Effects of biochar from gasifier stove and effluent from biodigester on growth of maize in acid and fertile soils

Pham Thi Luyen, Duong Nguyen Khang and T R Preston*

Nong lam University, Vietnam
nguyenkhang.ptnlmt@gmail.com
* TOSOLY, AA48 Socorro, Santander, Colombia

Abstract

The study was conducted at the experimental farm of Nong Lam University, Ho Chi Minh City from October 2010 to May 2011. A  maize biotest was used to evaluate three factors: biochar (at levels 0, 2, 4 and 6%), two kind of soils (acid and fertile soil), biodigester effluent (with and without). There were in total 16 treatments with 4 repetitions, arranged in a complete randomized block design.

The combination of biochar and effluent increased the  height of the maize (from 48 to 157 cm) and the biomass yield (from 27 to 114 g/plant) compared with the control treatment. There were improvements in soil pH after addition of biochar and in mineral status after application of effluent.

Key words: Carbon sequestration, global warming, organic fertilizer, terra preta

Introduction

The recent interest in biochar (Lehman 2005) as a soil amender has its origins in the discovery of Terra Preta by Sombroek (1966, cited by Glaser 2007). Terra preta is an artificial, human-made soil, which originated before the arrival of Europeans in South America (http://en.wikipedia.org/wiki/Terra_preta). Indigenous people made the soil by applying charcoal, bone, and manure to the otherwise relatively infertile Amazonian soil.  

Biochar in the modern context is produced by the combustion of organic matter in a low oxygen environment. It is rich in minerals including potassium, phosphorus, calcium, zinc, and manganese. But the most important ingredient is carbon, giving the dark colour. Biochar is not oxidized by soil micro-organisms, compared with traditional forms of charcoal which eventually are completely broken down when applied to soils. The chemical structure of biochar is characterized by the presence of poly-condensed aromatic moieties, giving prolonged stability against microbial degradation and oxidation, and high nutrient retention (Glaser 2007).

It has been proposed that biochar can reduce  the effects of global warming since the carbon that it contains is resistant to attack by soil micro-organisms thus acting as a “sink” for carbon (Lehman et al 2006). According to these authors, about 10% of the total global fossil fuel carbon emissions could be sequestered in soils as biochar. Debate has taken place concerning potential negative effects on food production if land is diverted to growing and harvesting biomass solely to produce “biochar”. Another issue relates to the problems involved in transport of low density biomass for production of biochar in large scale centralized processing facilities.

A recent approach that seeks to avoid these negative aspects of  biochar is the use of small scale biomass gasifier stoves that combine the advantages of a clean-burning fuel, that avoids the pollution and health hazards from open fires, and at the same time produces biochar as a by-product (Olivier 2011).

The results from applying biochar to soils have been quite dramatic, especially on acid soils when the biochar has been used in conjunction with organic fertilizer in the form of biodigester effluent (Rodríguez et al 2009).

The present study aims to evaluate the use of biochar as a soil amender in acid and fertile soils used to grow maize. 

Hypothesis

The beneficial effects of biochar on maize growth will be greater in acid soils and there will be a positive synergism when biochar is combined with effluent from biodigesters charged with animal excreta.

Materials and Methods

Location of study

The study was conducted at Nong Lam University, Ho Chi Minh City, Vietnam, using the biotest model (Boonchan Chantaprasarn and Preston 2004) with maize as the indicator plant (Photo 3).

 Experimental design

Sixteen treatments were compared in a 4*2*2 factorial arrangement with 4 replications. The factors were:

Biochar: Four levels of biochar (0, 2, 4 and 6%) added to the soils in the plastic bags

Soil type: Acid soil or fertile soil

Biodigester effluent: With or without effluent at 50 kg N/ha over 35 days

Biochar

The biochar was the solid residue from an up-draft gasifier stove charged with  rice husks as fuel (Photo 2).

Biodigester effluent

Effluent was collected from a plug-flow biodigester constructed with High Density Polyethylene (HPDE) (Photo 3) located in a commercial pig farm.

 Experimental soils

Two types of soil were used in the experiment. The acid soil (pH 4.5) was taken from the top 10cm in an un-shaded area in the Nong Lam University campus. The almost neutral soil (pH 6.4 ) was taken from the top 10cm in the same area but under trees that provided shade.

Photo 4. The acid soil	Photo 5. Close to neutral soil

.

Maize seeds

These were of a local variety.  Three seeds were placed in each bag. After germination, two seedlings were removed to leave only one plant for the experimental growth period of 42 days.

Measurements

At 7, 14, 21, 28, 35 and 42 days after seeding the height of the maize was measured at the tip of the highest leaf.  At the end of the growth period of 42 days, the complete plant was removed from the bag and the aerial part separated from the roots which were washed free of soil. Both fractions were weighed. The pH of the soil was measured with a digital pH meter at the time of harvesting the maize. The ash content of the biochar was determined by incineration at 700°C (AOAC 1990). Soil analysis was according to AOAC (1990) as follows: physical characteristics by density gauge; total nitrogen (N) by Kejdah'; total phosphorus (P_2O5) by colorimetry; total potassium (as K₂O) by flame photometry.

Statistical analyses

The data were analysed by the General Linear Model of the ANOVA program in the Minitab (2000) Software. Sources of variation were: level of biochar, soil type, effluent, interaction biochar*effluent and error.

Results

The two soils were very different in physical and chemical properties (Table 1).The fertile soil had higher proportions of clay and silt and lower content of sand; and was higher in N and K₂O than in the acid soil. The high pH of the biochar is a common feature of biochar produced from both downdraft gasifiers and updraft gasifier stoves (9.5 and 9.8, respectively according to Sokchea and Preston 2011).  The residual ash was 45% (DM basis) which is lower than the value of 77% recorded by Southavong et al (2012) for biochar derived from stove gasification of rice hulls.  

 There was a linear increase in the height of the maize and in biomass yield with increase in biochar up to 4% in the soil with no further increase with 6% of biochar (Tables 2 and 3; Figures 1 - 4). Application of biodigester effluent increased the height of the maize and biomass yield, at all levels of application of biochar. There were tendencies for increases in yield of leaf and above ground biomass on the fertile compared with the acid soil. These differences were significant for weights of stem, root and total biomass. 

Figure 1. Effect of biochar and biodigester effluent on height of maize after 42 days	Figure 2. Effect of biochar and biodigester effluent on green biomass (leaf + stem) of maize after 42 days

Figure 3.  Effect of biochar and biodigester effluent on root biomass of maize after 42 days	Figure 4. Effect of biochar and biodigester effluent on total biomass of maize after 42 days

Figure 5.  Effect of soil type on nutrient status of the soil at the end of the 42 day growth trial	Figure 6.  Effect of effluent on nutrient status of the soil at the end of the 42 day growth trial

The beneficial effects of the biochar on growth of the maize confirm earlier reports on use of biochar from a downdraft gasifier (Rodríguez et al 2007) and updraft gasifier stove (Sokchea et al 2011). Contrary to the findings of Rodríguez et al (2007), responses to biochar application tended to be greater on the fertile soil than on the acid soil. 

There were no residual effects on soil levels of N and K₂O due to application of biochar; however, levels of P₂O₅ were lower in the soils that received biochar (Table 4). As expected,  the fertile soil had higher levels of macro-nutrients than the acid soil, and there were positive effects on soil nutrient status from application of biodigester effluent.

Conclusions

• There was a linear increase in maize biomass yield with increasing levels of  biochar up to 4% in the soil with no further increase with 6%.
• Application of biodigester effluent increased biomass yield, at all levels of application of biochar.
• There was a greater response to biochar and to effluent application on yield of biomass on the fertile compared with the acid soil.

Acknowledgments 

The authors gratefully acknowledge the support for this research received from the MEKARN program financed by Sida.

References

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

Boonchan Chantaprasarn and Preston T R 2004: Measuring fertility of soils by the bio-test method. Livestock Research for Rural Development. Volumr 16, Article No. 78. http://www.lrrd.org/lrrd16/10/chan16078

Glaser B 2007 Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century. Philosophical Transactions of the Royal Society. 362, 187–196 http://rstb.royalsocietypublishing.org/content/362/1478/187.full

Lehmann J 2007 A handful of carbon. Nature 447: 143-144
 

Lehmann J, Gaunt J and Rondon M 2006 Bio-char sequestration in terrestrial ecosystems—a review. Mitigation Adaptation Strategies. Global Change 11: 395–419 http://www.css.cornell.edu/faculty/lehmann/publ/MitAdaptStratGlobChange%2011,%20403-427,%20Lehmann,%202006.pdf

Olivier P A 2010: The Small-scale Production of Food, Fuel. Feed and Fertilizer from recycled wastes. International conference. Live stock production, climate change and resource depletion. 9 - 11 November 2010, Pakse, Lao PDR. http://www.mekarn.org/workshops/pakse/html/olivier.docx

Rodríguez 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

Sokchea H and Preston T R 2011: Growth of maize in acid soil amended with biochar, derived from gasifier reactor and gasifier stove, with or without organic fertilizer (biodigester effluent). Livestock Research for Rural Development. Volume 23, Article #69. Retrieved March 13, 2012, from http://www.lrrd.org/lrrd23/4/sokc23069.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. http://www.lrrd.org/lrrd24/2/siso24039.htm

Received 12 January 2012; Accepted 15 April 2012; Published 7 May 2012

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