Element Uptake by Plants at Higher Soil Element Concentrations
5.2 Experimental Setting
5.3.2 Soil Concentration Data of the Basalt Influenced Soil near Bühren Figure 5.4 shows 6 locations where soil samples were taken in combination with a Figure 5.4 shows 6 locations where soil samples were taken in combination with a
ge-ological map. These sample locations follow the basalt body indicated in the geologic map. At each location several samples were obtained (except ID Nr. 3, one sample) and the data averaged. For sample points 3, 4 and 5 the mean values of Co and Ni were below 10 mg/kg and 25 mg/kg, respectively and therefore comparable to the values for the soils of the main field trials Garte Nord and Sömmerling (Table 7.1).
In all soil samples around Bühren, larger variations in element concentrations were detected (Table 5.4). Even within one field plot the Co concentrations ranged from 18 to 44 mg/kg, depending on the mixture of soil material with remnants of basalt rock pieces. There was very good correlation for Ni-Fe, Ni-Co and Fe-Co, as expected (Figure 5.5). The scatterplot matrix revealed that the rocks composition was slightly different, with higher concentrations and different element ratios in all selected ele-ments in the plot (Co, Ni, Mn, Mg, Fe and Cr). High pearson correlation coefficients show a stable element ratio, which is reasonable, as these elements behave geochem-ically similar. For example the ionic radii for Co and Ni are similar with 72 pm and 69 pm, respectively.
48 Chapter 5. Element Uptake by Plants at Higher Soil Element Concentrations
Figure 5.4: Soil sample locations near village Bühren (Dransfeld), left:
ID of sample sites, n= number of samples, mean Co and Ni total el-ement concentrations in mg/kg, map: cOpenStreetMap contributors, openstreetmap.org,licensed as CC BY-SA; right: Overlay of geologic map (GK25), green: Miocene basalt, yellow: Miocene age sandstones, pink:
Tertiary aged sandstone from 'Mittlerer Buntsandstein', Geologische Karte 1:25 000. cLandesamt für Bergbau, Energie und Geologie, LBEG).(NIBIS
Kartenserver, 2014).
Table 5.4: Concentrations of selected elements in soil samples close to Bühren for each eld ID shown in Fig. 5.4.
ID Subgroup Co Cr Ni Mg Mn Mo Fe
mg/kg %
R1 Rock 39.4 203 205 37 600 1210 2.80 7.67
R2 Rock 44.4 211 186 22 100 1110 2.29 8.14
R2 Rock 43.1 202 193 31 400 1180 2.64 8.31
1
Soil 33.9 96.5 125 9380 1420 1.44 5.78
Soil 30.5 82.7 106 6280 1300 1.36 5.27
Soil 35.4 95.3 123 8870 1580 1.48 6.24
Soil 32.0 87.7 109 8200 1210 1.20 5.64
2
Soil 37.9 138 139 8230 1130 1.54 5.99
Soil 38.1 205 135 8250 1160 1.58 6.02
Soil 27.1 81.9 89.8 8800 1040 1.07 4.64
Soil 44.0 123 184 7170 1240 1.80 6.90
Soil 24.8 81.6 85.2 6450 1030 1.04 4.13
Soil 17.9 47.4 58.3 5510 877 0.84 3.20
3 Soil 9.5 27 20.9 3520 793 0.63 1.84
4
Soil 7.7 24.5 17.2 3880 718 0.60 1.78
Soil 8.4 25.3 18.8 3510 705 0.64 1.73
Soil 10.1 27.8 25.5 3480 758 0.67 1.93
Soil 8.2 22.9 18.4 3800 822 0.68 1.76
5 Soil 7.2 19.9 14.8 3140 813 0.59 1.57
Soil 7.7 21.4 17 3300 863 0.68 1.69
6
Soil 22.0 62.6 70.1 7610 929 1.23 3.92
Soil 15.5 38.1 41.4 3940 751 0.88 2.58
Soil 7.5 25.4 19.9 3020 412 0.52 1.68
Will (BSc)3 Soil 24.9 54.5 84.1 7380 1090 0.99 4.32 field trial Soil 34.2 186 118 10 700 1700 1.51 6.51
pot4 Soil 34.7 146 131 8190 1260 1.49 5.98
1rock sample from basalt outcrop pillars;
2rock samples from field
3soil used in bachelor thesis M. Willerding-Möllmann
4Bühren soil used in pot trial
5.3. Results and Discussion 49
10 20 30 40 50 100 150 200 600 90012001500 100002000030000 20000400006000080000 50 100 150 200 0.00
Figure 5.5: Scatterplot matrix of concentrations (mg/kg) in soil samples (triangle) and rocks samples (circles) around Bühren. Upper panel shows
pearson correlation coecient.
50 Chapter 5. Element Uptake by Plants at Higher Soil Element Concentrations 5.3.3 Soil Element Concentrations
Table 5.5 contains the mean concentrations for selected trace elements, which are im-portant for biogas production (Co, Mn, Mo, Ni) and plant nutrition (Cu, Fe, Zn). Fur-thermore, elements indicating adhering dust or which are of environmental concern (Ti, Al, Cd) are shown.
The site in Bühren showed the greatest mean value of Co (23 mg/kg) and Ni (75 mg/kg). The two main field trials Garte Nord and Sömmerling have comparably low Co concentrations of 7 and 8 mg/kg and low Ni concentrations of 16 and 12 mg/kg, respectively. Table 5.5 also lists the concentrations of local loess (Schnetger, 1992), Upper Continental Crust (UCC), (Rudnick and Gao, 2003) and European Soil median concentrations (Reimann et al., 2018). The median European agricultural soil concentrations (GEMAS1) are 7.5 mg/kg for Co and 15 mg/kg for Ni (from 2108 sam-ples in total) (Reimann et al., 2018). The trace elements in the main field trials and at most of the other sites have similar values comparable to the loess and the GEMAS soil concentrations. The geochemical situation on site Bühren is unique and the trace elements are better comparable to the values of the UCC because of the basalt compo-nent. Mn median concentrations by Reimann et al. (2018) are 445 mg/kg (median) and 701 mg/kg (75th percentile, Q75). Most sample sites do correspond to Q75 of Mn, and only the soils at site Sömmerling have lower values. The mean values of all measured main and trace elements are shown in Appendix Table A.10.
Table 5.5:Mean total concentrations in mg/kg DM for all soil sample locations used in the study in alphabetical order, with additional values for loess, Upper Continental Crust and median European
Soil (GEMAS).
Location State n Al Cd Co Cu Fe Mn Mo Ni Ti Zn
Aholfing BY 6 30 577 0.16 5.2 7.9 13 190 761 0.44 12.7 2904 44 Bühren LS 23 56 023 0.33 22.6 19.0 39 610 1026 1.06 76.1 8113 93 Deppoldsh. LS 3 66 070 0.49 13.0 17.8 29 726 917 1.19 29.6 4593 103 Dornburg Th 6 50 463 0.29 9.9 16.8 23 504 705 0.5 21.9 4909 59 Gr. Ellersh. LS 1 49 682 0.28 12.6 26.5 28 823 805 0.64 44.0 5243 75 Garte Nord LS 21 47 245 0.25 7.3 14.0 17 576 703 0.48 16.4 4046 54
Lindau LS 2 42 866 0.26 6.6 16.4 16 981 723 0.55 15.2 3810 62
Sömmerling LS 22 41 394 0.24 8.2 7 14 440 479 0.68 11.6 3348 50 Straubing BY 6 51 117 0.19 11.1 19.1 24 041 942 0.48 27.3 4936 64
Trögen LS 1 42 190 0.27 7.2 10.7 17 570 814 0.62 14.2 4255 52
UCCa 81 500 0.09 17.0 28 39 200 770 1.1 47.0 3800 67
Würm loessb 48 200 0.10 10.0 10 21 500 460 25.0 4400 39
GEMASc 0.18 7.5 15 445 0.42 15.0 45
aRudnick and Gao, 2003 (Upper Continental Crust)
bSchnetger, 1992
cReimann et al., 2018 (Median of European Soil)
1geochemical mapping of agricultural soil, cooperation project of the Euro-GeoSurveys Geochemistry Expert Group.
5.3. Results and Discussion 51 5.3.4 Element Data from Plants grown in Bühren Soil
The element concentration of plants grown in Bühren soil (on the small-scale field trial and in pot experiments) were comparable to the median concentrations of plants grown on the main field trials. All plant element concentrations were corrected for adhering particles with Method 3 from Chapter 4. The dotted shapes in Figures 5.6 and 5.7 resemble plants on Bühren soil, either as field samples or pot experiments, and the median of the field trials are marked with yellow triangles. Dark green points mark the plants grown in small pots in 2015.
The plants grown in soil Bühren soil show the greatest element concentrations of Co, Ni and Mn in the aboveground plant tissue (Fig. 5.6). Ryegrass and cereal crops (rye, triticale) have very similar low Co values of 0.01 mg/kg .
The samples from pot and fields trial match very well in their Ni concentrations (yel-low and green circles). Amaranth, summer and winter faba bean, hairy vetch and ryegrass plants show greater element concentrations than the same plants grown on the main field trials. No elevated Ni concentrations of the cereal crops (winter rye and winter triticale) grown in Bühren soil were measured. The amaranth, summer and winter faba bean and hairy vetch plants from the small and large pot trials (darkgreen and green circles) contain less Mo than plants in the field, which were even lower than median Mo concentration of both main field trials Garte Nord and Sömmerling.
Another striking observation was that all (small) pot samples from 2015 (dark green circles in the figures) show maximum content of Co and Ni.
For plants grown in Bühren soil it was also worth looking at other elements which are naturally enriched in this particular setting, such are Fe, Mg, Cr and Zn, shown in Fig. 5.7. Greater concentrations of Fe, Mg and Zn in all samples from Bühren were measured relative to those on the two main field trials (Fig. 5.7). Cr content only increased in samples from the field trial (triangles). Faba bean samples from small pots were also elevated in Cr and Zn concentrations. Additional element data can be found in the Appendix (Tables A.16 and A.17).
52 Chapter 5. Element Uptake by Plants at Higher Soil Element Concentrations
Figure 5.6:Trace element concentrations in mg/kg of Co, Ni, Mn and Mo in whole aboveground plants from Bühren, cultivated in small pots (2015), larger pot trials (2016) and median concentrations (triangle) from both main
eld trials Garte Nord (GN) and Sömmerling (SÖ).
Figure 5.7:Trace element concentrations in mg/kg of Fe, Mg, Cr and Zn in whole aboveground plants from Bühren, cultivated in small pots (2015), larger pot trials (2016) and median concentrations (triangle) from both main eld trials Garte Nord (GN) and Sömmerling (SÖ). For Cr and Fe one outlier
is excluded (ryegrass).
5.4. Conclusions 53 5.3.5 Extraction Results
All sample site soils were extracted with 1 M NH4NO3 according to DIN 19730 (DIN Deutsches Institut für Normung e. V., 1997). This technique was used to determine the potential bioavailability of trace elements to plants. The greatest extraction concentra-tions for Co, Ni, Fe and Mn were obtained for soil in Lindau, followed by Trögen and Bühren (Fig. 5.8). The extraction rates rose with a lower soil pH. The soil from the site in Lindau with the lowest pH of 4.6, had the highest rates. The extraction results indicated, that the soil obtained from Bühren had a greater bioavailability of these el-ements than at the two main field trials with lower total soil concentrations of Co, Ni, Fe and Mn.
Figure 5.8: Results from soil extractions with NH4NO3 in mg/kg DM for Co, Ni, Fe and Mn. Soil pH values are shown in the upper text row. Each data point represent one extraction and the points are horizontally jittered
to reduce overplotting.
5.4 Conclusions
Three basic conclusions can be drawn. Firstly, the samples grown in the soil from Bühren show greater concentrations of most samples of Co, Ni, Mo, Mg and Zn in aboveground plant matter. Secondly, the pot samples have greater element concen-trations than plants from the main field trials, except for Mo. Thirdly, the small pot samples from 2015 are not comparable to the other pot samples. This was especially the case with amaranth samples from small pots having Mn concentrations about 3 times greater than all other plant species. The faba bean samples from the small pots show maximal values for Co, Ni and Cr. The amaranth and faba bean plants grown in the small pots (dark green points) may have beenn affected by different growing conditions. They grew in small pots so they were most likely to suffer deficiencies
54 Chapter 5. Element Uptake by Plants at Higher Soil Element Concentrations resulting in a shorter height. The plants in the second pot experiments of 2016 had much larger pots each containing almost 20 kg of soil. Their height and structure were much better comparable to the samples from open field. Also it may be the case, that the root system could not develop freely in the small pots.
The results from NH4NO3extractions also indicated a potentially higher bioavailabil-ity of Co, Ni, Fe and Mn from the soil in Bühren. The extraction concentration results anti-correlated to the soil pH. The main field trials show very small extraction concen-trations.
55