Adhering Particles - Methods of Correction
4.5 Results and Discussion
4.5.4 Influence of Species and Cutting Height
The quantity of adhering soil particles largely depends on the plant structure, the roughness of foliar surface area, and on the plant’s height. Crop plants with long blades and small foliar surfaces at lower plant parts, e.g. rye, have significantly less content in adhering particles than crop plants with rough or large foliar surface, e.g.
maize, amaranth (see graphical abstract and Supplements).
In order to make the effect of cutting height on the amount of adhering particles vis-ible we compare plant samples cut at 1 cm and 10 cm above ground on a similar soil
4.5. Results and Discussion 39
Figure 4.3: Coviariance biplots of PlantSample (upper, uncorrected) and Plant(lower, corrected) of a principal component analysis of log-ratio trans-formed (clr) data (712 samples with 29 elements). The proportion of the explained variance is 0.52 for the upper plot and 0.49 for the lower plot.
The position of the element labels can be interpreted as follows (van den Boogaart and Tolosana-Delgado, 2013; Greenacre, 2010): the link between two element labels represents the log-ratio between these two elements. A short link indicates that the elements have a quasi-constant log-ratio. An angle of 90◦C at the origin means that the log-ratios of the two elements are uncorrelated. Several samples and elements had to be excluded from this examination because of special circumstances (i.e. heavy metal con-taminated locations.) The general pattern of the links between elements
remains unchanged by this adaption.
40 Chapter 4. Alteration of Trace Element Concentrations in Plants by Adhering
PlantSample − analyzed Plant − corrected M.2 Plant − corrected M.3
Loc. A, cut at 10 cm, N = 37Loc. B, cut at 1 cm, N = 36
Species ●Faba Bean Rye Ryegrass Triticale Vetch
Figure 4.4:Inuence of cutting height on the Al and Ti concentrations of dierent plant species, without correction (Plant - analyzed), corrected by the smallest possible content of adhering soil - Method 2 (Plant - corrected M.2) - and corrected via Method 3 (Plant - corrected M.3) using the median
of several very small xfor calculating the content of adhering soil.
(Fig. 4.4). At Location A (field trial Sömmerling) plants were cut at 10 cm and at Lo-cation B (field trial Garte Nord) the plants were cut at 1 cm and the LoLo-cations have similar soil properties and total element concentrations.
In each location five different plant species were analyzed: Faba bean, rye, ryegrass, triticale and vetch. Both data sets had been corrected with method 2 and 3 (Fig. 4.4, Plant-corrected-M.2, and Plant-corrected M.3). In order to show the effect of adher-ing soil particles and the impact of the two correction methods two typical "indicator elements" (Elind), Al and Ti, are shown (Fig. 4.4).
We assume the concentrations in the analyzed plant material (PlantSample) to be bi-ased by adhering soil particles because (1) Al and Ti should show very little to no uptake at pH 6-7 in the soils but nearly all samples show considerable high concen-tration values (Fig. 4.4, Plant- analyzed), (2) none of the species are known as Al- or Ti-accumulator species and (3) the ratios of Al/Ti of the plants (median 9.8) is very close to the ratio Al/Ti in the soils (median 12.3) and there is no species-dependency which would be expected for elements with different chemical characteristics.
The concentrations prior to correction also show a very huge spread. For samples cut at 10 cm (Location A) Al range from 11 - 350 mg/kg and Ti from 1 - 33 mg/kg. For samples cut close to the ground at 1 cm (Location B) Al range from 21 - 2850 mg/kg and Ti from 2 - 375 mg/kg. Most probably the amount of soil adhering is greater at Location B.
After applying a correction on the plants the concentrations of Ti and Al are notably reduced for most samples and the ratio Al/Ti is smaller (median 3.7 for method 2)
4.6. Conclusions 41 and more variable. That indicates that for most samples Al and Ti concentrations after correction are far less biased by adhering particles.
Nevertheless, there are different results for correction method 2 and 3. Correction method 2 is less intense because only the smallest possible amount ofAPis removed and this probably results into undercorrection for some samples. For example some samples of faba bean the concentration of Al and Ti calculated via method 2 and cut at 10 cm are elevated (maximum for Al >100 mg/kg).
Correction method 3 shows very good and reliable results for samples with small amount of adhering particles (Location A). But for very high amount of adhering par-ticles, which is the case for the samples cut at 1 cm in Location B, concentrations after correction show a huge spread. More than 15 samples were overcorrected (Al = 0), while some samples show almost no correction (two ryegrass and one rye samples with Al >50 ppm). Only for samples with the lowest Al- and Ti-concentration prior to correction show reasonable Al- and Ti concentrations after correction. Overcorrection can occur if the concentrations of elements of the group ofElind are so high that the absolute error of these elements overlaps with the error of micro-nutrients, hence the algorithm cannot discriminate betweenElindand other elements. In this case the me-dian will be calculated by a mixture ofElindand micro-nutrients and ¯xwill be far too high. On the other hand for samples where the smallestxis very small the error range does not overlap with the error range ofElindwith very high concentrations, hence ¯x will be calculated by only very fewElindand might lead to undercorrection. For these low cut samples one solution would be to choose a fixedElindelement (Al, Ti) for all samples to overcome these problems.
4.6 Conclusions
We provide three mathematical methods to correct plant samples for adhering parti-cles to obtain real trace element concentrations in plants by using total element con-centrations of plant and soil materials in the calculations. The sampling techniques (for example cutting height) can influence the amount of adhering particles to a great extent and the correction method becomes less precise at high adhering particles con-centrations. We therefore recommend for research projects on trace elements with a possible bias by adhering material (e.g. Mn, Ni, Ba, Co, Fe, Cs) to adjust the cutting height to at least 10 cm, or correct the analyzed concentration data with one of these three methods.
While adhering soil particles hardly change concentrations of major nutrient elements (P, Mg, K, S, Ca) and some minor nutrient elements (Cu, Zn, Mo) they can have a strong impact on other trace elements in plants, such as Fe, Ni, Co, REE, Al, Ti, Hf, Zr and Th.
Acknowledgement
This research was conducted with funding of the FNR (Agency for Renewable Re-sources, Gülzow, Germany) on behalf of the BMEL (German Federal Ministry of Food and Agriculture, Berlin), the MWK (Ministry of Science and Culture of Lower Sax-ony, Hannover, Germany), and the StMELF (Bavarian State Ministry of Food, Agricul-ture and Forestry). We thank Prof. Dr. Rolf Rauber and Katharina Hey (Division of
42 Chapter 4. Alteration of Trace Element Concentrations in Plants by Adhering Particles - Methods of Correction
Agronomy, Department of Crop Sciences, Georg-August-University Göttingen, Ger-many) for conducting field trials and providing some of the samples. We also thank Dr. Maendy Fritz and Veronika Eberl from the Technology and Support Centre (TFZ) in Straubing, Germany, for providing Amaranth samples.
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