Effect of different levels of biochar on the yield and nutritive value of Celery cabbage (Brassica chinensis var), Chinese cabbage (Brassica pekinensis), Mustard green (Brassica juncea) and Water spinach (Ipomoea aquatica)

Chhay Ty, Vor Sina, Khieu Borin and T R Preston*

Center for Livestock and Agriculture Development. Pras Teat village, Rolous Commune, Kandal Stung district, Kandal province.
PO Box 2423 Phnom Penh 3, Cambodia
chhayty@celagrid.org
* Finca Ecológica, TOSOLY, AA #48, Socorro, Santander, Colombia

Abstract

The experimental design in a field plot trial (soil pH 5.8; OM 17%) conducted in the rainy season (September to October 2012) involved 24 treatments arranged in a 6*4 factorial arrangement with 3 replications. The first factor was level of biochar (0, 1, 2, 3, 4 and 5 kg/m²); the second factor was the type of vegetable (Water spinach,  Chinese cabbage, Celery cabbage  and Mustard green).  Fertilization was with biodigester effluent (10kg N/ha applied to all treatments. The area of each plot was 1.6m² (2.0m length x 0.8m width) with spacing between each plot of 0.5m. The experiment lasted 35 days. The biochar (pH 9.3; OM 29.4% in DM) was from a paddy rice drier (combustion temperature with rice husks as feedstock was about 500°C).

Increasing the application of biochar  from 0 to 5 kg/m² led to linear increases in biomass DM yield of  39, 100, 300 and 350 % for Water spinach, Chinese cabbage, Celery cabbage and Mustard green, respectively. Soil quality was improved after the 35 day trial (pH 6.82-7.13; OM 22.6 - 25.7%). The chemical composition of the biomass DM showed average increases in crude protein from 13.7 to 18.1% for leaves and from 7.23 to 9.16 for stems.  By contrast, crude fiber in leaves decreased from 14.5 to 9.27% in DM while in stems it fell from 15.6 to 10.7%.

Key words: biodigester effluent, crude fiber, crude protein, nutritive value, pH, soil, vegetables

Introduction

In Cambodia, diesel fuel for running the generator in rice mills is increasing in price and prices are not stable, thus rice mill owners try to find alternative ways to reduce the cost of fuel. Following the introduction to Cambodia of an Indian-made gasifier in 2004 by CelAgrid (Phalla and Preston 2005), several local companies have begun to construct gasifiers using rice husks as the feedstock. Gasification offers a more sustainable pathway as a means to extract energy from renewable biomass. Gasification is the way to convert solid fibrous biomass by pyrolysis into producer gas which can be used as fuel for internal combustion engines and gas turbines, as well as a source of heat. Additional benefits are that the system is “carbon-neutral” (does not add to global warming), produces negligible amounts of sulphur compounds (the cause of “acid” rain), reduces waste disposal and has fewer negative environmental impacts. The residue from biomass after processing in a gasifier is known as BIOCHAR.  

Biochar is a fine-grained porous substance that resembles charcoal produced by natural burning. However, biochar is produced by the combustion of biomass under oxygen limited conditions at high temperatures (from 600 to 1000 °C) in a gasifier. As most of the mineral matter in biomass is composed of salts of K, Na and Ca, it has a strong alkaline reaction giving rise to a pH of between 8 and 10 (Rodriguez et al 2009). Thus application of biochar as a soil amender is especially appropriate in acid soils with a low content of organic matter. Biochar is unlikely to have a major role as a fertilizer but, because of its structure, it can be expected to increase water-holding capacity, and be a good habitat for microbes and plant nutrients. A study by Rodriguez et al (2009) using 50g biochar/kg soil applied to fertile soil or sub-soil with and without effluent of 100 kg N/ha, showed that biochar with effluent markedly increased the biomass growth of maize especially on the poor sub-soil. Soil pH was increased from 4-4.5 to 6.0-6.5 due to addition of biochar. 

In Cambodia, most farmers after rice is harvested burn the rice straw in order to facilitate subsequent plowing, but this has negative effects on soil fertility as organic matter is lost and valuable soil microbes are destroyed. Application of biochar which increases water holding capacity and is a good habitat for plant nutrients and microbes can thus bring about improvement in soil fertility and yield of rice. This was recently demonstrated in Cambodia in recent studies by Boun Suy Tan (2010) (http://biocharinnovation.wordpress.com/workshop-cambodia) and Sokchea et al (2013). In the former case, the rice yields were more than doubled (3.76 tonnes/ha) by application of 40 tonnes/ha of biochar compared with the control (without biochar) which yielded only 1.25 tonnes/ha. In the second study, application of 30 tonnes/ha biochar to a rice crop increased grain yield by 30% and straw yield by 40%. 

In Vietnam, biochar has been applied successfully  to increase the yield of mustard green vegetable (Pham Van Luu et al 2013). However, there appear to be no reports in Cambodia on the use of the biochar for growing vegetables.

The present study examined the effect of biochar on the production and nutritive value of a range of vegetables commonly grown by local farmers in Cambodia.

Materials and Methods

Location

The experiment was carried out at the Center for Livestock and Agriculture Development (CelAgrid) located in Prah Theat village, Sangkat Rolous, Khan Dangkor, approximately 25 km from Phnom Penh city. The experiment was conducted in the rainy season from September to October 2012. 

Experimental design

The experiment design was a Randomized Complete Block  (RCBD) with 24 treatments in a 6*4 factorial arrangement with 3 replications. The first factor was level of biochar (0, 1, 2, 3, 4 and 5 kg/m²); the second factor was the type of vegetable (Water spinach - WS,  Chinese cabbage – ChC, Celery cabbage – CeC, and Mustard green - MG).  

Land preparation

The land was plowed 2-3 times and sun-dried for a week before making the beds; the area of each bed was 1.6m² (2.0m length x 0.8m width) and spacing between each bed was 0.5m.   

Planting vegetables

Chinese cabbage, celery cabbage and mustard green were germinated in a nursery without applying any fertilizer and the best plants selected for transplanting at 14 days with 20 cm distance from plant to plant. The dry-land water spinach species was chosen for this species. The seeds were kept in water at ambient temperature for 12 hours before planting and seeding density was 62.5g/m².

Irrigation and biochar application

The biochar was the residue from combusting rice husks in a paddy rice dryer in which the furnace temperature was from 500 to 600⁰C. This temperature is similar to that in a conventional down-draft gasifier and it has been shown that there were no differences in the yield response of rice to biochar from the paddy rice dryer and a conventional gasifier (Sokchea et al 2013).  The biochar was incorporated in the upper 10 cm of the soil in each of the beds (thus 1 kg/m² is equivalent to 10 tonnes/ha).

The biodigester effluent was from a fixed dome brick and concrete model which had a capacity of 15m³. It was charged with manure from pigs fed a commercial concentrate feed. All treatment plots received the same level of biodigester effluent at a level of 10 kg N/ha. This was applied in amounts equivalent (as a proportion of the total application) to 20% at 14 days (time of transplanting), 40% at 21 days and 40% after 28 days. The effluent was diluted with water in proportions of 50:50 (fresh basis) before application. The plots were irrigated uniformly based on weather conditions, usually around 2 times a day. 

Measurements

The plant height and numbers of leaves were measured at 14, 21 and 28 days after planting. At the end of the experiment (35 days), representative plants were harvested including the roots in order to measure total biomass yield of the vegetables.  

Chemical analysis

Soil samples were analyzed before and after completing the experiment). Soil and biochar samples were analyzed for pH, organic content (OM) and N by methods from "Soil chemical analysis": http://www.icarda.org/Publications/Lab_Manual/PDF/part5.pdf).  The biodigester effluent was analyzed for DM and N at each application. The vegetable biomass was analyzed for moisture, organic matter,  N and crude fibre following the methods in AOAC (1990), except for moisture content which was determined using the method of Undersander et al. (1993); ash and N were done according to the methods of AOAC (1990).

Statistical analysis

The data were  recorded in MS Excel and analyzed by the General Linear Model option in the Analysis of Variance (ANOVA) program of the Minitab software (2000). Sources of variation were levels of biochar, type of vegetable, interaction between level of biochar * type of vegetable and error.

Results and discussion

Chemical composition of biochar and effluent 

Effects of biochar on the soil

The soil used in the experiment showed improvements as reflected in increased content of organic matter, nitrogen and pH as a result of the addition of biochar. The effects were most notable between zero and 1% biochar, with little change noted for higher applications of biochar (Table 2). Similar responses have been reported in soils that were amended with biochar (eg: biochar from a downdraft gasifier [Rodriguez et al 2009], from an updraft stove [Southavong et al 2012] and a paddy rice dryer [Sokchea et al 2013]).

Effects of biochar on the chemical composition of the plants

There were linear changes in the composition of the leaves and stems of the vegetable (Table 3; Figures 1 and 2). The DM content of leaves and stems was not affected by the level of biochar that was applied; however, in both leaves and stems the crude protein increased (on average by some 30%) and the crude fiber decreased (by some 30%) as the application of biochar was increased from zero to 5 kg/m². Responses were similar for the different vegetables (P  for the biochar*species interaction was 0.66).

Figure 1: Relationship between level of biochar and crude protein content of leaves and stems of four vegetables (mean values of Celery cabbage,  Chinese cabbage, Mustard green and Water spinach)	Figure 2: Relationship between level of biochar and crude fiber content of leaves and stems of four vegetables (mean values of Celery cabbage,  Chinese cabbage, Mustard green and Water spinach)

Growth in height and increase in leaves

Both growth in height and in the numbers of leaves recorded for the different vegetables showed linear increases to level of added biochar (Tables 4 and 5).  These effects of treatments are discussed in detail in the subsequent section on biomass yields.

Biomass yield

For each type of vegetable, application of increasing quantities of biochar led to positive linear or curvilinear increases in biomass yield of leaves, stems and roots (Table 6; Figures 1-4). Yield increases for biochar application of 5 kg/m² (50 tonnes/ha) were of the order of 300%, 100%, 350% and 39% for Celery cabbage, Chinese cabbage, Mustard green and Water spinach, respectively. Responses were much less for water spinach than for the three types of cabbages.

Figure 3: Relationship between level of biochar and green biomass DM yield of Celery cabbage	Figure 4: Relationship between level of biochar and green biomass DM yield of Chinese cabbage
Figure 5: Relationship between level of biochar and green biomass DM yield  of mustard green	Figure 6. Relationship between level of biochar and green biomass DM yield of water spinach

Biomass yield: proportions of leaf, stem and root

The vegetables differed markedly in the proportions of leaves and stems, the proportion of the latter being much higher in Water spinach (Table 6). The vegetables also responded differently to soil amendment with biochar. For the Chinese cabbage and Mustard green (Figures 8, 9 and 11), the proportions of leaf, stem and root showed little change with increasing yield. However, in the case of Celery cabbage and Water spinach, the response was quite different as the increase in biomass yield was reflected in a decrease in the yield of leaf and increase in stems (Figures 7, 10 and 11).

Figure 7: Relationship between level of biochar and DM biomass yield of Celery cabbage as root, stem and leaf	Figure 8: Relationship between level of biochar and DM biomass yield of Chinese cabbage as root, stem and leaf
Figure 9: Relationship between level of biochar and DM biomass yield of mustard green as root, stem and leaf	Figure 10: Relationship between level of biochar and DM biomass yield of Water spinach as root, stem and leaf

Figure 11. Effect of level of biochar on change in proportion of leaf biomass as proportion of leaf + stem

Apart from the greatly enhanced yield of the vegetables, the improvement in nutritive value (more protein; less fiber) as a result of soil amendment with biochar is especially promising. This appears to be the first report from a replicated field experiment showing these changes. A long term field demonstration in Canada (latitude 45°N),  in which biochar was applied at 3.9 tonnes/ha to mixed grass-clover forage plots (Husk and Major 2011),  demonstrated increased yields of forage (4.1%) in the third year and associated increases in nutritive value (Crude protein increased by 10%, NDF decreased by 5.9%; predicted improvement in milk production from 20 to 44%). However, the trial plots were not replicated and the forage composition of the plots also changed, with the biochar  plot showing clover increasing from 35 to 51% of the sward and ryegrass decreasing from 60 to 40%. These changes in botanical composition would explain part of the changes in nutritive value. Nevertheless, these findings lend support to the results we report from  the present study, and urge the necessity for more detailed long-term  research  on the effects on plant composition in soils amended with biochar.

It is difficult to develop an explanation for these marked effects of biochar on the nutritive value of the vegetables, but if confirmed in other studies this would represent a major virtue to be added to the list of attributes apparently possessed by biochar as a component of farming systems, at least for biochar derived from rice husks.

Conclusions

• Increasing the application of biochar to a fertile soil (pH 5.8; OM 17%) from 0 to 5 kg/m² during a 35 day trial led to linear increases in biomass DM yield of  39, 100, 300 and 350 % for Water spinach, Chinese cabbage, Celery cabbage and Mustard green, respectively,

• Soil quality was inproved after the 35 day trial (pH 6.82-7.13; OM 22.6 to 25.7%).

• The chemical composition of the biomass DM showed average increases in crude protein from 13.7 to 18.1% for leaves and from 7.23 to 9.16 for stems.  By contrast, crude fiber in leaves decreased from 14.5 to 9.27% in DM while in stems it fell from 15.6 to 10.7%.

Acknowledgements

The authors would like to express their gratitude to the MEKARN project financed by the SIDA-SAREC Agency and to the Center for Livestock and Agriculture Development (CelAgrid), for providing resources for conducting this experiment.

References

AOAC 1990 Official Methods of Analysis. Association of Official Analytical Chemists. 15^th edition (K Helrick editor). Arlington pp 1230

Boun Suy Tan 2010 Biochar Innovation from the UK Biochar Research Center. http://biocharinnovation.wordpress.com/wokshop-cambodia/

Husk B and Major Julie 2011 Biochar Commercial Agriculture Field Trial in Québec, Canada – Year Three: Effects of Biochar on Forage Plant Biomass Quantity, Quality and Milk Production. http://opensourceecology.org/w/images/5/55/BlueLeafBiocharForageFieldTrial-Year3Report.pdf

Huy Sokchea, Khieu Borin and Preston T R 2013 Effect of biochar from rice husks (combusted in a downdraft gasifier or a paddy rice dryer) on production of rice fertilized with biodigester effluent or urea;  Livestock Research for Rural Development. Volume 25, Article #004. Retrieved , from http://www.lrrd.org/lrrd25/1/sokc25004.htm

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Pham Van Luu, Duong Nguyen Khang and Preston T R 2011 Effects of biochar from gasifier and effluent from biodigester for improving  soil fertility and yield of green mustard Brassica juncea (L.). Workshop on Reducing Greenhouse Gas Emissions from Livestock and Soils (Editors: Reg Preston and Sisomphone Southavong). National Institute of Animal Science, Hanoi, 14-15 November 2011. httm://www.mekarn.org/workshops/GHG-CC/luu.htm

Rodrigues L, Salazar P and Preston T R 2009. Effect of biochar and biodigester effluent on growth of maize in acid soils. Livestock Research for Rural Development. Volume 21, Article#110. http://www.lrrd.org/lrrd21/7/rodr21110.htm

Southavong S, Preston T R and Man N V 2012  Effect of biochar and charcoal with staggered application of biodigester effluent on growth of water spinach (Ipomoea aquatica). Livestock Research for Rural Development. Volume 24, Article #39. Retrieved December 17, 2012, from http://www.lrrd.org/lrrd24/2/siso24039.htm

Undersander D, Mertens D R and Theix N 1993. Forage analysis procedures. National Forage Testing Association. Omaha pp 154.

Received 23 November 2012; Accepted 18 December 2012; Published 4 January 2013

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