen application rates of 150, 300, and 450 kg/ha, respectively, six substances – TP, CAF, TC, theanine, epigallocatechin (EGC), and AA – as key contributors to the taste quality of LTDC. Additionally, five substances with variable importance in projections (VIP) ≥ 1 and odor activation values (OAV) ≥ 1, notably linalool and cis-linalool oxide (furanoid), significantly contributed to the tea's overall aroma. Furthermore, applying 300 kg/ha nitrogen upregulated the dihydroflavonol reductase (DFR)gene, likely causing catechin decrease.

Productivity and water use efficiency of summer soybean-winter wheat rotation system under limited water supply in the North China Plain

Development of novel crop rotations with superior water- and N-use efficiency will be fundamental in the quest for securing sustainable food supplies under environments that are increasingly resource limited. Here, our aim was to examine how replacing maize with soybean as part of winter wheat rotations impacted the nutrient-equivalent yield (EY), evapotranspiration (ET) and water-use efficiency (WUE) of rotation systems. We contrasted summer soybean-winter wheat (SW) and summer maize-winter wheat (MW) cropping systems under three nitrogen (N) fertilization regimes: no, medium, and high nitrogen application rates (0 N, MN, and HN, respectively). Results showed that SW not only resulted in lower annual yields, but also caused more variable inter-annual wheat productivity compared with MW. SW had similar annual productivities to MW in wet (2019–2020) and dry (2020–2021) years, but lower productivity than MW in an average precipitation year (45% reduction, 2018–2019). As well, SW had higher average annual ETs (633–854 mm) than MW, mainly was attributed to higher ETs (268–440 mm) in summer. SW reduced WUEs by 17% and 28% in average (2018–2019) and dry (2020–2021) years, respectively. Regardless of cropping system, N fertilization increased annual EYs and ETs by 10–18% and 5–18% compared with no fertilization, respectively. Together these comparable increments in EY and ET, we found that N fertilization had rare effects on annual WUE of both systems. Overall, our study demonstrated that replacing maize with soybean in winter wheat rotations increased annual ET and neither maintained productivity nor improved water productivity. Thus, we suggest that practitioners explore other drought tolerant grain legumes to generate more reliable yields and less water consumption under legume-based crop rotations.

Optimizing nitrogen, phosphorus, and potassium fertilization regimes to improve maize productivity under double ridge-furrow planting with full film mulching

Optimizing nitrogen, phosphorus, and potassium fertilization regimes to improve maize productivity under double ridge-furrow planting with full film mulching

NITROGEN AND BIOFERTILIZATION EFFECTS ON BIOCHEMICAL, QUALITATIVE, AND PHYSIOLOGICAL TRAITS OF SORGHUM (SORGHUM BICOLOR L.)

A field experiment done in the spring of 2022 on Sorghum bicolor L. cultivars with different nitrogen and biofertilizer fertilizer regimes proceeded at the Ibn-Al-Bitar Vocational Preparatory School, District Al-Hussainiya, Holy Governorate of Kerbala. Sowing in a randomized complete block design (RCBD) with a factorial experiment and three replications took place in the third week of March 2022, and harvesting in the third week of July 2022. The trial included two factors; the first had three sorghum cultivars (V1 = Al-Khair, V2 = Rabeh, and V3 = Bohuth 70). The second factor was combinations of nitrogen and biofertilizers, i.e., F0 = the complete dose of nitrogen fertilizer (320 kg N ha-1 ); F1 = 3/4 nitrogen fertilizer + Azotobacter; F2 = 1/2 nitrogen fertilizer + Azotobacter; F3 = 1/4 nitrogen fertilizer + Azotobacter, and F4 = Azotobacter with no nitrogen fertilizer. The results showed the superiority of cultivar Bohuth 70 for the traits yield per plant (116.2 g plant-1 ) and nitrogen, phosphorus, and protein percentages in grains (2.212%, 0.3212%, and 13.82%, respectively). Cultivar Al-Khair excelled in total chlorophyll, ash, and potassium percentages in grains (1.057 mg g-1 , 2.165%, and 2.085%, respectively). As for the interaction, the combined treatments V3F0 excelled in the traits of yield per plant (134.4 g plant-1 ), nitrogen (2.610%), and protein percentages (16.31%), while the interaction of V1F3 performed better for the variables ash and potassium percentages (2.600% and 2.160%, respectively). However, the reaction of V3F1 surpassed phosphorus and potassium percentages (0.3615% and 2.160%). The research happened to know the extent to reducing the quantities of recommended chemical nitrogen fertilizers and their effect on the qualitative.

Nitrogen fertilization and irrigation types do not affect the overall N2O production potential of a sandy soil, but the microbial community structure and the quantity of functional genes related to the N cycle

Nitrous oxide (N2O), one of the major greenhouse gases, features a 273-fold higher global warming potential compared to carbon dioxide (CO2). Soil-born N2O emissions are based on microbial processes, while the microbial processes are affected by environmental factors and agronomic management measures. The objective of this study was the exploration of the effects of different irrigation and nitrogen (N) fertilization regimes on N2O emissions in relation to the microbial community structure and the quantities of genes involved in the N cycle. The following four treatments were investigated in a sandy soil during the potato cropping season in 2019 in Brandenburg, Germany: drip irrigation without N fertilization (DI-ZN), drip irrigation with broadcasted N fertilization (DI-N), simultaneous application of dissolved N in irrigation water, the so-called fertigation (F), and fertigation without crops (F-ZC). N2O fluxes were measured with the closed chamber method. Microbial biomass was analyzed using phospholipid fatty acids (PLFAs). The bacterial functional genes amoA (ammonium monooxygenase), nxrB (nitrite oxidoreductase), narG (nitrate reductase), nirS/nirK (nitrite reductase), and nosZ (N2O reductase) were determined using quantitative real-time polymerase chain reaction (qPCR). N2O fluxes varied over the season and could mainly be explained by temperature changes. The fertilized treatments showed slightly higher area-related cumulative N2O emissions (DI-ZN: 1.13 kg N2O-N ha−1, DI-N: 1.28 N2O-N ha−1, F: 1.26 N2O-N ha−1, median values). Additionally, N2O flux rates as well as the area- and yield-related N2O emissions of DI-N and F were approximately at the same level, even though the quantities and correlation patterns of the investigated functional genes differed. Highest seasonal median flux rates were detected under DI-N (15.0–100.1 μg N2O-N m−2 h−1), where a greater influence of a nirS/nosZ harboring microbial community was found. In contrast, under F more diverse correlation patterns were found, especially regarding a predominance of nirK and nirS/nosZ harboring microbial community. F-ZC showed the lowest N2O flux rates (−8.7–44.2 μg N2O-N m−2 h−1), which might be explained by the lack of plant carbon sources, particularly root exudates. To conclude, the applied treatments affected the microbial community structure and their genetically determined potential for N2O production, whereby the overall N2O flux rates and hence N2O emissions remained unaffected. Although fertigation is considered to be more demand-based particularly in terms of N fertilization, this study indicates that agronomic management measures according to good faming practice might feature an oversupply of N, neglecting the real N demand of cultivated crops and hence hindering the mitigation of N2O emissions.

Spectral Response of Camelina (Camelina sativa (L.) Crantz) to Different Nitrogen Fertilization Regimes under Mediterranean Conditions

Knowledge about the spectral response of camelina under different regimes of nitrogen (N) fertilization is very scarce. Therefore, 2-year open-field trials were carried out in the 2021 and 2022 growing seasons with the aim of evaluating the spectral response of spring camelina to four different N fertilization regimes by using remote (UAV) and proximal (leaf-clip Dualex) sensing techniques. The tested treatments were: (i) control: no N application (T0); (ii) top dressing: 60 kg N ha−1 before stem elongation (T1); basal dressing: 60 kg N ha−1 at sowing (T2); basal + top dressing combination: 60 kg N ha−1 at sowing + 60 kg N ha−1 before stem elongation (T3). Camelina seed yield and N use efficiency were strongly affected by fertilization regimes, with the best results obtained at T2. A reduction in plant development and seed yield was detected in 2022, probably due to the rise in air temperatures. A significant effect of both growing season and N fertilization was observed on the photosynthetic pigments content with the T1 highest values in 2022. The highest seed oil content was achieved at T1, while the protein content increased with increasing N, with the best values at T3. Positive and significant correlations were observed among several vegetation indices obtained through UAV flights (NDVI, MRS705, FGCC) and seed yield, as well as between FGCC and leaf N concentration. Overall, these findings demonstrate the feasibility of utilizing remote sensing techniques from UAVs for predicting seed yield in camelina.

Low nitrogen fertilization enriches nitrogen‐fixing bacteria in the Brassica seed microbiome of subsequent generations

AbstractIntroductionThe consequences of overfertilization on agricultural and native ecosystems are well‐documented, but the impact of reduced fertilization on plant–microbe interactions is less understood. Here, we analysed the impact of different nitrogen (N) fertilization regimes over two subsequent growing seasons on the seed microbiome of winter oilseed rape (Brassica napus L.).Materials and MethodsSeed microbial diversity, composition, and abundance were analysed by a combined approach of amplicon sequencing, quantitative real‐time PCR, and microscopy. A germination assay was conducted to quantify bacteria and nifH genes in roots.ResultsTwo consecutive years of either low or high N fertilization resulted in a significant shift in seed microbiota; nine discriminating bacterial orders and 32 bacterial features were identified. Among them, potentially N‐fixing bacteria (Rhizobiales and Rhizobium) were identified as biomarkers for low N fertilization. Moreover, quantitative measurements revealed that 16S ribosomal RNA (rRNA) and bacterial nifH gene counts were significantly higher under lower N availability. Relative to total 16S rRNA genes, seeds and roots contained 0.002% and 0.3% nifH genes on average, respectively. The alternation of N levels between the first and the second growing season (high to low, or low to high) had, however, no impact on seed microbiota, suggesting that a low N availability for at least two generations is required to enrich N‐fixing taxa in seeds.ConclusionOur study revealed a flexible, environmentally influenced seed microbiome assembly and suggests innovative microbiome management via biological nitrogen fixation to optimize fertilization regimes in future agriculture.

The fate of amino acid and peptide as affected by soil depth and fertilization regime in subtropical paddies

Amino acids and peptides are important regulators of ecosystem functioning due to their potential role as direct nutrient sources for plants and soil microbes. However, the turnover and driving factors of these compounds in agricultural soils remain poorly understood. This study aimed to reveal the short-term fate of 14C-labeled alanine and tri-alanine derived C under flooding conditions of the top (0–20 cm) and sub-horizons (20–40 cm) of subtropical paddy soils taken from four long-term (31 years since treatment) nitrogen (N) fertilization regimes (i.e., without fertilization, NPK, NPK with straw return (NPKS) or with manure (NPKM)). Amino acid mineralization was strongly affected by the N fertilization regime and soil depth, while peptide mineralization was only distinct between soil layers. The average half-life of amino acid and peptide in the topsoil was 8 h across all treatments, which was higher than previously reported in uplands. The microbial turnover of amino acid and peptide was 7–10 times slower in the subsoil than in the topsoil, with a half-life of about 2–3 days. The half-life of amino acid and peptide for the respired pool was strongly associated with soil physicochemical characteristics, the total biomass, and the structure of soil microbial communities. The N fertilization regime and soil depth affected the substrate uptake rate by microorganisms, with greater uptake observed in the NPKS and NPKM treatments and the topsoil. Microbial amino acid uptake was correlated with the biomass of total and individual microbial groups, whereas microbial peptide uptake was associated with the soil microbial community structure and physicochemical characteristics. This suggests that there are various pathways of amino acid and peptide use by microorganisms under flooding conditions. We conclude that microbial mineralization of amino acid and its peptide in paddy soils under flooding conditions is slower than in upland soils, and that microbial uptake of these substrates is related to soil abiotic factors and the biomass and structure of soil microbial community. These findings have important implications for understanding nutrient cycling and ecosystem functioning in agricultural soils.

Interspecific interactions between crops influence soil functional groups and networks in a maize/soybean intercropping system

Despite increasing evidence that intercropping systems may increase crop productivity, little is known about whether and how soil biota change under interspecific competition among plants. A field experiment with maize/soybean intercropping and the corresponding monoculture systems was conducted under four nitrogen fertilization regimes to investigate the effects of interspecific plant interactions on grain yield, soil properties (β-glucosidase and water-soluble carbohydrates), and biotic communities (bacteria, fungi, and nematodes). The soils under maize and soybean in the intercropping system were sampled separately to represent intercropped maize and intercropped soybean, respectively. Compared to monocultures, the complexity and robustness of soil networks comprising bacterial, fungal, and nematode communities increased in intercropped maize soils, but densities of plant parasitic nematodes and β-glucosidase activity were reduced. Intercropped soybean soils had lower C availability due to chronic shading by maize, but a significant increase was found in saprophytic fungi, and plant parasitic nematodes compared to soybean monoculture soils. Although intercropped soybean suffered from interspecific competition with maize, the interactions within the fungal community increased for both crop species in the intercropping system. Our study demonstrates that increased carbon uptake in maize due to increased light capture in the intercropping system can facilitate nutrient cycling by altering the abundance of functional groups of soil organisms, such as saprophytic fungi, and enhancing network complexity and stability. We detected a trade-off between productivity and soil nematode diversity in the intercropping system under nitrogen fertilization, the yield of maize increased but soil nematode richness decreased at low nitrogen level, while the yield of soybean decreased but the nematode richness increased at high nitrogen level. These findings show that both trade-offs and benefits occur in intercropping systems and highlight the role of plant-soil biota interactions in such systems.

Widely untargeted metabolomic profiling unearths metabolites and pathways involved in leaf senescence and N remobilization in spring-cultivated wheat under different N regimes.

Progression of leaf senescence consists of both degenerative and nutrient recycling processes in crops including wheat. However, the levels of metabolites in flag leaves in spring-cultivated wheat, as well as biosynthetic pathways involved under different nitrogen fertilization regimes, are largely unknown. Therefore, the present study employed a widely untargeted metabolomic profiling strategy to identify metabolites and biosynthetic pathways that could be used in a wheat improvement program aimed at manipulating the rate and onset of senescence by handling spring wheat (Dingxi 38) flag leaves sampled from no-, low-, and high-nitrogen (N) conditions (designated Groups 1, 2, and 3, respectively) across three sampling times: anthesis, grain filling, and end grain filling stages. Through ultrahigh-performance liquid chromatography-tandem mass spectrometry, a total of 826 metabolites comprising 107 flavonoids, 51 phenol lipids, 37 fatty acyls, 37 organooxygen compounds, 31 steroids and steroid derivatives, 18 phenols, and several unknown compounds were detected. Upon the application of the stringent screening criteria for differentially accumulated metabolites (DAMs), 28 and 23 metabolites were differentially accumulated in Group 1_vs_Group 2 and Group 1_vs_Group 3, respectively. From these, 1-O-Caffeoylglucose, Rhoifolin, Eurycomalactone;Ingenol, 4-Methoxyphenyl beta-D-glucopyranoside, and Baldrinal were detected as core conserved DAMs among the three groups with all accumulated higher in Group 1 than in the other two groups. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that tropane, piperidine, and pyridine alkaloid biosynthesis; acarbose and validamycin biosynthesis; lysine degradation; and biosynthesis of alkaloids derived from ornithine, lysine, and nicotinic acid pathways were the most significantly (p < 0.05) enriched in Group 1_vs_Group 2, while flavone and flavonol as well as anthocyanins biosynthetic pathways were the most significantly (p < 0.05) enriched in Group 1_vs_Group 3. The results from this study provide a foundation for the manipulation of the onset and rate of leaf senescence and N remobilization in wheat.

Balancing high yields and low N2O emissions from greenhouse vegetable fields with large water and fertilizer input: a case study of multiple-year irrigation and nitrogen fertilizer regimes

Balancing high yields and low N2O emissions from greenhouse vegetable fields with large water and fertilizer input: a case study of multiple-year irrigation and nitrogen fertilizer regimes

Effects of irrigation and nitrogen fertilizer application on growth, yield and quality of different rice varieties in arid areas of Xinjiang

AbstractNitrogen fertilizer and water are two major nutrients required for the optimal production of rice worldwide. The utilization of different irrigation techniques to save water and fertigation to maximize rice production has been the main focus. A field experiment was conducted to explore the responses of 16 rice varieties to different irrigation and nitrogen fertilizer regimes. Two nitrogen treatments, 270 kg ha−1 and 225 kg ha−1 (urea N ≥ 46.4%), and two irrigation regimes, 8.7 t ha−1 and 5.22 t ha−1, were applied three times. Plant height and the soil and plant analyser development (SPAD) values were measured throughout the growth period. The total yield and quality characteristics of the rice varieties were also determined. Based on the yield, the 16 rice varieties were divided into three groups: high yield (I), middle yield (II) and low yield (III) using cluster analysis. A positive correlation was found between the growth period and yield of these 16 rice varieties. In the water-deficient regime, the growth period of the 16 varieties was reduced by 1.68–2.93%. Furthermore, nitrogen- and water-deficient regimes had significant effects on the polishing rate, protein content and taste values of all varieties. At maturity stage under these regimes, plant height and chlorophyll SPAD values were decreased by 1.25–6.05% and 1.60–31.48%, respectively. Deficient nitrogen fertilization, along with appropriate irrigation, is an effective method for the efficient utilization of irrigation and fertilizer resources in rice-growing areas.

Grain yield and nitrogen use efficiency in spring wheat (Triticum aestivum L.) hybrids under different nitrogen fertilization regimes

Grain yield and nitrogen use efficiency in spring wheat (Triticum aestivum L.) hybrids under different nitrogen fertilization regimes

Malting procedure and its impact on the composition of volatiles and antioxidative potential of naked and covered oat varieties

Grains from four naked oat varieties (Amant, Maczo, Polar and Siwek) and one covered oat variety (Kozak) grown with three different nitrogen fertilization regimes were malted in a laboratory setting using specifications typical for barley malt production (45% moisture content, temperature of germination equal to 15 °C, germination time equal to 120 h). The goal was to determine, whether malting process could be used to improve pro-health properties and aroma of the covered oat and naked oat grain. Malting increased concentration of phenolic compounds (from 44.92 to 64.39 mg GAE per 100 g of grain to 158.06–393.69 mg GAE per 100 g of malt) and increased the antioxidative potential of grains (analysed by ABTS, DPPH and FRAP assays) by 200–300%. Malting also had an effect on the changes in composition of volatile compounds: the HS-SPME-GC-MS detected 23 compounds in grain samples and 34 compounds were detected in malt samples. The total concentration of volatiles in malts was significantly higher (1659.70–39708.33 ng per 100 g) than in grain samples (882.45–2098.74 ng per 100 g). Malting mostly increased concentration of aldehydes, such as nonanal, decanal and undecanal and pyrazines, such as trimethyl- and tetramethylpyrazine in the acquired malts.

Impact of Combined Drought and Heat Stress and Nitrogen on Winter Wheat Productivity and End-Use Quality

Water deficit and heat stress are the main abiotic stresses affecting the yield and quality of winter wheat. The increasing frequency of the simultaneous occurrence of these two stresses might threaten global food security and drives the need to breed resilient high-quality cultivars. The aim of this study was to evaluate the grain yield, quality and gluten protein characteristics in 50 winter wheat cultivars and breeding lines during the harvest years of 2018 and 2019. The yield and grain quality components were affected more severely by the combined heat and drought in 2019 than the drought in 2018. Two nitrogen (N) fertilization regimes were studied, sustainable (S, 15/100/30 kg N ha−1) and high-input (HI, 15/100/100 kg N ha−1). The yield was higher in HI trials compared to S trials by 2.2 t ha−1 in 2018 and by 2.4 t ha−1 in 2019. Higher protein content and sedimentation volume and lower yield, test weight and starch content were observed under combined heat and drought stress in 2019 compared to 2018. Genotypes containing the Glu-D1 x5-y10 allele exhibited the higher amounts of unextractable polymeric proteins (%UPP = 58.5%) in gluten studied by size exclusion liquid chromatography (SE-HPLC) as compared to Glu-D1 x2-y12 allele (%UPP = 54.3%). Genotype was the main determinant of gluten protein characteristics regardless of the nitrogen application and the abiotic stress conditions. The results suggest that the relatively mild drought and heat events in Lithuania might not threaten gluten quality in the future; however, breeding efforts should be directed towards improved drought and heat stress resistance to ensure stable wheat productivity in the region.

Microbial communities in paddy soil as influenced by nitrogen fertilization and water regimes

AbstractPlastic film mulching (PM) cultivation is an important measure to alleviate the seasonal shortage of water resources. Long‐term nitrogen (N) fertilization under PM cultivation may be more conducive to enhance the ecological relationship between microbial communities involved in nutrient cycling. In this study, the effects of long‐term application of chemical N fertilizer (common prilled urea [PU]) or no N fertilization on the microbial community composition under the traditional flooding (TF) cultivation and PM cultivation were comparatively analyzed. The results demonstrated that water regimes had significant effects on all soil properties except alkali‐hydrolyzable N. Compared with TF cultivation, PM cultivation increased pH and available phosphorus (AP) by 1.14 and 13.67%, respectively, and decreased organic matter and available potassium (AK) by 6.07 and 8.39%, respectively. Nitrogen fertilization levels had significant effects on soil AP and AK, with increases of 1.39 and 1.82 mg kg−1 in PU treatment compared with CK, respectively. Neither water regime nor N fertilization level had a significant influence on soil microbial richness (Chao index) and diversity (Shannon index). However, water regimes played critical roles in driving microbial community changes. Network analysis showed that the microbial community had nonrandom co‐occurrence pattern. Myrmecridium, Defluviicoccus, Emericellopsis, Pseudarthrobacter, and Syntrophorhabdus were the keystone taxa. A higher relative abundance of Defluviicoccus, Emericellopsis, and Syntrophorhabdus was observed in the CKPM treatment, and a higher relative abundance of Myrmecridium and Pseudarthrobacter was observed in the PUPM treatment. Therefore, PM cultivation is an effective measure to improve potential beneficial taxa of soil microbial communities.

Influence of Variety and Nitrogen Fertilization on the Technological Parameters of Special Malts Prepared from Naked and Hulled Oat Varieties

Grains of four naked oat varieties (Amant, Maczo, Polar and Siwek) and one hulled oat variety (Kozak) from three consecutive years (2018, 2019 and 2020), grown under three different nitrogen fertilization regimes (40, 60 and 80 kg of nitrogen per hectare) were malted and then mashed in the laboratory conditions for the first time; this was carried out to determine whether hulled and naked oat grains possess favourable properties as a raw material for the production of malt. Most of the analysed samples possess a favourable Kolbach index (39.06–46.82%), good extractivity (81.07–81.97%) and rather good saccharification time (13.33–26.67 min); however, some disadvantages of the produced malts could be pointed out. During the congress mashing, the filtration time of the worts produced from the hulled and naked oat malts was long (96.67–110 min) and the wort volume was not satisfactory (155–228.53 mL). Subsequent studies over oat malting and mashing need to be performed to maximize oat potential as the raw material for the production of the malt.

Response of ‘Hass’ avocado under different nitrogen and potassium fertilizer regimes in subtropical Ecuador

Response of ‘Hass’ avocado under different nitrogen and potassium fertilizer regimes in subtropical Ecuador

Hyperspectral Characteristics of an Individual Leaf of Wheat Grown under Nitrogen Gradient

Since the application of hyperspectral technology to agriculture, many scientists have been conducting studies to apply the technology in crop diagnosis. However, due to the properties of optical devices, the reflectances obtained according to the image acquisition conditions are different. Nevertheless, there is no optimized method for minimizing such technical errors in applying hyperspectral imaging. Therefore, this study was conducted to find the appropriate image acquisition conditions that reflect the growth status of wheat grown under different nitrogen fertilization regimes. The experiment plots were comprised of six plots with various N application levels of 145.6 kg N ha−1 (N1), 109.2 kg N ha−1 (N2), 91.0 kg N ha−1 (N3), 72.8 kg N ha−1 (N4), 54.6 kg N ha−1 (N5), and 36.4 kg N ha−1 (N6). Hyperspectral image acquisitions were performed at different shooting angles of 105° and 125° from the surface, and spike, flag leaf, and the second uppermost leaf were divided into five parts from apex to base when analyzing the images. The growth analysis conducted at heading showed that the N6 was 85.6% in the plant height, 44.1% in LAI, and 64.9% in SPAD as compared to N1. The nitrogen content in the leaf decreased by 55.2% compared to N1 and the quantity was 44.9% in N6 compared to N1. Based on the vegetation indices obtained from hyperspectral reflectances at the heading stage, the spike was not suitable for analysis. In the case of the flag leaf and the 2nd uppermost leaf, the vegetation indices from spectral data taken at 105 degrees were more appropriate for acquiring imaging data by clearly dividing the effects of fertilization level. The results of the regional variation in a leaf showed that the region of interest (ROI), which is close to the apex of the flag leaf and the base of the second uppermost leaf, has a high coefficient of determination between the fertilization levels and the vegetation indices, which effectively reflected the status of wheat.

Soil dynamics of Cr(VI) and responses of Portulaca oleracea L. grown in a Cr(VI)-spiked soil under different nitrogen fertilization regimes.

The reduction potential of the highly toxic Cr(VI) to the inert Cr(III) in analkaline soil was studied during a 50-day experiment with Portulaca oleracea L. grown in pots. We aimed at assessing whether our test species can be a phytoremediation candidate for Cr(VI)-contaminated soils. We measured the Cr(VI) reduction rate in soil, determined the Cr(VI) and Cr(III) concentrations in aerial and root P. oleracea tissues, and calculated the transfer coefficient (TC = metal in plant over metal in soil) and the translocation factor (TF = metal in aerial biomass over metal in roots) in order to assess Cr(VI) uptake and distribution in plant tissues, while we also studied the effect of added nitrogen in the studied parameters. We added five different Cr(VI) levels (from the unamended T-0 to the treatment of T-4 = 150 mg Cr(VI) kg-1 soil) and also had two N levels (equivalent to 0 and 200 kg ha-1). The results indicated that Cr in plant tissues was mainly found in its reduced form (Cr(III)) and only a minor fraction of Cr was detected in its oxidized form (Cr(VI)), with only 1.04% of plant Cr being hexavalent at T-4 with no added N and 1.30% at T-4 with added N. The main remediation mechanism was found to be that of the naturally occurring Cr(VI) reduction that effectively produced Cr(III), followed by the uptake of Cr(VI) from our test plants (at T-4 with no N, 58% of soil added Cr(VI) was reduced and 0.1% absorbed, while at T-4 with added N, 63% was reduced and only 0.4% absorbed by plant). We also found that Cr(VI) in P. oleracea tissues was mainly found in roots and relatively low Cr(VI) concentrations were found in the above-ground tissues. We concluded that P. oleracea is a tolerant plant species, especially if assisted with a sufficient level of N fertilization, although it failed to approach the threshold of being categorized as an accumulator species. However, as this is a rather preliminary experiment, before reaching more conclusive suggestions about P. oleracea as a potential phytoremediation species, further investigation is necessary in order to verify the gained results with naturally contaminated soils with Cr under field conditions.