 |
 |
| Photo 1. Seedlings afteer 7 days | Photo 2. Seedlings after 15 days |
| Livestock Research for Rural Development 27 (9) 2015 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
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
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.
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.
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.
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 |
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. |
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 | |
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 |
At the age of 30 days (excluding 15 days of germination) the total vegetable biomass was collected and weighed.
 |
 |
 |
 |
| Photo 8. Activities of harvesting | |
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.
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).
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).
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.
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 |
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|
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 |
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|
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 |
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 |
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|
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 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 |
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|
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 |
Figure 4. Effect of level of biochar with different |
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 |
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