Wheat and Soil Response to Wood Fly Ash Application in ...

Published April 23, 2014 Agronomy, Soils & Environmental Quality

Wheat and Soil Response to Wood Fly Ash Application in Contaminated Soils Pavla Ochecova,* Pavel Tlustos, and Jirina Szakova

ABSTRACT

Wood fly ash from biofuel combustion plants is landfi lled commonly as a waste, but research of this material is needed because it may reduce future fertilizer requirements. We investigated the effect of the ash application on potential changes in pH, nutrient, and potentially toxic element (in our case As, Cd, and Pb) content and mobility in soils. Wood fly ash in doses up to 1% (w/w) was added to spring wheat (Triticum aestivum L.) grown in potentially toxic element-contaminated loam (Cambisol) and sandy clay loam (Fluvisol) soil material in 3-yr pot experiment. The potentially toxic element contents in soils exceeded the maximum permissible limits for Czech soils, but the plant availability was, thanks to ash addition, limited. The effect of wood ash was greater in the Cambisol where Cd, Zn, and also Pb showed similar trends, and their content in plant decreased (Cd by 60%, Zn by 50%, and Pb by 45%), whereas the nutrient contents tended to increase in plants. Differences were usually insignificant (α = 0.05) in the Fluvisol between treatments, and Ca, Mg, and P contents were highest in the treatment without ash addition. The influence of soil changes on element uptake and distribution within the aboveground plant biomass was also observed. These findings are an important step on providing evidence of the benefits of using wood fly ash as a fertilizer supplement, because potentially toxic element contents in wheat grown in contaminated soils with ash addition were low and decreased, whereas the concentrations of major nutrients increased.

Biomass is becoming increasingly important

worldwide as an alternative to fossil fuels. After combustion, the remaining ash contains several elements essential for agricultural crops, and therefore it would be beneficial to return the ash to soils. Currently, the majority of generated ash is sent to landfi lls in many countries worldwide (Kopecky et al., 1995; Insam et al., 2009; Saarsalmi et al., 2010; Vassilev et al., 2013). In the future, ash disposal will become more problematic since environmental regulations for landfi lls are becoming more stringent, landfi ll sites are becoming less available, and disposal costs are increasing. Land application of wood ash could be cheaper and more environmentally sound (Etiegni et al., 1990), because recycling of the ash could reduce the need for commercial fertilizers, counteracts the ongoing acidification, and can solve the potential problem of ash disposal (Etiegni et al., 1990; Zhang et al., 2002; Park et al., 2004). Application of wood ash to agricultural land provides an opportunity to recover Ca, K, Mg, P, S, and micronutrients that were contained in the wood. High Ca, Mg, and K contents are usually in the form of carbonates, because Czech Univ. of Life Sciences Prague, Dep. of Agroenvironmental Chemistry and Plant Nutrition, Kamýcká 126, Prague 6- Suchdol, CZ 16000. Received 30 July 2013. *Corresponding author ([email protected]). Published in Agron. J. 106:995–1002 (2014) doi:10.2134/agronj13.0363 Available freely online through the author-supported open access option. Copyright © 2014 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

during the combustion of wood at high temperature, organic compounds are mineralized and the basic cations are transformed to their oxides, which are slowly hydrated and subsequently carbonated under atmospheric conditions (Demeyer et al., 2001). The nutrient content of wood ash will vary depending on the burned tree species, soil type, and climate as well as the conditions of combustion, collection, and storage (Pasquini and Alexander, 2004). The change in soil nutrient availability is a combination of three factors: (i) nutrient addition from the ash; (ii) shifts in pH-dependent soil chemical equilibria; and (iii) changes (mostly increases) in microbial activity (Demeyer et al., 2001). However, in addition to macronutrients and micronutrients required for plant growth, wood ash also may contain harmful substances, including potentially toxic elements (Park et al., 2004; Patterson et al., 2004; Eichler-Löbermann et al., 2008). But the potentially toxic element content of wood ash is low compared to other residues used as fertilizers (such as sewage sludge), and therefore the chance of contaminants entering the food chain is also low (Omil et al., 2007). Moreover, the application of wood ash can result in immobilization of some metals in soil due to increased soil pH (Demeyer et al., 2001; Omil et al., 2007) because the ash is generally alkaline material. High pH value indicates that part of the dissolved metals in the ash occur as basic metal salts, oxides, hydroxides, and in particular carbonates (Zhang et al., 2002; Kuokkanen et al., 2009; Saarsalmi et al., 2010). Pitman’s (2006) opinion was that changes in soil pH caused by alkaline metals in added ash could be likely more limiting to wood ash use on soils than potentially toxic element contamination.

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Demeyer et al. (2001) stated that potential application of wood ash in agriculture does not present any major risk for the environment if (i) no excessive amounts are applied and (ii) only ash from the burning of pure wood residues is used. Many papers have been published concerning possible land application of coal fly ash (Adriano et al., 1982, 2002; Menon et al., 1990; Carlson and Adriano, 1991; Ghuman et al., 1994; Adriano, 2001; Sajwan et al., 2003). However, little is known about the use of wood fly ash. Relative to coal, biomass generally has less C, more oxygen, more silica, Cl, and K, less Al, Fe, Ti, and S, and more Ca (Khan et al., 2009). Therefore we can expect a different behavior of the ash produced from biomass. We investigated the effect of the wood fly ash application on potential changes in pH, nutrient, and potentially toxic element (in our case As, Cd, and Pb) content and mobility in soils. Another new aspect of the study is the use of two different potentially toxic element contaminated soils, because the available literature sources describe studies using common soils without potentially toxic element contamination; and the 3-yr cumulative effect of ash addition. In this context, soils contaminated by potentially toxic elements were chosen for the experiment to estimate the effect of the ash on the decrease of potentially toxic element content in these soils. Within the study, changes of nutrients and potentially toxic elements in soils after ash addition were studied as well as the accumulation of these elements by spring wheat including distribution of the elements within the aboveground plant biomass. Material and Methods Pot Experiment The 3-yr pot experiment (from April–July during the years 2010– 2012) was set up at the Czech University of Life Sciences Prague in an outdoor, atmospheric precipitation-controlled, vegetation hall with natural temperature and light conditions. Pots were regularly watered by deionized water if necessary to maintain optimal growth conditions during the course of the experiment. The leachate was captured in the bottom of the covered pot and returned back to the soil to prevent nutrient losses. Wood fly ash was applied into two soils with different physicochemical parameters and different levels of potentially toxic element contamination. Experimental soils: the Příbram Cambisol (loam) was taken from a field polluted by lead from the mining and smelting industry. The vicinity of the smelter is in the most polluted areas in the Czech Republic. The main source of Pb contamination was the atmospheric deposition of potentially toxic elements by galenite mining followed by ore smelting and Pb processing. Mining and metallurgical activities in this area led to enhancement of As, Cd, and Zn contents in soil, due to the high content of potentially toxic elements in the parent rock (Šichorová et al., 2004). The Fluvisol (sandy clay loam) slightly contaminated by river floods from Píšťany (80 km northwest from Prague) was used for different physicochemical properties as summarized in Table 1. The ash used in our experiment derived from heating plant (two boilers with outputs 2.5 and 3.5 MW; combustion temperature 300°C; and ash production 200 t per year) burning mix of wood chips, sawdust, and bark. The experiment was set up in seven treatments (Table 2). The treatment without ash addition (I) and three treatments with the addition of three increasing ash doses (II–IV) were 996

Table 1. The main characteristics of the ash and soils. Property Mean pHCaCl2 Total organic carbon, % Cation exchange capacity, mmol kg–1 Available Ca, mg kg–1 Available Mg, mg kg–1 Available K, mg kg–1 Available P, mg kg–1 Total As, mg kg–1 Total Cd, mg kg–1 Total Pb, mg kg–1 Total B, mg kg–1 Total Cu, mg kg–1 Total Fe, mg kg–1 Total Mn, mg kg–1 Total Mo, mg kg–1 Total Zn, mg kg–1

Wood fly ash 11.5 15.7 205 38,756 2,891 3,377 33.2 50.3 3.1 16.7 991 67.5 12,608 4,520 2.4 182

Fluvisol Cambisol 6.5 5.7 2 2.7 197 166 3,156 1,260 197 152 118 186 132 48.1 51.1 70.4 2.6 4.3 106 721 – – 24.7 11.9 21,196 19,463 951 758 0.6 0.3 370 273

designed on the Cambisol. The treatment without ash addition (V) and the treatments with the addition of two increasing ash doses (VI and VII) were designed on the Fluvisol. The 50 g ash pot–1 dose in Treatment IV was created to achieve similar pH values as in the Treatment VII because the Cambisol soil was more acidic compared to the Fluvisol. All treatments were fertilized by a uniform dose of N (0.1 g N in the form of NH4NO3 per 1 kg of soil). Ash was applied to the Treatments II to IV, VI, VII (to each pot separately), and mixed thoroughly with soils. The pots (5 L with 20 cm diam.) were sown with 30 seeds of spring wheat (Triticum aestivum L. ‘Scirocco’) per pot. The plants were treated against pests and diseases (in the second year pesticide Topsin M 500 SC against Erysiphe graminis was used and in the third year pesticide Mospilan 20 S against Oulema melanopus and Aphis was used), sampled at the booting stage (green biomass–age of plants approximately 50 d) and harvested at full maturity (straw and grain–age of plants approximately 90 d). The green biomass, straw, and grain samples were weighed, dried, and homogenized (grounded through 0.75-mm sieve). The soil samples were taken from 25-cm deep profile using the soil sampler (five samples from different places of each pot with total weight approximately 100 g). Then, the soil samples were air-dried at ambient temperature, ground in a mortar, passed through a 2-mm plastic sieve, and analyzed for mobile portions of the elements. Analytical Procedures The total concentrations of elements in the soils and wood fly ash were determined in the digests obtained by the following decomposition procedure: portions (0.5 g) of air-dried samples were decomposed in a digestion vessel with a mixture comprising 8 mL concentrated nitric acid, 5 mL hydrochloric acid, and 2 mL concentrated hydrofluoric acid (Kowalewska et al., 1998; Lastincova et al., 1999). The mixture was heated in an Ethos 1 (MLS GmbH, Germany) microwave-assisted wet-digestion system for 33 min at 210°C. After cooling, the digest was transferred quantitatively into a 50 mL Teflon vessel and evaporated to dryness at 160°C. The digest was then dissolved in a 3 mL concentrated nitric and hydrochloric acid mixture (1:3), transferred into a 25 mL glass tube, filled with deionized water, and Agronomy Journal • Volume 106, Issue 3 • 2014

Table 2. Experimental design. Treatment I II III IV V VI VII

Soil Cambisol Cambisol Cambisol Cambisol Fluvisol Fluvisol Fluvisol

Ash, g WFA† pot–1‡ 0 10 25 50 0 10 25

N, g pot–1 0.5 0.5 0.5 0.5 0.5 0.5 0.5

Table 3. Available contents (Mehlich III) of Ca, K, Mg, and P in soils after harvest at the end of the experiment according to individual treatments with regard to the soil. Treatment I II III IV F test V VI VII F test

† WFA: wood fly ash. ‡ pot: 5 kg of the soil.

kept at laboratory temperature until measurement. The certified reference material RM 7001 Light Sandy Soil (Analytika, Czech Republic) was applied for the quality assurance of analytical data. The soil pH was determined after extraction with 0.01 M CaCl2 (w/v = 1+2.5 and a WTW pH 340i meter with glass ion-selective electrode (WTW, Germany) was used for the pH determination. Cation-exchange capacity (CEC) was calculated as the sum of Ca, Mg, K, Na, Fe, Mn, and Al extractable in 0.1 M BaCl2 (w/v = 1+20 for 2 h) (ISO 11260, 1994). Total organic carbon (TOC) was determined spectrophotometrically after the oxidation of organic matter by K 2Cr2O7. The efficiency of this method is 98.6% (Sims and Haby, 1971). For determination of potentially available elements in soils after harvest Mehlich III extraction procedure (0.2 M CH3COOH + 0.25 M NH4 NO3 + 0.013 M HNO3 + 0.015 M NH4F + 0.001 M EDTA at a solid/liquid ratio of 1/10 (3 g + 30 mL) for 10 min) (Mehlich, 1984) was applied. For the determination of element contents in the aboveground biomass of plants, a portion (~500 mg of dry matter) of the plant sample was weighed into a digestion vessel. Concentrated nitric acid (8.0 mL; Analytika Ltd., Czech Republic) and 30% H2O2 (2.0 mL; Analytika Ltd., Czech Republic) were added. The mixture was heated in an Ethos 1 (MLS GmbH, Germany) microwave-assisted wet-digestion system for 30 min at 220°C. After cooling, the digest was transferred quantitatively into a 20 mL glass tube filled with deionized water. The concentrations of Ca, Mg, and K in the soil and plant digests and soil extracts were determined by flame atomic absorption spectrometry (F-AAS, Varian 280FS, Varian, Australia) (Száková et al., 2013). For determination of the remaining elements, inductively coupled plasma optical emission spectrometry (ICP–OES, Varian, VistaPro, Australia) was used (Száková et al., 2013). The certified reference material RM IAEA V-10 Hay Powder (Analytika, Czech Republic) was applied for the quality assurance of analytical data. Statistical Analysis The effects of wood fly ash application on grain yield, pH value, and element concentration in soils and spring wheat were examined by analyses of variance using STATISTICA 9.0 software (Statsoft, Tulsa, OK). When this test revealed significant differences, the mean values were compared by Fisher´s LSD test. Differences were considered significant at P = 0.05 for all the investigated parameters. The results of all three subsequent cultivation years were included into the evaluation within individual experimental variants.

Ca K Mg P ––––––––––––––– mg kg–1 –––––––––––––––– 2040a† 120a 193a 47.1a 2212b 137a 206b 52.8a 2486c 200b 223c 69.4b 3046d 253c 272d 74.3b 31.31 164.7 47.19 113.2 3300a 79.5a 192a 124a 3321a 99.2b 200aa 120a 3578b 116c 253b 119a 21.18 112.9 0.577 7.825

† Mean values (n = 3), the values labeled by the same letter did not significantly differ at P = 0.05 by Fisher’s LSD test.

Results and Discussion pH Changes in Soils The wood fly ash increased significantly (α = 0.05) the Cambisol soil pH from 5.6 to 7.5 (Treatment I: pH 5.55a, Treatment II: pH 6.15b, Treatment III: pH 6.87c and Treatment IV: pH 7.49d). This increase is attributed to the wood fly ash with pH value 11.5 which was higher than the 10.6 value reported by Park et al. (2004). In the Fluvisol, the pH value increased only slightly from pH 7.10a at Treatment V through 7.14a at Treatment VI to 7.32b at Treatment VII. Dimitriou et al. (2006) also reported that in all treatments where ash was applied, that a higher soil pH compared to the control was observed. From the literature, the ash supply resulted in the average soil pH increase by 0.8 pH units (Eichler-Löbermann et al., 2008) or even more (1.6–1.7 pH units) where the increase was apparent even 15 yr after ash application (Saarsalmi et al., 2010). In contrast, Park et al. (2004) reported no significant differences in the pH of the soil solution between pots treated with wood ash and controls. The pH differences between our controls and treated pots were significant (α = 0.05) and were as follows: With the Cambisol was the pH increase after 10 g wood fly ash addition 0.6 of unit; after 25 g addition, the increase was 1.3 of pH unit, and after a 50 g dose, it was 1.9 of unit. With the Fluvisol, only the higher dose caused an increase, which was 0.2 pH unit. Demeyer et al. (2001) with short-term laboratory incubations reported that pH increases were greater for soils with low pH and low organic-matter content. Differences between the Cambisol and Fluvisol are attributed to Cambisol having a lower cation exchange capacity and pH than the Fluvisol. Growth and Macroelements It is accepted generally that wood ash has a positive effect on the growth and yield of agricultural crops (Uckert et al., 2001; Patterson et al., 2004; Saarsalmi et al., 2010; Arshad et al., 2012; Park et al., 2012). In our case, the ash application did not significantly (α = 0.05) affect either the plant growth or the grain yield that varied between 11.4 and 14.8 g pot–1. The highest increase of grain yield (23% greater than control) was noted at 10 g ash addition in the Fluvisol. The same dose in the Cambisol increased the grain yield by only 7%. The results of available nutrients in soils at the beginning and at the end of the experiment are given in Tables 1 and 3, respectively. In the case of available Ca, a significant (α = 0.05) increase

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Table 4. Total Ca, K, Mg, and P content in green biomass, grain, and straw of spring wheat according to individual treatments with regard to the soil. Treatment I II III IV F test V VI VII F test

Treatment I II III IV F test V VI VII F test


Green biomass Mg P Ca K –––––––––––––––––––––– mg kg–1 ––––––––––––––––––––– 2055a† 20,764a 1057a 4302a 1644a 20,046a 914a 4130a 2667a 20,521a 942a 3684a 2738a 20,735a 950a 4280a 0.020 0.301 0.452 0.969 4011a 16,551a 1413a 5101a 3467a 15,274a 1130a 4494a 3407a 17,307a 1164a 4732a 0.282 0.819 0.321 0.139 Grain Ca K Mg P ––––––––––––––––––––– mg kg–1 ––––––––––––––––––––– 106a 4091a 1261a 4475a 115a 4099a 1215a 4251a 95.2a 4248a 1186a 3867a 154a 4665a 1339a 4806a 0.847 0.275 0.846 1.286 159a 4164a 1703a 4938a 127a 4113a 1369a 4265a 116a 4427a 1353a 4556a 0.931 0.754 0.763 1.806 Straw Ca K Mg P ––––––––––––––––––––– mg kg–1 ––––––––––––––––––––– 2479a 11825a 1099a 1940a 3178a 12634a 1074a 1050a 2911a 12094a 1040a 1038a 3229a 13080a 1166a 1504a 0.452 0.208 0.393 1.234 4938a 9202a 1330a 1382a 4114a 9898a 1185a 743a 3684a 10251a 1328a 1395a 0.652 0.591 0.291 0.930

† Mean values (n = 9), the values labelled by the same letter did not significantly differ at P = 0.05 by Fisher’s LSD test.

was observed in both soils after ash addition. The ash dose of 25 g pot–1 resulted in a 18% increase in Ca in the Cambisol treatment and a 8% increase in the Fluvisol. Similar positive effects on available K were also observed. Potassium in the ash probably was present in the soluble form available for plants, because values in spring wheat parts were several-times higher than in soils. Available contents of Mg in soils were, similar to Ca and K, significantly (α = 0.05) higher in ash-enriched treatments with comparable values of available Mg in both soils. Available contents of P significantly (α = 0.05) increased only in the Cambisol treatments. In terms of P, the Fluvisol was less sensitive to ash addition, and values were around 120 mg P kg–1 in all three treatments. Demeyer et al. (2001) explained why P can remain relatively insoluble and is the least available major nutrient in wood ash. Wood ash P is most probably occluded in aluminosilicates or in the form of weakly soluble aluminum phosphate. The average levels of total macronutrients in spring wheat are expressed in Table 4. The concentrations of major elements (Ca, 998

K, P, Mg) in wheat predominantly increased with the application of wood ash. Demeyer et al. (2001) reported that especially Ca and K contents of plants increased noticeably with the application of wood ash. Similarly, Saarsalmi et al. (2010) observed significant increases in Ca, Mg, P, and K concentrations in spruces after application of 3 t wood ash ha–1, even at 10 to 16 yr after application. With the Cambisol, the nutrient contents in plants tended (not significantly at α = 0.05) to increase with increasing ash dose. Besides K, the Fluvisol behaved conversely compared to the Cambisol, and Ca, Mg, and P contents were the highest in the treatment without ash addition. Zhang et al. (2002) noted a similar result to plants grown in the Fluvisol when K was the only macronutrient whose concentration in the lingonberries (Vaccinium vitis-idaea) significantly increased after ash fertilization. In our samples, Ca and K were distributed predominantly in the green biomass and subsequently in straw, only 4% Ca and 27% K of the total element content in plants was contained in grains. Grain contents were not significantly (α = 0.05) influenced by ash application or used soils. Magnesium was distributed equally in all analyzed parts of spring wheat (approximately 1200 mg kg–1 in each part), whereas P was noted at higher levels in green biomass and grain (both parts contained approximately 4500 mg kg–1) beside straw (1300 mg kg–1). Higher nutrient contents in green biomass than in straw are expected. Microelements The wood fly ash did not increase B or Cu concentrations in the soil (Table 5). These results are unexpected because their concentrations in the ash were relative high (Table 1). The decrease in Fe availability in ash-enriched treatments in the Fluvisol could be caused by high content of calcium carbonate in added wood ash. Singh and Dahiya (1976) also observed the decrease of available Fe with the increase of CaCO3. Although both soils contained originally similar amounts of Fe (approximately 2%), the available form was higher in the Fluvisol than in the Cambisol (average of 24%). The high Mn content in ash (4520 mg Mn kg–1) was reflected in increasing available Mn in both soils after ash application, specifically by 38% in the Cambisol and by 15% in the Fluvisol after application of 25 g ash pot–1 compared to no ash application. Available Mo in soils was not almost influenced by ash. In the case of Zn, a significant (α = 0.05) 20% decrease with ash addition occurred in the Cambisol, but changes of Zn availability in the Fluvisol were not significant. The decrease in the Cambisol was probably caused by ash alkalinity being imparted to the soil. The concentrations of microelements in spring wheat are seen in Table 6. Among the monitored elements was Zn the most affected one. The reduction of Zn accumulation in treatments where ash was applied was observed. This decrease could be caused by lower availability of this element at higher soil pH (Demeyer et al., 2001; Dimitriou et al., 2006; Omil et al., 2007). Iron increase after ash addition was consistent with the statement of Demeyer et al. (2001) who reported that Fe is the most abundantly present microelement in wood ash. We also observed an increase in B with ash addition, similar to results by Etiegni et al. (1990). Boron content in wheat straw increased by ~ 50% in both soils after 25 g of wood fly ash addition pot–1. Higher microelement contents occurred Agronomy Journal • Volume 106, Issue 3 • 2014

Table 5. Available contents (Mehlich III) of B, Cu, Fe, Mn, Mo, and Zn in soils after harvest at the end of the experiment according to individual treatments with regard to the soil. Treatment I II III IV F test V VI VII F test

B Cu Fe Mn Mo Zn –––––––––––––––––––––––––––––––––––––––––– mg kg–1 ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 19.9a† 8.1ab 244a 71.8a 0.07b 35.7c 4.3a 7.4a 228a 82.3a 0.04a 30.8ab 6.3a 7.9ab 243a 116b 0.05a 33.3bc 17.8a 8.4b 244a 134b 0.04a 28.6a 1.236 2.940 2.094 24.45 8.123 13.07 23.5a 14.9a 330b 70.5a 0.05a 54.3a 23.2a 14.3a 312ab 73.6a 0.04a 52.9a 25.2a 14.3a 302a 82.9a 0.04a 52.1a 0.014 0.776 6.159 2.828 0.976 0.414

† Mean values (n = 3), the values labelled by the same letter did not significantly differ at P = 0.05 by Fisher´s LSD test.

Table 6. Total B, Cu, Fe, Mn, Mo, and Zn content in green biomass, grains, and straw of spring wheat according to individual treatments with regard to the soil. Treatment I II III IV F test V VI VII F test



Green biomass B Cu Fe Mn Mo Zn –––––––––––––––––––––––––––––––––––––––––––––––––––––––––– mg kg–1 ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 12.8ab 5.6a 49.4a 20.0c 0.4a 157c 13.3ab 6.9ab 64.2a 14.1ab 0.5a 113b 16.6b 6.5ab 49.1a 11.6a 0.5a 76.4a 15.5b 5.7a 56.4a 14.4ab 0.8c 75.2a 0.903 0.652 1.129 10.47 3.692 4.347 10.1a 6.8ab 65.3a 12.6ab 1.0b 76.7a 9.7a 7.5ab 68.2ab 12.1ab 1.1b 63.0a 14.4ab 7.9b 104b 15.3b 1.0bc 69.5a 2.633 0.355 1.634 1.860 0.185 0.652 Grain B Cu Fe Mn Mo Zn –––––––––––––––––––––––––––––––––––––––––––––––––––––––––– mg kg–1 ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 1.8ab 12.8ab 24.7c 18.0b 0.5ab 73.3a 1.8ab 15.9ab 30.4ab 13.6a 0.4b 75.4a 1.3b 19.7b 30.2abc 11.9a 0.4b 62.9a 1.7ab 11.8ab 26.5ac 12.3a 0.6a 51.8a 0.509 0.764 1.902 3.990 1.607 0.975 2.0ac 9.7a 33.7b 11.1a 0.8c 62.4a 2.1ac 11.0ab 29.0abc 12.0a 0.7ac 52.7a 2.5c 14.7ab 31.5ab 12.4a 0.7ac 56.2a 0.304 1.012 1.100 0.349 0.359 0.458 Straw B Cu Fe Mn Mo Zn –––––––––––––––––––––––––––––––––––––––––––––––––––––––––– mg kg–1 ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 9.4a 22.8a 25.9a 9.0a 0.5ab 185e 12.9a 11.3a 33.7ab 7.5a 0.3a 113d 20.6b 9.7a 41.4ab 8.2a 0.5ab 85.7c 35.0c 30.3a 38.3ab 9.1a 1.0cd 60.1b 10.22 0.697 0.636 0.306 12.09 5.457 11.1a 25.1a 45.6b 7.7a 1.4d 42.1ab 13.0a 9.2a 40.1ab 7.3a 0.9bc 33.6a 21.1b 19.7a 39.0ab 6.4a 1.3cd 44.2ab 11.88 0.768 0.132 0.233 1.560 0.637



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Table 7. Available contents (Mehlich III) of As, Cd, and Pb in soils after harvest at the end of the experiment according to individual treatments with regard to the soil. Treatment I II III IV F test V VI VII F test

As Cd Pb ––––––––––– mg kg–1 ––––––––––– 1.0a† 1.6b 278c 1.1a 1.4a 251ab 1.6b 1.5b 266bc 1.8b 1.4a 231a 15.69 10.95 6.396 1.5a 0.7a 14.4a 1.9a 0.7a 15.0a 1.5a 0.8a 15.3a 0.107 0.243 3.015


Table 8. Total As, Cd, and Pb content in green biomass, grains, and straw of spring wheat according to individual treatments with regard to the soil. Treatment I II III IV F test V VI VII F test



Green biomass As Cd Pb ––––––––––––––––– mg kg–1 ––––––––––––––––– 1.8a† 2.7b 2.3a 1.4a 1.4a 1.8a 1.7a 0.8a 1.2a 1.4a 0.9a 1.3a 1.685 0.139 6.236 1.4a 0.3a 0.8a 1.7a 0.3a 0.8a 2.1a 0.3a 1.0a 0.915 0.480 0.091 Grain As Cd Pb ––––––––––––––––– mg kg–1 ––––––––––––––––– 0.4a 0.9c 0.4a 0.4a 0.7b 0.3a 0.4a 0.5a 0.4a 0.5a 0.5a 0.5a 1.018 0.420 9.718 0.4a 0.2a 0.3a 0.5a 0.2a 0.3a 0.7a 0.2a 0.4a 0.860 1.688 0.279 Straw As Cd Pb ––––––––––––––––– mg kg–1 ––––––––––––––––– 0.8a 1.9b 3.3a 0.9a 1.3a 2.0a 1.0a 1.0a 2.2a 1.1a 0.8a 1.8a 0.447 4.839 1.465 1.2a 0.4a 0.8a 1.1a 0.3a 0.9a 1.2a 0.2a 1.1a 0.095 1.273 0.186


1000

usually in straw than in grains, but Mn content was higher in grains (on average by 40%). It was surprising, because Pearson and Rengel (1994) reported that Mn was not remobilized from the leaves of wheat during grain development. Potentially Toxic Elements The Czech limits for maximal content of potentially toxic elements in soils (Anonymous, 1994) are divided by soil type, and stricter values are used for light soils because of easier elements release. In the case of the Fluvisol, belonging to the light soils, valid maximal values include Pb (100 mg kg–1), Cd (0.4 mg kg–1), As (30 mg kg–1), and Zn (130 mg kg–1). In the Cambisol, values must not exceed 140 mg Pb kg–1, 1 mg Cd kg–1, 30 mg As kg–1 and 200 mg Zn kg–1. It is seen (Table 1) that total potentially toxic element values in our experimental soils exceeded the threshold limits. In the Cambisol, Pb allowed content was exceeded by approximately fivefold, Cd fourfold, and As twofold. The Fluvisol contained 6.5 times more Cd, three times more Zn, and two times more As than the limits. Although the original total potentially toxic element contents in our soils were very high, only small amounts were taken up by plants. Mobile portions of potentially toxic elements in soils determined by the Mehlich III extraction procedure (Table 7) showed very low values of As and only a slight increase in treatments, although the As content in wood fly ash as well as in soils was high. It is seen that As was bound tightly in ash and in soils. An increased pH value due to ash application reduced the available Cd in the Cambisol, but the Fluvisol was not affected. The same effect as in the Cambisol was observed by Dimitriou et al. (2006) and Omil et al. (2007). It is most likely that due to the high pH in ash, was Cd associated with oxides of Ca, that turn into hydroxides in wet conditions (Hansen et al., 2001). When we compare As and Cd, Cd was more available in soils (38% Cd availability in the Cambisol and 27% in the Fluvisol treatments) as typical for this element (Verbruggen et al., 2009). Many studies have been devoted to As sorption on soil particles, among others on calcium carbonate or oxides of Al, Fe, and Mn (Garg and Singla, 2011). High Pb amounts in the Cambisol treatments corresponded to Pb contamination in the original soil. The Pb availability was 35% from the total content. The highest ash dose caused a decrease of Pb mobility by 17%. Lead availability in the Fluvisol was lower (14%) than in the Cambisol and similar to Cd, available Pb content in the Fluvisol treatments was not affected significantly (α = 0.05) by ash. The concentrations of the As, Cd, and Pb were relatively low in the wheat biomass (Table 8). Arsenic slightly increased with higher ash dose but not significantly (α = 0.05). Arsenic content in grain moved in the range 0.4 to 0.7 mg kg–1. Cadmium content in spring wheat usually did not exceed 1 mg kg–1 and Pb 2 mg kg–1, Pb contents in grains reached only 0.3 to 0.5 mg kg–1. Cadmium and Pb behaved similarly when their content in plant decreased with ash addition, in particular at the Cambisol (Cd by 60%, Pb by 45%). Differences in the Fluvisol were not significant (α = 0.05). Merry et al. (1986) found that the effect of decreasing Pb concentrations in plants with increasing soil pH is more pronounced in the highly contaminated soils. We can confirm that in the Cambisol, highly contaminated by Pb, the Agronomy Journal • Volume 106, Issue 3 • 2014

decrease in Pb content compared to the Fluvisol was observed. According to Nan and Cheng (2001), the accumulation levels of Pb by spring wheat parts increased as the total contents increased in the cultivated land. It was not confirmed in our experiment because although the Cambisol was approximately sevenfold more contaminated by Pb than the Fluvisol, accumulation of Pb by spring wheat grains was without significant (α = 0.05) differences in both soils. We can agree only with the further results of Nan and Cheng (2001) that contents of Pb in crop parts were several or even several-hundred times lower than the element concentrations in corresponding soils, because the alkaline pH does not favor higher Pb absorbed by spring wheat roots due to precipitation of carbonates and hydroxides, in which Pb was less soluble and hence less plant available. If we compare Cd and Pb, Pb was bound more tightly than Cd, and spring wheat roots restrict the movement of Pb into grains. Although the Cambisol was originally more contaminated by As (70.4 mg As kg–1) than the Fluvisol (51.1 mg As kg–1), As was more accumulated by spring wheat parts grown on the Fluvisol treatments. The possible explanation could be the decreasing As adsorption at higher pH levels (Melo et al., 2012) and expectable higher release of As in light soils (Wang and Mulligan, 2006), that is, in the Fluvisol in our case. Potentially toxic element values in spring wheat parts were generally very low although wood fly ash and contaminated soils were used. The knowledge that potentially toxic elements do not pose a risk when ash is used is also supported by other authors. For example, Omil et al. (2007) applied mixed wood ash to forest soils without increasing the availability of potentially toxic elements in the short or medium term (1–3 yr), even with multiple applications of the ash, and Zhang et al. (2002) pointed out that long-term application of wood ash to pine caused no significant increase of potentially toxic elements in soil and that ash application had no negative effect on the potentially toxic element concentrations in lingonberries. Conclusions This study evaluated spring wheat and contaminated soils responses on biomass ash addition. The 3-yr pot experiment showed that application of wood fly ash (material with typically high potentially toxic elements contents) could be beneficial for soils as amendment and even for potentially toxic elements contaminated soils. The ash-enriched treatments showed increases of nutrients in soils as well as in plants. Moreover, the pH increase caused decrease in mobility of potentially toxic elements and limited their plant uptake. Finally, we can conclude that cumulative wood fly ash addition (rates up to 1%) to potentially toxic element contaminated soils did not affect spring wheat growth negatively and even though the application of fly ash increased the total potentially toxic element contents of the soil, it had a minimal impact on potentially toxic element contents of wheat growing in the ash-treated soil but field studies are still required to strengthen these conclusions. Acknowledgments The authors wish to thank the NAZV Project no. QI102A207 for their financial support. This work has been supported by the Ministry of Agriculture (National Agency for Agricultural Research Project no. QI102A207), CIGA Project no. 20112006 and Klastr Česká peleta.

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