A portable energy dispersive X‐ray fluorescence (XRF) spectrometer furnished with an Rh X‐ray tube was evaluated for the determination of macronutrients and micronutrients in soybean leaves (Glycine max L.). XRF instrumental parameters were optimized in a univariate way, and emission intensities were measured for 60 s and under vacuum for macronutrients, and during 180 s, under air, and 305 μm Al/25.4 μm Ti filter, for micronutrients. Fresh and dried leaves were irradiated, and it was possible to identify P, K, Ca, S, Mn, Fe, Cu, and Zn Kα emission lines. For comparative purpose, the samples were also microwave assisted, digested and analyzed by inductively coupled plasma optical emission spectrometry. In general, linear correlations between K, Ca, Mn, Fe, Cu, and Zn concentrations in the tested samples and the corresponding portable XRF (pXRF) intensities were obtained. The linear correlation coefficients (R2) ranged from 0.42 to 0.86. In addition, the detection limits were suitable for plant nutrient diagnosis. It is demonstrated that pXRF is a simple and powerful tool for analysis of plant materials.
This study aimed to evaluate the potential of portable X-ray fluorescence (pXRF) equipment to quantify P in sugar cane leaves in vivo. Therefore, sugar cane seedlings were grown in soil fertilized with increasing doses of P, and the leaf P content was measured by pXRF and by induced coupled plasma optical emission spectrometry (ICP OES). This investigation included examination of the X-ray tube operational condition, analysis under vacuum or air, assessment of the number of spots measured per leaf, determination of the acquisition time per spot, and the best quantitative strategy for determining the P content in leaves. Using three points per leaf, an acquisition time of 60 s per point, a voltage of 40 kV, a current of 30 μA, analysis under vacuum, and an external calibration curve considering the densities of standards and leaves, we found a high correlation between the P content in sugar cane leaves by pXRF and ICP OES. A cross-calibration curve can be equally useful.
Background Brazil has the largest commercial herd of ruminants with approximately 211 million head, representing 15% of world’s beef production, in an area of 170 million hectares of grasslands, mostly cultivated with Brachiaria spp. Although nutrient reduction due to increased atmospheric carbon dioxide (CO2) concentration has already been verified in important crops, studies evaluating its effects on fiber fractions and elemental composition of this grass genus are still scarce. Therefore, a better understanding of the effects of elevated CO2 on forage quality can elucidate the interaction between forage and livestock production and possible adaptations for a climate change scenario. The objective of this study was to evaluate the effects of contrasting atmospheric CO2 concentrations on biomass production, morphological characteristics, fiber fractions, and elemental composition of Brachiaria decumbens (cv. Basilisk). Methods A total of 12 octagonal rings with 10 m diameter were distributed in a seven-ha coffee plantation and inside each of them, two plots of 0.25 m2 were seeded with B. decumbens (cv. Basilisk) in a free air carbon dioxide enrichment facility. Six rings were kept under natural conditions (≈390 μmol mol−1 CO2; Control) and other six under pure CO2 flux to achieve a higher concentration (≈550 μmol mol−1 CO2; Elevated CO2). After 30 months under contrasting atmospheric CO2 concentration, grass samples were collected, and then splitted into two portions: in the first, whole forage was kept intact and in the second portion, the leaf, true stem, inflorescence and senescence fractions were manually separated to determine their proportions (%). All samples were then analyzed to determine the fiber fractions (NDF, hemicellulose, ADF, cellulose, and Lignin), carbon (C), nitrogen (N), potassium (K), calcium (Ca), sulfur (S), phosphorus (P), iron (Fe), and manganese (Mn) contents and N isotopic composition. Results Elevated atmospheric CO2 concentration did not influence biomass productivity, average height, leaf, stem, senescence and inflorescence proportions, and fiber fractions (p > 0.05). Calcium content of the leaf and senescence portion of B. decumbens were reduced under elevated atmospheric CO2 (p < 0.05). Despite no effect on total C and N (p > 0.05), lower C:N ratio was observed in the whole forage grown under elevated CO2 (p < 0.05). The isotopic composition was also affected by elevated CO2, with higher values of δ15N in the leaf and stem portions of B. decumbens (p < 0.05). Discussion Productivity and fiber fractions of B. decumbens were not influenced by CO2 enrichment. However, elevated CO2 resulted in decreased forage Ca content which could affect livestock production under a climate change scenario.
Reports relating the separate and combined influences of soil aeration, nitrogen and saline stresses on the germination, growth and ion accumulation in sunflowers are lacking in the literature.The sunflowers of this report were grown in sand culture in the greenhouse. Separate and combined treatments of two levels of aeration, three levels of nitrogen and three levels of NaCl were applied to plants which were harvested at 40 and 56 days. Seed germination was excellent in all treatments. Plant height and dry weight decreased with each type of stress. Low oxygen (0.20 μg O 2 cm -2 min -1 ) and nitrogen (10 ppm) combined with 70 meq/1 NaCl caused the greatest reduction of plant growth. Leaf number was reduced by low nitrogen and excess salt. Low oxygen reduced the accumulation of K, Ca and Mg and increased the Na and N-NO 3 content of sunflower leaves. Potassium to sodium ratios in plant
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