Effect of different sources of biochar on growth of maize in sandy and feralite soils

Tran Thi Dao, Nguyen Tat Canh, Nguyen Xuan Trach and T R Preston*

Hanoi University of Agriculture, Vietnam
beleiveinmyself@gmail.com
* Finca Ecológica, AA#48 Socorro, Santander del Sur, Colombia

Abstract

This study was carried out on sandy soil (from Quang Binh) and feralite soil (Hoa Binh) in Vietnam to determine the interaction  between source of biochar and soil type of growth of maize. Different fibrouse residues were carbonized in an updraft gasifier stove and added to each type of soil held in plastic bags of one liter capacity. The design was a 4*2 factorial in a split plot layout with 4 replications. The factors were source of soil and type of feedstock (Bamboo, coconut hulls, sugarcane bagasse and rice husks). Mixtures were made of 80 g of biochar, 2 kg of soil, 0.4 g urea, 0.2 g potassium chloride and 0.4 g super phosphate, and put in plastic bags that had many holes in the lower part so any excess water could drain out. Two seeds of maize were planted in each bag. Water was applied uniformly to all bags every morning, except on rainy days. When the seeds had germinated, one plant was removed to leave only one seedling in each bag.

Compared with the control treatment (no biochar), growth of maize on these soils over 35 days was increased four-fold with biochar from sugar cane bagasse.  Biochar from coconut husk, bamboo and rice hulls, gave  increases in above ground biomass that were 3.4, 2.5 and 2.3 times the growth on the control plot that did not receive biochar. The impact of biochar on maize growth was much less on the neutral sandy soil.

Key words: amendment, biotest, carbonization, gasification, updraft stoves

Introduction

Sandy soil and feralite soil have low potential for agricultural production, because they have:  poor soil structure, a low inherent nutrient supply, low organic matter, low pH,  and limited capacity of water to hold water and plant nutrients and low microbial activity.  Soil management to ameliorate these limitations is important to avoid losses of nutrients and water by leaching, to reduce erosion and gaseous emissions of nitrous oxides and methane that contribute to the greenhouse effect (Vitousek and Matson 1985).

Biochar is the carbon-rich product obtained when fibrous biomass is heated in a closed container with little or no available air and at high temperature of 500 - 900 °C.  It can prevent the leaching of nutrients out of the soil, partly because it adsorbs and immobilizes nutrients and micro-organisms, thus increasing the available nutrients for plant growth, and increasing water retention  ( Lehmann and Joseph 2009). Additionally, it has been shown to decrease N₂O (Nitrous oxide) and CH₄ (Methane) emissions from soil, thus mitigating GHG emissions (Sohi. et al, 2009).  

The objectives of this study were to determine the effects of biochar produced from different agricultural residues on growth of maize in two contrasting soils of low fertility.

Materials and methods

Location and duration

The study was carried out in Hanoi University of Agriculture, Vietnam from January to December 2011. 
 

Experimental design
 

The experimental layout was a split-plot layout of a 2*4 arrangement with four replicates. The factors were:

Main plots: Sandy soil, feralite soil

Split plots: Source of biochar (bamboo, coconut shells, sugarcane bagasse, rice husks).

Materials

Soil samples

Sandy soil was taken from the costal province of Quang Binh; feralite soil was taken from the mountainous province of Hoa Binh (Table 1).

Biochar

The bagasse was the residue after extraction of the juice from sugar cane stalks using the simple two-roll mill traditionally used to extract sugar cane juice for drinking. It was chopped into pieces of 5-7 cm and sun-dried before being put in the gasifier stove. The bamboo stems and coconut shells were chopped into pieces of 5-7 cm prior to sun-drying. The different feedstocks were used as fuel in an up-draft gasifier stove (Photo 1),  described by Olivier (2010).

Photo 1. The updraft gasifier stove used to prepare the samples of biochar (Olivier 2010)

The biotest

Mixtures were made of 80 g of biochar, 2 kg of soil, 0.4 g urea, 0.2 g potassium chloride and 0.4 g super phosphate, and put in plastic bags that had many holes in the lower part so any excess water could drain out. Two seeds of maize were planted in each bag. Water was applied uniformly to all bags every morning, except on rainy days. When the seeds had germinated, one plant was removed to leave only one seedling in each bag.

Measurements

The biochar was analysed for ash content using the methods of AOAC (2000). The height of the maize plant and the leaf area index (leaf area/soil area) were measured every seven days. After 35 days, the plants complete with roots were removed from the bags, washed free of soil, and the green parts (leaves and stems) and the roots weighed.

Statistical analysis   

The data were analyzed with the General Linear Model option in the ANOVA program of the Minitab (2000) software. Sources of variation were: Soil type, source of feedstock, interaction soil*feedstock and error.

Results and discussion

After carbonization, the particle size of the bagasse was the largest, followed by rice husks (Photos 2 and 3); the pieces of bamboo and the coconut shell had the smallest particle size (Photos 4 and 5). However, both the rice husks and bagasse were readily reduced to powder form prior to mixing with the soil.

The ash content of the biochar was highest in biochar derived from sugar cane bagasse and lowest in biochar from coconut husk (Table 2).

Photo 2. Rice husks after carbonization	Photo 3. Sugar cane bagasse after carbonization
Photo 4. Coconut husks after carbonization	Photo 5. Bamboo stems after carbonization

The leaf area index was increased two-fold when the biochar originated from bamboo and coconut shells and almost three-fold when the biochar was from sugar cane bagasse (Table 3). Biochar from rice husks was the least  effective as soil amender, supporting a two-fold increase in leaf-aea index and above ground biomass.

For all criteria, the response to biochar on the acid soil (pH 3.72) was twice that on the neutral (pH 7.2) sandy soil (Figures 1 to 4). There were major differences in the response to biochar according to its origin (Table 3).  The fresh weight of leaf and stem and root of the maize showed similar responses to the different biochars as the leaf area index. Weights of leaf and stem were were increased four-fold over control values (no biochar) when the biochar was derived from sugar cane bagasse (Figures 3 and 4). Decreasing degrees of response were observed for biochar derived from coconut husk, bamboo and rice hulls, with increases in above ground biomass that were 3.4, 2.5 and 2.3 times the growth on the control plot that did not receive biochar.

Figure 1. Effect of soil type and source of biochar on leaf area index of maize after 35 days growth (Leaf area indx = leaf area/soil area; RH Rice husks; Ba Bamboo; CS coconut shells; SCB Sugar cane bagasse)	Figure 2. Effect of soil type and source of biochar on height of maize after 35 days growth ( RH Rice husks; Ba Bamboo; CS coconut shells; SCB Sugar cane bagasse)
Figure 3. Effect of soil type and source of biochar on above ground biomass of maize after 35 days growth ( RH Rice husks; Ba Bamboo; CS coconut shells; SCB Sugar cane bagasse)	Figure 4. Effect of soil type and source of biochar on root biomass of maize after 35 days growth ( RH Rice husks; Ba Bamboo; CS coconut shells; SCB Sugar cane bagasse)

As far as we are aware this is one of the first comparisons of biochar, produced from different feedstocks in the same updraft gasifier stove, and used as a soil amendment for growth of maize. On the basis of data available, there are no obvious explanations for what were quite major differences in the degrees of  response. There was no relationship between the carbon content of the biochar and the response in plant growth (R² = 0.069). The relative rates of carbonization were not recorded, nor was equipment available to have measured the temperature achieved during the carbonization process, criteria which might have shown some relationship between the nature of the feedstock and the observed stimulatory effects on growth of the maize.  In contrast to these results, Southavong and Preston (2011) observed no differences in growth response of rice to biochar derived from sugar cane bagasse from a downdraft gasifier compared with biochar from rice hulls carbonized in an updraft gasifier stove. Similar lack of difference in response was reported by Sokchar and Preston (2011) from the same two sources of biochar used as soil amendment for growth of maize. 

The relative ratio of surface area to weight of the particles in biochar is thought to be one of the major determinants of its efficacy as a soil amendment, as this criterion would be reflected directly in the adsorpcion characteristics of the biochar, and thus its capacity to adsorb nutrients and to facilitate the fermentative activities of soil micro-organisms.  However, the BETS gas adsorption test procedure  (http://en.wikipedia.org/wiki/BET_theory) to measure surface area of small particles requires equipment presently unavailable in Vietnam.

The amendment qualities of biochar are likely to be affected by many factors, among them: the chemical composition (ratio of C, H and O) of the feedstock, the ratio of carbon to ash in the biochar,  its density and particle size (which affects the rate of combustion in the gasifier), the temperature to which the feedstock is exposed (and the residence time at this temperature).

Conclusions

• Compared with the control treatment (no biochar), the 35-day growth of maize on acid feralite soils was increased 5.7 times by addition of 40 g biochar/kg of soil. The increases with biochar from coconut  husks, bamboo and rice husks were 3.4, 2.5 and 2.3 times the growth on the control plot that did not receive biochar.

• The growth responses to biochar from bagasse, coconut husks, bamboo and rice husks on sandy neutral soil were 2.0, 1.4, 2.0 and 1.4 times that on the control plot.
  

References

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

Lehman J and Joseph S (Editors) 2009 Biochar for Environmental Management. Earthscan.  United Kingdom and United State ISBN:978-1-84407-658-1

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

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. http://www.lrrd.org/lrrd23/4/sokc23069.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.

Southavong S and Preston T R 2011 Growth of rice in acid soils amended with biochar from gasifier or TLUD stove, derived from rice husks, with or without biodigester effluent. Livestock Research for Rural Development. Volume 23, Article #32. http://www.lrrd.org/lrrd23/2/siso23032.htm

Vitousek P M.and Matson P A 1985 Disturbance, nitrogen availability and nitrogen losses in an intensively managed loblolly pine plantation. Ecology, 66: 1360-1376

Received 18 July 2012; Accepted 30 March 2013; Published 2 April 2013

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