Synergism between biochar and biodigester effluent as soil amenders for biomass production and nutritive value of Mustard green (Brassica juncea)

Chhay Ty, Miech Phalla, 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

An experiment was conducted in the dry season (February to March 2013) involving ten treatments arranged in a 2*5 factorial arrangement of a random block design with 2 replications. The first factor was level of biochar (0 and 4 kg/m²); the second factor was level of effluent from biodigester (0, 2.5, 5.0, 7.5 and 10 kg N/ha). 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 40 days. The biochar was from a paddy rice drier (combustion temperature with rice husks as feedstock was about 500°C).

For all levels of effluent N application, the addition of biochar led to more than two-fold increases in above ground biomass yield. Biochar had no effect on biomass yield in the absence of effluent, and there were no further responses to effluent N when this exceeded a level of 2.5 kg N/ha. Biochar increased the crude protein in the leaves by an average of 16%, with the relative increase being greater when effluent was applied. A reduction in crude fiber content of the leaves due to biochar was  observed at low levels (< 5 kg N/ha) of application of effluent N, with the opposite effect being apparent at levels of N of 7.5 and 10 kg/ha.

Key words: fiber, leaves, pH, protein, stems, yield

Introduction

Biochar is the carbon-rich product obtained when biomass, such as wood, manure or leaves, is heated in a closed container with little or no available air and at high temperatures (from 600 to 1000 °C). (Lehmann and Joseph 2009). 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 (Thies and Rillig 2009).

Huy Sokchea et al (2013) showed that application of 30 tonnes/ha biochar to a rice crop increased grain yield by 30% and straw yield by 40%. A study by Boun Suy Tan (2010) also showed that the rice yields were more than doubled (3.76 tonnes/ha) by application of 40 tonnes/ha of biochar compared with without biochar which yielded only 1.25 tonnes/ha. In a recent experiment we found that the yield and nutritive value of different types of vegetable were increased linearly with the application of biochar from 0 to 5 kg/m²; soil quality after the experiment was improved. 

The aim of the present study was to examine the possible synergism between biochar and digester effluent as soil amenders for biomass production and nutritive value of mustard green.

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 dry season from February to March 2013. 

Experimental design

The experiment design was a Randomized Complete Block (RCBD) involving ten treatments arranged in a 2*5 factorial arrangement with two replications. The first factor was level of biochar (0 and 4 kg/m²); the second factor was level of biodigester effluent (0, 2.5, 5.0, 7.5 and 10kg N/ha).

Land preparation

The land was plowed 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

Mustard green was germinated in a nursery without applying any fertilizer and the best plants selected for transplanting at 18 days with 20 cm distance from plant to plant.

Irrigation, biochar and biodigester effluent 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 (Huy Sokchea et al 2013).  The biochar was incorporated in the upper 10 cm of the soil in each of the beds.

Photo 1: Biochar from paddy rice dryer	Photo 2: Soil without biochar	Photo 3: Soil mixed with biochar, 4kg/m2

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 and spent brewer's grain. The biodigester effluent was pumped into PVC containers located in the experimental area. It was applied at levels of  0, 2.5, 5.0, 7.5 and 10 kg N/ha. The amounts applied were as proportions of the total application) of 20, 40 and 40% at 21, 28 and 35 days of age of the plants, respectively. The effluent was diluted with water in proportions of 50:50 (fresh basis) before application. The plots were irrigated 2 times a day (morning and evening). 

Measurements

The plant height and numbers of leaves were measured at 21, 28, 35 and 40 days after planting. At the end of the experiment (40 days), representative plants were harvested including the roots in order to measure total biomass yield and composition.  

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, N and NH₃-N at each application. The mustard green biomass was analyzed for organic matter, N and crude fiber following the methods in AOAC (1990); DM was determined using the method of Undersander et al. (1993).

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: blocks, levels of biochar, level of biodigester effluent, interaction between level of biochar * level of biodigester effluent and error.

Results and discussion

Photo 4. Photos of the Mustard Green expeiment

Chemical composition of biochar and effluent 

The pH of the biochar was close to the level of 10.9 reported by Huy Sokchea et al (2013)  but the organic matter was higher in this study compared with the 10.3% reported by Huy Sokchea et al (2013).

Effects of biochar on the soil

The chemical composition of the soil showed improvements with increased content of organic matter, nitrogen and pH as a result of addition of biodigester effluent and the biochar at 4kg/m².  Similar effects were reported by Chhay Ty et al (2013) and Huy Sokchea et al (2013) using biochar from a paddy rice dryer. Other studies with biochar from a downdraft gasifier (Rodriguez et al 2009) and updraft stove gasifier (Southavong et al 2012) confirmed similar effects of biochar as soil amendment.

There were interactions between level of biochar and level of effluent application on organic matter, N and pH of the soil. Soil pH was increased by biochar by 3% when no effluent was applied but the increases were much higher (from 11 to 16%) when effluent was applied (Figure 1). Organic matter levels in soil were increased linearly by effluent N in presence of biochar but the response to effluent N was curvilinear in the absence of biochar with the maximuym at 5 kg N/ha (Figure 2). There was no effect of biochar on soil N when no effluent was applied but there were increases in soil N wwhen effluent was applied (Figure 3).

Figure 1. Effect of biochar on soil pH with increasing levels of application of nitrogen from biodigester effluent	Figure 2. Effect of biochar on soil organic matter with increasing levels of application of nitrogen from biodigester effluent	Figure 3. Effect of biochar on soil pH with increasing levels of application of nitrogen from biodigester effluent

Effects of biochar on the chemical composition of the plants

The DM content of leaves and stems were high on zero of biochar compared with 4kg/m² but crude protein content of leaves was affected by the level of biochar that was applied; however, it was not affect on crude fiber in leaves as the application of biochar was increased from zero to 4 kg/m². The value of DM content of leaves and stem in this study were contract with study of Chhay Ty et al (2013) who have been reported that the DM content of leaves and stems was not affected by the level of biochar that was applied (from 0, 1, 2, 3, 4 and 5kg/m²), but the crude protein content of leaves and stem increased 30% and the crude fiber decreased by 30% as the application of biochar was increased from zero to 5 kg/m². The improvement in nutritive value can be as a result of soil amendment with biochar.

The chemical composition of mustard green leaves were improvement as content of DM, crude protein and fiber as a result of level of biodigester effluent application. Meanwhile, there was interaction on crude protein and crude fiber (P<0.05) but not on DM content (P>0.05).

Application of biochar increased the crude protein in the leaves by an average of 16%, with the relative increase being greater when effluent was applied (Figure 4) . The reduction in crude fiber content of the leaves due to biochar was only observed at low levels of application of effluent N (Figure 5), with the opposite effect being apparent at levels of N of 7.5 and 10 kg/ha.

Figure 4: Relationship between level of biochar and level of effluent on crude protein content of mustard green leaves	Figure 5: Relationship between level of biochar and level of effluent on crude fiber content of mustard green leaves

Growth in height and numbers of leaves

The rate of growth in height of leaves was greater when biochar was applied and tended to increase (P=0.10) with increasing level of effluent N (Table 4; Figure 6). Similar responses were observed for effects of treatments on numbers of leaves (Figure 7). These effects of biochar were similar to those recorded previously by Chhay Ty et al 2013) with the same vegetable.

Figure 6: Relationship between level of biochar and level of effluent on growth in height of mustard green leaves	Figure 7: Relationship between level of biochar and level of effluent on numbers of leaves of mustard green leaves at 40 days

 Biomass yield

Over all levels of effluent N application, the addition of biochar led to more than two-fold increases in above ground biomass yield (Table 6). Biochar had no effect on biomass yield in the absence of effluent, but with 2.5 kg N/ha  there were two to three fold increases in yield (Figures 8 and 9). Maximum response to biochar was with 5 kg N/ha with no advantage from application of higher levels of N. Many researchers have emphasized the importance of nutrient supply, especially nitrogen, as a determinant of plant growth response to soil amendment with biochar (see review by Sohi et al 2009). Similar synergistic effects on plant growth by combining charcoal with chicken manure were observed by Steiner et al (2007).

Figure 8: Relationship between biochar and effluent N on fresh biomass yield (leaves + stems) of mustard green	Figure 9: Relationship between biochar and effluent N on biomass DM yield (leaves + stems) of mustard green

Conclusions

• For all levels of effluent N application, the addition of biochar led to more than two-fold increases in above ground biomass yield of mustard green.
  
  
• Biochar had no effect on biomass yield in the absence of effluent, and there were no further responses to effluent N when this exceeded a level of 2.5 kg N/ha.
  
  
• Application of biochar increased the crude protein in the leaves by an average of 16%, with the relative increase being greater when effluent was applied.
  
  
• A reduction in crude fiber content of the leaves due to biochar was  observed at low levels (< 5 kg N/ha) of application of effluent N, with the opposite effect being apparent at levels of N of 7.5 and 10 kg/ha.

Acknowledgements

The authors would like to express their gratitude to the MEKARN project financed by Sida, 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/workshop-cambodia/

Chhay T, Vor S, Borin K and Preston T R 2013 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). Livestock Research for Rural Development. Volume 25, Article #8. Retrieved March 18, 2013, from http://www.lrrd.org/lrrd25/1/chha25008.htm

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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Minitab 2000 Minitab reference Manual release 13.31. User’s guide to statistics. Minitab Inc., USA

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

Sohi S, Loez-Capel E, Krull E and Bol R 2009 Biochar's roles in soil and climate change: A review of research needs. CSIRO Land and Water Science Report 05/09, 64 pp.

Steiner C, Teixeira W, Lehmann J, Nehls T, Vasconcelos de Macêdo J, Blum W and Zech W  2007 Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil, Plant and Soil 291:1-2. http://www.css.cornell.edu/faculty/lehmann/publ/PlantSoil,%20online,%202007,%20Steiner.pdf

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Received 13 March 2013; Accepted 31 March 2013; Published 2 April 2013

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