J. Agric. Food Chem. 2006, 54, 3341−3350
3341
Effects of Fertilization, Crop Year, Variety, and Provenance Factors on Mineral Concentrations in Onions KAORU ARIYAMA,*,† TADASHI NISHIDA,‡ TOMOAKI NODA,‡ MASASHI KADOKURA,† AND AKEMI YASUI§ Center for Food Quality, Labeling and Consumer Services, 2-1 Shintoshin, Chuo-ku, Saitama-shi 330-9731, Japan; Hokkaido Kitami Agricultural Experiment Station, 52 Jiyayoi, Kunneppu-cho, Hokkaido 099-1496, Japan; and National Food Research Institute, 2-1-12, Tsukuba-shi, Ibaraki, 305-8642, Japan
Mineral concentrations of onions (Allium cepa L.) grown under various conditions, including factors (fertilization, crop year, variety, and provenance), were investigated to clarify how much each factor contributes to the variation of their concentrations. This was because the mineral concentrations might be affected by various factors. The ultimate goal of this study was to develop a technique to determine the geographic origins of onions by mineral composition. Samples were onions grown under various conditions at 52 fields in 18 farms in Hokkaido, Japan. Twenty-six elements (Li, Na, Mg, Al, P, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr, Y, Mo, Cd, Cs, Ba, La, Ce, Nd, Gd, W, and Tl) in these samples were determined by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. Fertilization conditions and crop years of onions caused variations of P, Ni, Cu, Rb, Sr, Mo, Cs, and Tl concentrations in onions; different onion varieties also showed variations in numerous element concentrations. However, the variations of mineral compositions of onions by these factors were smaller than the differences between production places with a few exceptions. Furthermore, Na, Rb, and Cs in group IA of the periodic table, Ca, Sr, and Ba in group IIA, and Zn and Cd in group IIB showed similar concentration patterns by group; this result demonstrated that elements in the same periodic groups behaved similarly in terms of their absorption in onions. KEYWORDS: Onion; mineral; geographic origin; fertilization experiment; correlation; element concentration
INTRODUCTION
Nowadays laws in many countries enforce labeling of the geographic origin of agricultural products due to demands for more information on foods by consumers and also to maintain domestic agricultural production. It therefore becomes important to find ways of preventing deceptive labeling of the geographic origin. The development of scientific techniques to determine the geographic origin of agricultural products is needed to cope with this issue. Numerous techniques based on organic constituents (1, 2), mineral contents or composition (3, 4), light (7, 8) or heavy element (9, 10) isotope ratios or their combination (11, 12) have already been reported. The technique based on mineral composition is the most commonly applied nowadays because inductively coupled plasma atomic emission spectrometer (ICP-AES) and inductively coupled plasma mass spectrometer (ICP-MS) have comparatively prevailed and can * Author to whom correspondence should be addressed (telephone 8148-600-2365; fax +81-48-600-2377; e-mail
[email protected]). † Center for Food Quality, Labeling and Consumer Services. ‡ Hokkaido Kitami Agricultural Experiment Station. § National Food Research Institute.
acquire considerable data simultaneously. We have been studying methods for using this technique to determine the geographic origin of onions (Allium cepa L.) from the experience of a previous study on the geographic origin of Welsh onions (3, 4). Mineral compositions in agricultural products, however, might vary by various factors such as fertilization, climatic condition in the cultivated year, differences in soil types, history of fields and varietyseven within a single farm field. This issue makes the development of reliable techniques of place-of-origin determination using mineral composition difficult. Therefore, it is important to know what elements are affected easily and how much those element concentrations vary by various factors. The objective of this study was to investigate the range and pattern of variance of mineral composition of onions grown under different conditions such as fertilization, crop year, variety, and provenance. This information was expected to be helpful in the development of methods for determining the geographic origins of onions by mineral composition. Onions from fields within Hokkaido, Japan, were used as provenance factors in this study because clearer differences between far-apart regions are expected if differences between near regions are observed.
10.1021/jf0525481 CCC: $33.50 © 2006 American Chemical Society Published on Web 04/01/2006
3342
J. Agric. Food Chem., Vol. 54, No. 9, 2006
Ariyama et al.
Table 1. Cultivation Conditions and Varieties of Onion Samples in 52 Fields sample
type of expt
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Zn 1 (nonfertilized) Zn 2 (nonfertilized)
47
Zn 1 (fertilized)
48 49 50 51 52
Zn 2 (fertilized
a
provenancea provenance provenance provenance provenance provenance provenance varietyb variety variety variety variety variety variety variety variety variety variety variety Nc (0 kg/a) N (0.5 kg/a) N (1.0 kg/a)
crop yeard 1
crop year 1
crop year 2
N (2.0 kg/a) N (3.0 kg/a) Ca (fertilized) Mg (fertilized) Ca + Mg (nonfertilized)
crop year 1 crop year 2 crop year 2
tentative name of farm
place of production
crop year
variety (abbreviation)
soil type
exptl farm 1 exptl farm 2 Kitami 1 Kitami 2 Tanno 1 Tanno 2 Kunneppu 1 Kunneppu 2 Bihoro 1 Bihoro 2 Bihoro 3 Bihoro 4 Furano 1 Furano 2 Furano 3 Iwamizawa 1 Iwamizawa 2 exptl farm 1 Kitami 2 Tanno 2 Kunneppu 3 Bihoro 3 Bihoro 2 Furano 1 Iwamizawa 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 expyl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 2 exptl farm 2 exptl farm 2
Wakaba, Kunneppu town Yayoi, Kunneppu town Hirosato, Kitami city Toyochi, Kitami city Kawamukai, Tanno town Kawamukai, Tanno town Kashiwaoka, Kunneppu town Jitsugo, Kunneppu town Tyohoro, Bihoro town Akino, Bihoro town Akino, Bihoro town Mihukita, Bihoro town Kitaonuma, Furano city Kamigoku, Furano city Gakudasanku, Furano city Nishikawacho, Iwamizawa city Nencho, Iwamizawa city Wakaba, Kunneppu town Toyochi, Kitami city Kawamukai, Tanno town Koen, Kunnepp town Akino, Bihoro town Akino, Bihoro town Kitanuma, Furano city Nishikawacho, Iwamizawa city Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Yahoi, Kunneppu town Yahoi, Kunneppu town Yahoi, Kunneppu town
1 8 29 >20 15 >20 >20 16 >50 7 >30 >30 15 >40 >30 27 30 1 >20 >20 >20 >30 7 4 27 6 6 6 6 6 6 6 6 6 6 6 6 1 1 1 1 1 1 1 8 8
Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Kitamomiji2000 (KM) Kitamomiji2000 (KM) Kitamomiji2000 (KM) Kitamomiji2000 (KM) Kitamomiji2000 (KM) Kitamomiji2000 (KM) Kitamomiji2000 (KM) Kitamomiji2000 (KM) Super-kitamomiji (SKM) Kitamomiji2000 Kamui Kairo’ohotsuku1 (KO1) Salari Wolf Iomante Kitahayate2 (KH2) Kitamikou38 (KMI38) Kitamikou39 (KMI39) Kitawase3 (KW3) Ohotsuku222 (O222) Kitamikou39 (KMI39) Kitamikou39 (KMI39) Kitamikou39 (KMI39) Kitamikou39 (KMI39) Kitamikou39 (KMI39) Kitamikou39 (KMI39) Super-kitamomiji (SKM) Super-kitamomiji (SKM) Super-kitamomiji (SKM)
gray lowland black volcanic gray highland brown lowland brown lowland brown lowland gray highland brown lowland brown forest brown lowland brown lowland peat peat brown lowland brown lowland peat gray lowland gray lowland brown lowland brown volcanic gray highland brown lowland brown lowland gray lowland peat gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland gray lowland black volcanic black volcanic black volcanic
exptl farm 1
Wakaba, Kunneppu town
8
Super-kitamomiji (SKM)
gray lowland
exptl farm 2 exptl farm 1 exptl farm 1 exptl farm 1 exptl farm 1
Yahoi, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town Wakaba, Kunneppu town
1 24 24 24 8
Super-kitamomiji (SKM) Super-kitamomiji (SKM) Kitamomiji2000 (KM) Kairo’ohotsuku1 (KO1) Kairo’ohotsuku1 (KO1)
black volcanic gray lowland gray lowland gray lowland gray lowland
fertilization for fertilizing expt
(NH4)2SO4: (NH4)2SO4: (NH4)2SO4: (NH4)2SO4: (NH4)2SO4: (NH4)2SO4:
0.0 kg/a 2.3 kg/a 4.7 kg/a 7.0 kg/a 9.3 kg/a 14 kg/a
particle-shaped CaCO3 coated with lignin MgSO4: 6.0 kg/a Azumin (fertilizer including 60% humus acid and zinc): 10 kg/a
Provenance experiment. b Variety experiment. c N, Ca, Mg, and Zn indicate the fertilization experiment of each element. d Crop year experiment.
This study also examined from several other viewpoints how differences in cultivation conditions or varieties affect contents of the 26 elements in onions. MATERIALS AND METHODS Samples. Samples were onions (A. cepa L.) grown under various conditions from 52 fields on 18 farms in Hokkaido, Japan, in 2004 (Table 1). About 20 kg of onions were collected from five spots in each field, dried, and processed in the same manner as onions for marketing, randomly sampled as 10 onions from each field and made into composites for analyses. The number of onions for a composite was decided by a previous examination (13) as follows. As a model case, 10 onions were randomly sampled from a field, and each onion was analyzed three times repeatedly to obtain sampling and analytical variations. The element that had the largest sampling variation was
Ni, and the variation coefficient by one-onion sampling was 39%. The variation coefficient by 10-onion sampling was calculated as 12%; this variation level was low enough to be considered representative from a field. Four individual onions were also sampled from 34 fields, in which onions for fertilization, crop year, variety, and provenance examples were cultivated, and each of the four individuals was used for mineral analysis to include individual differences within onions from the same field with an analytical variation. In fact, these samples were used for analyses of both 10-onion composite and 4 individual-onion concentrations. The details of samples from these 34 fields are described as follows. Onions from five fields fertilized with (NH4)2SO4 at 0, 0.5, 1, 2, and 3 kg of N/are (the normal level is ∼1.2 kg of N/a) were collected for the N fertilization experiment. Onions from fields fertilized and not-fertilized with particle-shaped CaCO3 (mixed with lignin to prevent
J. Agric. Food Chem., Vol. 54, No. 9, 2006
Mineral Concentrations in Onions
3343
Table 2. Operating Conditions for ICP-AES and ICP-MS Instruments ICP-AES plasma condition RP power plasma gas auxiliary gas nebulizer gas solution uptake rate signal acquisition integration time axial radial integration
1.15 kW 14 L/min 0.5 L/min 0.22 MPa 1.4 mL/min 20 s 10 s 1 time
ICP-MS plasma condition RP power plasma gas auxiliary gas nebulizer gas solution uptake rate signal acquisition data point integration time integration
1.4 kW 14.2 L/min 0.97 L/min 1.22 L/min 0.7 mL/min 3 points/peak 0.1 s/point 3 times
element
wavelength (nm)
observation direction
element
m/z
Na P K Mg Ca Mn Fe Zn Sr Ba
589.592 213.618 766.490 279.553 184.006 257.610 238.204 213.856 407.771 455.403
radial axial radial radial axial axial axial axial radial radial
Li Al Co Ni Cu Rb Y Mo Cd In Cs La Ce Nd Gd W Tl
7 40 51 59 60 63 85 89 98 111 115 133 139 140 146 157 205
Figure 1. Correlations between P, K, Mg, Ca, and Zn concentrations in 52 onion samples and these element concentrations extracted from soils. scattering) were collected for the Ca fertilization experiment. Onions from fields fertilized and not-fertilized with MgSO4 were collected for the Mg fertilization experiment. Onions from fields of two kinds of soil types, fertilized and not fertilized with 60% humus acid including Zn, were collected for the Zn fertilization experiment. For these fertilization experiments, fertilizers were applied 2 or 3 days before onions were planted, as is the common procedure for onion cultivation in Hokkaido. Fertilizers used for fertilization experiments of Ca, Mg, and Zn are applied if soil diagnosis indicates that such fertilization is required. The amounts of applied fertilizer in these experiments were within ordinary levels. The fields of onions compared in fertilization experiments had the same cultivation conditions except for fertilization and were planted in adjoining fields on an experimental farm in the town of Kunneppu. Onions of two varieties (Super-kitamomiji and Kairyo-ohostuku 1) from fields of crop years 1, 6, and 24 (years onions have been cultivated continuously in the field) were collected for crop-year experiments in this study. The fields for crop year 1 and 6 samples were adjoining, and these fields were located only ∼100 m from the crop year 24 field. Otherwise, each field had the same cultivation conditions. Continuous cropping is a common practice for onion cultivation in Hokkaido, and fields of 10 crop years or more are common in most of the main production regions. Onions of 12 varieties cultivated under the same conditions were collected from a field on an experimental farm in the town of Kunneppu for the variety experiment. Onions for the provenance experiment were collected from seven fields in six cities or towns representative of the production areas in Hokkaido. Soils were sampled by a total of 2 kg from plow layers of four corners and the midpoint of ∼100 m square sections showing average onion growth and soil conditions in onion-sampled fields and were homogenized. Determination of Onion Mineral Contents. Analyses were basically carried out according to the method reported by Ariyama et al. (4, 5), with some minor modifications. Each of 52 samples was prepared by homogenizing 10 onions, and 26 elements were determined. The target part of an onion sample was the bulb excluding the orange or
brown outer skins, the top edge, and the region within 1 cm from the base. To homogenize 10 onions, each target part of 10 onions was evenly cut into 16 or 24 along the axis, and the diagonal parts were placed in beakers; finally, they were pulverized by a mixer with ceramic cutting blades (B400, Nihon Bu¨chi, Tokyo, Japan). A test portion, ∼5 g (corresponds to ∼0.5 g in dry weight), of each pulverized sample was transferred to a Teflon beaker. Acid digestion was carried out in an open vessel by HNO3, HClO4, and HF. Acids used were 61% HNO3 (electronics industry grade, Kanto Kagaku, Tokyo, Japan), 60% HClO4 (atomic absorption spectroscopy grade, Tokyo, Kanto Kagaku, Japan), and 50% HF (semiconductor grade, Daikin, Osaka, Japan). Moisture was obtained by drying 5-6 g of a pulverized sample in an Al foil cup at 70 °C for 24 h under atmospheric pressure. This series of procedures was triplicated, and blank analyses without the test portion were also performed three times together with sample analyses. To investigate differences in mineral concentrations between samples with different factors (fertilization, crop year, variety, and provenance), 34 samples corresponding to types of experiments assigned in Table 1 were prepared by pulverizing one onion. This preparation was repeated with four onions. In these experiments, the entire target part of the onion was pulverized by a mixer with ceramic cutting blades. The following procedure was the same as the analysis of a sample prepared with 10 onions. This series of procedures, however, was not repeated but performed just once, and blank analyses without the test portion were performed three times together with sample analyses. Ten elements (Na, Mg, P, K, Ca, Mn, Fe, Zn, Sr, and Ba) were simultaneously determined by inductively coupled plasma atomic emission spectrometry (ICP-AES; IRIS Advantage, Thermo Electron, Waltham, MA). Sixteen elements (Li, Al, Co, Ni, Cu, Rb, Y, Mo, Cd, Cs, La, Ce, Nd, Gd, W, and Tl) were simultaneously determined by inductively coupled plasma mass spectrometry (ICP-MS; HP4500, Agilent Technologies, Palo Alto, CA) using In as an internal standard. Measurement conditions are shown in Table 2. Soil Analysis. Each soil sample was dried in air at ∼15 °C for 3 weeks, after passing through a 2-mm sieve, and analyzed according to the standard method in Hokkaido (14). Soil pH (H2O) was measured by glass electrode. Exchangeable cations of MgO, K2O, and CaO were
3344
J. Agric. Food Chem., Vol. 54, No. 9, 2006
Ariyama et al.
Table 3. Detection Limits, Results of N Fertilization Experiment, Averages of Element Concentrations in Four Onions from Each of the N-Fertilized Fields, Significance by ANOVA and t Tests, and Results of Soil Analyses concn in onion (µg/g)c
Li*d Na Mg Al P K Ca Mn Fe Co Ni Cu Zn Rb*d Sr Y Mo Cd Cs Ba La Ce Nd Gd W Tl**d
DLa (µg/g)c
0 kg/a, sample 38
0.5 kg/a, sample 39
1 kg/a, sample 40
2 kg/a, sample 42
0.001 14 2 0.6 11 41 4 0.1 2 0.001 0.04 0.6 1 0.04 0.1 0.001 0.002 0.001 0.001 0.2 0.001 0.001 0.001 0.001 0.001 0.001
0.005 330 811 ND 3090 18700 923 9.7 11 0.014 0.07 3.2 13.1 29.0 2.9 0.005 0.026 0.056 0.064 1.5 ND 0.002 ND ND ND 0.031
0.005 430 921 ND 3480 18900 887 12.2 23 0.019 0.15 3.6 16.4 32.5 2.7 0.001 0.021 0.077 0.098 1.4 ND 0.005 ND ND ND 0.029
0.004 440 940 ND 3610 17200 1090 11.6 18 0.015 0.19 4.1 13.3 32.5 3.5 0.001 0.024 0.069 0.100 1.1 ND 0.002 ND ND ND 0.026
0.003 330 1000 0.8 3550 18900 1330 13.3 19 0.015 0.13 4.0 13.2 40.4 3.2 0.001 0.025 0.059 0.094 0.9 ND 0.002 ND ND ND 0.017
5.8 0.47 0.57 0.19 3.25 4.3
Li*e Na*e Mg*e Al P K Ca Mn**e Fe*e Co Ni Cu Zn Rb*e Sr Y Mo**e Cd**e Cs*e Ba La Ce Nd Gd W Tl
3 kg/a, sample 43
variation in groupsb
0.009 70 1020 ND 3800 22000 1140 8.0 25 0.036 0.14 3.2 17.4 35.3 3.1 0.001 0.008 0.130 0.051 0.7 0.002 0.002 0.001 ND ND 0.016
0.001 145 688 0.5 430 2810 329 1.9 6 0.012 0.06 0.9 2 3.5 1.1 0.003 0.003 0.012 0.020 0.6 0.002 0.004 0.001
5.8
results of soil analyses (pH) 5.8 6.1
5.5
0.41
exchangeable MgO (mg/g) 0.42 0.39
0.39
0.49
phosphatic acid availability in soil (mg/g) 0.48 0.60
0.004
0.45
0.14
exchangeable K2O (mg/g) 0.16 0.17
0.21
2.75
exchangeable CaO (mg/g) 3.17 3.24
2.99
3.5
HCl-extracted Zn (µg/g) 3.7 4.0
5.0
a Detection limit; caluculated as 3 times the standard deviation of concentrations obtained by 12 blank analyses. b Square root of total variance within all groups divided by degree of freedom. c Concentration units shown on a dry weight basis. d Significance between samples 38, 39, 40, and 42: *, 5% significant; **, 1% significant. e Significance between samples 42 and 43: *, 5% significant; **, 1% significant.
extracted by batch method with ammonium acetate (pH 7) and determined by atomic absorption spectrometry. Available phosphoric acid was measured according to the Truog method (includes 0.001 mol/L sulfuric acid extraction for 30 min). Zinc was extracted in 0.1 mol/L HCl and determined by atomic absorption spectrometry. Li and Mo from fertilizers (CaCO3 and MgSO4) and soil samples 45 and 46 were extracted according to the extraction method of available Mo with acidic ammonium oxalate (15). Ca, Ni, Cu, Zn, and Sr from humus acid fertilizer and soil samples 1, 2, 47, and 48 were extracted by 0.1 mol/L HCl method. These elements in extracted solutions were determined by ICP-MS (HP4500, Agilent Technologies). Statistical Analysis. Mineral data above and at detection limits were used for statistical analyses, but t test and analysis of variance (ANOVA) on the data less than quantitation limits are not shown. The significance of differences between two samples was judged by a two-sided test that did not hypothesize the homoscedasticity, and the significance of differences between more than two samples was judged by ANOVA using the application software Microsoft Excel 2002 (Microsoft, Redmond, WA). Data for these statistical analyses were element concentrations of 4 individual onions sampled from each of 34 fields. Cluster analysis was carried out using the application software Statistica Pro 03J (StatSoft Japan, Tokyo, Japan). The elements used
for cluster analyses were the 21 elements (Li, Na, Mg, Al, P, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr, Y, Mo, Cd, Cs, Ba, and Tl) having analytical results above the detection limits for onion samples in more than half of the 52 samples. Cluster analyses for classifying all production places clearly were also tried by choosing elements used for analyses from 21 elements. Element data used for cluster analysis were standardized concentrations in 10-onion composites from each of 52 fields. Euclidean distance was used as the scale to calculate differences between samples as simple distances without weighting. The linkage rule was the Ward method, generally regarded as efficient for significant clustering (16). RESULTS AND DISCUSION
Correlation between Onions and Soils. Twenty-six elements in 52 onion samples were determined, and soils from fields where these samples were grown were analyzed. Figure 1 shows correlations between concentrations of 5 elements (P, K, Mg, Ca, and Zn) in 52 onion samples and those extracted from soil (available P2O5, exchangeable K2O, exchangeable MgO, exchangeable CaO, and HCl-extracted Zn). Correlations of P and K were not significant at the 5% level. For Mg, Ca, and Zn,
J. Agric. Food Chem., Vol. 54, No. 9, 2006
Mineral Concentrations in Onions Table 4. Results of Ca and Mg Fertilization Experiments: Averages of Element Concentrations in Four Onions from Each of the Nonfertilized and Fertilized Fields, Significance by ANOVA and t Tests, and Results of Soil Analyses
Table 5. Results of Zn Experiments at Two Types of Fields: Averages of Element Concentrations in Four Onions from Each of the Nonfertilized and Fertilized Fields, Significance by t Test, and Results of Soil Analyses
concn in onionb (µg/g)
Li Na Mg Al P K Ca Mn Fe Co Ni Cu Zn Rb Sr Y Mo Cd Cs Ba La Ce Nd Gd W Tl
concn in onion (µg/g)b
nonfertilized, sample 46
Ca expt, sample 44
Mg expt, sample 45
ND 70 933 ND 2760 17700 1910 10.3 14 ND 0.08 4.7 11 9.86 5.5 ND 0.110 0.059 0.004 2.3 ND ND ND ND ND 0.003
ND 70 839 ND 2480 17600 1800 9.2 13 0.002 0.04 4.4 10 9.77 5.3 ND 0.152c 0.059 0.003 2.7 ND ND ND ND ND 0.002
ND 70 860 ND 2570 17400 1950 9.9 12 0.002 0.10 4.8 10 10.0 5.8 ND 0.166d 0.069 0.003 2.7 ND ND ND ND ND 0.003
6.3
results of soil analyses (pH) 6.5
0.29
exchangeable MgO (mg/g) 0.28
variation in groupsa (µg/g)b 6 76 203 1020 372 1.8 2 0.012 0.06 0.9 2 0.8 1.0 0.026 0.009 0.006 0.5
0.001
gray lowland soil, crop year 1
black volcanic soil, crop year 8
nonfertilized, fertilized, variation sample 1 sample 47 in groupsa
nonfertilized, fertilized, variation sample 2 sample 48 in groupsa
Li 0.005 0.007 0.003 Na 190 160 6 Mg 1030 1130 95 Al ND ND P 3220 3820 202 K 17500 19700 1600 c Ca* 1540 2080 304 Mn 14.0 16.5 2.0 Fe 18 21 3 Co 0.013 0.014 0.004 Ni*c 0.10 0.14 0.02 Cu*c 2.6 5.4 1.0 Zn 14 17 2 Rb 35.1 34.3 4.6 c Sr** 5.9 8.1 0.5 Y ND 0.002 0.002 Mo 0.032 0.036 0.015 Cd 0.081 0.098 0.025 Cs 0.073 0.047 0.016 Ba 2.6 3.5 0.6 La ND 0.002 0.001 Ce ND 0.002 0.002 Nd ND ND Gd ND ND W ND 0.002 0.002 Tl 0.025 0.023 0.006
6.4 0.26
Li 0.001 0.001 Na 70 60 Mg 854 934 Al ND ND P 2410 2390 K 18200 17700 Ca 1550 2070 Mn 8.9 11.1 Fe 16 14 Co ND 0.002 Ni 0.07 0.13 Cu**c 1.9 5.7 Zn 9 10 Rb 11.0 10.8 Sr 4.3 5.7 Y ND ND Mo 0.109 0.108 Cd 0.061 0.091 Cs 0.004 0.004 Ba 1.9 2.7 La ND ND Ce ND ND Nd ND ND Gd ND ND W ND ND Tl 0.004 0.004
6.0
results of soil analyses (pH) 5.8 6.3
6.2
0.42
exchangeable MgO (mg/g) 0.44 0.32
0.32 1.61
1.34
phosphatic acid availability in soil (mg/g) 1.52
0.95
0.45
phosphatic acid availability in soil (mg/g) 0.48 1.63
0.58
exchangeable K2O (mg/g) 0.60
0.65
0.26
exchangeable K2O (mg/g) 0.20 0.56
0.61
5.39
exchangeable CaO (mg/g) 5.78 5.39
5.40
5.39 4.0
3345
exchangeable CaO (mg/g) 5.78 HCl-extracted Zn (µg/g) 4.7
4.92
0.001 7 64 184 673 328 1.8 4 0.003 0.03 0.3 1 0.6 0.9 0.017 0.017 0.000 0.6
0.001
HCl-extracted Zn (µg/g) 5.1
4.4
a
Square root of total variance within all groups divided by degree of freedom. b Concentration units shown on a dry weight basis. c Significance between samples 46 and 44: *, 5% significant. d Significance between samples 46 and 45: *, 5% significant.
positive correlations at the 1% significance level were obtained. However, correlations of Ca and Zn were low; the r2 values of these elements were 0.1882 and 0.2086, respectively, whereas the r2 of Mg was 0.3532. Correlations between 20 element concentrations in 52 onion samples and soil pH are shown in the Supporting Information. Concentrations of Mn and Cd had negative correlations with soil pH; r2 values were above 0.3. It was demonstrated that absorption of Cd, which is harmful for humans, is more easily affected by soil pH than those of the other 19 elements. The elements that obtained correlations at the 5% significance level (except Mn and Cd) were Na, K, Zn, Mo, Ba, and Tl. Of these elements, Na, K, Zn, and Tl had a tendency of higher concentrations in onions with lower soil pH. On the contrary, Mo and Ba had a tendency of higher concentrations with higher soil pH. As described above, correlations between element concentrations in onions and results of soil analyses were 1 or 5%
6.0
4.4
5.1
a Square root of total variance within groups divided by degree of freedom. Concentration units are shown on a dry weight basis. c *, 5% significant; **, 1% significant. b
significant only for some elements, so their correlations were not sufficient to estimate any element concentration in an onion from results of soil analyses. Fertilization Experiments. N Fertilization Experiment. Detection limits of minerals in onions and analytical results of onions from fields N-fertilized at five levels (0, 0.5, 1, 2, and 3 kg of N/a) and soils from these fields are shown in Table 3. Onions from fields fertilized at 3 kg of N/acre showed greatly different element patterns from the others: Li, Mg, P, K, Mn, Fe, and Cd had higher concentrations but Na, Rb, Mo, Cs, and Ba had lower concentrations than ones fertilized at 2 kg of N/a at 1 or 5% significance levels. The soil pH was obviously low, and the low concentration of Mo and high concentrations of Mn and Cd might have been due to this. In addition, these onions’ growth was suppressed, which is considered to be caused by overfertilization. This is likely why the element pattern differed greatly from those of onions at lower N levels of fertilization. In onions fertilized at
