Livestock Research for Rural Development 27 (9) 2015 Guide for preparation of papers LRRD Newsletter

Citation of this paper

Carry-over effects of biochar on yield of Mustard Green vegetable (Brassica juncea) and on soil fertility

Huy Sokchea, Khieu Borin and T R Preston1

Center for Livestock and Agriculture Development.
Pras Teat village, Sangkat Rolous, Khan Dong Kor, Phnom Penh.
PO Box 2423 Phnom Penh 3, Cambodia
huy.sokchea@celagrid.org
1 Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV),
Carrera 25 No 6-62 Cali, Colombia

Abstract

Increasing levels of biochar (0, 1.5, 3, 4.5 and 6 kg DM/m2) derived from rice husk were applied to plots cultivated with Mustard Green vegetable for three successive crop cycles. The biochar was applied 15 days prior to transplanting the Mustard Green seedlings in the first cropping cycle only. Biodigester effluent or urea (100 kg N/ha) were applied during each cropping cycle.

The initial application of biochar showed carry-over effects in soil amendment as measured by: (i) increases in pH and in water holding capacity of the soil in each of the three cycles; and (ii) higher biomass vegetable yield in each of the three cropping cycles. However, the relative increases in yield for the best biochar treatment over the control (zero biochar) decreased from the first to the third cropping cycle.

Key words: CEC, pH, residual effects, WHC


Introduction

Growing vegetables contributes to ensuring food security, injecting further revenue to farmers, and improving environmental balances. The need of vegetable production in Cambodia is estimated at about 70 to 80 tonnes a day (reference??). At the present, Cambodia is dominated by vegetable imports from Vietnam and Thailand while local producers only produce about 40-50% of total needs with total land size of 52,706 ha (COrAA 2011). It is estimated that every person needs between 1,700 and 2,200 kcal per day, of which vegetables should contribute 15-20 percent, making the vegetable net consumption between 30 and 35 kg per year per capita (The South East Asia Weekly 2012).

Cambodia imported about 433,120 tonnes of NPK fertilizer products in 2011 compared with 137,877 tons in 2002. There is no policy to “protect” or favor local fertilizer production plants; the government promotes a free market, allowing fertilizer suppliers to compete in quality and prices at all levels along the supply chain. To meet the demands of crop intensification, fertilizer is essential, but farmer understanding of fertilizer use efficiency for crop productivity in Cambodia is still limited. Therefore, there is a need to expand scientific research and public extension services to enhance the role of fertilizers in transforming agriculture for food security (Theng et al 2014).

Biochar is the carbon-rich residue obtained by combustion of fibrous biomass (Hemicellulose, Cellulose and lignin) in oxygen-restricted condition which is utilized for soil amendment and for long term carbon sequestration (Winsley 2007). Biochar has been reported to boost soil fertility and improve soil quality by raising soil pH, increasing moisture holding capacity, attracting more beneficial fungi and microbes, improving cation exchange capacity (CEC), and retaining nutrients in the soil (Lehmann et al 2006). According to Zheng et al (2010), the use of nitrogenous fertilizer can be reduced when the soil is amended with biochar, due to its negative surface charge, facilitating strong adsorption of NH4 +.Thus its addition to soils is expected to improve the retention and availability of ammonium salts to the plants.

When major attention was drawn to the potential role of biochar in improving soil fertility (eg: Lehmann et al 2006), reference was made to observations that areas of soils in the Amazon rain forest, thought to be have been settlements of indigenous tribes thousands of years ago, were more fertile than adjacent soils in non-settled area. It was theorized that these indigenous tribes had amended these soils by application of biochar derived from burning of the forest biomass, and that some of the beneficial effects of the biochar were still present even some thousands of years later.


Objectives

Despite the implications about the potential long-term effects of soil amendment with biochar there have been few studies to estimate the possible carry-over benefits in repeated cropping systems. The objective of the experiment described in this paper was therefore to generate some preliminary information on yields of vegetables through three cropping cycles following application of biochar in the first crop cycle.


Materials and methods

Location and design

The experiment was done in the Center for Livestock and Agriculture Development, Phnom Penh, Cambodia. The ambient temperature during the experiment was in the range 34-37 0C. Biomass yields and effects on soil parameters were studied over three cropping cycles with Mustard Green vegetable, following applications in the first crop cycle of biochar derived from combustion of rice husks.

The experiment was designed as a 5*2 factorial in a completely randomized block design (CRBD) with 4 replications (Table 1). The factors were:

Level of biochar: 0, 1.5, 3, 4.5, 6 kg DM/m2

N fertilizer: Urea or Effluent from a biodigester charged with pig manure

The biochar was applied at the start of the first cropping cycle. Fertilizer was applied in similar quantities in each crop cycle.

Table 1. Layout of experiment

1

2

3

4

5

6

7

8

9

10

SB0

SB4.5

SB6

EB1.5

EB0

EB6

SB3

EB4.5

EB3

SB1.5

11

12

13

14

15

16

17

18

19

20

SB4.5

SB0

EB6

SB1.5

EB1.5

EB3

EB4.5

SB6

SB3

EB0

21

22

23

24

25

26

27

28

29

30

EB3

SB3

EB1.5

SB1.5

EB4.5

SB0

SB4.5

EB6

SB6

EB0

31

32

33

34

35

36

37

38

39

40

SB3

SB4.5

EB0

EB3

SB6

EB1.5

EB6

EB4.5

SB0

SB1.5

The biochar was obtained from a paddy rice drier, operated with a furnace temperature of 400 to 700 ºC. It was spread on the surface of each plot and incorporated in the top soil by using a hoe to make sure that the biochar was completely mixed with the soil particles.

Sources of fertilizer were the effluent from a concrete fixed-dome biodigester and urea. The biodigester was charged daily with manure from pigs fed brewery waste and rice bran. The effluent was analyzed for nitrogen content before it was applied to the plots. The fertilizers were applied equally every 7 days at overall rates of 100 kg N/ha/crop.

Germination

Soil was collected from the farm of CelAgrid, broken down into small particles and then mixed with compost (from cattle and green manure) before putting in the germination tray. The seed of green mustard was bought from a market in Phnom Penh city and spread on the surface of the germination tray at the rate of 2 or 3 seeds in each hole of the tray. After germination plant density was reduced to 2 per hole. The germination phase lasted 15 days with watering 2 times a day (morning and evening).

Photo 1. Seedlings afteer 7 days Photo 2. Seedlings after 15 days
Application of biochar

Soil beds were formed (0.8 *2.7 m) and the biochar incorporated in the top 5 cm 15 days prior to transplanting the seedlings (Photos 3 and 4).

Photo 3.  Incorporating biochar into the soil Photo 4. The appearance of the plots after incorporation of the biochar.
Transplanting

At the end of the 15 day germination, two seedlings with attached soil were taken from the germination tray for transplanting in the plots with space between plants of 20 cm. Five days after transplanting seedlings were removed so as to leave only one plant per hill.

Photo 5. Transplanting activity
Fertilizing, watering and management

Watering was done daily (morning and evening). The fertilizers (effluent and urea) were applied every 7 days at the rate of 100 kg N/ha per cropping cycle (Photos 6 and 7).

Photo 6. Preparing the soil prior to
application of fertilizer
Photo 7. Application of fertilizer
Harvesting

At the age of 30 days (excluding 15 days of germination) the total vegetable biomass was collected and weighed.







Photo 8.  Activities of harvesting
Analytical procedures

Soil samples were analyzed before and after each crop cycle for determination of texture, pH, water holding capacity (WHC), organic matter (OM), organic carbon (OC) and cation exchange capacity (CEC). The effluent from the biodigester was analyzed for N, P and K.

pH

Soil samples were dried in the oven at 100 ºC, then ground into a powder. 5g of the ground sample were put in a beaker and 25 ml of distilled water were added. The suspension was stirred 3 times at 15 minute intervals, and then filtered. pH in the filtrate was determined with a digital pH meter (Photo 9).

WHC

Samples (10g) of dried and ground soil were put in a filter paper cone, and 10ml of distilled water were added. After 24 hours the total soil mass was weighed for calculation of the water retention in the soil (Photo 10).

Photo 9. pH measurement Photo 10. Water holding capacity measurement

Analytical methods for other elements were according to AOAC (1990).

Statistical analysis

The data were analyzed by the GLM option in the ANOVA program of the Minitab software (Minitab 2000). Sources of variation were: cropping times, fertilizer source, biochar level, interactions between cropping times*fertilizer source*biochar level and error.


Results and discussion

Composition of soil, biochar and effluent

The chemical elements of the biochar (Table 2) were in the range reported by Jindo et al (2014) for pH, nitrogen and organic matter, organic carbon and cation exchange capacity.

Table 2. Chemical composition (%) of biochar, urea, effluent and soil (prior to initiating the experiment)

Sample

OM

OC

DM

pH

N

P

K

CEC

 

Biochar

13.4

7.80

90.6

8.8

0.61

0.34

0.6

26.2

 

Urea

N/A

N/A

99.6

N/A

46.3

0

0

N/A

 

Effluent

N/A

N/A

N/A

N/A

0.091

0

0.10

N/A

 

Soil

3.46

18.52

86.8

6.4

2.8

0.60

1.41

20.5

 


Table 3. Chemical composition of the soil in the different treatments of the first crop cycle

Urea application

Effluent application

Biochar level, kg/m2

Biochar level,kg/m2

Parameter

0

1.5

3

4.5

6

0

1.5

3

4.5

6

N

2.8

2.8

3.5

3.15

3.85

2.45

2.45

3.5

3.15

4.2

P

0.6

0.75

0.92

1.26

0.83

1.09

0.56

0.92

1.15

0.89

K

1.41

2.24

2.72

4

3.77

1.79

2.54

2.5

3.14

4.13

OM

3.95

3.99

4.86

4.52

5.89

3.68

4.02

5.22

4.36

7.26

Carbon

23.01

23.2

26.32

28.3

34.3

23.4

21.45

25.36

30.35

42.21

C/N

8

8

8

9

8

10

10

9

9

8

CEC

20.5

23

23

25

22.6

22.6

20.5

23

21.5

25.5

Clay

25.8

26.4

10.25

22.5

22.6

31.2

22.95

32.85

26.8

23.4

Fine silt

28.8

28.85

42.4

33.4

27.7

19

29.05

16.3

28.3

23.8

Coase silt

16.68

13.06

16.95

10.49

11.63

13.32

16.05

16.72

14.74

13.57

Fine sand

24.87

26.42

25

27.23

32.42

34.01

30.17

31.07

24.76

32.89

Coase sand

4.62

4.6

4.63

5.74

4.52

3.39

2.5

3.49

3.77

3.44


Table 4. Chemical composition of the soil after the second crop cycle

Urea application

Effluent application

Biochar level,%/m2

Biochar level,%/m2

Parameter

0

1.5

3

4.5

6

0

1.5

3

4.5

6

N

1.75

2.1

2.1

2.45

2.5

1.75

2.1

2.45

1.75

2.8

P

0.86

0.85

0.78

0.96

0.76

0.98

0.74

0.78

0.82

0.72

K

3.4

2.2

2.92

2.59

2.86

2.69

2.82

2.56

2.88

3.34

OM

3.46

4.02

3.58

3.68

4.18

3.01

3.52

3.18

4.02

4.19

Carbon

18.5

23.4

20.8

21.5

24.3

17.5

20.4

20.1

23.4

24.3

C/N

9

11

10

10

12

9

10

11

10

11

CEC

21

25

20.5

21.5

24.5

19.41

22.5

21.36

23.64

25.3


Table 5.  Chemical composition of  the soil after the third  crop cycle

Urea application

Effluent application

Biochar level,%/m2

Biochar level,%/m2

Parameter

0

1.5

3

4.5

6

0

1.5

3

4.5

6

N

2.1

2.1

1.75

1.75

1.4

1.4

1.75

1.4

1.45

1.75

P

0.93

0.79

0.91

0.87

0.85

1.03

0.89

1.26

0.89

0.94

K

1.74

1.83

2.65

2.6

2.05

2

2.41

2.83

2.78

3.17

OM

4.26

3.88

3.46

3.37

2.91

2.71

3.47

2.81

2.99

3.37

Carbon

16.9

19.6

20.1

22.5

24.8

15.7

17.4

16.3

20.1

19.6

C/N

11

11

12

12

12

11

12

12

12

11

CEC

20.5

18.6

19.5

19.5

20.5

20.0

22.0

23.5

21

22.5

Effect of biochar on soil pH

The pH of the soil increased gradually in all three cropping cycles with increasing level of biochar applied in the first cycle (Table 6; Figure 1). Similar results were reported by Rodriguez et al (2007), Chhay Ty et al (2013), Sokchea et al (2013), Southavong et al (2012), Nguyen Huu Yen Nhi (2008) and Arnoldus (2011). Soil pH also increased in each crop cycle, the effect appearing to be greater in the plots containing biochar (Figure 1). Soil pH was not affected by the type of fertilizer (Figure 2).

Table 6.  Effect of biochar and fertilizer  on pH of soil

Biochar level

Biochar level

Harvest times

B*H

0

1.5

3

4.5

6

SEM

p

SEM

p

SEM

p

 

First harvest

6.36

6.57

6.61

6.80

6.96

 

Second harvest

6.51

7.06

7.10

7.18

7.25

0.052

<0.001

0.04

<0.01

0.091

???

 

Third harvest

6.71

7.22

7.36

7.35

7.41

 

 

Biochar level

Biochar level

Fertilizers

B*F

 

Effluent

6.52

7.00

7.09

7.12

7.30

0.071

<0.001

0.045

??

0.100

??

 

Urea

6.54

6.91

6.96

7.11

7.12

 


Figure 1. Mean values of soil pH with level of
biochar at different harvest times
Figure 2. Mean values of soil pH according to
application of urea or biodigester effluent
Water holding capacity

Water holding capacity was affected positively with biochar addition to the soil but was not different among the three crop cycles (Table 7; Figure 3) nor between sources of fertilizer (Figure 4). Kristin (2011), Verheijen et al (2009) and Samantha (2012) also reported that biochar addition into the soil improved the water retention of the soil.

Table 7.  Effect of biochar and harvest cycle on water holding capacity

Biochar level

Harvest times

B*H

0

1.5

3

4.5

6

SEM

p

SEM

p

SEM

p

First harvest

17.4

19.6

22.9

25.3

26.5

 

 

 

 

 

 

Second harvest

16.7

20.3

23.3

26.2

30.0

1.12

<0.001

0.872

>0.05

1.95

>0.05

Third harvest

18.0

18.0

24.8

26.3

27.1

Biochar level

Fertilizers

 

 

B*F

Effluent

17.9

19.5

23.5

27.4

28.0

1.10

<0.001

0.70

>0.05

1.57

>0.05

Urea

16.8

19.1

23.9

24.5

27.7

 

 

 

 

 

 


Figure 3. Effect of level of biochar at each harvest
cycle on soil water holding capacity

Figure 4. Effect of level of biochar with different
fertilizers on soil water holding capacity

Biomass yield

Biomass yield for the three crop cycles showed increasing curvilinear trends according to the level of biochar applied in the first cycle (Figures 5, 6 and 9). For the first two harvest cycles the trend was for increasing response to biochar according to the level of biochar applied. However, for the third harvest cycle the relative response increase to the original application of biochar was for this to decrease with the quantity applied. Considering the responses in yield with harvest cycle (ie: residual effect of the biochar) then this showed a steady decline with cropping cycle (Figure 11).

Biomass yields at each harvest were increased when urea was the fertilizer source compared with biodigester effluent (Table 9; Figures 7 and 8).

The data in Figure 9 show that the relative response in biomass yield to biochar, applied only in the first crop cycle, declined in succeeding crop cycles.

There are few reports on the residual effect of biochar over successive crop cycles. Afeng et al (2012) showed that a biochar amendment rate of 10, 20 and 40 tonnes/ha in the first crop cycle with rice increased yield in the first and the second crop cycle. Sarah et al (2013) reported that application of rice husk biochar at the rate of 150g/kg of soil increased the yield of lettuce and cabbage in three successive cycles but the relative increase in yield due to the original application of biochar was less in the third crop cycle than in the first.

Table 8. Mean values for fresh and DM biomass yield according to level of biochar and harvest cycle

Biochar level

Harvest time

B*H


0

1.5

3

4.5

6

SEM

Prob

SEM

p

SEM

p

Fresh biomass, kg/ha

First harvest

6371

6859

7268

8097

16276

1026

<0.001

794

<0.001

1777

>0.05

Second harvest

7875

6384

7529

9299

14087







Third harvest

16857

21720

24490

23728

25238







Biomass DM yield, kg/ha

First harvest

328

329

349

355

880

56.7

<0.001

43.9

<0.001

98.3

>0.05

Second harvest

525

477

519

609

961







Third harvest

1105

1390

1474

1438

1575








Table 9. Mean values for fresh and DM biomass yield according to level of biochar and source of fertilizer

Biochar level, kg/m2

Fertilizers

B*F


0

1.5

3

4.5

6

SEM

p

SEM

p

SEM

p

Fresh biomass, kg/ha

Effluent

8709

9153

10393

11612

16456

1641

<0.05

1038

<0.05

2321

>0.05

Urea

12026

14155

15799

15803

20612







Biomass yield DM kg/ha








Effluent

542.4

652.5

655.8

724.5

1041.7

103

<0.05

65.34

<0.05

146

>0.05

Urea

763.4

812.1

905.8

876.9

1235.6








Figure 5. Effect of level of biochar at each harvest
cycle on yield of fresh biomass
Figure 6. Effect of level of biochar at each harvest
cycle on yield of biomass DM.

Figure 7. Effect of level of biochar and fertilizer
source on yield of fresh biomass
Figure 8. Effect of level of biochar and fertilizer
source on yield of biomass DM

Figure 9. Responses over 3 cropping cycles in fresh biomass yield
to initial application of biochar in the first cycle

Table 10. Yield of fresh and dry biomass of vegetable according to crop cycle

Crop cycle

Fertilizer

H*F


First

Second

Third

SEM

p

SEM

p

SEM

p

Fresh biomass, kg/ha

Effluent

5332

7853

20609

829

<0.001

677

<0.001

1173

>0.05

Urea

12616

10216

24204







Dry biomass, kg/ha

Effluent

304

565

1300

48.9

<0.001

39.9

<0.001

69.2

>0.05

Urea

592

671

1493








Figure 10. Effect of effluent or urea on fresh biomass
yields in successive crop cycles
Figure 11. Effect of effluent or urea on dry biomass
yields in successive crop cycles


Conclusions


Acknowledgement

This paper forms part of the requirement for the degree of PhD to be submitted to Nong Lam University in Vietnam. The authors express their appreciation to the MEKARN program, financed by Sida (Sweden), for the grant which made possible this research, and to staff members and students in CelAgrid for their assistance in the experimental work.


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Received 11 June 2015; Accepted 28 June 2015; Published 1 September 2015

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