Plant growth and soil fertility comparisons between fertilizer and compost-amended soils

A paired comparative study of compost versus conventionally-fertilized vegetable plots has been conducted for 11 years in a sandy loam soil near Truro, Nova Scotia; likely the longest study of its kind in Canada. The fertility treatments have been applied annually to six rotation plots planted with six to eight different vegetable crops. Compost and fertilizer applications have been based on the results of soil sampling and the Nova Scotia Soil Test Recommendations, and assuming 50 or 100% availability of the total N in the mature composts or fertilizers, respectively. The composts consist of animal manure, food waste, yard waste and straw or racetrack manure bedding. Marketable yields have been taken annually since 1990 and the plant tissue samples have been analysed for macro- and micronutrients, while soils have been sampled for pH, organic matter and Mehlich-3 extractable nutrients since 1994. This paper reports the results of the 1999 and 2000 cropping years.

Crop yield response was inconsistent between the two amendments; yields of tomatoes and broccoli varied from year to year. The fertilized plots, however, produced higher bean yields and numerically higher carrot and pepper yields, while the compost-amended plots produced higher onion yields in both years. There were few significant effects of treatments on plant tissue content; only Fe and B were higher in the organically-amended plant leaves in 1999. Of 19 soil parameters evaluated, the cation exchange capacity and the Mehlich-3 extractable Ca, Mn and Pb content of compost-amended soils were higher following the harvest in both study years. This six crop rotation study ended in 2001; in addition to the above parameters, emphasis is directed to soil biochemical changes which may have occurred from the continuous agronomic applications of the compost or fertilizer.

Introduction

Numerous authors from various countries have examined different characteristics of vegetable crops whose soils were amended with compost and/or fertilizer. Ozores-Hampton and Obreza (2000) wrote an extensive review describing the use of composted waste on Florida vegetable crops. In Scotland, Purves and Mackenzie (1973) evaluated Cu, Zn and B uptake by garden vegetables from municipal compost applications in three successive years; as expected, the vegetables responded differently to the compost treatments. Vogtmann et al. (1993) described the effects of composts on the yield and quality of some vegetables in Germany. Compared with chemical fertilizers, compost treatments lowered vegetable yields the first two years, but yields did not differ after the third year of fertility applications. Generally, composts positively affected food quality and storage performance while reducing nitrates and improving the nitrate to vitamin C ratio.

The quality of conventionally and organically grown foods have been reviewed by Woese et al. (1997). They identified “some differences in quality between products” of the two fertilization systems. More recently, in their review of the literature, Brandt and Molgaard (2001) stated “organic plant foods may in fact benefit human health more than corresponding conventional ones”. However,most previous studies were somewhat flawed since they were short-term and did not compare identical cultivars grown in the same soil type with similar soil and crop management practices. Also, many projects used high fertility soils or those with a history of fertilizer use or agronomically inappropriate rates of compost or fertilizer. Some studies have evaluated the differences in yield as well as quality, while others have examined differences in nutrient composition.

Past studies on peppers, cabbage, carrots, beans and broccoli, crops used in this study, have produced mixed results. Roe et al. (1997) grew peppers and cucumbers in a sandy soil supplemented with compost or fertilizers; yields were usually higher when compost was combined with fertilizer, while pepper leaf P, K, Ca and Mg increased and Cu levels decreased in plots amended with only compost. Reider et al. (2000) compared four composts with dairy manure and conventional fertilizer in a three-year rotation (which included peppers) and showed no significant yield differences among treatments for the three years; the authors used a 40% N availability factor for compost. In a three- crop vegetable rotation and a comparison of four organic amendments with chemical fertilizer, Blatt and McRae (1998) found equivalent marketable yields of cabbage and carrot from organic or fertilizer plots, but green bean yields were higher from 17-17-17 fertilizer. Treatment effects on soil and foliar nutrient contents varied with the element evaluated. Baziramakenga and Simard (2001) and Wen et al. (1997) compared compost fertilization with mineral fertilizers for snap bean and other crops, whereas, Buchanan and Gliesman (1990) evaluated broccoli production. These three studies emphasized P use efficiency or P uptake.

Warman and Havard (1996,1997,1998) conducted an extensive comparison of four vegetables grown organicallyand conventionally using non-rotational practices between 1990 and 1992. At the end of the first year of that study it was decided to maintain one set of six plots using compost and inorganic fertilizer treatments in a long-term (six year) vegetable crop rotation. The author has reported the experimental results for 1995 and 1996 (Warman, 1998) and for 1997 and 1998 (Warman, 2000). This paper reports on the 1999 and 2000 production years, with the objectives to compare the yield and nutrient content of different vegetables grown in a crop rotation system using either composted farmyard manure or commercial fertilizer, and evaluate the extractable nutrient content, pH, total C and N, and CEC of the treated soils.

Materials and Methods

This field trial began in 1990 and has continued on the same site to this date. A Pugwash sandy loam (Humo-Ferric Podzol) in Lower Onslow, N.S. was selected because the site had no history of inorganic fertilizer or pesticide use. The site was used to grow cabbage and carrots in 1990 as part of the study documented in Warman and Havard (1996, 1997). Table 1 lists the crops grown in the plots for the last eight years. Each plot has an area of 11 m2 and all the crops are planted into four rows/plot of 2.25 m long with a 1.2 m wide separation between plots. Each year an equal number of seeds or transplants were planted into each paired compost and fertilizer plot. Since the beginning of cropping, the six plots of each of the two treatments have been assigned to alternate plot areas. Fertility amendments for each crop species were applied to the soil according to the Soil Test Recommendations of the Nova Scotia Department of Agriculture and Marketing (Table 2). Lime was applied to half the plots in 1998 to bring the soil pH of all plots to about 6.5; lime has not been applied since that time. The conventional method of growing the six types of vegetables followed the recommendations of the Vegetable Crops Guide to Cultivar Selection and Chemical Pest Control for the Atlantic Provinces (1989; Publication #1400A). Initially, organic vegetable production followed the Organic Crop Improvement Association guidelines; however, after 1992, only organic fertilization with compost was maintained and and insects were controlled using rotenone, pyrethrum or Bacillus thuringensis powder or liquid formulations. Plots were hand-weeded or rototilled; fungicides were not used.

TABLE 1 Crop rotation (1993-2001) of the eleven crops among the six plots at the study site

1993

1994

1995

1996

1997

1998

1999

2000

2001

1

POT

CAR

SWC

BRO/

CAU

ONI

TOM

BEA

CAR

CAU/

B.SP

2

CAR

ONI

SWC

TOM

BEA

CAR

PEP

BRO/

TOM

3

ONI

SWC

TOM

ONI

BRO/

PEP

CAR

B.SP

BEA

ONI

4

BEA

SWC

ONI

TOM/

B.SP

CAR

BEA

TOM

ONI

PEP

5

BRO

SWC

CAR

PEP

BEA

TOM

ONI

BRO/

PEP

CAR

6

CAB

TOM

BEA

CAR

PEP

BRO/

CAB

ONI

TOM

BEA

BEA: Beans

CAR: Carrots

CAU

BRO: Broccoli

CAU: Cauliflower

POT: Potatoes

B.SP: Brussels Sprouts

ONI: Onions

SWC: Sweet Corn

CAB: Cabbage

PEP: Peppers

TOM: Tomatoes

TABLE 2 Quantities of Amendments Applied to the Plots in 1999 and 2000 Crop Moist YMFC NPK Fertilizers (kg ha-1)

(Mg ha-1) N P205 K20

Tomatoes

25

60

85 - 225

30 - 60

Carrots

25

60

60 - 85

30

Peppers

34

80

60 - 85

30 - 50

Beans

13

30

50

0 - 30

Onions

50

120

150 - 225

30 - 50

Broccoli/ Cabbage or

63

150

150 - 225

30 - 50

The compost was made the year prior to its application using the aerated static pile method with a combination of chicken manure, food waste, grass clippings/weeds, and straw/racetrack manure bedding (designated YMFC). The mature compost was analysed for total N using a LECO CNS Analyzer and applied at rates appropriate to each crop assuming 50% availability of the N during the growing season. The analysis of the compost has varied slightly from year to year; the nitric acid procedure for compost digestion and ICP analysis is reported in Warman and Havard (1997). Based on the average values of the compost used in the two years, some chemical properties of the compost are shown in Table 3 (elemental analysis in g kg-1 or mg kg-1 on a dry weight basis); in addition, the YMF compost was 44% solid with a pH of 6.84.

TABLE 3 Mean Elemental Analysis of the YMFC Compost used in the Study (dry weight basis)

YMFC

g kg-1

YMFC

g kg-1

YMFC

mg kg-1

C

318

Mg

1.22

Cu

77

N

25.3

S

4.26

Zn

107

P

13.6

Na

5.83

B

39

K

13.4

Fe

6.03

Ca

36.1

Mn

1.32

Marketable fresh weight yields were taken annually from each plot at maturity, while leaf/petiole tissue samples were taken at flowering, fruit-set or root elongation. Five mature plant leaves from each row (20 in total) were sampled from each vegetable plot each year. Tomatoes, peppers and snap beans were harvested 6-10 times until the frost in the fall. Soil samples were taken in September of both years at the 0-15 cm depth. Plant tissue samples were washed with water, air dried for 48 hours, oven dried at 65C for 48 hrs and ground in a Wiley Mill to pass through a 1.0 mm stainless steel sieve. Tissue was digested in nitric acid and analysed by ICP for macro-, micro-, and trace elements, except N, which was analysed using a CNS analyzer (Warman and Havard 1997, 1998). After harvest, soil samples were taken from each plot from the 0 to 15 cm layer using a stainless steel probe. The soil was extracted with Mehlich-3 solution and analysed by ICP. Soil samples were also evaluated for pH, total C and N, and cation exchange capacity (CEC) using the calcium acetate saturation procedure.

Treatment results for crop yields, tissue content and extractable soil elements were statistically analyzed using a paired, two-tailed t-test or ANOVA at p%uF03C0.05.

Results and Discussion

Crop yield response was inconsistent between the two amendments; yields of tomatoes and broccoli varied from year to year (Table 4). The fertilized plots, however, produced higher bean yields and numerically higher carrot and pepper yields, while the compost-amended plots produced higher onion yields in both years. I noted that the % of Class A carrots, which had shown a higher % for organic carrots in 1997 – 1999, changed in 2000. Onion yields, however, were greater in the organic plots, as they had been in 1997 and 1998 (Warman, 2000).

TABLE 4 Fresh Crop Yields (kg) from the Six Paired Rotation Plots

Plot #

  1. Beans*

  2. Peppers

  3. Carrots

    % Class A

  4. Tomatoes

5. Broccoli Cabbage

6 Onions**

1999

2000

NPK

Compost

NPK

Compost

15

14

Carrots

13

13

% Class A

87

83

17

15

Broccoli

1.7

1.0

25

22

Beans*

11

9

70

86

33

42

Onions**

12

14

3

4

Peppers

7

6

10

9

16

21

Tomatoes

13

11

* Yields significantly higher with the NPK treatment

**Yields significantly higher with the compost treatment

There were few significant effects of treatments on plant tissue content (Tables 5 and 6); of the essential plant nutrients, only Fe and B were higher in the organically-amended plant leaves in one year (1999). Although the edible portion of the crops were not evaluated the last few years of the study, we have found a positive correlation between leaf tissue and edible portions of carrots (Warman and Havard, 1997) and other crops. Therefore, based on mineral analysis, our results do not support the belief that compost-grown vegetables are more nutritious.

Of 19 soil parameters evaluated, the CEC and the Mehlich-3 extractable Ca, Mn and Pb content of compost-amended soils were higher following the harvest in both study years (Tables 7 and 8). I noted that the compost-amended plots also had higher levels of Mehlich-3 Cu, Zn, and B in 2000, and this was the first year since 1996 that C was not significantly higher in the compost-amended plots. The 11 years of continual compost or fertilizer applications have significantly reduced the original differences in soil fertility between the plots so there are fewer differences between the treated soils in N-P-K but more differences between the soils in extractable micronurients. Furthermore, compared to the composts produced and used in 1990-1992 (Warman and Havard, 1997), the compost we are now making and using is of higher nutrient quality, probably due to the higher nutrient feedstocks we are using (more weeds and food wastes), and the improvement in our ability to make a better quality compost.

TABLE 5 Leaf tissue analysis of macronutrient (g kg-1), micronutrient and trace elements (mg kg-1) of the NPK fertilizer and YMFC compost plots from 1999

C

N

P

K

Ca

Mg

S

Carrot-NPK

420

27.0

2.00

1.85

4.9

3.13

4.67

Carrot-YMFC

406

22.2

2.01

1.09

8.9

3.32

6.17

Broccoli-NPK

391

35.3

2.25

7.05

10.6

2.95

6.48

Broccoli-YMFC

411

27.4

3.11

8.95

11.1

2.70

5.54

Pepper-NPK

408

49.3

3.19

1.88

13.7

6.40

4.70

Pepper-YMFC

395

53.5

2.55

1.86

15.2

6.55

5.09

Bean-NPK

406

32.9

1.71

1.17

11.0

4.75

3.26

Bean-YMFC

415

31.5

1.81

1.19

11.6

5.02

3.11

Tomato-NPK

414

29.6

1.86

0.95

13.0

5.72

6.41

Tomato-YMFC

412

31.8

2.52

1.16

13.8

5.30

5.90

Onion-NPK

411

36.3

2.63

7.63

7.4

4.25

6.43

Onion-YMFC

414

32.3

2.37

9.45

6.8

4.82

6.77

p-value

0.929

0.341

0.618

0.286

0.141

0.589

0.775

Fe

Mn

Cu

Zn

B

Cr

Na

Pb

Carrot-NPK

140

60

8.4

40

27.7

1.3

1835

1.5

Carrot-YMFC

160

64

7.1

32

30.6

1.7

2626

9.0

Broccoli-NPK

60

42

8.1

31

11.6

1.0

2084

4.6

Broccoli-YMFC

70

45

9.9

27

25.9

2.4

1332

11.3

Pepper-NPK

70

48

4.9

49

18.2

1.7

54

11.9

Pepper-YMFC

90

36

8.9

25

19.1

1.7

42

2.5

Bean-NPK

60

43

6.5

38

13.7

1.0

57

1.2

Bean-YMFC

90

42

7.1

25

16.2

1.0

45

2.1

Tomato-NPK

40

36

4.7

25

9.6

1.2

2065

1.5

Tomato-YMFC

70

40

9.3

37

17.1

1.6

1967

3.1

Onion-NPK

90

27

5.6

18

8.7

1.3

515

0.9

Onion-YMFC

140

28

9.0

31

16.6

1.2

1024

0.9

p-value

0.005

0.886

0.066

0.537

0.031

0.201

0.758

0.654

TABLE 6 Leaf tissue analysis of macronutrient(g kg-1), micronutrient and trace elements(mg kg-1) of the NPK fertilizer and YMFC compost plots from 2000

C

N

P

K

Ca

Mg

S

Carrot-NPK 414

27.4

2.03

12.7

10.2

2.95

4.42

Carrot-YMFC 426

25.7

1.45

10.4

7.7

2.97

3.59

Broccoli-NPK 401

35.7

1.05

13.0

14.0

27.0

1.17

BroccoliYMFC 414

37.4

1.43

15.0

19.0

34.0

1.35

Br.Sprout-NPK 414

49.5

1.28

3.3

8.0

1.39

3.27

Br.SproutYMFC 399

51.5

2.02

3.9

8.5

1.38

5.59

Pepper-NPK 408

32.1

1.23

14.1

16.0

6.17

5.29

Pepper-YMFC 413

31.7

1.50

14.7

15.6

5.83

6.75

Bean-NPK 417

29.9

1.41

7.0

9.8

3.16

1.77

Bean-YMFC 414

31.7

2.20

7.3

10.5

3.06

3.33

Tomato-NPK 419

36.8

1.50

10.0

16.2

5.85

6.01

Tomato-YMFC 412

35.2

1.50

10.4

17.3

5.08

6.93

Onion-NPK 426

34.8

1.24

6.3

5.6

1.47

2.58

Onion-YMFC 431

32.6

1.87

6.8

5.3

1.54

2.18

p-value 0.725

0.938

0.133

0.559

0.521

0.727

0.135

Fe

Mn

Cu

Zn

B

Cr

Na

Pb

Carrot-NPK

78

22

7.5

17

20.0

0.5

2398

4.8

Carrot-YMFC

69

20

5.1

12

12.8

0.5

1242

3.1

Broccoli-NPK

178

32

13

40

15

1.3

640

6.5

BroccoliYMFC

167

31

18

38

38

1.7

2010

3.1

Br.Sprout-NPK

30

13

2.4

10

7.4

0.3

973

4.3

Br.SproutYMFC

33

10

2.8

11

9.7

0.4

837

4.0

Pepper-NPK

153

30

6.0

21

11.5

0.7

61

2.6

Pepper-YMFC

182

27

5.2

21

17.6

0.6

123

2.6

Bean-NPK

179

33

5.0

8

8.8

0.4

48

1.9

Bean-YMFC

154

35

7.9

14

9.0

0.6

81

2.7

Tomato-NPK

180

37

7.6

10

17.8

0.6

431

2.6

Tomato-YMFC

192

37

8.2

13

20.3

0.7

290

3.4

Onion-NPK

119

16

1.4

2

2.5

0.2

191

1.7

Onion-YMFC

122

17

3.8

8

8.5

0.4

384

2.0

p-value

0.967

0.289

0.262

0.435

0.226

0.078

0.912

0.422

TABLE 7 Soil pH, CEC [cmol ]kg-1, C and N (g kg-1) and Mehlich-3 extractable nutrients (mg kg-1) from the 1999 plots.

Fertilizer Treatment

pH

CEC

C

N

P

K

Ca

Mg

S

Fe

Bean

6.09

11.3

27.0

2.27

65

83

1070

292

50

67

Broccoli

6.76

11.2

17.0

1.52

58

105

1350

384

49

76

Carrot

6.14

10.5

23.4

2.13

44

83

1240

333

52

87

Onion

6.92

11.7

16.3

1.28

62

65

1150

254

50

81

Pepper

6.75

10.4

28.2

2.28

43

75

1690

314

68

80

Tomato

6.52

10.1

16.7

1.37

54

92

1130

218

62

76

mean

6.53

10.9

21.4

1.81

54

84

1270

299

55

78

±s.d.

±0.35

±0.6

±5.5

±0.47

±9

±14

±230

±59

±8

±7

Compost Treatment

Bean

6.31

13.4

29.2

2.56

44

77

1460

343

56

75

Broccoli

6.66

11.6

23.4

1.83

52

100

1540

403

50

88

Carrot

7.01

11.4

27.5

2.34

41

78

1470

346

55

84

Onion

6.94

12.5

29.6

2.34

41

63

1270

237

66

83

Pepper

6.56

12.0

27.0

1.69

40

62

1730

320

56

84

Tomato

6.84

11.4

29.0

2.04

42

84

1320

263

83

68

mean

6.72

12.1

27.6

2.13

43

77

1470

318

61

80

±s.d.

±0.26

±0.8

±2.3

±0.34

±5

±14

±160

±60

±12

±7

p-value

0.280

0.005

0.045

0.025

0.005

0.010

0.010

0.118

0.281

0.423

Fertilizer Treatment

Mn

Cu

Zn

B

Cd

Cr

Na

Ni

Pb

Bean

21

1.19

3.21

0.56

0.03

0.18

24.5

0.85

1.33

Broccoli

19

1.23

2.96

0.68

0.06

0.24

36.5

0.98

0.78

Carrot

25

0.90

4.93

0.51

0.07

0.19

20.5

0.75

0.53

Onion

24

1.36

3.52

0.56

0.05

0.25

23.1

0.99

0.82

Pepper

15

1.41

3.53

0.82

0.04

0.23

36.5

0.91

1.01

Tomato

15

1.37

3.84

0.72

0.07

0.34

38.5

0.82

0.75

mean

20

1.24

3.67

0.64

0.05

0.24

29.9

0.88

0.87

±s.d.

±4

±0.19

±0.69

±0.12

±0.02

±0.06

±8.1

±0.09

±0.27

Compost Treatment

Bean

28

1.49

4.50

0.99

0.10

0.32

25.9

0.81

1.69

Broccoli

23

1.39

2.93

0.89

0.07

0.19

21.2

0.73

0.87

Carrot

29

1.42

4.90

0.98

0.14

0.18

34.2

0.91

1.48

Onion

29

1.36

3.42

0.97

0.05

0.28

28.8

0.80

1.40

Pepper

19

1.25

3.05

0.78

0.05

0.15

25.2

0.80

1.09

Tomato

22

1.36

3.69

0.66

0.07

0.40

27.2

0.89

1.24

mean

25

1.38

3.75

0.88

0.08

0.25

27.1

0.82

1.30

±s.d.

±4

±0.08

±0.79

±0.13

±0.03

±0.10

±4.3

±0.07

±0.29

p-value 0.000 0.236 0.753 0.060 0.112 0.664 0.571 0.389 0.025

TABLE 8. Soil pH, CEC[cmol ]kg-1, C and N (g kg-1) and Mehlich-3 extractable nutrients (mg kg-1) from the 2000

plots

Fertilizer Treatment

pH

CEC

C

N

P

K

Ca

Mg

S

Fe

Bean

6.92

11.4

27.9

2.34

89

45

1560

131

83

209

Broccoli

6.09

11.1

22.9

1.75

124

65

1200

211

110

178

Carrot

6.75

10.7

23.1

2.24

131

161

1400

158

92

227

Onion

6.25

11.3

26.5

2.45

99

47

1260

192

81

181

Pepper

6.52

10.2

26.2

2.05

125

66

1120

214

96

116

Tomato

6.76

10.4

26.7

2.07

231

104

2140

252

107

183

mean

6.55

10.9

25.5

2.24

133

81

1450

193

95

182

±s.d.

±0.32

±0.49

±2.06

±0.25

±51

±44

±370

±43

±12

±38

Compost Treatment

Bean

6.94

13.9

29.1

2.41

95

41

1700

171

91

180

Broccoli

6.31

11.7

23.2

1.72

138

66

1970

243

85

248

Carrot

6.56

11.9

24.5

2.31

143

184

1620

176

97

173

Onion

6.34

12.8

27.4

2.37

105

52

1570

180

87

210

Pepper

6.84

12.4

25.8

2.17

132

63

1640

201

87

195

Tomato

6.66

11.7

27.0

2.11

208

95

2210

239

80

190

mean

6.61

12.4

26.2

2.18

137

84

1790

202

88

199

±s.d.

±0.26

±0.85

±2.12

±0.25

±40

±52

±250

±32

±6

±27

p-value 0.478 0.003 0.075 0.340 0.535 0.657 0.025 0.424 0.334 0.468

Fertilizer Treatment

Mn

Cu

Zn

B

Cd

Cr

Na

Ni

Pb

Bean

19

1.48

2.08

0.68

0.01

0.20

100

0.91

0.52

Broccoli

30

1.18

3.95

0.76

0.03

0.22

188

0.81

0.91

Carrot

28

1.72

2.84

0.71

0.01

0.19

110

0.78

1.17

Onion

28

1.80

2.37

0.78

0.04

0.21

99

0.41

0.55

Pepper

22

1.83

2.71

0.86

0.03

0.25

114

0.57

0.27

Tomato

34

1.27

3.07

1.17

0.06

0.30

157

0.72

2.07

mean

27

1.55

2.84

0.83

0.03

0.23

128

0.70

0.92

±s.d.

±6

±0.28

±0.65

±0.18

±0.02

±0.04

±36

±0.18

±0.65

Compost Treatment

Bean

47

1.94

2.78

1.10

0.05

0.22

98

0.75

1.47

Broccoli

35

1.68

4.50

1.15

0.01

0.22

107

0.62

2.47

Carrot

41

2.67

3.00

1.18

0.05

0.20

122

0.71

3.15

Onion

35

1.87

3.17

0.98

0.02

0.19

102

0.56

1.15

Pepper

37

1.91

3.17

1.12

0.03

0.19

87

0.54

1.82

Tomato

43

2.01

3.15

1.35

0.04

0.19

88

0.44

2.27

mean

40

2.01

3.30

1.15

0.03

0.20

100

0.60

2.06

±s.d.

±5

±0.34

±0.61

±0.12

±0.02

±0.01

±13

±0.11

±0.73

p-value 0.012 0.023 0.011 0.001 0.793 0.246 0.149 0.175 0.009

In conclusion, mineralization of recently added and previously applied compost influence plant response in a particular crop year, especially for the high nutrient-demanding crops (brassica species). Seasonal variation in soil moisture and temperature seem to have a greater influence on plant production, through mineralization, than the source and amount of mature compost applied. In some years, compost is providing a higher level of available nutrients than the literature would predict, probably because the soil environment has more biological activity and is more conducive to mineralization from long-term organic applications

References

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