Co-Recycling of fly ash and poultry manure in nutrient-deficient sandy soil

Resources and Conservation, 13 (1987) 291-304 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

291

CO-RECYCLING OF FLY ASH AND POULTRY MANURE IN NUTRIENT-DEFICIENT SANDY SOIL*

J.W.C. WONG and M.H. WONG**

Department of Biology, The Chinese University of Hong Kong, Shatin (Hong Kong)

(Received May 31.1986; accepted July 11, 1986)

ABSTRACT

This experiment was aimed at studying the effects of adding coal fly ash and poultry manure to a sandy soil on the yields and elemental uptake of Brassica parachinensis and B. chine&s. Three rates of fly ash (0, 3 and 12% w/w) and three rates of poultry manure (0, 2.5 and 6.0% w/w) were mixed separately and in combinations (3% ash + 2.5% manure, 12% ash + 2.5% manure, 3% ash + 6% manure, 12% ash + 5% manure) with the sandy soil. Manure applications were effective in increasing crop yields for both species as compared with the control (sandy soil alone) or fertilizer treatment. Highest yields were recorded with the highest manure treatment. Addition of 12% ash + 2.5 or 5% manure decreased crop yields of B. chinensis but not those of B. parachinensis. Mean tissue concentrations of Zn and Mn were significantly lower (p < 0.05) with increase in ash application rate for both crops while MO concentration was consistently higher. The changes in metal availability were possibly due to the high alkalinity of the soil after ash addition. The lower electrical conductivity and pH of the soil following cropping indicates the high leachability of elements in sandy soil. Therefore, continuous fertilization is essential if continuous cropping is carried out.

INTRODUCTION

Changes in energy consumption patterns in Hong Kong have caused shifts from fuel oil to coal in power plants. As a result, the production of coal residues is expected to increase in the next few decades [l] . Land application for agricultural use seems to be an economic and efficient way of disposing of the wastes. Electrical conductivity, pH and boron contents are the three main constraints limiting the growth of plants in ash-amended soils [2,3]. However, it has been observed that excessive salts in ash/soil mixtures are substantially decreased following cropping. No phytotoxic symptom has ever been reported for plants growing on ash-amended soils except for boron toxicity [ 4,5], although the enhanced metal contents

*Paper presented at the International Symposium on Recycling of Organic Wastes for Fertilizer, Food, Feed and Fuel, Hong Kong, August 28-30,1985. **Present address: Department of Biology, Hong Kong Baptist College, Waterloo Road, Kowloon, Hong Kong.

0166-3097/87/$03.50 0 1987 Elsevier Science Publishers B.V.

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in the fly-ash matrix have been found to be readily available for plant uptake [5--71.

The use of fly ash in agriculture has been unpopular [3,8], due to the low availability of nitrogen and phosphorus. Nitrogen is almost absent in fly ash since N in coal is usually lost as oxide during high-temperature combustion [ 31. Phosphorus, although present in sufficient amounts ranging from 400 to 800 pg/g [9], is low in availability [8]. Therefore, application of fly ash to soil deficient in these two elements must be accompanied by fertilizers containing N and P.

Unlike fly ash, dry poultry manure is usually high in N, P and Ca [lO,ll] . The high N and P values make dry poultry manure an excellent fertilizer as compared with inorganic fertilizers [ 121. Moreover, application of organic wastes to soil will increase the organic-matter content of the soil [13]. This will improve the soil conditions and result in an improved soil environ- ment for root growth and nutrient uptake [ 141.

The aim of the present study was to investigate the advantages of co- recycling fly ash and poultry manure in a nutrient-deficient sandy soil and its effects on crop yields. The high fertility of poultry manure should remedy the nutrient deficiency of an ash/soil mixture sufficiently to make it suitable for plant growth.

MATERIALS AND METHODS

Sample collection and preparation

Dried and unweathered fly-ash samples were collected directly from pipelines just before entering the electrostatic precipitator of Castle Peak Power Station in 1982.

Dried poultry manures were obtained from the Pat Heung Drier Plant of the Agricultural and Fisheries Department in 1982. Manure samples were ground and sieved through a 2-mm sieve. Samples were then stored in sealed plastic bags at 4°C in order to supress microbial activity.

Surface samples (O-30 cm) of a sandy soil were collected from the side of a freshwater stream on the campus of The Chinese University of Hong Kong. They were air-dried in the greenhouse at 25-5°C for ‘7 days and stored in plastic containers.

Chemical analysis of samples

All samples were sieved through a 2-mm soil sieve for various analyses: pH (sample:distilled water = 1:2.5), electrical conductivity (sample:distilled water = 1:2.5), total organic carbon [15], total nitrogen (micro- Kjeldahl digestion) [16], total phosphorus (concentrated sulphuric acid digestion, followed by the molybdenum blue method) [17], Olsen-phosphorus [18], exchangeable K, Mg and Ca (1 N ammonium acetate at pH 7) [ 171 and texture (hydrometer method) (Bouyoucos, in Ref. [ 171).

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Total metal contents of samples were determined by the mixed-acid digestion method (cont. HNO,:60% HC104:conc. H,SO, = 5:1:0.5) [17], while extractable and soluble trace elements were determined by DTPA (0.005 M, pH 7.3) [19] and distilled water [17], All extracts were stored in polyethylene bottles at 4°C until subsequent analysis by an atomic absorption spectrophotometer (Varian, model AA 1475).

Plan t-growth experiment

Three rates of fly ash (0, 3 and 12% w/w) and poultry manure (0, 2.5 and 5.0% w/w) were mixed with the sandy soil to produce all possible combinations. Ten seeds of B. parachinensis or B. chinensis were sown in each pot and the two strongest seedlings were chosen for the experiment. The plants were grown in the greenhouse at a temperature ranging from 25°C to 35°C for a period of 45 days. A separate fertilizer treatment, twice weekly application of 200 mL of a solution containing reagent-grade KH,PO, (0.001 M) and KN03 (0.005 M) [20], was also given. After harvesting, surface-soil samples from each pot were collected for the analysis of pH and electrical conductivity (EC). Aerial portions of plants were clipped and rinsed with distilled water thoroughly prior to analysis.

The dry weight of plant tissues per plant was recorded. The metal contents in plants were determined by the mixed-acid digestion method [17] and subsequently measured by atomic absorption spectrophotometry (Varian, model AA 1475). All data were subjected to one-way analysis of variance; where significant F values were obtained, Duncan’s multiple- range test was used to test the significance between treatment means [21] using the SPSS computer package through an IBM OS/VSl operating system [=I.

RESULTS AND DISCUSSION

Chemical composition of experimental materials

From the standpoint of nutrient status, the sandy soil was considered nutrient-deficient with N-P-K values of 0.17-0.0005-0.1% (Table 1). The manure had comparatively higher N-P-K value than fly ash and sandy soil indicating its high fertilizer potential. Although the fly ash had a low N-P content, it had a high concentration of inorganic cations. The high silt contents of fly ash would possibly increase the water-holding capacity and water availability of recipient soils after its application, especially for coarse-texture soil [23,24], although the organic matter of the manure could be expected to have a more profound effect.

The results of total-metal analysis (Table 2) indicate that the fly ash was highly enriched with macro-elements, and the essential and non-essential micro-elements Ca and Fe were comparatively abundant in fly ash, being the major constituents of the fly-ash matrix [25,26]. On the other hand, K, Ca and Mg were high in the manure and only Ca was highly exchangeable

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(Table 1). Moreover, Cu and Zn were considerably high in manure, indicating its potential to remedy soil deficient in these elements.

Table 3 indicates that trace elements in manure were more readily available than in fly ash as shown by the high values of the available levels expressed as a percentage of the total metal levels. Only a very small amount of the trace elements in fly ash exists in soluble forms [25]. However, in terms of actual concentration @g/g), fly ash had a comparatively higher avail-

TABLE 1

General properties of fly ash, poultry manure and sandy soil”

Parameter Fly ash Poultry manure Sandy soil

PH Electrical conductivity

(mmhos/cm) Texture (%)

Sand Silt Clay

Organic carbon (W) Total nitrogen (%) Total phosphorus (/q-j/g) Olsen-phosphorus (fig/g) Exchangeable cations (pg/g)

Ca K Mg

12.80 (0.06)

8.70 (0.09)

42.10 48.48

9.42 0.63 (0.11) 0.02 (0.00)

181.00 (68.36) 71.2 (16.7)

16090.88 (1016.06) 16.82 (4.12)

2779.69 (393.66)

6.60 (0.08)

17.67 (0.37)

b b

28.;0 (2.45) 3.46 (0.26)

4667.00 (237.00) 7080.0 (62.0)

7620.26 (900.96) 380.96 (16.73)

2047.62 (196.91)

7.26 (0.04)

0.06 (0.00)

81.00 10.00

9.00 0.14 (0.03) 0.02 (0.00)

64.00 (9.64) 16.9 (0.6)

1183.14 (292.04) 29.46 (2.46)

170.82 (10.06)

aVahres between brackets indicate standard deviation. bNot determined.

TABLE 2

Total metal contents of fly ash, poultry manure and sandy soila

Metal Fly ash Poultry manure Sandy soil

Ca (%) E (%) Mg (%) Fe (%)

9.19 ( 1.21) 0.13 ( 0.02) 2.67 ( 0.02) 6.70 ( 0.02)

Cd (fig/g) 36.03 ( 1.43) Co (erg/g) 164.19 (12.44) cu (rg/g) 47.89 (22.28) Mn (CcgIg) 363.09 (13.26) Mo (rgIg) 47.72 ( 0.68) Ni (fig/g) 144.76 (16.80) Pb (rglg) 116.17 ( 3.82) En (rglg) 44.69 ( 6.09)

3.36 ( 0.02) 0.36 ( 0.03) 1.81 ( 0.16) 0.10 ( 0.02)

3.70 ( 0.00) 42.91 ( 2.17)

140.72 (36.36) 236.14 (37.97)

9.66 ( 0.42) 36.96 ( 4.86)

4.36 ( 0.00) 230.66 ( 9.22)

0.40 ( 0.12) 0.10 ( 0.01) 0.03 ( 0.00) 0.44 ( 0.16)

2.76 ( 0.82) 20.10 ( 3.47) 12.07 ( 3.47) 97.42 (19.03) 29.62 ( 3.26) 18.04 ( 1.46) 14.46 ( 1.83) 69.89 (20.21)

aValues between brackets indicate standard deviation.

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TABLE 3

DTPA-extractable trace element contents of fly ash, manure and sandy soil, expressed as both actual concentration and percentage of the total ( T)a

Metal Fly ash

Cont. (rglg)

Poultry manure Sandy soil

T (%) Cont. (crglg) T (%) Cont. (rg/g) T(W)

Cd 0.37 ( 0.03) 1.06 0.58 ( 0.06) 15.68 0.16 (0.03) 5.79 co 2.25 ( 0.26) 1.46 3.26 ( 0.12) 7.60 1.53 (0.05) 7.61 Fe 103.88 (15.79) 0.16 270.12 (18.24) 27.01 16.88 (1.09) 0.38 Mn 3.26 ( 0.34) 0.92 136.19 ( 3.94) 57.92 29.24 (0.90) 30.01 MO 7.99 ( 1.69) 16.74 3.82 ( 0.29) 39.96 1.45 (0.48) 4.90 Ni 1.65 ( 0.21) 1.14 7.17 ( 0.85) 19.40 0.08 (0.05) 0.44 Pb 0.62 ( 0.09) 0.54 1.23 ( 0.06) 26.57 5.62 (0.68) 38.87 Zn 0.36 ( 0.08) 0.81 69.89 (20.31) 30.31 10.65 (0.27) 15.24

aValues between brackets indicate standard deviation.

ability of trace elements than sandy soil except for Zn, Mn and Pb. Hence, the addition of manure and fly ash to sandy soil in the present study would possibly correct soil deficiencies in these elements.

The effects of ash manure amendment on chemical properties of soil

Figure 1 shows the pH changes in soil treated with ash or manure alone, or both and the residual effect after cropping. Fly ash caused an upward shift in pH of recipient soils or manure-treated soils. With fly-ash amendment alone, pH changed tremendously, from 7.3 for the control to 9.7 at a 12% application rate. However, application of manure significantly (p

10 (a) E.parachinensis I -

-- manure(%) 0 2.5 5

before . . . after (I 1

7 0 3

fly ash in soil %(&A? 0 fly 3 %(w/if ash in soil

Fig. 1. Changes of soil pH for the various treatment groups after cultivation of B. paru- chinensti (a) and B. chinen& (b), respectively.

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< 0.05) lowered the pH of the 3% and 12% ash-amended soil. It is common- ly observed that solubility and plant availability of most trace metals in any given soil are inversely related to pH [27,2&S]. Hence, application of manure to fly-ash-amended soil may enhance uptake of trace metals, due to reduced pH.

Following cropping, pH values of all treated soils were reduced but the residual effect was more obvious for sandy soil with fly-ash amendment than manure-amended soils. The low resistance to pH changes for the sandy soil might be due to its rather low water-holding capacity and carbon content [29].

Ash and manure amendment acted additively in increasing the electrical conductivity (EC) of recipient soil (Table 4). The increase can be attributed to the high cation contents of both fly ash and manure. The high EC could affect crop growth by reducing the availability of water in soil receiving manure or ash treatment [2,30]. Following cultivation, the EC of all treat-

TABLE 4

Electrical conductivity changes of soils under various treatments after cultivation of B. parachinensis and B. chinensisa-b

Treatment Electrical conductivity (wmhos/cm)

Fly ash (W) Manure (%) B. parachinensis B. chinensis

Before After Before After

0 0 56.45 a 22.30 a 56.45 21.85 a (4.65) (5.10) (4.65) (1.75)

(4. fertiliser)’ 56.45 a 34.35 ab 56.45 a 28.25 a (4.65) (10.58) (4.65) (2.25)

3 0 245.50 b 49.25 bc 245.50 b 71.20 c (4.50) (0.75) (4.50) (20.90)

12 0 2035.00 f 50.30 bc 2035.00 f 108.25 d (75.00) (8.13) (75.00) (12.65)

0 2.5 694.67 c 28.75 a 694.67 c 27.40 a (14.50) (0.85) (14.50) (4.30)

3 2.5 738.00 c 39.35 ab 738.00 c 58.05 b (3.00) (0.15) (3.00) (24.65)

12 2.5 1574.17 d 35.45 ab 1574.17 d 39.65 a (189.52) (1.25) (189.52) (4.05)

0 5 1876.67 e 49.45 bc 1876.67 e 53.65 bc (55.08) (0.65) (55.08) (1.35)

3 5 1652.00 d 59.15 c 1652.00 d 42.30 ab (83.00) (28.25) (83.00) (4.80)

12 5 2493.33 g 27.55 a 2493.33 g 50.53 b (25.16) (0.35) (25.16) (1.85)

aSimilar letters within a column indicate that means do not differ significantly at 6% level according to the Duncan’s multiple range test. bValues between brackets indicate standard deviation.

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ments diminished tremendously indicating the low retention of both soluble anions and cations in sandy soil. Hence, leaching and cropping is an im- portant means of stabilizing the high EC after the amendment of fly ash and manure. However, the high leachability of nutrients implies the need of continuous nutrient suppliment for sandy soil.

Crop production

Figure 2 presents the dry weights of B. parachinensis and B. chinensis of various treatment groups. No obvious phytotoxic symptom was observed. Application of fly ash without manure increased yields at the 3% application rate but 12% gave similar yields to the control. On the other hand, manure enhanced the yield significantly when compared with both the control and the fertilizer treatment (p < 0.05). Higher manure application rates further increased the yield of each corresponding treatment. This is presumably due to the high N-P-K value of the manure, but it could have been partly due to improved soil conditions [14] through an increase in aggregation, a decrease in bulk density, and an increase in water-holding capacity [ 30,311 .

Although fly ash alone exerted a beneficial effect on sandy soil at 3% application rate, application of fly ash to manure/soil mixtures did not improve crop yield. This suggests that addition of fly ash to nutrient-sufficient soil would not exert a beneficial effect on crop yields.

-B. parachinensis - -

e

bc

cde cde

fly ash in

lzl25%

- B. chinensis 7 --

Fig. 2. Dry weight of aerial portions of B. parachinensis and B. chinensis under various combinations of fly-ash and manure treatments. Similar letters above bars indicate that the value represented by the bars do not significantly differ at the 5% level by Duncan’s multiple-range test (w/f = fertilizer treatment).

298

Plant elemental up take

The mean tissue concentrations of Cu, Fe, Mn, MO, Ni, Pb and Zn in the aerial portions of both plants are presented in Figs. 3-9. Fe, Ni and Pb did not show obvious changes with treatment in either plant species (Figs. 3-5). There were some reductions with fly-ash addition (Figs. 6 and 7) for Cu and Mn. Of the trace elements studied, only Zn showed consistent effects, a significant reduction in both B. parachinensis and B. chinensis

- E parachinensis - -6. chinensis - --

0 0 w/f 3 12 0 3 12 0 3 12 0 w/t 3 12 0 3 12 0 3 12

fly ash in soil% hv/w)

00% m 2.5% El 5% llU”“E

Fig. 3. Fe concentration in aerial portions of B. parachinensis and B. chinensis under various combinations of fly-ash and manure treatments. Similar letters above bars indicate that the values represented by the bars do not significantly differ at the 5% level by Duncan’s multiple-range test (w/f = fertilizer treatment).

-II. parachinensis - - B. chinensis - _- c

fly ash in soil% (w/w)

Fig. 4. Ni concentration in aerial portions of B. parachinensis and B. chine&8 under various combinations of fly-ash and manure treatments. Similar letters above bars indicate that the values represented the bars do not significantly differ at the 5% level by Dun- can’s multiple-range test (w/f = fertilizer treatment).

299

10 7 _ parachinensis - - 6. chinmsis -

0 owt 3 12 0 3 12 0 312 0 w/t 3 12 0 3 12 0 3 12

fly ash in soil% (w/w)

0 0% la 2.5% IJZI 5% manure

Fig. 5. Pb concentration in aerial portions of B. parachinensis and B. chinensis under various combinations of fly-ash and manure treatments. Similar letters above bars indicate that the values represented by the bars do not significantly differ at the 5% level by Duncan’s multiple-range test (w/f = fertilizer treatment).

zor r - a. parachinensis - - - - B. -- chinensis

b

Ow/t312 0 312 0 312

00%

fly ash in soil % (w/w)

m 2.5% a 5% manure

Fig. 6. Cu concentration in aerial portions of B. parachinensis and B. chinensis under various combinations of fly-ash and manure treatments. Similar letters above bars indicate that the values represented by the bars do not significantly differ at the 5% level by the Duncan’s multiple-range test (w/f = fertilizer treatment).

(p < 0.05) (Fig. 8). A significant increase was observed for MO (p < 0.05) with increase in ash application (Fig. 9).

As the availability of soil trace elements is strongly influenced by soil pH [32,33], correlations between soil pH before cultivation and tissue concentrations in each plant species for each element were calculated (Table 5). All manure treatment groups were combined for calculation. Depression in Zn concentration was significantly correlated with soil pH for B. parachinensis and B. chinensis (p < 0.001). Cu and Mn also showed negative correlations with soil pH but only B. parachinensis had significant negative correlations for Cu 0, < 0.001). Although application of fly ash depressed

the availability of Zn, the deficiencies in Zn which have been reported elsewhere [34] were not noted in the present study, perhaps due to the sufficient Zn availability in the sandy soil and manure. Nevertheless, Zn availability should be considered when Zn-deficient soils are being used for ash disposal or amendment.

On the other hand, MO showed significant positive correlations with soil pH for both plant species. It is well documented that application of fly ash to soil increases tissue MO content [35,36]. However, despite accumulation of MO, no phytotoxicity in any crop has ever been reported. Indeed, MO is of special interest because of its essentiality and toxicity to farm animals. MO concentrations of 5-10 pg/g are considered toxic to cattle

200 --_E parachinensis - - B. chinensis - --

h

fly ash in soil%bv/

0 0% El 2.5% m 5% manure

Fig. 7. Mn concentration in aerial portions of B. parachinensis and B. chinensis under various combinations of fly-ash and manure treatments. Similar letters above bars indicate that the values represented by the bars do not significantly differ at the 6% level by Duncan’s multiple-range teat (w/f = fertilizer treatment).

200 -g. parachinensis - -B. chinensis - . .

0 own 3 12 0 312 0 312 0 W/f 3 12 0 3 12 0 312

fly ashin soil%(wlw)

00% 0 2.5% a 5% manure

Fig. 8. Zn concentration in aerial portions of B. parachinensis and B. chine&s under various combinations of fly-ash and manure treatments. Similar letters above bars indicate that the values represented by the bars do not significantly differ at the 5% level by Duncan’s multiple-range test (w/f = fertilizer treatment).

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-& parachinensis- - 0. chinensis - -_ f

d

c

b

O 0 soil

b

i

a

UO% fly ash in

IEfl 2.5% EJ5% manure

Fig. 9. MO concentration in aerial portions of B. parachinensis and B. chinensis under various combinations of fly-ash and manure treatments. Similar letters above bars indicate that the values represented by the bars do not significantly differ at the 5% level by Duncan’s multiple-range test (w/f = fertilizer treatment).

TABLE 5

Correlation coefficient (r) of soil pH with tissue concentrations in Bmssica parachinensis and B. chinensis for each element

Plant tissues Correlation coefficient, r

cu Fe Mn MO Ni Pb Zn

B. pamchinensis -0.4972c 0.26658 -0.1123 0.6630d 0.1384 0.3017b -0.9865d B. chinensis -0.2726a 0.2463a -0.0224 0.7315d -0.0338 -0.0356 -0.8995d

Probability level: “p< 0.05; bp < 0.01. cp < 0.005. dp < 0.001.

[ 371. According to the present study, both plant species growing on sandy soil or sandy soil/manure mixtures with fly-ash application had accumulated MO to levels well above the critical range. Therefore, careful consideration should be made when pasture species for grazing are cultivated on ash- disposal sites.

CONCLUSION

Application of manure to sandy soil or ash/sandy soil mixtures significantly enhanced crop yields of both B. parachinensis and B. chinensis as compared with control and fertilizer treatment groups. The highest yield was recorded at the highest manure application rate (5%). The increase was attributed to the high nutrient status of manure which might remedy the

302

N-P-K deficiency of sandy soil and ash/soil mixtures. However, no positive effects of fly ash were found which could not be attributed to its effect on pH. The silt fraction of fly ash is high and could be expected to have major beneficial effects on soil physical properties. This, however, was not tested in a greenhouse experiment.

Therefore, although co-disposal of fly ash and manure on sandy soil of the present study is promising, further experiments should be conducted to obtain a more appropriate combination of fly ash-manure application rate in order to obtain maximal crop yields in field trials as well as in greenhouse experiments. Moreover, studies concerning the co-disposal of fly ash with other organic wastes, such as compost or sewage sludge, should also be conducted to explore the potential of fly ash in agricultural soil.

ACKNOWLEDGEMENTS

We would like to thank Professor A.D. Bradshaw for invaluable comments and Dr. J.C. Muskett for providing the ash samples.

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Co-Recycling of fly ash and poultry manure in nutrient-deficient sandy soil